Giao Trinh Thi Cong Nha Cao Tang BTCT - Pgs Le Kieu

1

B xy dng Trxng i hc kin trc h{ ni

Pgs L kiu

gio trnh thi cng Nh cao tng

b tng ct thp

H{ ni thng 07.2002

1Share-connect.blogspot.com

2

Phn M u Gio trnh ny l gio trnh chuyn nhm h}ng dn nhng iu c bn lp thit k bin php cng ngh thi cng, gip cho vic gim st v nghim thu phn th nh cao tng xy chen ti cc thnh ph. Do tnh thc tin ca gio trnh nn ni dung khng gii thch nhng nguyn tc ca thi cng c s m }c th hin theo dng cc ch dn cng ngh. Gio trnh ny c s dng cc Tiu chun Xy dng ban hnh v thi cng nh cao tng nh} : TCXD 194 : 1997 Nh cao tng - Cng tc kho st a k thut TCXD 203 : 1997 Nh cao tng - K thut o c phc v cng tc thi cng TCXD 199 : 1997 Nh cao tng - K thut ch to b tng mc 400-600 TCXD 200 : 1997 Nh cao tng - K thut ch to b tng bm TCXD 197 : 1997 Nh cao tng - Thi cng cc khoan nhi TCXD 196 : 1997 Nh cao tng - Cng tc th tnh v kim tra cht l}ng cc khoan nhi. TCXD 202 : 1997 Nh cao tng - Thi cng phn thn TCXD 201 : 1997 Nh cao tng - K thut s dng gio treo TCXD 206 : 1998 Cc khoan nhi - Yu cu v cht l}ng thi cng Gio trnh ny }c s dng lm c s lp cc yu cu k thut nu trong b h s mi thu v cc bn v. Nu trong b h s k thut c H s mi thu th nhng ni dung b sung ca gio trnh ny s lm phong ph cc yu cu cng ngh cho thi cng nh cao tng. Tun theo nhng khuyn ngh ca gio trnh ny sau khi }c ch u t} chp thun c th }c coi nh} c s lp gi thi cng.


3

Chong I Nhng iu cn bit chung

1.1 Kim tra h s thi cng vw thc t hin trung H s thi cng bao gm phn Cc yu cu k thut trong b H s mi thu, ton b bn v s dng thc hin d n, ton b d liu v a hnh, a cht thu vn, a cht cng trnh , catalogues v vt liu xy dng theo yu cu , catalogues v bn thnh phm v cc vn bn khc cn thit phi l}u gi ti phng k thut thi cng. Cn c tng tin yu cu. Cn kim tra tnh trng thc t cng nh} cc kch th}c v cao trnh ti hin tr}ng. Tr}c khi thi cng cn nghin cu rt k h s thit k v cc yu cu k thut trong b h s mi thu. Cn kim tra mi kch th}c v cao trnh trong cc bn v, ch m bo s trng khp cc d liu gia cc bn v vi nhau. Khi thy nhng iu gia h s v thc tin ch}a khp hoc thiu st cn bn bc cch s l thng nht v nhng khc bit pht hin }c vi ch u t} tr}c khi tin hnh cng vic. Cn c k s} trin khai thit k chi tit v qun trit cc bin php thi cng mi }c vch c tnh cht ph}ng h}ng khi np h s thu. Phi r xot li tng tin thi cng do H s mi thu ch nh phi hp ng b cc khu t xy n lp nhm vch k hoch phi hp trong tng tin . Khi s dng cc bn thnh phm th}ng phm hoc cn c thu ph tham gia cn thit lp bn v ch dn thi cng hoc yu cu phi hp b sung trnh ch u t} duyt tr}c khi thi cng. Trn cng tr}ng c nhiu bn tham gia th thng th}ng bn thu chnh l ng}i duy nht chu trch nhim v bo m phi hp v kt cu, c kh v cc cng tc k thut khc nn khi r sot tng tin cn c cch nhn tng qut. Nu cng tr}ng n gin th vic t chc phi hp th}ng do ch u t} trc tip n c. Cc bn v trin khai thi cng cn l}u n cc chi tit k thut s t trong b tng hoc khi xy cng nh} cc l cha nh tr}c trnh c o sau ny. Bn thu chnh phi pht hin cc sai st ca thit k v s thiu ch phi hp chung ch u t} nht tr tr}c khi thi cng. Thng th}ng cc bn v phn xy ch}a tm bao qut cc phn lp, phn trang b m qu trnh thi cng phi phi hp to iu kin trnh c o hoc lm ri phi lm li hoc chnh sa. 1.2 iu cn ch chung v an town, bo h khi thi cng :


4

Cn thit l}u tm n tn hiu an ton hng khng khi cng trnh thi cng v}t ln cao .Khi cng trnh xy t cao v}t qu 10 mt, phi lm v thp n v cm c bo hiu cao theo qui nh an ton hng khng. C th b tr n v c trn nh cn trc thp hoc thp cao nht cng trnh. n phi pht ra nh sng mu da cam v c cng sut ln hn 100 W. Chp n trong sut, khng cn sng do n pht ra. n v c c th nhn thy t bt k v tr no trn khng. Phi lm bng bo hiu s tng ang thi cng v bo hiu nhng tng d}i thi cng. Bn hiu vit ch c chiu cao ch t nht 1 mt, b dy nt ch 10 cm. Ch sn mu m khc bit mu vi cc b phn kt cu chung quanh ch. }ng dy dn in i l trn khng }c nm trong vng nh h}ng ca cn trc. Cp in v cc ph}ng tin vin thng i trong ng ngm theo ng ch dn nghip v chuyn ngnh. Khi }ng dy ct ngang lung vn chuyn, }ng dy trn khng phi m bo cao theo qui nh, }ng cp ngm phi t su trn 1 mt so vi mt }ng v phi t trong trong ng bao ngoi bng thp hoc ng b tng bo v. Mi cng vic gy n v chn ng lm nh h}ng s ngh ngi v yn tnh ca dn c} gn cng tr}ng khng nn tin hnh t 23 gi n 5 gi sng. Trong tr}ng hp khn thit cn c s tho thun vi nhng h s b nh h}ng v rt hn ch xy ra. Hn ch ti a vic pht ra ting n ca my bng cc ph}ng tin gim chn cng nh} ca cc ph}ng tin loa i. Cn tun th nghim cc quy nh v an ton , bo h lao ng. Qun, o, m, gng tay, giy ng, knh bo h cho mi dng lao ng u }c trang b y . Cc khu vc nguy him nh} phm vi hot ng ca cn trc, ca my o v cc my mc khc, phm vi c th c kh nng nguy him do vt trn cao rt xung, phm vi c th rt xung h o su, cung tr}t t, u c ro chn tm v c bo hiu mu sc n v c cng nh} }c sn theo quy nh. Khng cht ti quanh mp h su. Nhng sn c cao h trn 2mt cn c lan can chng ri ng v l}i chn pha d}i. Ni lm vic phi m bo sng theo qui nh v mc n d}i mc quy nh. Ni pht sinh bi, hi v mi c hi, ni pht ra nh sng h quang in cn }c che chn v cng nhn lm vic ni ny }c trang b mt n chuyn dng. Cn tun th s qun l Nh n}c ca cc c quan qun l th .Vic s dng h }ng, cn c s tho thun ca c quan qun l t}ng ng v nn hn ch n mc ti thiu.


5

1.3. Nhng iu cn luu c bit khi thi cng xy chen. Cn kho st v nh gi y v tnh trng cc cng trnh hin hu lin k c v phn ni cng nh} phn chm c gii php thi cng v chi ph ph hp, bo m tuyt i an ton cho cng trnh hin hu . Vic kho st v nh gi phi lm ng cc qui nh hin hnh, c ghi hnh nh l}u tr v lp bin bn c xc nhn y ca cc bn lin quan. Khi nghi ng v a gii v phn ngm ca cng trnh hin hu s nh h}ng n thi cng cng nh} s an ton cho cng trnh hin hu phi cng ch u t} thng nht bin php gii quyt cng nh} v kinh ph s l. Cn bn bc v thng nht ch v trch nhim bo him cho cng trnh hin hu v s bo him ny c s tham gia ca c quan bo him chuyn trch. m bo an ton tuyt i khi gp cng trnh lin k hin hu qu ru r, c kh nng xp trong qu trnh thi cng, cn thng qua ch u t}, bn bc vi ch s hu cng trnh hin hu gii php hp l m cc bn cng chp nhn }c. Vic chng cho cng trnh lin k hin hu trong qu trnh thi cng l mt trong nhng kh nng nu thy cn thit. Qu trnh thi cng ngoi vic theo di kch th}c hnh hc v bin dng ca cng trnh xy dng cn cn theo di bion dng ca cng trnh lin k c gii php ngn chn s c ng tic c kh nng xy ra. Vi mng cc nhi to l kiu xoay nn li ng vch cho nhng cc st nh lin k hin hu. Mng cc nhi o bng my gu ngom phi lm c chn su ti }ng phn gii khu t v khng nht thit thu hi sau khi lm xong mng cng trnh. H mc n}c ngm khi thi cng xy chen th}ng nh h}ng n s ln cng trnh lin k nn hn ch hoc khng s dng bin php h n}c ngm v l do an ton. Nu c phn ngm ca cng trnh lin k hin hu ln vo mt bng thi cng cn bn bc s l tr}c khi tin hnh thi cng phn nn mng. Khi cn neo t}ng chn trong t cn }c tho thun ca c quan hu quan v ch s dng t lin k. Cng trnh xy dng nm cch sng nh hn 100 mt phi c tho thun ca c quan qun l iu v cc bin php thit k v thi cng phn ngm. Khi thi cng st nh bn c ti ln tc ng ln t cng nh} khi cng trnh lm h mng su hn y mng nh bn , cn c bin php chng thnh vch bng c thp hoc c b tng ng lc tr}c gi an ton khi thi cng cng trnh cng nh} m bo an ton cho nh lin k. Thit k t}ng c phi ch n vng chng v neo


6

m bo bin dng trong phm vi }c php. Bin php cn thng qua Ch nhim d n v }c ph duyt lm c s php l thi cng. Khi cng trnh v}t khi im cao nht ca cng trnh hin hu lin k st l gii hai bn cn lm sn che chn m bo an ton chng va hoc vt liu ri trc tip v c tho thun ca ch cng trnh lin k v cc gii php thch hp cho an ton. Vic lm hng ro v pan gii thiu cng trnh phi tun theo quy tc ca thnh ph ( hng ro cao trn 2,5 mt, chc chn v kn kht, phn trn c on chch chch 30o h}ng vo trong cng tr}ng khng nh hn 0,5 mt ). Vi nh hin hu lin k khuyn khch lm ro kn ti cao theo quy tc chung v c s bn bc thng nht vi ch s dng nh lin k v cc mt an ton v thch nghi trong qu trnh thi cng. Khi c li i li cng cng khng th trnh }c nm trong vng nh h}ng ca phm vi thi cng cn lm thnh ng giao thng an ton cho ng}i qua li. ng ny }c che chn an ton v c hai u phi nm ngoi phm vi nguy him. Cn che ph kn mt dn gio ngoi cng trnh bng l}i kn v chc chn m bo khng ri rc xy dng ra khi khu vc thi cng. Rc xy dng t trn cc tng cao }a xung bng thng kn do cn cu chuyn xung hoc qua ng dn kn m u d}i phi c vi bt chm st t gim ti a l}ng bi gy trn cng tr}ng. Xe ch t o ra trong cng tr}ng v cht gy bn cho }ng ph phi kn kht khng chy ra }ng ph, phi ra sch gm v bnh xe tr}c khi ln bnh ra }ng cng cng. N}c thi ra cng cng cng phi gn lng cn v bn, t v }c tho thun ca c quan qun l n}c thi th. Cn thit k tng mt bng cho nhiu giai on thi cng v tun th theo thit k tng mt bng ny nhm trnh by ba vt liu v cu kin ra }ng cng cng, trnh hin t}ng phi di chuyn kho bi, sn phc v thi cng lm tng chi ph v di chuyn cng nh} tng hao ht thi cng. Khi thit k cc bin php thi cng nn s dng b tng ch trn sn v }a vo v tr cng trnh bng bm b tng gim n mc ti a nhng cng vic phi lm ti hin tr}ng. Cn gia cng nhng cu kin v bn thnh phm ti a im khc v chuyn ch n lp ti hin tr}ng . Tranh th nhng din tch va thi cng xong lm mt bng thi cng , gia cng nh}ng phi tun theo cc qui nh k thut v thi gian }c cht xp ti trn sn hoc mt bng.


7

Cn t chc nhng nhm }c phn cng lm v sinh cng nghip , m bo mt bng thi cng an ton , sch s , khng gy tai nn hay tr ngi cho thi cng tip tc cng nh} thun li cho di chuyn trn mt bng.


8

Chong II

Cng tc chun b Cng tc chun b y }c hiu l chun b xy dng. 2.1 Kim tra hin trung vw h s thi cng: Vic di chuyn, ph d cng trnh c hin tr}ng khng nm trong i t}ng ca gio trnh ny nh}ng phi hon tt khi bn giao mt bng cho thi cng. Khi thi cng trn nn t yu phi gia c nh} gia ti, gia ti kt hp bc thm hoc cc bin php khc cn c h s kim tra c kt ca t, h s ghi nhn nhng d liu hin t ca nn t }c c quan thu thp d liu pht biu bng vn bn, c s ph duyt d liu chnh thc ca ch u t}. Nh thu phi kim tra k mt bng l}ng ht mi kh khn xy ra trong qu trnh thi cng sau ny. Mi sai lch vi iu kin u thu cn bn bc vi ch u t} c gii php tho ng ngay tr}c khi thi cng. 2.2. Chun b mt bng thi cng: Giao nhn mc gii v cao trnh cn tin hnh chu o, c s chng kin v xc nhn ca chnh quyn a ph}ng lin quan. Sau khi nhn a gii cn xy dng ngay ro chn bo v khu vc }c giao. Mc cao trnh phi }c thit lp chnh thc theo ng yu cu k thut v }c ro chn bo v, lm cn c thi cng sau ny. Cn s l ngay vic thot n}c mt bng. Vic thot n}c mt bng gn lin vi cc gii php tng mt bng xy dng giai on thi cng phn ngm. Mi iu kin cung cp k thut cho thi cng nh} cp in, n}c, ph}ng tin thng tin phc v thi cng }c chun b tr}c nht. u cung cp k thut phi }c ch u t} giao ti bin gii cng tr}ng. Nu nh thu nhn lun c khu cung cp ny th phn vic ngoi a gii thi cng phi tin hnh tr}c khi trin khai tng mt bng thi cng. Cng trnh s dng cc nhi v cc barrettes , t}ng trong t th trong thit k thi cng, cn thit k thu hi dung dch khoan bentonite vi hai ngha m bo v sinh cng nghip v kinh t. Tu theo thit k trnh t thi cng cc nhi v t}ng barrettes m vch h rnh thu hi dch khoan cng nh} v tr cc h tch ct, my tch ct v my bm dch s dng li.


9

Gn cng ra vo ca ph}ng tin vn chuyn cn lm h thu n}c thi cng v cu ra gm xe, ra bnh xe t ch t trong qu trnh thi cng phn ngm m bo v sinh v an ton th. H ny tch bit vi h thu hi dch khoan. Phi gi cho mt bng thi cng cc giai on ( k c thi cng phn ngm) lun kh ro v gn, sch. 2.3 Chun b vw xy dng kho bi : Kho bi phi ph hp vi cc yu cu bo qun cng nh} gia cng. Kho, bi vt t}, thit b cn sp xp chu o, d nhp xut hng cng nh} an ton, bo qun tt, chng mt mt, h} hng. Phn nn kho, bi cn cao ro, khng b ngp ng khi m}a to v di ngy. Kho bi phi bm ly }ng, x thun tin chuyn ch. Bi ngoi tri phi lm k, m hng ct cha khng t trc tip ln nn. Bi vt liu ri phi c nn tt , khng ln, khng trn vi vt liu ct cha v thu hi }c ht vt liu. Kho thong ch c mi m khng c t}ng phi m bo m}a, nng ht, ri vo trong lm bin i tnh cht ca vt liu ct cha. Kho cha trong nh, nh phi thng thong, c sn k. S sp xp sao cho hng ct cha d tm, d bo qun, nguyn tc l hng nhp tr}c phi d ly ra s dng tr}c. H thng bo v chc chn, tin cy, chng mt mt. Cn l}u n nhng hng c th t chy, hoc chy }c do kch thch ca ngun do con ng}i gy ra c gii php ngn chn chy n ng yu cu. Nhng hng c ch bo qun ring phi tun theo nhng yu cu bo v, cn c gii php ct cha ring. 2.4 Chun b ung thi cng: Tt nht l kt hp }ng lu di vi }ng thi cng. Nn lm nn }ng lu di tr}c s dng trong qu trnh thi cng. Sau ny khi thi cng xong, ch cn tu chnh phn nn cht t v lm o }ng hon chnh s dng lu di . Cn ch khu thot n}c cho }ng thi cng trnh hin t}ng ln st cn tr trong qu trnh thi cng. Khng nn v h tin cht t chi ph trong khu thot n}c nn }ng thi cng m gy cn tr thi cng v mt v sinh cng nghip. }ng l giao thng trong cng tr}ng theo ph}ng ngang cng nh} ph}ng thng ng cho mi loi ph}ng tin ( k c ng}i i b ) cn m bo cht l}ng nn, iu kin gn kt n nh cng nh} chiu rng ngang v cc trang b che chn (lan can, l}i chn) an ton, m bo v sinh cng nghip v thun tin cho s dng.


10

Cc }ng cp ( in mnh v in yu) , }ng ng ( cp thi n}c v nng l}ng , kh cc loi) }c gi chung l }ng k thut khi ct ngang }ng giao thng, phi b tr l dn cao an ton nu cc }ng y i trn khng, nu }ng k thut y i ngm th phi b tr i trong ng v chn su. }ng l k thut cn b tr hp l, m bo an ton chng tai nn. Khi thit k }ng cho xe c phi kt hp nghin cu ng thi h thng dn k thut m bo vn hnh cc h thng }c thun li v an ton. 2.5 iu kin v sinh vw an town : Cng tr}ng cn b tr khu toilet m bo sch s v v sinh. Khu toilet phi cui gi v cao ro sch s, c n}c p ng yu cu c ra th}ng xuyn v c rnh thot n}c. }ng vo khu toilet phi d i, trn mt lt gch hoc lng va xi mng , khng ch nn t, trn tr}t khi tri m}a. C ch m bo v sinh hng bui lao ng th hin vn minh cng nghip. Trm x cp cu v bo m sc kho phi d tm. Mi ni trn cng tr}ng c th nhn thy }c v tr trm x y t . Ti trm x phi c bin hiu , c hiu mu trng c ch thp gia c, ban m phi c n bo hiu . V tr trm y t, cp cu phi gn }ng i li , tin s dng t cp cu khi cn thit cng nh} vi kh hu mi tr}ng d chu. Khng b tr trm x gn cng tin cng nh} ni pht sinh bi bm, ting n. Nn b tr trm x gn ni trc an ton lao ng chung ca cng tr}ng. Cn b tr in thoi, trang b b m d s dng. Mt bng khu vc thao tc ca my thi cng nh} cn trc , my o, cn }c ro chn tm thi bng cc kim loi c chng dy thng sn vn - trng gii hn phm vi di chuyn ca ng}i trn mt bng cng nh} bo hiu nguy him. Khu vc n mn, khu vc ph d phi c che chn c bit theo iu l an ton ring. Quanh h su phi c ro chn ng}i khng b tt ng xung h bt ng. }c lm ro th}a nh}ng thanh ngang ca hng ro phi c t nht ba hng ngang v phi sn vn - trng gy ch cho ng}i qua li. Ban m phi c n bo hiu khu vc ro. Ht sc ch n an ton lao ng khi thi cng trn cao. Phi c lan can an ton cho mi v tr thi cng c kh nng ri xung thp. Cn c l}i che nhng ni thi cng mt ngoi trn cao. Gio mt ngoi cn c l}i bc bn ngoi v c sn , ngn vt liu, rc ri t trn cao xung thp. Sn khng thp hn v tr thi cng qu 3 mt. 2.6 Ln tri, vn phng :


11

Cn b tr ti vn phng iu hnh thi cng y ph}ng tin lin lc i ni v i ngoi. Cn trang b in thoi v my faximine, my tng m v h loa thng bo ra hin tr}ng. Ti vn phng k thut thi cng ngoi mt b h s bn v thi cng y k s}, k thut tra cu bt k lc no phi c t l}u tr mt b thit k v h s thi cng y ch s dng c bit do lnh k s} tr}ng thi cng. Cc ti liu a cht cng trnh v a cht thu vn ( lm theo TCXD 194:1997, Nh cao tng - Cng tc kho st a k thut ) phi by ch m ng}i thi cng c th ly tham kho bt k lc no. Dng c kim tra cht l}ng bentonite cng nh} cc dng c kim tra n gin khc nh} my theodolites, niveleurs, th}c dy, th}c cun, niv, qu di, th}c tm chun 2m, 4m, . . . phi y v sn sng s dng }c. Ph}ng tin lin lc in thoi, my faximile, e-mail v my tnh in t lun lun trong tnh trng sn sng s dng }c v c ng}i trc ban. Ph}ng tin ra lnh bng ting ni ( micro-ampli-loa - i) lun trong tnh trng vn hnh }c nh}ng phi hn ch s dng v c th gy s khng tp trung cho cng vic ca cng nhn. Nn trang b b m ni b iu khin t trung tm vn phng k thut n cc k s}, i tr}ng thi cng cc v tr trn khp cng tr}ng. K thut o c k thut phc v thi cng v nghim thu tun theo TCXD 203:1997, Nh cao tng - K thut o c phc v cng tc thi cng.


12

Chong III

Thi cng phn ngm. Trong iu kin xy chen ti H ni, thnh ph H Ch Minh, nn thi cng cc khoan nhi hoc t}ng barrette tr}c khi o t lm i v tng hm nu c. 3.1 Thi cng cc khoan nhi: 3.1.1. iu chung: Thi cng cc khoan nhi tun theo TCXD 197:1997, Nh cao tng - Thi cng cc khoan nhi. TCXD 196:1997, Nh cao tng - Cng tc th tnh v kim tra cht l}ng cc khoan nhi. TCXD 206:1998. Cc khoan nhi - Yu cu v cht l}ng thi cng. Thi cng cc khoan nhi cn tun th cc yu cu ghi trong b h s mi thu ca cng trnh. Nhng iu ghi trong gio trnh ny }c coi nh} li khuyn quan trng cn }c cc bn ch u t}, bn thi cng v kim tra cht l}ng tham kho , nu chp nhn s }c coi l iu kin hp ng. Cn lm tt cng tc chun b tr}c khi thi cng. Mt ct a tng phi treo ti phng k thut v h s i cht }c lin k . C khoan }c 2m su cho mi cc k s} phi i chiu gia lp t thc t v a tng do kho st cung cp. Khi c khc bit phi thng bo cho i din k thut ca ch u t} c gii php ng ph kp thi. Tr}c khi thi cng cn ti phng k thut y dng c kim tra cht l}ng dung dch gi thnh vch khi khoan. Cn ph bin y qui trnh thi cng v cc yu cu k thut, cc iu kin an ton cng nh} s phi hp cho mi thnh vin tham gia thi cng tr}c khi bt tay vo cng tc. Vic ghi chp qu trnh thi cng cn }c thc hin nghim tc theo qui nh v bng biu trong TCXD 197:1997, Nh cao tng - Thi cng cc khoan nhi. 3.1.2. Trnh t hp l tin hnh khoan nhi nh} sau: (1). Tin hnh cc cng tc chun b nh} lm h rnh v h thu hi dch khoan. Ch to dch khoan. t ng dn dch khoan ti h o. (2). Quy nh s di chuyn my o theo trnh t cc cc nhm tun th nguyn tc k thut v s hp l trong di chuyn my. (3). nh v l khoan ( nn s dng d}ng b tng ct thp ). (4). Khoan mi khong 1 mt u. (5). Lp v }a ng vch vo v tr.


13

(6). Khoan to l c s dng dung dch gi thnh vch . (7). Lp ct thp. (8). Lp ng tremi v ng xc kh (9). Xc ra gim hm l}ng ct trong l khoan (10). b tng (11). Rt ng vch. 3.1.3. S di chuyn l khoan trong qu trnh khoan nhiu cc L khoan mi phi cch l khoan va thi cng trong vng 7 ngy mt khong cch ti thiu l 3 ln }ng knh cc nhi trnh nhng rung ng nh h}ng cht l}ng b tng cc ang pht trin c}ng . Cn so snh cc ph}ng n di chuyn sao cho thi cng hp l v s dng trang thit b, tng di my o phi di chuyn l ngn nht trong nhng ph}ng n c th t thi gian nhanh nht. Cng cn ch n cc cng trnh ln cn, chiu c n cc yu cu v s dng v m bo an ton cho cc cng trnh ny. 3.1.4. Cng tc nh v H thng mc chun }c vch vo ni khng dch chuyn qua qu trnh thi cng, }c s dng th}ng xuyn kim tra trong thi gian thi cng. Nn lm d}ng nh v ming l khoan bng tm b tng ct thp ghp hai na m ngoi ng vch. Tm ny }c tho ra s dng cho l khoan khc khi khoan }c su n ht tm ng vch. 3.1.5 Nguyn tc chnh v thit b thi cng Vic chn my khoan nhi ph thuc }ng knh, su cc v tnh cht cc lp t theo su... Cn la chn cng sut my ln hn sc lm vic thc t xp x 20%. My mc cn }c kim tra k mi b phn ( b phn pht ng lc, truyn ng, dy cp, cht khp ni, gu ...) tr}c khi tin hnh cng tc khoan. Nhng my ph tr cho thi cng cc nhi nh} my khuy trn bentonite, my tch ct khi phi thu hi bentonite, my nn khi xc ra h khoan phi }c kim tra vn hnh tt tr}c khi tin hnh mt l khoan. 3.1.6 Gi thnh vch v thi ra khi khoan su i vi lp t trn cng }c gi l lp mt , s dng vch bng ng cun bng tn c chiu dy tn l 8 ~ 20 mm. }ng knh trong ng tn ny bng }ng knh cc. ng vch ny li trong t khi cc thi cng st ngay nh ln cn k st. Nu cc xa nh ln cn k st th nn rt ln s dng cho cc thi cng tip . Nu rt ln


14

th thi im rt ng l 15 pht sau khi b tng xong. Nu chm sau 2 gi s gp kh khn do hnh thnh lc bm dnh gia b tng cc v vch ny. Dung dch gi thnh khi o qua ng vch tn c th s dng mt trong hai th sau: dung dch bn bentonite hoc dch khoan supermud. Khi s dng cn c k h}ng dn s dng ca tng loi theo h s bn hng. * S dng dung dch khoan bentonite: Nn ch sn dung dch khoan dng cho mt ngy cng tc nu dng bentonite. S dng bentonite cn c b khuy trn bentonite v c sil cha. L}ng cha ti hin tr}ng nn khong s dng cho 3 n 4 cc nu kh nng thi cng }c 3 ~ 4 cc.

Dung dch }c trn trong mt b c dung tch khong 10 m3 ri bm ln silo cha. Cn m bo ngun n}c cp cho vic ch to dung dch. Ti b trn b tr my khuy to }c dung dch ng u. Nu thu hi dch khoan nn lm giu dch khoan dng li bng cch bm bentonite thu hi vo b trn v cho thm bentonite cho t cc ch tiu.

iu 2.6 ca TCXD 197:1997 nu cc yu cu ca dch khoan. * S dng dung dch khoan SuperMud: Vic s dng cht SuperMud lm dung dch khoan l ng khuyn khch. Liu l}ng s dng l 1/800 ( supermud/ n}c). SuperMud l dng cht do trng, hi nho ho tan trong n}c. SuperMud to lp v siu mng gi thnh vch. SuperMud khng cha cc thnh phn ho gy nhim mi tr}ng E.P.A. SuperMud khng bn, b phn hu sau 8 gi sau khi tip xc vi Chlorine, Calcium. Khng cn c bin php phng h lao ng c bit. C th ho trc tip SuperMud vo n}c khng cn khuy nhiu hoc ch cn cho n}c chy qua SuperMud, khng tn sil cha. N}c thi trong h khoan ra th}ng t khi thu hi v c th x trc tip vo cng cng cng v cha cn bn khng ng k. S dng SuperMud chi ph cho khu dch khoan th}ng nh hn s dng bentonite. to p lc y ng}c t trong h khoan p ra thnh vch khng cho xp thnh, cn cung cp dch khoan gi cho cao trnh ca mt dung dch trong l khoan cao hn mc n}c ngm tnh t bn ngoi ti thiu l 1,5 mt. Th}ng nn mc cao hn l 3 mt.


15

Khi khoan n su thit k cn kim tra su cho chnh xc v ly mu dung dch bentonite ti y l khoan kim tra hm l}ng ct. Sau khi ngng khoan 30 pht, dng gu y thoi vt ct lng ng.

Sau tin hnh thi ra.

+ Thi gian thi ra : ti thiu 30 pht , trc khi thi ra phi kim tra cc c trng ca bn bentonit theo cc ch tiu nu . Ty tnh hnh cc thng s kim tra ny m d bo thi gian thi ra . Phi thi ra n khi t cc c trng yu cu . + Ch , trong thi gian thi ra phi b sung lin tc dung dch bn ti cho s bn ln ct v mn khoan b qu trnh thi y hoc ht ra . Chiu cao ca mt trn lp dung dch bn phi cao hn mc nc ngm n nh ca khu vc h khoan l 1,5 mt . Nu khng cao ny c kh nng xp thnh vch h khoan do p lc t v nc bn ngoi h gy ra . Nu khng bo m dung trng ca bn ti nh yu cu cng gy ra xp vch h khoan do iu kin p lc bn ngoi h . V su y cc khoan nhi : do ngi thit k ch nh . Thng thng y cc nn t trong lp ct to ht c hm lng si cui kch thc ht trn 10 mm ln hn 20% t 1,5 n 2 mt tr ln . iu kin c th ca tng cng trnh , quyt nh su ca cc phi theo ti trng tnh ton m mi cc phi chu . S c hay gp khi khoan to l l xp vch do mc bentonite trong h thp hn mc n}c ngm bn ngoi, phi nhanh chng b sung bentonite. Bentonite long qu cng gy xp vch. Nhiu khi khoan ch}a n su thit k gp phi thu knh bn hay thu knh cui si mt dy c hoc c ht ln ( hin t}ng trm tch y ao h x}a). Khi gp ti bn cn s dng dung dch khoan c mt ln thm khoan qua. Khi gp cui si dy c hoc }ng knh ht ln cn i gu khoan. Gu thng khng thch hp vi }ng knh cui si c c ht bng 1/2 chiu rng khe h no t. Tr}ng hp ny phi dng gu xon (augerflight) hoc dng mi khoan }ng knh nh c qua lp cui si. 3.1.7 Cng ngh lp ct thp :


16

Ct thp trong cc khoan nhi su t ngha chu ti m ch c tnh cht cu to . Ty ngi thit k quy nh nhng thng thp t khi lm chiu su ca cc . Thanh thp lin hin nay ch to di 11,7 mt nn ct thp ca cc khoan nhi hay chn l bi s ca 11 mt . Ct thp c khuych i thnh lng tng on 11,7 mt . Khi c php s th xung h khoan tng lng . Lng di ni vi lng trn theo cch buc khi th lng di gn ht chiu di , ngng thanh t ln vch chng la qua lng buc ni thp . Sau th tip . Ton b lng thp c mc treo vo ming vch chng bng 3 si )16 v nhng si ny dng h quang in ct i trc khi ly vch ln . Thp dc ca lng thp hay dng )25 ~ )28 , cc thanh dc cch nhau 150 ~ 200 mm . ai c th vng trn hay xon . ng knh thp ai hay dng )10 ~ )12 . Khi dng my LEFFER khoan, phi treo lng thp vo mc cu ca my o. Khi tho ng v kim mi o cho ng ra sau khi b tng phi tho mc treo ct thp, sau li phi mc treo li khi xoay rt nhng on ng tip trc. Nu thp t xung y h khoan, phi c tn hiu theo di s c mt ca ct thp ti v tr. Nu thy thp c kh nng b chm, phi treo gi ngay. 3.1.8 Cng ngh b tng: B tng c khi kim tra sch h khoan v vic t ct thp. Thng lp li ng trmie dng khi thi ra lc trc lm ng dn b tng . Cp phi b tng do thit k tha thun v phi thng qua ch nhim d n. Nn dng b tng ch trn sn th}ng phm. Th}ng dng c ph gia ko di thi gian ng kt ng thi vi ph gia gim n}c ( loi R4 ca Sika vi t l #0,8 ~ 1% ) phng qu trnh vn chuyn b ko di cng nh} ch i tuyn thi cng ti cng tr}ng. st ca b tng thng chn t 120 mm n 160 mm p ng iu kin thi cng ( workability ) . Nu khng st theo yu cu m lng nc vt qua mc cho php phi dng ph gia ha do . Khng nn st qu ln ( qu 160 mm ) s nh hng n cht lng b tng. (i) Thit b s dng cho cng tc b tng : - Btng ch trn sn ch n bng xe chuyn dng ; - ng dn b tng t phu xung su yu cu ; - Phu hng b tng t xe ni vi ng dn ; - Gi ng v phu . Gi ny m t trn .


17

(ii) Cc yu cu b tng : - B tng n cng cng tr}ng }c ngn li kim tra : phm cht chung qua quan st bng mt. Kim tra st hnh cn Abrams v c mu kim tra ph hu mu khi n tui.

- ng dn b tng c nt bng bao ti cha va do ximng ct 1:3 hoc nt bng ti nylng cha ht bt xp trnh s to nn nhng ti kh trong b tng lc ban u . Nt ny s b b tng y ra khi . - Ming di ca ng dn b tng lun ngp trong b tng ti thiu l 1 mt nhng khng nn su hn 3 mt . - Khi b tng , b tng c a xung su trong lng khi b tng, qua ming ng s trn ra chung quanh , nng phn b tng n lc u ln trn , b tng c nng t y ln trn . Nh th , ch c mt lp trn cng ca b tng tip xc vi nc , cn b tng gi nguyn cht lng nh khi ch to . - Phm cp ca b tng ti thiu l C 25 ( tng ng mc 300 th nghim theo mu lp phng ). - B tng phi n cao . Khi rt m cui cng , lc nng rt vch c 1,5 mt nn thm b tng b vo ch b tng chy lan vo nhng hc quanh vch c to nn, nu c , khi khoan su . Cn cho b tng tro khi ng vch khong 20 ~ 30 cm v y l lp b tng tip xc vi bentonite s rng cht l}ng xu. 3.2 Kim tra trong qu trnh thi cng cc khoan nhi : Cc c tr}ng k thut dng kim tra cc khu trong qu trnh thi cng cc nhi v cc, t}ng barrette ch yu nh} sau: (1) c trng nh v ca cc v kim tra : * c trung:

-V tr cc cn c vo h trc cng trnh v h trc gc . - Cao trnh mt h khoan - Cao trnh mt t ti ni c h khoan - Cao trnh y h khoan

* Kim tra : - Dng my kinh v v thy bnh kim tra theo nghip v o c . ( Ngi thc hin nhim v o c phi c chng ch hnh ngh o c ).


18

(2) c trng hnh hc ca h khoan v kim tra : *c trng : - ng knh h khoan hoc s l ng knh cc . - nghing l thuyt ca cc . nghing thc t . - Chiu su l khoan l thuyt , chiu su thc t . - Chiu di ng vch . - Cao trnh nh v chn ng vch .

* Kim tra : o c bng thc v my o c . Phi thc hin nghim tc quy phm o kch thc hnh hc v dung sai khi o kim . (3) c trng a cht cng trnh :

* c trng : -C 2 m theo chiu su ca h khoan li quan st thc t v m t loi t gp phi khi khoan i chiu vi ti liu a cht cng trnh c c quan kho st a cht bo thng qua mt ct l khoan thm d ln cn . Phi m bo tnh trung thc khi quan st . Khi thy khc vi ti liu kho st phi bo ngay cho bn thit k v bn t vn kim nh c gii php s l ngay . (4) c trng ca bn khoan :

* c trng : Nh cc ch tiu bit : Dung trng , nht , hm lng ct , lp v bm thnh vch ( cake ) , ch s lc , pH .

* Kim tra : Trn hin trng phi c mt b dng c th nghim kim tra cc ch tiu ca dung dch bn bentonit . (5) c trng ca ct thp v kim tra :


19

* c trng : - Kch thc ca thanh thp tng loi s dng - Hnh dng ph hp vi thit k - Loi thp s dng ( m hiu , hnh dng mt ngoi thanh , cc ch tiu c l cn thit ca loi thp ang s dng ). - Cch t hp thnh khung , lng v v tr tng i gia cc thanh . - sch ( g , bm bn , bm bn ), khuyt tt c di mc cho php khng . - Cc chi tit chn ngm cho kt cu hoc cng vic tip theo : chi tit sau hn , mc st , chn bu lng , ng quan st khi dng kim tra siu m , dng kim tra phng x (carrota ).

* Kim tra : Quan st bng mt , o bng thc cun ngn , th nghim cc tnh cht c l trong phng th nghim , nu cn. (6) c trng v b tng v kim tra :

* c trng : - Thnh phn , cp phi . - Cht lng ct liu ln , ct liu mn ( kch thc ht , gc , ln cc ht khng t yu cu , sch vi cht bm bn ) - Xi mng : phm cp , cc ch tiu c l ,cc hm lng c hi : kim , sunpht ... - Nc : cht lng - Ph gia : cc ch tiu k thut , chng ch ca nh sn xut . - st ca hn hp b tng , cch ly st . - Ly mu kim tra cht lng b tng ha cng . - Kim tra vic b tng ( chiu cao , ct nh cc , chiu di cc trc hon thin , khi lng l thuyt tng ng , khi lng thc t , d gia thc t v l thuyt ...) - ng cong b tng ( quan h khi lng - chiu cao k t y cc tr ln )

* Kim tra : 19Share-connect.blogspot.com

20

Chng ch v vt liu ca ni cung cp b tng Thit k thnh phn b tng c s tha thun ca bn k thut kim tra cht lng . st ca b tng. Cch ly mu v qu trnh ly mu . Kim tra giy giao hng ( tch k giao hng ) Bin bn chng kin vic p mu 3.3 . Cng ngh kim tra cht lung cc nhi ch yu nhu sau: Cc yu t ch yu nh h}ng cht l}ng cc nhi * iu kin a cht cng trnh v a cht thu vn.

Kim tra cht l}ng cc khoan nhi

Trong qu trnh thi cng Khi lm xong cc

Cc qu trnh: * Chun b * Khoan to l * Hon thnh khoan * Ct thp * b tng * Ph u cc * i cc

Kim tra cht long nn: * Cc ph}ng php tnh * Th cc kiu phn tch ng lc (PDA) Kim tra cht long cc: * Khoan ly mu * Th nghim cc ton vn (PIT) hoc m di (PET) * Th nghim siu m, v tuyn, phng x, hiu ng in - thu lc, o sng ng sut.


21

* Trang thit b thi cng * Cng ngh thi cng. * Cht l}ng ca tng cng on thi cng. * Vt liu thi cng. Vic kim tra k cht l}ng thi cng tng cng on s lm gim }c cc khuyt tt ca sn phm cui cng ca cc nhi. Cn luu cc khuyt tt c th : + Trong khu chun b thi cng ch}a tt nh} nh v h khoan khng chnh xc dn n sai v tr. + Trong khu thi cng : Cng on to l xp vch, co tit din cc, nghing cc qu mc cho php. Nhiu khi thi cng ch}a n chiu su tnh ton m bn thi cng dng khoan lm cc khu tip theo, c khi s dng ny }c ng tnh ca ng}i gim st hoc thit k khng c kinh nghim quyt nh m khuyt tt ny ch }c pht hin l sai khi th ti khi ngy.

Cng on b tng khi y h khoan cn bn lng ng, rt ng nhanh lm cho cht l}ng b tng khng ng u, b ti bn trong thn cc. C khi thn cc b t on. Cng on rt ng vch c th lm cho cc b nhc ln mt on. cc b tht tit din. Nhng khuyt tt ny trong qu trnh thi cng c th gim thiu n ti a nh khu kim tra cht l}ng }c tin hnh ng thi im, nghim tc v theo ng trnh t k thut, s dng ph}ng tin kim tra m bo chun xc. Kim tra cht l}ng sau khi thi cng nhm khng nh li sc chu ti tnh ton ph hp vi d bo khi thit k. Kim tra cht l}ng cc sau khi thi cng l cch lm th ng nh}ng cn thit. C th kim tra li khng ch cht l}ng chu ti ca nn m cn c cht l}ng b tng ca bn thn cc na. Kim tra truc khi thi cng: (i) Cn lp ph}ng n thi cng t m, trong n nh ch tiu k thut phi t v cc b}c cn kim tra cng nh} s chun b cng c kim tra. Nhng cng c kim tra }c c quan kim nh kim v ang cn thi hn s dng. Nht thit phi th}ng trc nhng dng c kim tra cht l}ng ny k vi ni thi cng v lun lun trong tnh trng sn sng phc v. Ph}ng n thi cng ny phi }c t} vn gim st cht l}ng tho thun v k s} i din ch u t} l ch nhim d n ng .


22

( ii) Cn c ti liu a cht cng trnh do bn khoan thm d cung cp cho thit k ngay ti ni thi cng s dng i chiu vi thc t khoan.

(iii) Kim tra tnh trng vn hnh ca my thi cng, dy cp, dy cu, b phn truyn lc, thit b hm, cc ph tng my khoan nh} bp chut, gu, rng gu, cc my ph tr phc v khu bn khoan, khu lc ct nh} my bm khuy bn, my tch ct, sng ct. (iv) Kim tra l}i nh v cng trnh v tng cc. Kim tra cc mc khng ch nm trong v ngoi cng trnh, k c cc mc khng ch nm ngoi cng tr}ng. Nhng my o c phi }c kim nh v thi hn }c s dng ang cn hiu lc. Ng}i tin hnh cc cng tc v xc nh cc c tr}ng hnh hc ca cng trnh phi l ng}i }c php hnh ngh v c chng ch. Kim tra trong khi thi cng: Ngoi nhng iu nu trong phn 3.2 trn, q trnh thi cng cn kim tra cht ch tng cng on yu cu kim tra:

(i) Kim tra cht l}ng kch th}c hnh hc. Nhng s liu cn }c khng nh: v tr tng cc theo hai trc vung gc do bn v thi cng xc nh. Vic kim tra da vo h thng trc gc trong v ngoi cng tr}ng. Kim tra cc cao trnh: mt t thin nhin quanh cc, cao trnh mt trn ng vch. thng ng ca ng vch hoc nghing cn thit nu }c thit k cng cn kim tra. Bin php kim tra thng ng hay nghing ny gii trnh v }c k s} i din ch u t} duyt. Ng}i kim tra phi c chng ch hnh ngh o c. (ii) Kim tra cc c tr}ng ca a cht cng trnh v thu vn. C khoan }c 2 mt cn kim tra loi t v tr thc a c ng khp vi bo co a cht ca bn kho st lp tr}c y khng . Cn ghi chp theo thc t v nhn xt nhng iu khc nhau, trnh bn k s} i din ch u t} cng thit k quyt nh nhng iu chnh nu cn thit. c cng trnh ngay ti H ni vo cui nm 1994, khi quyt nh ngng khoan lm tip cc khu sau khng i chiu vi mt ct a cht cng nh} ng}i quyt nh khng am t}ng v a cht nn phi b hai cc }c b tng khng m bo su v kt qu p tnh th ti ch t 150% ti tnh ton cc hng.

(iii) Kim tra dung dch khoan tr}c khi cp dung dch vo h khoan, khi khoan su v khi xc ra lm sch h khoan xong. (iv) Kim tra ct thp tr}c khi th xung h khoan. Cc ch tiu phi kim tra l }ng knh thanh, di thanh ch, khong cch gia cc thanh, sch du m.


23

(v) Kim tra y h khoan: Chiu su h khoan }c o hai ln, ngay sau khi va t su thit k v sau khi lng v vt li. Sau khi th ct thp v th ng trmie, tr}c lc b tng nn kim tra xc nh lp cn lng. Nu cn c th ly thp ln, ly ng trmie ln vt tip cho t sch y h. y h khng sch s gy ra ln d} qu mc cho php. (vi) Kim tra cc khu ca b tng tr}c khi vo h. Cc ch tiu kim tra l cht l}ng vt liu thnh phn ca b tng bao gm ct liu, xi mng, n}c, cht ph gia, cp phi. n cng tr}ng tip tc kim tra st Abram's, c mu kim tra s hiu, s b nh gi thi gian s ninh. (vii) Cc khu cn kim tra khc nh} ngun cp in nng khi thi cng, kim tra s lin lc trong qu trnh cung ng b tng, kim tra thng ca mng , m}ng n dung dch tro t h khi b tng ... Cc phung php kim tra cht lung cc nhi sau khi thi cng xong: Kim tra cht l}ng cc khoan nhi da vo TCXD 196:1997, Nh cao tng - Cng tc th tnh v kim tra cht l}ng cc khoan nhi. Tiu chun ny mi cp n ba loi th: nn tnh, ph}ng php bin dng nh PIT v ph}ng php siu m. Nhng ph}ng n c th s dng do ch nhim d n quyt nh: (i) Kim tra bng phung php tnh : Phung php gia ti tnh : Ph}ng php ny cho n hin nay }c coi l ph}ng php trc quan, d nhn thc v ng tin cy nht. Theo yu cu ca ch u t} m c th thc hin theo kiu nn, ko dc trc cc hoc y theo ph}ng vung gc vi trc cc. Th nghim nn tnh }c thc hin nhiu nht nn ch yu cp y l nn tnh. C th chn mt trong hai qui trnh nn tnh ch yu }c s dng l qui trnh ti trng khng i ( Maintained Load, ML ) v qui trnh tc dch chuyn khng i ( Constant Rate of Penetration, CRP ). Qui trnh nn vi ti trng khng i (ML) cho ta nh gi kh nng chu ti ca cc v ln cu cc theo thi gian. Th nghim ny i hi nhiu thi gian, ko di thi gian ti vi ngy. Qui trnh nn vi tc dch chuyn khng i ( CRP) th}ng ch dng nh gi kh nng chu ti gii hn ca cc, th}ng ch cn 3 n 5 gi. Nhn chung tiu chun th nghim nn tnh ca nhiu n}c trn th gii t khc bit. Ta c th so snh tiu chun ASTM 1143-81 ( Hoa k), BS 2004 ( Anh) v TCXD 196-1997 nh} sau:


24

Qui trnh nn chm vi ti trng khng i

Ch tiu so snh ASTM D1143-81 BS 2004 TCXD 196-1997Ti trng nn ti a, Qmax ln cp tng ti Tc ln n nh qui }c Cp ti trng c bit v thi gian gi ti ca cp ln cp h ti

200%Qa* 25%Qa 0,25 mm/h 200%Qa v 12d t d 24h 50%Qa

150%Qa~200%Qa 25%Qa 0,10mm/h 100%Qa, 150%Qa vi t t 6h 25%Qa

200%Qa 25%Qmax 0,10 mm/h (100%&200%)Qa = 24h 25%Qmax

Qui trnh tc chuyn dch khng i Ch tiu so snh

ASTM D 1143-81

BS 2004 TCXD 196-1997

Tc chuyn dch Qui nh v dng th nghim

0,25- 25mm/min cho cc trong t st 0,75~2,5mm/min cho cc trong t ri t ti trng gii hn nh tr}c Chuyn dch t 15%D

Khng th qui nh c th t ti trng gii hn nh tr}c Chuyn dch tng trong khi lc khng tng hoc gim trong khong 10mm Chuyn dch t 10%D

Ch}a c qui nh cho loi th kiu ny.

Ghi ch: Qa = kh nng chu ti cho php ca cc V i trng gia ti, c th s dng vt nng cht ti nh}ng cng c th s dng neo xung t. Tu iu kin thc t c th m quyt nh cch to i trng. Vi sc neo kh ln nn khi s dng bin php neo cn ht sc thn trng. i b phn cc cng trnh th ti tnh dng cch cht vt nng lm i trng. Cho n nay, ch c mt cng trnh dng ph}ng php neo th ti l cng trnh Grand Hanoi Lakeview Hotel s 28 }ng Thanh nin do Cng ty Kinsun ( Thi lan) thuc tp on B&B thc hin.


25

Do chng ta ch}a c qui phm nh ra cht l}ng cc khi th xong nn cn bn bc thng nht tr}c vi ch u t} xc nh cc tiu ch cht l}ng tr}c khi thi cng. Phung php gia ti tnh kiu Osterberrg: Ph}ng php ny kh mi vi th gii v n}c ta. Nguyn tc ca ph}ng php l mt lp b tng dy d}i y ri th h hp kch ( O-cell ) xung , sau li tip phn cc trn. H iu khin v ghi chp t trn mt t. S dng ph}ng php ny c th th nghim ring bit hoc ng thi hai ch tiu l sc chu mi cc v lc ma st bn ca cc. Ti th nghim c th t }c t 60 tn n 18000 tn. Thi gian th nghim nhanh th ch cn 24 gi, nu yu cu cng ch ht ti a l 3 ngy. su t trang thit b th nghim trong mng c th ti trn 60 mt. Sau khi th xong, bm b tng xung lp h kch cho cc }c lin tc. (Tin s Jorj O. Osterberg l chuyn gia a k thut c tn tui, hin sng ti Hoa k. ng hin nay ( 1998 ) v h}u nh}ng l gio s} danh d ca Northwestern University, Vin s Vin Hn lm K thut, 1985 l ging vin tr}ng Tersaghi, nm 1988 l thnh vin Vin nn mng su. Nm 1994 ph}ng php th tnh Osterberg ra i vi tn O-Cell , }c cp chng ch NOVA. Chng ch NOVA l dng }c coi nh} gii Nobel v xy dng ca Hoa k. Ph}ng php th tnh O-Cell c th dng th ti cc nhi , cc ng, t}ng barettes, th nghim ti hng cc, th nghim cc lm kiu gu xoay ( Auger Cast Piles ). N}c ta c mt s cng trnh s dng ph}ng php th ti tnh kiu Osterberg. Ti H ni c cng trnh Thp Vietcombank , ti Nam b c cng trnh cu Bc M thun s dng cch th cc kiu ny). (ii) Phung php khoan ly mu li cc: Dng my khoan khoan vo cc, c th ly mu b tng theo }ng knh 50~150 mm, dc sut su d nh khoan. Nu }ng knh cc ln, c th phi khoan n 3 l nm trn cng mt tit din ngang mi tm c khi nim v cht l}ng b tng dc theo cc. Ph}ng php ny c th quan st trc tip }c cht l}ng b tng dc theo chiu su l khoan. Nu th nghim ph hu mu c th bit }c cht l}ng b tng ca mu. u im ca ph}ng php l trc quan v kh chnh xc. Nh}c im l chi ph ly mu kh ln. Nu ch khoan 2 l trn tit din cc theo chiu su c cc th chi ph xp x gi thnh ca cc. Th}ng ph}ng php ny ch gii quyt khi bng cc ph}ng php khc xc nh cc c khuyt tt. Ph}ng php


26

ny kt hp kim tra chnh xc ho v s dng ngay l khoan bm pht xi mng cu cha nhng on hng. Ph}ng php ny i hi thi gian khoan ly mu lu, qu trnh khoan cng phc tp nh} phi dng bentonite tng mt khoan ln b, phi ly mu nh} khoan thm d v tc khoan khng nhanh lm. Ph}ng php ny c }u im l c th nhn dng }c ngay cht l}ng m ch yu l chc c ca b tng. Nu em mu th nn ph hu mu th c kt qu sc chu ca mu . Tuy ph}ng php phc tp v tn km nh}ng nhiu nh u t} vn ch nh ph}ng php ny. (iii) Phung php siu m:

Ph}ng php th l dng k thut nh gi kt cu khng ph hu mu th ( Non-destructive evaluation, NDE ). Khi th khng lm h} hng kt cu, khng lm thay i bt k tnh cht c hc no ca mu. Ph}ng php }c Chu u v Hoa k s dng kh ph bin. Cch th thng dng l qut siu m theo tit din ngang thn cc. Tu }ng knh cc ln hay nh m b tr cc l dc theo thn cc tr}c khi b tng. L dc ny c }ng knh trong xp x 60 mm v l l ng nha hay ng thp. C khi ng}i ta khoan to l nh} ph}ng php kim tra theo khoan l ni trn, nu khng l tr}c. u thu pht c hai kiu: kiu u thu ring v u pht ring, kiu u thu v pht gn lin nhau.

Nu }ng knh cc l 600 mm th ch cn b tr hai l dc theo thn cc i

xng qua tm cc v nm st ct ai. Nu }ng knh 800 mm nn b tr 3 l. }ng knh 1000 mm, b tr 4 l... Khi th, th u pht siu m xung mt l v u thu l khc. }ng qut kim tra cht l}ng s l }ng ni gia u pht v u thu. Qu trnh th u pht v u thu cn m bo hai u ny xung cng mt tc v lun lun nm cng su so vi mt trn ca cc.

Qui phm ca nhiu n}c qui nh th nghim kim tra cht l}ng cc b

tng bng ph}ng php khng ph hu phi lm cho 10% s cc.

(iv) Phung php th bng phng x ( Carota ): Ph}ng php ny l mt ph}ng php nh gi khng ph hu mu th ( NDE- non destructive evaluation ) nh} ph}ng php siu m. Cch trang b th nghim khng khc g ph}ng php siu m. iu khc l thay cho u thu v u pht siu m l u thu v pht phng x. N}c ta sn xut loi trang b ny do mt c s ca qun i tin hnh. Ging nh} ph}ng php siu m, kt qu c biu thu phng x c th bit }c ni v mc ca khuyt tt trong cc.


27

(v) Phung php o m di: Ph}ng php ny th nghim kim tra khng ph hu mu bit cht l}ng cc , cc nhi, cc barrettes. Nguyn l l s dng hin t}ng m di ( Pile Echo Tester, PET ). Nguyn tc hot ng ca ph}ng php l g bng mt ba 300 gam vo u cc, mt thit b ghi gn ngay trn u cc y cho php ghi hiu ng m di v my tnh s l cho kt qu v nhn nh cht l}ng cc. My tnh s dng s l kt qu ghi }c v m di l my tnh c nhn tiu chun ( standard PC ) , s dng phn cng b sung ti thiu, mi tn hiu thu nhn v s l qua phm mm m phn mm ny c th nng cp nhanh chng, tin li ngay c khi lin h bng e-mail vi trung tm GeocomP. Phm mm da vo c s Windows theo chun vn hnh hin i, }c nghin cu ph hp vi s hp l ti a v cng thi hc (ergonomic). Mt ng}i lm }c cc th nghim v m di vi nng sut 300 cc mt ngy. Khi cn thit nn tip xc vi http://ww.piletest.com/PET.HTM ta c th c }c kt qu chun mc khi th cc v }c cung cp min ph phn mm cp nht theo }ng e-mail. Vi s tin li l chi ph cho kim tra ht sc thp nn c th dng ph}ng php ny th nghim cho 100% cc trong mt cng trnh. Nh}c im ca ph}ng php l nu chiu su ca cc th nghim qu 20 mt th chnh xc ca kt qu l thp. (vi) Cc phung php th ng: C rt nhiu trang thit b th ng nh} my phn tch ng cc th theo ph}ng php bin dng ln ( PDA), my ghi kt qu th theo ph}ng php bin dng nh (PIT), my ghi saximeter, my phn tch hot ng ca ba ( Hammer Performance Analyzer, HPA ), my ghi kt qu gc nghing ca cc ( angle analyzer), my ghi kt qu ng cc ( Pile installation recorder, PIR ), my phn tch xuyn tiu chun ( SPT analyzer) ... * My phn tch cc theo ph}ng php bin dng ln PDA c loi mi nht l loi PAK. My ny ghi cc th nghim nng cho mi tr}ng xy dng c nghit. My ny ghi kt qu ca ph}ng php th bin dng ln cho cng trnh nn mng, cho thm d a k thut . Phn mm s l rt d tip thu. S liu }c t ng l}u gi vo a s dng v sau. Ch}ng trnh CAPWAP ci t }c vo PAK nn vic nh gi kh nng ton vn v kh nng chu ti ca cc rt nhanh chng. * S dng ph}ng php th Bin dng nh ( PIT ) l cch th nhanh cho s ln cc. Php th cho bit cht l}ng b tng cc c tt hay khng, tnh ton vn ca cc


28

khi kim tra cc khuyt tt ln ca cc. Cc loi my phn tch PIT dung ngun nng l}ng pin, c ng nhanh chng v s dng n chic. Dng c ca ph}ng php PIT dng tm cc khuyt tt ln v nguy him nh} nt gy, tht c chai, ln nhiu t trong b tng hoc l rng. (vii) Phung php tr khng c hc: Ph}ng php ny quen thuc vi tn gi ph}ng php phn tch dao ng hay cn gi l ph}ng php truyn sng c hc. Nguyn l }c p dng l truyn sng, nguyn l dao ng c}ng bc ca cc n hi. C hai ph}ng php thc hin l dng tr khng rung ng v dng tr khng xung. Ph}ng php tr khng rung s dng m t in ng }c kch hot do mt my pht tc ng ln cc. Dng mt my ghi vn tc sng truyn trong cc. Nhn biu sng ghi }c, c th bit cht l}ng cc qua ch tiu ng u ca vt liu b tng cc v tr . Ph}ng php tr khng xung l c s cho cc ph}ng php PIT v PET. Hai ph}ng php PIT v PET ghi sng m di. Ph}ng php tr khng xung ny ghi vn tc truyn sng khi p ba to xung ln u cc. S khc nhau gia ba ph}ng php ny l my ghi }c cc hin t}ng vt l no v phn mm chuyn cc dao ng c l hc y d}i dng sng ghi }c trong my v th hin qua biu nh} th no. 3.4 nh gi cht lng cc :

Cht lung bn thn cc: (i) B tng thn cc mt tng mng do b tng c st qu ln . (ii) B tng cc mt tng mng do c ti nc trong thn h khoan . (iii) B tng thn cc mt tng on do gp ti nc ln trong thn h khoan. (iv) Mi cc mt mt on b tng do y xc ra khng sch . (v) Thn cc thu nh tit din , l mt khi b tng bo v do rt ng khi b tng s ninh , mt phn ngoi b tng b ma st vi thnh vch chng i ln . (vi) Cc b mt thng ng do khi rt ng c tc ng ngang trong qu trnh rt ng . (vii) Cc b thiu mt s b tng do thp qu dy , b tng khng chy dng kn ht khng gian . (viii) Thn cc nham nh do b tng c st nh . (ix) Thn cc c on ch c si hoc c cc l rng ln do b tng b gin on .


29

Cht lng cc chu ti tnh khng p ng :

(i) Do khng khoan n su cc quy nh thi cng cc cng on sau. (ii) Do cn lp bn qu dy tn y h khoan b tng . (iii) B ln ti 2% }ng knh ca cc vi ti trng th bng hai ln ti trng thit k sau 24 gi. B ln ti 2,5% }ng knh ca cc vi ti trng th bng hai ln r}i ti trng thit k sau 24 gi. (iv) ln d} ln hn 8 mm. Cht lng ct thp khng t : (i) t khng ng khong cch gia cc thanh , lng thp b mo m , bin hnh so vi thit k . (ii) Thp b bn . Nh rng mi trng lm vic rt sn bn dy bn ct thp. ( iii) Ni thp khng ng quy nh cch ni , v tr ni .

iu kin cng tc km : (i) Mt bng lun ngp nga trong bn . Khi b tng th tch b tng n hng chc khi bn ra mt t , gy ngp nga bn quanh ch lm vic m khng c bin php thu hi hoc lm rnh v h tch t . (ii) Mt bng ngp nga cn tr thi cng nhng cc tip , dy bn ra thp , ra cc thit b khc trn cng trng , chy lnh lng ra ng ph v cng thot nc chung ca thnh ph . (iii) Phi c thit k tr liu kh nng to bn trn mt bng c gii php khc phc t u .

3.5 Lp h s cho ton b mt cc nhi c thi cng :

Qu trnh thi cng cc no phi tin hnh lp h s ngay cho cc y. Da vo cc c trng nu m bn thi cng phi bo co y cc ch tiu , kt qu kim tra tng ch tiu c trng . Kt qu v h s ca cc kim tra cui cng bng tnh ti , bng cc phng php khc.


30

Trong h s c y cc chng ch v vt liu , kt qu th nghim kim tra cc ch tiu c cp chng ch . Mt bo co tng hp v cht lng v cc ch tiu l thuyt cng nh thc t ca tng cc . 3.5 Mt s luu khi thi cng cc nhi: Khi cng trnh c h o su hn mt y mng ca cng trnh hin hu lin k t 0,2 mt tr ln phi lm c quanh }ng bin h o. C c su theo tnh ton khng b p lc y x vo trong sau khi o. C khng cho n}c qua theo ph}ng ngang. Vic la chn c thp, c b tng ct thp , c b tng ct thp ng lc tr}c, c g hay c nha cn c vo thit k cng ngh thi cng. Nhng loi c s dng c hiu qu l c thp Lacsen, Zombas. C nha polyurthan mi vo th tr}ng n}c ta l loi hu hiu. Cn cn nhc khi s dng c cc thp I-20, b}ng vn g v hiu qu k thut v kinh t khng cao. Cng ngh c b tng ct thp ng lc tr}c mi nhp vo n}c ta v }c ch to nhng nm gn y c th s dng }c. Khi ch}a c c kn kht khng nn h mc n}c ngm. T}ng c }c chng nh neo, cy chng hoc khung chng, m bo khng dch chuyn, khng bin dng trong sut qu trnh thi cng. H chng t}ng c }c thit k, tnh ton k tr}c khi thi cng, v l bin php m bo cht l}ng cng trnh quan trng. H chng ny c th lp t theo tng mc su o t nh}ng nm trong tng th nh. t t cc h o ly ra khng nn ct cha ti mt bng m cn di chuyn khi cng tr}ng ngay. Khi cn dng t lp s cung cp chng loi t c cc tnh cht ng theo yu cu. Cn bm n}c thun li cho thi cng , ch nn h mc n}c bn trong phm vi vng chn t}ng c hoc trong phm vi kt cu vy quanh v l do an ton cho cng trnh hin hu lin k. Tr}c khi lp t phi dn sch v san phng mt lp. Mi chi tit kt cu v h ng k thut s nm trong t phi lp t xong, thc hin y cc gii php bo v cng nh} chng thm. Cn nghim thu cng trnh khut tr}c khi lp t. Vic lp }c tin hnh thnh tng lp dy 20 cm ri m k. 3.6 Qui trnh thi cng cc vw tung barrette :


31

Cc hay t}ng barrette l kt cu dng t}ng hoc tr btng ct thp c chiu su t}ng }ng vi cc nhi. Chiu ngang tit din barrette th}ng l 600 mm , 800 mm hay hn na. Chiu di ca t}ng th}ng theo chu vi nh hoc do kt cu bn trn nh ot. Cc barrette c tit din ngang l hnh ch nht th}ng l 600x2400mm, 800x2400mm . C th loi cc ny c tit din ngang hnh sao 3 nhnh u, t tm n u nhnh l 2400mm ( ch Y ), c th tit in ngang to thnh ch I m hai u cnh l hai hnh ch nht 600x2400mm }c ni vi nhau bng on bng cng 600x2400mm. C th cc barrette c tit din ngang hnh ch U ging hnh I trn nh}ng on bng chuyn dch ra mp ca hai cnh. Qui trnh thi cng t}ng trong t ch khc thi cng cc nhi khu to l. Nhng khu khc t}ng t nh} thi cng cc nhi. Cng c to l l gu clamshell c b phn dn h}ng ni pha trn gu.. Phi lm khoang dn h}ng cho on o lp trn cng cho n khi o su bng chiu cao gu. Qu trnh o cng dng dung dch gi thnh vch nh} i vi cc nhi. o thnh tng on c chiu di khong 2400mm ( gi l cc panel). t thp v b tng xong mi lm tip cc panel sau. Dng b phn ni nm trong hp thp di ngn n}c c th thm qua mi ni gia hai panel. B phn ni ny l sng ch ca cng ty Bachy-Soletanche c tn l mi ni ngn n}c (WaterStop Joint). Vic th thp, xc ra, b tng v kim tra hon ton ging nh} cc nhi. Ring kim tra nn tnh phi dng ph}ng php Osterberg v ti cho mi cc kh ln, hng ngn tn. 3.7 Phung php Top-down thi cng phn hm nhw: Ph}ng php Top-down l ph}ng php lm hm nh theo kiu t trn xung. i vi nhng nh s dng t}ng barrette quanh chu vi nh ng thi lm t}ng cho tng hm nh nn thi cng tng hm theo kiu top-down. Ni dung ph}ng php nh} sau: * Lm sn tng trt tr}c khi lm cc tng hm d}i. Dng ngay t ang c lm coppha cho sn ny nn khng phi cy chng. Ti sn ny mt l trng khong 2mx4m vn chuyn nhng th s cn chuyn t d}i ln v trn xung. * Khi sn cng, qua l trng xung d}i m moi t to khong khng gian cho tng hm st trt. Li dng nn lm coppha cho tng hm tip theo. Ri li moi tng d}i na cho n nn cui cng th lp nn y. Nu c ct th nn lm ct lp ghp sau khi sn d}i.


32

* Ct thp ca sn v dm }c ni vi t}ng nh khoan xuyn t}ng v la thp sau. Dng va ximng trn vi Sikagrout bm st vo l khoan t thp. 3.7.1. Thit b phc v thi cng : - Phc v cng tc o t phn ngm th}ng dng cc my o t loi nh, my san t loi nh, my lu nn loi nh, cc cng c o t th cng, my khoan b tng. - Phc v cng tc vn chuyn : hay s dng cn trc nh phc v chuyn t t ni tp kt sau khi o trong lng nh ra ln xe t chuyn t i xa; b tr thng cha t , xe ch t t . - Phc v cng tc khc : b tr my bm, thang thp t ti li ln xung , h thng n in chiu sng cho vic thi cng d}i tng hm. - Phc v cng tc thi cng b tng : trm bm b tng , xe ch b tng th}ng phm , cc thit b phc v cng tc thi cng b tng khc - Ngoi ra tu thc t thi cng cn c cc cng c chuyn dng khc. 3.7.2. Vt liu : (i). B tng : Do yu cu thi cng gn nh} lin tc nn nu ch b tng tng trn c}ng ri mi tho vn khun v o t thi cng tip phn d}i th thi gian thi cng ko di. m bo tin nn chn b tng cho cc cu kin t tng 1 xung tng hm l b tng c ph gia tng tr}ng c}ng nhanh c th cho b tng t 100% c}ng sau t ngy (nn thit k cng trnh khong 7 ngy) . Cc ph}ng n sau : - Tng c}ng b tng bng vic s dng ph gia gim n}c - B sung ph gia ho do hoc siu do vo thnh phn gc , gim n}c trn , gi nguyn st nhm tng c}ng b tng cc tui. Nn dng ph gia siu do c th t 94% c}ng sau 7 ngy . Ct liu b tng l dm c 1-2 . st ca b tng 60 - 100 mm. Ngoi ra cn dng loi b tng c ph gia tr}ng n v u ct , u li thi cng sau , neo u cc vo i ... Ph gia tr}ng n nn s dng loi khong khi t}ng tc vi n}c xi mng to ra cc cu t n 3CaO.Al2O3.3CaSO4(31-32)H2 (ettringite) . Ph gia ny c dng bt th}ng c ngun gc t : + Hn hp phn (Alunit) sau khi }c phn r nhit trit ( gm cc khong hot tnh (Al2O3 , K2SO4 hoc Na2SO4 , SiO2) v thch cao 2 n}c . + Mnsulfcanxialuminat 3CaO.Al2O3.CaSO4.nH2O , khong silic hot tnh v thch cao 2 n}c. Hm l}ng ph gia tr}ng n th}ng }c s dng 5-15% so vi khi l}ng xi mng. Khng dng bt nhm hoc cc cht sinh kh khc lm b tng tr}ng n. i vi b tng tr}ng n cn ch s dng :


33

+ Ct ht trung, ht th Mdl = 2.4 - 3.3 + st thp = 2 - 4 cm ; max = 8cm

(2). Vt liu khc : - Khi thi cng sn - dm tng hm th nht ( th}ng ct -4.05m) , li dng t lm vn khun ton b kt cu . Do vy , t nn phi }c gia c m bo c}ng khng b ln , bin dng khng u . Ngoi vic lu ln nn t cho phng chc cn phi gia c thm t nn bng ph gia . Mt trn nn t }c tri mt lp vi nha Polyme nhm to phng v cch bit t vi b tng khi nh h}ng n nhau cng nh} chng thm, chng cc tc nhn n mn cho b tng. - Khi thi cng phn ngm c th gp cc mch n}c ngm, nu l n}c ngm c p , ngoi vic b tr cc trm bm thot n}c cn chun b cc ph}ng n vt liu cn thit kp thi dp tt mch n}c nh} l b tng ng kt nhanh. - Cc cht chng thm nh} va SiKa hoc nh t}ng Laticote hoc sn Insultec. 3.7.3 . Quy trnh cng ngh : Qu trnh thi cng theo ph}ng php top-down th}ng i theo trnh t tng b}c nh} sau: (1). Giai on I : Thi cng phn ct chng tm bng thp hnh Chng tm theo ph}ng ng l dng cc ct chng tm bng thp hnh cm tr}c vo cc cc khoan nhi ng v tr cc ct sut chiu cao t mt t n nh cc nhi . L do phi c ct chng tm ny l trong khi phi thi cng phn thn nh bn trn ln cao dn ng thi vi thi cng tng hm, phn thn nh bn trn ch}a c kt cu chnh thc ti trng do thn nh trn tc ng xung cc nhi bn d}i. Cc ct ny }c t ti nh cc nhi ngay trong giai op hon thnh vic thi cng cc khoan nhi. (2). Giai on II : Thi cng phn kt cu ngay trn mt t ( tng 1 ct 0.00m ) Giai on ny bao gm cc cng on sau : - o mt phn t c su khong chng 1.66m to chiu cao cho thi cng dm sn tng 1 - Ghp vn khun thi cng tng 1 - t ct thp thi cng b tng dm - sn tng 1 - Ch 10 ngy cho b tng c ph gia 90% c}ng yu cu. (3). Giai on III : Thi cng tng hm th nht ( ct su khong chng -4.00m ) Gm cc cng on sau : - Tho vn khun dm - sn tng 1 - Bc t n ct su trn d}i mc - 6.80m


34

- Ghp vn khun thi cng tng ngm th nht - t ct thp v b tng dm - sn tng ngm th nht - Ghp vn khun thi cng ct t}ng t tng hm th nht n tng 1 - Ch 10 ngy cho b tng c ph gia 90% c}ng yu cu. (4). Giai on IV: Thi cng tng hm th hai ( ct -8.00m ) Gm cc cng on sau : - Tho vn khun chu lc tng ngm th nht. - o t n ct mt d}i ca i cc ( su khong chng -12.5m) - Chng thm cho phn mng - Thi cng i cc - Thi cng chng thm sn tng hm - Thi cng ct thp b tng sn tng hm th hai - Thi cng ct v li t tng hm th hai ln tng hm th nht Cn lp bin php thi cng theo ph}ng php top-down tht chi tit v }c ch nhim d n duyt tr}c khi thi cng.


35

Chong IV Chng thm cho cng trnh ngm 4.1 iu chung:

Gii php chng thm cho cng trnh phi }c thit k cn thn v phi thi cng ph hp vi giai on cn thit. Cch t vn chng thm cho phn ngm cng trnh l : phi xem xt chng thm l khu tng th gn b mt thit t thit k, thi cng , vt liu cho n khu khai thc s dng cng trnh.. Mi khu gn vi nhau thnh mt th thng nht. Thi cng chng thm cn c cn b, k s} }c phn cng chuyn trch theo di v n c . Vic kim tra cht l}ng chng thm phi }c thit k v thng qua ch nhim d n. H s khi hon thnh tng b}c trong thi cng chng thm cng nh} ch to vt liu , thu mua vt liu cn ghi chp v thu l}m y v l}u tr cn thn. Khi nim chung v s cn thit phi lm tng ngm:

Tnh hnh xy dng n}c ta nn s dng vi tng ngm di t v iu ny em li kt qu tit kim t xy dng. Ngoi ra, lm tng hm cho nh cao tng c li r rt nh: + Do phi o t b i ly khng gian s dng nn ti trng ln nn gim, c li cho s chu lc ca nn t. + Thm khng gian s dng cho cng trnh m khng tng din tch t ai xy dng. + Cng trnh c su, mng nh thm n nh vi cc dng ti trng ngang. + a cc tng k thut xung su, gim ting n, nhim ... Cho n nay, chng ta c th ni l cha s dng phn t ngm. H cng trnh k thut ca th th c vch ty tin. ng thot nc, ng cp nc, ng in, ng in yu thng tin ... mnh ai ny o, bi. H thng ngm chng cho, dng dt, khng theo mt quy hoch chung no.


36

Nu chng ta cha tn dng di t lm nh cng cng nh nhiu nc th cng c th ngh n h thng l ngm k thut hp khi theo quy hoch. Cn ch xe ngm, u mi giao thng ... Vn t ra l cn thit s dng tng su kt hp vi s tp trung ln tng cao. Thi cng tng ngm phi gii quyt cc vn sau: * Cc phng php thi cng cng vic di mt t. * Phng php o hm tin tin. * Gii php chng t st khi bc l. * Chng thm v chng n mn cho cc cng trnh di mt t. * Vn chng rung v chng m cho cng trnh ngm. * Chiu sng cho cng trnh. * Thng gi, cung cp -xy v iu ha khng kh. * Xy dng cng trnh ngm trn mt t c nh. S dch chuyn nh bn trn v xy li theo mu c. * Quy hoch kt hp cng trnh ngm vi cng trnh ni. T quy hoch n cng trnh hin thc.

4.2 Tnh hnh chng thm cho cng trnh ngm nuc ta thi gian qua: Vic xy dng cng trnh ngm nc ta trc nm 1954 l rt nh nhoi. Phn ln l tunen qua ni cho ng xe la , yu cu chng thm khng cao. Phn ln gii php l c ni lm tunen, mt ng t rnh hai bn thot nc chung. Nhng ni c c qua l ni . Mt s nh ln c tng hm khng su. Khng c gii php chng thm c bit g. T nm 1954 v sau, gii php chng thm cho cng trnh ngm ty thuc nc cung cp thit k v vin tr cho cc cng trnh. (1) Cc cng trnh do Trung Quc thit k (vi cng trnh c trng) Nh my phn ln Vn in:


37

Ti cng trnh ny cn chng thm cho cc hng mc: B cha nguyn liu v sn phm, rnh ng ng k thut. su t -3m n -4m so vi mt t thin nhin ti ch. su nc ngm l -1m. Ngha l cng trnh ngm trong nc ngm 2 n 3m. Gii php chng thm ca nh my phn ln Vn in - Thnh b bng b tng ct thp dy 300mm - Lp trt va xi mng 1:3 ct vng dy 15mm. - Lp chng thm: 5 lp nha nng, 3 lp giy du. - Lp va trt bo v dy 20mm. - Tng bo v lp chng thm bng gch ch dy 110mm. - Lp trt bo v lp gch xy va xi mng ct vng dy 15mm Nha dng l bi tum s 4, giy du l rubrt. Cng ti nh my phn ln ny cn dng cu to thay i cht t. Gii php chng thm cho nh my phn ln Vn in thay i * Ngoi cng l gch xy dy 220 mm * Lp trt va xi mng 1:3 dy 15 mm * Ba lp giy du dn bng 5 lp nha nng * Lp trt 20 mm va xi mng ct 1:3 * Lp tng b tng bo v chung c chiu dy 150 mm. Nh my dt 8/3 H ni Ti nh my ny c cc hng mc sau y c yu cu chng thm cao: + Hm cung bng, yu cu tuyt i kh + Hm dn nhit, t cc my nhit, khi vn hnh, s dng nhit cao. + Mng rnh thng hi, thi bi.


38

Nhng hng mc ny c y nm su t 0,70 mt n 3,205 mt trong khi nc ngm su 0,50 mt. so vi mt t thin nhin. Gii php chung ca ngi thit k l tng lm hm bng b tng ( cho hm cung bng v hm dn nhit), tng gch xy ln b tng cho h mng thi bi, mng thng gi. Chng thm l 5 lp giy du rubrt dn bng nha nng. Ni chung sau khi thi cng vn b s c thm. Mt rt nhiu cng sa cha. Nh my luyn cn thp, khu gang thp Thi nguyn: Tt c cc cng trnh di mt t nh mng l, mng rnh, b ngm u dng tng b tng, trt ph ngoi bng va chng thm. Va chng thm dng cht phng nc ( CPN) trn vi xi mng Poc lng thng thng ri ph ngoi kt cu. Cht phng nc dng nhiu nht iu ch ti ch bng cc ha cht gm sunpht ng, bicrmat Kali, sunphat st, sunpht nhm, thy tinh nc. Mt s ch cht phng nc dng sunphat Natri. Trn Aluminat Natri vi xi mng super lm va phng nc. T l pha trn ph thuc p lc nc ti ni s dng. Ngoi ra mt s ch s dng b tng phng nc c trn xi mng Puzlan vi ph gia l Colophan Natri. Ch thch chung: Nhng cch ch to cc lp ngn nc, u nhc im ca nhng gii php ny s nu chung phn di. Ni chung cc gii php ca Trung quc s dng cho cc cng trnh nc ta cng theo cc gii php thng dng ca th gii trong cng thi k. Mt s cng trnh chng thm theo thit k Lin x: Nh my supe pht pht Lm Thao: Cc kt cu di mt t cn chng thm c cht lng cao : Kho supe, kho Apatit, kho pyrit, xng c kh, phng th nghim trung tm.


39

Thc t th sau khi hon thnh cng trnh nhng hng mc ny b thm lin tc. Cc kho qung, thm nc lm m qung, gy bin cht qung, lm lng ph cho sn xut. Kho thnh phm super b ngm trong nc lm gim cht lng hng ha. Nh c kh v th nghim trung tm, do m nn h thng in mt ra ngoi, gy tai nn. Mc nc ngm -1,5 mt di mt t trong khi nn cng trnh t su -3,5 mt. Nn c ci to li l t st nn. Tng b tng thng mc 200. S d thit k khng c gii php chng thm c bit v khi cung cp s liu thy vn ch r mc nc ngm n nh t -3,4 mt n -3,85 mt so vi mt t thin nhin. Thc t th mc nc ngm dao ng, ma kh ng l -3,4 mt. Ma ma mc nc ngm gi 5 thng mc -1,5 mt. Khu hc tp trng i hc Bch khoa Hni: Trm bm nc thi, tng rnh cp trm bin p s 1, b du cc trm bin p s 2 cn chng thm. Mc nc ngm -0,5 mt so vi mt t thin nhin.Kt cu chng thm: tng btng mc 200. trt va xi mng dy 20 mm. Chng thm bng cch dn 3 lp giy du trn nha nng. Nh my in Ung b : Trm bm nc mn, trm bm nc ngt, mng cp, mng thi nc l nhng hng mc yu cu chng thm. Kt cu chng thm l tng b tng hoc tng gch. Trt va xi mng ct dy 20 mm. Trt ph lp va mt tt t phan ngui. Lp va mt tt t phan ngui dy t 15~20 mm. Hiu qu chng thm tt. Kt qu ca Ung b: chy n nh: 120oC khng b rt va. chy mi dc: 70-80 oC trong 7 gi khng b chy khi dc i=45o. thm qua mu 70,7 mm lp phng, th 70 gi di p lc thm 1 atmostphe thm qua 10 cm3.


40

Nhng cng trnh lm trong thi k chin tranh ph hoi min Bc: Vo thi k ny c hai loi dng: kho dng hang ng thin nhin v hm phng khng cho cc c quan quan trng. Hang ng t nhin khng c gii php chng thm c bit m ch dng bt, tm mng mng PVC che nc. Vic thng gi, thot m khng c iu kin c kh v nhng l do nng lng pht ng cng nh tnh bo mt v tnh tm thi ca kho cha. Hm phng khng cho cc c quan quan trng phn ln dng kt cu b tng ct thp, chiu dy tng 300-400 mm, b tng mc 300, dng xi mng Pooclng mc 400 liu lng 350 kg/m3 b tng tr ln. y hm t su -8 ~ -10 mt. Nc ngm H ni l -0,5 mt v Hi phng cng tng t. Lp ngn nc chnh l lp b tng ny. Mt s hm thm mt lp nha nng qut ngoi tng b tng. thm chc chn, thit k cn yu cu dng t st nn cht quanh tng hm bn ngoi c chiu dy 300 mm. Li xung hm l mt ng b tng ct thp tit din vung hoc ch nht ni vi hm. Bn thn hm chng thm tt theo phng php ni trn nhng nc vn vo cng trnh theo cc khe nt gia thang xung v hm. T nhng nm 1967, chng ti i nhiu cng trnh, tham gia gii php v quan st kt qu chng thm cho cc cng trnh ngm ca nc ta. c bit t 1968 n 1970 chng ti c tham gia cc cng trnh hm ti H ni nh Nh khch Chnh ph, hm bnh vin Vit x, hm c quan Bo Nhn dn, ti Hi phng , cc hm K1, K2, K3, K5. Phn nu tnh hnh chng thm cho cc cng trnh ngm nc ta chng ti ch chn la nhng gii php c trng tiu biu. Trn th gii vic chng thm quan st thy c thc hin nhng cng trnh xy dng t nhng nm 5000 trc Cng nguyn. n , nhng cng trnh c tm thy nhng mng ngn nc c s dng mng ngn nc vi vt liu l t phan thin nhin hay ni cch khc i, c s dng cht k nc c du thin nhin pha trn lm va trong xy dng cng trnh .


41

Cc n i Msopotamie, Babylon, Assyrie cng thng dng chng thm bng va trn du tho mc. Cng trnh c Trung quc nh C cung, T hp vin dng va lm mng ngn chng thm. Gch xy, gch lt cng nh va u trn du tru lm cht k nc, ngn khng cho nc chui qua l thm va cng trnh. Tru l loi cy cng nghip m du p t qu tru c gi tr kinh t cao, hin nay c khuyn khch trng nc ta ly du xut khu. Ngy nay, sau khi cng nghip khai thc du m pht trin, cng nghip ha du tha mn vic ch to ra cht k nc dng bitum, vic chng thm ph bin l giy du dn bng nha bitum nng. Ti cc nc pht trin, c nhiu nh my ch to giy du. Vic chng ct du m sn xut hng nghn tn bitum mt nm. Vic s dng giy du dn bng nha nng thi cng kh phc tp ti hin trng, ngoi ra cn li kh nhiu nhc im. Giy du b mn theo thi gian. Giy du b cng gy khi nhit xung di 00C. Giy du b chy khi nhit ln trn 500C. Qu trnh s dng giy du cng l qu trnh tm ti khc phc nhng nhc im nu trn. Nhng vic s dng giy du vn ph bin v mng ngn loi ny kh a dng. Do c n hi cao nn khc phc c nhiu khe nt do khuyt tt ca thit k cu to cng nh thi cng phn xng ct gy nn. Ti M, Lin x, Tip, c, ngi ta khc phc s phc tp ca thi cng giy du bng s dng mttt atphan ngui. Vic ch to mttt atphan ngui n gin hn so vi nha nng, s dng an ton, ct gi c trong mt thi gian v nht l cht lng chng thm khng thua km giy du dn nha nng. Mttt atphan ngui s dng nhiu cc tunen qua ni, cc ging m, cc cng trnh cng nghip.


42

Tuy th, giy du v nha nng vn c s dng rt rng ri v ngoi kh nng chng thm, giy du v nha nng kh bn vng trong mi trng chu axt nn, trong nhng cng trnh cng nghip c s dng axt, nc thi nhim axt cng hay dng gii php chng thm bng giy du dn nha nng. Cc ti liu dn trong th mc cn cho thy nc ngoi cn s dng chng thm cho b nc bng b tng thng v va thng cng nh b tng v va c ph gia ha cht. Lin x c gii thiu mt s ph gia nh Clorua st, Nitrat canxi v cc ha cht khc trong vic pha thm vo va hoc b tng. Vic s dng ph gia ha cho vo va khng c vn qun ngi ln trong s dng cng trnh lu di. Nhng vic cho ph gia ha c hot tnh cao thng dn n quy trnh thao tc cng ngh phi thay i. Thi gian thi cng b tng phi nhanh ln m thi cng b tng c bit bao cng on phi thc hin. Ngoi ra cn tc hi v n mn ca ha cht ca ph gia vi ct thp trong b tng th cha nghin cu c thu o. Thi gian tc hi c khi nhanh, c khi chm ri. Tc hi th hin ra khi cng trnh xp . Theo bo B tng v b tng ct thp Lin x, c nhng ko b tng ct thp ln t gy v thp t do b ph gia n mn. Nhiu cng trnh ngm Philadenphia (M) dng mng chng thm l t st. Tm li, trong nc cng nh ngoi nc, lp chng thm tht a dng. Chn loi no cho ph hp cn c c s. Chn ri thit k ra sao, cng ngh nh th no t yu cu. 4.3 Gii php chng thm: 4.3.1 Gii php chung: Qu trnh nghin cu tng kt, tuyn chn, i chiu vi l lun, chng ti thu c bng phn loi logic nh sau:


43

Tm nguyn nhn gy thm cho cc dng cng trnh

Bin php s l khc phc ngn chn nc vo cng trnh

Mao dn Tun theo quy lut thm ca Darcy

Khe k Do kho st sai nn c gii php sai. Do cu to kin trc khng chnh xc. Do dng vt liu ngn nc c tnh co ngt. Do ni lc. Do thi cng c s c tiu cc. Do s dng khng theo quy trnh gn gi ng. Do cc nguyn nhn khc.

Khc phc nguyn nhn gy ra khe k. Lm cc dng mng ngn: *Mng ngn cng * Mng ngn mm (Mi gii php u xem xt cc mt: Vt liu s dng Liu lng Thao tc cng ngh)


44

4.3.2 Nguyn nhn thm : Nc vo cng trnh theo hai cch: mao dn v qua khe k. 1.Mao dn: Gch, va, b tng u c l mao dn. S lng l mao dn cng nhiu nu chc c cng b. L mao n c ng knh biu kin cng nh th chiu cao mao dn cng ln. ng knh ca l mao dn tng quan tuyn tnh vi h s thm. ng knh ny trong thc t rt nh. Chuyn ng thm l chuyn ng thm ca cht lng trong l mao dn v khe k mi trng xp. nh lut thc nghim acxy t c s cho l lun thm: V = kJ (1) trong : V lu tc thm k h s thm J dc thy lc dH J = (2) dl dQ dQ V = = (3) dZ d (Zrng + Zc) Theo kt qu thc nghim , cht lng thm coi nh mt cht lng c bit ca mi trng lin tc c nhng c tnh:


45

x cht lng c bit l dng ring ca mi trng lin tc cht lng l tng, chuyn ng xuyn qua khe rng v c ct rn ca mi trng xp coi nh khng c ct rn.

x cht lng chu sc cn khi chuyn ng, sc cn ny tnh nh mt lc khi, do

khng c ng sut tip. x cht lng khi chuyn ng tun theo nh lut acxy, coi chuyn ng thm

l chuyn ng th vi V = gradM , M = -kH. x cht lng c bit ny c U nh cht lng thc. U l mt ca cht lng. Biu 1 l tng quan gia h s thm v chiu cao mao dn. Biu 1

H s thm ca b tng t t 0,00002 n 0,002 cm/h. Nu t l N/X (nc : xi mng) xp x 0,5 thi cng m cht, cp phi tt, h s thm t b hn 0,0005 cm/h. Theo thc nghim, lng nc thm qua b tng: hn Q = Kb F t (4) L

10-7 10-6 10-510-410-310-20

5

10

15

20

25

30

35

40hk mt

K7 cm/pht


46

trong : Q - lng nc (cm3) Kb - h s thm ca b tng (cm/h) F - din tch tip xc vi nc (cm2) t - thi gian tip xc vi nc (gi) L - chiu dy lp b tng (cm) hn - p lc nc tc dng (cm) Vi tit din 1m2, trong 24 gi m v nhit bnh thng, thot gi t nhin, bc hi c 500 cm3 nc. Mun bo m cho cng trnh s dng tin nghi theo iu kin m 60 c/c, nhit 250C, thng gi t nhin tt, cng trnh c tng b tng dy 40cm, p lc nc 8m th b tng phi m bo c h s thm l 0,00001 cm/h. C th chn tng quan gia chiu dy cng trnh v p lc nc thch hp theo iu kin h s thm ti a ca b tng: L Kb max = 0,002 (5) hn L thng chn = 0,01 n 0,1 th Kbmax = 0,00002 n 0,0002. hn Ta cn ch c mi quan h nh hng n thm l nht ca nc. Thnh phn ha ca nc quyt nh nht ca nc. nht cng ln th cht lng cng kh chy. G Vj W = Pjk = P (6) G xk P l h s nht ph thuc nhit , khng ph thuc tc bin hnh. Ti ni tip xc gia cht lng nht v thnh rn, th nghim chng minh cht lng bm cht vo thnh rn, tc V = 0. iu ny khc vi cht lng l tng.


47

S chuyn dch cht lng v trong mi trng mao dn khng bo ha c nu trong nh lut Washburn : r. J v = . cos - 4.d.K Trong : r - bn knh l mao dn J- sc cng mt ngoi -- gc tip xc d- chiu su xm nhp K- nht ca dch th H s thm k, qua tit din A, cho qua lng cht lng Q , cht lng y c nht K v di gradient p lc dP/dZ rng buc vi nhau qua nh lut Darcy, nh lut ny c th c trnh by li theo dng sau y : A dP Q = -k . . K dZ Tnh phc tp ca s dch chuyn cht lng qua vt liu rng lm cho n khng tun th mt cch n gin nh lut Darcy. Thc ra s dch chuyn cht lng qua vt th rng c coi l mt hin tng khuych tn theo nh lut Fick: dC j = - D . dL Trong j - dng dch chuyn dC/ dL -gradient nng D - h s khuych tn T nhng tng va nu trn, li ct ca cht lng b tng theo quan im cng , tnh chng thm, v nhng tnh cht u vit khc rt ph thuc vo t l nc/ximng. Cng gim c nc c th gim c trong b tng cht lng cng tng.Gim c lng nc trong b tng, mi ch tiu cht lng u tng, trong


48

c tnh cht chng thm. Ch : gim nc nhng vn phi m bo tnh cng tc ca b tng. 2. Khe k, nt n: Cng trnh ngn cch v kt cu c th bng b tng, c th bng gch cng u c kh nng xut hin vt nt, c th do mt nguyn nhn, c th do nhiu nguyn nhn tc ng ng thi. x Vt nt xy ra do b tng b co ngt khi khng tun th ch m v lp b

tng trong cng ngh thi cng b tng. Loi vt nt ny cn do trnh t thi cng b tng khe thi cng b tr khng hp l. dng nc trn b tng m ta bit lng nc ny nhiu hn lng nc cn cho thy ha xi mng rt nhiu nn chuyn co ngt l iu chc chn xy ra. C gii php cng ngh tt hn ch s sinh ra vt nt co ngt l nhim v ca ngi k s.

x Vt nt do s ta nhit ca khi b tng khi b tng khi ln. Thng vt

nt loi ny c dng chn chim. Cn thit chia khi b tng thnh nhng khi c th tch phi chng nhit sinh ra ta vo khng kh cng nh dng cc bin php h nhit nh dng nc lnh trn b tng, qut gi thi vo b tng, h nhit mi trng cha b tng ...

x Vt nt do qu trnh chu ti ca b tng sinh ra. Chng ta u bit b tng ct

thp l kt cu n hi. Nh vy c ti trng tc ng th c bin dng. Khi bin dng qu gii hn no th ta quan st thy c vt nt. Nhng b cha v cng trnh ngm cn chng thm khi tnh theo trng thi gii hn cn kim tra thm iu kin khng cho hnh thnh khe nt. C th do cha c kinh nghim m cu to kt cu khng bo m s ngn nga nhng khe nt ngoi mun ngi thit k. iu m nhng ngi thit k kt cu b tng ct thp cha c kinh nghim c th xy ra l s phn b cc thanh ct thp ng knh qu ln v b tr khong cch gia cc thanh qu xa cng c th gy vt nt loi ny.

x Vt nt do hin tng ln khng u. Nhiu khi do mun tn dng mt mt tng

c sn lm kt cu lp chng thm, qu trnh s dng cc b phn tip xc vi t ln khc nhau pht sinh vt nt.


49

Nh th, c th ln sinh nt do nn t c tnh cht chu ti khng ng u, nhng c th do ti trng tc ng khng ng u xung nn. Cng c th do kt cu kh di t trn nhng phay t khc nhau sinh hin tng ln khng u x kt cu bng nhng vt nt. Cc hm phng khng c kt cu hm chnh rt nng, trn hm chnh li c cc lp t, hc cao, dy ln trong khi cnh cu thang ca hm nh, mng, li khng c cc lp nng. Nh vy khi hm chnh b ln nhiu hn cc cnh cu thang lm x ch ni gia hm chnh v cu thang. x Nu trong cng trnh ngm phi mc nhng ng xuyn qua m khng x l tt

nhng khe k quanh ng, nc s vo trong cng trnh theo khe k quanh cc ng ny.

x Trong qu trnh phn xy lm xong, bn giao mt bng cho phn lp t thit

b, ngi lp t thit b khng ch bo qun cng trnh chng thm, lm sinh nhng khe k cho nc thm vo cng trnh.

x Trong iu kin nc ta hin nay ,nhiu cng trnh ln cn nhau lm sau khi

cng trnh trc chng thm m ng cc kiu gy xung lc ln, rung ng nh hng chung quanh kh xa lm nt n cng trnh ngm c ( Nh chiu bng Khn qung v vic thi cng tr s Hi ng Nhn dn thnh ph H ni).

4.3.3 Cch s l - phn loi gii php cng ngh ch to Chng thm cho cng trnh ngm nn c xem xt di con mt tng th cc vn t khu kho st, thit k, ch to, thi cng v c vic s dng cng trnh na. (1). Kho st : S cung cp s liu thy vn phi m bo s chnh xc. Mc nc ngm ma kh. Mc nc ngm ma ma. Thnh phn ha hc ca nc ngm. Cu to


50

a cht cng trnh. Ht sc ch n s khng ng u ca nn t. Cc phay, cc vt t gy, lch s to thnh nn khu vc t mng. Cng trnh Supe-pht pht Lm thao l in hnh ca s cung cp s liu thy vn cng trnh khng chnh xc dn n gii php chng thm khng ng. (2). Thit k: * Cu to kin trc : Vic la chn gii php lm t tng qut n chi tit. Chn gii php chung ri mi chn chi tit. Nhng vn v tng th c: Gii php chung v v tr lp chng thm Chng thm mm hay cng Cc khe co dn v khe nhit Phn on, phn khu chng nt do khong cch v cc chiu kt cu qu ln. Chi tit cu to ch : La chn cc lp ngn nc Cu to chng t gy cc b Cu to chng x, trt gy gp ri t lp chng thm. Lp bo v mng chng thm Cc gii php cu to khe ln, khe nhit L chn ng thm Cu to v chn nht chung quanh ng xuyn qua cng trnh. Bn tm tt ny ch nu mt s trng hp cu to kin trc hay gp phi s l: x Lp chng thm cng gin n v hnh dng cng tt. (3). Thi cng: Cc gii php thi cng phi thc hin ng quy trnh thao tc, bo m cht lng trong tng khu cng tc. Cn c cn b c trch theo di cht lng v


51

hng dn thi cng chng thm t u cng trnh. C th mt gii php thi cng cp phn di. (4). S dng cng trnh: Cng trnh cn lun lun c bo tr, duy tu theo ng hn k. Mi khi c bin ng nh cn c o, thay i nhim v cht ti cng nh c cc tc nhn lm suy gim cht lng khc cn c kin ca nhng ngi c chuyn mn. c o ba bi cng l nguyn nhn quan trng gy nt n cng trnh, ph hoi lp chng thm. (5). Gii php: (1) Phn loi: V hng chung chia ra * H mc nc ngm, loi tr ngun nc vo

cng trnh. * To lp mng ngn khng cho nc thm vo cng trnh.

V s dng lp mng ngn chia ra * Mng ngn cng, dng cho kt cu thnh khi c

n hi thp, bin dng coi nh khng c hay khng ng k. * Mng ngn mm, kt cu di rng hn loi cng c bin dng nhng khng vt qu gii hn lm t mng ngn.

(2) Gii php v cng ngh: x H mc nc ngm :


52

Ti nhng ni c mc nc ngm ln xung theo ma trong nm, cng trnh khng thng xuyn ngm trong nc nn dng gii php h mc nc ngm. To rnh thu nc su hn y cng trnh. Trong rnh ny t cc loi vt liu thot nc nhanh nh ct to ht, rm, 4x6. y mng t ng dn bng b tng c ng knh trong ca ng khong I30. Thnh ng c l nc bn ngoi c th chy d dng vo trong ng. H rnh ny dn ti mt trm bm hoc nu a hnh cho php v y rnh cao hn mc trn ca sng, ngi, mng th cho tho nc ra sng ngi hoc mng, mng. H mc nc ngm l bin php ch ng. Nhng yu cu s dng lu di ch nn dng khi thi gian bm nc trm bm khng nhiu qu. Gii php ny ch thch dng khi xy dng cng trnh trung du, trn cao tng i kh ln so vi khu vc xung quanh. Nc ngm ch tm thi trong thi k ma nhiu. Vic s dng mng mng phi thng xuyn chm sc, khng cho t mn lp khe k, ngn cn vic rt nc . x Chng thm bng mng ngn: Mng ngn cng: Mng ngn cng l mng ngn khng c c bin dng, khi ln th ln ng u ton kt cu. Khng cho php c un. Mng ngn cng c nhiu loi: * Gch nung gi xy bng va k nc. Phng php ny dng khi mc chng thm khng cao. nc c c cch lm l ly gch nung lm t t st ngm vo bitum lm ct liu cho tng xy chng thm. em bitum nu n 1800C n 2000C, nhng gch vo n khi bitum thm su vo trong gch 10 n 20mm vt ht l b mt gch lm cho b mt vin gch c mu en ng u. Va xy c thnh phn l: Bitum, xi mng, ct. Trn xi mng vi ct cho u. un bitum n nhit 1800C - 2000C. Dng bitum ang si ny trn vi hn hp xi mng ct


53

trn u ri em thi cng ngay. Nhit yu cu khi thi cng cn t trn 1500C. Ti mt s nc, thay cho bitum ngi ta dng ptrolatum. Gi thnh ca ptrolatum r hn bitum 15 ln. Gch v va k nc ngn khng cho nc thm vo cng trnh. Theo cc ti liu ca Trung quc th thay cho bitum trong cc cng trnh ca Chu u, Trung quc dng du tru lm cht k nc cho cc lp ngn nc. Nm 1957, bo ch Trung quc gii thiu vic chng nc cho cung vn ha Thi nguyn, tnh sn ng dng loi va xanh lm cht k nc. Va xanh l hn hp gm bt mt loi cha du nm trn cc qung than ( schiste ?). Cng ti liu ni v vic chng thm cho cung vn ha Thi nguyn ny gii thiu C Cung v mi T Hp Vin ca Trung Quc cng dng loi va xanh chng thm. Dng cht k nc ngn nc l vic thng lm. Nhng s dng tho mc cng cn xem xt n tnh bn lu theo thi gian. Bitum hoc ptrolatum to thnh mng kh bn nhng du tho mc c th d dng khuych tn n mt lc no khng mt ngn nc th vic s dng cng trnh s ra sao. Nu s dng va xanh m thc t cc kt qu nh ti liu Trung quc th i vi nc ta c c mt vng than rng ln Qung ninh, Hi d}ng m t trn m phi bc b i s l ngun nguyn liu v cng v tn. * Dng b tng thng v va thng: thm nc ca b tng thng v va thng ph thuc vo cp phi, t l nc trn xi mng (N/X), iu kin v phng php ch to b tng v va. Chng ta nn s dng cc thnh tu khoa hc mi vo vic nng cao cht lng b tng. l s dng cc cht gim nc v ph gia c silica fume gim lng nc trong b tng. Dng ph gia c silica fume v cht t cht gim nc khng nhng lm tng cng b tng ln nhiu m b tng chc c hn, tnh chng thm cao hn ln. Th nghim cho thy, vi xi mng PC40, c 8% SiO2 +1,6% cht gim nc, nu s dng 400 kg xi mng cho 1m3 b tng th sau 7 ngy t cng b tng l 40Ma, n 28 ngy t 70 MPa, ngha l b tng mc 700, v d nhin rng trong b tng gim nhiu, tnh chng thm ci thin r rt.


54

th thm ca b tng c nhiu cch. Nhng ph bin l cch th nh mu hnh tr. Khun hnh tr c ng knh bn trong khun l 190mm. Trong lng khun c cn nh. Chiu cao ca khun l 200mm. Hai u khun c mt bch. u khun ln c np ni thng vi ng dn n mt bm p lc. u kia ch lp bch khi chn bng knh. C th h quan st. Bm p lc nc c th dng loi bm th cng thng dng th p lc ng ng nc. c b tng vo chnh khun ny. Khi n tui do ngi thit k phng n th yu cu th nn cho mu ra khi khun. Bo dng theo yu cu ca thit k. Trc khi th phi cho mu kh, khng cn m mt. Ly bn chi st c mnh hai u mu. Pht quanh khun bng parafin mng ri p li mu vo khun. Dng l m cao su mng ri lp mt bch ni vi bm p lc nc. Ch kn ca h thng. Bm p lc c bnh cha iu chnh p lc. Bt u th, bm cho tng p ln 0,5 at gi trong 6 gi. Quan st k bng knh lp pha u khun h. Nu khng thy c nc thm qua li tng thm mt cp na atmotphe na. Li quan st sau khi gi hng p trong 6 gi. Khi mt h ca mu thy c nc thm qua th ngng th nghim. p lc lc b tng b thm gi l mc chng thm ca b tng. B tng thng, xi mng Pooclng 400, mc b tng 200 thi cng m k theo ng quy trnh yu cu c th t mc 2 atmotphe. K hiu mc chng thm l B2. Cp phi tt, t l N/X hp l c th t B4. Ngha l b tng chu c 4 atmotphe mi thm. Cn c th to c b tng thng chu c B6 nhng phi ht sc tun th quy trnh thao tc mt cch nghim ngt, ong lng cp phi, sch ca ct liu, bo dng b tng tt . Lng xi mng Pooclng PC 40 dng cho b tng thng chng thm phi trn 300 kg cho mt mt khi b tng. T l N/X ti a l 0,6 - 0,65. T l N/X tt l 0,5 - 0,55. Nhng vi t l ny, vic m b tng phi ht sc cn thn v y l t l N/X ca b tng kh. Khi dng cht gim nc v ph gia Silica fume, t l N/X c th rt cn 0,40~0,45


55

Xi mng chng thm tt l loi xi mng trng th tch v loi xi mng khng co ngt. Lng xi mng tt cho chng thm l 330 - 360 kg/m3 b tng. Nhiu cng trnh ngm chng ti c tham gia thi k chng chin tranh ph hoi ca M min Bc chn lng xi mng Pooclng mc 400 cho mt khi b tng l 450 kg. Trong khi li bc thm lp ngn nc mm dn bng va bitum nng. Theo chng ti nh vy qu tha. Nu thit k v bc l lp ngn nc th kt cu ch nn tha mn tnh chu lc. Nhim v chng thm giao cho lp ngn nc. Nhn vo nhng cng trnh cn chng thm s dng b tng lm lp ngn nc chng ti c nhn xt: B tng mc 200 thi cng m my thng thng, t l nc trn xi mng l 0,6 nu tng b tng dy 200mm c th chng thm ln hn 2 atmotphe. Nhiu hm ca ta thit k chiu dy thnh tng ln hn hoc bng 300mm. Cng trnh t khi c mc nc ngm qu 10 mt. Thc t cho thy nc khng thm qua c cng trnh theo kiu mao dn. Nhng cng trnh b thm nc u vo qua nhng khuyt tt ca thi cng b tng nh b tng b r hoc vo qua khe ln, qua ch ni gia cc on cng trnh. i vi nhiu cng trnh ngm hoc b nc, dng phng php phun thay cho b tng. Phun b tng th cht ca b tng rt cao nn chng thm tt. nc ta, phng php phun b tng hay dng sa cha b tng khi b r nhiu. Cng c thi k dng phng php phun va xi mng lm cc thuyn xi mng li thp. nc ngoi hay dng phng php phun b tng xy dng nhng b nc. Ngi ta lm mt b nc cha nc nng 1000m3 dng tr trn ng knh 19m, cao 4m nm chm 2m di mt t. Dng my phun b tng loi C320 phun thnh b tng lp 15-20m theo cc di chiu cao 1m quanh chu vi. Phun mt lp ri tri li thp. Sau phun tip 100mm li tri lp thp na. Phun thm mt


56

lp 20mm lm lp bo v thp. Mi lp phun khng qu 20mm trnh nt do co ngt. Vt liu l ct sng, cp phi l 1:2,5 (xi mng: ct). Lng nc cho t, ch nh loi va kh. Sau thi gian bo dng, b c bm nc nng 600C n 800C th. Tuy c nhng ng ng qua thnh b nh hai l to ng knh l l 1,20 mt, ba ng I 250mm nhng tn tht nc cho mi mt vung b mt ch l 2 lt trong khi quy nh c 3 lt trong ba ngy m. Va trt thng cho cng trnh ngm c thi cng tt, va trn u, va do, khi trt c trt thnh tng lp 3 n 4mm ngn ng thm hoc ch t cng ko di ng thm c th t h s thm l 0,00001 n 0,0004 mt / ngy m. * B tng v va c ph gia: Ph gia cho vo b tng v va c th nm trong ba loi:

x Loi k nc nh xrzit, du nng, bitum, du tho mc. x Loi c ht mn bt l rng nh bt vi, bt lmit, bt

vi canxit, bt thch anh, t st... x Loi ph gia tng n ca b tng v va, vit ln khe mao dn nh

aluminat natri, clorua canxi, clorua natri, tricozan, hydroxit st, clorua st, nitrat canxi, cc loi cht phng nc ly thy tinh lng lm gc...

Cn loi ph gia to bt, to mng dng cho b tng v va gc l cc loi nha tng hp. Trong thc t cng nh kinh nghim dn gian cn dng mt lng nh cc cht lin kt hu c hoc phn t thp nh m, phenon phc, ng, mt cho vo va v b tng thc y qu trnh to thnh lin kt khong hoc ci thin mt s thnh cht ca b tng v va. Nhng cht ny ch thc y ch bn thn n khng tham gia vo cu trc lin kt.


57

Ph gia k nc lm gim cng ca b tng v va nn vic kt hp vic dng ngay kt cu chu lc ng thi l kt cu chng thm phi kim tra tnh chu lc b gim yu khi thm ph gia k nc. Th nghim cho thy ch cho vo va xi mng mt lng ph gia 2,5 n 3% (so vi trng lng xi mng) cht nh tng cao su, cht latex, mt lp va 10mm c latex chu c 19 atmotphe. Phn di y trnh by mt s b tng v va c ph gia ha cht m chng ti tham gia ch to hoc thi cng. Mt s ph gia t nu kim chng cng ngh, a vo cng trnh thc t thi cng. * Colophan Natri: Cht ny thit k Trung quc dng cho chng thm c cht cao khu gang thp Thi nguyn. Cch ch to Colophan Natri nh sau: Nguyn liu dng l nha thng v st k ngh. Nha thng em tn nh, ry qua mt sng 1mm. St dng l st 13% c t trng d=1,14 - 1,16. Nu st 13% ln nhit 800C th cho colophon vo quy u. Khuy cho n khi nha tan ht, cho vo bnh snh dng dn. Liu lng s dng l 5 phn vn so vi trng lng xi mng. Dng nhiu hn b tng s b gim cng . Ph gia ny lm tang nhanh tc ng kt ca xi mng nn phi b tr thi cng nhanh mi m bo cht lng. Xi mng dng cho chng thm pha clphan natri l xi mng puzlan. Cu to ha hc nh sau: C19 H29 COOH + OHNa o C19 H2 CONa + OH2 Nha thng St Colophan Natri Nc


58

Colophan Natri l loi x phng to bt ln v dng thch hp lm tng phm cht b tng. Dung dch colophan Natri lm tng tnh lu ng, st ca b tng tng, thi gian kh qunh lc trn ko di. Kho dung dch colophan Natri cho vo b tng th nhng ht xi mng ht mng bt. Phn nc khuych tn vo b hn ch do qu trnh ha tan v tc dng ko di hn. B tng c colophan Natri chn t l tt lm tng tnh chng thm cao v bt c lp lm chc c phn b tng cn li. Thit k mc b tng : X R28 = K RK ( - 0,5 ) ( 1 - 0,04 A ) N A l lng ngm hi RK l mc xi mng * Aluminat Natri : Bin php ny c dng trong nhiu cng trnh thy li nh trm bm Thy Phng, H ni nm 1960. Nguyn liu lm Aluminat Natri l phn nhm v st k thut. Cch ch to : nu phn ln 40 - 500C, cho st k thut vo, c cht kt ta. Lc, xy kh nhit 100 - 1050C ta c Al(OH)3 t trng cao. Li cho Al(OH)3 tc dng vi OHNa ln na s thu c NaAlO2. Cn lc c NaAlO2 tinh khit. Liu lng s dng : Lng Aluminat Natri l 3-5% trng lng xi mng. Va Aluminat Natri c s dng cng trnh Gang thp Tha Nguyn. Ti cng trnh ny s dng cc loi va:

x Va ng cng trong 6 pht: Xi mng Pooclng 400 dng 1kg th Aluminat Natri 0,200 kg Nc sch 0,220 kg


59

x Va ng cng trong 5 pht: Xi mng Pooclng 400 dng 1kg th Aluminat Natri 0,260 kg Nc sch 0,160 kg

x Va ng cng trong 7 pht

Xi mng Pooclng 400 dng 1kg th Aluminat Natri 0,160 kg Nc sch 0,260 kg

Do va c Aluminat Natri lm cho ng cng nhanh ln nn ch ch trn tng m nh, dng xong li trn ko b ng cng ph phm. Khi dng va ny bt l r thm khng dng ct. Nu dng trt mt tng dng thm ct. Ct trn trc vi xi mng. Khi cho nc th cho ng thi Aluminat Natri . Cng trnh nh my thy in Bn thch (Thanh ha), trm bm Thy phng (nam Ngh an) cng dng Aluminat Natri trn trong b tng hoc va thy kt qu tt. Kt qu th nghim trn hai cng trnh ny cho biu hnh 14. p lc thm 10 8 7 5 2 1/10 1/8 1/6 1/4 Aluminat / Nc

Hnh 14: Tng quan gia p lc thm v lng Aluminat Natri Aluminat Natri

th hin qua t s Nc * Va dng loi ph gia gc thy tinh lng:


60

Thi k nc ta xy dng nhiu cng trnh theo thit k ca Trung quc v c s tham gia hp tc ca chuyn gia Trung quc hay dng cc loi va thm ph gia loi ny. Theo ti liu ca Ph Chn Hi trong cun Cch chng nc tt nht gi l cht phng nc hn hp. Ch to cht phng nc hn hp: Nguyn liu :

Sunfat ng 5 ncSunfat st Bicromat Kali Phn chua Thy tinh nc Nc l sch

Cu SO4 5H2OFe SO4 K2 Cr2 O7 K Al(SO4)2 12H2O Na2 Si O3

1 phn 1 phn 1 phn 1 phn 400 phn 60 phn

Cng ngh iu ch: Cho nc l vo ni un si 1000C. B ln lt Cu SO4 5H2O, Fe SO4, K2 Cr2 O7 vo ni ln lt. B tng cht khuy cho tan u. Cht n tan ht mi cho cht kia. Khi tan ri, cho tip phn chua gi nh v tip tc khuy cho tan ht. Ch nhit vn phi l 1000C. Khi c cht lng ng nht th bc ni khi bp ngui dn. Dng nhit k kim tra, khi nhit h cn 550C th cho dung dch ny vo thy tinh lng. Va cho va khuy lun tay bng a thy tinh. Tip tc khuy trong thi gian khong 30 pht. Khi khuy phi phi thy cm gic nh tay, khng c gn. Nu khuy lu m cn gn tay chng t hn hp b kt ta, phi b khng dng c. Yu cu rt nghim ngt l hn hp khng c kt ta. C hin tng kt ta l nguyn liu khng tinh khit. Cn kim tra cht lng nguyn liu. C th chn loi t l phi liu khc:

Sunfat ng 5 ncSunfat st Bicromat Kali Phn chua Thy tinh nc Nc l sch

Cu SO4 5H2OFe SO4 K2 Cr2 O7 K Al(SO4)2 12H2O Na2 Si O3

4 phn 2 phn 4 phn 4 phn 800 phn 120 phn


61

Chng ti trnh by vic s dng giy du dn bng va nng nh my dt 8-3 H ni c nhng s c. Cc chuyn gia Trung quc xy dng nh my ny dng nhng cng thc ca Ph Chn Hi lm cht ngn nc cha nhng h hng thm cng trnh. Chng ti ghi chp c mt liu lng dng cho nh my dt 8-3 ny:

Sunfat ng 5 ncSunfat st Bicromat Kali Thy tinh nc Nc l sch

Cu SO4 5H2OFe SO4 K2 Cr2 O7 Na2 Si O3

0,50 kg 1 kg 1 kg 200 kg 30 lt

un nc cho si 1000C cho ln lt sunfat ng, sunfat st, bicromat kali khuy tan tng cht mi cho cht sau. Khi tan ht bc khi bp, ngui n 500C th rt dung dch ny vo thy tinh lng khuy trong na gi. Nu khng b kt ta th dng pha vo va bt thm. Ta nhn xt thy trong phi liu ny vng mt cht phn chua. Nhng kinh nghim thc tin bn thn chng ti rt ra c trong qu trnh thc tin: x C th nhn bit nguyn liu: sunfat ng mu xanh nht, nh trong sut mu

xanh. Sunfat st mu vng t, bicromat kali mu . x Thy tinh lng yu cu m c c d = 1,4. x Yu cu ca hn hp cht phng nc phi t 1,55 Baum. l yu cu,

thc t chng ti theo di nhiu m ch t 1,52 n 1,54 Baum. Thp hn 1,5 khng nn s dng.

*

* * 61Share-connect.blogspot.com

62

Cht phng nc dng trong cng thc ca Ph Chn Hi cn c nhng bin i v thnh phn v phi liu, gia gim cht t. Nhng gc vn phi l thy tinh lng. thy tinh lng bt buc phi c mt trong tt c cc gii php phi liu m n cn cn dng s lng ln. d trnh by cc dng phi liu chng ta t tn: Sunfat ng 5 nc Kali Bicromat Sunfat st 2 Phn chua Sunfat kp Kali nhm Phn crm Sunfat kp Kali nhm Thy tinh lng Nc sch

l cht s 1 l cht s 2 l cht s 3 l cht s 4 l cht s 5 l cht s 6 l cht s 7

bn thnh phn cc cht phng nc theo

ph chn hi

Hp cht T l Mu hp cht Loi 1:

1 2 3 4 5 6 7

Loi 2: 5 2 4 1 6 7

1 1 1 1 1

400 60

1,25 1,25 1,25 1,25 400 60

Mu g Mu xanh nht


63

Loi 3: 1

2 3 6 7

Loi 4: 5 2 4 6 7

Loi 5:

5 2 1 6 7

Loi 6:

1 3 4 6 7

2 2 1

400 60

1,66 1,66 1,66 400 60

1,66 1,66 1,66 400 60

1,66 1,66 1,66 400 60

Mu g Mu xanh nht Mu x

Documents

Giao Trinh Thi Cong Nha Cao Tang BTCT - Pgs Le Kieu