TCXD 205-1998

Tiu chun xy dng tcxd 205 : 1998

Mng cc - Tiu chun thit k

Pile foundation - Specifications for design

1. Nguyn tc chung1.1. Phm vi p dng ca tiu chunTiu chun thit k mng cc c p dng cho cc cng trnh thuc lnh vcxy dng dn dng v cng nghip, giao thng, thu li v cc ngnh c linquan khc. Nhng cng trnh c yu cu c bit m cha cp n trong tiu chun ny sc thit k theo tiu chun ring hoc do k s t vn ngh vi s chp thun ca ch cng trnh.1.2. Cc tiu chun hin hnh c lin quan :- TCVN 4195 4202 : 1995 t xy dng - Ph ng php th;- TCVN 2737 1995 - Ti trng v tc ng - Tiu chun thit k;- TCVN 5574 1991 - Kt cu b tng ct thp - Tiu chun thit k;- TCVN 3993 3994 : 1985 - Chng n mn trong xy dng kt cu b tng v btng ct thp;- TCXD 206 : 1998 - Cc khoan nhi - Yu cu v cht lng thi cng;- TCVN 160 : 1987 - Kho st a k thut phc v cho thit k v thi cng mng- TCXD 174 : 1989 - t xy dng - Phng php th nghim xuyn tnh;- TCXD 88 :1982 Cc - Phng php th nghim hin trng;- ASTM D4945 :1989 - Th nghim ng cc bin dng ln - Phng php tiu chun ( standard test Method for High-Strain Dynamic Testing of Piles );- BS 8004 :1986 - Mng (Foundations)- SINP 2.02.03.85 - Mng cc ( Svainu fudamentu);- SINP.2.02.01.83 - Nn nh v cng trnh ( Osnovania zdanii i soorujenii)1.3. K hiu quy c chnh.AP - Din tch tit din mi dc;As - Tng din tch mt bn c th k n trong tnh ton;B - B rng ca y mng quy c;c - Lc dnh ca t;d - B rng tit din cc dp - ng knh mi cc;ES - M - un bin dng ca t nn;EP - M - un bin dng ca vt liu cc; FS - H s an ton chung ca cc;FSS -H s an ton cho ma st bin ca cc;FSP - H s an ton cho sc chng ti mi cc;G1 - Gi tr m - un ca lp t xung quanh thn cc;


G2 - Gi tr m - un ct ca lp t di mi cc;

L - Chiu di cc;IL - Ch s st ca t;MX,MY - gi tr m men tc dng ln i cc theo cc trc x v y;N - Ti trng nn tc dng ln cc; NK - Ti trng nh tc dng ln cc;NH - Ti trng ngang tc dng ln cc;Nc, Nq,Ny - Thng s sc chu ti ly theo gi tr gc ma st trong nn tNSPT - Ch s SPT t th nghim xuyn tiu chun (SPT); Qa - Sc chu ti trng nn cho php ca cc;Qak - Sc chu ti trng nh cho php ca cc;Qah - Sc chu ti trng ngang cho php ca cc; Qu- Sc chu ti trng nncc hn ca cc;Quk- Sc chu ti trng nh cc hn ca cc;Quh- Sc chu ti trng ngang cc hn ca cc;Qs- Sc chu ti trng cc hn ca cc n do ma st bn; Qp- Sc chu ti trng cc hn ca cc n do lc chng;S - ln gii hn ca cng trnh; Sgh -Trng lc cc;W - Lc chng ct khng thot nc ca t nn;ca- Lc dnh gia cc v t xung quanh cc;cu - Sc chng ct khng thot nc ca t nn;fi - Ma st bn ti lp t th i;fc - Cng chu nn ca b tng;fpe - Gi tr ng xut trc ca tit din b tng k n tn tht;fy - Gii hn do ca thp;li - Chiu dy ca lp t th i trong chiu di tnh ton cc;qp - Cng chu ti cc hn ca t mi cc;qc - Sc chng th nghim xuyn tnh;u - Chu vi tit din ngang thn cc;

- Khi l ng th tch t nhin ca t; - H s pot xng ca t; - Gc ma st trong ca tn- Gc ma st gia cc v t;

1.4. Cc nh ngha v thut ng.- Cc : l mt kt cu c chiu di so vi b rng din ngang c ng, n hay thi cng ti ch vo lng t, truyn ti trng cng trnh xung cc lp t su hn nhm cho cng trnh xy dng t yu cu ca trng thi gii hn quynh.


- Cc chim ch: l loi cc c a vo lng t bng cch yxu ra xungquanh, bao gm cc loi cc ch to c a xung su thit k bng phng php ng (c gi l cc ng), n (c gi l cc p) v rung, hayloi cc nhi ti ch m phng php to l c thc hin bng phng phpng.

- Cc thay th : l loi cc thi cng bng cch khoan l v sau lp y bng vt liu khc ( v d cc nhi ti ch ) hoc a cc loi cc ch to sn vo.- Cc th nghim : l cc c dng nh gi sc chu ti hoc kim tra cht lng cc.- Nhm cc : gm mt s cc c b tr gn nhau v cng c chung mt i cc.- Bng cc : gm nhng cc c b tr theo 1 - 3 hng di cc mng bng.- B cc : gm nhiu cc c chung mt i vi kch thc ln hn 10

10m.- i cc : l phn kt cu lin kt cc cc trong mt nhm cc vi cng trnh bn trn- Cc i cao : l h cc trong i cc khng tip xc vi t.- Cc chng : l cc c sc chu ti ch yu do lc ma st ca t ti mi cc.- Cc ma st : l cc c sc chu ti ch yu do ma st ca t ti mt bn cc.- Lc ma st m : l gi tr lc o t tc dng ln thn cc c chiu cng vi chiu ti trng ca cng trnh tc dng ln cc khi chuyn dch ca t xung quanh cc ln hn chuyn dch ca cc.- Th nghim xuyn tiu chun SPT (Sandard Penetration Test ): l th nghim thc hin trong h khoan bng cch ng mt ng mu c kch thcquy nh vo lng t bng lng ri t do ca mt qu ba l 65,5 kg vi chiu cao ri ba l76cm.- Ch s NSPT : l kt qu thu c t th nghim SPT, th hin bng s nht ba cn thit ng c mi xuyn vo t mt khong l 30cm.- Sc chu ti cc hn : l gi tr sc chu ti ln nht ca cc trc thi im xyra ph hoi, xc nh bng tnh ton hoc th nghim.- Sc chu ti cho php : l gi tr ti trng m cc c kh nng mang c, xcnh bng cch chia sc chu ti cc hn cho h s an ton quy nh- Ti trng thit k (ti trng s dng): l gi tr ti trng d tnh tc dng ln cc.

2. Yu cu i vi kho st.2.1. Kho st a cht cng trnh2.1.1. Nhng vn chungNhim v k thut cho kho st iu kin t nn phc v thit k mng cc do nv t vn hoc thit k xut v c ch u t nht tr, sau chuyn giao chon v chuyn ngnh kho st cn nu r d kin cc loi cc, kch thc cc v cc gii php thi cng lm c s cho cc yu cu kho st.Trn c s cc nhim v k thut ca ch u t, n v thc hin kho st lp phng n k thut thc hin.2.1.2. Cc giai on kho st


Cng vic kho st thc hin theo yu cu ca Tiu chun Kho st a k thutphc v cho thit k v thi cng mng cc TCXD 160:1987. Thng thng ni dung kho st c thc hin lm 2 giai on ty theo yu cu ca ch u t, bao gm:- Kho st s b, giai on ny c thc hin trong trng hp quy hoch khu vc xy dng, nhm cung cp cc thng tin ban u khi tho cc gii php cng trnh v nn mng d kin.- Kho st k thut: giai on ny c thc hin sau khi phng n cng trnh c khng nh, nhm cung cp cc chi tiu tnh ton phc v cho vic thit kchi tit cc gii php nn mng.2.1.3.Khi lng kho st.- i vi giai on kho st s b: S lng im kho st cn phi tu theo iu kin phc tp ca t nn v ln ca din tch xy dng c th cung cp cc thng tin s b v t nn theo su, trong t nht mt im phi khoan n su ca lp t c kh nng chu lc thch hp.- i vi giai on kho st k thut: S lng im kho st cn phi tu theo ln ca din tch xy dng nhng khng qu 3 im cho khu vc hoc cng trnh d kin xy dng. i vi tr v m cu, ti mi v tr thc hin t nht mt im thm d.2.1.4. su thm d- i vi giai on kho st s b: ty theo c im cng trnh, su im thmd c kt thc khi NSPT > 50 - 100 v lin tip trong 5 ln th nghim tiptheo. Khong cch gia hai ln th nghim lin nhau khng ln hn 1,5m.Trong trng hp khng s dng th nghim SPT, c th s dng cc ph-ng php sao cho vn tha mn yu cu xc nh c lp t c tin cy ta cc.- i vi giai on kho st k thut: su thm d khng nh hn mt trong 2 gitr sau: 10 ln ng knh di su mi cc v 6m. Tuy nhin i vi cc cng trnh giao thng khi s dng nhm cc, su thm d di mi cc khng nh hn 2 ln chiu rng ln nht ca nhm cc c thit k chng trn mt hocngm trong . Khi cc c thit k chng hay ngm trong , ti mi v trthmd cn khoan vo mt chiu su khng nh hn 6m hay 3 ln ng knh cc.2.1.5. Cc phng php kho st phc v cho thit k :- Khoan- Ly mu t v nc th nghim;- Th nghim xuyn tiu chun ( SPT );- Th nghim xuyn tnh ( CPT );- Th nghim ct cnh;

- Cc th nghim quan trc nc di t;- Th nghim nn ngang trong h khoan;- Th nghim xc nh sc chu ti v kh nng thi cng cc;- V.v2.1.6. Cc thng s ch yu cn cho thit k bao gm :- Ch s Nspt theo su;- Gi tr sc chng mi, qc v ma st bn, fs theo su;


- Gi tr sc chng ct,cU theo su;- Ch nc di t;- Cc ch tiu c l ca t, tnh n mn ca t v nc.2.2. Kho st cng trnh ln cn.Cc cng trnh ln cn khu vc xy dng (nh, cu, ng, cng trnh ngm, h thngng ng k thut,v.v) cn c kho st hin trng lp bin php thi cng v thi cng cc chng nh hng bt li i vi vic s dng bnh thng ca cc cng trnh . Ni dung v gii php kho st do k s t vn quyt nh.

3. Nguyn tc c bn cho tnh ton3.1. Nhng yu cu chung3.1.1.Cc v mng cc c thit k theo cc trng thi gii hn. Trng thi gii hn ca mng cc c phn lm hai nhm sau:

Nhm th nht gm cc tnh ton :- Sc chu ti gii hn ca cc theo iu kin t nn;- bn ca vt liu lm cc v i cc;- n nh ca cc v mng;

Nhm th 2 gm cc tnh ton :- ln ca nn cc v mng;- Chuyn v tr ngang ca cc v mng;- Hnh thnh v m rng vt nt trn cc v i cc bng b tng ct thp

Ch thch :

1) Khi trong nn t di mi cc c lp t yu th cn phi kim tra sc chu ti ca lp ny m bo iu kin lm vic tin cy ca cc.

2) Khi cc lm vic trong i cao hoc cc di v mnh xuyn qua lp t nu c sc chu ti gii hn nh hn 50 kPa (hoc sc chng ct thot nc nh hn 10 kPa) th cn kim tra lc nn cc hn ca thn cc.3) Khi cc nm sn dc mp bin cnh h o , cn kim tra tnh n nh ca cc cc vmng. Nu c yu cu nghim ngt i vi chuyn v ngang, phi kim tra chuyn v ngang.

4) Tnh ton kh nng chng nt v m rng khe nt ca cc v i cc bng b tng ct thp theo tiu chun thit k kt cu b tng ct thp hinhnh.3.1.2.Ti trng dng trong tnh ton theo nhm trng thi gii hn u l t hp ti trng c bn v ti trng c bit (ng t, gi,) cn theo nhmtrng thi v gii hn th hai theo t hp ti trng c bn vi ti trng nh quy nh ca tiu chun trng ti v tc ng.3.1.3.Mi phng n thit k cn tho mn cc yu cu sau y:a) m bo mi yu cu ca trng thi gii hn theo quy nh;b) H s an ton s dng cho vt liu cc v t nn l hp l;c) Phng n c tnh kh thi v mt kinh t - k thut, m bo vic s dng bnh thng cc cng trnh ln cn.3.1.4.Nhng cng trnh c mt trong nhng iu kin sau y phi tin hnh quan trc ln theo mt chng trnh quy nh cho n khi ln -c coi l n nh:- Cng trnh c tnh cht quan trng


- iu kin a cht phc tp;- Dng cng ngh lm cc mi;3.2. Chn loi cc3.2.1. Vic la chn loi cc v nguyn tc phi da vo iu kin 3.1.3, trong phi c bit ch n cc yu t chnh sau y:- c im ca cng trnh;- iu kin c th ca t nn v nc ngm;- Nhng rng buc khc ca hin trng xy dng (mc n v rung ng cho php, hin trng cng trnh ln cn, h thng ngm nc di t v v sinh mi trng khc );- Kh nng thi cng ca nh thu;- Tin thi cng v thi gian cn thit hon thnh;- Kh nng kinh t ca ch u t.3.2.2. Cn nm vng phm vi s dng ca tng loi cc cng nh kh nng v mc hon thin ca thit b thi cng, trnh ngh nghip ca n v thi cng, nht l phng n cc khoan b tng ti ch.Nn lp khng t 2 phng n so snh hiu qu kinh t k thut v tnh kh thi la chn.

Ch thch :

1) Theo bin php thi cng, cc c phn lm 3 loi chnh:

a) Cc gy dch chuyn ln trong qu trnh thi cng l loi cc thng th-ng, c h bng phng php ng, p hoc rng;b) Cc gy dch chuyn nh trong qu trnh thi cng : bao gm cc loi cc thp hnh c mt ct h, cc ng m t c th chui vo lng cc mt cch d dng hoc cc c h bng phng php ng, p v rung c khoan dn vi ng knh l khoan nh hn b rng tit din cc.

c) Cc thay th : l cc loi cc khoan nhi hoc cc c h bng phng phpng, p vrng c khoan dn vi ng knh l khoan bng ln hn b rng tit din cc.

2) Khi s dng loi cc dch chuyn ln, cn ch ti nh hng bt li n cng trnh ln cn v cc c thi cng trc do dch chuyn ngang ca nn t. Cc dch chuyn ny c th lm cc cc thi cng trc b nng ln v b dch chuyn ngang qu mc cho php.Trong qu trnh h cc, nn t b xo ng, hiu ng ny cn phi c k n trong thit k nhm cc. Cc hin tng nu trn c th khc phc c bng cch s dng cc loi cc gy dch chuyn nh, khoan dn trc khi h cc khoan nhi.3) Khi s dng gii php cc khoan nhi trong nn t ri bo ho nc, nc trong t, c bit l nc c p, c th lm nh hng n cht lng cc v kh nng chu ti ca cc lp t xung quanh thn cc, mt khc vi s tn ti ca nc t do trong cc lp t ri s lm nh hngn qu trnh linh kt ca xi mng. Trong trng hp ny cn s dng ng vch bo v cho cc.4) Khi thi cng mng cc cnh cc cng trnh t trn nn t hay t bi trng thi ri, bo ho nc, nht thit phi trnh s dng cc phng php gy tc dng lm gim cng chng ct ca cc lp t di y mng ca cc cng trnh ln cn.3.3. Cng ca vt liu cc3.3.1.Nhng vn chungCc ch to sn phi c thit k c th chu c gi tr ni lc sinh ra trong qu trnh cu, vn chuyn, lp dng, thi cng h cc v chu ti vi hs an tonv hp l. i vi cc khoan nhi, m bo cng , cn ch n sch


ca y h khoan, thng ng ca cc, m bo kch thc thn cc, ngnht v c chc ca b tng.

3.3.2.ng xut trong cc

ng xut cho php ln nht khng c vt qu gii hn sau :- Vi cc b tng ct thp : 0.33 fc;- Vi cc b tng ct thp ng xut trc : 0.33 fc 0.27 fpe;- Vi cc thp hnh ch H c trn khng c b tng nhi : 0.25 fy;- Vi cc thp hnh trn c b tng nhi : 0.25 fy + 0.40 fc;

ng xut cho php ln nht (trong qu trnh ng cc c th sinh ra hai loi sng ng xut nn v ko) do ng cc, khng c vt qu gii hn sau:- Vi cc b tng ct thp : 0.85 fc (cho trng hp sng nn );0.70 fy (cho trng hp sng ko);

- Vi cc b tng ct thp ng xut trc : 0.85 fc-fpc(cho trng hp sng nn);fc+fpc (cho trng hp sng ko);- Vi cc thp 0.90 fy (cho trng hp sng nn v sng ko).

Ch thch:

1) Nu mt phng u cc khng vung gc vi hng ri ca qu ba, lc ngang s xut hin gy m - men un cho cc. Gi tr m - men ny s tc dng li dn ba v lm cho cc cc b nghing.2) Nu tit din chu v chm ca cc khng ln, vt liu u cc s b ph hoi. Hin tng ny thng xy ra i vi cc g v cc thp c ng trc tip m khng c mi cc, tuy nhin nu mi cc khng che ht c u cc th cng xy ra cc hin tng nh trn.3) Nu cc phi ng qua mt lp st cng hoc lp ct cht i xung lp chu lc su hn, th do u cc chu va cham trong thi gian di nn d b h hng. Mi cc khi m vo cc lp cui hoc si cng d b ph hoi.4) Khi ng cc vi qu ba nh so vi trng lng cc v chiu cao ri ba ln s gy ng xut tip xc ln lm hng u cc. Thng thng t s gia trng lng ba v cc khng nh hn0.25 v c ly ty theo loi ba s dng.

5) Khi ng cc qua lp t yu, nu chiu cao ri ba ln c th gy ng xut ko di lm hng cc.3.3.3.Cc b tng ct thp c snCc c thit k vi cc loi ti trng thng xut hin trong qu trnh bc d, vn chuyn v ng cc.a) B tngNhng yu cu v b tng cc c ly theo cc tiu chun thit k cu b tng ct thp hin hnh. B tng cc cn c tht k chng c cc tc nhn bn ngoi c trong nn t.Da trn iu kin lm vic ca cc, mc ti thiu cho b tng cc c th ly theo bng 3.1 :

Bng 3.1 - Mc ti thiu ca cc b tng cc

Cc phi ng n chi 40iu kin bnh thng v d 25


b) Ct thpCt thp cc phi tho mn cc iu kin quy nh v cht lng ct thp c th chu c cc ni lc pht sinh trong qu trnh bc d, vn chuyn v p lc ko cc m - men un ca cng trnh bn tc dng vo cc, cng cn xt n tr ng xut ko c th pht sinh do hin tng nng nn khi ng cc cc tip theo.

Ct thp ch yu cn c ko di lin tc theo sut chiu di cc. Trong tr-ng hp bt buc phi ni ct thp ch, mi ni cn c tun theo quy nh v ni thp v b tr mi ni ca cc thanh.Trong trng hp cn tng kh nng chu m - men, thp c tng cng phnu cc, nhng cn b tr sao cho s gin on t ngt ca ct thp khng gy ra hin tng nt khi cc chu tc ng xung trong qu trnh ng cc.Ct thp dc c xc nh theo tnh ton, hm lng thp khng nh hn 0,8%ng knh khng nn nh hn 14mm. i vi nhng trng hp sau,nht l cccc cho nh cao tng, hm lng ca ct thp dc c th nng ln 1 - 1.2%:- Mi cc xuyn qua lp t cng;- mnh ca cc L/d >60;- Sc chu ti thit k ca cc n kh ln m s cc ca 1 di t hn 3 cy.Ct ai c vai tr c bit quan trng chu ng xut ny sinh trong qun trnhng cc. Ct ai c dng mc, ai kn hoc xon. Tr trng hp c s dng mi ni c bit hoc mt bch bao quanh u cc m c th phn b c ng xut gy ra trong qu trnh ng cc, trong khong cch bng 3 ln cnh nh ca ccti hai u cc, hm lng ct ai khng t hn 0,6% ca th tch vng nu trn.Trong phn thn cc, ct ai c tng tit din khng nh hn 0,2% v c b tr vi khong cch khng ln hn b rng tit din cc. S thay i cc vng c khong cch cc ai ct khch nhau khng nn qu t ngtc) Mi ccMi cc c th l mt phng hay nhn. trong trng hp phi ng xuyn qua qu, st ln cui si hoc cc loi t nn khc c th ph hoi phn b tng nn mi cc cn thit bng thp hoc gang c. Trong nn st ng nht, mi cc khng nht thit phi nhn.d) Ni ccMt cy mc khng nn c qu 2 mi ni (tr trng hp cc thi cng bng phng php p); khi cc c trn hai mi ni phi tng h s an ton i vi sc chu ti. Ni chung mi ni cc nn thc hin bng phng php hn. Cn c bin php bo v mi ni trong cc lp t c tc nhn n mn.e) Ct u cc.Trong trng hp cc khng c ng n su thit k, u cc c ct n cao sao cho phn b tng cc nm trong i m bo t 5 -10cm nu lin kt khp cc di. Phn ct thp nm trong i c tho mn theo yu cu ca thit k. Khi ct u cc, phi m bo cho b tng cc khng b nt, nu c, cn c b phn nt v v li bng b tng mi.g) Ko di ccTrong trng hp phi ko di cc m u cc khng c thit k mi c bit, th phi p b mt phn b tng u cc khng t hn 200mm v phi trnh lm


hng b tng cc. Thp ch c hn theo ng quy phm v v hn ct thp. Khikhng c my hn th c th s dng cch ni bng phng php buc, chiudion buc khng nh hn 40 ln ng knh ct thp.3.3.4.Cc b tng ng sut trcThit k cc b tng ct thp ng sut trc cn tun th cc yu cu ca Tiu chun thit k kt cu b tng ct thp hin hnh v cn lu n cc im sau:- Bo v chng n mn;- Hn ch pht sinh vt nt trong qu trnh thi cng cc;- S dng ba c t s trng lng ba trng lng cc ln vi chiu cao ri ba thp hn ch hng cc.3.3.5.Cc thpCc thp thng c tit din h nh cc ch H, Ch I, hoc c tit din kn nh hnh trn, hnh hp. T l gia ng knh ngoi v chiu dy thnh ng khng ln hn 100. Chiu dy nh nht ca thnh ng l 8mm.a) ThpThp s dng lm cc cn tun theo tiu chun tng ng c ban hnh v thp hoc cc tiu chun khc tu theo quy nh ngi thit k.b) B tng nhiTrong trng hp c cc tit din kn c nhi y hoc mt phn b tng tham gia chu lc th lng xi mng trong hn hp b tng khng nn nh hn 300 kg/m3 v st khng nh hn 75mm.c) Thit kc1. Truyn ti vo ccTi trng ca cng trnh c truyn xung cc thng qua i cc bng b tng ct thp, mt chiu di on cc c ngm trong i. i cc phi dy v c li thp hoc thp tm ph ln u cc trnh hin tng chc thng. Trong phn cc ngm i, cn lm sch b mt thp. Nu ti trng cng trnh c thit k cho phn b tng nhi trong cc ng hay cc tit din kn, ng xut cho php tc dng ln phn b tng cn tun theo tiu chun thit k kt cu b tng ct thp hin hnh.c2. Chng n mnTrong trng hp c kh nng xut hin hin tng n mn vt liu thp, cn phi c bin php chng n mn, theo nh tiu chun quy nh trong tiu chun chngn mn kim loi. Chiu dy ca thp c xc nh da vo tc n mn, tui th d kin ca cng trnh v tng thm d tr n mn l 2mm.d) Mi cci vi cc cc c tit din h khng i hi phi c mi. Trong trng hp cc cc c ng vo lp t cng, thi gian ng cc di, mi cc cnc gia cng bng thp bn tng cng. Khi cc c ng vo phi c mi c bit. i vi cc cc c tit din kn, nu yu cu phi bt y cc th vic bt yc thc hin bng cch lm thm bn bng tm thp hoc mi bng gang c hay thp ch to sn.3.3.6.Cc nhi


Cc nhi l cc c thi cng to l trc trong t, sau l c lp y bngb tng hoc khng c ct thp. Vic to l c thc hin bng ph-ng php khoan, ng ng hay cc phng php o khc. Cc nhi c -ng knh bng vnh hn 600mm c gi l cc nhi c ng knh nh, cc nhi c ng knh ln hn 600mm c gi l cc nhi ng knh ln.Ngi thit k v ngi thi cng cn c hiu bit y v iu kin t nn cng nh c im ca cng ngh d nh thc hin m bo cc quy nh v cht lng cc.a) B tngB tng dng cho cc khoan nhi l cc loi b tng thng thng. Ngoi iu kin v cng , b tng phi c st ln m bo tnh lin tc ca cc. st b tng c nu trong bng 3.2. Mc b tng s dng cho cc nhi ni chung khng thp hn 20 Mpa

Bng 3.2 - t st ca b tng cc nhi

t do trong nc, ct thp c khong cch ln cho php b tng dch 7,5 12,5Khong cch ct thp khng ln, cho php b tng dch chuyn d dng, khi ct u cc nm trong vng vch tm.

10 17,5Khi b tng c di nc hoc trong dung dch st ben - t - nit qua ng >15

Thng thng b tng ca cc nhi c hm lng xi mng khng nh hn350kg/m3. trnh s phn tng do b tng c st ln hoc b tng b mt nc trong iu kin ma h, nn s dng cc loi ph gia thch hp.b) Ct thpCt thp dc ca cc nhi xc nh theo tnh ton, ng thi phi tho mnmt s yu cu cu to sau :- Trong trng hp cc nhi chu ko, ct thp dc cn c b tr theo sut chiu di cc. Khi ct thp dc c ni cn phi hn theo yu cu chu lc. Khi lc nh l nh, ct thp dc c b tr n su cn thit lc koc trit tiu hon ton thng qua ma st cc.- i vi cc chu nn dc trc, hm lng ct thp khng nn nh hn 0,2 0,4%.ng knh ct thp khng nh hn 10mm v b tr u theo chu vi cc.i vi cc chu ti trng ngang, hm lng ct thp khng nh hn 0,4 0,65%

Ct ai cc nhi thng l 6 10, khong cch 200 300mm. C th dng ai hn vng n hoc ai c xon cha lin tc. Nu chiu di lng thp ln hn 4m, tng cng cng tnh ton khi th b sung thp ai 12 cch nhau2m, ng thi cc ct ai ny c s dng gn cc ming k to lp bo v ct thp.Chiu dy lp bo v ct thp dc ca cc nhi khng nh hn 50mm.


Thng thng cc nhi c to l t cao mt t, t trong lng cc c lyra. Hin tng dn t trong qu trnh thi cng s gy ra ng sut ko cho cc vn tn ti n khi cc c ti . Do ct thp cc cn c b tr chu lc ko trn cho n khi gi tr lc ko ny b trit tiu do ti trng ca cngtrnh truyn xung.3.4. Cc chu ti dc trcThng thng cc c ng thng ng v ngp hon ton trong t, khi xcnh sc chu ti theo vt liu cc th khng cn phi xt n n nh ca cc. i vi cc chng xuyn qua nn t yu (sc chng ct khng thot nc nh hn 10kPa) th cn xt n n nh ca cy cc.3.5. Cc chu ti trng ngangCc c ng thng ng c th phi chu lc ngang trong mt s trng hp nh : cc i cao, kt cu bn trn chu ti trng ngang, khi xut hin lc x ngang hoc ti trng ng t. Ti trng ngang lc ny cn c k nv c th s gy bt li cho s lm vic ca cc.3.6. Cc xinCc xin s dng khi ti trng ngang ln. Trong tnh ton phn b ti trng, ccc xem l lm vic dc trc v c xc nh bng phng php hnh hc hoc gii tch. Tuy nhin trong thc t lun c mmen tc dng ln cc. ln ca m- men un ni trn ph thuc vo ln ca nhm cc, nghing ca cc v kiulin kt gia cc v i cc.3.7. Cc chu ti lch tmThng thng ti trng ti chn ct l ti trng lch tm hoc c mt gi tr ti trng ngang v m- men nh hn so vi gi tr ti trng thng ng. Mt khc cc khng th thi cng c ng v tr nn lm tng lch tmca h cc; iu c ngha l lun tn ti mt gi tr lch tm no . V vy cc nn c thit k chu c nhng tnh hung ti trng nu trn.3.8. Cc chu nhTrong nhiu trng hp cc lm vic vi cc nh, nh cc neo, cc ca mng cc cng trnh vi dng thp, trong gi tr ti trng thng ng l nh hn so vi lc ngang v m- men. Cc c thit k nh cc thanh chu ko.

Nu cc c lm bng b tng ct thp, ct thp s chu ton b gi tr lc nh. B tng cc neo thng b nt, v vy cn ch n cc tc nhn n mn, gy h hng ct thp cc lm nh hng n kh nng chu ti lu di ca cc.3.9. Nhm cc3.9.1. H ccTrong nhm cc, hin tng cc ng trc b nng v b y ngang trong qu trnh thi cng nn c lu khi chn la loi cc, khong cch gia cc cc v trnh t thi cng. Trong nn ct, st ng v cui si c th ng tt c cc cc trong nhm n su thit k, th t ng nn tinhnh t gia nhm ra pha ngoi. Trong trng hp cn thit c th s dng bin php khoan dn. Khi nhm cc t gn cc c hoc cng trnh c sn th nn tin hnh ng cc t phn tip gi v ra xa dn trnh lm dch chuyn tng c v cng trnh ln cn. Cc khoan nhi trong trng hp ny l gii php thch hp3.9.2. Khong cch cc


Khong cch gia cc cc trong nhm c quan h vi iu kin t nn, i xtng cc n trong nhm v gi thnh ca cng trnh.Khong cch gia cc cc gm cn la chn sao cho hin tng nng cc, lm cht t gia cc cc l nh nht ng thi tn dng c ti a sc chu ti ca cc v cn phi c th h c tt c cc cc n su thit k m khng lm h hng cc cc khc v cng trnh ln cn.Gi thnh ca i cc v ging mng cng lm nh hng n vic la chn khong cch v kch thc cc.Khong cch gia cc cc c th xc nh nhng iu kin sau :a) Phng php thi cng (cc ng hay cc nhi);b) Kh nng chu ti ca nhm cc.Thng thng, khong cch tm gia hai cc k nhau ln ly nh sau :- Cc ma st khng nh hn 3d;- Cc chng khng nh hn 2d;- Cc c m rng dy, khng nh hn 1,5 ng knh m rng D hoc D +1m(khi D > 2m).3.9.3. Hiu ng nhmDo s tng tc gia cc cc trong nhm nn ln ca nhm cng nhSc chu ti ca cc trong nhm s khc vi cc n. Hiu ng ny cn c xt n trong thit k. Chiu su v vng nh hng phn t di nhm cc ph thuc vo kch thc ca nhm v ln ca ti trng.3.9.4. ln ca cc. ln ca mt cc ma st c s lng cc nhiu s cao hn so vi nhm c t cc hn cng mt iu kin t nn v ln ca ng xut di y mi cc.Khi d tnh ln ca nhm cc ngi ta thng tnh cho khi mng quy c, trong

din tch ca khi mng quy c x nh ty theo iu kin lm vic cacc.3.9.5. Kh nng chu ti ca nhm ccTrong nn t ri qu trnh h cc bng phng php ng hay p thng nn chtt nn, v vy sc chu ti ca nhm cc c th ln hn tng sc chu tica cc ccn trong nhm.Trong nn t dnh, sc chu ti ca nhm cc ma st nh hn tng sc chu ti ca cc cc n trong nhm. Mc gim sc chu ta ca cc cc n trong nhm. Mc gim sc chu ti ca nhm cc trong trng hp ny ph thuc vo khong cch gia cc cc trong nhm, c tnh ca nn t, cng ca i cc v s tham gia truyn ti cng trnh ca i xung cc v t.i vi cc chng, sc chu ti ca nhm cc bng tng sc chu ti ca cc cc n trong nhm.Cc trong nhm chu ti trng lch tm nn b tr sao cho im t ca hp lc ti trng l gn nht so vi trng tm ca mt bng nhm cc.3.10. Ma st mMa st m l gim kh nng chu ti ca cc, nht l i vi cc nhi, do cn xen xt kh nng xut hin ca n khi tnh ton sc chu ti ca cc trong cc trng hp sau:


- S c kt cha kt thc ca trm tch hin i v trm tch kin to;- S tng cht ca t ri tc dng ca ng lc;- S ln t ca t khi b ngp nc;- Tng ng sut hu hiu trong t do mc nc ngm b h thp;- Tn nn quy hoch c chiu dy ln hn 1m;- Ph ti trn nn kho ln hn 20 kPa;- S gim th tch t do cht hu c c trong t b phn hu.- S c cha kt thc ca trm tch hin i v trm tch kin to;- S tng cht ca t ri di tc dng ca ng lc;- S ln t ca t khi b ngp nc;- Tng ng sut hu hiu trong t do mc nc ngm b h thp;- Tn nn quy hoch c chiu dy ln hn 1m;- Ph ti trn nn kho ln hn 20 kPa;- S gim th tch t do cht hu c trong t b phn hu.3.11. i cci cc thng c lm bng b tng ct thp, c thit k nh cu kin di tcdng ca ti trng cng trnh v phn lc ca cc. Tu theo cch lin kt gia cc i cc, c th xem i cc lm vic nh h cc kt cu c lp, h kt cu phng hoc khng gian.3.12. Lin kt cc v iCc c th c lin kt vi i di dng khp hoc ngm.Trong trng hp lin kt khp, cc cn c cm vo i vi chiu su 5-10cm. khng bt buc phi ko di ct thp cc vo i.

Trong trng hp lin kt ngm, th chiu di ngm cc hoc ct thp cc ko di trong i ly theo yu cu ca tiu chun thit k kt cu b tng ct thp. Trong trng hp cc b tng ng sut trc, khng c dng ct thp ko cng ca cc ngm vo i m phi cu to h ct thp ring.Khi cc c lin kt ngm vi i, cn k n gi tr m-men pht sinh ti lin kt.3.13. H s an tonKhi thit k mng cc, cc loi h s an ton c p dng bao gm:a) H s an ton cho vt liu lm cc v i cc nh l nhng thnh phn ca kt cu, ly theo cc tiu chun thit k kt cu b tng ct thp hoc thp;b) H s an ton p dng cho vic xc nh sc chu ti theo t nn cn k n trng thi t nhin ca nn t, tin cy ca phng php xc nh cc thngs tnh ton v c im lm vic ca cng trnh.Thng thng h s an ton c s dng nm trong khong t 1,2 n 3,0 nhtrnh by cc ph lc A,B,C,D v E.

Ch thch:

1) Khi c yu cu c bit v ln tuyt i v ln lch (nh hn quy nh thng thng), gi tr h s an ton cn phi ly ln hn cn trn, khi ln khng phi l iu kin quytnh cho thit k, c th s dng mt gi tr h s an ton nh hn cn d-i.


2) H s an ton nn ly ln hn trong tng trng hp cc chu nhng ti trng va chm ln, dao ng, ti trng lp hoc nhng ti trng tng t m c th lm suy gim cng cat trong qu trnh chu ti.

3) i vi nhm cc, ngi thit k nn xem xt nhng ch dn trong mc 3.9. kh nng chu t ca nhm cc cn xem xt n iu kin lm vic ca khi t cc v tng sc chu ti ca cc cc n trong nhm. Lc ny nn d tnh ln ca nhm cc di ti trng lm vic.4) Trong trng hp cc nhi c ng knh ln, thng thng phi thit k ns khc nhau gia quan h ti trng- ln ca sc chng mi v ma st bn. s khc nhau ny c th hin bng cc gi tr h s an ton nh nhau cho mi cc v mt bn khi tnh ton sc chu ti.4. Sc chu ti ca cc n4.1. Yu cu chung4.1.1.Sc chu ti ca cc theo t nn c d tnh trn c s:a) Ch tiu ca t nn xc nh t th nghim trong phng hoc hin tr-ng (xem ph lc A, B, C);b) Th cc bng ti trng tnh (xem ph lc E);

c) Th cc bng ti trng ng (xem ph lc D);

Ch thch:

1) Trong cc phng php k trn, phng php th cc bng ti trng tnh cho kt qu c tin cy cao nht.2) Kt qu th cc bng ti trng ng cn c hiu chnh theo th tnh.

3) Trong thit k s b c th s dng kinh nghim c trong iu kin t nn v cng trnh tng t ca a phng.4.1.2.Cng thc chung d tnh sc chu ti cho php ca cc n theo t nn l:

Qa= Qu (4.1)FSCh thch: Mt s gi tr ca h s an ton c kin ngh trong cc ph lc km theo tiu chun ny.4.1.3.Tnh ton cc theo bn ca vt liu theo yu cu ca cc tiu chun thit k kt cu b tng ct thp hoc thp. Trong trng hp chu nn, cc c xem nh mt thanh ngm cng trong t ti su cch y i mt khong Le (xem ph lc G).4.1.4.Sc chu ti cho php ca cc n dng trong thit k ly bng gi trnh nht t kt qu tnh ton theo iu 4.1.2. v 4.1.3.4.2. Sc chu ti trng nn ca cc n4.2.1.Ti trng nn truyn ln cc phi tho mn iu kin:

N QaTrong Qa ly theo quy nh ca iu 4.1.4.

(4.2)4.2.2.Sc chu ti cc hn ca cc theo t nn bao gm hai thnh phn- sc chng mi v ma st bn ca cc:Qu= Qp+ Qs (4.3)Ch thch:

1) Cn k n trng lng cc nh ti trng tc dng trong trng hp cc chu ma st m.


2) Khi cc lm vic nh cc chng, nn b qua ma st bn tr trng hp c kh nng xy ra ma st m.4.3. Sc chu ti trng nh ca cc n4.3.1. Ti trng nh truyn ln cc phi tho mn iu kin:

N k QakTrong Qak ly theo quy nh ca iu 4.1.4.

(4.4)

4.3.2. Sc chu nh cc hn ca cc theo t nn ly bng tng ma st bn cc c k thm trng lng cc:

Quk

Qsk w

(4.5)

Ch thch: Mt s phng php tnh ton kh nng chu ti trng nh ca cc c gii thiu trong cc ph lc A v B.4.4. Sc chu ti trng ngang ca cc4.4.1. Ti trng ngang H, tc dng ln cc phi mn iu kin:

H QahTrong Qah ly theo quy nh ca iu 4.1.4.

(4.6)4.4.2. Sc chu ti trng ngang cc hn ca cc c tnh ton khi cc chu tc dng ng thi ca m men un, lc ngang, lc dc trc v phn lc ca nn t.

Ch thch:

1) nh hng ca lin kt gia cc v i cc cn c k n trong tnh ton.

2) Mt s phng php tnh ton sc chu ti trng ngang ca cc c gii thiu trong ph lc G.4.5. Th nghim xc nh sc chu ti ca ccCng tc th nghim nn c thc hin bi mt n v c lp v c nng lc chuyn mn cao v thc hin theo tiu chun th cc hin hnhTCXD 88:1982.4.5.1. Phng php th bng ti trng ng4.5.1.1. Th nghim ng c kt hp vi th nghim tnh xc nhquy trnh ng cc thch hp v sc chu ti ca cc.4.5.1.2. Th nghim ng bao gm hai phng php thng dng:a- Dng cng thc ng d tnh sc chu ti theo chi khi ng th (xem ph lc D);b- Dng l thuyt truyn sng ng sut x l kt qu o bin dng v gia tc dch chuyn ca u cc khi ng th theo tiu chun ASTM D4945-89.

Ch thch: Kt qu do bin dng v gia tc dch chuyn ca cc khi ng cn c s dng pht hin cc khuyt tt trong cc hoc kim tra chiu di cc.4.5.1.3. Cng tc th nghim ng bng cch o chi phi c thc hin theo yu cu ca tiu chun v th nghim cc hin hnh vi s lng ti 1% tng s cc ti cng trnh ang xt nhng khng t hn 5 cc.4.5.2. Phng php th bng ti trng tnh.

4.5.2.1. Phng php ny bao gm:- Th nghim nn dc trc;- Th nghim nh dc trc;- Th nghim nn ngang vung gc vi trc cc.


Ch thch: Ty theo yu cu, cng tc th nghim c th c thc hin trn cc n hoc trn nhm cc.4.5.2.2. S lng cc th nghim trong giai on kho st (trc khi thit k)theo tiu chun th cc hin hnh v c la chn trn c s:- iu kin t nn v s bin ng chiu dy ca n trong phm vi cng trnh;- Quy m v tm quan trng ca cng trnh;- Kinh nghim c i vi cng loi cc trong iu kin t nn a ph-ng;- Trnh cng ngh thi cng cc;- S lng cc d kin s dng trong cng trnh.4.5.2.3. Nn b tr cc th nghim ti cc v tr c iu kin t nn in hnh ca khu vc xy dng.4.5.2.4. Vic thi cng cc th nghim c thc hin bng nhng thit bv quy trnh md kin s s dng khi thi cng hng lot.4.5.2.5. Quy trnh th nghim cc o n v t vn lp ra trn c s c im ca t nn ti trng cng trnh v ph hp vi quy nh ca tiu chun v th nghim cc hin hnh.4.5.2.6. Trong qu trnh thi cng v trc khi nghim thu cng tc thi cng,c th thnghim b sung mt s cc. S lng v v tr cc th nghin b sung c xcnh trn c s h s theo di ca t vn gim st xy dng.

Ch thch:

1) Ti trng th phi t ti trong th nghim nn tnh giai on ny phi ln hn sc chu ti thit k ca cc v do t vn thit k quyt nh.2) nh gi cht lng thi cng cc ni chung c trnh by trong mc 7 ca tiu chun ny.

5. Tnh ton nn mng cc theo bin dng5.1. Vic tnh ton mng cc ma st v nn ca n theo bin dng c th hin thng qua ln tuyt i, ln lch, chuyn v ngang, nghing hoc xon ca cng trnh trn cc v mng cc. Cc c trng bin dng tnh ton ni trn phi tho mn iu kin:

S S gh

(5.1)

y S c hiu nh bt k c trng tnh ton bin dng no cn xem xt; cn Sghl tr php ca c trng bin dng .

Ch thch:

1) Cc c trng bin dng ni trn (xem ph lc H) c th l:

- ln tuyt i ca tng mng c lp Si;- ln trung bnh ca nn cng trnh Stb;- ln lch tng i S/L ca 2 mng gn nhau, tc l t s gia hiu s ca hai chuyn thngng vi khong cch L gia chng;

- nghing I ca mng hay ca cng trnh ni chung-tc l t s gia hiu s ln ca nhngim mp ngoi cng ca mng vi chiu rng hoc chiu di ca mng;

- vng hoc vng ln tng i f/L- tc l t s gia mi tn vng f vi chiu di ca phn cng trnh chu un;- cong ca on chu un 1/ R ;- Gc xon tng i ca cng trnh / L ;


- Chuyn v ngang ca mng u, v.v.

2) Trong trng hp cn k n qu trnh lu di th phi tnh ln theothi gian. ln ca mng cc trong qu trnh xy dng cho php khng k n nu nh chng khng nh hng n tnh s dng thun li ca cng trnh.3) Tr gii hn ca cc c trng bin dng ni trn c th thay i khi dng gii php xy dng nhm gim tnh nn ln v tnh khng ng nht ca nn cng nh cc gii php cu to nhm gim tnh nhy ca cng trnh i vi bin dng ca nn.5.2. Tnh ton mng cc theo bin dng nn tin hnh mi loi t tr tr-ng hp cc ta trn t hn ln, ct cht v st cng. Vic tnh ton ny cng cn thit khi cc chu ti trng ngang v c th gy ra nhng chuyn v ngang ng k.5.3. Ti trng dng trong tnh ton bin dng l t hp ti trng c bn truyn ln mngk c ti trng trn nn kho hoc thit b t gn mng; trong trng hp c tn nn cao hn 2m bng t v trong nn cc c lp t yu dy hn 30cm hoc khi xut hin p lc ph thm do h mc nc ngm th cn k n cc tc ng ny trongtnh ton ln ca mng.

Ch thch:

1) Ni chung khng cn tin hnh d tnh ln ca mng cc trong cc tr-ng hp sau y: cc chng, cc n chu nh v nhm cc chu lc nh v khi tnh ton chng theo sc chu ti hin nhin m bo c v bin dng.2) ln ca mng cc chng ch yu l do bin dng n hi ca vt liuthn cc di tc dng ti trng cng trnh ln ny c th xc nh bng ln ca cc n ly t kt qu nn tnh ng vi ti trng u cc hoc cng c th tnh ton theo phng php trnh by ph lc H.3) Khng cn d tnh ln m cu ng st c nhp di 50m v m cu ng b c nhp di100m thuc h kt cu tnh nh. Trong trng hp cn d tnh ln ca m cu, c th thc hin theo im ca ch thch ny vi mt s b sung sau y.4) Cc trong m lm vic nh cc chng;

5) Khong cch gia cc tim cc ln hn 6d;

6) S hng cc theo chiu dc khng qu 3 hng.

7) Vic tnh ton mng cc cho cc m cu v cng phi thc hin theo nhm trng thi gii hn v bn c kim tra ln v chuyn v ngang nh m.5.4. Tu theo kch thc ca mng v cch b tr ca cc trong mng, vic d tnh ln c th phn ra: ln ca nhm cc, bng cc, b cc hoc cc n.5.4.1. ln ca nhm cc (khi cc c b tr di cc ct, tr hoc m cu) thng da vo kch thc ca mng quy c vi ti trng tng ng xc nh. su v kch thc ca mng quy c thay i theo iu kin c th ca t nn (xem ph lc H).5.4.2. ln ca nhm cc (khi cc c b tr di cc mng bng thnh mt v hai hng vi khong cch gia cc cc 3-4d) c tnh ton theo l thuyt bi ton phng (xem ph lc H).5.4.3. ln ca b cc (khi b tr u khp di cc mng b c kch thc ln hn 10 x10m) c th xc nh bng phng php lp bin dng tuyn tnh (xem ph lc H).5.4.4. ln ca cc n (thng l cc nhi khng hoc c m rng y, b tr di cc ct) c tnh ton theo l thuyt bn khng gian bin dng hoc theo kt qu nn tnh cc ti hin trng.

6. Thit k mng cc6.1. Yu cu chung


6.1.1. Ti trng ly trong thit k mng cc cn theo ch dn iu 3.1.2. ca tiu chunny.

6.1.2. Khi thit k mng cc cn thc hin cc cng vic sau:- Thu nhp v nghin cu cc d kin ca nn t v cng trnh bn trn;- Ti trng c t hp ti trng trn mng cng c im ca tc ng v nhng khnng thay i ti trng trong qu trnh s dng cng trnh;- Kiu mng cng bin dng gii hn tuyt i tng i ca cng trnh;- La chn loi mng cc, lp t chu lc t mi cc v xc nh kch thc cc, b tr cc trong mng.6.1.3. Thit k i cc phi bo m cc yu cu v cu to ca tiu chunthit k kt cu b tng ct thp, trong cn kim tra chc thng, lc ct v chu un ca i cc.6.1.4. Lin kt i cc vi cc cn theo ch dn iu 3.11 v 3.12 ca tiu chun ny.6.1.5. su y i cc c quy nh tu thuc vo cc gii php kt cu phn di mtt ca nh v cng trnh (c tng hm hoc tng hm k thut) v theo thit k san nn ca khu vc xy dng (o bt i hoc p cao thm), cn chiu dy ca ic xc nh bng tnh ton theo quy nh ca tiu chun thit k kt cub tngct thp.6.1.6. Ti trng tnh ton trn cc N nn xc nh khi xem mng nh l kt cu khung chu ti trng ng, ngang v m men un. Ti trng dc trc tcdng ln tng cc trong nhm gm cc cc thng ng xc nh theo cng thc:

P Mx.y My.xN

Trong :

N y 2x 2

(6.1)P- ti trng thng ng tnh ton tc dng ln nhm cc, kN;Mx, My- M men tnh ton ng vi cc trc chnh x v y ca mt bng nhm cc ti ta y i cc, kN.m;xi v yi- to ca cc th i, m;x v y- to ca cc m ti trng tc dng ln cc c tnh ton, m.

Ch thch:

1) Vic phn b ti trng gia cc cc ca mng di cao theo ch dn ca iu 6.2.5. ca tiu chun ny.2) Khi c cc xin th ti trng phn b cho cc cc theo cch gii h ny nh kt cu khung.

i

i

6.1.7. Ti trng ngang tc dng ln tng cc trong nhm gm cc cc thng ng v c cng tit din ngang, c phn b u ln cc cc trong nhm.6.2. c im thit k mng cu v cng trnh thu li6.2.1. Thng thng i vi tr cu v cc cng trnh thu li c ti trng ngang ln, vic dng cc xin thng l gii php hp l. Mng cc ca cc m cu nn b tr mt hoc vi hng cc xin theo pha lng sng. Mng cc ca tr cu nn c i cao nn thit k vi cc xin theo bn hng cng vi ccthng ng.6.2.2. i vi mng ca m v tr cu, do c im lm vic ca n, cn thit k theo cc yu cu b sung sau y:a) Kt cu ca mng cc v su mi cc c thit k c th k n bo mn v xi l ca t do dng chy;


b) Cc ca cc m cu cn kim tra di tc dng ca p lc ngang ca t;c) Cc cho php chng ln hoc chn vo . Trong trng hp trn mt c tng trm tch khng b bo mn vi iu kin trong tng y cc tip thu ht tc dng ca m men un th cho php khng ngm cc vo . Khi khng tho mniu kin va nu th su chn cc vo khng nh hn 0,5n khi c cng chng nn, ln hn 50Mpa v khng nh hn 1m trong cc loi cn li.Ch thch: tnh ton c th khi mi cc ta ln nn c th tham kho iu A.2 ca ph lc Athuc tiu chun ny.6.2.3. Khi thit k mng cc cho cu, cn ch :a) Cc kch thc ca i cc (hoc ca m ni bng b tng ct thp) trn mt bng phi quy nh sao cho khong cch t mp i n cc gn nht khng c nh hn 0,25m (khong cch mp-mp);b) i vi cc c ng knh ln hn 2m, bn i khng cn c mp tha.6.2.4. y i cc ca mng cu cn k n chiu su dng nc, vic xi l nu iu6.2.2 cng nh sc chu ti tnh ton v bn lu di ca mng trong iu kin khhu a phng.6.2.5. Vic phn b ti trng gia cc cc ca mng i cao nn xc nh bng cch tnh chng nh kt cu khung.6.2.6. Mng cc ca cc m cu v ca cc tr trung gian trn cc mi dc nn kim tra n nh chng trt su.6.3. c im thit k mng cc trong nhng vng c ng t6.3.1. Khi thit k mng cc trong nhng vng c ng t, ngoi nhng yu cu ca tiu chun ny cn cn phi tun theo nhng yu cu v xy dng trong nhng vng cng t c quy nh tiu chun v ti trng v tc ng.6.3.2. Mng cc ca nh v cng trnh c k n tc ng ca ng t c tnh ton vit hp ti trng c bit theo trng thi gii hn th nht. y cn ch :

a) Xc nh kh nng chu ti ca cc di tc ng ca ti trng nn v nh theo yu cu nu trong tiu chun ny;b) Kim tra cc theo iu kin bn vt liu di tc dng ng thi ca cc lc tnh ton (lc nn, m men un v lc ngang);c) Kim tra n nh ca t theo iu kin hn ch p lc truyn ln t qua cc mt bn ca cc.Ngoi nhng yu cu nu iu ny, trong tnh ton cn cn phi ch n nhng yu cu b sung nu trong ph lc I ca tiu chun ny.Ch thch: Khi xc nh tr s tnh ton ca ti trng ng t tc dng lnnh v cng trnh, th mng cc di cao nn xem nh tng khung cui cng.6.4. c im thit k mng cc cho cc tuyn ng dy ti in trn khng;6.4.1. Khi kho st a cht cng trnh cho cc tuyn ng dy ti in trn khng vi cc tr in c khong chuyn tip ln cn phi thc hin ton b ni dung nu chng2 ca tiu chun ny. trong trng hp cn li cho php thc hin khng t hn 3im thm d cho mi km chiu di tuyn.

Ch thch: S phn loi cc ng dy ti in trn khng v khong chuyn tip c ly theo tiu chun lp t thit b in.6.4.2. Chiu su h khoan quy nh nh sau:


a) i vi tr trung gian- su hn 2m di mi cc;b) i vi tr gc- su hn 4m di mi cc;6.4.3. Mng cc cho cc tr ng dy v trm phn phi in ngoi tri -c ghp dng trong tt c cc loi t.6.4.4. Khng c php dng cc cc dng hnh kim, hnh nm v hnh thoi cho mng trng dy.6.4.5. i vi cc cc chu ti trng ngang hoc ti trng nh, chiu su h cc vo trongt khng c nh hn 4m, v khng 3m i vi mng ca cc tr g.6.4.6. Tnh ton sc chu ti ca cc mng ng dy ti in trn khng c trnh by trong ph lc K.6.5. Thit k mng cc trong mt s iu kin c bit khc6.5.1. Mng cc trong t than bn v t p cn phi c thit k c k n ma st m ca t.6.5.2. Mng cc trong t ln t nn thit k xut pht t iu kin l t trong mng c th b t hon ton no nc G 0,8.Khi kho st a cht cng trnh nI xy dng c t ln t nn xc nh t lnt v tch lp t c ln t tng i s0,02 p lc p= 3 kg/c6.5.3. Cc loi t ln t v cc loi t khc m cc c trng bn v bin dng chng gim i khi t, trong mi trng hp khi chiu dy ca cc lp y

n 3cm th nn dng cc xuyn sut cc lp v chn vo lp v chn vo lp khng ln t.6.5.4. Khi thit k mng cc trong t trng n cho php cc xuynht chiu dy t trng n hoc xuyn mt phn (chng mi cc trc tip ln t trng. tuy nhin cn phi c nhng tnh ton mng cc theo cctrng thi gii hanh trong t trng n c k n kt qu nn tnh cc v tri ca cc khi n t.6.5.5. i vi vng t trng n, ngoi nhng yu cu chung thit k mng cc trnh by trong tiu chun ny, cn phi thc hin y cc ch dn b sung sau y:a) Trn vng xy dng phi tin hnh th tnh cc c lm t t v xc nh nng cao ton b mt t khi n;b) Vic th tnh cc cn bt u gia ti i vi cc ng trong t c m t nhin, cho ti ti trng bng ti trng d kin dng trong tnh ton cc. Sau khi gia ti cn lm t t v o chuyn v ca cc;c) Cng lc kt thc qu trnh trng n ca t, vic th cc phi tin hnh theo phng php nh l i vi t thng thng, khng trng n.6.5.6. Khi thit k mng cc trong vng khai thc m, ngoi nhng yu cu ca tiu chun thit k nh v cng trnh trong vng khai thc m; ycng vi nhng ti liu kho st cng trnh thit k mng cc trnh by y cng vi nhng ti liu v kho st a cht m v cc thng tin v nhng bin dng d tnh ca mt t.6.5.7. Vic tnh ton mng cc ca nh v cng trnh xy vng khai thc m cn theo cc trng thi gii hn bng t hp c bit ca ti trng, c k n tc ng theo cc pha nn b bin dng khi khai thc.6.5.8. Nhng tnh ton khc v mng cc xy dng trong vng t ln t, vng t trng n hoc vng khai thc m c th tham kho SNIP 2.02.03-85 v cc ti liu lin quan khc.


7. Yu cu k thut v nh gi cht lng cc7.1. Cc ng v p7.1.1.Trc khi tin hnh thi cng cc cn lp chng trnh thi cng v bin php qunl cht lng cc. Trong h s cn th hin:- Loi cc, cu to cc v h s c cc ca nI sn xut;- V tr v cc sai s cho php;- Chiu di cc, cao mi cc v nh cc d kin;- S lng cc;- Trnh t ng p cc;- Yu cu chnh i vi thit b ng v p cc, khi cn c th phi kim tra mt s thng s chnh ca thit b trc khi thi cng hng lot;- D kin cc kh khn c th gp trong qu trnh thi cng v bin php x l;- Sc chu ti cho php ca cc.7.1.2.Qu trnh ng/p tt c cc cc phi c theo di v lp l lch thi cng cho tng cc.7.1.3.L lch cc bao gm cc im sau:

- Loi cc v thit b h cc;- S k hiu ca cc;- Ni v ngy sn xut cc;- Tit din cc, chiu di v loi ct thp ( cho cc b tng ct thp);- Thi gian thi cng(ngy, gi bt u, kt thc) v cc s c gp phi khi thi cng cng bin php khc phc;- i vi cc ng cn ghi cc gi tr trng lng ba, chiu cao rI ba, s nhtp, chi. i vi cc p cn ghi chi tit lc p cho tng on v lc p cui cng;- Cc chng ngi vt gp phi khi thi cng;- Sai lch v tr, nghing v cao thc t ca nh v mi cc.7.1.4.H s theo di thi cng cc cn c lu tr theo quy nh ca nh nc. Bn vhon cng cc cn c lu tr lu di.7.1.5.Th nghim kim tra cht lng thi cng c th c b sung nu vic theo di thi cng cho thy cc khng t cht lng yu cu. Cc th nghim cn thc hin gm:- Kho st li t nn;- ng v cc nu cc chng b tri ln khi ng cc cc ln cn;- Kim tra pht hin khuyt tt ca cc do thi cng;- Kim tra sc chu ti;- Kim tra vt liu thn cc ( c chc v cng ).7.2. Cc nhi7.2.1.Trc khi tin hnh thi cng cn lp chng trnh thi cng v bin php qun lcht lng cc. Trong h s cn th hin:- Loi cc, cu to cc;


- V tr v cc sai s cho php;- Chiu di cc, cao mi cc v nh cc d kin;- S lng cc;- Trnh t thi cng cc;- Thit b v cng ngh thi cng n nh trc khi thi cng hng lot;- Sc chu ti ca cc v t l % cc cn kim tra cht lng;- Cc kh khn c th gp trong qu trnh thi cng cng vi bin php d kin xl.7.2.2.Qu trnh thi cng ca tt c cc cc phi c theo di ht sc cht ch. Phi lpl lch thi cng cho tng cc, c ch k xc nhn ca cc bn c lin quan.7.2.3.L lch cc bao gm cc im sau:- Loi cc v thit b to l;- S k hiu ca cc;- ng knh cc, chiu di, sch y l, nghing ca l khoan;- Thi gian thi cng (ngy, gi bt u, kt thc) v c bit l cc s c gp phi khi thi cng cng bin php khc phc.

- Loi ct thp;- Mc b tng, st, th tch b tng, phng php b tng;- T trng, PH, nht v thnh phn ht ca dung dch khoan (nu dng);

- p lc bm va hoc b tng, ng knh trong v ngoi ca ng bm;- Cc lp t gp trong qu trnh khoan, qu trnh thi ra y l khoan;- Cc chng ngi vt gp phi khi thi cng;- Sai lch v tr v cao thc t ca u v mi cc;- Kt qu kim tra cht lng cc theo quy nh ca chng trnh qun l cht lng.7.2.4.H s theo di thi cng cc cn c lu tr theo quy nh ca nh nc.7.2.5.Nu qua kt qu theo di v kim tra cho thy cc khng t cht lngyu cu, cn b sung mt s th nghim kim tra. Cc th nghim cn thc hin lc ny gm:- Kho st li t nn;- Th nghim kim tra ng nht ca vt liu cc bng cc phng php gin tip (siu m, rung, bin dng nh, bin dng ln);- Khoan ly mu b tng cc xc nh trc tip cht lng b tng, trong c cng ;- Kim tra kch thc thc hnh hc (ng knh, su,..);- Th nghim kim tra sc chu ti ca cc.

Ch thch: vic kim tra cht lng thi cng thc hin theo tiu chun TCXD 206:1998 cc khoan nhi - yu cu v cht lng thi cng.Ph lc AXc nh sc chu ti ca cc theo ch tiu c l ca t nn (theo SNIP 2.20.03.85)


A.1. Cc ch tiu c l dng trong tnh ton ca ph lc ny c xc nh theo TCVN4195: 1995 TCVN 4202: 1995- t xy dng.Sc chu ti cho php ca cc n, theo t nn, c tnh:

QtcQa K

Trong :tc (A.1a)Qa- sc chu ti cho php tnh ton theo t nn bng phng php nu trong ph lc ny;Qtc- sc chu ti tiu chun tnh theo t nn ca cc n; Ktc- H s an ton, ly bng:1,2- Nu sc chu ti xc nh bng nn tnh cc ti hin trng;

1,25- Nu sc chu ti xc nh theo kt qu th ng cc c k n bindng n hi ca t hoc theo kt qu th t ti hin trng bng cc mu;1,4- Nu sc chu ti xc nh bng tnh ton, k c theo kt qu th ng cc mkhng k n bin dng n hi ca t;1,4 (1,250- i vi mng m cu i thp, cc ma st, cc chng, cn khi cc i cao- khi cc chng ch chu ti thng ng, khng ph thuc s lng cc trong mng;i vi i cao hoc i thp m y ca n nm trn t c tnh nn ln v i vi cc ma st chu ti trong nn, cng nh i vi bt k loi i no m cc treo, cc chng chu ti trng nh, tu thuc s lng cc trong mng,tr s ktc ly nh sau:- Mng c trn 21 cc: ktc=1,4 (1,25);- Mng c t 11 n 20 cc: ktc= 1,55 (1,4);- Mng c t 6 n 10 cc: ktc= 1,65 (1,5);- Mng c t 1 n 5 cc: ktc=1,75 (1,6).S trong hoc n l tr s ca ktc khi sc chu ti ca cc c xc nh t kt qunn tnh hin trng.

Ch thch:

1) Nu vic tnh ton mng cc c k n ti trng gi v ti trng cu trcth c php tng ti trng tnh ton trn cc cc bin ln 20% (tr mng tr ng dy ti in).2) i vi mng ch c cc ng, mang ti trn 60 tn (600 kN) hoc 1 cc nhi mang ti trng 250tn (2500 kN) th:

ktc=1,4 - Nu sc chu ti xc nh theo th tnh cc;ktc=1,6- Nu sc chu ti xc nh theo cc phng php khc;ktc=1- i vi mng b cc ca cng trnh c cng ln, ln gii hn ln hn hoc bng 30cm (vi s cc ln hn 100), nu sc chu ti ca cc xc nh theo th tnh.A.2. Sc chu ti tiu chun ca cc chng trn t t nn co (khi Es= 500 kg/cm2) xcnh theo cng thc:

Trong :

Qtc

mq p Ap

(A.1b)m- H s iu kin lm vic ca cc trong t, ly bng m=1;


Ap- Din tch ta ln t ca cc trn rng v cc ng ly bng din tch tit dinngang, cn i vi cc trn rng v cc ng ly bng din tch tit din ngang cathnh cc khi khng nhi b tng phn rng n chiu cao khng nh hn 3 lnng knh cc;qp- cng chu ti ca t mi cc, T/m2, ly nh sau:a. i vi mi loi cc ng m mi cc chng ln , t hn ln ( tng, cui, dm, si sn c n ct) cng nh trong trng hp chng ln t st cng (tr lp ph c bo ho G< 0,85 v t trng n), qp =2000T/m2;b. i vi cc nhi, cc ng c nhi b tng ngm vo khng b phong ho(khng c cc ph lp yu) khng nh hn 0,5m, theo cng thc:

q tc hq pn ( 3

1,5)

Trong :tck d d 3(A.2)q pn - Cng chu nn tiu chun mt trc, (trung bnh cng) ca trngthi no nc, t/m2;k- h s an ton theo t, ly bng 1,4;h3- chn su tnh ton trong , m;d3- ng knh ngm ca phn chn vo , m.c) i vi cc ng chng ln b mt bng phng khng b phong ho, lpnyc ph bi lp t khng b xi l c chiu dy khng nh hn 3 ln ng knh cc ng, theo cng thc:

q tcq pnp kd (A.3)

tcTrong pn v k c ngha nh trong cng thc (A.2).

q

p

Ch thch: Khi cc chng ln nn b phong ho cng nh c th b xi l

th sc chng tiutcchun ca t pn phi da trn kt qu th cc bng phng php tnh.A.3. Sc chu ti tiu chun ca cc ma st thi cng bng phng php ngc b rng tit din n 0,8m, chu ti trng nn, c xc nh theo cng thc:

Trong :

Qtc

m(mR q p Ap

u m f f si li )

(A.4)qp v fs- cng chu ti mi v mt bn ca cc, ly theo bng A.1 v A.2;m- H s iu kin lm vic ca t ln lt mi cc v mt bn cc c k nnh hng ca phng php h cc n sc chng tnh ton ca t, xc nh theo bng A.3.Trong cng thc (A.4) vic ly tng cng chu ti ca t phi c tin hnh trn tt c cc lp t m cc xuyn qua. Trong trng hp khi san nn cn gt b hoc c th b xi trI t I, phi tin hnh ly tng sc chng tnh ton ca tt c cc lp t nm ln lt bn di mc san nn (gt b hoc di ct xi l cc b khi b l).

Ch thch:


1) Sc chu ti ca cc ng c m rng y khi xc nh theo cng thc (A.4): chu vi u thn ccl chu vi tit din ngang ca thn cc, cn phn m rng l chu vi tit din ngang ca phn m rng.

q

Bng A1- Sc chng ca t mi cc qp

su ca mi

Sc chng mi cc ng v cc ng khng nhi b Ca t ct cht

Si Th - Th va Mn Bi -Ca t st vi ch s st IL bng

0 0.1 0.2 0.3 0.4 0.5 0.6

3 750 660(400)

300 310(200)

200(120)

110 60

4 830 680(510)

380 320(250)

210(160)

125 70

5 880 700(620)

400 340(280)

220(200)

130 80

7 970 730(690)

430 370(330)

240(220)

140 85

10 1050 770(730)

500 400(350)

260(240)

150 90

15 1170 820(750)

560 440(400)

290 165 100

20 1260 850 620 480(450)

320 180 110

25 1340 900 680 520 350 195 12030 1420 950 740 650 380 210 13035 1500 1000 800 600 410 225 140

Bng A.2 ma st bn fs


8101520253035

6,26,57,27,98,69,310

4,44,65,15,66,16,67

3,33,43,84,14,44,75

2,62,72,833,23,43,6

1,91,92222,12,2

111,11,21,21,21,3

0,80,80,80,80,80,90,9

0,70,70,70,70,70,80,8

0,60,60,60,60,60,70,7

Ch thch ca bng A.1 v A.2:

1) Trong nhng trng hp khi m bng A.1 cc gi tr s ca qp trnh by dng phn s, th ts l ca ct cn mu s l ca st.

2) Trong bng A.1 v A.2, su ca mi cc l su trung bnh ca lp t khi san nn bng phng php gt b hoc p dy n 3m, nn ly t mc a hnh t nhin, cn khi gt b v

su trung bnh ca lp

t,m

Ma st bn cc, f , T/m2

Ca t ct,Th vth va

mn Bi - - - - - -Ca t st khi ch st IL bng

0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1123456

3,54,24,85,35,65,8

2,33

3,53,84

4,2

1,52,12,52,72,93,1

1,21,72

2,22,42,5

0,51,21,11,61,71,8

0,40,70,80,911

0,40,50,70,80,80,8

0,30,40,60,70,70,7

0,20,40,50,50,60,6

p thm dy t 3 10m th ly t ct quy c nm cao hn phn b gt 3 m hoc thp hn mcp 3m.

su h cc trong cc lp t vng c dng chy ca nc nn ly c lu n kh nng chng b xi trI mc l tnh ton.Khi thit k cc cho cc ng vt qua ho rnh th chiu su ca mi cc nu bng A.1 nn ly t ct a hnh t nhin v tr mng cng trnh.3) i vi cc gi tr trung gian ca su v ch s st IL th xc nh qp v fs t bng A.1 v A.2bng phng php ni suy.

4) Cho php s dng cc gi tr sc chng tnh ton, qp theo bng A.1 vi iu kin chn su ca cc trong t khng b xi trI hoc gt b khng nh hn:- i vi cng trnh thu li: 4m;- i vi nh v cc cng trnh khc: 3m.

5) Khi xc nh ma st bn fs theo bng A.2, t nn c chia thnh cc lp nh ng nht c chiu dy khng qu 2m6) Ma st bn tnh ton fs ca t ct cht nn tng thm 30% so vi gi tr trnh by trong bngA.2.

Bng A.3- cc h s mR v mf


3. H cc c xi nc trong t ct vi iu kin ng tip cc mt cui

1 0,9

4. Rung v p cc vo:a) t ct, cht va:- Ct th v th va- Ct mn- Ct bib) t st c st IL= 0,5:- ct- st- Stc) t st c st IL 0

1,21,11

0,90,80,7

111

0,90,90,95. Cc rng h mi h bng ba c kt

cu bt ka) Khi ng knh l rng ca cc 40cm 1 16. Cc trn rng, bt mi, h bng phngphp bt k, ti su 10m, sau c m rng mi cc bng cch n mn trong t ct cht va v trong t st c st IL 0,5, khi ng knh m rng bng: 0,9 1

Ph|ng php h cc

H s iu kin lm vic ca t|c k n mt cch clp vi nhau khi tnh tonD|i mi

cc mR mt bn cc mf

1. H cc c v cc rng c bt mi cc, bng ba hi

1 1

2. H cc bng cch ng vo l khoan mi vi su micc khng nh hn 1m d|i y h khoan, khi |ngknh l khoan mi:a) Bng cnh cc vungb) Nh hn cnh cc vung 5cmc) Nh hn cnh cc vung hoc |ng knh cc trn

(i vi tr |ng dy ti in) 15cm.

111

0,50,61

Ch thch: H s mR v mf im 4 bng A.3 i vi t st c st 0,5 > IL>0 c xc nh bng cch ni suy.

A.4. i vi cc ng m mi ca n ta ln t ct c cht tng iD 1 hoc3trn t st c ch s st IL>0,6 th sc chu ti ca cc nn xc nh theo kt qu thtnh cc.A.5. Tnh sc chu ti ca cc nm, cc hnh thang, hnh thoi, xuyn qua t ct v t st nn tin hnh c k n sc chu ti tng thm ca t mt bn cc, sc chng ny ph thuc vo m un bin dng ca t t kt qu th nn trong phng th nghim cc loi t m cc xuyn qua, nn xc nh theo cng thc:

Trong :

Qtcm q p Ap

Li (ui f iuoi ic E j k 'i p )

(A.5)m, qp, Ap, li v fi- K hiu ging nh trong cng thc (A.4);ui- chu vi ngoi ca tit din I ca cc, m;uoi- Tng cc cnh tit din I, m, c nghing vi trc cc;ic- nghing mt hng ca cc tnh bng phn lng ca n v, l t s ca na cnh tit din ngang u trn v u di trn chiu di ca on c mt nghing, khi ic 0,025 th nn ly ic=0,025;


Ei- M un bin dng ca lp t th I quanh mt hng cc, T/m2; xc nh t kt qu th t trong my nn;Ki- H s, xc nh theo bng A.4;

p - h s l u bin, ly bng 0,8.

I

Loi H sCt v ct st

St: khi ch s do Ip=18khi ch s do Ip=25

0,50,60,70,9

Ch thch: i vi st c ch s do 18 < Ip

Ch thch: i vi cc hnh thoi, tng sc chng ca t mt bn phn c nghing ngc trong cng thc A.5 khng tnh n.Bng A.4- h s ki

A.6. Sc chu ti trng nh, ca cc xc nh theo cng thc:

Trong :

tc m(mR q p Ap

u m f f i li ) (A.7)m- h s iu kin lm vic, trong iu kin ta ln t st c no nc G

Bng A.5- H s mf


1. Cc ch to bng bin php ng ng thp c bt kn mi ri rt dn ng thp khi b

0,8 0,8 0,8 0,7

2. Cc nhi rung p 0,9 0,9 0,9 0,93. Cc khoan nhi trong k c m rngy, b tng:a) khi khng c nc trong l khoan(phng php kh) hoc khi dng ng chng

0,7 0,7 0,7 0,6

4. Cc ng h bng rung c ly 1 0,9 0,7 0,65. cc tr 0,7 0,7 0,7 0,66. Cc khoan nhi, cc c ltrn rng gia, khng c nctrong l khoan bng cch dng

0,8 0,8 0,8 0,7

7. Cc khoan phun ch to c ng chng hoc bm hn hp b tng vi p lc 2-4 atm.

0,9 0,8 0,8 0,8

A.8. Cng chu ti ca t qp, T/m2, di mi cc nhi cc tr v cc ng h c lyt ra khi rut ng sau b tng cho php ly nh sau:a) i vi t hn ln c cht n l ct v i vi t ct trong trng hp cc nhi c v khng c m rng y, cc ng h c ly ht nhn t v cc tr- tnh theo cng thc (A.8). cn trong trng hp cc ng h c gi nhn t nguyn dng chiu cao 0,5m- tnh theo cng thc (A.9):

Loi cc v ph|ng php thi cng cc

H s iu kin lm vic ca t Ct ct st S

1 2 3 4 5

q p 0,75 ( ' I p k

I

LB 0 )

(A.8)

Trong :

, A0 , B 0

q p ( ' I p k

I

LB 0 )

(A.9)k k - H s khng th nguyn ly theo bng A.6;

'I - Tr tnh ton trung bnh (theo cc lp) ca trng l ng th tch t, t/m3, nm pha trn mi cc (khi t no nc c k n s y ni trong nc);L- chiu di cc, m;dp- ng knh, m ca cc nhi hoc ca y cc (nu c m rng y cc ).b) i vi t st, trong trng hp cc nhi c v bun c khng c m rng y, cc ng c ly li t ra (ly mt phn hoc ly ht) v nhi b tng vo rut ng v cc tr cng chu ti ca t ly theo bng A.7.

Ch thch: Nhng nguyn tc nu iu A.8 c p dng khi chn su ca mi cc vo t nn khng nh hn ng knh ca cc (hoc phn m rng i vi cc c m rng y), nhng khng nh hn 2m.Bng A.6- cc h s ca cng thc (A.8) v (A.9)


K hiu cc h

Cc h s Ao , B o, v khi cc tr tnh ton ca gc ma trong ca t ,

A

k

A

k

do

do

oAk

9,518,6

12,824,8

17,332,8

24,445,5

34,664

48,687,6

71,3127

108185

163260

khiLd p

457,51012,51517,52022,5

25

0,780,750,680,620,580,550,510,490,460,44

0,790,760,70,670,630,610,580,570,550,54

0,80,770,70,670,630,610,580,570,550,54

0,820,790,740,70,670,650,620,610,60,59

0,840,810,760,730,70,680,660,650,640,63

0,850,820,780,750,730,710,690,680,670,67

0,850,830,80,770,750,730,720,720,710,7

0,860,840,820,790,70,760,750,750,740,74

0,870,850,840,810,800,790,780,780,770,77

khidp=

0,8m

0,310,25

0,310,21

0,290,23

0,270,22

0,260,21

0,250,20

0,240,19

0,280,18

0,280,17

A.9. Cng chu ti qp, T/m2 ca t di mi cc ng khng nhi b tngm c nhnt lu li giai on sau cng lc h cc c chiu cao 0,5m (vi iu kin l nhnt c hnh thnh t t c cng c trng vi t c dng lm nn mi ccng) nn ly theo bng A.1 ca ph lc ny vi h s iu kin lm vic c k n phng php h cc ng nh iu 4 bng A.3 thuc ph lc ny, ng thi sc chng tnh ton trong trng hp ny l ca din tch tit din ngang ca thnh cc ng.A.10. Sc chu ti trng nh cc hn ca cc nhi xc nh theo cng thc:

Trong :

Quk

m.u m f f i li w

(A.10)m- ngha nh trong cng thc (A.6);u, mf, fi v li- k hiu ging nh trong cng thc (A.7).

Bng A.7- Tr s qp


121518203040

155180210230330450

140165190240300400

125150170190260350

110130150165230300

95100130145200250

80100115125--

708095105--

Ch thch :

i vi mng ca m cu, cc gi tr qp trnh by bng A.7 nn:a) Tng ln (khi m cu nm trong vng nc) mt i lng bng 1,5 (

n hn ) trong : n - trng l ng ring ca nc, 1 T/m3;

hn- chiu cao ca lp nc, m, k t mc nc ma kh n mc bo xi cn l tnh ton.

Ph lc B

Xc nh sc chu ti ca cc theo ch tiu cng ca t nnB.1. Yu cu chungB.1.1. Sc chu ti cc hn ca cc tnh theo cng thc:

Qu As f s

Ap q p

(B.1)B.1.2. Sc chu ti cho php ca cc tnh theo cng thc:

Trong :

Chiu su mi cc h,m

C|ng chu ti q , T/m2, d|i mi cc nhi c v khng m rng y, ccptr v cc ng h c ly t v nhi b tng vo rut ng,

0 0. 0. 0. 0. 0. 0.35710

85100115135

7585100120

657585105

50657595

10506080

30405070

25354560

Q Qs FS s

Q pFS p

(B.2)FSs- H s an ton cho thnh phn ma st bn, ly bng 1,5-2,0; FSp- H s an ton cho sc chng di mi cc ly bng 2,0-3,0.B.1.3. Cng thc chung tnh ton ma st bn tc dng ln cc l:

Trong :

f s ca 'h tan a (B.3)

Ca- Lc dnh gia thn cc v t, T/m2; vi cc ng b tng ct thp, ca=0,7c, trong c l lc dnh ca t nn;

'h - ng sut hu hiu trong t theo ph ng vung gc vi mt bn cc, T/m2;

a- gc ma st gia cc v t nn; vi cc b tng ct thp h bng ph ngphpn ly a= , i vi cc thp ly a=0,7 , trong l gc ma st trong ca t nn.B.1.4. Cng chu ti ca t di mi cc tnh theo cng thc:


Trong :q p cN c

'vp N qd p N

(B.4)c- Lc dnh ca t, T/m2;

'vp - ng sut hu hiu theo ph ng thng ng ti su mi cc do trng lng bn thn t, T/m2;

Nc, Nq,

N - H s sc chu ti, ph thuc vo ma st trong ca t, hnh dng micc phng php thi cng cc;

- Trng l ng th tch ca t su mi cc, T/m3.B.2. Sc chu ti cc hn ca cc trong t dnh tnh theo cng thc:

a

Trong :Qu As cu

Ap N c cu

(B.5)Cu- sc chng ct khng thot nc ca t nn, T/m2;

- H s khng th nguyn. i vi cc ng ly theo hnh B.1, i vi cc nhi ly t 0,3-0,45 cho st do cng v bng 0,6-0,8 cho st do mm;Nc- H s sc chu ti ly bng 9,0 cho cc ng trong st c kt bnh thng vbng 6,0 cho cc khoan nhi.

Ch thch:

1) H s an ton khi tnh ton sc chu ti ca cc theo cng thc (B.5) ly bng 2,0-3,0.2) Tr gii hn ca cu trong cng thc (B.5) ly bng 1 kg/cm2.B.3. Sc chu ti cc hn ca cc trong t ri tnh theo cng thc:

Trong :Qu As K s 'v tan a+ Ap 'v pNq (B.6)Ks- H s p lc ngang trong t trng thi ngh, ly theo hnh B.2;

'v - ng sut hu hiu trong t ti su tnh ton ma st bn tc dng ln cc, t/m2;

a- Gc ma st gia t nn v thn cc; 'v

p- ng sut hu hiu theo phng php thng ng ti mi cc, T/m2;Nq- H s sc chu ti, xc nh theo hnh B.3.B.3.1. Cng chu ti di mi cc v ma st bn tc dng ln cc trong tri su gii hn, ngha l:fs(z>zc)=fs(z=zc)qp(z>zc)=qp(z=zc)Ch thch: su gii hn zc xc nh theo gc ma st trong ca t nn (hnh B.4).B.3.2. H s an ton p dng khi s dng cng thc tnh ton B.6 ly bng 2,0-3,0.



Xc nh sc chu ti ca cc theo kt qu th nghim xuynC.1. Tnh ton theo kt qu xuyn tnhC.1.1. Sc chu ti ca cc c tnh trn c s sc chng xuyn u mi qc.

C.1.2. Thit b xuyn s dng u xuyn chun: ng knh y mi cn bng 35,7mm, gc nhn mi cn bng 600. Nu s dng loi u xuyn khcvi chun nu trn cn quy i gi tr tng ng vi u xuyn chun trn c s cc tng quan c xc lp cho tng thit b.C.1.3. Phng php tnh theo tiu chun TCXD 174:1989.C.1.3.1. su ngm cc ti hn zc, l su m vt qu gi tr th c-ng chu ti gi nguyn gi tr khng i:- Trng hp t nn 1 lp: zc= 6d, trong d l kch thc cnh tit din hocng knh tit din cc;- Trng hp t nn nhiu lp:Zc= 3d khi v

0,1 MpaZc= 3d 6d khi v


20 30 2840 32 3070 34 32120 36 34200 38 36300 40 38

C.5.2. Tng quan gia sc chng xuyn qc v sc chng ct khng thot nc ca tdnh, cu, xc nh theo cng thc:c qc vu 15

(C.1.5)Trong v l p lc thng ng do ti trng bn thn ca t nn.




C.2. Tnh ton sc chu ti ca cc theo kt qu xuyn tiu chunC.2.1. Kt qu xuyn tiu chun (SPT) trong t ri c tnh ton sc chu ti ca cc(Meyerhof, 1956).

C.2.2. Sc chu ti cc hn ca cc tnh theo cng thc ca Meyerhof (1956)Qu= K1NAp+ K2NtbAs (C.2.1)Trong :N- ch s SPT trung bnh trong khong 1d di mi cc v 4d trn mi cc; Ap- Din tch tit din mi cc, m2;Ntb- ch s SPT trung bnh dc thn cc trong phm vi lp t ri;As- Din tch mt bn cc trong phm vi lp t ri, m2;K1- h s, ly bng 400 cho cc ng v bng 120 cho cc khoan nhi.H s an ton p dng khi tnh ton sc chu ti ca cc theo xuyn tiu chun ly bng 2,5-3,0.C.2.3. Sc chu ti ca cc theo cng thc ca Nht Bn:

1

Trong :Qa N a Ap3(0,2N s LsCLc ) d (C.2.2)Na- ch s SPT ca t di mi cc;Ns- ch s SPT ca lp ct bn thn cc;Ls-chiu di on cc nm trong t ct, m; Lc- chiu di on cc nm trong t st, m;

- H s, ph thuc vo ph ng php thi cng cc;- Cc b tng ct thp thi cng bng phng php ng: =30;- Cc khoan nhi: =15

Ph lc D

Xc nh sc chu ti ca cc theo cng thc ngD.1. Khi xc nh sc chu ti ca cc theo cng thc ng c th s dngcng thc caGersevanov (iu D.2) hoc cng thc ca Hilley (iu D.3) ca ph lc ny.D.2. Xc nh sc chu ti ca cc theo cng thc ca Gersevanov. Sc chu ti cho php ca cc: QtcQa ktcTrong :(D.1a)Qtc- sc chu ti tiu chun tnh theo cng thc ng ca Gersevanov, T; Ktc- H s an ton, xc nh theo iu A.1 ph lc A.D.2.1. Sc chu ti cc hn ca cc, T, xc nh theo cng thc :

Q Qutc

d(D.1)


Trong :Qu- sc chu ti cc hn ca cc, T, xc inh theo cng thc D.2 hoc D.3Kd- H s an ton theo t, ly theo iu D.2.2 ca ph lc ny.D.2.2. Trong trng hp s cc c th nhng iu kin t nh nhau, m nh hn 6chic, ly Qu= Qu min v kd= 1,0.Trong trng hp s cc c th nhng iu kin t ging nhau, bng hoc ln hn 6 chic th sc chng gii hn Qu xc nh trn c s kt qu x l thng k cc gi tr ring ca sc chu ti ca cc theo s liu th.D.2.3. Khi th ng cc ng, nu chi thc t (o c) ef 0,002m, Qu xc nh theo cng thc:

nFM

4 w 2 w w 1 p . n c 1 1 2 nFe fw n w c w 1 (D.2)Nu chi thc t (o c) ef

M- h s ly bng 1,0 khi ng cc bng ba tc dng va p, cn khi h cc bng dung th ly theo bng D.1 ph thuc vo loi t di mi cc;AP - Nng lng tnh ton ca mt va p ca ba, T.m ly theo bng D.2 hoc nnglng tnh ton ca my h bng rung- ly theo bng D.3;ef - chi thc t, bng ln ca cc do mt va p ca ba, cn khi dng my rung l ln ca cc do cng ca my trong thi gian mt pht, m;c- chi n hi ca cc ( chuyn v n hi ca t v cc), xc nh bng my o chi, m;W- trng lng ca phn va p ca ba,T;W1 - Trng lng ca cc dn ( Khi h bng rung W1=0 ), T; Wn - Trng lng ca ba hoc ca my rung, T;

- h s phc hi va p, khi ng cc v cc ng b tng ct thp bng ba tcng p c dng m m g, ly 02 = 0,2 khi h bng rung, ly 02=0;- h s, l/t, xc inh theo cng thc:

nn W 2 g H h

(D.4)1 0 4 F

W Wc

n0, nh- H s chuyn t sc chng ng sang sc chng tnh ca t, ly ln lt bng i vi t di mi cc n0= 0,0025s.m/T v i vi t mt hng cc nh=0,25 s.m


- Din tch mt bn cc tip xc vi t, m2;g- gia tc trng trng, ly bng 9,81m/s2;h - chiu cao ny u tin ca phn va p ca ba i vi ba diesel ly bng h=0,5m i vi cc loi ba khc h=0;H- Chiu cao ri thc t ca phn ng ca ba, m.

Ch thch:

1. Cc gi tr ca Wn, W, Wc v W1 dng trong cng thc tnh ton ni trn khng c h s vt ti2. Trong trng hp c chnh lch hn 1,4 ln v sc chu ti ca cc xc nh theo cc cng thc

h

(D.2 v D.3) vi sc chu ti xc nh bng tnh ton da vo tnh cht c lca t cn kim tra thm bng phng php nn tnh.Bng D.1 H s MLoi t di mi cc H s M1. Si cn c cht lp nht ct2. Ct th va, cht trung bnh v ct cng3. Ct mn cht trung bnh4. Ct bi cht trung bnh5. st do, st v st cng6. st v st na cng7. st v st kh do

1,31,21,11,00,90,80,7

Ch thch: trong ct cht, gi tr ca h s M ni im 2,3 v

Bng D.2 Nng lng tnh ton AP ca ba

Bng D.3- Nng lng tnh ton ?p ca ba rung

Lc kch thch ca 10 20 30 40 50 60 70 80Nng lng tnh ton tng ng va p ca my 4,5 9 13 17,5 22 6,5 31 35

Kiuba

Nng l|ng tnh ton ca va p ba A , p

1. Ba treo hoc tc dng n ng2. Ba di-e-den ng3. ba di-e-den cn va p n4. Ba di-e-den khi ng kim tra li bng vap n

WH0,9WH0,4WHW(H-h)

Ch thch: im 4, h chiu cao ny u tin phn va p ca badiesel do m khng kh gy ra, xc nh theo th|c o, m. tnh tons b cho php h= 0,6m i vi ba kiu ct v h=0,4m i vi ba kiu ng


D.3. Cng thc ng HilleyD.3.1. Sc chu ti gii hn xc nh theo cng thc:

2

Q kWh W e Wc(D.4)

Trong :e f 1 / 2 c1 c2c3 W Wck - Hiu xut c hc ca ba ng cc; mt s gi tr c kin ngh s dng nhsau:- 100% i vi ba ri t do iu khin t ng v ba diesel;-75% i vi ba ri t do nng bng cp ti;- 75%- 85% i vi cc loi ba hi nc n ng; Wc -Trng lng ca cc, T;W - trng lng ca ba ng, T;h - Chiu cao ri ba, m;e- H s phc hi, mt s gi tr ca e nh sau:+ Cc c u bt thp: e=0,55;+ Cc thp c m u cc bng g mm: e=0,4;+ Cc b tng ct thp, m u bng g: e=0,25.ef - ln ca cc di mt nht ba khi th nghim( chi ),m;c1 - Bin dng n hi ca u cc, m u cc v cc dn, m;c2 - Bin dng n hi ca cc,m:c2=Qu.L/AEc3- Bin dng ca t nn, thng ly bng 0,005m; A - Din tch tit din cc,m2;E- Mdun n hi ca vt liu cc, T/m2.D.3.2. H s an ton khi p dng cng thc Hilley Fs 3,0.Ph lc E

Xc nh sc chu ti theo kt qu nn tnh ccE.1. Quy trnh th nghim xc nh sc chu ti bng th nghim nn tnh c thc hin trn c s tho thun vi ch u t hoc c quan t vn ca ch u tE.2. Khi la chn quy trnh xc nh sc chu ti cho php ca cc cn ch ti nhng cim ca iu kin a cht ti trng cng trnh v yu cu ca thit k.E.3. Phng php ca SNIP2.02.03.85:E.3.1. Sc chu ti trng nn thng ng cho php ca cc tnh theo cng thc: Qtc

u

Q a k

(E.1)tcTrong :Qa - Sc chu ti cho php ca cc; Qtcktc - H s an ton, xc nh theo iu A.1 ph lc A.


E.3.2. Sc chu ti tiu chun theo kt qu th chng bng ti trng nn, nh c v theohng ngc c xc nh theo cng thc:

Q m Qu(E.2)

Trong :tcdm- H s lm vic cho tt c cc loi nh v cng trnh tr tr ng dy tica l thin,ly bng:m=1.0 i vi cc chu nn dc trc hoc nn ngang;m=0,8 i vi cc chu nh khi su cc vo t 4m;m=0,6 i vi cc chu nh khi su cc vo t < 4m;Qu - Sc chu ti cc hn ca cc, t, xc nh theo cc iu E.3.3. n E.3.5 ca ph lc 1Kd - H s an ton theo t, ly theo nhng ch dn ca iu E.4.3 ca ph lc ny. E.3.3. Trong trng hp nu s cc c th nhng iu kin t nn nh nhau t hn 6chic QuQumin,cn h s an ton theo t k=1.Khi s lng cc th cng iu kin a cht cng trnh bng hoc ln hn6 chic th cc i lng Qu nn xc nh trn c s kt qu x l thng k.E.3.4. Sc chng gii hn Qu ca cc c xc nh nh sau(hnh E.1)- L gi tr ti trng gy ra ln tng lin tc- L gi tr ng vi ln Sgh trong cc tr ng hp cn li: = Sgh (E.3)Trong :Sgh-Tr s ln gii hn trung bnh cho trong tiu chun thit k nn mng,-c quinh theo nhim v thit k hoc ly theo tiu chun i vi nh v cng trnh;

- H s chuyn t ln lc th n ln lu di ca cc, thng thng ly =0,1.Khi c c s th nghim v quan trc ln y , c th ly =0,2

k

Nu ln xc nh theo cng th (E.3) ln hn 40mm th sc chu ti cchn ca cc Qu nn ly ti trng ng vi =40mm


i vi cc cu, sc chu ti cc hn ca cc chu ti trng nn phi ly ti trng bhn 1 cp so vi ti trng m di ti trng ny gy ran;a) S tng ln sau mt cp gia ti ( tng ln ln hn 40mm0 vt qu 5 ln s tng ln ca mt cp gia ti trc b) ln khng tt dn tron thi gian mt ngy m hoc hn ( tng ln ca cc ln hn 40mmNu khi ht,ti trng ln nht t c c tr s bng hoc ln hn1,5Qtc(trong Qtc - Sc chu ti ca cc tnh theo cc cng thc ca ph lc A), m lnca ccb hn tr s xc nh theo cng thc(E.3), i vi cu th b hn 40mm, trongtrng hp ny, sc chu ti cc hn ca cc cho php ly bng ti trng ln nht cc lc th.

Ch thch:Cc cp ti trng khi th cc bng nn tnh thng qui nh trong phm vi 1/10-1/15 sc chu ti cc hn tnh ton ca ccE.3.5. Khi th ti bng ti trng tnh theo hng ngang hc nh th sc chuti gii hn(iu E.3.3 ca ph lc ny) ly ti trng m di tc dng ca n, chuyn v ca cc tng khng ngng.

Ch thch: Kt qu th tnh cc chu ti trng ngang gii hn cho php ca nh v cng trnh. Loi ti trng nh th i vi nh v cng trnh (tr nhng cng trnh c bit nhy i vi bin dng ngang) cho php ly ti trng m tr bin dng ngang ca cc mc mt t khi th bng tr s gii hn cho php nhng khng qu 10mm.E.4. Mt s phng php thng thng khc dng xc nh sc chu ti gii hn ca cc khi khng th th cc n ph hoi, nht l i vi cc c -ng knh ln.E.4.1. Phng php ca Canadian Foundation Engineering Manual(1985)

Sc chu n gii hnca cc l ti trng xc nh t giao Im ca biu quan hti trng- ln vi ng thng(hnh E.2)Sf= +d/30 (E.4)


Trong :Sf- ln ti cp ta trng ph hoi,m

- Bin dng n hi ca cc,m

= QLp (E.5)AEpQ -Ti trng tc dng ln cc,T Lp- Chiu di cc, mA-Din tch tit din cc, m2Ep- M un n hi ca vt liu cc,T/m2E.4.2. Phng php ca Davisson:sc chu ti gii hn ca cc l ti trng ngvi ln trn ng cong ti trng- ln c c lc th tnh:

QLpS f E p A

0,0038

d (m)120

(E.6)E.4.3. Trong trng hp cc dI th sc chu ti gii hn ng vi ln:

2QL

- Khi Lp/d>80 :S p3E p A0,00380,02(m)(E.7)- Khi Lp/d>100 : Sf = 60 80 mm (E.8)Ch thch: Cch xc nh Sf ni Iu E4-2 v E4-3 thc hin nh nu Iu E4-1.E.4.4. Sc chu ti trng nn cho php xc nh theo cng thc:

Q Qu a FS

(E.9)


E.4.5. Thng thng h s an ton FS 2,0. H s an ton cao hn nn c p dng chocc trng hp sau y:- i vi cc ma st trong t dnh- Khi Iu kin iaj cht phc tp nhng s lng cc th nghim hn ch- Cc trong ct ri, sc chu ti suy gim theo ti gian- Khi cn m bo yu cu cao v ln.

Ph lc G

Tnh cc di tc dng ng thi ca ti trng ng v ti trng ngang v m men

Tnh ton theo phng php ca SNIP II-17-77G.1. Tnh cc di tc dng ng thi ca ti trng ng, ngang v m men theo s nu trn hnh G1,bao gm:a) Chuyn v ngang n v gc xoay, ca u cc cn tho mn iu kin sau:n Sgh (G1)

gh (G2)Trong :

n v -Nhng gi tr tnh ton t ng ng chuyn v ngang, m, v gc xoay,radian,ca u cc,xc inh theo nhng ch dn Iu G.4 trong ph lc ny

Sgh v gh-Nhng gi tr t ng ng chuyn v ngang, m, gc xoay, radian, ca u cc, c qui nh t nhim v thit k nh v cng trnh.

f

b) Tnh ton s n nh ca t nn xung quanh cc, hc hin theo nhng yu cu ca iu 6 ph lc ny.c) Kim tra tit din ca cc theo bn ca vt liu, theo trng thi gii hn th nht v th hai di tc dng ng thi ca lc dc trc, m men un v lc ngang.Cc Gi tr tnh ton ca m men un, lc ngang v lc dc trc, tc dng lnnhng tit din khc nhau ca cc, c xc nh theo iu G7 ca ph lc ny.Trong trng hp cc c ngm cng vo i, gc xoay =0, tnh ton m men ti ngm theo iu G.8 ca ph lc ny.Ch thch:Khng cn tnh ton n nh ca t nn xung quanh cc c b rng tit din d 0,6m vi chiu di trong t ln hn 10d, tr tr ng hp cc c h vo bn hoc t st trng thi chy hoc do chy.G.2. Khi tnh ton cc chu ti trng ngang, t quanh cc c xem nh mitrng n hi bin dng tuyn tnh c trng bng h s nn Cz,(T/m3)Khi khng c nhng s liu th nghim, cho php xc nh s liu tnh ton ca hs nn Cz ca t quanh cc theo cng thc:Cz=K.z (G.3)Trong :K - H s t l,T/m4,c ly theo bng G1z - su ca v tr tit din cc, m, k t mt t i vi cc di cao, hoc k t yi i vi cc i thp

Bng G1-H s t l k


Loi t quanh cc v c trng ca n

H s t l k,T/m4 cho

ng Nhi, cc ng St, st do chy (0,75

trong t, Ze, v c chiu su tnh i h cc trong t, Le, xc nh theo cng thc sau:

Trong :Ze= bdz (G.4) Le= bd L (G.5)z v L - Chiu su thc t v tr tit din cc trong t v chiu su h cc thc t(mi cc) trong t tnh t mt t vi cc i cao v t y i vi cc i thp, m

bd-H s bin dng, I/m, xc nh theo cng thc:

Trong :

bd= 5 K .bcEbI

(G.6)K - k hiu nh tron cng thc G3Eb - M un n hi ban u ca b tng cc hi nn v ko,T/m2, ly theotiu chun thit k kt cu b tng ct thpI - M men qun tnh tit din ngang ca cc, m4bc - Chiu rng qui c ca cc, m c ly nh sau:+ Khi d 0,8 th bc=d+1m+ Khi d

Trong : 0

2 0 2Eb I Hl0 Eb I

(G.8)H v M - Gi tr tnh ton ca lc ct,T,v m men un,T.m,ti du cc(xem hnh g.1l0 - Chiu di on cc,m,bng khong cch t y i cc n mt tY0 v

o -Chuyn v ngang, m, v gc xoay ca tit din ngang ca cc, radian, mt t vi cc i cao, mc y i thp v c xc nh theo iu G5 ca phlc ny.

Ch thch: Cc i lng trong ph lc ny c coi l dng trong cc trng hp sau:

- M men v lc ngang ti u cc:m men theo chiu quay ca kim ng h v lc ngang hng vpha bn phi

- M men un v lc ct trong phn di ca tit din ct:m men theo chiuquay ca kim ng h v lc ngang hng v pha bn phi- Gc xoay v chuyn v ngang ca tit din cc:gc xoay theo chiu quay ca kim ng h vchuyn hng v bn phi.

G.5. Xc nh chuyn ngang y0,m v gc xoay o , radian, theo cng thc:

Trong :y0 H 0 HH M 0 HM

0 H 0 MH M 0 MM(G.9)

(G.10)

Hl

H0 - Gi tr tnh ton ca lc ct, T, ly H0=H M0-M men un, T.m, ly M0=M+Hl0

HH - Chuyn v ngang ca tit din, m/T, bi lc H0=1(hnh G.2a) HM - Chuyn v ngang ca tit din, l/T, bi m men M0=1(hnh G.2b) MH - Gc xoay ca tit din,l/T (T.m) MH-Gc xoay c tit din,

l/T, bi lcH0=1(hnh G.2a)

MM - Gc xoay ca tit din,l/T (T.m),bi m men M0=1(hnh G.2b) Chuyn v HH, MH = HM v MM c xc nh theo cng thc:1 A

(G.11)HH 3 E I 0

bd b 1 B

(G.12)

Formatted: Font: 13 pt, ComplexScript Font: 14 ptMH HM

3 E I 0bd b1 C

(G.13)Formatted: Font: 13 pt, Bold,Complex Script Font: 14 ptFormatted: Font: 13 pt, ComplexMM 3 E I 0Script Font: 14 pt

Trong :bd bFormatted: Font: 13 pt, Bold, Complex Script Font: 14 ptA0,B0,C0 - Nhng h s khng th nguyn ly theo bng G.2 ty thuc vo chiu su tnh i ca phn cc trong t Le xc nh theo cng thc G.5. Khi Le nm gia hai gi tr ghi trong bng G.2 th ly theo gi tr gn hn tra bng


G.6. Khi tnh n nh ca nn quanh cc,phi kim tra iu kin hn ch p lc tnh ton z ln t mt bn ca cc theo cng thc:4 '

Trong : z 1 2 v .tg 1

cos 1C1

(G.14)

z - p lc tnh ton ln t T/m2, mt bn cc,xc nh theo cng thc (G.16)ti su z, m, k t mt t cho cc i cao v t y di cho cci thp:a) Khi Le2,5:ti 2 su z=L/3 v z= Lb) Khi Le>2,5:ti su z=0,85/bd,trong /bd, xc nh theo cng thc (G6)

1-Khi l ng th tch tnh ton ca t,T/m3v - ng sut c hiu theo phng thng ng trong t ti su z,T/m

, 21,C1 - Gi tr tnh ton ca gc ma st trong, v lc dnh, T/m2 ca

t - H s,ly =0,6 cho cc nhi v cc ng,=0,3 cho cc loi cc cn li;

1 - H s, ly bng 1, tr tr ng hp tnh mng ca cc cng trnh chn ly bng0,7;


2 - H s, k n phn ti trng th ng xuyn trong tng ti trng, tnh theo cngthc:

Trong :M M v2 nM p M v

(G.15)Mp - Mmen do ti trng ngoi thng xuyn, tnh ton tit din mng ti mc mi cc, T.m;Mv - Mmen do ti trng tm thi, T.m;n , h s, ly bng 2,5 tr cc trng hp sau y:a) Nhng cng trnh quan trng:+ Khi Lc 2,5 ly n = 4;+ Khi Lc 5 ly n = 2,5;+ Khi Lc nm gia cc tr s trn th ni suy n .b) Mng 1 hng cc chu ti trng lch tm thng ng nn ly n = 4, khng ph thuc vo Lc.Ch thch: Nu p lc ngang tnh ton ln t z khng tha mn iu kin (G.14) nhng lc ny sc chu ti ca cc theo vt liu cha tn dng ht v chuyn v ca cc nh hn tr s chuyn v cho php khi chiu su tnh i ca cc Lc > 2,5 th nn lp li vic tnh ton vi h s t l K gimi (iu G.2 ca ph lc ny). Vi tr s mi ca K cn kim tra bn ca cc theo vt liu,chuyn v ca cc cng phi tun theo iu (G.14).

G.7. p lc tnh ton, z, T/m2, lc ct Qz, T, trong cc tit din ca cc tnh theo cng thc:

K z y A 0 B

p

z

M 0 C H 0 D

(G.16) bd

c 0 1

bd

2 EI 12bd b1 ;

M 2 E Iy A

E I B M C H 0 D

(G.17)z bd b 0 3

bd b 0 30 33 ;bdQ 3 E Iy A

2 E I B M C

H D ; (G.18)z bd b 0 4bd b 0 4bd 0 40 4Nz = N (G.19) Trong :K - H s t l xc nh theo bng G.1 ca ph lc ny;

bd, Eb, I - C ngha nh cng thc (G.6);ze - Chiu su tnh i xc nh theo cng thc (G.4) ty theo su thc t z m xc nh z, Mz, Qz;H0, M0, y0 v 0 c ngha nh nu iu G.4 v G.5 ca ph lc ny;A1 B1 , C1v D1 A3 B3 , C3 v D 3

bd

E I

1

A B , C v D - Cc h s ly theo bng (G.3);

N - Ti trng tnh ton dc trc ti u cc.


Formatted: Justified, Space Before:4 pt

4 4 4 4

G.8. Mmen ngm tnh ton, Mng, T.m, khi tnh cc ngm cng trongi v u cckhng b xoay, tnh theo cng thc sau:

MH

l0 MM

2 0 M ng 2Eb I Hl(G.20)

MM 0 Eb I

y, ngha cc k hiu u ging nhau, nh nhng cng thc nu trn. Dum c ngha l vi lc ngang H hng t tri sang phi, mmen truyn ln u cc t pha ngm c hng ngc vi chiu kim ng h.

Tnh ton sc chu ti trng ngang theo phng php ca Broms (1964)G.9. Ty theo cng ca cc v phn b phn lc nn theo phng ngang,cc t ti sc chu ti gii hn theo nhng c ch khc nhau. i vi cc cng, sc chu ti trng ch ph thuc vo t nn trong khi sc chu ti ca cc mm hon ton ph thuc vo kh nng chu un ca vt liu cc.


Cc cng thc tnh ton v cc biu c thit lp cho trng hp cc nm trongt dnh v trong t ri.G.9.1. Cc trong t dnha) Cc cng : Sc chu ti gii hn, Hu, c tnh ton trn c s biu quan h gia su ngm cc tng i L/d v sc chu ti gii hn tng i, Hu/Cud2,(hnh G.3a). Trng hp lin kt ngm gia cc v di cc cng c k n trong phng php tnh.b) Cc mm : Sc chu ti gii hn. Hu, c tnh ton trn c s biu quan hgia kh nng chu un gii hn tng i ca vt liu cc, Mu/cud3 (hnh G.3b).G.9.2 Cc trong t ria) Cc cng : Sc chu ti gii hn, Hu, c tnh ton trn c s biu quan h

l

gia su ngm cc tng i, L/d, v sc chu ti trng gii hn tng i, Hu-/Kp d3 (hnh G.4a).b) Cc mm: Sc chu ti gii hn, Hu, c tnh ton trn c s biu quan h gia kh nng chu un gii hn tng i ca vt liu cc, Mu/Kp d4, v sc chu ti gii hn t ng i, Hu/Kp d3 (hnh G.4b).



H.1. ln ca cc nPh lc H

Tnh ton ln ca mng cc ln ca cc n, xuyn qua lp t c mun ct G1, Mpa (T/m2) v h s pot - xng 1 v chng ln lp t c xem nh bn khng gian bin dngtuyn tnh c trng bi mun ct g2 v h s poat- xng 2 c tnh theo cng thc sau y viiu kin ti trng truyn ln cc N Qa v khi Lp/d>5, G1 lp/G2d>1:a) i vi cc n khng m rng mi;

Trong :NS G1 L p

(H.1)N - Ti trng ng truyn ln cc, MN(tn);

- h s xc nh theo cng thc:

Trong : ' 1

1 ' / '

=0,17 x ln(k G1Lp/G2d) - h s ng vi cc c cng tuyt i (EA=

); = 0,17 x ln ( kvLp/d) - h s i vi nn ng nht c cc c tr ng G1

v 1; = EA/G1K2p - cng tng i ca cc;

1 - Thng s, xc nh vic tng ln do thn cc chu nn v tnh theo cng thc:2.123/41 1 2.123/4

k , k 1- Cc h s tnh theo cng thc : k = 2,82 - 3,78 + 2,81 2 ln lt khi = ( 1 + 2)/2 v khi = 1; Qtc - sc chu ti ca cc xc nh theo ph lc Ab) i vi cc n m rng y: Trong :db - ng knh phn m rng ca ccCc c trng G1 v 1 c ly trung bnh i vi tt c cc lp t trong phm vi chiu su h cc, cn G2 v 2 trong phm vi 10 ng kch cc hoc ng knh phn m rng( i vi cc c m rng mi ) k t mi cc tr xung vi iu kin l di mi cc khng c than bn, t bn c st chy.

H.2. Tnh ton ln ca nhm ccH.2.1. D tnh ln ca nhm cc c da trn m hnh mng quy c. C hai cch xcnh mc quy c nh sau:Cch 10: ranh gii mng quy c (hnh H1)- Pha di l mt phng AC i qua mi cc c xem l y mng;


- Pha trn l mt t san nn BD, vi AB = Ll su t mng;- Pha cnh l cc mt phng ng AB v CD qua mp ngoi cng ca hng cc binti khong cch Ltbtg ( tb/4) nh ng khng ln hn 2d (d - ng knh hoc cnh gc vung) khi di mi cc c lp st bi vi ch s st IL > 0,6; khi c cc xin th cc mt phng ng ni trn i qua mi cc xin ny;

Trong

tbi li

Ltbi - Gc ma st trong ca lp t c chiu dy li;

Ltb- su h cc trong t k t y di, Ltb = li.Ch thch:

1. Nu trong chiu di ca cc c lp t yu ( bn, than bn,.v.v.) dy hn 30 cm th kch thcy mng quy c gim i bng cnh ly Ltb l khong cch t mi cc n y lp t yu;2. Trng lng bn thn ca mng quy c gm trng lng cc, di v t nmtrong phm vi mng quy c.Cch 20:a) Ranh gii mng quy c khi t nn l ng nht

Cch xc nh mng quy c trng t cch 10, ch khc l ly gc m bng 300 cho mi loi t k t su 2Ltb/3 (hnh H2).b) Ranh gii ca mng quy c khi cc xuyn qua mt s lp t yu ta vo lpt cng cnh xc nh mng quy c nh m t trong cnh 1, ring gc m ly bng300 k t su 2L1/3, vi L1 - phn cc nm di lp t yu cui cng (hnh H.3)c) Ranh gii ca mng quy c khi t nn nm trong phm vi chiu di cc gm nhiu lp c sc chu ti khc nhau.- Chiu rng v chiu di bn mng quy c l y hnh khi c cnh m rngso vi mt ng ca hng cc bin bng 1/4 cho n su 2Lp/3, t tr xung n mt phng mi cc gc m bng 300 (hnh H.4);- su t mng quy c l ti mt phng mi cc.

H.2.2. ng sut ph thm phn b trong t nn, di mi cc c th tnh ton theo li giiBoussinesq vi gi thit bn mng quy c t trn bn khng gian n hi.H.2.3. ln ca mng quy c c tnh theo phng php quen bit nh i vimng nng trn nn thin nhin.

H.3. ln ca mng bng cc.H.3.1. ln S, m, ca mng bng vi 1 hoc 2 hng cc ( khi khong cch gia cc cc bng 3d - 4d) c tnh theo cng thc:

P(1 2 )

Trong :S 0

E(H.3)p - Ti trng phn b u trn mp di kN/m ( kg/cm) c k n trng lng ca mng trong khi t v cc vi ranh gii nh sau: pha trn l ct nn; pha cnh l mt phng ng i qua hng cc ngoi cng; pha di l mt phng i qua mi cc;


E, - Gi tr mun bin dng kPa (kg/cm2) v h s pot xng ca t trong phmvi chiu dy ca lp t chu nn di mi cc;

0 - ly theo biu (xem hnh v) ph thuc vo h s pot xng b rng quyi ca mng b = b/h ( trong b b rng ca mng ly ti mp ngoi ca hngcc bin;h - su h cc, v dy quy i ca lp t chu nn Hc/h (Hc - dy ca lp

t chu nn xc nh theo iu kin nh tnh ln i vi nn thin nhin);Gi tr ca h s 0 xc nh theo biu bng cch sau y: Trn th v qua im ng vi Hc/h mt ng thng song song vi trc honh ct ng cong b tng ng,t giao im ny v ng vung gc n gp ng . T giao im nay v mtng thng song song vi trc honh n ct trc tung, y chnh l gi tr ca hs 0.H.3.2. ng sut trong nn t di mi cc, xc nh theo li gii ca bi tonphng vi gi thit ti trng mi cc l phn b u theo chiu rng v di ca mng.

H.4. ln ca mng b ccH4.1. D tnh ln ca mng b cc c kch thc hn 10 x 10 m c th thc hin theo phng php lp bin dng tuyn tnh nh trong tiu chun thit k nn nh v cng trnh. y vic tnh ton nn ly theo p lc trung bnh ln nn ti mt phng ydi, v tng chiu di tnh ton ca lp ln mt i lng bng su h cc vimun bin dng ca lp m cc xuyn qua ly bng v cng hoc bng min bin dng ca vt liu cc.H.4.2. ln tnh ton ca mng gm nhiu cc m mi cc ta ln t c mdun bin dng E 20 Mpa c th xc nh theo cng thc:

Trong :0,12 pBS E

(H.4)P - p lc trung bnh ln nn y i; B - Chiu rng hoc ng knh mng;E - Mun bin dng trung bnh ca lp chu nn di mt mi cc vi chiu dy bng B:1E [E h k

E h k

...

E (B

h 1)k ]

Trong :B 1 1 1

2 2 2i i iE1, E2, Ei - Mdun bin dng ca lp 1, 2 v lp i;h1, h2, hi - Chiu dy ca lp 1,2 v lp i;k1, k2, ki - H s k n su ca lp ly theo bng H.1 tu theo su ca lp y.


Bng H.1 Tr s k

su ca y lp (0 - 0,2) (0,2 -0,4) (0,4 - (0,6 - (0,8 - 1) H s ki 1 0,85 0,6 0,5 0,4

H.5. Cc c trng bin dng nu iu 5.1 ca tiu chun l nhng i l-ng sau y(hnh H6, H7,H8 v H9):- ln S l chuyn v i xung ca mt im ang xt, v d ln ca im B l SB;- ln lch S l chuyn v ca mt im ny i vi mt im khc, nh chuynv ca im B i vi im A l SBA;- Bin dng gc ti mt im l s thay i dc ti im ny, nh A =SAB/LBA + SBC/LBC;- Gc xoay l gc m ca vt th rn ca mt n v cng trnh so vi phng thng ng;- Gc xon tng i l t s / L;- nghing i l t s S/L ca 2 im mp ngoi cng ca cng trnh (i vi mng cng tuyt i);- vng (hay vng), f, l chuyn v ln nht din ra gia hai im so vi -ng thng v gia chng (i vi mng mm);- xon tng i l xoay ca mt ng thng gia hai im mc c lin quan ti s nghing;- mo gc (hay vng hoc vng tng i) f/L l t s ca vng gia haiim vi khong cch gia chng.Trong bng H2 v H3 nu cc bin dng gii hn ca nn v kt cu do ln gy ra

Bng H.2 Bin dng gii hn ca nn ( theo SniP2.02.01.83)

Cng trnh ln lchtng i( S/L)U

nghingiu

ln trung bnh Su hoc ln nht Smax (trong

1. Nh sn xut mt tng v nh dn dng nhiu tng c khung hon ton:- Bng b tng ct thp- Bng thp

0,0020,004

--

(8)(12)

2. Nh v cng trnh m trong kt cu khng xut hin ni lc do ln 0,006 - (15)3. Nh nhiu tng khng khung vi tng chu lc:


- Bng tm lp- Bng khi ln hoc c th xy gch khng c thp- Nh trn nhng c thp, trong c ging b tng ct

0,00160,0020

0,0024

0,0050,0005

0,0005

1010

154. Cng trnh thp cha vn thng bng kt cu b tng ct thp;- Nh cng tc v xi l kt cu ti ch lin khi trn cng mt mng b- Nh trn nhng kt cu lp ghp- Xi l c lp kt cu ton khi ti ch

-

--

0,003

0,0030,004

40

3040

5. ng khi c chiu cao H, m :- H 100 m-100< H < 200- 200 < h 300- H > 300

----

0,0051/(2H)1/(2H)1/(2H)

40302010

6. Cng trnh cng cao n 100m, ngoi nhng iu ni im 4 v

- 0,004 20

7. Cng trnh lin lc, ng ten :- Thn thp tip t- Thn thp pht thanh cch in vit- Thp pht thanh- Thp pht thanh sng ngn

--

0,0020,0025

0,0020,001

--

2010

--

8. Tr ng dy ti in trnkhng- Tr trung gian- Tr neo, neo gc, tr gc trung gian, tr vng cung,ca chnh ca thit b phn phi kiu h.

0,0030,0025

0,0030,0025

--

Ch thch cho bng H.2:1) Tr gii hn ca vng (vng ln) tng i ca nh ni im 3 ly bng 0,5( S/L)U


2) Khi xc nh ln lch tng i S/L ni im 8, L l khong cch gia 2 trc block mng theohng ti trng ngang, cn cc tr ko dy - l khong cch gia cc trc ca mong chu nn v neo.

3) Nu nn gm cc lp t nm ngang ( vi dc khng qu 0,1) th tr gii hn v ln trung bnh cho php tng ln 20%.4) i vi cng trnh ni im 2 v 3 c mng dng b th tr gii hn ca ln trung bnh cho php tng ln 1,5 ln.5) Trn c s tng kt kinh nghim thit k xy dng v khai thc cc loi cng trnh khc nhau, cho php ly tr bin dng gii hn ca nn khc vi tr cho bng ny.

Bng H.3 - Gii hn bin dng gc (Theo Skempton v McDonald, 1956; Bjerrum, 1963 v Wroth, 1975)

1/5000

1/30001/10001/7501/6001/500

1/3001/250

Vt ran li ti quan st thy trong cng trnh gch khng ctthp; cc tng chu lc bcong.Cc vt nt nhn thy cc tng chu lc.Cc vt nt nhn thy cc tng gch chn khung.Gii hn thc t ngn chn s mt cn bng ca mymc c chnh xc caoMc qu ng sut cho php trong cc cu kin nghing tr ln ng k.Gii hn thc t ngn chn cc vt nt trm trng trong nh khung v cng trnh hini.


Ch thch cho bng H.3

1) i vi cng trnh bnh thng, bin dng gc gii hn ly nh hn 1/500

2) Cn trnh h hi khi cc khe nt nhn thy c nu bin dng gc nh hn 1/1000.

3) H hi cng trnh t sy ra vi gi tr f/L < 1/150.



Ph lc I

c im thit k mng cc trong vng c ng t

I.1. Khi tnh ton sc chu ti ca cc lm vic di ti trng nn hoc nh,gi tr Qp vFi nn nhn vi h s gim thp iu kin lm vic ca t mm Mcl v Mc2 cho trongbng I.1 tr trng hp cc chng ln v t hn ln.Gi tr Qp cng phi nhn vi h s iu kin lm vic Mc3 = 1 khi Le 3 v Mc3 =0,9 khi Le < 3 trong Le - Chiu di tnh i ca cc xc nh theo h-ng dn ph lc G. Ma st bn cc, Fi trong khong gia mt t n su hu ly bng 0:4

Trong :hu

bd(1.1)

bd - h s bin dng, xc nh theo cng thc (G.6) trong ph lc G ca tiu chun ny.I.2. Khi tnh ton cc theo iu kin hn ch p lc ln t qua mt bn ca cc nu trong ph lc G, di tc dng ca ti trng ng t, ly gi tr ca gc ma st trong tnh ton 1 gim nh sau: i vi ng t tnh ton cp 7-2 , 8-4 , cp 9-7 .I.3.

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TCXD 205-1998