CE656 Tutorail 1- Collapsible Soils

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CE 656 Tutorial 1 – Collapsible Soils 24th June 2016

(1) (a) Collapsible soils have the property of volume reduction when water added to it. When

in unsaturated condition it can withstand high pressure without any volume change. But

with addition of moisture, soils undergo large volume reduction with or without any

additional stress on it and could cause structural damages.

(b) Honeycombed structure are developed with in particle sies of !.!!" mm to !.!"

mmwhich are classified as silt and clay. When those soil particles are setting, they are

bonded with chemical agents such as iron o#ide, calcium carbonate which are critical

with large void ratios as following figure. $his structure is called honeycombed

structure.But when water penetrates in to the voids those bonds are bro%en.

(c) Collapsible soils rarely found in areas with very wet

climates due to the bro%en of critical bonds in the

honeycombed structure and already settled with water in

the large voids.

(")

i. &'*+ (1-1)

Coefficient of subsidence, / 0 (oid ratio at 22) 3 (atural void ratio)

ii. H+2$4 and H2 (1-51)

6 soil that has a voids ratio large enough to allow itsmoisture content to e#ceed its li7uid

limitupon saturation issusceptible to collapse.

*aturated moisture content, (wsat) 80 22

or saturated soils. e! 0 w 9s where 9s is specific gravity.

1PG/E/GT/2016/01 Indunil J!G




Combining above two e7uations,

e!80 (22) 9s

atural dry unit weight re7uired for collapse is:

γ d≤Gs γ w

1+e0=

G s γ w

1+ (¿ ) (Gs)

ig : 2imiting values of dry unit weight against the corresponding li7uid limits

iii. ;'9* and /9H$ (1-<)

= $a%e undisturbed soil samples at natural moisture content in a consolidation ring

= 6pply step loads upto a pressure level of "!! %>a

= lood the specimen for saturation and leave for "? Hours

= Collapse potential is calculated as:





C p=∆ ϵ =

e1−e

2

1+e0

e1, e" @ oid ratios at "!!%>a before and after saturation

e! @ natural moisture content of soil, "# @ vertical strain

Collapse potential:

(A) Considerin$ the %&'T( and %I') *ethod+Spe,i-, $ra.it o soil+ 26 and unit ei$ht o ater+ 31 /*

sing e7uation,

γ d≤Gs γ w

1+e0=

G s γ w

1+ (¿ ) (Gs)

PG/E/GT/2016/01 Indunil J!G




So or '' 7 8+ Gs 7 26 and 9r unit ei$ht 7 15/*+

Soil is liel to ,ollapse due to the ''708+ 9r :nit ;ei$ht point o the sele,ted

soil sa*ple is lin$ loer re$ion o the ,ur.e

<4= P0 7 56 /*2

e0 7 0>5 ?ro* e@lo$ p ,ur.e or C"p 7 4 PaP0 A "p 7 56 A 4

7 0 Pa" en 7 0>5 – 0> ?ro* e@lo$ p ,ur.e or C

7 002" e, 7 0> – 055 ?ro* e@lo$ p ,ur.e or C

7 015St 7 Sn A S,

7 %, <" en A " e, =/ <1Ae0=7 6 <002A015= / <1A0>5=

7 052 *7 52 **





<5= b= P0 7 5 B 157 >5 /*2

,= P, 7 400 Pa ? ro* e@lo$ p ,ur.e or &C

d= e0 7 0>? ro* e@lo$ p ,ur.e or &C "p 7 >10 Pa P0 A "p 7 >5 A >10

7 30>5 Pa

" en 7 0> – 065? ro* e@lo$ p ,ur.e or &C7 003

" e, 7 065 – 0525? ro* e@lo$ p ,ur.e or &C7 0125

St 7 Sn A S,

7 %, <" en A " e, =/ <1Ae0=7 <003A0125= / <1A0>=7 10665 **


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CE656 Tutorail 1- Collapsible Soils