TITLE : Direct Shear Box Test
INTRODUCTION : The test is carried out on either either undisturbed undisturbed samples or remolded samples. To facilitate the remolding purpose, a soil sample may be compacted at optimum moisture content in a compaction mould. Then specimen for the direct shear test could be obtained using the correct cutter provided. Alternatively, Alternatively, sand sample can be placed in a dry state at a required density, in the assembled shear box. A normal normal load is applied to the specimen specimen and the specimen is sheared sheared across the pre- determined horiontal place bet!een the t!o halves of the shear box. "easurements of shear load, shear displacement and normal displacement are recorded. recorded. The test is repeated for t!o or more identical specimens under di#erent normal loads. $rom the results, the shear strength parameters can be determined.
OBJECTIVE : To To determine the the parameter of shear shear strength strength of soil, cohesion, c and angle of friction, Ø
THEORY : The general relationship bet!een maximum shearing resistance, t i and normal stress , ón for soils can be represented by the equation and known as Coulomb’s law :
where c
= cohesion, which is due to internal forces holding soil particles together in a solid mass. = friction, which is due to the interlocking of the particles and the friction between
them when subected to normal stress. = shearing resistance of soil at failure. total normal stress on failure plane
=
!he friction components increase with increasing normal stress but the cohesion components remains constant. "f there is no normal stress the friction disappears. !his relationship shown in the graph below . !his graph generally appro#imates to a straight line , its inclination to the hori$ontal a#is being equal to the angle of shearing resistance of the soil, and its intercept on the %ertical &shear stress' a#is being the apparent cohesion, denoted by c.
c normal stress
EQUIPMENTS : %. &. (. *. +. .
Shear box carriage 'oading pad )erforated plate )orous plate etaining plate rease
PROCEDURES : %. /nternal measurement is verify by using vernier calipers. The length of the side , ' and the overall depth, B &. Base plate is 0xed inside the shear box . Then porous plate is put on the base plate. )erforated grid plate is 0tted over porous so that the grid plates should be at right angles to the direction shear. (. T!o halves of the shear box is 0xed by means of 0xing scre!s. *. $or cohesive soils, the soil sample is transfer from square specimen cutter to the shear box by pressing do!n on the top grid plate. $or sandy soil, compact soil in layers to the required density in shear box. +. "ount the shear box assembly on the loading frame. . The dial is set of the proving ring to ero. 1. The loading yo2e is placed on the loading pad and carefully lift the hanger into the top of the loading yo2e. 3. The correct loading is applied to the hanger pad. 4. 5arefully the scre!s clamping the upper half is removed to the lo!er half. %6. The test is conducted by applying horiontal shear load to failure .ate strain should be 6.&mm7min %%. eadings of horiontal is recorded and force dial gauges at regular intervals. %&. 5onduct test on three identical soil samples under di#erent vertical compressive stresses , %.1+2g, &.+2g and (.&2g.
RESULT AND CALCULATION : Specimen 8o. % 'oading
9 %.1+ 2g
'ength
9 6mm : 6.6m
Area
9 (.()m a (.()m = *.) # +(- m
Displacemen Dial &L (mm) $a%$e (x10ˉ')
%.1+ 2g x 4.3% 8 x % 28 : 6.6%1 ;n % 2g %6668
P!"#in$ !in$ Dial L"a() $a%$e P*+n, (x 10ˉ-)
S.ea! s!ess *+N/m0,
S!ain (x 10ˉ1)
(x 10ˉ³)
6.& 6.* 6. 6.3 %.6 %.& %.* %. %.3 &.6 &.& &.* &. &.3 (.6 (.&
* 3 %& % &6 &* &3 (& ( *6 ** *3 +& + 6 *
%* &+ (* *% ** +6 ++ +4 ( + 1 4 16 16 16 16
&.4 +.% .4 3.* 4.6 %6.& %%.& %&.6 %&.4 %(.( %(.1 %*.% %*.( %*.( %*.( %*.(
3.% %*.& %4.& &(.( &+.6 &3.6 (%.% ((.( (+.3 (.4 (3.% (4.& (4.1 (4.1 (4.1 (4.1
.1 %(.( &6.6 &.1 ((.( *6.6 *.1 +(.( 6.6 .1 1(.( 36.6 3.1 4(.( %66.6 %6.1
Specimen 8o. & 'oading
9 &.+ 2g
'ength
9 6mm : 6.6m
Area
9 (.()m a (.()m = *.) # +(- m
Displacemen Dial &L (mm) $a%$e (x10ˉ')
(./ (.0 (.) (.2 +.( +./ +.0 +.) +.2 /.( /./ /.0 /.)
0 2 +/ +) /( /0 /2 */ *) 0( 00 02 3/
%.1+ 2g x 4.3% 8 x % 28 : 6.6&+ ;n % 2g %6668
P!"#in$ !in$ Dial L"a() $a%$e P*+n, (x 10ˉ-) /( */ /2 )( 1+ 2/ 4/ 41 +(( +(/ +(/ +(/ +(/
0.+ ).3 3.1 +/./ +0.3 +).1 +2.2 +4.2 /(.0 /(.2 /(.2 /(.2 /(.2
S.ea! s!ess *+N/m0, (x 10ˉ³) ++.0 +2.+ /).( **.4 0(.* 0).0 3/./ 33.( 3).1 31.2 31.2 31.2 31.2
S!ain (x 10ˉ1)
).1 +*.* /(.( /).1 **.* 0(.( 0).1 3*.* )(.( )).1 1*.* 2(.( 2).1
Specimen 8o. ( 'oading
9 (.&+ 2g
'ength
9 6mm : 6.6m
Area
9 (.()m a (.()m = *.) # +(- m
Displacemen Dial &L (mm) $a%$e (x10ˉ')
%.1+ 2g x 4.3% 8 x % 28 : 6.6(& ;n % 2g %6668
P!"#in$ !in$ Dial L"a() $a%$e P*+n, (x 10ˉ-)
S.ea! s!ess *+N/m0,
S!ain (x 10ˉ1)
(x 10ˉ³)
6.& 6.* 6. 6.3 %.6 %.& %.* %. %.3 &.6 &.& &.* &. &.3 (.6
* 3 %& % &6 &* &3 (& ( *6 ** *3 +& + 6
&3 *1 * 33 %6& %%+ %&% %&1 %(* %(+ %(1 %(3 %(3 %(3 %(3
+.1 4. %(.% %1.4 &6.3 &(.+ &*.1 &+.4 &1.( &1.+ &1.4 &3.& &3.& &3.& &3.&
%+.3 &.1 (.* *4.1 +1.3 +.( 3. 1%.4 1+.3 1.* 11.+ 13.( 13.( 13.( 13.(
.1 %(.( &6.6 &.1 ((.( *6.6 *.1 +(.( 6.6 .1 1(.( 36.6 3.1 4(.( %66.6
CALCULATION : +. 5isplacement = dial gauge # (.((/ = (./ # (.((/ = 0 # +(< mm /. 6ro%ing ring = dial gauge = +0 # (.((/(7+((( = /.4 # +(= k87m *. 9hear stress &(./ mm dial gauge' = 5ial gauge # (.((/(07+((( rea = +0&(.((/(0'7+((( ;n (.() m # (.() m = 2.+ # +(- k87m 0. 9train &(./ mm dial gauge' = displacement 7 total length = 0 # +(< mm 7 )( mm = ).1 # +(> 3. 8ormal 9tress, &k87mm' a'
). *.+ cm
0.0 cm !an @ = *.+ 7 0.0
@ = *3>
