Question

A series of three Direct Shear Tests have been conducted on a certain soil type. The tests were performed on a circular 10 cm-diameter soil sample. The results of these tests taken at the peak failure stress are as follows: Normal Load Shear Load Normal Stress | Shear Stress Test Number (kN) (kN) (kPa) (kPa) 1.178 0.785 1.963 1.374 2.356 256 1.571 a) Use the space provided below to plot the failure envelope and obtain the shear strength parameters. T (kPa) O' (kPa) b) Now that you have drawn the failure envelope. Consider a normal stress of 200 kPa and obtain the shear strength .... What is a safe shear stress to apply to this soil if you use a factor of safety of two (2): c) In the direct shear test you can obtain the peak and residual strength. Indicate how you can obtain these parameters from the stress-strain results ?

Answer 1

Test Number	Normal Load	Shear Load	Area	Normal stress	Shear stress
	kN	kN	mm^2	kPa	kPa
1	1.178	0.785	7853.98	149.99	99.95
2	1.963	1.374	7853.98	249.94	174.94
3	2.356	1.571	7853.98	299.98	200.03

Considering test 2 and 3 to determine c and phi

Shear stress vs normal stress 250.00 200.00 T = 0.50130 + 49.657 R2 = 1 150.00 Shear stress t kPa 100.00 50.00 0.00 0.00 50.00 100.00 250.00 300.00 350.00 150.00 200.00 Normal stress o kPa

τ = 0.5013σ + 49.657

compare with
T=C+0 * tano

c = 49.657 kPa
$tan\phi$ = 0.5013

$\phi$=26.62 kPa

b

$\tau = 49.657+200*tan26.62$

T= 149.896k Pa = 150kPa

allwable shear stress = 150 /2 75 kPa

c.

Peak o peak o residual Residual Strain Stain residual Strain peak

from above graph we can find out peal and residual parameters.

.

comment for any doubt about this solution thank you

Don't forget to upvote if you got your answer