Directs Hear Test

DIRECT SHEAR TEST

Applications of Direct shear strength parameters (c , Ø)

Concept of Dilatancy and Shear Resistance

TYPICAL TEST RESULTS - SAND Stress-Displacement 3.000

normal stress = 1000 psf normal stress = 2000 psf

2.500

shear stress (ksf)

normal stress = 500 psf 2.000

1.500

1.000

0.500

0.000 0.00

0.10

0.20

0.30

0.40

horizontal displacement (in)

0.50

0.60

Dilatancy in dense sand horizonta l displa ce m e nt (in) - 0.035

vertical displacement (in)

- 0.030

- 0.025

- 0.020

- 0.015

- 0.010

- 0.005

normal stress = 500 psf normal stress = 1000 psf

0.000

normal stress = 2000 psf 0.005 0

0.1

0.2

0.3

0.4

Dilatancy Behavior

0.5

0.6

Mohr’s Failure envelope using the peak stresses obtained from the previous plots

Mohrs Failure Envelope (clay) 25000

1800 1600 1400

15000

S h e a r s tre s s (p s f)

shear stress (psf)

20000

10000

5000

0

1200 1000 800 600 400

0

5000

10000

15000

20000

25000

30000

normal stress (psf)

35000

200 0

nomral Vs shear stress (psf)

0

200

400

600

800

1000

1200

Normal stress (psf)

SANDS, c=0, Ø ≈ 40 degrees

CLAYS, USUALLY Ø ≈ 0, “c” exists

Shear box with alignment screws

Sample preparation

Place the shear box under the load cell

Align the load cell

Adjust the LVDT to complete contact

Clamp the shear box, so that only the lower half moves

Run the DIGISHEAR software and obtain parameters c , Ø