State whether the following sentence is true or false.

In the direct shear test, the shearing of sand always happens in a pre-determined horizontal plane.

According to the lab video, what are the dimensions of the standard direct shear box used in the laboratory?

In the direct shear test, the corrugated sheets used at the top and bottom of the sample should be positioned

What would happen if we forgot to remove space screws of the shear box before conducting the direct shear test?

Which statements are true regarding the direct shear test results of loose and dense sand samples?

A)      Dense sand has the highest peak shear stress.

B)      Both dense and loose sand samples have similar ultimate/critical shear stresses.

C)      Loose sand has a positive dilation angle.

A cylindrical siltstone specimen was obtained from a borehole drilled in a site where a high-rise building is proposed to be constructed. A laboratory unconfined compressive strength (UCS) test was carried out on this specimen to estimate its strength properties. It was found that the specimen failed at a normal load of 52.9 kN. The height and diameter of the specimen was measured to be 100 mm and 50mm respectively.

Using the provided data,

Calculate the Normal stress (σ₁) at failure.

(Type your answer in MPa)

According to the Mohr-Coulomb failure criteria, what is the maximum shear stress that can be applied to this siltsone when the normal stress is 80 MPa?

(Type your answer in MPa)

Will the siltstone layer at this depth fail or not by shear? 

(Hint: Draw the Mohr circle for the new stress state and check it with the failure envelope)

Determine the maximum shear stress on the siltstone layer due to the applied load stated in Question 8.

Hint: Draw a Mohr circle for the new stress state in the same graph sheet.

(Type your answer in MPa)

It was estimated that after the construction of the building, the siltstone at a depth of 10m below the surface will be subjected to an effective normal stress of 68.5 MPa.

Determine the effective horizontal stress 10 m below the ground surface on the siltstone layer due to this applied load.

(Type your answer in MPa)