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)

A a tri-axial test was carried out for the same siltstone material.

It was found out that the cohesion (C’) of the siltstone is 8 MPa. Determine the friction angle ϕ’ of the siltstone.

(Type your answer in degrees)

Hint:

Draw a Mohr circle for the failure state of the UCS test  and then draw the Mohr-coulomb failure envelope for the siltstone in the same graph sheet.

Which of the following stress-strain response can be expected during an unconsolidated-undrained (UU) test?

The maximum shear stress τ_max, for a soil mass is equal to ___________

Which of the following is not true for unconsolidated-undrained (UU) test?