Engineering properties of ROcks

Question 1

Rock strength

Answer 1

The maximum value of the applied stress that the rock can sustain under a given set of conditions before failure occurs

Question 2

Characteristics of rock strength

Answer 2

1. Compressive strength
2. Shear strength
3. Tensile strength

Question 3

Compressive strength

Answer 3

Stress required to break a loaded sample when unconfined at the sides MPa

Question 4

Shear strength

Answer 4

Depends on the resistance of parts of the rock to slide relative to one another

Question 5

Tensile strength

Answer 5

Maximum tensile strength that a rock can withstand before failure. Depends on the ability of the components of rock to resist seperation. Point load test

Question 6

Factors influencing strength of rock

Answer 6

1. Texture- grain size, grain shape, nature of grain contacts. Finer grained stronger
2. Amount and type of cement- that binds grains. If cement binds its stronger. Amount of cement and type is important.
3. Pore water- role in compressive strength and deformation. Reduce compressive strength by 30-60%. Reduce shear stress to make grains slip
4. Confining pressure- increase srtength of rock by increasing stress required to cause failure =. Holding rock together.

Question 7

Discontinuities

Answer 7

1. Bedding planes
2. Folds
3. Faults
4. Shear zones
5. Dykes
6. Joints

Question 8

Bedding planes

Answer 8

Divide sedimentary rocks into beds or strata. Interruptions in the course of deposition of rock mass. Some cohesion

Question 9

Folds

Answer 9

Attitude of beds are changed by flexture by tectonic forces. Alter orientation of beds locally

Question 10

Faults

Answer 10

Fracture on which indentifiable shear displacement has taken place