Problem Sheet 1 Questions

Question 1

A square footing of side width B = 2.5 m is to be founded at a depth of D = 1.5 m in a stiff clay with an undrained shear strength cu = 130 kPa and saturated unit weight γsat = 22 kN m–3, the water table lies at the ground surface.
Compute the maximum allowable design load for the footing using EC7 Design Approach 1b.

What is the 3 step method in completing this problem?

Answer 1

1 - Establish the design parameters to get a value for the undrained shear strength

2 - Compute the bearing capacity factor Nc

3 - Find the design bearing capacity ….

V/A = Sc * Nc * Cu + p0

Question 2

Exercise 3.2:
The same footing as in Exercise 3.1 will be loaded at an inclination angle of 35◦
.Calculate the reduced bearing capacity of the foundation, as a result of the inclined loading.

Answer 2

1 - Find the inclination factor, ic ( SHEAR STRESS / UNDRAINED SHEAR STRENTH = sin 2 theta )

2 - Calculate the reduced bearing capacity, using the value for ic.

Question 3

Exercise 3.3:
A strip footing of width B = 1.5 m is to be founded at a depth of D = 2 m in a deposit of sand that extends to a depth of at least 5D. The water table may be assumed to lie at foundation depth. The measured unit weight of sand above the water table is γ =16 kN m–3, and the saturated unit weight of the sand is γsat = 18 kN m–3. Laboratory testing reveals the critical state friction angle to be φ
′
cv = 35◦
.
Calculate the maximum allowable design load for the footing using EC7 Design Approach 1b.

What is the step by step process for answering this question?

Answer 3

1 - Establish design parameters to get a value for the critical angle

2 - Find Nq and Ny

3 - Compute the design bearing capacity

V/A = (Nq -1)p0’ + 1/2Ny*y’ * B’ + p0

Question 4

Exercise 3.4:
A footing is required to support a column, inclined at an angle of 15◦
, carrying a permanent design load of 1250 kN. The footing is to be founded at a depth of D = 1 m in a deposit of sand that extends to a depth of 6 m, beyond which a clay layer lies. The water table may be assumed to lie at foundation depth. The measured unit weight of sand above the water table is γ = 14 kN m–3, and the saturated unit weight of the sand
is γsat = 17 kN m–3. Laboratory testing reveals a peak friction angle of φ
′
max = 39◦ and
a critical state friction angle of φ
′
cv = 36◦

What is the step by step process to answer this question?

Answer 4

1 - Establish design parameters to find critical angle

2 - Decompose load into vertical and horizontal

3 - Calculate bearing factors, iq, Nq and Ny

4 - Find shape factors, sq and sy

5 - Form bearing capacity equation to find B through iteration

Question 5

Exercise 3.5:
A strip footing of width 2 m is placed at a depth of D = 2 m in a overconsolidated clay.
The water table may be assumed to lie at foundation depth. Laboratory testing reports an undrained shear strength of cu = 165 kPa and a saturated unit weight of γsat =20 kN m–3. A permanent line load of 800 kN m–1 is to be supported by the footing,
with an additional 300 kN m–1 of imposed loading caused by a temporary structure.
Establish if the footing will fail in bearing using EC7 Design Approach 1b.

Answer 5

1 - Establish design parameters to find undrained shear strength

2 - Calculate bearing capacity factor, Nc

3 - Compute design bearing capacity

4 - Compare with unfavourbale temporary action factor`