Confession

I am ahead of schedule. I created posts for the days of the schedule. I am currently about half way through Thursday's stuff. I'm going to go ahead and post it when I finish it - but I'm leaving the dates where they are, because I may get back on schedule at some point.

Retaining Walls - Answers

I marked these pages:

Retaining Wall Analysis - Section 11 - Page 37-6

And today's answer's are:

Retaining Walls - Questions

1. A retaining wall is designed for free-draining granular backfill. After several years of operation the weep holes become plugged and the water table rises to within 8 feet of the top of the wall.

a) What is the resultant force for the drained case?

b) What is the point of application of the drained case?

c) What is the resultant force for the plugged case?

d) What is the point of application of the resultant force for the plugged case?

2. Retaining Wall Design:
A reinforced concrete retaining wall is used to support a 15 ft cut in sandy soil. The backfill is level, but a surcharge of 450 lbf/ft^2 is present for a considerable distance behind the wall. Factor of safety of 1.4 against sliding and overturning are required. Customary and reasonable assumptions can be made. Passive pressure is disregarded. The need for a key must be established.

Soil drained specific weight = 125 lbf/ft^3
Angle of internal friction = 35°
Coefficient of friction against concrete = 0.45
Allowable soil pressure = 4800 lbf/ft^2
Frost line = 3.5 ft below grade

a) What is the minimum stem height?

For b-j, assume a base length B of 12 ft and a base thickness d = 2 ft. A stem thickness at base of 2 ft. And a stem thickness at top of 1.5 ft. A stem height above base of 19 ft. And a heel extension (past back of stem) = 7 ft.

b) What thickness of backfill is equivalent to the surcharge?
c) What is the horizontal reaction due to the surcharge?
d) What is the active soil resultant?
e) What is the total overturning moment, taken about the toe, per foot of wall?
f) What is the factor of safety against overturning?
g) What is the maximum vertical pressure at the toe?
h) What is the minimum vertical pressure at the heel?
i) What is the factor of safety against sliding without a key?
j) What is the factor of safety against sliding if a key of 2 ft wide and 1 ft deep is used?

Retaining Walls and Deep Foundations - Day 1

Chapter 37 in Lindeburg.

These are the chapters in the practice problems book:
Chapter 37 – Rigid Retaining Walls - 3 problems

Soils, Foundations, and Settlements - Part 2 - Answers

I marked these pages:

Bearing Capacity - Sections 4 (and on) - Starts of Page 36-3

Taylor Slope Stability - Figure 40.6 - Page 40-7



And today's answer's are:

Soils, Foundations, and Settlements - Part 2 - Questions

1. A mat foundation is used to support a building with dimensions 75 ft by 45 ft and a total load of 5400 tons. The mat is at a depth of 7.5 ft below ground surface. The soil beneath the mat has a density of 115 lbf/ft^3 and an average SPT N-value of 18.
a) Find the allowable bearing capacity.
b) Find the factor of safety against bearing capacity.


2. A 2.5 m by 2.5 m square spread footing is designed to support an axial column load of 650 kN and a moment of 155 kN*m. The footing is place 1m into a sandy soil with a density of 2050 kg/m^3 and an angle of internal friction of 30°.
a) Find the eccentricity of the resultant load.
b) Find the equivalent width that should be used for the footing design.
c) Use the Meyerhoff theory, what is the value of the bearing capacity factor Ny to be used in calculating bearing capacity?
d) Use the Meyerhoff theory, what is the value of the bearing capacity factor Nq to be used in calculating bearing capacity?
e) Use the Meyerhoff theory, what is the value of the shape factor for Ny to be used in calculating bearing capacity?
f) What is the value of the net bearing capacity?
g) What is the value of the allowable bearing capacity?
h) What is the total allowable load?
i) What is the maximum soil pressure on the bottom of the footing?
j) What is the factor of safety against bearing capacity?


3. A 12 ft x 12 ft footing exerts a pressure of 4000 lbf/ft^2 on the soil below it. What is the increase in vertical soil stress 8 ft below and 6 feet from center of the footing?


4. A 2:1 (horizontal :vertical) sloped cut is made in homogeneous saturated clay. The clay's specific weight is 110 lbf/ft^3 and ultimate shear strength is 1050 lbf/ft^2. The cut is 45 ft deep. The clay extends 12 ft below the toe of the cut to the rock layer. What is the cohesive factor of safety of this cut?

Soils, Foundations, and Settlements - Part 2

Chapters 36 and 40 in Lindeburg.

These are the chapters in the practice problems book:
Chapter 36 – Shallow Foundations - 4 problems
Chapter 40 – Special Soil Topics - 9 problems