1.364 ADVANCED GEOTECHNICAL ENGINEERING
FALL SEMESTER 2003
HOMEWORK NO.2
Due: Friday October 10th 2002
Question No I
A new industrial development for a port extension consists of several large container warehouses
for storage of cargo. The site is located at Labenne in France. The stanchions of the new
warehouses are to be supported on shallow foundations of which typical dimensions are shown
in Figure 1.1. The site is underlain by sands and the variation of the standard penetration
resistance, cone penetration resistance and pressuremeter limit pressures are depicted in Figure
1.2. The soil friction angles derived from shear box tests are summarized in Figure 1.3. Figure
1.4 shows index properties reported from the site investigation. NOTE: Although the data in
Fig. 1.4 are quite reliable above the groundwater table, the data are affected by significant
sampling disturbance effects below the groundwater table (due to cave-in of the borehole).
Based on the data available to you, carry out the following tasks:
a. Estimate the ultimate bearing capacity of the foundation using the methods given in the 1.364
Course Notes.
b. Calculate the factor of safety for a vertical working load of 2000 kN acting at each stanchion.
c. How would your answer change if there is an additional moment of 500 kNm due to lateral
loads on the stanchions?
d. Use the method of Burland and Burbridge (1984) to calculate the immediate settlement of the
foundation. Consider only the vertical load of 2000 kN. What would be the settlement after a
period of operational life of 90 years?
e. For the same loading condition and operational life as in (e), re-calculate the immediate and
long term settlements using the method of Schmertmann (1970).
Question No. 2
At the Post Office Square site in Homework No. 1, the Owner suggested that an alternative
scheme involving a single basement be explored. The new scheme is shown in Figure 2.1. A
raft would be constructed at an elevation of 0.0 feet (based on Boston City datum) to carry the
foundation loads of the entire building. The soil profile and the soil parameters are summarized
in Figures 2.2 and 2.3. The coefficient of consolidation cv = 0.2 ft2/day and the coefficient of
secondary compression ca = 0.001 for the clay layers. Based on the information given, carry out
the following tasks:
a. Interpret the undrained shear strength of the clay using the SHANSEP approach of Ladd and
Foot (1974) assuming S = 0.2 and m = 0.8.
b. Calculate the ultimate bearing capacity of the raft.
c. If a factor of safety of 2.0 is required by the local Building Authority, how many floors can
the building be designed to, if the working live load is 0. 1 tsf per floor and 0.2 tsf for the
basement. Assume the structural dead load to be 0.5 tsf per floor and 0.36 tsf for the
basement.
After much discussion, a 13 storey high structure with a single basement was chosen. For this
case:
d. Calculate the immediate settlement using the method of D'Appoloniaet al (1971). Assume K0
= K0NC (OCR)n, where K0NC = 0.5 and n = 0.4.
e. Estimate the consolidation settlement assuming that the loads are applied instantaneously.
f. Estimate the long term creep settlement for a design life of 90 years.
g. If the actual construction period is 12 months, what amount of settlement can be expected
after the end of construction for the same design life?
500 kNm
500 kN
2000 kN
2000 kN
1.5m
1.5 m
20 m
20 m
2m
10 m
5m
Figure 1.1 Foundation layout
3m
0
0
4
5
6
6
0
50
100
1.0
2.0
Menard
12.7% organic
content
13
5
Pressiopenetrometer
2
Fine-medium
light brown
uniform sand
7
Borehole log
CPT qc (MPa)
SPT blows /
300 mm
Pressuremeter
CPT fc (kPa) limit pressure
pL (MPa)
Figure 1.2. Insitu Test Data
100
Dr (%)
75
50
25
45
fp
40
Angle of friction (f )
Depth (m)
Some clay
traces
2
3
4
15
1
GWL
2
35
fcv ;
33o
LEGEND
Shear box data:
Soil-soil, peak
Conditions at constant volume
30
25
0.45
0.50
0.55
0.60
0.65
0.70
Initial voids ratio ei
Figure 1.3. Soil Friction Angle Obtained from Shear Box Tests
Water content
0
0
2
2
Depth (m)
Depth (m)
Bulk density
4
6
4
6
Yb (kN/m3)
15
w (%)
20
0
10
0
0
2
2
Depth (m)
Depth (m)
100
6
30
Relative density
Sr - Degree of saturation
4
20
Dr (%)
50
0
4
6
Sr (%)
0
50
e
100
0.4
0.6
Void ratio
0.8
LEGEND
BH IC 1
BH IC 2
Open symbols : average of complete sample
'Organic' sand
Figure1.4. Physical Properties obtained from Laboratory Tests
Pore Water Pressure,
uo, u (TSF)
20
1.0
0.5
1.5
2.0
2.5
0 10 20 30 40 50 60
FILL
0
U-1
PZ
11A
U-1
U-1
-10
uo
U-2
-20
CLAY
U-2
PZ
11B
U-3
U-3
Hydrostatic Pore Water
Pressure (Assuming
Water Level
at EL. = 9.0
-30
U-4
-40
-60
-70
TILL
-50
u
PZ
1(A)
ROCK
Elevation in Feet (Boston City Base)
10
0
Natural Water Content,
Atterberg Limits (Percent)
PZ
1(B)
B1
PZ
3(B)
B2
B3
PZ
12
PZ
14
B11 B12 B14
Observed in-situ
pore water
pressure
Symbol
OB. Well
No.
Plastic Limit, Wp
Symbol Boring
No.
Piez.
No.
B2
B1
PZ1(A)
B3
B1
PZ1(B)
B3
B11
PZ3(A)
PZ3(B)
PZ11(A)
B12
B11
PZ11(B)
B14
B12
PZ12
B14
PZ14
B9
B11
B3
Liquid Limit, WL
Natural Water Content, WN
Origin of Data:
Postoffice SQ. Garage
One Post office SQ.
(H & A File No. 4207)
Figure 2.2. Pore water pressures, natural water content and Atterberg Limits
Vertical Effective Stress,
σvo, σv, σp (TSF)
Compressibility Parameters,
CR, RR
20
10
FILL
0
0
U-1
6.0
8.0
Best Estimate of σp' Preconsolidation Pressure
U-1
-10
σv - Vertical Effective
U-2
Stress (Based on
observed
in-situ pore
water pressure)
CLAY
U-2
PZ
11B
U-3
U-3
-30
U-4
-40
-60
-70
TILL
RR
CR
-50
10.0
CR
PZ
11A
U-1
ROCK
Elevation in Feet (Boston City Base)
4.0
Mean
RR
-20
2.0
PZ
3(B)
PZ
1(A)
PZ
12
0.01
0.1
0.02
0.2
0.03 0.04
0.3 0.4
PZ
14
Compression Ratio, CR
PZ
1(B)
B1
0
0
Recompression Ratio, RR
B2
B3
B11
B12
B14
σ vo -Vertical Effective Stress
(Assuming Water Level @ EL. 9.0)
Symbol
Boring
Sample
B2
B2
B12
U2
U4
U3
B14
U1
B2
U1
B2
B12
U3
U1
B14
U2
Figure 2.3. Compressibility parameters and vertical effective stress