2020/2021
University of Gondar
Institute of Technology
Department of Civil Engineering
Foundation Engineering-II Group Assignment - 4th year Civil Engineering
5 Students per group
Submission Date: 26/08/2013 E.C
Mark (20%)
Direction: Attempt all questions; afford complete answers briefly and neatly; clarity and
organization of the answer also is treasured.
1. A square concrete pile 18 m long and 45 cm in cross section is fully embedded in a
saturated clay layer for which 𝛾𝑠𝑎𝑡 = 19.5 kN/m3, ϕ = 0º and cu = 73.5 kN/m2.
Determine the allowable load that the pile can carry:
a. Using the 𝜶 method to estimate the skin friction and Vesic’s method for point
load estimation. (Use FS = 3 and Irr = 50).
b. Using the 𝝀 method for estimating the skin friction and Meyerhof’s method for
the point load estimation.
2. A square concrete pile 20m long and 0.45m in cross section is shown in Figure 2.
Calculate the ultimate skin friction resistance by using the
a. 𝜶-method
b. 𝜷-method
c. 𝝀-method
3. Calculate the factor of safety of a 10 m long circular tapered timber pile which is
embedded in saturated sandy soil with a load of 150kN. The diameters of the pile are
Foundation Engineering-II Group Assignment
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2020/2021
University of Gondar
Institute of Technology
Department of Civil Engineering
Foundation Engineering-II Group Assignment - 4th year Civil Engineering
0.5m at the pile top and 0.25m at the pile tip. The soil data: ϕ' = 30º, 𝛾𝑠𝑎𝑡 = 20 kN/m3, 𝛿
= 0.75ϕ', k =1.5.
4. Refer to Fig. 3a below; Let, length of pile (L=20 m), diameter of pile (D = 0.45m), Hf =
4 m, 𝛾𝑓 = 17.5 kN/m3, and 𝜙𝑓′ = 25º. Determine the total downward drag force on the
pile,
a. Assuming that the fill is located above the water table and that 𝛿′ = 0.5𝜙𝑓′.
b. Assuming that the water table coincides with the top of the fill and 𝛾𝑠𝑎𝑡 (𝑓) = 20
kN/m3.
5. Refer to Fig. 3b below; Let, L = 17m, Hf = 3.5 m, D = 40cm, 𝛾𝑓 = 19.29 kN/m3, 𝛾𝑠𝑎𝑡 (𝑐𝑙𝑎𝑦)
= 19.5 kN/m3 and 𝜙′cl𝑎𝑦 = 20º. The water table coincides with the top of the clay layer.
Determine the total downward drag force on the pile. Assume 𝛿′ = 0.6𝜙′cl𝑎𝑦
Figure 3: Negative skin friction on piles
6. The plan of a group pile is shown in the next Figure. Assume that the piles are
embedded in a saturated homogeneous clay, having cu = 86 kN/m2 and γsat = 19.21
kN/m3.
Foundation Engineering-II Group Assignment
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University of Gondar
2020/2021
Institute of Technology
Department of Civil Engineering
Foundation Engineering-II Group Assignment - 4th year Civil Engineering
Given: center-to-center spacing of piles; S= 0.6m, diameter of piles (D) =0.35m and
length of piles = 20 m. Find the allowable load-carrying capacity of the pile group.
Use FS = 3.
L
S=0.6m
S
7. A 2 x 2 pile group consists of four solid concrete piles with Ep = 30Gpa, 0.3m in
diameter and 7.6m long installed in a firm clay, for which G = 9.6Mpa, Poisson’s ratio
ν = 0.25, both of which are constant with depth. The piles are spaced at 1.5m center to
center, and the group is to carry a vertical working load of 4000kN.
a. Determine the pile head stiffness and settlement of a single isolated pile of the
same dimension in the same soil under the working load of 1000kN.
b. Treating the pile cap as flexible determine the settlement of each pile in the group.
The pile cap is eccentrically loaded with Mx = 100kN-m and My = 50kN- m.
8. A square pile group consisting of 9 piles of 0.4m diameter are planned to support
720kN load in one of the column of a 20 story building. The engineering parameters
of the soils in different layers are given in the table below. The ground water table is
located 0.2m below the ground surface but can rise to the surface due to seasonal
fluctuations. The piles are spaced at 1m center to center. Neglecting the effect of pile
cap and using safety factor of 2.5, determine
Foundation Engineering-II Group Assignment
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2020/2021
University of Gondar
Institute of Technology
Department of Civil Engineering
Foundation Engineering-II Group Assignment - 4th year Civil Engineering
a. The total length of the pile.
b. The group efficiency factor.
Soil type
Depth(cm)
Soil Design parameters
Layer 1(clay)
0 - 500
Cu = 20kPa, γsat = 16.5kN/m3, α = 0.4
Layer 2(clay)
500 - ?
Cu = 50kPa, γsat = 17.5kN/m3, α = 0.8
9. A pile foundation is proposed to support 600kN total load coming from supper
structures on layered soil with the following data. Pile diameter = 0.4m, depth of pile
cap surface below GL is 1m. Column size = 0.5m × 0.5m. Moment along x and y axes
are 1000kN-m and 500kN-m respectively. The pile length is 12m with point bearing
of 1500kpa. Use FS = 2, C-30 and S-300.
Soil data:
Layer -I: Loose sand with ϕ = δ= 28º, γ = 20kN/m3, ko = 0.45 and thickness =2m
Layer -II: soft clay with ϕ = 20º , δ= 15º, γsat = 18kN/m3, ko = 0.40 and thickness =2m
Layer -III: dense sand with ϕ’ = δ’= 30º, γsat = 20kN/m3, ko = 0.42 and thickness =8m
a. Find the number of piles required to get the required capacity
b. Design the pile cap using limit state Design (LSD) method.
10. Wind energy is a renewable energy source and it is gaining a vast reputation for
environmental reasons. In establishment of such a project, a geotechnical engineer
has a remarkable contribution such as designing the foundation part. Due to wind,
the pole and its foundation are subjected to significant horizontal forces besides axial
forces an moments. Thus, a pile foundation is found to be a better option. A circular
concrete pile of diameter 0.25m and 15m long are available in the market. The
prevailing soil condition is NC clay with Cu=37.5kPa, =0.9, sat=20kN/m3 and mv=
0.0001m2/kN. The ground water table coincides with the ground surface. One of the
Foundation Engineering-II Group Assignment
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2020/2021
University of Gondar
Institute of Technology
Department of Civil Engineering
Foundation Engineering-II Group Assignment - 4th year Civil Engineering
pile foundations is subjected to unfactored vertical actions of DL=900kN and
LL=400kN.
a) Based on the following assumptions determine the number and spacing of the
pile:

Converse–Labarre formula works out well;

Piles are vertically driven

Allowable vertical settlement = 35mm and use factor of safety; Fs=3.5
b) Check the adequacy of the foundation in (a)for the horizontal load (H=1200kN)
using Broms’ method for the following conditions:

Properties of each pile: EI=480MN.m2 and My =30kN-m

Soil parameter: coefficient of horizontal subgrade reaction, K=25MN/m3,

Allowable horizontal displacement =5mm and

Adopt restrained head piles.
c) Design a pile cap using S400 steel reinforcement, C-25 concrete and a circular pole
of 50cm in diameter and
d) Provide the structural detailing.
Foundation Engineering-II Group Assignment
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