Post on 05-Jul-2018
8/16/2019 1 - Introduction - Foundation
1/45
CE 152
GEOTECHNICAL ENGINEERING 2
INTRODUCTION
ENGR. ROGELIO FRETTEN C. DELA CRUZINSTRUCTOR
8/16/2019 1 - Introduction - Foundation
2/45
FOUNDATION ENGINEERING
–Art and science of applying engineering judgment and the principles of soil mechanics.
Two parts consisting an engineering structure:
1. Superstructure –
upper part2. Substructure/Foundation – lower part
- part of the structure which is usually placedbelow the surface of the ground and which
transmits the load to the underlying soil or rock.
8/16/2019 1 - Introduction - Foundation
3/45
8/16/2019 1 - Introduction - Foundation
4/45
Two principal kinds of failure for foundation:
1. Structural failure of foundation (bending,shear, bearing).
2. Bearing capacity failure of the supporting
soil.
8/16/2019 1 - Introduction - Foundation
5/45
Three types of bearing capacity failures:
1. General shear failure
– It occurs in soils that are relatively incompressible and
reasonably strong, in rock, and in saturated, normally
consolidated clays that are loaded rapidly enough that
the undrained condition prevails. The failure surface is
well defined and failure occurs quite suddenly. Although
bulges may appear on both sides of the foundation,ultimate failure occurs on one side only, and is often
accompanied by rotations of the foundation.
8/16/2019 1 - Introduction - Foundation
6/45
2. Local shear failure
– The shear surfaces are well defined under the
foundation, and then become vague near the ground
surface. A small bulge may occur, but considerable
settlement, perhaps on the other half of the foundation
width, is necessary before a clear shear surface forms
near the ground. Even then, a sudden failure does notoccur, as happens in the general shear case. The
foundation just continues to sink deeper into the ground.
8/16/2019 1 - Introduction - Foundation
7/45
8/16/2019 1 - Introduction - Foundation
8/45
8/16/2019 1 - Introduction - Foundation
9/45
8/16/2019 1 - Introduction - Foundation
10/45
8/16/2019 1 - Introduction - Foundation
11/45
FOUNDATION CLASSIFICATIONS:
1. Shallow Foundation
- Satisfactory soil directly underlies the structure.
- Spread footings, combined footings
2. Deep Foundation
- Adequate soil is not found immediately below the
structure.
- Caisson foundation, pile foundation
8/16/2019 1 - Introduction - Foundation
12/45
Typical Foundation Types
1. Foundation for buildings (controlled mainly byvertical loads)
2. Foundations for smoke stacks, radio & televisiontowers, bridge, piers, etc. (lateral loads)
3. Foundations for ports & marine structures(lateral loads & impact loads)
4. Foundations for machinery, turbines,generators, etc. (vibration & weight)
5. Foundation elements to support open cuts orretain earth masses or bridge abutments.
8/16/2019 1 - Introduction - Foundation
13/45
8/16/2019 1 - Introduction - Foundation
14/45
ULTIMATE BEARING CAPACITY
THEORYReference: Fundamentals of Geotechnical Engineering 3rd Ed.
by Braja M. Das
8/16/2019 1 - Introduction - Foundation
15/45
8/16/2019 1 - Introduction - Foundation
16/45
Later investigators, however, have suggested that foundations with
D f equal to 3 to 4 times the width of the foundation may also beconsidered as shallow foundations.
8/16/2019 1 - Introduction - Foundation
17/45
The failure zone under the foundation can be separated into
three parts:
8/16/2019 1 - Introduction - Foundation
18/45
Terzaghi expressed the ultimate bearing capacity in the form:
(12.3)
8/16/2019 1 - Introduction - Foundation
19/45
8/16/2019 1 - Introduction - Foundation
20/45
8/16/2019 1 - Introduction - Foundation
21/45
8/16/2019 1 - Introduction - Foundation
22/45
8/16/2019 1 - Introduction - Foundation
23/45
8/16/2019 1 - Introduction - Foundation
24/45
8/16/2019 1 - Introduction - Foundation
25/45
8/16/2019 1 - Introduction - Foundation
26/45
8/16/2019 1 - Introduction - Foundation
27/45
8/16/2019 1 - Introduction - Foundation
28/45
8/16/2019 1 - Introduction - Foundation
29/45
8/16/2019 1 - Introduction - Foundation
30/45
8/16/2019 1 - Introduction - Foundation
31/45
8/16/2019 1 - Introduction - Foundation
32/45
8/16/2019 1 - Introduction - Foundation
33/45
8/16/2019 1 - Introduction - Foundation
34/45
P
8/16/2019 1 - Introduction - Foundation
35/45
= 349.55 + 132.43 + 38.88
qu
= 520.86 kN/m2
4
86.520
2
all
kN/m22.130q
8/16/2019 1 - Introduction - Foundation
36/45
Hence, the allowable load, P
LBP
APall
q
LBP all q
m5.1m5.1kN/m22.130 2
kN293P
8/16/2019 1 - Introduction - Foundation
37/45
P
8/16/2019 1 - Introduction - Foundation
38/45
Case I is applicable,
12.85 kN/m2
8/16/2019 1 - Introduction - Foundation
39/45
Hence,
= 700.77
= (12.85)(23.18)(1.625)(1.23)
3
77.700
FS
u
all
2
all kN/m59.233q
LBP all q
= 233.59 × (1.2)2
P = 336.37 kN
8/16/2019 1 - Introduction - Foundation
40/45
8/16/2019 1 - Introduction - Foundation
41/45
Solution
8/16/2019 1 - Introduction - Foundation
42/45
8/16/2019 1 - Introduction - Foundation
43/45
8/16/2019 1 - Introduction - Foundation
44/45
SEATWORK:
1. Determine the gross allowable bearing capacity for a strip
footing given the following:m2.1m,5.0,kN/m2.14',20',kN/m2.18
23 B Dc f
Use FS = 4, Eq. 12.3 and Table 12.1
2. A 2 m×
2 m square footing has the following conditions:0',34',kN/m9.15m,5.1
3 c D f
Determine the allowable gross vertical load that the column
could carry if FS = 3. Use Eq. 12.9
8/16/2019 1 - Introduction - Foundation
45/45
END