12 Apr Based on the geotechnical report, the dominant soil type is GP at Site A and CL at Site B. The soil will be excavated before the installation of the foundation. Answe
Assume two construction sites: Site A and Site B. Based on the geotechnical report, the dominant soil type is GP at Site A and CL at Site B. The soil will be excavated before the installation of the foundation. Answer the following questions based on the information provided:
Q1. Check the table in Figure 2.3 in your textbook and answer the following questions:
a) Which soil categories do the soils at sites A and B fall under (coarse-grained or fine-grained)?
b) Describe what symbols of GP and CL mean.
c) Which soil type is frictional and which one is cohesive?
Q2. Answer the following questions regarding the excavation process:
a) For a shallow cut above the water table for installing the utility lines, which soil type might be able to hold itself in place without the need for support?
b) For a deep excavation, a supported system should be considered. You need as much space as possible at the site and prefer less clutter of the excavation support braces. Sort the following bracing systems starting from the most preferable bracing system: 1) Cross-lot, 2) Raker, 3) Tieback
Q3. A deep excavation will go below the water table. You need to keep the bottom of the excavation dry during the excavation. As a result, you might need a dewatering system.
a) Compare the soil permeability at sites A and B. Which one is more permeable?
b) Which site would you expect to require you plan for a dewatering system? Why?
Q4. A multi-story building will be constructed at these sites that require a soil bearing capacity of 4500 psf. To estimate the bearing capacity of the soils at sites A and B, check the table in Figure 2.6.
a) Which soil type would you expect to have a higher bearing capacity (soil at site A or B)?
b) Assume a bedrock is located in a relatively shallow depth. As a result, an end-bearing deep foundation can be constructed. What type of foundation would the structural engineer design (shallow foundation or deep foundation)? Explain your rationale.
c) Assume the bedrock is located in very great depth (not reachable). Discuss the foundation type(s) that could be designed.
34 / Chapter 2 Foundations and Sitework
them. The ability of these soils to sup-
port building loads without shifting
depends primarily on friction between
the particles to keep the particles from
sliding past one another. This resis-
tance to internal sliding, called shear strength, varies with the degree of inter-
locking between particles and the con-
fining force of the surrounding soil.
Where coarse-grained soils are densely
packed with little space between par-
ticles and securely confined by sur-
rounding soils, it is relatively difficult
for particles to move past one another.
Soils such as these exhibit relatively
high strength and can support greater
loads. Where coarse-grained soils are
loosely packed or poorly confined,
particles can more easily slide past one
another, and less load can be safely
supported. Soils that rely primarily
on internal friction for strength are
termed frictional or cohesionless. Smaller-grained soils may be sub-
ject to a wider array of interparticle
forces. As particle size decreases, sur-
face area increases in relation to weight
and size, and the spaces between the
particles, called soil pores, get smaller.
In essence, the particles become
lighter and more easily pushed and
pulled by electrostatic forces, chemi-
cal interactions, and forces related to
the presence of water in the soil.
For example, whereas gravels are
generally little affected by moisture in
the soil, the properties of sand can vary
noticeably with moisture content. As
any beachgoer knows, wet sand makes
a stronger sand castle than dry sand, as
capillary forces acting between parti-
cles help to hold the particles in place.
And wet sand responds more firmly
to the pressure of our feet as we walk
on the beach than does dry sand, as
the hydrostatic pressure of the water
helps to distribute the load exerted
on the soil. A dramatic example of the
effects of moisture on smaller-grained
soils is a phenomenon called soil liq- uefaction. Water-saturated sands or silts
may lose virtually all of their strength
and behave as a liquid when subjected
to sudden, large changes in load, such
as may occur during an earthquake.
Figure 2.3 The Unified Soil Classification System, from ASTM D2487. The Group Symbols are a universal set of abbreviations for soil types, as seen, for example, in Figure 2.6.
Group Symbol Descriptive names of soil within this group
C oa
rs e-
G ra
in ed
S oi
ls
G ra
ve ls
C le
an
G ra
ve ls
GW Well-graded gravel or well-graded gravel with sand, little or no fines
GP Poorly graded gravel or poorly graded gravel with sand, little or no fines
G ra
ve ls
w
it h
Fi ne
s GM Silty gravel, silty gravel with sand
GC Clayey gravel, clayey gravel with sand
Sa nd
s
C le
an
Sa nd
s
SW Well-graded sand or well-graded sand with gravel, little or no fines
SP Poorly graded sand or poorly graded sand with gravel, little or no fines
Sa nd
s w
it h
Fi ne
s
SM Silty sand, silty sand with gravel
SC Clayey sand, clayey sand with gravel
ML Silt or silt-sand-gravel mixtures, low plasticity
Fi ne
-G ra
in ed
S oi
ls
Si lt
s an
d C
la ys L iq
ui d
L im
it <
5 0
CL Lean clay or clay-sand-gravel mixtures, low plasticity
OL Organic clay or silt (clay or silt with significant organic content), or organic clay- or silt-sand-gravel mixtures, low plasticity
L iq
ui d
L im
it ≥
5 0
MH Elastic silt, silt-sand-gravel mixtures
CH Fat clay or clay-sand-gravel mixtures, high plasticity
OH Organic clay or silt (clay or silt with significant organic content), or organic clay- or silt-sand-gravel mixtures, high plasticity
H ig
hl y
O rg
an ic
So
ils
PT Peat, muck, and other highly organic soils
Allen, Edward. Fundamentals of Building Construction : Materials and Methods, John Wiley & Sons, Incorporated, 2013. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/washington/detail.action?docID=7103638. Created from washington on 2023-04-10 04:35:52.
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