According of soft clays requires a wide study





According to a paper written by Bjerrum, the primary pore
pressures gradients occur in a centrifugal manner, hence determining that the
process for consolidating occurs via pore water flowing radially away from the
pile, and the soil particles will make movement towards the pile via axial symmetry
and plane strain conditions. Therefore, this determines that the majority of soil
particles will endure the unloading in shear process and result in a
deformation of the skeleton of the soil during the process of consolidation.

As previously mentioned, development area 3 is covered by
zone C where bored piles will be designed which will contain soft clay
underneath at a depth below ground level. Significantly large excess pore
pressures are created nearby the driven pile in cohesive soils. Due to the
excessive pore pressures being produced down the shaft of the pile, there will
be a reduction in effective stresses and result in enabling the required penetration
for the pile driving process. After the completion of the installation,
dissipation of the pore pressures commences to allow the soil around the pile
to consolidate. This is the process of improving the strength of the soil and
the capacity of the pile bearing increases accordingly.

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Determine an appropriate arrangement of ground improvement
techniques to deal with the need for ground raising on site above the soft
alluvial deposits and hence provide recommendations on how to engineer the
roads, services and drains so that they remain in a serviceable state (focus on
the geotechnical processes occurring in the soft alluvial deposits and hence
provide detailed calculations to support your solution to deal with any
expected ground movements).

Task 2


Development area 3 is covered by zone C where bored piles
will be designed and these problems are likely to occur. To understand the behaviour
of soft clays requires a wide study of the geotechnical parameters, hence extracted
samples can be used during laboratory tests from either remoulded or cored

Ground improvement techniques

Soil characterisation

Behaviour modelling

Geotechnical structure stability

Field investigation

There are a lot of well-known issues regarding the use of
soft clays. The problems can occur at any point on site and these problems can be
faced with:



With consideration to the building of a 2
to 3 storey residential housing estate, the structure load can be estimated to
be between 715kN and 750kN, therefore:

Hence the following has
been calculated:

Concrete Density        =          25kN/m3
D = Pile Cap Depth    =          0.4m
B = Pile Cap Breadth  =          0.6m/pile
H = Pile Cap Height   =          0.6m/pile


The formula to calculate a pile cap is as

Cap Design

To determine the value for Qb, the
following calculation was made:

resistance Qb

Using the same formula, the following has
been calculated:


Lower Layer

With the assumption that d = 0.25m, the following is given:

The following equation has been used to determine the value
for Qs:

Upper layer

Shaft Resistance (Qs)




In this area, a low rise 2 to 3 storey residential housing
estate with associated access and site infrastructure is to be built. This area
covers a majority of zone C and although the buildings may have light loads and
a typical option of a shallow foundation for this structure type, the upper
strata can be used to determine a pile foundation as calculated below:

Development Area 3


Hence from this it can be
determined that for a point load, P, acting on a rectangular pad foundation,
length (L), width (B), and the bearing pressure (Q) is calculated as:

Made ground in zone B is
mostly granular, hence C = 0

Bearing Capacity

Nc        =          35
Nq        =          4.5
Ny        =          2.5
L          =          3.5m   
B         =          3m
H         =          1.531m

The Meyerhof deep foundation chart can be used to obtain the
values for the bearing capacity factors
Nc, Nq, and Ny, considering the value
of ? is given. Therefore:

? =10?

Due to the fact that development area 2 includes
construction of both zones A and B, the weak strata must be considered solely
for the purpose of construction, in other words, for zone B. Due to the fact
that granular soil in zone B is unable to hold piles, the solution for this
type of strata would be determined with the deep foundation calculation as
shown below:

Development Area 2: Rectangular Deep


Net Safe Bearing
Capacity at depth