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.

3.1

Consolidation

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).

3

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

specimens.

·

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

Where,

The formula to calculate a pile cap is as

follows:

Pile

Cap Design

To determine the value for Qb, the

following calculation was made:

Base

resistance Qb

Using the same formula, the following has

been calculated:

Stiff

Clay

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:

2.3

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:

2.2.4

Development Area 2: Rectangular Deep

Foundation

Net Safe Bearing

Capacity at depth