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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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 < D   From the surface, the water table level at 1.8m has D = 3m Water Table at depth < D   Net Safe Bearing Capacity at depth D to (D+B) Water Table at depth D to (D+B)    Net Safe Bearing Capacity at depth D ? (B+D) Water Table at depth D ? (B+D) 2.2.3       Effect of Water Table Level   Therefore this determines that the long term drained capacity of 488kN/m2 is greater than the short term undrained capacity which was calculated previously to be 179.66kN/m2. Net Safe Bearing Capacity   Y is applied when the soil is above the water table (partially saturated) YSat is applied when the soil is below the water table (fully saturated) Shape Factor ? = 26° with bearing capacities of: NC       =          22.3     NQ            =          11.19 NY       =          7.9 Effective strength parameters apply due to fully drained conditions. 40 years after construction   Net Safe Bearing Capacity Ultimate Bearing Capacity With the use of Skempton's chart, the value of Nc is determined as 7.4 Therefore, Cu        =          55kN/m2 C         =          3.0 fu         =          0 B         =          4.5m L          =          4.5m D         =          3m Y         =          22kN/m3 Immediately after construction 2.2.2       Development Area 2: Shallow Foundation   The calculations determine that the pile foundation with 6 piles for zone A, development area 2 is able to carry the proposed load of 3500kN. Hence the following has been calculated: Concrete Density        =          25kN/m3 D = Pile Cap Depth    =          0.5m B = Pile Cap Breadth  =          1m/pile H = Pile Cap Height   =          1m/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     Very Stiff Clay Using the same formula, the following has been calculated: Stiff Clay Lower Layer And with the values input into the equation, with the assumption that d = 0.5m, the following is given: The following equation has been used to determine the value for Qs: Upper layer Shaft Resistance (Qs) 2.2.1       Development Area 2: Pile Foundation Approximately half of Development Area 2 is covered by zone A as displayed in Figure 1, and 40% of it is covered by zone B. Pored piles and shallow foundation could be applied to zone A. 2.2       Development Area 2     Therefore this determines that the long term drained capacity of 391kN/m2 is greater than the short term undrained capacity which was calculated previously to be 178.8N/m2. Net Safe Bearing Capacity   Y is applied when the soil is above the water table (partially saturated) YSat is applied when the soil is below the water table (fully saturated) Shape Factor ? = 26° with bearing capacities of: NC       =          22.3     NQ            =          11.19 NY       =          7.9 Effective strength parameters apply due to fully drained conditions. 40 years after construction   Net Safe Bearing Capacity Ultimate Bearing Capacity With the use of Skempton's chart, the value of Nc is determined as 7.8 Therefore, Cu        =          55kN/m2 C         =          3.0kN/m2 fu         =          0 B         =          2.5m L          =          2.5m D         =          2.5m Y         =          21.5kN/m3 Immediately after construction In this area of the development, the loads are considered to be light and likewise the upper layer of zone A involves cohesive soil with a layer of clay underneath. Over time, the clay will gradually become stiffer and stiffer which will provide sufficient strength to the soil and result in a shallow foundation which can therefore be designed to construct the mixed retail, with consideration to the practicability and any economical issues. 2.1.2       Development Area 1: Shallow Foundation     The calculations determine that the pile foundation with 6 piles for zone A, development area 1 is able to carry the proposed load of 1000kN. Hence the following has been calculated: Concrete Density        =          25kN/m3 D = Pile Cap Depth    =          0.5m B = Pile Cap Breadth  =          0.5m/pile H = Pile Cap Height   =          0.5m/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 And with the values input into the equation, with the assumption that d =0.3, the following is given: The following equation has been used to determine the value for Qs: Upper layer Shaft Resistance (Qs) 2.1.1       Development Area 1: Pile Foundation A major portion of the development area is under zone A (as shown in Figure 1) and this will be considered as the ground strata. The mixed retail can be developed towards the North and North-East location of the site and this is where the design of bored piles can be placed. ·       Strip loading ·       Point loading There are 2 types of loading involved in this development area: 2.1       Development Area 1   ·       Soil Zone C – Green ·       Soil Zone B – Turquoise ·       Soil Zone A – Yellow Figure 1: Site Model (from analysis of ground investigation report and development proposals) Carry out bearing capacity calculations for shallow foundations for the scheme, alongside calculations for deep and piled foundations, so that a comparison can be made of the relative dimensions of the shallow and piled foundation solutions. 2        Task 1   There are three areas of development, each with a foundation of which will be designed dependent upon the soil conditions. In the case of the site being unable to bear the structure load, typical treatment schemes for this situation will include piling, shallow and deep foundations. The primary objective for this report includes evaluating the issues regarding ground engineering and to propose solutions for these issues, which include the design of shallow, deep and piled foundations, slopes, retaining walls and schemes for ground improvement. 1.1       Objectives     1        Introduction