Construction Methods for Geotechnical Engineering Projects

Construction Methods 1
CONSTRUCTION METHODS
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Construction Methods 2
Executive Summary
Geotechnical engineering knowledge plays a very crucial part in the construction of a project to
determine the soil properties and the dangers that the building may be exposing itself to incase
the soil structure is determined to be not suitable for construction. Our company was mandated to
carry out the geotechnical aspects of the construction of a project for our client who is to put up a
concrete industrial building with plan dimensions of 15 × 40 m. The building is to have a mat
concrete foundation with a thickness of 500 mm, with a finished RL of 14.0 m. Since the site
was used as a storage of petrochemical products some years back, it was under threat of losing its
form and structure. It was therefore important to carry out the soil test analysis to determine its
suitability and the methods that can be employed in the construction process.
The building structure will also have a steel water tank. The first to be carried out was the
Standard Penetration Test to determine the soil consistency and the N values that would be
relevant in drilling the boreholes. Geostudio software was used to determine the ground layer by
producing the ground cross section. The methods to be used in the construction was then
discussed with a preliminary layout of the retaining walls to be used in construction. The mat
foundation was then designed and the determination of the maximum settlement calculated using
the Young’s Modulus. The water tank foundation was then designed and an estimation of the
settlement tank footing identified using Young’s modulus. Finally a recommendation was given
for future research on soil explorations to help in the future designs.

Construction Methods 3
Table of Content
Executive Summary.......................................................................................................................2
Introduction....................................................................................................................................3
Scope of work...............................................................................................................................4
Consistency of the soil layers based on SPT N-values................................................................5
Cross section of the ground layers of the site..............................................................................7
The construction methods that should be adopted in the construction....................................8
Use of lattice beams.....................................................................................................................8
Using Anchors in the ground.......................................................................................................9
The top-down method.................................................................................................................10
A general layout of the retaining walls around the proposed building..................................12
Retaining walls...........................................................................................................................12
Gravity retaining wall............................................................................................................13
Pile retaining wall..................................................................................................................14
Cantilever retaining walls......................................................................................................14
Anchored retaining walls.......................................................................................................15
Condition of stability of Retaining walls...................................................................................15
Loads on Retaining Walls..........................................................................................................16
Preliminary design of a retaining wall.......................................................................................17
The retaining structure employed between proposed building and water tank.........................17
The retaining structure employed between proposed and existing building plus proposed
building and planned car park...................................................................................................18
The retaining structure employed between proposed building and car park............................18
Factor of safety of the large mat foundation proposed for the building.................................18
Maximum Settlement of the footing...........................................................................................20
Circular tank footing...................................................................................................................20
Settlement of the footing.............................................................................................................22
Recommendations........................................................................................................................23
References.....................................................................................................................................24

Construction Methods 4
Introduction
In most cases, a typical Geotechnical engineering projects starts with the definition of the
material properties, followed by a site investigation of the soil, fault distribution, rock, and
bedrock properties on and beneath the site area to determine the engineering properties which
include how the soil will interact with the proposed construction (Allen & Iano, 2017). Site
investigation help the project engineers to understand the site, These include the assessment of
risk to property, human, and the environment from the natural hazards which include landslides,
earthquakes, soil liquefaction, sinkholes, rock falls and debris flows (Allen & Iano, 2017).
Geotechnical engineers role is to design the earthworks, type of foundation and pavement
subgrades required to build the structure (Bahrami, et al., 2012). Foundation designs depend on
the type of the structure such as the high rise buildings, commercial structures, small structures
and bridges (Rose, et al., 2012). There are different types of foundations that are built above the
structure such as retaining walls, shallow and deep foundations (Bahrami, et al., 2012).
Earthworks include tunnels, reservoirs, embankments, channels, dikes and levees sanitary
landfills and hazardous wastes.
Cargo transporting company in Melbourne has approached Maestro Company which is our
geotechnical company to carry out an assessment on their site in Melbourne on geotechnical
aspects to determine the effectiveness of the soil for construction since the site was used before
as a storage area of petrochemical company, which means there has been oil spillage that have
happened on site for a long period of time which might contaminate the soil structure and
condition.
Scope of work
The building project will consist of
 A concrete industrial building with plan dimensions of 15 m × 40 m. The building is to
have a mat concrete foundation with a thickness of 500 mm, with a finished RL of 14.0
m. The walls are load bearing and there are some internal columns carrying the weight of
the roof and other elements.

Construction Methods 5
 A steel water tank having an external diameter of 13 m and an effective height of 8 m,
with its base at RL 17 m (top of the footing).
 There is an existing one-storey double brick building on the site. The RL of the slab on
the ground is 17.5 m (top of the slab on ground).
A Site Plan is attached below, showing the location of the tank, the car park (RL 17.5 m, finished
surfacing) the proposed and existing buildings. The Structural Engineer for the project has
determined the proposed building loads and they are as follows:
 Total vertical loads: 250 MN per meter run (NOTE: the weight of foundation is
included.)
 Total moment in each direction: 500 MN.m
 Total horizontal loads: 50 MN.
Consistency of the soil layers based on SPT N-values
Standard Penetration Test (SPT) is a test done on site to determine the geotechnical engineering
properties of the soil. The [procedure is mostly described in ISO 22476-3, Australian Standards
AS 1289.6.3.1, and ASTM D1586 (Lovisa, et al., 2010). It is the most common test used
worldwide in geotechnical engineering (Boly, et al., 2012).
Figure 1: standard penetration test (spt) (astm d1586-11) Source (Umass Lowell 2013)

Construction Methods 6
Soil consistency is the ability of the soil materials to hold itself by resisting any form of pressure
that may lead to the deformation or rupture of the soil (Chotia, et al., 2012). It is measured for
dry soil and wet moist samples. When it comes to the wet soil sample, it is expressed as both
plasticity and thickness (Long & Vietnam, 2010).
The boreholes are usually drilled deeper and the test repeated again. During this process, errors
might occur per interval due to the poor state of soil recovery (Clayton, et al., 2012). The number
of the hammer strikes it takes for a tube to dig deep or penetrate the 2nd and 3rd 6 inch depth is
referred to as “standard penetration resistance” or referred to as ‘N-value (Clayton, et al., 2012).
For 3 or 4 increments of six inches each
Three increments: we get the sum of the last 2 increments in SPT N value. For 4 increments, the
same procedure is repeated (Chotia, et al., 2012).
Correction to SPT N Value
Nmeasured = Raw SPT value obtained from the field test
N60 = corrected N values corresponds to 60% of energy efficiency
N60 = CE CB CS CR Nmeasured
Factor Term Equivalent Variable Correction
Energy Ration CE =ER/60 Donut hammer
Automatic hammer
Safety hammer
0.5 -1.0
0.8 – 1.5
0.7 – 1.2
Borehole diameter CB 65mm to 155mm
150mm
200mm
1.0
1.05
1.15
Sampling method CS Non Standard
sampler
standard sampler
1.1 – 1.3
1.0
Rod length CR 3m - 4m 0.75