Construction Methods for Geotechnical Engineering Projects

This article discusses the construction methods used in geotechnical engineering projects. It covers topics such as soil consistency, retaining walls, and the top-down method. The article also includes a general layout of retaining walls around a proposed building. The scope of work for a specific project is also discussed. The article is written by an expert and is suitable for students and professionals in the field of geotechnical engineering.

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.

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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.

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 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

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4m - 6m
6m – 10m
>10m
0.85
0.95
1.00
Table 1: STP Corrections Source: (Eswaraiah, et al., 2011)
Note: it is important that the ER value should be measured according to the ASTM D4633
Soil engineering property in regard to the insitu testing
Soil Consistency/ Density N
SANDS
Very Loose
Loose
Medium dense
Dense
Very dense
0 -4
5 – 10
11 – 30
31 – 50
>50
COHESIVE SOIL
Very soft
Firm
Stiff
Very stiff
Hard
0 -2
2– 8
9 – 15
15 –30
>30
Table 2: Consistency of soil layers as per the SPT N values

Construction Methods 8
Cross section of the ground layers of the site
Soil profile sample
The construction methods that should be adopted in the construction
This construction is more involving in the deep ground and therefore the existence of
groundwater is required to be considered that can lead to limit the working space. In every deep
ground construction, methods of soil supports, sub-soil condition, and the layout requirement of
the building must be considered to design for the method of works (Allen & Iano, 2017).
Provision of a retaining structure such as the diaphragm wall or sheet piles wall, any is needed
during excavation at the sides of the walls. This method is most effective method that can be
used to construct ordinary basement (Kato, et al., 2012).
Use of lattice beams
A series of steel trusses is put in place to span between the top of opposite diagram walls. The
retaining walls act as propped cantilevers (Bahrami, et al., 2012). After the construction of
internal slab, the trusses can be removed since the slab will support the lateral forces from soil
(Boly, et al., 2012).

Construction Methods 9
Figure 2: Lattice beam Source: (Boly, et al., 2012)
Using Anchors in the ground
The ground anchors are used to provide stabilization of the walls as the works is in process, since
the diagram walls are directly exposed to earth pressure during the excavation stages (Chotia, et
al., 2012). The method is suitable for basement of very large spans, without the intermediates
floors as lateral support (Clayton, et al., 2012).

Construction Methods 10
Figure 3: Ground Anchors Source: (Clayton, et al., 2012)
The top-down method
It involves the construction of floor slab as support, where after the perimeter diaphragm walls
have been constructed, the ground floor slab and beams are cast providing tip edge lateral
support to the walls (Das & Shukla, 2013). An opening in the slab provides access for labors and
material as the excavation continue to the lower stages. The process continues until the attaining
of the required depth (Eswaraiah, et al., 2011).

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Figure 4: Ground floor slab and beam cast before basement excavation commence Source:
(Eswaraiah, et al., 2011)

Construction Methods 12
Figure 5: Ground floor slab and beam cast before basement excavation commence Source:
(Halpern, et al., 2014)
A general layout of the retaining walls around the proposed building
Retaining walls
This is a structure designed using either concrete insitu, precast concrete, stone blocks in order to
resist the lateral pressure coming from the soil to prevent it from collapsing or rapturing
(Clayton, et al., 2012). The lateral pressure can also be as a results of the liquid pressure, sand,
earth filling and any other granular material used to fill the wall on its back side after it has been
constructed (Clayton, et al., 2012). In most cases, these walls are normally used as the
transporting structures when construction is happening on top of the hill or a raised ground,
bridge wing walls, masonry dams, abutments (Das & Shukla, 2013). The type of material to be

Construction Methods 13
used in the construction of the retaining wall depends on the site condition, height of the wall to
be constructed and the type of material to be retained (Clayton, et al., 2012).
The primary role of a retaining wall is to hold the earth back in its position without instances of
soil instability where there is sliding, overturning or structural failure. Earth fill, water table, and
surcharge are important in retaining the wall design (Eswaraiah, et al., 2011). However, disaster
may occur when the soil can bear the compressional force that acts upon it due to excess axial
load or shear force causing a lot pressure which might force the soil to tip off (Kravchenko &
Robertson, 2011). Therefore, its use in the construction projects is always very crucial since it
helps in maintaining the ecological condition of the landscape hence avoiding more cut and fill
process which might be very expensive (Eswaraiah, et al., 2011). In addition, the project design
will try and blend in with the environment by maintain the gradient at some point. Some of the
retaining wall that will be used in the proposed project include:
Gravity retaining wall
Gravity retaining wall depends on its own weight, whereby it only stands alone. This retaining
wall is always massive (Eswaraiah, et al., 2011). To design this retaining wall, it is important to
take in certain consideration such as sliding, overturning forces and bearings which should be
tested to ensure its suitability (Eswaraiah, et al., 2011). Mostly used where there is a lot of
pressure applied.
Sliding of retaining wall Overturning retaining wall Global stability of retaining
wall
Source: https://civildigital.com/retaining-wall-types-retaining-walls-design-considerations/

Construction Methods 14
Pile retaining wall
Piles are normally driven deep into the earth surface so that the forces acting from the top of the
wall are prevented from collapsing the wall over instead it is held back in position (Eswaraiah, et
al., 2011). It uses counter forces by holding back the force acting downwards and balancing it
with the upward resistance hence preventing the wall from tipping off (Halpern, et al., 2014).
Pile retaining wall can be used in a permanent works or temporary works since they provide high
stiffness retaining elements which have got large excavation depths which cause no disturbance
to the surrounding structures (Kato, et al., 2012).
Figure 6: Pile retaining wall Source: https://civildigital.com/retaining-wall-types-retaining-
walls-design-considerations/
Cantilever retaining walls
They are always constructed using reinforced concrete. Cantilever retaining wall consist of a slab
base and a thin stem (Eswaraiah, et al., 2011). The base has got two parts referred to as the toe
and the heel. The heel is located at the base under the backfill. This wall in most cases uses less
concrete than the retaining walls, but it needs keen concentration during design and construction.
This wall is usually 25 feet in height and can either be pre cast in factories or formed insitu
(Halpern, et al., 2014).

Construction Methods 15
Figure 7: Cantilever retaining wall Source: https://civildigital.com/retaining-wall-types-
retaining-walls-design-considerations/
Anchored retaining walls
Where there is high retaining walls, deep wires are driven deep along the earth sideways after
which the ends are anchored with concrete to keep the wires and soil in position (Halpern, et al.,
2014). They are referred to as tie backs. They are used when the spaces required to construct the
retaining wall is small or a thinner retaining wall is needed (Kato, et al., 2012). They are deemed
to be more effective on the loose soil compared to the solid rocks. Anchored retaining walls have
been employed in the construction of highways whereby they keep the soil lumps and rock from
falling into the highway (Kato, et al., 2012).
Condition of stability of Retaining walls
The stability of retaining walls can be achieved by certain requirements or conditions such as
 The wall should be structurally sound to resist any form of pressure.
 The wall should be proportionate to avoid instances of being overturn by lateral forces.
 The wall should be safe from sliding

Construction Methods 16
 The weight of the wall and the resultant force of the earth causing the pressure should not
cause stress on its foundation to a value exceeding the bearing capacity of the soil
(Lovisa, et al., 2010).
 Long retaining walls should be constructed with expansion joints positioned at 6 – 9m
apart (Kravchenko & Robertson, 2011).
 The backfilling materials used to fill the back of the retaining walls should not have the
ability of retaining water.
 Water pressure could be relieved by providing water holes.
Figure 8: Basic retaining wall Source: https://civildigital.com/retaining-wall-types-retaining-
walls-design-consideration
Loads on Retaining Walls
Major loads that act on retaining walls are as follows.
 The walls self-weight
 Vertical earth pressure
 Lateral earth pressure
 Horizontal water pressure
 Horizontal live load surcharge
 Vertical live load
 Buoyancy due to water table,
Pedestrian access from the car park to this building
Access for pedestrians

Construction Methods 17
Preliminary design of a retaining wall
The purpose of this is provide clear properties and aspects that can be during the detailing design
of the retaining wall (Das & Shukla, 2013).
Theses aspects to be put in place are
The location of the retaining wall. Put into consideration the existing site features and the show
how they impact the impact the retaining wall (Kato, et al., 2012). The location should cater for
the drainage patterns, which one can specify the type of drainage incorporated
Specify the geometry of the retaining wall. Calculate the height of the retaining wall. Specify the
thickness and shape to be used. Incorporate the effect of surcharges and some cases seepage
(Kato, et al., 2012).

Construction Methods 18
Suggest the structural required to be used in the design. This should provide the bearing capacity
of the soil, moment from resultant forces (Allen & Iano, 2017). Specify if geo-grids are being
used to come with the total wall envelope (Kravchenko & Robertson, 2011).
With all this specified will be used by the structural engineering to come up with the structural
design and some cases of a concrete wall provide reinforcement at the most economical (Lovisa,
et al., 2010).
The retaining structure employed between proposed building and water tank
The retaining structure that should be employed between the proposed building and the water
tank is the pile retaining wall. This retaining walls provide high stiffness retaining elements
giving them more strength due to the deep piles penetrated into the soil (Das & Shukla, 2013).
Due to their strength, Pile retaining walls will be able to resist the lateral pressures that will be
coming from the steel water tanks compression pressure that results into the lateral pressures.
(Halpern, et al., 2014) The resistance makes the wall to remain steady and not topple over to the
proposed concrete block walled building (Halpern, et al., 2014).
The retaining structure employed between proposed and existing building plus proposed
building and planned car park
The retaining structure that should be employed between the proposed and the existing building
as well as the proposed building and the planned car park will be cantilever retaining wall. This
type of retaining wall is mostly used as a boundary in separating two building structures (Kato, et
al., 2012). Also used when a sloppy land is being levelled to carry out construction, where by it
is used at the upper side of the slope to retain the soil in construction before construction
commence. The heel makes the retaining wall to have extra strength when used in earthworks
(Kravchenko & Robertson, 2011).
The retaining structure employed between proposed building and car park

Construction Methods 19
The retaining structure that should be employed between the proposed building and the planned
car park is the gravity retaining wall. This retaining wall makes it easier to have steps that will
help pedestrians walk towards the proposed building after coming from the car park area, due to
its strong self-weight, it will be able to handle the heavy traffic that will be experience in that
areas (Boly, et al., 2012). Since the gravity retaining wall will cover a distance of more than
30m, expansion joints will be introduced in the wall to allow for expansion in order to relieve
excess pressure that might be experience hence avoiding cracking or rapture (Halpern, et al.,
2014).
Factor of safety of the large mat foundation proposed for the building
A factor of safety to range from 2.5 -3.0. The footing is 4m below the ground surface. It is above
the sandy soil layer (Halpern, et al., 2014).
Calculation
N=22
N60= EH CB CS C R N
0.60
0.6 ×1 ×1 ×0.85 ×22
0.6 =19
The unit weight γsat =16.0+0.1 N 60
16.0+0.1 ×19=17.9 kN /m2
Correction of N, ( N1 )60=0.77 log( 200
σ ' ) N60=14
Angle of friction, ϕ =2.7+0.3(N 1)60
27+0.3× 14
¿ 31.2 °

Construction Methods 20
The bearing capacity
qult=0.5 γB N γ sγ dγ + γZ Nq sq dq
Where ϕ =31.2
Nq =tan2
( 45o + ϕ
2 )
eπ tan ϕ
=34o
Nc= ( N q−1 ) cot ϕ=22.98o
Nγ =2 ( Nq +1 ) cot ϕ=28.55o
sq =1+ 4
15 × 22.98
28.55 =0.21
sγ =1−0.4 × 4
15 =0.89
d z=1+ ( 2 tan 31.2 ) ( 1−sin 31.2 )2
( 4
15 )=1.07
19.65 × 4 ×0.21 ×1.07+ 0.5× 19.65× 15× 28.55 ×0.89
qult=3762.4 kN /m2
Therefore, qall= qult
F where F=3.0
¿ 3762.4
3 =1254.14 kN /m2

Construction Methods 21
Maximum Settlement of the footing
qall=11.98 (1+0.33 ( Df
B ) )[ Se
25.4 )
Se=244.3 mm
Circular tank footing
The footing will be designed as a rigid footing. You need to consider it as axisymmetric. The
design depends on the SPT perform (Long & Vietnam, 2010).
The depth of the upper layer of which is sand.
Calculation
N=10
N60= EH CB CS C R N
0.60
0.6 ×1 ×1 ×0.85 ×10
0.6 =9
The unit weight γsat =16.0+0.1 N 60
16.0+0.1 ×9=16.9 kN /m2
Correction of N, ( N1 )60=0.77 log( 200
σ ' ) N60=14
Angle of friction, ϕ =2.7+0.3(N 1)60
27+0.3× 14
¿ 31.2 °

Construction Methods 22
The bearing capacity
qult=1.3 c N c+0.3 B N γ + γZ Nq
Where ϕ =31.2
Nq =tan2
( 45o + ϕ
2 )
eπ tan ϕ
=34o
Nc= ( N q−1 ) cot ϕ=22.98o
Nγ =2 ( Nq +1 ) cot ϕ=28.55o
0.3 ×13 ×16.8 × 28.55+ 1× 16.9× 22.98
qult=2270 kN /m 2
qnet =qult−q
¿ 2270−8 ×10=2190 kN /m2
Therefore, qall= qult
F where F=3.0
qall=2190
3 =730 kN /m2
This is the maximum allowable with the depth of the footing is 1m.
Settlement of the footing
The requirement is to find the allowable bearing capacity that the footing can settlement to a
maximum 50mm (Rose, et al., 2012).
Calculate the average Es
The depth of the base of the mat to the bed, H= 7- 1 = 6m

Construction Methods 23
Each layer modulus
Es 1=40+12=52
Es 2=40+17=57
Es 3=40+18=58
Es 4=40+22=62
Es ( av ) = 1 ( 52 ) +1 ( 57 ) +2.5 ( 58 ) +2 ( 62 )
6 =63
Where μ=0.3 for all layers
I s=0.408+ 1−2 ( 0.3 )
1−0.3 ( 0.37 ) =0.429
Estimating D/B =0.1, from FFACTOR I f =0.9
∇ H =qo B'
( 1−μ2
Es ) m I s I F
∇ H
qo
=6.5 ( 1−0.32
63000 ) ( 0.92× 0.429 ) × 0.9=6.67× 10−5
For settlement ∇ H =50 mm
qa= 0.05
6.67 ×10−5 =749.61 kPa
Recommendations
The settlement of the rafter footing is expected to be greater than the allowable because the
settlement gotten from the applying the factor of safety on the ultimate bearing capacity
produced settlement of 244.3mm which exceeds the allowable 50mm. recommendation of using
pile foundation for the new building which will transfer the loads directly to the bedrock. For the
retaining wall recommend concrete walls which weep holes.

Construction Methods 24
References
Allen, E. and Iano, J., 2017. The architect's studio companion: Rules of thumb for preliminary
design. John Wiley & Sons.
Bahrami, M., Bazzaz, D.H. and Sajjadi, S.M., 2012. Innovation and improvements in project
implementation and management; using FMEA technique. Procedia-Social and Behavioral
Sciences, 41, pp.418-425.

Construction Methods 25
Boly, M., Garrido, M.I., Gosseries, O., Bruno, M.A., Boveroux, P., Schnakers, C., Massimini,
M., Litvak, V., Laureys, S. and Friston, K., 2011. Preserved feedforward but impaired top-down
processes in the vegetative state. Science, 332(6031), pp.858-862.
Chotia, A., Neyenhuis, B., Moses, S.A., Yan, B., Covey, J.P., Foss-Feig, M., Rey, A.M., Jin,
D.S. and Ye, J., 2012. Long-lived dipolar molecules and Feshbach molecules in a 3D optical
lattice. Physical review letters, 108(8), p.080405.
Clayton, C.R., Woods, R.I., Bond, A.J. and Milititsky, J., 2014. Earth pressure and earth-
retaining structures. CRC Press.
Eswaraiah, V., Aravind, S.S.J. and Ramaprabhu, S., 2011. Top down method for synthesis of
highly conducting graphene by exfoliation of graphite oxide using focused solar
radiation. Journal of Materials Chemistry, 21(19), pp.6800-6803.
Das, B.M. and Shukla, S.K., 2013. Earth anchors. J. Ross Publishing.
Halpern, Y., Choi, Y., Horng, S. and Sontag, D., 2014. Using anchors to estimate clinical state
without labeled data. In AMIA Annual Symposium Proceedings (Vol. 2014, p. 606). American
Medical Informatics Association.
Kato, H., Onda, Y. and Teramage, M., 2012. Depth distribution of 137Cs, 134Cs, and 131I in
soil profile after Fukushima Dai-ichi Nuclear Power Plant Accident. Journal of environmental
radioactivity, 111, pp.59-64.
Kravchenko, A.N. and Robertson, G.P., 2011. Whole-profile soil carbon stocks: The danger of
assuming too much from analyses of too little. Soil Science Society of America Journal, 75(1),
pp.235-240.
Long, P.D. and Vietnam, V.W., 2010. Piled raft—a cost-effective foundation method for high-
rises. Geotechnical Engineering, 41(1), p.149.
Lovisa, J., Shukla, S.K. and Sivakugan, N., 2010. Behaviour of prestressed geotextile-reinforced
sand bed supporting a loaded circular footing. Geotextiles and Geomembranes, 28(1), pp.23-32.

Construction Methods 26
Rose, P., Boguslawski, M. and Denz, C., 2012. Nonlinear lattice structures based on families of
complex nondiffracting beams. New Journal of Physics, 14(3), p.033018.