Basement Construction Methods Comparison

The assignment content discusses different basement construction methods, including open cut, vertical cut, and top-down methods. Each method has its advantages and disadvantages. The open cut method is suitable for shallow basements with a low budget, while the vertical cut method requires perimeter walls and temporary props but can be used for small to medium-scale basements. The top-down method starts from the top and builds down, requiring complex support construction and high budgets. The content also covers excavation lateral support systems, including sheet pile walls, diaphragm walls, and secant piling. Each system has its advantages and disadvantages. Finally, the assignment provides a cost comparison of different foundation systems, including pad footing, raft footing, strip footing, and diaphragm wall.

BASEMENT CONSTRUCTION METHODS:
Open cut basement construction method:
This method is applied for shallow basement which need to be excavated with sloping side. The
form is considered to be economical because foundation wall is not necessary in this case. The
angle of slope and the area of ground will be distinguished based on design, analysis and
evaluation result.
Advantages:
 Low budget
 Save construction time for shallow basement
 High quality
 No lateral support
Disadvantages:
 Not able to use for deep basement.
 Require large space during construction process
 High risk of collapsing in high moisture content or flowing water
Application:
 Cohesive soil, less prone
 Small scale of basement
Vertical cut construction method:
Bracing excavation method is another name of this method. Unlike Open cut method, vertical cut
requires perimeter wall around the area being excavated. On another hand, perimeter wall is able
to replace by secant piling, diaphragm walling and steel piling. During construction process,
temporary braces and props have to be a part of system to maintain the walls.
Advantages:
 Minimize the excavation area
 Keep the side of deep excavation stable
 The effect of the flow groundwater is reduced
Disadvantages:
 Not able to use for large scale of basement
 Require temporary system
 Require supporting perimeter wall
 High budget
Application:
 Small to medium scale basement

 Type of soil depend on perimeter wall.
Top down construction method:
Construction of this begins from the top to the bottom of excavation and the first slab is
completed before starting superstructure construction. Constructing slab after each stage of
excavation, hence, slabs are considered as strut in holding earth pressure. The process of
construction is: retaining wall construction and pile construction under column of superstructure;
applying formwork and placing columns on piles for the 1st slab at the top, then, other slabs
would be built after each excavation.
Advantages:
 Short time for construction
 Construction area safer as slabs are stronger than struts
 Low risk of ground movement
 Reduce the effect of bad weather
Disadvantages:
 High budget
 Require complex support construction
 Require lighting and ventilation
 Restrict the access of material handling.
Application:
 Very large scale and complex basement.
 Soil nail
EXAVATION LATERAL SUPPORT SYSTEM:
Sheet pile wall:
Sheeting pile wall is retaining wall that constructed to retain earth, water and any other filling
material. There are 2 type of materials. One is steel pile which is U or Z shape and 12m long.
And another one is reinforce concrete pile which is heavy and bulky. Vibration, pressing
excavation are three method installing sheet pile wall.
Advantage of steel sheeting pile wall:
 Easy to storage and light weight
 Provides high resistance to driving stresses
 Able to be reused on various project
 Long service life above or below water

 Easy to adapt the pile length
 Joints are less apt to deform during driving.
Disadvantages:
 Sections can rarely be used as part of the permanent structure.
 Installation of sheet piles is difficult in soils with boulders or cobbles. In such cases, the
desired wall depths may not be reached.
 Excavation shapes are dictated by the sheet pile section and interlocking elements.
 Sheet pile driving may cause neighbourhood disturbance
 Settlements in adjacent properties may take place due to installation vibrations
 High budget.
Application:
 Water front structures, i.e. in building wharfs, quays and piers.
 Building diversion dams, such as cofferdams
 River bank protection
 Retaining the sides of cuts made in earth.
Diaphragm wall:
Diaphragm wall is a reinforced concrete structure constructed in-sity panel by panel. The wall is
usually designed to reach very great depth, sometimes up to 50m, mechanical excavating
method is applied.
Advantages:
 Can be used as permanent structural wall
 Water retainable
 Can be installed to deeper depths and for load bearing element
 Less temporary propping needed
 Can be applied for top-down construction method
 Rigid structure so that ground movement induced by basement excavation is less than
other flexible retaining wall
 Vibration and noise generated from installation of diaphragm wall is less than other
methods
Disadvantages:
 Large site area and limit headroom
 High cost for mobilization.
Secant piling:
The secant pile uses The secant pile uses concrete of different strengths for a series of piles that
overlap each other, creating a sealed wall face. The primary piles are made with unreinforced
concrete. They are driven first. After they have been allowed to set, they drill for the reinforced
concrete piles, or secondary pile, by drilling into a portion of the primary pile.
Advantages:

 Increased construction alignment flexibility to fit complex site boundaries, maximising
land use.
 Increased wall stiffness compared to sheet piles. Reducing the risk of adjacent ground
movements.
 Suit difficult ground (cobbles/boulders) and confined site space.
 Minimal vibration and low noise.
Disadvantages:
 Difficulty in joint and verticality control
 Lower reinforcement efficiency
 Higher cost compared to sheet piles and slow operation
For construction process, please use
Basement construction method: Vertical cut
Excavation lateral support system: sheet pile wall
Foundation: raft foundation
Cost comparison: here is example of that
Foundation System
Pad footing Simple and most cost
effective
Raft footing Economic due to
combining
foundation and floor
slab
Foundation required
less than others
leading to decrease
resources / labor /
cost
Strip footing Low cost – long
service life

Excavation Lateral
Support System
Sheet pile Unit cost $40 UC-50
Unit cost $50 UC-75
Expensive and
imported
Skilled person
needed for carrying
out installations
(increase cost)
Diaphragm wall Price N/A
Low cost and speed
construction for
temporary and
permanent soil
support
Carry structural load
– foundation cost
reduction
High mobility cost
Construction
component
Vertical cut It has no actual cost
arraignment leading
to the most cost
efficient strategy for
basement
construction cost
Top down It has one of the
highest cost for
excavation and faster
construction leads to
faster completion
Cost increase due to
ELSS support
requirements
Economical for multi
level basements
Open cut Best economical
choice for
minimization of
operation and
equipment leading to
lower cost
Increase of
excavation leads to
economical problems