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5.2 Basement construction methods - Coggle Diagram
5.2 Basement construction methods
Bottom-up method
Uses
Conventionally used in buildings with an underground basement
info
Also known as cut and cover method
Excavation carried out to the formation level
Basement constructed upward from formation level
Sequences
For basement construction
1.Excavate and strut until formation level
2.Construct from bottom up
3.Backfill
For underpass construction
1.Construct diaphragm wall or temp support wall
2.Drive king posts
3.Excavate top soil
4.Install struts and working platform
5.Excavate and install struts until final level
6.Construct base/top slab structure
7.Remove temp supports and working platform
Advantages
It is a conventional construction method well understood by contractors.
Waterproofing can be applied to the outside surface of the structure.
The inside of the excavation is easily accessible for the construction equipment and the delivery, storage and placement of materials.
Drainage systems can be installed outside the structure to water or divert it away from the structure.
Disadvantages
Somewhat larger footprint required for construction than for top-down construction.
The ground surface cannot be restored to its final condition until construction is complete.
Requires temporary support or relocation of utilities.
May require dewatering that could have adverse effects on surrounding infrastructure
Top-down method
Uses
Suitable for the gigantic projects with limited construction time and/or with site constraints.
Tall buildings with deep basements and underground structures such as car parks, underpasses and subway stations.
Sequence
1.Construct ERSS (usually D-Wall).
2.Install foundation bored piles to support the building load
3.Install steel H-piles (Plunge-in columns) by inserting them into the bored piles.
4.Plunge-in columns are structural columns formed before basement excavation. (The exposed H-piles will be encased in concrete to form columns)
5.Construct ground floor slab and beams with openings for machinery and removal of spoil.
6.Proceed to the first stage of excavation.
7.Cast the floor slab of first basement level with the openings.
Proceed to the second stage of excavation; cast the floor slab of the second basement level.
8.Repeat the same procedure until the desired depth is reached.
9.Construct the foundation slab. Complete the basement.
10.When the formation level is reached, construct pile caps, ground beams etc. excavation as the slabs act as the permanent horizontal supports.
11.Excavation proceeds without the need for strutting to support the
12.Keep constructing the superstructure until it gets finished.
Advantages
Shortened construction period due to simultaneous construction.
It is highly suitable for construction for tall buildings with deep basements to be constructed in urban areas.
These can be installed in close proximity to existing structure with minimal loss of support to existing foundations.
More operational space gained from advanced construction of floor slabs.
Disadvantages
Higher cost.
The lateral displacement of retaining wall or ground settlement may be possible.
The construction quality may be influenced.
It requires highly skilled supervision and labor force.
Geotechnical Instrumentation for monitoring of Soil Movement
Inclinometers
Info
Inclinometers are used to measure the subsurface lateral displacement of soil or rock.
The probe is then pulled up while the inclination information of the probe in two orthogonal planes is registered at certain intervals. Inclinometers – to monitor lateral ground movements
From this information, profiles of the borehole in the two planes can be derived and reviewed graphically.
The lateral displacements of the borehole can be determined by comparing the measured profiles of the borehole obtained at different times.
Boreholes of up to 200 m in depth can be measured using inclinometers.
An electrical probe is usually lowered through a guide casing to the base of a near vertical borehole.
Applications
Monitoring slopes and landslides to detect zones of movement and establish
whether movement is constant, accelerating, or responding to remedial measures.
Monitoring diaphragm walls and sheet piles to check that deflections are within design limits, that struts and
anchors are performing as expected, and that adjacent buildings are not affected by ground movements.
Monitoring the effects of tunneling operations to ensure that adjacent structures are not damaged by ground movements.
Water Standpipes
Uses
Monitor ground water level
Applications
monitoring pore-water pressure to determine stability of slopes and embankments
monitoring the effectiveness of dewatering schemes
monitoring seepage and ground water movements in embankments, landfill dykes and dams.
Sequence
Ground water level is measured by using water level indicator. The probe of water level indicator is lowered down into the water standpipe until light or buzzer indicates contact with the water. Depth to water level is measured from the measuring tape attached to the indicator.
Pneumatic piezometer
Uses
to monitor ground water pressure
Sequence
1.Lower piezometer tip and put in sand fill
2.Then bentonite seal is placed
3.Additional backfill material is placed
Tilt meter
Uses
Tiltmeters are used to monitor changes in the inclination of a structure. They can provide an accurate history of movement and early warning of potential structural damage.
Applications
monitoring the inclination/rotation of retaining walls, piers and piles.
monitoring the behaviour of structures under load,
documenting effects of nearby excavations and providing early warning
of potential damage.
to provide warning of potential structural damage
Settlement Markers
to monitor vertical ground movement when measured against a known datum