Basement Construction

-


Basement Construction


In the general context of building a basement can be defined as a storey which is below the ground storey and is there for constructed below ground level. 
Basements are common in tall buildings as car parks, storage of services and underground shopping centres. The term “basement” has been regarded as synonymous to the term “deep pit”, which applies to excavations over 4.5 m deep.

The main purpose of constructing basements are:
  •  to provide additional space,
  •  as a form of buoyancy raft,
  •  in some cases, basements may be needed for reducing net bearing pressure by the removal of the soil.

Basement can be classified into three groups:

Types of basement


Basement can be constructed by following method:

  1. Open cut method.
  2. Cut and cover method.
  3. Top down method.

Open Cut Method

This is the simplest and most straight forward technique of providing an excavation to the required depth. The sides of the excavation are sloped to provide stability, with possible slope protection to maximize the angle of the slope. Upon excavating to the required depth, the basement is constructed from bottom upwards. After the completion of the basement, the remaining excavated areas between the basement and the side slope are back filled.
Open Cut Method

Cut and Cover Method

This technique is usually employed in constrained sites where ground movements to the adjacent surrounding has to be kept to the minimum. Retaining walls are required to support the excavation with the provision of bracing as the excavation proceeds downward until the deepest basement level. The basement is then constructed in the conventional way, bottom upwards in sequence with removal of the temporary struts.
Cut and Cover Method

Top Down Method

Similar to the cut and cover technique, permanent perimeter walls are first constructed. Prefounded columns are then constructed, followed by the construction of the ground floor slab. Prefounded columns are structural columns/piles formed before basement excavation. Boreholes are formed to the hard strata. Steel stanchion/H-sections are inserted and concrete pumped in to slightly over the lowest basement slab level. The holes are then backfilled with soil. This lower part of the stanchions embedded in concrete will later form the integral part of the foundation for the structure. The upper part of the stanchions not embedded in concrete serves as the column supports for the subsequent basement floors. Excavation then proceeds downward and basement slabs are constructed while construction of the superstructure proceeds simultaneously.

Top Down Method
If you have any doubt or correction please command  



Comments

Post a Comment

Popular posts from this blog

Dewatering Methods - Groundwater Control

-
Image
Groundwater Control When rainwater collects in surface depressions, it is called surface water; when it percolates down into the permeable subsoil and collects in tiny soil voids, it is called groundwater; the upper surface of the groundwater is called the water table. Following some problems of water in the subsoil effect the construction work: A high water table could cause flooding during wet periods. Subsoil water can cause problems during excavation work by its natural tendency to flow into the voids create by the excavation activities. It can cause an unacceptable humidity level around finished buildings and structures. Civil engineers are must restrict the major problems of ground water and keep the excavation to safe. Therefore, they introduce many dewatering methods for controlling the ground water.These methods can be classified into two groups: Permanent exclusion of groundwater Temporary exclusion of groundwater Permanent Exclusion of Groundwater This c...
Read more

Bentonite Slurry

-
Image
Bentonite Slurry in Civil Engineering Bentonite is a controlled mixture of fullers earth and water which produces a slurry or mud which has thixotrapic properties(ie. as the material is placed under stress to flow). When placed in the borehole it exerts a pressure in excess of earth and hydro-static pressure present on side of excavation. This also finds its application in the construction of special foundations for digging diaphragm walls and bored piles. Bentonite is implemented for self-hardening mixtures which are then resorted to build cut off walls, grouting mortars, and grouting. Finally, bentonite waterproofing properties are best exploited in environmental engineering, to seal off soil infiltration, and line the base of landfills. Bentonite is a kind of clay which has an ability to swell and gel when it is dispersed in water. This is used in construction mainly in excavation and foundation works. Bentonite contains more than 85% clay mineral, montmorillonite, a...
Read more