A Complete Guide On Construction Substructure
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Summary of Topics Building Substructure Functions Components Substages Types of foundation Keypoints
What is Substructure
The substructure or foundation is the part of the building that is built below the ground level and is hidden from view. The substructure is the first stage of the construction process. Substructure transfers the load of the superstructure to the ground beneath. Superstructure should be designed with proper technique because it assures the stability of the superstructure too.
FUNCTIONS OF SUBSTRUCTURE It provides stability to the structure as a whole
It distributes the loads from the superstructure from soil beneath Substructure is to support and anchor the superstructure safely into the Earth. It must be designed to accommodate both the form and layout of the superstructure.
COMPONENTS OF SUPERSTRUCTURE Foundations
Abutments
Retaining walls
Use of grouting
Use of semi-integral
Use of three-sided
methods for
and integral abutments,
precast wall culverts; use
improving foundation
with a single row of
of modular retaining
soil.
piles.
walls.
COMPONENTS OF SUPERSTRUCTURE Precast concrete
Piers:
sheeting
Bearings:
Goal is to prevent
It has been used as retaining
timber fender damage
Elastomeric, multi-
walls, wing walls, and
around piers from
components of the bridge
vessel collision.
abutment.
rotational, or isolation types.
Excavation
Levelling & P.C.C. for foundation
Substructure Stage R.C.C. for foundation
R.C.C. columns up to plinth level Backfilling of excavated earth
Excavation, Compaction & Levelling Substructure Stage
Excavation
Setting out of all columns should be carried out prior to excavation as per approved centreline drawings Proper Compaction of soil layer for foundation decreases settlement and prevents undesired accidents Compaction of soil improves shear strength and decreases soil permeability Foundation should always be placed on the levelled surface in order to uniformly distribute the loading into the ground and prevent uneven settlement Sometimes the surface is not levelled even after doing levelling activity. Hence, it is always recommended place P.C.C. in all footings
P.C.C. (Plain Cement Concrete) Substructure Stage
P.C.C. Casting
1.Main purpose of P.C.C. is to act as a levelled surface for footings and transfer the load evenly into the ground 2.Remove all the loose materials from the excavation pits and do the shuttering by planks and runners wherever possible 3.After concrete pouring the surface is to be rammed and finished smoothly
Levelling
Substructure Stage
Isolated Slope Footing
Isolated Footing Cober blocks should be placed above P.C.C. to prevent direct contact or reinforcement with the surface New shuttering material should be used while constructing footings Column reinforcement to be aligned vertically for proper transfer of loads into the footing Curing in footing should be carried out for a period of 7 days
Isolated Stepped Footing
Substructure Stage
Backfilling of Excavated Earth Recording initial ground level Approved samples should be used for backfilling. Big boulders are not advisable. Backfilling should be carried out in layers. The thickness of each layer should not exceed 300mm. Each layer should be properly compacted before starting backfilling of the second layer. Required watering, compaction should be done. While compacting due care should be taken to protect foundations, columns, plinth walls, etc. which have been already constructed. Trained operators or skilled labor shall be engaged for backfilling.
Types Of Foundation 1. Open Foundation 2. Shallow Foundation Types of shallow foundation 1.Stepped Foundation 2.Combined Foundation 3.Raft Foundation 3.Deep Foundation
Open Foundation
Types of foundation
This is simply a layer of foundation concrete provided at the base of a column, pedestal, or wall. This type of foundation is provided when a hard stratum is available at a very shallow depth or the work is unimportant e.g. Compound wall, pillars for barbed wire fencing, etc.
Shallow Foundation
Types of foundation
When the foundation is placed immediately below the lowermost part of the structure it is called a shallow foundation. It can also be defined as, when the depth of foundation is less than or less than equal to the width
Deep Foundation
Types of foundation
When the depth of foundation is more than its width the foundation is called a deep foundation. If the depth of foundation is more than 2.00 m, it is called a deep foundation.
Keypoints
Before commencement of project work make sure the site is clear. There are no trees, plants, bigger stones, etc. Roads should be wide so as to allow the truck for loading and unloading construction material. If the site ground is uneven it should be made plain. Substructure Construction should be preferably completed before the rainy season
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