CONSTRUCTION OF OPEN FOUNDATIONS

 

 CONSTRUCTION OF OPEN FOUNDATIONS

 

This item of work deals with construction of open foundations with approved materials as per the terms of contract agreement.

1. General

This item of work shall be dealt in compliance of the Technical specifications.
The construction shall confirm to the specific alignment, lines and grades given in the drawing.

The materials used shall adhere to the  technical specifications. The concrete used shall be of approved design mix

2. Procedure

Survey:

a) The location points were fixed by a Total station or a Theodolite from the established survey interfacing points.

b) The reference pillars will be fixed in such a way that they are not disturbed during the course of excavation.

Excavation:

a) Excavation will be done to the size of the foundation plus safe working area including necessary slopes as per site condition.

b) At some locations if the surface is below sub soil water level requires de watering, and then the same will be done by installing adequate capacity pumps. Necessary cofferdams and cribs shall be constructed and shall be removed after completion. All necessary sheeting, shoring, bracing if required shall be provided.

c) If hard rock is encountered while excavation, suitable procedures will be adapted like

1. Pneumatic breaking using compressor and pavement breakers

2. Wedge and hammer method i.e. drilling and splitting of rock

3. Control blasting and de mucking

Any one of the procedures will be adapted to suit the site conditions.

d) Excavation will be carried out to the required depth as per the foundation details given in the drawings and if there are any obstructions /hindrances are there in the course of the work then they will be immediately brought to the notice of the Engineer for their necessary instruction/action.

Surface dressing will be done before doing the PCC.

e) If Excavation done more than required depth, the extra depth of exaction should be filled with sand or by soil compacted in layers till it reaches the desired level of PCC.

 

PCC:

Marking will be given as per the drawing on dressed surface by using Total Station/ Theodolite.

Side shuttering should be provided of the required thickness and size of the footing plus offset for PCC

Required grade of concrete should be laid by using Transit Mixtures and chute. compaction should be done by hand rammer.

PCC of required thickness and grade will be laid on the dressed surface.

Reinforcement & Form Work:

Marking will be given as per the drawing over PCC by using Total Station/Theodolite

Bar Bending schedule should be prepared as per Drawing and IS1786.Fabrication of Reinforcement should be done as per the B.B.S.

Reinforcement will be tied over the PCC for footing and substructure as per the drawings and proper formwork will be fixed to suit the requirement and as per drawings.

 

Concreting:

Concreting shall be done either by  concrete pump or manually whichever suits the situation and grade of concrete will be maintained as per drawings.

3. Major Equipments and Machinery

1. Poclain/ JCB
2. Total Station/ Theodolite with accessories
3. Auto level with accessories
4. Measuring tape
5. Concrete pump
6. Transit Mixers as required
7. Needle Vibrators
8. Cube Moulds.

4. Tolerance

1. Variation in dimensions                                                  :     +50mm -10mm
2. Misplacement from specified position in plan                :     15mm
3. Surface irregularities measured with 3m straight edge   :    +5mm

      4.  Variation of levels at the top                                           : +-10mm.