May 29, 2022
Excavation

Excavation is process of digging, especially when something specific is being removed from the ground or for any foundation work.

File:Continued excavation of the Track A approach structure. (CH061A, 1-17-2018) (27989254549).jpg - Wikimedia Commons

Excavation Types

1.Common excavation

It includes the open excavation of all material, except snow and ice, as well as individual rock fragments, boulders and detached rock blocks having a volume of 1.5 m’ or less which can be removed by dozer, ripper, power shovel, dragline or by other mechanical equipment, except snow and ice.

2.Overburden tunneling

It is defined as underground excavation of unconsolidated overburden materials including boulders, regardless of size.Overburden tunneling may involve both the use of hand tools and mechanical equipment as well as drilling and blasting for the removal of or penetration through large boulders. It will generally require the use of steel support sets and lagging or shotcrete together with the use of forepoling for temporary support. It may also require the use of grouting and drainage holes to control water inflows.we should be very careful during excavation as there may be Perforated drainage pipes

3.Rock excavation

It includes the excavation of all rock mass which requires the use explosives to remove it from its original position.

4.Heading excavations

It is defined as an underground excavation which is performed with drilling parallel to the direction of advance.

5.Bench excavation

It is defined as that which is performed with vertical drillings.

6.A round

It is defined as a single cycle of drilling and blasting, including scaling, mucking and
moving of heavy equipment.

7.Forepoling

is defined as a support technique that may be employed in poor quality rock or overburden materials to create temporary arch action above the crown of an advancing tunnel.
The techniques involve drilling a fan of holes ahead of and over the crown of the advancing tunnel face and installing steel dowels, girders, channels and angles in theseholes.

All these act to restrain the movement of rock and soil materials into the advancing tunnel, helping to maintain a natural arch action and facilitating the installation of other temporary or permanent tunnel support.

what are excavation lines?

The minimum excavation line shown on the drawings defines the limit within which excavation must be completed.

No projection of unexcavated material can be left inside this limit. The pay line, shown on drawings, corresponds to the payment line for the excavation.

What is Controlled Perimeter Blasting?

“Controlled perimeter blasting” requires special drilling and blasting methods to produce
smooth rock faces conforming to the prescribed neat excavation lines and to minimize blasting-induced fractures in the rock outside the excavation lines.

These methods include presplitting, cushion blasting, smooth blasting and line drilling.
“Presplitting” consists of drilling a single row of closely spaced holes, loading all the holes
lightly and continuously, stemming the entire length of each hole and then firing them as a
completely separate operation before any adjoining main excavation area is blasted, to
produce a crack along the line of presplit holes to which a subsequent primary blast can
break.

Completion of blasting to remove the adjoining rock requires a burden/spacing ratio a reduced explosive charge in the line of holes nearest the presplit line and a limit on the distance between these lines.

How to do excavation planning?

Excavation Planning

The removal of overburden shall precede the rock excavation by at least 5 m.At least 15 days prior to commencement of rock excavation, Contractor shall submit for approval to client its detailed plan of proposed excavation methods and sequences, together with pertinent data for each specified area.However, the Contractor shall be entirely   responsible for the results of the excavation. Such data shall be furnished for all excavations as shown on the drawings or as required by client. Such data includes:

The location,

depth and area of blast; 

The diameter,

spacing,

depth,

pattern and inclination of blast holes;

The type, strength, amount, column load and distribution of explosives to be used per hole per delay and per blast;
The sequence and pattern of delays to be used per blast;The description and purpose of any special methods to be adopted by Contractor.The plans shall be in conformity with detailed requirements for excavation sequencing, for controlled perimeter blasting and for rock reinforcement, as described hereafter and as shownon the drawings.

No drilling or blasting shall be carried out in any area for which the plan has not been auuiüveu by client. If approval is withheld, a new plan in whole or in part shall be submitted by Contractor at least 48 hours before the beginning of drilling operations.

Generally, blasting within 30 m of concrete structures or grouted areas is permitted only after the concrete or grout is seven days old and only. after the submission by. Contractor,and approval by client,of a plan showing the relative positions of structures or grouted areas and the area to be blasted, and Contractor’s proposed drilling and blasting plan, together with a description of precautions to be taken. All completed work shall be protected by limiting thesize of blasts and by other protective means as deemed adequate by client.

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