Trenching & Excavation

Diffrent Methods and Equipments used in Trenching and Excavation

1. TRENCHING & EXCAVATION Shivananda roy b.TECH, M.TECH, AMIE

2. Trenching Trenching is a construction method that involves digging a trench in the ground to install, maintain or inspect pipes, conduits or cables underground. When the installation of the pipe, conduit or cable is completed, the trench is backfilled and disturbed grounds are returned to their original state, insofar as possible . The main methods of the execution of trenches are:  1. Conventional methods: excavators +/- rock breakers  2. Drill & Blast   3. Trenching

3. DIFFERENCE BETWEEN EXCAVATION AND TRENCHING EXCAVATION An excavation is any opening or depression in the earth’s surface. It can be as narrow as a backhoe bucket or as wide as an open pit mine. All excavations are man­made and have unsupported walls of earth or rock as its borders . TRENCH An excavation in which material removal forms a narrow opening in the ground. Unlike large excavations, a trench is generally deeper than it is wide. OSHA considers an excavation to be a trench if it is 15 feet wide or less at the bottom of the excavation. All trenches are excavations, but not all excavations are trenches.

4. METHOD OF TRENCHING DRILL & BLAST HYDRAULIC ROCK BREAKERS AND BACKHOES (+/- RIPPING) CHAIN TRENCHERS Application   In very strong, abrasive, massive rock. Not suitable for rock masses composed of small, loose blocks. Relatively easy to set up and execute. Backhoes and dump trucks required to remove blasted material. Particularly useful on steep slopes. Application   In rock masses composed of small, loose blocks. Not suitable in very strong, abrasive, massive rock. Easy to set up but can be very time consuming. Useful for tight curves. Useful where the ground changes from soil to rock over short distances. Application   In weak to strong rocks. Generally not economic in very strong, abrasive, massive rock. Unsuitable for rock masses containing loose cobbles and boulders or those containing pockets of wet clay. Larger machines require considerable lateral working space and operate most efficiently over long distances in relatively h omogeneous rocks. Excavation effects   Significant over-excavation effect. Very irregular, possibly unstable trench walls and floor. Sidecast spoil causes ecological damage and increases risk of sediment release to watercourses. Alternatively, spoil transported to temporary or permanent disposal sites. Excavation effects Moderate over-excavation. Irregular trench walls and floor. Sidecast spoil may cause ecological damage locally . Some spoil may have to be transported to temporary or permanent disposal sites . Excavation effects   Minimal over-excavation. Regular trench walls and floor. Spoil is deposited in a continuous windrow alongside the trench. Where space is limited, spoil must be discharged to dump trucks and transported to temporary sites for processing: no sidecast spoil. Security Issues   Potential restrictions on use of explosives. Cannot be used in built-up areas or in proximity to utilities, structures and other pipelines . Security Issues   Suitable for use in built up areas or in proximity to utilities, structures and other pipelines     Security Issues   Smaller machines. Suitable for use in built-up areas or in proximity to utilities, structures and other pipelines .

5. SELECTION OF TRENCHING METHOD Examples of rock type Appropriate trenching method Chain trencher tooth Wear Potential Reuse of spoil Limestone Chain trencher Moderate Good to fair Dolomite Chain trencher Moderate Good to fair Sandstone Chain trencher Moderate - Severe Fair Basalt Gneiss Chain trencher ( may need hydraulic breaker for high spots) Severe Fair to minimal Granite Andesite Hydraulic breaker + Backhoe Blasting . (Note : Chain trencher economically marginal) Extreme Fair to minimal Chert Ryolithe Hydraulic breaker + Backhoe. Blasting Does not apply Minimal to zero

6. PARTS OF A TRENCH WALL: ( FACE, SIDES) The sides of the trench . BOTTOM: ( BASE, FLOOR) The bottom of the trench . SPOIL: The pile of excavated earth that was removed to form the trench. The leading edge of this pile is called the TOE . SURCHARGE LOAD : Any weight on top of the surface of the soil, which would add extra stress to the walls of the trench. Spoil piles, backhoes, rocks, vehicles, buildings, or other loads placed near the trench opening would be surcharge loads . BEDDING: A material that is usually placed around a pipe prior to backfilling. In most cases, bedding is gravel, sand, or fine crushed rock, and it extends from 5 inches below the pipe to 6 inches above the pipe.

7. SHAPE OF THE TRENCH The shape of a trench is determined by: Purpose of the trench The type of soil the trench is being dug in T he size of pipe or conduit that is going into the trench Availability of shielding or shoring Location of buildings, utilities, etc. Location of the trench (roadway, open field, etc.); Conduit loading requirements.

8. SHAPE OF THE TRENCH STRAIGHT TRENCH A trench where the sides are parallel and at right angles to the base. Straight trenches are usually used in areas where there is limited surface area to disturb, such as a roadway or near buildings. Protection systems such as shoring or trench boxes would be required . SLOPED TRENCH A trench where the sides have been angled to prevent cave in. The angle of the slope is determined by the soil type, trench depth, and in some cases, the time that the trench will remain open.

9. SHAPE OF THE TRENCH BENCHED TRENCH A trench where the sides have been cut away to form steps. Vertical distances (height of step) are determined by soil type. Multiple bench or single bench systems can be used BELL­BOTTOM PIER HOLE A trench which is usually used in footing placement. Its top is usually narrower than its bottom, thus giving it a bell shape in cross-section. With the sides sloping inward over the floor of the hole, the possibility of collapse is much greater than in other styles of trenches. Additional protection systems are required for those who work in this type of excavation.

10. TRENCHERS Trenchers or Trenching machines are used to excavate trenches in soil. These trenches are generally used for pipeline laying, cable laying, drainage purposes etc. Trenching machines are available in two types namely chain trenchers and wheeled trenchers. Chain trenchers contains a fixed long arm around which digging chain is provided. Wheeled trenchers contains a metal wheel with digging tooth around it. To excavate hard soil layers, wheeled trenchers are more suitable. Both types of trenchers are available in tracked as well as wheeled vehicle forms

11. EXCAVATORS Excavators are heavy construction equipment consisting of a boom, dipper (or stick), bucket and cab on a rotating platform known as the "house ". The house sits atop an undercarriage with tracks or wheels. All movement and functions of a hydraulic excavator are accomplished through the use of hydraulic fluid, with hydraulic cylinders and hydraulic motors. Due to the linear actuation of hydraulic cylinders, their mode of operation is fundamentally different from cable-operated excavators which use winches and steel ropes to accomplish the movements .

12. Usage Digging of trenches, holes, foundations Material handling Brush cutting with hydraulic saw and mower attachments Forestry work Forestry mulching Construction Demolition with hydraulic claw, cutter and breaker attachments General grading/landscaping Mining, especially, but not only open-pit mining River dredging Driving piles, in conjunction with a pile driver Drilling shafts for footings and rock blasting, by use of an auger or hydraulic drill attachment Snow removal with snowplow and snow blower attachments

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