This document provides information on trench and excavation safety. It defines excavation and trenching, and outlines various safety methods like sloping, benching, shoring and shielding based on soil type. It discusses hazards like cave-ins, underground utilities, hazardous atmospheres, and recommends practices like atmospheric testing, protective systems, and inspections to ensure worker safety during excavation work.

1. A Report On Trench & Excavation
Safety
SH16030 & SH16031 | PGP-HSEM

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A REPORT ON TRENCH AND EXCAVATION SAFETY
INTRODUCTION
Excavation and trenching are among the most hazardous construction operations. It
is generally used for foundation purpose, laying down sewer lines, electrical lines,
phone lines, etc. So while performing this activity safety precautions needs to be
taken because it can cause harm to life of worker and property as well. Most of the
times the accident is happened because of cave-ins which may sometimes leads to
death of worker.
Definitions
Excavation – Any man made cut, cavity, trench or depression made in the earth’s
surface formed by earth removal.
Trench – A narrow excavation made below ground surface.
In general, the depth is greater than width, but the width is no greater than 15 feet.
Shoring – A structure such as a metal hydraulic, mechanical or timber system that
supports the side of excavation and designed to prevent cave-ins.
Shield - A structure able to withstand a cave-in and protect employees
Sloping - A technique that employs a specific angle of incline on the sides of the
excavation. The angle varies based on assessment of impacting site factors
METHODOLOGY
The extent of soil and rock strata is found by making trial pits in the construction
site. The excavation and depth is decided according to the following guidelines in
the site
i. For Isolated footing the depth to be one and half times the width of the foundation

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A REPORT ON TRENCH AND EXCAVATION SAFETY
ii. For adjacent footings with clear spacing less than twice the width (i.e.) one and
half times the length
iii. 1.5m in general and 3.5 m in black cotton soils.
Setting out or ground tracing is the process of laying down the excavation lines and
centre lines etc. on the ground before the excavation is started. The centre line ofthe
longest outer wall of the building is marked on the ground by stretching a string
between wooden or mild steel pegs. Each peg may be projected about 25 to 50 mm
form the ground level and 2m from the edge of the excavation. The boundary is
marked with the chalk powder. Similarly, outer lines ofthe foundation trench ofeach
cross walls and are set out
Removal of Excess Soil
Estimate the excavated stuff to be re-utilized in filling, gardening, preparing roads,
etc. As far as possible try to carry excavation and filling simultaneously to avoid
double handling. Select and stack the required material in such a place that it should
not obstruct other construction activities. The excess or unwanted material should
immediately be carried away and disposed off by employing any of the following
methods.
 Departmental labour.
 Tractor.
 Trucks.
QUALITY CHECKS FOR EXCAVATION
 Recording initial ground level and check size of bottom.
 Disposal of unsuitable material for filling.
 Stacking suitable material for backfilling to avoid double handling.
 Strata classification approval by competent authority.
 Necessary safety measures observed.

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A REPORT ON TRENCH AND EXCAVATION SAFETY
QUALITY CHECKS FOR FILLING
 Recording initial ground level
 Sample is approved for back filling.
 Necessary marking/ reference points are established for final level of backfilling.
 Back filling is being carried out in layers (15cm to 20cm).
 Required watering, compaction is done.
 Required density is achieved.
EXCAVATION HAZARDS
 Soil collapse or cave-ins
 Underground utilities
 Hazardous atmosphere
 Stability of adjacent structures
 Falls / falling loads
 Access and egress
 Vehicle traffic and mobile equipment
 Water accumulation hazards
SOIL CLASSIFICATION
■ Stable rock;
■ Type A soil;
■ Type B soil;
■ Type C soil.

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A REPORT ON TRENCH AND EXCAVATION SAFETY
Stable Rock –
Natural solid mineral matter that can be excavated with vertical
sides and remain intact while exposed.
Type A –
Cohesive soils with an unconfined compressive strength of 1.5 tons
per square foot (tsf)(144 kPa) or greater.
Examples include: clay, silty clay, sandy clay, and clay loam. Certain conditions
preclude soil from being classified as Type A. Forexample, no soil is Type A if it is
fissured or has been previously disturbed.
Type B –
Includes cohesive soil with an unconfined compressive strength
greater than 0.5 tsf (48 kPa) but less than 1.5 tsf (144 kPa) and granular cohesion-
less soils (such as angular gravel, similar to crushed rock, silt, silt loam, sandyloam,
and, in some cases, silty clay loam and sandy clay loam).
Type C –
Cohesive soilwith an unconfined compressive strength of 0.5 tsf (48
kPa) or less, granular soils (including gravel, sand, and loamy sand), submerged soil
or soil from which water is freely seeping, submerged rock that is not stable, or
material in a sloped, layered system where the layers dip into the excavation or with
a slope of four horizontal to one vertical (4H:1V) or steeper.
PROTECTIVE SYSTEMS
■ Sloping and benching the sides of the excavation;
■ Supporting the sides of the excavation; or
■ Placing a shield between the side of the excavation and the work area.

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A REPORT ON TRENCH AND EXCAVATION SAFETY
I. Sloping system
Maximum allowable slope for excavation less than 20 feet
Soil type Height/depth Slope angle (degree)
Stable rock Vertical 90
Type A ¾ : 1 53
Type B 1 : 1 45
Type C 1½ :1 34
TYPE B SOIL

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A REPORT ON TRENCH AND EXCAVATION SAFETY
II. Benching system
 This method is applicable only for type A and type B soil.
 Two basic types of benching are used
a. Simple and
b. Multiple
 The type of soil determines the horizontal to vertical ratio of benched side
 As a general rule, the bottom vertical height of the trench must not exceed 4
feet (1.2 m) for the first bench. Subsequent benches may be up to maximum
of 5 feet (1.5 m) vertical in type A and 4 feet (1.2 m) in type B to total trench
depth of 20 feet.
 All subsequent benches must be below the maximum allowable slope for that
soil type.
 For the type B soil, the trench excavation is permitted in cohesive soil only.
TYPE C SOIL

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A REPORT ON TRENCH AND EXCAVATION SAFETY
III. Shoring system
 Shoring is the provision of support system for trench faces used to prevent
movement of soil, underground utilities, roadways, and foundations.
 Shoring or shielding is used when the location or depth of the cut makes
sloping back to the maximum allowable slope impractical.
 Shoring system consists of posts, wales, struts and sheets.
 There are two type of shoring available
a. Hydraulic shoring
b. Pneumatic shoring

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A REPORT ON TRENCH AND EXCAVATION SAFETY
 Hydraulic shoring
i. The trend todayis towards the use of hydraulic shoring, a prefabricated
strut and/or wale system manufactured of Al or steel.
ii. Hydraulic shoring provides a critical safety advantage over timber
shoring because workers don’t have to enter trench to install shoring.
iii. All shoring should be installed from the top-down and removed from
bottom-up.
 Pneumatic shoring
i. Works in similar manner to hydraulic shoring. The primary difference
is that pneumatic shoring uses air pressure in place of hydraulic
pressure.

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A REPORT ON TRENCH AND EXCAVATION SAFETY
IV. Shielding system
 They are different from shoring because instead of shoring up or otherwise
supporting the trench face they are intended primarily to protectworkers from
cave-ins and similar incidents.
 The excavated area between the outside of trench box and the face of trench
should be as small as possible.
 The spacebetween trench boxes and excavation side are backfilled to prevent
lateral movement of the box.
 Trench boxes are generally used in open areas but they also may used in
combination with sloping and benching.
 The box should extend at least 18 inches above surrounding area if there is
sloping towards excavation.
 This can be accomplished by providing a benched area adjacent to the box.
Fig. Trench Shields

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A REPORT ON TRENCH AND EXCAVATION SAFETY
Additional Hazards and Protections
In addition to cave-ins and related hazards, workers involved in excavation
work are exposed to hazards involving falling loads and mobile equipment.
To protect workers from these hazards, employers must take certain
precautions. For example, employers must:
■ Protect workers from excavated or other materials or equipment that could
pose a hazard by falling or rolling inside the excavation by placing and
keeping such materials or equipment at least 2 feet (0.61 meters) from the
edge and/or by using a retaining device to keep the materials or equipment
from falling or rolling into the excavation.
■ Provide a warning system (such as barricades, hand or mechanical signals,
or stop logs) when mobile equipment is operated adjacent to an excavation,
or when such equipment must approach the edge of an excavation, and the
operator does not have a clear and direct view of the edge.
■ Protect workers from loose rock or soil that could fall or roll from an
excavation face by scaling to remove loose material, installing protective
barricades at appropriate intervals, or using other equivalent forms of
protection.
■ Institute and enforce work rules prohibiting workers from working on faces
of sloped or benched excavations at levels above other workers unless the
workers at the lower levels are adequately protected from the hazards of
falling, rolling, or sliding material or equipment.
■ Institute and enforce work rules prohibiting workers from standing or
working under loads being handled by lifting or digging equipment.
■ Require workers to stand away from vehicles being loaded or unloaded to
protect them from being struck by any spillage or falling materials.
Water accumulation
Water in an excavation can undermine the sides of the excavation and make
it more difficult for workers to get out of the excavation.
Precautions can include special Trenching and Excavation Safety supportor
shield systems to prevent cave-ins, water removal to control the water level,
or the use of a safety harness and lifeline.

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A REPORT ON TRENCH AND EXCAVATION SAFETY
Hazardous atmosphere
Atmospheric testing is required before workers enter an excavation greater
than 4 feet (1.22 meters) in depth where an oxygen deficiency or a hazardous
atmosphere is present orcould reasonably be expected, suchas in excavations
in landfill areas orexcavations in areas where hazardous substances are stored
nearby.
If there are any hazardous conditions present, the employer must ensure that
adequate precautions are taken to prevent employee exposure to those
conditions.
Such precautions include providing workers with proper respiratory
protection or ventilation.
In addition, when controls are used to reduce the level of atmospheric
contaminants to acceptable levels, testing must be conducted as often as
necessary to ensure that the atmosphere remains safe.
Access and Egress
Worker generally enter into excavation by ladder. So separate ladders should
be provided for access and egress.
No worker shall move more than 15 feet in excavation area.
Trenches more than 4 feet in depth should be provided with fixed means of
egress.
Ladders must be secured and extended minimum of 36 inches above landing.
Metal ladders should beused with caution particularly when electrical utilities
are present.
Underground utilities
Such as sewer, water, gas lines, communication and electrical lines must be
identified and physically located.
If any utility line is passing through the excavation then first relocate it and
then give work permit for them.

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When to conduct site inspections?
i. After rain, competent personshould inspect the site before giving work
permit for further work, becausethere is chance of hazard due to water
seepage and loose soil.
ii. Daily and before start of each shift.
iii. When there is change in size, location or placement of the soil.
iv. When there is any indication of change or movement of adjacent
structures.
Checklist of excavation work

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CONCLUSION
When employers share the details of their safety and health programs with workers,
they should emphasize the critical role workers play in keeping the jobsite safe.
Employers also need to emphasize specific practices that will help reduce the risk of
on-the-job injuries at excavation sites. Such practices can include the following:
■ Know where underground utilities are located before digging.
■ Keep excavated soil (spoils) and other materials at least 2 feet (0.61 meters) from
trench edges.
■ Keep heavy equipment away from trench edges.
■ Identify any equipment or activities that could affect trench stability.
■ Test for atmospheric hazards such as low oxygen, hazardous fumes, and toxic
gases when workers are more than 4 feet deep.
■ Inspect trenches at the start of each shift.
■ Inspect trenches following a rainstorm or other water intrusion.
■ Inspect trenches after any occurrence that could have changed conditions in the
trench.
■ Do not work under suspended or raised loads and materials.
■ Ensure that personnel wear high-visibility or other suitable clothing when
exposed to vehicular traffic.
REFERENCES
1. IS 3764 : CODE OF SAFETY FOR EXCAVATION WORK
2. OSHA 2226 : TRENCHING AND EXCAVATION SAFETY
3. www.osha.gov
4. Google