Excavation Safety

Excavation

Is any man made cut, cavity or depression in an earth surface that is formed by earth removal

112%

The fatality rate for excavation work is ________ higher than the rate for general construction

Trench excavation

Is a narrow excavation where the depth of a trench is greater than its width, and the width measured at the bottom is not greater than 15 ft

5 ft (1.5m)

Trenches _________ deep or greater require a protective system, unless if the excavation is my entirely of stable rock. If less than ______, no protective system required.

20 ft (6.1m)

Trenches _________ or deeper required a protective system designed by a registered professional engineer.

• Pre-planning

• Protective systems

• Safety measures

• Inspections

Eliminate hazards and control risks by implementing precautions in excavations and trenches with:

Hazards of excavation work

• Soil collapse

• Falling objects

• Underground utilities

• Working surfaces

• Confined space conditions

Soil

Is a mixture of rock, water, air and a variety of other substances

Voids

Soil is made up of rock in the form of small particles and spaced called _______.

Normally, some parts of the ______ are filled with water.

Types of soil collapse

• Sliding

• Bulge

• Toppling

• Boiling

• Heave

Sliding

Soil shifts downwards along a slip plane, often caused by excessive loading or water saturation weakening the soil structure.

Bulge

Soil deforms outward, creating a protruding area, typically due to internal pressure or lateral forces from excavation or nearby construction.

Toppling

Soil or rock tips over around a pivot point, commonly caused by undercutting or destabilizing forces at the base.

Boiling

Soil is displaced upward due to water pressure, often caused by high groundwater pressure or rapid infiltration disrupting soil stability.

Heave

Soil rises and expands, usually due to moisture changes such as sweating and drying cycles or freezing and thawing, which affect soil volume.

Undercutting

Principal causes of soil collapse

• Steep cutting angle

• Super imposed load

• Shock and vibration

• Water pressure

• Drying

Excavation

In general, ______ means loosening and taking out materials, living space above or below ground.

Earthworks phase

In civil engineering, this is usually performed during the ____________.

Level of risk for collapsing

Corresponding safety measures

Each type of soil has a certain ___________, and _____________.

Stable rock

Natural solid mineral matters

• Examples are rock, hilly terrain

Type A

Cohesive soil with unconfined compressive strength of 1.5 tons per square foot or greater

• Examples are clay, silt, sandy clay

Type B

Cohesive soil with strength greater than 0.5 tsf but less than 1.5 tsf

• Examples are angular gravel (similar to crushed rock)

Type C

Cohesive soil strength 0.5 tsf or less

• Examples are granular soil such as grave, sand and loamy sand

Vertical ; 90

Max Slope of stable rock (H:V)

¾ : 1; 53°

Max slope of Type A

1:1; 45°

Max slope of Type B

1- ½ : 1; 34°

Max slope of type C

Shoring

This involves the use of supports or structures to prevent the collapse of soil and provides the ability to excavation sites

• Hydraulic shoring

• Metal shoring

• Adjustable shoring

Shoring systems can include:

Hydraulic shoring

Uses hydraulic pressure to support the excavation walls. This type can be adjusted as needed and is often used in deeper excavations.

Metal shoring

Uses steel plates and beams to provide support. It's durable and can be used in a variety of soil conditions.

Adjustable shoring

Consists of adjustable props and struts that can be modified to accommodate changes in the excavation depth

Timbering

This is an older method where wooden planks and beams are used to support the sides of an excavation.

• Timber sheeting

• Timber bracing

Timbering involves:

Timber sheeting

Wooden planks are placed vertically against the excavation walls to prevent soil from collapsing.

Timber bracing

Wooden beams are used to brace and support the timber sheeting or excavation walls.

5 cm x 15 cm

Sheeting

10 cm x 15 cm

Wales

10 cm x 15 cm

Struts

OSHS RULE 1413: EXCAVATION

• Before shoring or timbering, the walls of an excavation shall be stripped of loose rocks or other materials that might slide, roll, or fall on workers.

• Every excavation over 1 m shall be kept free of water at all times.

1 m deep

Excavation over __________ shall be supported by adequate shoring and timbering. This shall not apply to such excavation if:

• A worker is not required to enter for any purpose

• Cut in solid rock

• Walls are sloped to 45° from the vertical or cut to the angle of repose.

6.1 m

Shoring or timbering in excavation over ________ deep shall be designed by a structural engineer and approved by the proper authority.

Shielding/boxing

• Refers to the use of protective systems designed to safeguard workers and equipment from the risks associated with soil collapse during excavation activities. Unlike shoring and timbering, which actively support and stabilize the excavation walls, ______ involves creating a protective barrier to prevent soil from falling into the excavation area.

Berms

A safe distance from the edge of excavation. Are constructed in order to prevent erosion and sedimentation, and in some cases as a means to provide for a safe working environment during excavation by controlling surface runoff.

Minimum berm

Not less than 1/3 of depth of excavation

• Materials being excavated are stable

• Shoring to carry the additional load

• Barriers are provided to prevent rollback of excavated material

A berm of reduced width of not less than 1 m may be allowed if:

Prevention of falling materials

• Barricades should be provided

• Signs must be posted to prevent the public from going near the excavation

1 m

Provision for barricades

• The top of the walls of an excavation more than 2 m deep shall be barricated to a height of at least_____.

Prevention of fall: surface crossing of trenches

• Walkways or bridges must be provided

• Minimum clear width of 20 in.

• With standard rails

• Extended a minimum of 24 in. past the surface edge

Working surface

• Excavation shall be kept free of water at all times

• In muddy areas, workers should be provided with boots to reduce the hazard of slipping

Underground facilities

• Determine the location of underground facilities and take necessary steps to prevent damage to these facilities

Groundwater

Causes extreme geotechnical problems in excavations such as sand running for most of construction projects such as tunneling

Two major methods for controlling groundwater

Pumping technique

Exclusion technique

Pumping technique

Involves digging a sump where groundwater collects, which is then simply drawn out using a pump

Exclusion technique

Achieved by constructing an impermeable or low permeability cut off wall to keep the groundwater out of the excavation

Groundwater control

Less than 19.5% oxygen

Oxygen deficient atmosphere

• Natural gases from potential leaks or cut lines

• Methane from decayed matter

Potential for other gases to be present include but not limited to:

4 ft deep or greater

Test for atmospheric hazards like low oxygen levels and presence of hazardous fumes and toxic gases is required when the excavation is ________

Working in excavation

Prior to opening

• Check excavation permit

• Protect all underground installations

• Remove trees, boulders, stump add other surface emcumbrances and hazards before starting excavation.

Working in excavation

During operations

• Wear goggles and hard hats

• Store excavated materials at least 1 m from edge

• Remove boulders or other materials that may roll

• Do not stockpiles materials or store equipment near edge or excavation

• Give special attention to side slops, adversely affected by weather, moisture content or vibration

• In case of undercut, safely support overhanging materials

• Safe working distance between workers

• Control groundwater

• Provide walkways, bridges, guardrails, barricades, warning flags/lights for pedestrian and vehicular traffic

Working on excavation

Equipment operations

• Shore and brace sides of excavation to resist superimposed loads if necessary to operate equipment above or near excavation

• Use stop logs, warning signs, or barricades if mobile equipment is utilized adjacent to excavations

• Use horn or give signals to ensure safety

Working in excavation

Excavation and confined space

• Check the atmosphere condition before entry

• Do not work alone in a confined space

• Provide lifeline

• Provide ventilation or blower before entering

• Provide emergency rescue equipment such as breathing apparatus, safety harness line, and basket stretcher

Working in excavation

• During break time, workmen should never stand or take rest on high banks of soft material

• Maintain guard rails, fences, or other barricades and warning lights from sunset to sundown

• Do not leave tools, materials, or debris in walkway ramps or near the edge of excavation

• Do not use guard rails as resting place

Competent person

An individual who is capable of identifying existing predictable hazards or working conditions that are unsanitary or dangerous (eg safety officers)

Inspection

• Daily, before start of each shift:

Every part of an excavation over 2 m deep where workers work shall be inspected by the person in charge at least once a day

This must take performed by a competent person

• After heavy rain

• When there is any indication of change or movement in adjacent structures

• When there is a change in size, location, or placement of spoil pile

• When fissures, tension cracks, undercutting, water seepage, occur at the bottom