topic 3: excavation safety Flashcards
Is any man-made cut, cavity or depression
in an earth surface that is formed by earth
removal.
EXCAVATION
The fatality rate for excavation work is ()% higher than the rate for general construction.
112%
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.
TRENCH EXCAVATION
() require a protective system, unless if the excavation is made entirely of stable rock. If less than 5ft, no protective system required.
Trenches 5 ft (1.5m) deep or greater
() required a protective system designed by a registered professional engineer
Trenches 20 ft. (6.1m) or deeper
Eliminate hazards and control risks by implementing precautions in excavations and trenches with: (4)
Excavation Safety
1. pre-planning
2. protective systems
3. safety measures
4. inspections
Hazards of Excavation Works (5)
- Soil Collapse
- Falling Objects
- Underground Utilities
- Working Surfaces
- Confined Space Conditions
- A () is a mixture of rock, water, air and a variety of other substances
- () is made up of rock in the form of small particles and spaced called voids.
- Normally, some parts of the voids are filled with water.
soil
Types of soil collapse: (5)
- sliding
- bulge
- toppling
- boiling
- heave
Types of soil collapse
Soil shifts downwards along a slip plane, often
caused by excessive loading or water saturation weakening the soil structure.
Sliding
Types of soil collapse
Soil deforms outward, creating a protruding area, typically due to internal pressure or lateral forces from excavation or nearby construction.
Bulge
Types of soil collapse
Soil or rock tips over around a pivot point,
commonly caused by undercutting or destabilizing forces at the base.
Toppling
Types of soil collapse
Soil is displaced upward due to water pressure,
often caused by high groundwater pressure or rapid infiltration disrupting soil stability.
Boiling
Types of soil collapse
Soil rises and expands, usually due to moisture
changes such as wetting and drying cycles or freezing and thawing, which affect soil volume.
Heave
Principal Causes of Soil Collapse (5)
- Steep cutting angle
- Super imposed load
- Shock and vibration
- Water Pressure
- Drying
In General, excavation means loosening and taking out materials, leaving space above or below ground. In Civil Engineering, this is usually performed during the
Earthworks phase.
Each type of soil has a certain level of risk for collapsing, and corresponding safety measures.
Principles of Soil Collapse
Soil types (4)
Stable rock
Type A
Type B
Type C
Description: Natural solid mineral matters
Examples: Rock, hilly terrain
Stable rock
Description: Cohesive soil with unconfined compressive strength of 1.5 tons per square foot or greater
Examples: Clay, slit sandy clay
Type A
Description: Cohesive soil with strength greater than 0.5 tsf but less then 1.5 tsf
Examples: Angular gravek (similar to crushed rock)
Type B
Description: Cohesive soil strength 0.5 tsf or less
Examples: Granular soil such as grave, sand & loamy sand
Type C
Stable rock:
Max Slope (H:V)
degrees
vertical
90 degrees
Type A
Max Slope (H:V)
degrees
3/4:1
53 degrees
Type B
Max Slope (H:V)
degrees
1:1
45 degrees
Type C
Max Slope (H:V)
degrees
1-1/2:1
34 degrees
This involves the use of supports or structures to prevent the collapse of soil and provide stability to excavation sites.
Shoring
Shoring systems can include: (3)
- Hydraulic Shoring
- Metal Shoring
- Adjustable Shoring
Uses hydraulic pressure to support the excavation walls. This type can be adjusted as needed and is often used in deeper excavations.
Hydraulic Shoring
Uses steel plates and beams to provide support. It’s durable and can be used in a variety of soil conditions.
Metal Shoring
Consists of adjustable props and struts that can be modified to accommodate changes in the excavation depth.
Adjustable Shoring:
This is an older method where wooden planks and beams are used to support the sides of an excavation.
Timbering
Timbering involves: (2)
Timber Sheeting
Timber Bracing
Wooden planks are placed vertically against the excavation walls to prevent soil from collapsing.
Timber Sheeting:
Wooden beams are used to brace and support the timber
sheeting or excavation walls.
Timber Bracing
Sheeting - ()cm x ()cm
Wales - ()cm x ()cm
Struts - ()cm x ()cm
Sheeting - 5cm x 15cm
Wales - 10cm x 15cm
Struts - 10cm x 15cm
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 1m shall be kept free of water at all times.
OSHS RULE 1413: EXCAVATION
Excavation over 1m deep 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 deg. from the vertical or cut to the angle of repose.
Shoring or timbering in excavation over 6.1m deep
shall be designed by a structural engineer and
approved by the proper authority.
Provision of Shoring and Timbering (OSH Rule 1413: Excavation)
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.
Shielding/Boxing:
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 runnoff
Minimum (): Not less than 1/3 of depth of
excavation.
Berms
A berm of reduced width of not less than 1m may be allowed if:
- Materials being excavated are stable
- Shoring to carry the additional load
- Barriers are provided to prevent roll back of excavated material
Prevention of falling materials
* () should be provided
* () must be posted to prevent the public from going near the excavation
Barricades
Signs
Provision for Barricades
The top of the walls of an excavation more than () shall be barricaded to a height of at least ()
2m deep
1m
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 () at all times
* In muddy areas, workers should be provided with () to reduce the hazard of slipping.
free of water
boots
Underground Facilities
Determine the () of underground facilities and take
necessary steps to prevent damage to these facilities
location
() causes extreme geotechnical problems in
excavations such as sand running for most of construction projects such as tunneling.
Groundwater
Two Major Methods for Controlling Groundwater: (2)
Pumping Technique
Exclusion Technique
() involves digging a sump where groundwater collects, which is then simply drawn out using a pump
Pumping Technique
() - achieved by constructing an impermeable or low permeability cut-off wall to keep the groundwater out of the excavation
Exclusion Technique
CAN EXCAVATION BE A CONFINED SPACE?
Oxygen-deficient atmosphere: less than () oxygen
19.5%
CAN EXCAVATION BE A CONFINED SPACE?
Potential for other gases to be present include but not limited to
* () from potential leaks or cut lines
* () from decayed matter
natural gases
methane
CAN EXCAVATION BE A CONFINED SPACE?
Test for atmospheric hazards like low oxygen levels and presence of hazardous fumes and toxic gases is required when the excavation is ()
4 feet deep or greater
Working in Excavation
- check excavation permit
- protect all underground installations
- remove trees, boulders, stump and other surface emcumbrances and hazards before starting excavation.
Prior to Opening
Working in Excavation
- wear goggles and hard hats
- store excavated materials at least 1m 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
During Operations
Working in Excavation
- 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
Equipment Operations
Working in Excavation
- check the atmosphere condition before entry
- do not wok alone in a confined space
- provide life line
- provide ventilation or blower before entering
- provide emergency rescue equipment such as breathing apparatus, safety harness line, and basket stretcher
Excavation in Confined Space
Working in Excavation
- during break time, workmen should never stand or take rest on high banks of soft material
- maintain guardrails, 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 guardrails as resting place
- Daily, before start of each shift
- Every part of an excavation over 2m deep where workers work
- shall be inspected by the person in charge at least once a day.
- This must be performed by a competent person
- After heavy rain
- When fissures, tension cracks, undercutting, water seepage, occur at the bottom
- when there is a change in size, location, or placement of spoil pile
- when there is any indication of change or movement in adjacent structures.
Inspection
an individual who is capable of identifying existing predictable hazards or working conditions that are unsanitary or dangerous. (e.g. safety officers)
Competent person
