topic 3: excavation safety Flashcards by Febbyjean Hartt Jumamoy

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

EXCAVATION

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The fatality rate for excavation work is ()% higher than the rate for general construction.

112%

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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

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() 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

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() required a protective system designed by a registered professional engineer

Trenches 20 ft. (6.1m) or deeper

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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

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Hazards of Excavation Works (5)

Soil Collapse
Falling Objects
Underground Utilities
Working Surfaces
Confined Space Conditions

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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

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Types of soil collapse: (5)

sliding
bulge
toppling
boiling
heave

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Types of soil collapse

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

Sliding

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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

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Types of soil collapse

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

Toppling

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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

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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

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Principal Causes of Soil Collapse (5)

Steep cutting angle
Super imposed load
Shock and vibration
Water Pressure
Drying

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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

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Soil types (4)

Stable rock
Type A
Type B
Type C

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Description: Natural solid mineral matters
Examples: Rock, hilly terrain

Stable rock

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Description: Cohesive soil with unconfined compressive strength of 1.5 tons per square foot or greater
Examples: Clay, slit sandy clay

Type A

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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

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Description: Cohesive soil strength 0.5 tsf or less
Examples: Granular soil such as grave, sand & loamy sand

Type C

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Stable rock:
Max Slope (H:V)
degrees

vertical
90 degrees

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Type A
Max Slope (H:V)
degrees

3/4:1
53 degrees

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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