Excavation Safety

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EXCAVATION SAFETY

By: Engr. Joji C. Valenciano, C.E., M.C.M., S.C.

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OVERALL GOAL

• employees who work in or around excavations

• the general public who work or travel in the vicinity of excavations.

ASSURE THE SAFETY OF:

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TOPIC OBJECTIVE

• Look back on the principle of soil mechanics in applying excavation safety;

• Analyze case and assess the proper orientation of backhoe during operation;

• Become aware of the OHS requirements on excavation work.

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INTRODUCTION

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EXCAVATION SAFETY

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SOIL MECHANICS

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DEFINITIONS

SOIL MECHANICSSOIL MECHANICS

In trenching and excavation practices, SOIL is defined as any materials removed from the ground to form a hole, trench or cavity for the purpose of working below the earth’s surface.

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EXCAVATION - a man-made cavity or depression in the earth’s surface.

OPEN EXCAVATION (Bulk Excavation) - an excavation where the width is equal to or greater than the depth.

TRENCH EXCAVATION - an excavation having a depth which exceeds its width (max. 15 ft. for US, 12 ft. in UK measured at the bottom.

DEFINITIONS

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SOIL MECHANICS

Overburden PressureOverburden PressureSoil Mechanics point of view:

1 foot 1 foot

500 psf250 psf

250 psf 250 psf

250 psf

1 foot

Figure 1. Forces exerted by a column of

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Figure 2. Mechanics of Trench Failure.

(2a) (2b)

TRENCH FAILURESTRENCH FAILURES

(2c) (2d) (2e)

SOIL MECHANICS

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SOIL MECHANICS

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SOIL CLASSIFICATIONSOIL CLASSIFICATION• Stable Rock - natural solid mineral matter that

can be excavated with vertical sides and remain intact while exposed.

• Type A - cohesive soil with unconfinedcompressive strength of 144 kPa or

greater. Examples;

clay, silty clay, clay loam, sandy clay, clay loam

and silty clay loam and sandy

clay loam.

SOIL MECHANICS

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SOIL CLASSIFICATIONSOIL CLASSIFICATION• Type B - cohesive soil with unconfined

compressive strength greater than 48 kPa but less than 144 kPa.

Examples;angular gravel, silt, silt loamsandy loam

• Type C - cohesive soil with unconfinedcompressive strength of 48 kPa or

less. Examples; gravel, sand, loamy sand submerged soil

SOIL MECHANICS

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TYPES OF SOIL COLLAPSETYPES OF SOIL COLLAPSE

• General zone of exposure (fracture point)The area where workersare exposed to masssoil/rock movement.

• Spoil pile slide Poor excavatingprocedures where thethe excavated material isnot placed far enough awayfrom the edge of the excavation.

SOIL MECHANICS

1/2-3/4 of depth or 1:1

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TYPES OF SOIL COLLAPSETYPES OF SOIL COLLAPSE

• Side wall Shear Common to clay type soilswhich are exposed to drying.

• Slough-in (Cave-in) Common to previously excavatedmaterial, sand and gravel.

• Rotation Clay-type soils when saturated with water.

SOIL MECHANICS

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Six Factors for Soil InstabilitySix Factors for Soil Instability

SOIL MECHANICS

• Increase in depth• Saturation• Hydrostatic Pressure (water table)• Weight of excavated soil materials or equipment near excavation• Shock or vibration• Frost faction

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OSH REQUIREMENTS

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OSH REQUIREMENTS

GENERAL REQUIREMENTSGENERAL REQUIREMENTS

• TRAIN WORKERS

Employees who work in or around excavations must be provided training according to their work.

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OSH REQUIREMENTS

• PERSONAL PROTECTIVE EQUIPMENT (PPE)

All workers doing excavation work must wear approved safety footwear and safety headgear. Additional PPE is required depending on the risk assessment for the work to be undertaken.

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OSH REQUIREMENTS

• PUBLIC PROTECTION & TRAFFIC CONTROL

Traffic around the site must be controlled, and barricaded, signs and/or flag persons used as needed to control both vehicular and pedestrian traffic.

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OSH REQUIREMENTS

GENERAL REQUIREMENTSGENERAL REQUIREMENTS• PROTECTION SYSTEMS

The excavation or trench must either be sloped or supported as required to comply with OSHS.

Excavation over 1 m deep: a. protection/support system must

be installed except when:- There are no exposure- Cut in solid rock- With angle of repose- Workers are protected during

installation of shoringb. Kept free of water all the times

ANGLE OF REPOSE

Jump to first pageBy: Engr. Joji C. Valenciano, C.E., M.C.M., S.C.

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Maximum Allowable Slopes

Soil Type Vertical Horizontal Remarks

for excavation less than 20 feet

Stable rock

90 deg

1/2 <12 feet @ 63 deg*

>12 feet @ 53 deg*

*short-term only

1 45 deg

1 1.5 34 deg

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OSH REQUIREMENTS

1/3 depth

GENERAL REQUIREMENTSGENERAL REQUIREMENTS• LOCATION OF EXCAVATED

MATERIALS AND EQUIPMENT

Tools and excavated materials must be piled in a manner that it cannot rollback into the excavation. It must never be closer than 1 meter from edge of excavation.

Equipment and heavy machinery shall not be place near the edge of excavation at least 1/3 of its depth.

1/3 depth, 1 m

. min.

1/3 depth, 1 m

. min.

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Near the edge of excavation?

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OSH REQUIREMENTS

• PROVISION FOR ACCESS/ EGRESS

A suitable means of access/egress (ladders,stairways,etc) must be provided for workers entering an excavation.

A ladder must be located within 25 ft or 8m of a worker’s working position.

0.83 m

SAFE ACCESS/EGRESS?

A SAFE ACCESS/EGRESS

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OSH REQUIREMENTS

• PROVISION FOR BARRICADES

BARRICADES?

ANY HAZARDS?

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OSH REQUIREMENTS

• EXPERIENCED SUPERVISOR

An experienced and trained worker is designated to directly supervise each excavation project.

- sloping and benching- shoring requirements- emergency rescue procedures.

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OSH REQUIREMENTS

GENERAL REQUIREMENTSGENERAL REQUIREMENTS• SITE INSPECTION

Every part of an excavation over 2 m deep where workers work shall be inspected.

A competent person shall conduct daily inspections of excavations, adjacent areas, and protective systems for evidence of a situation that could result to an accident.

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EXCAVATION SAFETY

What’swrongwiththis

excavation situation?

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THE END

Excavation Safety

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