Definitions
Cave-In: means the separation of a mass of soil or rock material from the side of an excavation, or the loss of soil from under a trench shield or support system, and its sudden movement into the excavation, either by falling or sliding, in sufficient quantity so that it could entrap, bury, or otherwise injure and immoblize a person.
Definitions
Excavation: any man – made cut, trench, or depression in an earth surface, formed by earth removal.
Trench: A narrow excavation below the surface of the ground, less than 15 feet wide, with a depth no greater than the width.
General Requirements
Before any excavation actually begins, the standards requires the employer to determine the estimated location of utility installations: Sewer, telephone, fuel, electric, water lines, or any other under ground installations that may be encountered during digging.
General Requirements
The standard requires that a competent person inspect, on a daily basis, excavations and adjacent areas for possible cave-ins, failure of protective systems and equipment, hazardous atmospheres, or other hazardous conditions.
Takes prompt corrective measures to eliminate hazards.
General Requirements
Adequate protective systems will be utilized to protect employees. This can be accomplished through: Sloping, Shoring, or Shielding.
Workers must be supplied with and wear any PPE deemed necessary to assure their protection.
General Requirements
If a trench is 4 feet or deeper, stairways, ramps, or ladders will be used.
The employees must not have to travel any more than 25 feet to reach the stairways, ramps, or ladders.
4 feet and more trenches – Toxic and hazardous atmosphere will be tested daily.
Soil Classification
The OSHA Standards classify soil into four categories:
Stable Rock
Type A Soil
Type B Soil
Type C Soil
Stability is greatest in stable rock and degreases through Type A and B to Type C, which is the least stable.
Stable Rock
Is defined as natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed.
Example:
Granite or Sandstone
Type A Soil
Are cohesive soils with unconfined compressive strength of 1.5 tons per square foot or greater .
Example:
Clay, silty clay, sandy clay, clay loam.
Type B Soils
Are cohesive soils with unconfined compressive strength greater than 0.5 tons per square foot but less than 1.5 tsf.
Example:
Angular Gravel, Silt, Silt Loam
Type C Soil
Are cohesive soils with an undefined compressive strength of 0.5 tsf or less.
Example:
Gravel, sand and loamy sand, soil from which water is freely seeping.
Soil Test & Identification
Pocket Penetrometer: Are direct-reading spring-operated instruments used to determine the unconfined compressive strength of saturated cohesive soils.
Once pushed into the soil, an indicator sleeve displays the reading.
Soil Tests
Thumb Penetration Test: Involves an attempt to press the thumb firmly into the soil. If the thumb makes an indentation in the soil only with great difficulty, the soil is probably Type A. If the thumb penetrates no further than the length of the thumb nail, it is probably Type B, and if the thumb penetrates the full length of the thumb, it is Type C.
Excavation Protection Systems
There are three basic protective systems for an excavation and trenches:
1- Sloping and Benching Systems
2- Shoring Systems
3- Shields Systems
Sloping and Benching Systems Sloping Systems Maximum allowable slopes for excavations less than 20 feet (6.09 m)
Type A Soil
Type B Soil
Type C Soil
Benching Systems
Two types of benching systems, simple and multiple.
The bottom vertical height of the trench must not exceed 4 feet for the first bench, subsequent benches 5 feet.
Benching System
Benching System
2- Shoring Systems
Support system for trench faces used to prevent movement of soil, underground utilities, foundations.
There are two basic types of shoring, timber and aluminum hydraulic.
Hydraulic Shoring
Pneumatic Shoring
3- Shielding Systems
A- Trench Boxes:
The space between the outside of the trench box and the face of the trench should be small as possible, and backfilled to prevent lateral movement of the box.
Combined Use
Trench boxes may also be used in combination with sloping and benching.
The box should extend at least 18 inch (0.45 m) above the surrounding area if there is sloping toward excavation.
This can be accomplished by providing a benched areas adjacent to the box.
Type A Soil
Type B Soil
Type C Soil
Spoil
Temporary spoil must be placed no closer than 2 ft (0.61 m) from the surface edges of the excavation.
Cave-Ins
Excavation
