Showing posts with label Excavation. Show all posts
Showing posts with label Excavation. Show all posts

Excavation Safety Procedure

Excavation      
Any man-made cut, trench, or depression in an earth surface, formed by earth removal.

Benching:       
A method of protecting employees from cave-ins by excavating the sides of 
an excavation to form one or series of horizontal levels or steps, usually with 
vertical or near vertical surfaces between levels.

     Cave-In  
The separation of a mass of soil or rock materials 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 failing or sliding, in sufficient quantity so that it could entrap, bury, or otherwise injure and immobilize a person.

Competent Person
One who is capable of identifying existing and predictable hazards in the surroundings or working conditions, which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them.

Trench  
A narrow excavation below the surface of the ground, less than 15 feet wide, with a depth no greater than the width.

Protective
System   A method of protecting employees from cave-ins, from material that could fall or roll from an excavation, or from the collapse of adjacent structure. Protective systems include support systems, sloping and benching systems, shield systems, and other systems that provide necessary protection.

Shield   
A structure that is capable of with standing the forces imposed on it by a cave-in and
There by protects employees within the structure. Shields can be permanent structures or can be designed to be portable and moved along as work progresses.

Sloping 
A method of protecting workers from cave-ins by excavating to form sides of an excavation that are inclined away from the excavation to prevent cave-ins. The angle of incline required to prevent a cave-in varies with differences such as soil type, length of exposure, and application of surcharge loads.


GENERAL REQUIREMENTS:

1-The following specific site conditions should be taken into accounts for safe excavations:
a-       Traffic
b-        Nearness of structure and their conditions
c-        Soil
d-        Surface and ground water - the water table
e-        Overhead and underground utilities
f-         Weather

2-  Before any excavation actually begins, the standard 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.

3- No employee should operate a piece of equipment without first being properly trained to handle it and fully alerted to its potential hazards.

4-  The standard requires that a competent person inspect, on a daily basis, excavations and the adjacent areas for possible cave-ins, failures of protective systems and equipment, hazardous atmospheres, or other hazardous conditions.

5- Adequate protective systems will be utilized to protect employees. This can be accomplished through sloping, shoring, or shielding.

6-  Workers must be supplied with and wear any personal protective equipment deemed necessary to assure their protection.

7- All spoil piles will be stored a minimum of two (2) feet from the sides of the excavation. The spoil pile must not block the safe means of egress.

8-   If a trench or excavation is 4 feet or deeper, stairways, ramps, or ladders will be used as a safe means of access and egress. For trenches, the employee must not have to travel any more than 25 feet of lateral travel to reach the stairway, ramp, or ladder.

9-  No employee will work in an excavation where water is accumulating unless adequate measures are used to protect the employees.

10-A competent person will inspect all excavations and trenches daily, prior to employee exposure or entry, and after any rainfall, soil change, or any other time needed during the shift. The competent person must take prompt measures to eliminate any and all hazards.

11-Excavations and trenches 4 feet or deeper that have the potential for toxic substances or hazardous atmospheres will be tested at least daily. If the atmosphere is inadequate, protective systems will be utilized.

12-If work is in or around traffic, employees must be supplied with and wear orange reflective vests. Signs and barricades must be utilized to ensure the safety of employees, vehicular traffic, and pedestrians.

SOIL CLASSIFICATION AND IDENTIFICATION

The OSHA standards define soil classifications within the simplified soil classification systems, which consist of four categories:
a-             Stable Rock
b-            Type A Soil
c-             Type B Soil
d-            Type C Soil

Stability is greatest in stable rock and decreases 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 Soil: are cohesive soils with an 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 unconfined compressive strength of 0.5 tsf or less.(Example: gravel, sand and loamy sand, submerged soil, soil from which water is freely seeping.

SOIL TEST & IDENTIFICATIONS:

Many kinds of equipment and methods are used to determine the type of soil prevailing in an area, as described below:

Pocket Penetrometer: Penetrometers 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.

Visual Test: If the excavated soil is in clumps, it is cohesive. If it breaks up easily, not staying in clumps, it is granular.

Thumb Penetration Test: The thumb penetration procedure involves an attempt to press the thumb firmly into the soil in question. 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 soil, and if the thumb penetrates the full length of the thumb it is type C.

Dry Strength Test: Try to crumble the sample in your hands with your fingers. If it crumbles into grains, it is granular. Clay will not crumble into grains, only into smaller chunks.

Wet Manual Test: Wet your fingers and work the soil between them. Clay is a slick paste when wet, meaning it is cohesive. If the clump falls a part in grains, it is granular.

EXCAVATION PROTECTION SYSTEMS:

There are three basic protective systems for an excavation and trenches:
a-                 Sloping and Benching Systems
b-                 Shoring Systems
c-                 Shields Systems
The protective systems shall have the capacity to resist without failure all loads that are intended or could reasonably be expected to be applied to or transmitted to the system.

SLOPING & BENCHING SYSTEMS:

Sloping Systems:
Maximum allowable slopes for excavations less than 20 feet (6.09 m) based on soil type and angle to the horizontal are as follows:
Soil Type
Height/Depth ratio
Slope Angle
Stable Rock
Vertical
90 deg.
Type A
¾ : 1
53 deg.
Type B
 1 : 1
45 deg.
Type C
1½ : 1
34 deg.

Benching Systems:
There are two types of benching, simple and multiple. The type of soil determines the horizontal to vertical ratio of the benched side.
As a general rule, the bottom vertical height of the trench must not exceed 4 feet (1.2 m) for the first bench. Subsequent benches may be up to a maximum of 5 feet (1.5 m) vertical in Type A soil and 4 feet (1.2 m) in Type B soil to a total trench depth of 20 feet (6.0 m).


Shoring Systems:
Shoring is the provision of a support system for trench faces used to prevent movement of soil, underground utilities, roadways, and foundations. Shoring is used when the location or depth of the cut makes sloping back to the maximum allowable slope impractical. Shoring systems consist of posts, wales, struts, and sheeting. There are two basic types of sharing, timber and aluminum hydraulic.

Hydraulic Shoring:

Hydraulic Shoring is a prefabricated strut and/or wale system manufactured of aluminum or steel. Hydraulic shoring provide a critical safety advantage over timber shoring because workers do not have to enter the trench to install or remove hydraulic shoring.
All shoring should be installed from top down and removed from bottom up.


Pneumatic Shoring:
Works in a manner similar to hydraulic shoring. The primary difference is that pneumatic shoring uses air pressure in place of hydraulic pressure. A disadvantage to the use of pneumatic shoring is that an air compressor must be on site.
Shielding Systems:
A- Trench Boxes:
Are different from shoring because, instead of shoring up or otherwise supporting the trench face, they are intended primarily to protect workers from cave-ins and similar incidents. The space between the outside of the trench box and the face of the trench should be as small as possible. The space between the trench boxes the excavation side are backfilled to prevent lateral movement of the box.
Combined Use:
Trench boxes are generally used in open areas, but they also may 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.
Spoil:

Temporary spoil must be placed no closer than 2 ft. (0.61 m) from the surface edge of the excavation