Excavation Guidelines

Transcription

1 Excavation Guidelines Date Issued: May 1, Basic Requirement: Planned excavations deeper than 4 ft (1.22 m) are appropriately assessed to ensure the area being excavated is free of recognized hazards and all engulfment risks have been eliminated. 2.0 Scope: These guidelines apply to Cargill facilities worldwide engaged in excavation activity including trenching, pile driving, or use of a backhoe or mechanical equipment to extract and move dirt. 3.0 Definitions: Cave In - means the movement of soil or rock into an excavation, or the loss of soil from under a trench shield or support system, in amounts large enough to trap, bury, or injure and immobilize a person. Competent Person - one who can identify existing and predictable hazards associated with the excavation, its surroundings, and the working conditions associated with the job task, and has the authority to take corrective measures to eliminate the hazards (Contract Maintenance, Construction or Safety). Excavation - any man-made cut, cavity, trench, or depression in the earth's surface, formed by earth removal. Sloping - a method of cave-in protection done by forming sides of an excavation that incline away from the excavation. Shoring - a framework support system of wood, metal, or a combination of these that supports the sides of an excavation and is designed to prevent cave-ins (sheeting or sheet piles). Shielding - a method of shoring using a prefabricated box constructed of wood or steel plates (trench boxes). Soil Types - Soil Type A (> 144 kpa compression strength): Soil type examples: Undisturbed or nonfissured clays. Note: Soil subject to vibration may not be classified as Type A. Soil Type B (Compression strength < 144kPa but > 48 kpa) Soil type examples: Silt, silt loam, some sandy clays. Soils that meet the requirements of Type A soil but are fissured or subject to vibration. Soil Type C (Compression strength < 48 kpa): Soil type examples: Granular soils such as sand and gravel, submerged soil, any soil from which water is freely seeping. 4.0 Reference: 2.1 General - On-Site ContractorsT Construction Safety Guidelines Operational Safety - Excavation OSHA 29 CFR : 5.1 Excavation Excavation and trenching operations are controlled through permits or pre-job plans. Authorization 5.2 Soil Characterization Prior to excavation, soil conditions shall be assessed and characterized by a qualified geotechnical person to assist in determining safe excavation requirements.

2 5.3 Site Inspections 5.4 Underground Installation and Site Assessment Daily inspections of the excavation by a competent person shall be required prior to starting work for evidence of conditions that could result in a cave-in, indications of protection systems failure, hazardous atmospheres, or other hazardous conditions. Inspections shall be made after every rainstorm or other hazardous occurrence. All utility installations, such as sewer, telephone, fuel, electric, water lines, and any other installations expected to be in area shall identified and appropriately managed to minimize any hazards of disturbance prior to commencing excavation. Cables damaged by piling Sites designated for excavation shall be inspected for possible chemical or biological contamination including animal/bird feces. Areas suspected of being contaminated (e.g. bird roosting sites) shall not be disturbed until a health and safety assessment of the site has been completed and specified controls and employee personal protection equipment specified. 5.5 Confined Spaces 5.6 Protective Measures Where the excavation meets the definition of a confined space, entry into the excavation shall be authorized through a formal permit process as defined by Cargill Corporate EHS Basic Requirement Confined Space Entry. Sound engineering requires that excavations be controlled through either shoring/shielding or techniques. When shoring/shielding is selected, it shall be designed by an engineer to structurally withstand the anticipated loads of the excavation. When techniques are deployed, the angle of slope or bench depend upon soil characterization. Excavation Example: Insufficient Sloping Insufficient Sloping Insufficient Shoring Trench with no shoring or

3 5.6.1 Sloping Guidelines for Sloping Trenches and Excavations Up to 20 ft (6.1 m): Appropriate and shoring angles shall be determined based upon geotechnical recommendations. In general most soils will be classified as either B or C type soils. Note: Because of the vibration and soil disturbance that occurs on most construction sites, soils should generally not be classified as type A. If there is any doubt about soil classification, assume type C. Type B 45-Degree slope Type C 34-Degree Slope A 10-foot-deep trench in Type B soil shall be sloped to a 45-degree angle, or sloped 10 feet back in both directions. Total distance across a 10-foot-deep trench would be 20 feet, plus the width of the bottom of the trench itself. In Type C soil, the trench shall be sloped at a 34- degree angle, or 15 feet back in both directions for at least 30 feet across, plus the width of the bottom of the trench itself Shoring Note: Sloping and benching of excavations or trenches greater that 20 ft (6./1 m) requires additional engineering review. Guidelines for Shoring Systems: All shoring systems shall be designed by a qualified engineer to withstand all anticipated loads. All shoring shall be installed with care from the top down and removed from the bottom up. Care shall be taken when removing support members to ensure the safety of employees. Hydraulic shoring shall be checked at least once per shift for leaking hoses and/or cylinders, broken connections, cracked nipples, bent bases, and any other damaged or defective parts. Improper Shoring Excavation of no more than 2 feet (.6 m) below the bottom of the support is allowed. Examples of Engineered Shoring Systems:

4 5.6.3 Shielding/ Trench Box 5.7 Safe Exit 5.8 Adjacent Structures 5.9 Barriers Guidelines for Shielding Systems: All shielding systems (Trench boxes) shall be designed by a qualified engineer to withstand all anticipated loads. The manufacturer shall approve any modifications to the shields. Shields may ride two feet above the bottom of an excavation, provided they are calculated to support the full depth of the excavation and there is no caving under or behind the shield. Workers shall enter and leave the shield in a protected manner, such as by a ladder or ramp. Workers shall not remain in the shield while it is being moved. A safe means of exit (stairway, ladder, etc.) shall be provided for any excavation 4 feet (1.2 m) or greater in depth. A safe means of exit shall not located more than 25 feet (8.2 m) away from any point at which individuals will be working while in the excavation. Ladders shall extend at least 3 feet above ground level for ease of access and egress. If the excavation is to be done adjacent to a building, wall or other existing structure, it shall be determined that the integrity of the structure will not be compromised by possible undermining. This may require support of the adjacent structure by shoring, bracing, or underpinning, or removal of the structure. Structure collapse no shoring or If an excavation is near personnel or vehicular traffic areas, it shall be barricaded to warn others of its location. If it is not readily visible, a designated area, 6 feet (1.8 m) back from the edge of the opening, shall be in place. No Safe Exit No Shoring/Sloping Trench Box Example Unprotected Excavation 5.10 Operation Of Mobile Equipment 5.11 Excavated Material If mobile equipment shall be operated near an excavation site and the equipment operator does not have a clear view of the excavation, a warning system shall be used to ensure that the equipment does not pose a threat to the excavation site and personnel in it. The excavated material shall be removed at least 3 feet (.95 m) back from the edge of the excavation. Spoil piles stored too close to excavation. No shoring or 5.12 Walking Under Loads No one shall stand or walk underneath loads handled by lifting or digging equipment.

5 5.13 Walkways Over Excavations 5.14 Water Accumulation If walkways or bridges are provided over the excavation site, they shall be equipped with standard guardrails if there is greater than a 4-foot (1.22 m) fall hazard. Additional precautions, such as a pump, shall be considered in excavations in which there is accumulated water or in which water could accumulate. If the excavation interrupts the natural drainage of surface water, suitable means shall be provided to divert the water from entering the excavation and provide adequate alternate drainage.