Excavation is an important part of the construction process such as foundations, drainage work and underground services. Soil conditions can vary widely; it cannot be relied upon to support its own weight especially if subjected to additional loads from plant and materials. A cubic meter of earth weighs approximately 1.3 tonnes or more when wet. A small fall of earth is capable of causing serious injury. Main hazards of excavation: •Collapse - Excavation sides can be protected by battering the sides to a safe angle, supporting them with shuttering and sheeting, the use of trench boxes or hydraulic support systems •Person Falling into the Excavation - Substantial barriers (guardrail, intermediate rail, toe board), warning tape and signs should be provided where there is a risk of persons falling 2 meters or more. •Materials Falling into Excavation - Excavated spoil and materials should be placed at a safe distance from the excavations as the extra weight can contribute to a collapse. •Over Running Vehicles - Stop blocks should be placed at a distance of approximately 1.5 meters from an excavation to prevent a vehicle falling and minimize the risk of surcharging (excavation collapsing due to the weight of the vehicle). •Underground Services - Electricity Cables, Gas Pipes, Water Pipes, Sewerage, Other Pipelines, Telecoms. It is necessary to locate any underground services and it is not sufficient to rely on maps, safe digging practice should be employed at all times together with cable and metal detection equipment. •Access and Egress - Safe access and egress must be supplied to the excavation. •Hazardous Atmospheres - Noxious or flammable gases could occur naturally in an excavation, exhaust from nearby plant or leak from pipes. Gas tests should be carried out before work starts and periodically as the work continues. •Undermining Adjacent Structures - If there is any doubt that an excavation could undermine an adjacent structure an engineer should be consulted prior to starting work. •Flooding - Groundwater, surface waters and rain water could flood an excavation and undermine its integrity. Ground de-watering systems can be used to lower the water table by drilling boreholes and draining the excess water into a drain or ditch. •Contamination - The soil itself may be contaminated from previous industrial activities, biological contaminants may be present such as Leptospirosis or anthrax spores from farming, slaughterhouse or tanneries. It may be necessary to conduct land surveys and take soil samples prior to commencing work and to wear protective clothing while conducting the work. Source: Buildsafe SA
