What is most likely to cause an excavation to collapse?

Some of the most common reasons for trench or excavation collapses are attributed to unstable soil, vibrations due to machinery being used nearby, vibrations from heavy traffic passing close to the trench, flooding, heavy rainfall, and excessive pressure placed on the edge of a trench.

Probably the most common hazard at any work site is the threat of cave-in. A cave-in occurs when walls of an excavation collapse. Cave-ins can be deadly. Wall failures often occur suddenly, with little or no time for the worker to react.

Here are five factors that cause cave-in trench accidents:

What are the Hazards in Excavation?

Cave-ins pose the greatest risk in trenching and excavation operations, and are much more likely than other excavation-related accidents to result in worker fatalities. Other potential hazards include falls, falling loads, hazardous atmospheres, and incidents involving mobile equipment.

Soil failure is defined as the collapse of part or all of an excavation wall. The most common soil failure is typically described as an unexpected settlement, or cave-in, of an excavation. Soil sliding is the most common factor leading to soil failure.

5: For every 5 meters of excavation depth, the trench walls should slope back 4 meters. 4: For every 4 meters of depth, slope back 3 meters. 3: For every 3 meters of depth, slope back 2 meters. 2: For every 2 meters of depth, slope back 1.5 meters. 1: For every 1 meter of depth, slope back 0.5 meters.

There are four common types of trench collapse hazards: (1) the spoil pile slide, (2) the shear wall collapse, (3) the belly slough, and (4) the slip slide. Spoil Pile slides (figure 1) are very common and occur when dirt is piled too close to the edge of the trench.

Collapse of excavations

Battering the excavation sides - Battering the excavation sides to a safe angle of repose may also make the excavation safer. In granular soils, the angle of slope should be less than the natural angle of repose of the material being excavated.

The Five Ps of Safe Excavation – Plan, Prepare, Pothole, Protect, Proceed.

OSHA requires that protective systems be in place for all trenches five feet and deeper. Thirty-seven percent of all accidents occur in trenches which are less than five feet deep, so even a shallow trench can be hazardous. However, most fatalities happen in trenches that are five to fourteen feet deep.

What is the difference between an excavation and a trench? OSHA defines an excavation as any man-made cut, cavity, trench, or depression in the Earth's surface formed by earth removal. A trench is defined as a narrow excavation (in relation to its length) made below the surface of the ground.

The Hazards of Deep Excavations

Ground Instability: Excavating deep into the earth can disturb the stability of the surrounding soil or rock formations, leading to ground instability. This may result in slope failures, landslides, or even collapse of the excavation walls.

Leakage Through Retaining Wall

This type of deep excavation issues occur when retaining wall is damaged or not adequately waterproofed, and the type of project site soil is sandy soil with high level of groundwater. Figure 1 shows leakage of ground water through retaining wall of deep excavation.

Cave-ins, however, pose the greatest risk and are much more likely to result in fatalities. To raise awareness of the hazards, OSHA encourages all employees exposed to excavations deeper than 5 feet (not in rock) to follow the three S's of trenching safety: Slope It, Shore It, and Shield It!

This is called a trench collapse. It happens when the walls of the trench fail and thousands of pounds of dirt or soil collapse into an excavation site. Trench collapses are among the most dangerous types of construction site accidents that can happen.

A single point of failure (SPOF) is a potential risk posed by a flaw in the design, implementation or configuration of a circuit or system. SPOF refers to one fault or malfunction that can cause an entire system to stop operating.

The “6-foot” rule is a general rule of thumb in the construction industry. Basically, it requires that fall protection be provided when work occurs at heights of six feet or greater above a lower level.

A stairway, ladder, ramp or other safe means of egress shall be located in trench excavations that are 4 feet (1.22 m) or more in depth so as to require no more than 25 feet (7.62 m) of lateral travel for employees. Exposure to vehicular traffic.

The slope angle for a Type B excavation is a 1:1 ratio or a 45-degree angle. For every foot of depth, the sides of the excavation must slope back 1 foot. Type B soil is cohesive with an unconfined compressive strength greater than 0.5 tsf, but less than 1.5 tsf.

Type C soil is not permitted to be benched at any time.

OSHA is focusing on reducing trenching and excavation hazards. Trench collapses, or cave-ins, pose the greatest risk to workers' lives.

Soil arching occurs at the ends of a trench cave-in at the middle of the trench span, similar to the way hydraulic shores prevent a cave-in between the horizontal and vertical locations of the shore, and. The time the trench excavation is left open is short (typically 1 hour or less).

Specialized shoring systems, bracing, and/or underpinning may be required to ensure the stability of these structures and to protect workers. Loose Soil or Rock — Spoil piles (and equipment) must be set back at least 2 feet from the edge of a trench or excavation.

Shoring – Shoring systems provide lateral support against the walls of a trench to prevent a collapse. Shoring systems can utilize metal or timber uprights, driven sheet piling, or other recognized methods.

Trench collapses, or cave-ins, are more likely than other excavation-related. incidents to result in worker fatalities. It only takes seconds to become buried in thousands of. pounds of soil. Trench hazards can be controlled when employers act responsibly, train employees, and follow.