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802 Trench and Excavation Safety
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Heaving or Squeezing

Bottom heaving or squeezing is caused by the downward pressure created by the weight of adjoining soil. This pressure causes a bulge in the bottom of the cut, as illustrated below. Heaving and squeezing can occur even when shoring or shielding has been properly installed.

Example of how Heaving or squeezing effect soil xample of how Heaving or squeezing effects soil xample of how Heaving or squeezing effecs soil

Boiling

Boiling is evidenced by an upward water flow into the bottom of the cut. A high water table is one of the causes of boiling. Boiling produces a "quick" condition in the bottom of the cut and can occur even when shoring or trench boxes are used.

Example of Boiling effects soil in a trench Example of Boiling effects soil in a trench Example of Boiling effects soil in a trench

Knowledge Check Choose the best answer for the question.

3-5. Which soil failure is caused by a high water table?