A trench is defined as a narrow excavation (in relation to its length) made below the surface of the ground. In general, the depth of a trench is greater than its width, but the width of a trench (measured at the bottom) is not greater than 15 feet. Trench excavation protection is used for the installation of linear drainage or electrical features that will result in trenches deeper than 5 ft. It provides vertical or sloped cuts, benches, shields, support systems, or other systems providing the necessary protection in accordance with

OSHA Standards and Interpretations, 29 CFR 1926, Subpart P, Excavations

.

Temporary special shoring is used for installations of walls, footings, and other structures that require excavations deeper than 5 ft. Temporary special shoring is designed and constructed to hold the surrounding earth, water, or both out of a work area. In general, typically used wall systems for temporary special shoring are: sheet piles, soldier pile walls, soil nails, and temporary MSE walls (Temporary MSE or Welded Wire Face Wall as specified in Chapter 6, Section 3). It provides vertical or sloped cuts, benches, shields, support systems, or other systems to provide the necessary protection in accordance with the approved design. Unless complete details are included in the plans, the Contractor is responsible for the design of the temporary special shoring. The Contractor must submit details and design calculations bearing the seal of a licensed professional engineer for approval before constructing the shoring. The design of the shoring must comply with

OSHA Standards and Interpretations, 29 CFR 1926, Subpart P, Excavations

. Design structural systems to comply with AASHTO LRFD Bridge Design Specifications. Design shoring subject to railroad loading to comply with railroad

Guidelines for Temporary Shoring

and any additional requirements of the railway being supported.

Standard specification Item 403 is for cut shoring. When temporary MSE walls are used for fill situations, construct these walls in accordance with the requirements of standard specification Item 423, Retaining Walls, and include the standard sheet RW(TEW) as well as RW (TEW) DD sheet.

Consider temporary shoring concurrently with the permanent wall layout and design or grade change requirements of any given project. The best wall design or project geometry is difficult to execute and may put both workers and the traveling public at risk if proper shoring requirements are not addressed. In extreme cases, the cost of temporary shoring required to construct a wall can exceed the cost of the permanent wall. Avoid this and reduce negative effects with proper planning and proper wall selection.

Design temporary shoring like a permanent retaining wall. Determine the proper design loading that will act on the shoring wall. Consider the effect of surcharges or slopes behind the shoring wall. Due to the impermeable nature of some shoring types such as sheet piling, consider water pressure or additional drainage details in design. In the case of temporary shoring walls: some increase in prescribed resistance factors may be acceptable depending on the site condition and the availability of subsurface soil data.

Consider temporary shoring for the following conditions: