§ 33.297. Sheet piling, shoring, bracing and underpinning.

 (a)  General requirements. All shoring, bracing, or sheet piling shall be consistent with the magnitude of the work and the character of the soil or material in which the excavation is made. All materials used for shoring, bracing, and sheet piling shall be sound straight-grained timber equal to long leaf yellow pine, Douglas fir or other material of equal strength. All timber shall be free from splits, shakes, large or loose knots, and shall be of the required dimensions throughout. Wooden sheet piling shall be not less than two inches in thickness and the thickness shall be increased as may be necessary to adequately support the sides of the excavation.

 (b)  Temporary sheet piling. The following procedure shall be followed:

   (1)  Temporary sheet piling which has been installed to permit the construction of a retaining wall shall not be removed until the wall has acquired its full strength.

   (2)  Where temporary sheet piling is used during excavation work, the shoring and bracing to be provided shall comply with the following requirements:

     (i)   When shores and braces are required they shall be placed at intervals of not more than 8 feet measured parallel with the sheet piling.

     (ii)   Shores or braces shall bear at the earth against a footing of sufficient area to keep within the allowable soil pressure, ‘‘dead men’’ being buried when necessary to resist the thrust of the braces.

     (iii)   Shores or braces at the sheet piling shall not be cut to a bevel but shall be held by wedges and the wedges shall be nailed.

     (iv)   The timber shores or braces shall be designed as columns and the following formula is recommended:

       P=A (1,300—20L/D)

   where:

       P=total permissible load in pounds

       A=cross sectional area of timber in square inches

       L=unbraced length of timber in inches

       D=Least dimension of cross section timber in inches

   (3)  The shores or braces shall make an angle not greater than 30 degrees with the horizontal.

 (c)  When used. The following procedure shall be followed:

   (1)  If the stability of adjoining buildings or walls is endangered by excavations, shoring, bracing or underpinning shall be provided as necessary to ensure their safety. This shoring, bracing, or underpinning shall be frequently inspected by a competent person in the employ of the contractor in charge of or the contractor doing the excavation work and the protection effectively maintained.

   (2)  If workmen are engaged near the face of an excavation, where the ground is cracked or of such character that caving is likely to occur, sheet piling with shoring and bracing necessary to prevent caving shall be provided.

   (3)  Except in hard rock, excavations below the level of the base or footing of any foundation or retaining wall shall not be permitted unless the wall is underpinned and all other precautions taken to ensure the stability of the adjacent walls for the protection of persons or property in, on, or in the vicinity of the excavation work.

   (4)  If it is necessary to place or operate power shovels, derricks, trucks, materials or other heavy objects on a level above and near an excavation, the side of the excavation shall be sheet-piled, shored and braced as necessary to resist the extra pressure due to such superimposed loads.

   (5)  Whenever any part of an excavation is protected by a masonry wall, this wall shall be braced to ensure stability. This shall not include reinforced concrete walls or similar walls of ample strength.

   (6)  For excavations more than 16 feet in depth, or when heavy lateral pressures are encountered, interlocking steel sheet piling or equivalent material shall be used. Choice of piling shall be made from recognized standard tables. Piling shall be driven sufficiently below the bottom of the excavation or otherwise installed to resist the overturning moment. Adequate bracing shall be used when necessary.

 (d)  Undercutting. Undercutting of earth banks are not permitted unless they are adequately shored.