129. Depth of trenches.- The employer shall ensure at a construction site of a building or other construction work that,- (a) where the depth of a trench requires two lengths of sheet piling, one above the other, the lower piling is set inside the bottom strings or wales of the upper piling and such sheet piling is driven down and braced as the excavation continues; (b) all metal sheet piles used in excavation or a trench are welded end to end and secured by other similar means. | 
