Explain what a tieback is and the two types of tiebacks that are commonly used.
What will be an ideal response?
Tiebacks are steel cables, or tenons, that are inserted into holes drilled through the sheeting and into the rock or subsoil. The drilled hole is filled with concrete grout. When the grout has set, the cables are tightened with hydraulic jacks and fastened to the wales to provide an excavation free of barriers. A second type of tieback uses a screw anchor that is installed with the same rotary drilling equipment used in the grouted anchor construction. The screw anchor is rapidly installed and does not require the drilling of an anchor hole or the injection of grout. They are especially useful in loose sandy and clay soils where a drilled hole may collapse. Screw anchors can be withdrawn and reused.
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Fill in the blank(s) with the appropriate word(s).