To provide polygonal frame body earth retaining for an excavation groove characterized by being joined by a hinge by forming a polygonal annular frame body by an adjusting device by hydraulic pressure or atmospheric pressure for adjusting a boom length in a timbering material of a sheet pile construction method for preventing the collapse of the natural ground for burying a manhole under the ground.

A hydraulic cylinder is built in a frame 3 capable of sliding an inner cylinder 1 and an outer cylinder 2. The base end of the hydraulic cylinder and the end of the inner cylinder 1 are fixed with a pin via a pin hole of the base end of the hydraulic cylinder and a pin hole formed at the end with of the inner cylinder 1. Both the tip of the hydraulic cylinder and the outer cylinder 2 are fixed with the pin via a pin hole of the tip of the hydraulic cylinder and a pin hole formed at the end of the outer cylinder 2. The pin hole adjusts the maximum length of the frame 3. The frame body earth retaining is formed by connecting a plurality of upper suspension metal fittings 15a and a plurality of hinge members 1 14 having lower suspension metal fittings as a wale block.