Earth anchor and method of setting and removing same

For use in an earth bore-hole to anchor an excavation site structure, an earth anchor comprising:

• a cone-shaped anchor-wedge;
• a cable fastening collar secured to said excavation site structure;
• a central tie-back cable secured at one end to said anchor-wedge and at its other end to said cable fastening collar;
• a sleeve encasing said central tie-back cable between said anchor-wedge and said cable fastening collar;
• a plurality of tie-back cables arranged in parallel about the periphery of said anchor-wedge and secured thereto at their one ends and secured at their other ends to said cable fastening collar;
• means to seal said plurality of cables and said sleeve against penetration by a frangible fluid hardenable material;
• encasement of said sealed plurality of cables in said frangible fluid hardenable material, said material being pre-weakened in compressive, shear and tensile strengths to render said material when hardened readily destructable when stressed;
• and means to stress said frangible hardened material to destruction including means to tension said central tie-back cable at the entrance to said bore-hole whereby said anchor-wedge is pulled through the hollow center of said frangible hardened material formed by said sealed plurality of cables to fracture said frangible hardened material, thereby to permit removal of said central tie-back cable and said anchor-wedge from said bore-hole.

The method of preparing an earth anchor for insertion in and removal from an earth bore-hole to temporarily anchor an excavation site structure comprising the steps of:

• (a) inserting a tie-back cable in a rigid sleeve;
• (b) securing the ends of said tie-back cable between an anchor-wedge and a cable fastening collar;
• (c) sealing said sleeve against intrusion of a fluid but hardenable substance;
• (d) inserting a combination anchor-wedge, tie-back, cable-sleeve, fastening collar assembly anchor-wedge first into a bore-hole;
• (e) anchoring said cable fastening collar to said excavation site structure;
• (f) preparing a low strength hardenable material which is frangible when hardened and having predetermined low compressive, tensile and shear strengths;
• (g) injecting said hardenable material into said bore-hole to encase said anchor-wedge, tie-back, cable-sleeve assemblage;
• (h) permitting said hardenable material to harden;
• (i) withdrawing said anchor-wedge from said bore-hole by applying tension to said tie-back cable at the bore-hole entrance whereby said anchor-wedge crushes said frangible low strength hardened material as it is being drawn toward the bore-hole entrance.