Method for Evaluating the In-Plane Shear Strength of H-Steal-Reinforced Wall-Type Ground Improvement

Grid-wall ground improvement has been widely used as a countermeasure to mitigate liquefaction. During earthquakes, the shear force is concentrated on the grid-wall ground improvement, thus the shear force generated in the ground could be controlled. If excavation works to construct the foundation or basement of the structure using the grid-wall ground improvement, the outer perimeter wall of the grid- wall ground improvement could be used as a retaining wall to prevent water flow and support earth pressure. This eliminates the need for retaining walls and potentially reduces environmental impact.  If the ground improvement could not withstand the earth pressure or water pressure during excavation, H- steel might be inserted into the ground improvement to reinforce it. Although the insertion of H-steel provides out-of-plane reinforcement for the wall-type ground improvement, it does not provide in-plane reinforcement. It has been pointed out that because the skin friction between the surface of the H-steel and the ground improvement was small, the ground improvement and the H-steel did not become integrated. And the horizontal force in the in-plane direction could not be supported by the whole cross-sectional area of the wall-type ground improvement. As the size of the H steel increases, the area of the wall ground improvement that can support the horizontal force decreases, and the liquefaction prevention effect decreases. This paper describes shear strength test results of the ground improvement inserting H-steel at approximately 1/3 of the practical scale. In this test, the effect of the difference in skin friction between the H-steel and the ground improvement was investigated by changing the number of reinforcing bars on the surface of the H-steel. Based on the shear test results, an evaluation method for the in-plane shear strength of the wall-type ground improvement when H-steel is installed in the ground improvement was proposed.