Effect of Micropiles on Seismic Shear Strain

The use of inclined micropiles as reinforcement to prevent soil liquefaction in level ground has been investigated experimentally. Deposits of loose (D_r = 0.2 to 0.4), dry sand were prepared inside a large (2.0 m deep by 1.8 m long by 0.8 m wide) laminated box and subjected to shaking of different intensities on a one-dimensional shake table. For low intensity shaking (up to 0.12 g) the cyclic shear strains were modest (up to 0.11 percent) and there was a modest settlement (0.31 percent). For higher intensity shaking, (0.16 g) there was a significant transformation in response with much greater cyclic shear strain (0.65 percent) and settlement (3.1 percent). Other deposits were reinforced by use of Titan 26-14 self-drilling micropiles installed at 30 degrees inclination. Reinforcement by one inclined micropile was found to have little effect on response to shaking but installation of two diagonally opposed, inclined micropiles was found to reduce cyclic shear strain by half and settlement to one fifth that of similar unreinforced deposits.