Model Tests and Assessment Techniques for Mitigating Liquefaction Damage of Building: Deep Foundation Countermeasures.

Currently, there are many countermeasures have been developed to mitigate liquefaction induced damages of buildings and to prevent liquefaction occurrence. The selection of the countermeasure against liquefaction must consider the importance and the required performance of building structures, the cost and applicability of the countermeasure. For example, foundation reinforcement method, solidification method, densification method, and ground water controlling method may be selected. Among them, the foundation reinforcement method is usually the top priority choice for ordinary small area and low-rise buildings when considering engineering economy. In the previous studies, the applicant has performed several dynamic centrifuge tests to investigate the reducing effect of post-liquefaction settlement and tilt of low-rise building by increasing the dimensions of shallow foundation seating on liquefiable deposit. The preliminary results showed that the reducing effect did exist but not significant. Therefore, this project will focus on the use of deep foundation for reducing the settlement and tilt of buildings.The deep foundations that will be studied include small size pile, basement (partial floating) foundation, and slurry wall. The small size pile and basement foundation are used for low-rise buildings. The slurry wall is used for medium high-rise buildings. It is hoped to develop a more economic design strategy of deep foundation for mitigating liquefaction hazard to the buildings. This is a three-year project. In the first two years, the experimental works include dynamic centrifuge tests and laboratory tests. A series of centrifuge tests will be performed to investigate the reducing effect of post-liquefaction deformation of building by using small size pile, basement foundation and slurry wall with variable number of floor and penetration depth into non-liquefying layer. The laboratory works will include the tests of physical index test, triaxial test, cyclic direct simple shear test and resonant column test on the sand used to prepare the model ground in the centrifuge. All the parameters of the test sand will be used in the numerical calibration work in the third year. In the third year, the numerical model for simulating the liquefied soil-pile-structure interaction will be established using FLAC2D Ver.8.0. The numerical analysis will be a fully dynamic effective stress analysis taking the pore pressure generation, dissipation and nonlinear modulus degradation into account. The parameters of the PM4 constitutive law will be calibrated by the laboratory test results in the previous two years. Then, numerical tests will be carried out by varying different design conditions and compare the calculated results with those measured by dynamic centrifuge tests.Through the project, it is expected to establish a complete research data base of the centrifuge test, laboratory test and numerical test for investigating the reducing effect of post-liquefaction deformation of building by using deep foundation method. It is also hoped this data base can be continually used and referenced by anyone who is interested in this topic.