Design method for horizontal drains in liquefiable soil

The paper describes a fast design method for horizontal drains to be used as a mitigation technique for liquefaction, developed in the framework of the European project LIQUEFACT. During the earthquake, this ground improvement technique allows to reduce the pore pressure build up under existing buildings, where more conventional vertical drains cannot be used (being it difficult to install them). By reducing the pore pressure increments, the horizontal drains can reduce the liquefaction risk for shallow foundations. The problem is modelled with a bidimensional geometry, applying the consolidation equation in the hypothesis of Terzaghi-Rendulic and solving it with a finite difference method. The solution is calculated for different geometrical layouts and removing the simplified hypothesis (used to design vertical drains) of an indefinite symmetry; moreover, it takes into account the influence of a vertical water flow when drainage is allowed at the ground level. The pore pressure build-up is introduced in a simplified manner with an accumulation term suggested in literature. A parametric analysis has been performed and is reported in the paper to obtain design charts. They may be used to define the spacing between drains once the geometric layout, the ground conditions and the seismic input are defined.