Application of FLAC3D to the construction process of crossing structure

The underdrain of ancient canal beneath Shi-Tai Expressway is a large-scale graff cross structure of main channel in middle route project of South-to-North water diversion. It is a three-arch culvert structure, where the construction condition is very complex and constructed with partial excavation method. The soil stratum of the underdrain are fine sand and medium fine sand mostly. The traveling vehicle load on the expressway above is heavy; and the excavation width (25.6 m) is the widest in similar engineering in China, so the construction is the most difficult on the route. According to actual construction sequence and craft, the process is simulated by using FLAC(3D) software, which adopts three dimensional explicit difference formulation and simulates three dimensional mechanical behavior of geotechnical engineering commendably. The stratum deformation, the stress and the distribution of plastic zone are discussed in detail. The calculation results indicate that the construction scheme of the underdrain underpass segment is reasonable; it also provides basis for the range of stratum reinforcement, thus guiding the underdrain construction scheme. The practice of construction process proves that the assistant reinforcement measures have obvious effect for the safety of road route and underdrain construction, based on the results of numerical simulation.