Investigation On Surcharge Preloading For Improved Soft Soil Ground Under Expressway

As an effective method of strengthening the soft soil, the surcharge preloading with pack sand wells is used widely to treat the soft ground in lots of projects which have strict requirement on post-construction settlement and uneven settlement. Observation of the settlement and stability is the most reliable method that controls the construction speed for ensuring the safety and stability of the embankment and evaluates the effects of surcharge preloading. In this paper, the behavior of the deformation and consolidation of soft ground under highway embankment were studied thoroughly according to large amounts of in-site observation data in Xiamen Haicang expressway, moreover, the determination of construction control index and the precompression period were discussed.The elaborate work involves several aspects as follow:1,The unsuitability of the in-use construction control index was analyzed by showing that the construction control standard should consider the deformation mechanism of soft soils, and a new settlement rate index for highway was suggested by considering the geological conditions and soft soil properties.2,Based on large amounts of field observation data, characters of the deformation and consolidation of soft clay foundation under embankment were studied in details, and the behaviors of the settlement, lateral displacement and pore water pressure were analyzed systematically.3,By means of comparing and stat., the influences of the construction methods, the thickness of soft clay and the cofferdam on the soft ground deformation were discussed, and a reasonable construction method was proposed .It was found that the thickness of soft clay is the key factor to affect the ground settlement. Moreover, the additional settlement induced by lateral displacement was discussed.4,The evaluation of surcharge preloading and the determination of precompression period were studied in theory. The calculation methods of post-construction settlement were developed based on field observation data. Finally, the effects of surcharge preloading in Haicang expressway were evaluated through analyzing the post-construction settlements and consolidation degrees.