Soil Nail Design And Optimization To Deep Foundation Pit Of Soil-stone Mixture Backfill

With the development of China's economic construction, the urbanization process speeded up gradually, meanwhile urban expansion and land conflicts are becoming more prominent. People solved the question of increasingly more land for construction projects by "mountains to the valley" "digging for valley". People lived in some mountain areas used local resources which mixed with many small stones in the valley soil, which resulted a large different between such landfill sites filling and normal consolidation of soil. First, the structure of fill is changed, the structure of soil deformation is an important factor in the decision; Second, fill became smaller in volume, porosity, strength, density and stability had a great changes. It will be re-compacted; Again, the size and ratio of small rocks in the fill also had a impact on nature of fill. How to make the fill to meet the needs of economic construction, is in urgent problems for foundation engineering. In order to resolve the problem of pit fill slope retaining, we not only met security needs but also concerned about saving the economy. The most optimal solution was not only safe but also the lowest cost.In this paper, currently available research results, relying on a soil-stone mixture backfill of deep foundation pit engineering examples of soil nailing in chongqing city as the background, used numerical simulation to comparative analysis .According to analysis result, we established optimization procedure with direct cost as object function and performs optimal design in a certain project. The main work and achievement of the study were as follows:1.The contrastive analysis of the character of internal forces, displacements and the failure mode rod anchored support in the homogeneous earth deep foundation and soil-stone mixture backfill of deep foundation pit.2.Analysis the stress in soil nails which were in the deep foundation of same soil-stone ratio in the three condition. Condition1, soil nails did not encounter small rock. Condition2 , part of small rock soil encountered soil nails. Condition3, under the conditions of meeting stochastic distribution, small rock encountered soil nails by the greatest extent or degree.3.According to soil nailing design calculation, using the modificatory coefficient, we established optimization procedure with direct cost as object function. According to the optimization process, combined with practical engineering examples, the paper optimizes the design and checked the feasibility of the procedure.This topic comes from the national "Eleventh Five-Year" scientific and technological support projects"Excavation of rock and soil reinforcement underground key technologies" in one of the sub-topics; Foundation pit optimal calculation method. Sub-topic item number: 2008BAJ06B04-2.