Study On The Deformation Mechanism Of Dry Earth-fetching Rectangular Scant Pile And Its Application In The Deep Excavation Of Soft Soil Area

Nowadays, bored pile is the primary supporting pile of deep excavation in Ningbo region. It is estimated that the annual clean water consumption and slurry emission are 35 million cubic meters and 20 million cubic meters, respectively, which has heavily threatened water safety and regional environmental balance. This area's stratums are covered mainly by saturated soft soil, so that the total costs of temporary supporting measures are about billion RMB per year. Theories and practices have confirmed that although the circular section pile is unreasonable to be subjected to bending moment, it is still widely used in soft soil areas due to the process constraints.Dry earth-fetching rectangular scant pile (DER-SP) is a new supporting pile, which can not only avoid using clean water and eliminate slurry pollution, but also can save materials,reduce costs and improve supporting performances. This new pile has characteristics of economic,reasonable,green environment and convenient construction. It has solved the existing problems of circular bored pile, and it has promising future for practical use and good economic environmental protection. Its local engineering practice also has achieved satisfactory effect. In this paper, the technology of DER-SP is introduced combined with the actual engineering; the comparative analysis of rectangular pile and circular pile is made by theoretical calculations; the main design parameters of DER-SP is analyzed by virtue of numerical experiments; furthermore, the forced deformation regularity and supporting effect of compound supporting structure of the new pile-circular beam are briefly analyzed.DER-SP is explored and studied in this subject, which is combined with the foundation pit application in Ningbo. The main contents are as follows:Contrast calculations of rectangular and circular bite piles indicate that, the conversion thickness of the former pile is only 4% smaller than that of the latter one, but its cross-sectional area is about 16% smaller when the section height and bite width are equal. So the rectangular bite pile has superior mechanical behavior and can save materials in the same condition. The rectangle and round section piles are calculated under the triangle, rectangle and trapezoid distributed load separately. The results show that the rectangular pile has higher stiffness, smaller maximum internal force, and smaller deflection and rotation when its cross-sectional area and height are both same with the circular one.The soil arching effect in soft soil area is studied by using numerical experiment. The results show that the significant soil arching effect can only exist when the pile spacing is one time bigger than pile's width. At this time, the load sharing of pile and soil arching are about 15% and 85%, respectively. The numerical experiment indicates that the internal force and position of the ring beam are alterable dynamic equilibrium processes with working conditions.Because of the small sample characteristics of LS-SVM, the complex nonlinear relationship model between the limited displacement values and several soil parameters can be established and used in the inversion analysis. The inversion verifies that its effect is good and can be used in the subsequent numerical modeling. The deformation influence law of foundation pit and pile affected by parameters, such as the section's aspect of the main pile and bite pile, pile's length, pile's material strength, the physical and mechanical indicator of surrounding soil and so on, has been analyzed by FLAC3D.