Research On Environmental Protection Supporting Structure Of Foundation Pit In Soft Soil Layer

As one of the main categories of geotechnical engineering,foundation pit engineering develops rapidly in the process of new rural construction and urbanization,and a large number of shallow excavation projects in soft soil are excavated.Because of its great difficulty in construction and high technical requirements,deep foundation pit has been widely concerned and studied deeply.However,the support works of shallow foundation pit are often neglected.It is worthy of concern that how to achieve economic and environmentally friendly,safety and stability in shallow foundation pit support in soft soil.Environmental protection supporting materials need to be found,and corresponding supporting structure of foundation pit needs to be studied.The research status and development trend of soft soil foundation pit supporting scheme at home and abroad are analyzed synthetically,it is found that the research on supporting engineering for shallow foundation pit is less.Comparing and analyzing the material and structure type which can be used in foundation pit support,it is concluded that bamboo is a new type of material with economic and environmental protection.Bamboo has large production and good mechanical properties,it can be used for temporary support in shallow foundation pit.It is put forward to use bamboo tube as foundation pit supporting material,and by the row pile supporting structure used in the soft soil foundation pit supporting engineering.Through the field investigation,the foundation pit engineering with a depth of four meters was simulated,and a similar model test was carried out in the laboratory to simulate the supporting effect and deformation characteristics of bamboo pipe single row micro pile and steel pipe single row micro pile under the condition of loading.Midas GTS NX finite element numerical simulation software is used to simulate and analyze the large shallow foundation pit actual excavation in the soft soil layer,and analyze the support effects of single row and double row pile supporting structure of bamboo tube.The conclusions are as follows:(1)through the large scale indoor model test,compared and analyzed two kinds of micro pile supporting effect,the deformation of steel pipe pile is smaller than bamboo pipe pile,but the deformation of the two is not very different,and all of them meet the requirements of support,it is preliminarily indicated that the bamboo pipe pile can be applied to the shallow foundation pit support,and also verify the bamboo pipe can be used as new materials for row pile.The deformation rule of bamboo pipe pile is similar to steel pipe pile,the design of bamboo piles can be referred to the regulations and calculation methods of the corresponding steel pipe piles.(2)Midas GTS NX simulation adopts single row pile supporting structure of bamboo pipe.Analysis shows that when excavation to two meters,the deformation of single row pile of bamboo pipe is similar to that of model test,and the foundation pit is stable;when the excavation reaches four meters,the pile top produce a larger displacement,the pile end present the " skirting" instability trend,the pile body present bending deformation,the bottom of the pile end have a larger uplift.Compared with the model test,it is concluded that the foundation pit support structure of bamboo pipe single row pile should not be used in the poor soil quality engineering.For this foundation pit,the stiffness and embedment depth of single row pile supporting structure of bamboo pipe are not enough,not enough to meet the support requirements.(3)Midas GTS NX simulation adopts the double row pile supporting structure with the same pile diameter,pile length and pile spacing of single row pile of bamboo pipe.The analysis shows that the control of the bamboo pipe double row pile supporting structure is better than the single row pile,the bottom uplift of the foundation pit is small,the deformation of the front and rear pile piles is similar,the displacement near the top of the pile top is the smallest,the front and rear piles are all subjected to alternating bending moment,the bending moment near the top of the pile is the largest.The pile top coupling beam of double row pile increases the stiffness of the pile top,the inner force of the pile between the pile is adjusted and the overall stiffness and the overall stability of the double row piles is improved by inter pile soil.The foundation pit deformation and the internal force of the supporting structure are small,for this foundation pit engineering,the supporting structure of bamboo pipe double row pile meets the support requirements.