Technical Optimization Of Drilling And Pile Jiont Stress Mechanism Of Superposition Between Wall And Precast Pile

Compared with the traditional method, supporting by permanent structures has lots of advantages. The building envelope can be used as part of the main structure,and make full use of limited resources. The new method can reduce the thickness of the basement wall and save the underground space in prosperous area. Precast components can be made in factory, which speed up the development of underground engineering industry. The technology of structure combined permanent and temporary has broad application prospect under the background of advocating green,civilization and sustainable development in engineering construction.Taking Yan Mazhuang station of Jinan R1 metro as the background, the concept of precast piles affect as building envelope and main structure was introduced and the deformation and stress mechanism of precast piles was studied, The main research contents are as follows:(1) Precast piles affect as building envelope when the foundation pit wsa excavated and as main structure when construction was compled,which could make full use of limited resources and speed up the development of underground engineering industry. (2) In order to facilitate construction and transportation, prefabricated piles are divided into two sections, which are connected by special pile joints.Through the experimental study on the flexural behavior of precast pile joints, the stress mechanism and deformation law of pile joints were studied, which provides a theoretical basis for the deformation control of precast piles. (3)The deformation law of precast pile in foundation pit excavation was analyzed by numerical simulation,a special monitoring program was formulated for pile piled composite pile,provide data support for the technology.The main conclusions are as follows:(1) Optimization of supporting by permanent structures was made.Aaccording to a new mechanism of spiral drilling machine the drilling rig was improved. Kd which represents efficiency was put forward by calculation to guide construction. Cement soil grouts could preventing the bore hole from collapsing and fixing pile, improving the quality of cement soil grouts by optimizing the mix proportion of cement soil, proportion coefficient of coefficient of slide bed was calculated by horizontal static load test, and the horizontal displacement of pile was obtained by m method.(2) Deformation and stress mechanism of precast piles was analysed by bending test, the study shows that bending stiffness, crack width,deflection and strains change with load. The stress process of pile joint can be divided into three stages:in stage I , at the beginning moments borne by bolt in pile joint; in stage II, tensile stress borne by pressor area of ventral and top surface and compressive stress borne by bottom web;in stage III, flexural capacity of pile joint continues to increase with the increase of load, the compression zone enters the plastic hardening stage.(3) The numerical model was established by the FLAC3D, and Horizontal deformation of prefabricated pile and vertical settlement of soil after pile were analyzed. With the increase of excavation depth, the horizontal displacement of prefabricated pile increases gradually, and soil settlement was expanding continuously, From the near to the distant settlement of soil increased first and then decreased.