Research On Bolt Supporting Technology Of Foundation Pit Based On Fuzzy Mathematics Theory

With the increase of the depth of excavation of deep foundation pits and the increasing scale,the subject areas involved are more and more,the complexity is getting higher and higher,and the theoretical guidance and technical requirements are more strict.At present,the relative lag of the research on the design of foundation pit support has far exceeded its scope as an auxiliary measure for foundation pit construction.In practical engineering,the actual construction of foundation pit support tends to pay more attention to past practical experience,ignoring the importance of theoretical guidance.The engineering example of this paper is selected as the foundation pit project of the Zhongliang Yingcheng Yihaoyuan Project in Pingdingshan City.Firstly,the paper makes a fuzzy evaluation of the support selection of foundation pits by means of fuzzy mathematics theory.Secondly,through the software numerical simulation,the variation of the sidewall displacement,vertical stress and plastic zone of the foundation pit before and after the bolt support is compared and analyzed,which visually reflects the effectiveness of the selected support method.The paper mainly includes the following aspects:(1)Summarize the design criteria to be followed in the foundation pit support scheme,classify the current types of support at home and abroad,analyze the basic theory of earth pressure in foundation pit support,the structural composition of the anchor and its design principle.(2)With the aid of AHP,the proportion of the importance of each element in the selection of foundation pit support is analyzed,and fuzzy mathematics theory is used to fuzzyly evaluate the selection of foundation pit.(3)The numerical simulation of FLAC3 D software was carried out to observe the soil displacement,stress distribution and plastic zone change law during the whole construction stage of the foundation pit,and the simulation design of multiple sets of support optimization was carried out.Through the fuzzy evaluation of the foundation pit scheme selection of Zhongliang Yingcheng Yihaoyuan project,and combined with numerical simulation to verify its rationality.The conclusions of the paper can be divided into the following points:(1)On the basis of comprehensive consideration of the safety and stability ofthe foundation pit support,quality assurance,economic cost,technical requirements and environmental impacts,and 13 single factors,the evaluation of the alternative three support schemes is obtained through fuzzy evaluation.The integrated value sequence is 0.344>0.334>0.299,and it is determined that the bolt support is the most suitable support scheme.(2)If the foundation pit is not supported by the anchor rod,when the excavation is 4.5 meters away from the top surface of the foundation pit,the displacement of the soil exceeds the alarm value,and the shear strength of the soil reaches the limit,and the instability collapse occurs.If the foundation pit is effectively anchored,the soil displacement can be well controlled within the standard reference value during three excavation to the bottom of 6.5m.The foundation pit remains stable and the bolt is supported.The effect is significant.(3)The angle set by the anchor has a great influence on the anchoring effect.In the interval of 13°~23°,the anchoring effect is better with the setting angle decreasing,and the effect is best at 13°.Similarly,the anchoring position of the anchor also affects the anchoring effect.In this project,the anchoring effect is most suitable when the anchor is placed at a position of 1.9 m from the top of the foundation pit.