| CFG pile is widely used in foundation treatment.Using coal gangue as coarse aggregate to mix pile concrete can not only make effective use of coal gangue,but also reduce its accumulation area and environmental pollution.CFG pile is buried in the soil,there are a variety of erosion media,which affects the performance.Therefore,it is considered to be wrapped by corrugated plastic casing on the outside of the pile to form a unified whole,which can better improve the lateral friction resistance and durability of the pile.Based on concrete test,model test and numerical simulation,the feasibility and bearing characteristics of corrugated plastic casing coal gangue CFG pile composite foundation were studied and analyzed.The main research contents and conclusions are as follows:(1)The influence of the parameters on the compressive strength and slump of coal gangue concrete was analyzed by using three test variables:the ratio of fly ash replacing cement,the ratio of coal gangue replacing gravel and curing age.Based on the C20 compressive strength grade and combined with the working performance requirements of CFG pile,the number F40M40(water:cement:fly ash:sand:ordinary gravel:coal gangue:water reducing agent=1:1:0.67:2.98:3.32:2.22:0.01)was determined as the optimal mix ratio of coal gangue concrete,and the elastic modulus was measured at the same time.It provided a basis for subsequent model test and numerical calculation.(2)According to the similarity theory,four groups of model control tests were designed and completed:natural foundation,gangue concrete pile composite foundation,corrugated plastic casing+gangue concrete pile composite foundation,geogrids+corrugated plastic casing+gangue concrete pile composite foundation.The results show that the corrugated plastic casing pile has obvious characteristics of friction pile,which can fully mobilize the soil around the pile to bear the upper load.The higher the pile top load value is,the more fully the pile side friction resistance can play,and the settlement deformation control effect of composite foundation is remarkable.Geogrid can give full play to its tension film effect when the load is higher.And it can increase the pile-soil stress ratio and pile load-sharing ratio,and reduce the ratio of pile tip stress to pile top stress.Thus,the bearing capacity and settlement deformation of composite foundation can be further improved.(3)The numerical calculation model was established based on the model test condition.Compared with the model test results,it is confirmed that the variation law of the two was basically consistent.The control group of the composite foundation of smooth casing pile was set up,and a new pile optimization method was proposed based on this,that is,partially smooth corrugated casing pile.The results show that there is a mutation point of pile axial stress at the boundary of casing type,and the mutation point gradually tends to the neutral point with the increase in a smooth interval no higher than 0.4 times the pile length.Compared with the composite foundation of corrugated casing pile,there is little difference in settlement deformation between the smooth zone of 0.1 and 0.2 times the pile length,and the control stress of pile decreases,which can effectively reduce the adverse effect of negative friction on pile.The numerical calculation results of the control group with different pile lengths,pile spacing and pile modulus were compared,and the influence of various factors on the axial stress of pile,differential settlement on the top of pile and soil,and pile-soil stress ratio were analyzed.On this basis,the variation law of each index was compared and its working mechanism was revealed,which provided ideas for the optimal design of piles. |
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