Study On Quality Testing And Evaluation Standards Of Composite Foundation Piles In Loess Tunnel

After the loess tunnel is excavated,the bearing capacity of the natural base is generally difficult to meet the force requirements of the tunnel structure.In most cases,people will use composite foundations to reinforce the tunnel base to meet the requirements of the base force.The strength of the composite foundation of loess tunnel is growing slowly.The specification requires that the quality of the pile can not be detected until 28 days after the completion of construction of the pile.However,due to the poor surrounding rock of the loess,in order to prevent the excessive deformation of the surrounding rock,the tunnel construction requires an early arch as soon as possible.Closed(usually less than 15 days),and the pile to be completed before the closure of the arch,which contradicts the test specification.This project is based on the Fujiayao No.1 tunnel.The tunnel is 802 m in length,with a maximum depth of 112 m and a minimum depth of 20 m.The bottom of the tunnel is reinforced with high-pressure rotary jet pile composite foundation.The length of the pile is 6m.The diameter is 0.6m,using plum-shaped cloth piles.In order to study the testing and evaluation criteria for early strength and construction quality of composite foundations,this paper uses indoor testing methods to prepare lime soil compaction piles and high-pressure jet-spray-pile specimens according to the corresponding laboratory test specifications,and put them on different water cuts.Rate of conservation in the loess,in accordance with a certain age sequence on the specimen ultrasonic wave velocity,unconfined compressive strength,indirect tensile strength test,and test data analysis,the main research content is as follows:(1)Through the lime soil compaction test,the best lime-soil ratio,optimum moisture content and maximum dry density of the lime soil compaction pile specimen were obtained;(2)Through the ratio test of high-pressure jet-spray-pile specimens,the best ratio of specimens was determined;(3)By analyzing the test data of the unconfined compressive strength,indirect tensile strength,and wave speed of the two kinds of specimens with age,the rule of their variation with age is obtained;(4)By analyzing the effect of curing moisture content on wave velocity,it is concluded that there is a significant difference between ultrasonic wave velocity and unconfined compressive strength of specimens cured with different water contents;(5)Through the regression analysis of the test data,a fitting curve chart was drawn,and the regression equations of wave speed and age,unconfined compression strength and wave velocity of the test piece were obtained.Finally,the evaluation criteria of the pile quality were given.