| China’s expressways were built in the 1950 s.The early highways were mostly two-way,four-lane due to factors such as traffic volume,technical level,and social development.In recent years,with the continuous development of society,the number of transport vehicles has increased,the road load has increased dramatically,and traffic congestion has become a common concern and a social problem to be solved.Therefore,the expansion and reconstruction of expressways to improve traffic capacity has become a key and difficult issue facing China’s traffic engineering.The primary difficulty faced in the process of expansion and reconstruction of the expressway is the differential settlement of new and old roadbed caused by the uneven settlement of the foundation and related additional problems.Especially in the loess areas in the northwest,highway reconstruction and expansion projects are being carried out in deep collapsible loess areas.The collapsibility evaluation of loess foundations,the depth of treatment,and the mechanism of the action of pile foundations are important difficulties in design and construction.In this paper,the objective of the study is to investigate the mechanical behavior of pipe pile composite foundation in collapsible loess during the process of highway widening subgrade,and to use the 60 gt centrifugal model test system of Chang’an University to construct a similar model of broadened roadbed in accordance with the actual stress.The centrifugal test flooding rainfall device was upgraded,and stress displacement monitoring systems such as fiber gratings and laser displacement meters were used.Under the different collapse conditions of loess foundations,the frictional resistance,axial force,and soil pressure between piles were investigated.The law of change;and the use of finite element software Midas simulation analysis of the foundation when the collapsibility of the settlement of the foundation and the impact of the pipe pile.This article mainly draws the following research results:(1)An indoor centrifugal model test was conducted to simulate the operation of the new and old roadbed of the subgrade.The subsidence of the subgrade,the stress of the pile and the earth pressure between the piles were monitored during the whole process of the test.The settlement deformation law of embankment foundation under widening foundation treatment and untreated condition is compared and analyzed.The effect of pipe pile foundation on differential settlement control of new and old embankments is verified.A series of stresses such as side friction resistance and axial force are analyzed.characteristic.(2)Using a modified and upgraded centrifuge test water immersion device,we conducted water immersion tests under three different conditions of wetting on top of loess foundations,internal wetting,and overall wetting,and monitored and analyzed the settlement deformation of new and old roadbeds under widened subgrade loads.And pile foundation stress characteristics.Further,by comparing and analyzing the settlement deformation law and stress characteristics of the subgrade and the collapsible subsidence,the influence of the collapse of loess foundation on widening the roadbed is studied.(3)Using the finite element software Midas to establish a three-dimensional model for widening the subgrade,simulation analysis and analysis of subgrade settlement and deformation characteristics of the subgrade under the three conditions of untreated subgrade,treatment of foundation pipe piles and foundation submerged collapse And so on,and the results of the centrifugal model test are compared with each other,confirmed each other,and the reliability of the test results is determined.(4)In order to reduce the negative impact on the widening of the roadbed,the pile side negative frictional resistance appears in the upper part of the pile during the collapse of the loess foundation.Through the numerical simulation analysis of pile spacing,pile side,piles and other factors on the impact of the pile side friction distribution and size changes,proposed to reduce the side friction resistance of the widening foundation treatment optimization measures. |
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