| With the continuous growth of urban economy and population,ground transportation has been unable to meet the needs of urban development.Subway has become the first choice to solve the problem of traffic congestion in big cities because of its strong carrying capacity and independence of ground transportation.Due to the large cohesive force of cohesive soil,the settlement change of soil during shield construction is continuous and gradual,which is different from shield construction under other geological conditions.When the overlying soil of shield excavation is deeper,it is more likely to adversely affect other structures.Therefore,it is of great significance to study the construction parameters of surface and other structures induced by shield construction in deep clay strata and give a reasonable range.The main research work is as follows :Based on the construction case of a deep clay stratum shield obliquely crossing the railway,according to the geological survey report and the special construction scheme,the three-dimensional model of double-line shield construction is established by using the finite element analysis software Midas GTS NX.The information of model hypothesis,constitutive model,model size and construction steps in the process of finite element analysis is introduced.The changes of excavation surface and surface settlement are analyzed.The simulation results of surface settlement and actual monitoring data are compared and analyzed to verify the reliability and accuracy of the model.In order to analyze the influence of the change of construction parameters on the stratum and railway in shield construction,the influence mechanism of shield construction on the surrounding stratum is introduced and the causes of stratum settlement are introduced.It is concluded that the surface settlement is mainly affected by the construction parameters such as soil properties,support pressure,shield tail grouting filling rate,shield tail grouting pressure,overburden thickness H and shield outer diameter D.The influence law and influence strength of different parameters are analyzed by means of numerical simulation results.A three-dimensional numerical model of shield obliquely crossing the railway in deep clay stratum is established to reveal and analyze the influence of three construction parameters,including support pressure,filling rate of shield tail grouting and grouting pressure distribution,on soil and railway.The support ratio is used to represent the change of support pressure,the filling rate of shield tail grouting is used to represent the filling rate,and the grouting pressure coefficient is used to represent the distribution of grouting pressure.The variation law of soil and railway is analyzed by means of simulation results,and the recommended value range of construction parameters is given.Finally,the analysis results are verified by practical engineering cases,and the Peck formula suitable for deep clay strata is obtained by processing and analyzing the surface subsidence monitoring data.The main conclusions are as follows:(1)When the shield machine in deep clay layer crosses the ballasted track obliquely,the main influence range of the surface transverse settlement is within 2.5 times of the excavation diameter,and the main influence range of the surface longitudinal settlement is within 15 m in front of and 25 m behind the excavation surface.When the support ratio increases from 0.6 to 0.8,the direction of the soil displacement of the excavation surface points from the pressure along the soil bin to the direction of the excavation surface,that is,the lateral pressure coefficient of the hard plastic clay layer is between 0.6 and 0.8 times of the static earth pressure.(2)For shield construction in deep clay layer,when the buried depth of shield tunnel is24 m and the soil depth is less than 13 m,the soil settlement increases linearly with the increase of buried depth,which shows elastic deformation;When the buried depth of the soil is 13～18 m,the settlement of the soil shows a power function change trend with the increase of the buried depth,which shows the elastic-plastic deformation;When the buried depth of the soil is greater than 18 m,the soil is near the failure stage.(3)When the gap appears at the shield tail,it has a great impact on the settlement of the ground surface.When the gap appears at the top of the shield tail segment,the settlement curve shows a narrow and deep shape,and the width of the settlement groove changes little;When the gap appears at the bottom of the shield tail segment,the settlement curve shows a wide and deep shape,and the width of the settlement groove increases.At the same time,stress concentration will occur at the segment position where the gap occurs.The degree of stress concentration is related to the gap position.The maximum stress value of the gap at the waist of the shield tail segment is 1.95 times of the maximum stress value of the gap at the top of the shield tail segment,and 1.6 times of the maximum stress value of the gap at the bottom of the shield tail segment.Therefore,when the gap appears at the waist of the segment,the stress concentration is the most serious.At the same time,when the grouting pressure coefficient is greater than 1,the shield excavation has little impact on the stratum and segments.(4)In the numerical simulation,the change of gravel subgrade follows the change of the ground surface,and the settlement value presents a normal distribution,which conforms to the Peck settlement curve.The maximum settlement point also appears at the center line of shield excavation.Because the shield machine is inclined to cross the track,the horizontal displacement of the subgrade is the same as the excavation direction on the right side of the excavation axis,and the left side of the excavation axis is opposite to the excavation direction.In the actual monitoring data,the settlement trend of subgrade and rail is slightly different from the simulated value,but the maximum settlement value is consistent.In the monitoring data,the settlement trend of subgrade and rail is funnel-shaped.Beyond 5m from the excavation center line,the settlement value of subgrade and rail decreases sharply by 65.5%.(5)In the analysis of actual monitoring data,Peck is applicable to shield construction in deep clay layer in Hefei area,but the actual settlement data is greater than the theoretical value,so the Peck formula is fitted and analyzed.By comparing the fitting curve with the actual monitoring curve,the function equation fitted by the linear regression method is obtained.The Peck formula is modified to make it suitable for Hefei thick clay layer,and the correction coefficient of the maximum surface settlement value α Between 1.02 and 1.18,β It is between 0.98 and 1.11,the maximum settlement value of the surface is between 3.85 and 4.45 mm,and the main impact range of the surface is between 12.9 and 14.7m,between2 D and 2.5D.Figure [85] table [27] reference [66]... |
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