Research On Temperature-stress Field Of Tunnel Lining Based On Test Of Mechanical Properties Of Early Age Concrete

After the concrete lining of the open-cut tunnel is completed,the concrete’s own hydration reaction will cause temperature stress.In order to speed up the construction progress,the lining is demolished in advance,and the lining deformation will be affected by temperature stress,self-weight and restraint,so that the internal tensile stress can easily exceed the tensile strength at the current age to form cracks.Therefore,it is necessary to study the temperature-stress field variation law of tunnel lining in the early age,to find the best time for lining demoulding,and to avoid the formation of cracks due to premature demoulding while achieving rapid construction.In response to the above problems,the work and research results of this paper are as follows:(1)Different proportions of concrete were designed,and the effects of fly ash content,water-binder ratio and aggregate volume content on the basic mechanical properties of early-age concrete were studied.The variation of compressive strength,tensile strength and elastic modulus of cubes under different proportions of concrete with age is obtained.By fitting and correcting the data,the fitting formulas of mechanical properties and ages under different proportions of concrete are obtained,which provides a basis for determining the mechanical parameters of the finite element model.(2)Combined with the location of cracks in the lining,the sensors are targeted,and the changes of concrete pressure,strain and axial force are measured on site.The variation of stress and strain of the lining with time and space is obtained.(3)Using ABAQUS secondary development to simulate the concrete hydration heat release process,based on FORTRAN language,the UMATHT user subroutine was developed to simulate the internal hydration heat release of concrete and the FILM user subroutine simulates the heat exchange with the surrounding environment and the dynamic change of the ambient temperature.The example verifies the correctness of the user subroutine.(4)The sequential thermal stress analysis method is used to analyze the temperature-stress field of tunnel lining in early age,and the distribution law of temperature and stress field of actual engineering tunnel lining with time and space and the best time for lining demoulding are obtained.The relationship between the temperature field and the stress field is explored,and the measured data is compared with the finite element calculation results to further verify the rationality of the model.(5)The temperature-stress field related results were optimized from the concrete materials.Based on the test results,the temperature-stress field analysis was carried out with different proportions of concrete lining,and the fly ash content and water-to-binder ratio were obtained.The influence of the change of the volume content of the aggregate on the temperature-stress field,and the optimal demoulding time of the concrete lining under different ratios.SK-0 to SK-6 were 54h,52h,58h,56h,66h,0,58h,respectively,and the SK-5 group did not have a suitable demoulding time in the study time range,according to 0.The best concrete mix ratio considered from the temperature crack level is cement:fly ash:water:sand:gravel=1:0.18:0.41:1.69:2.88.