| Loess foundations have uneven settlement characteristics after collapsing in water,which will inevitably harm the prefabricated pipe gallery structures built on them.At the same time,the collapse of the foundation often occurs in the form of local collapse,which makes the prefabricated pipe gallery structure possibly cracked,staggered,twisted or even collapsed,which affects the safe operation of the prefabricated pipe gallery project.Therefore,it is particularly important to carry out research on the influence of collapsible loess foundation on the mechanical characteristics and deformation laws of prefabricated pipe gallery structures.Based on the research background of a prefabricated pipe gallery crossing the collapsible loess area in Xi’an,this paper uses a combination of theoretical calculations and model tests to study the stress on the structure of the prefabricated pipe gallery after the uneven settlement of the collapsible loess foundation in contact with water.deformation effects.The main research results are as follows:(1)The cause,mechanism and influencing factors of loess collapsibility are analyzed,so as to clarify the types of disasters caused by collapsible loess to underground engineering.By analyzing the research methods and influence laws when underground engineering passes through the collapsible loess area,combined with the stress characteristics of the prefabricated pipe gallery structure,the model test conditions of the base of the pipe gallery are formulated(the entire base is uniformly flooded,and the half of the base is unevenly flooded).(2)The model material and size were determined through the similarity theory,and a self-designed model test device was used to carry out model tests under different water immersion conditions for the prefabricated pipe gallery base with water subsidence as the core target.The study found that under different water immersion conditions,the prefabricated pipe gallery structure may suffer tensile failure,and the half-width immersion of the base has a more obvious and strong influence on the stress and deformation of the prefabricated pipe gallery structure than the full-width immersion.When the half width is submerged in water,a collapsible extension section will be formed at the junction of the submerged side and the non-submerged side.In the test,the length of the subsidence extension section is about 1.5l(the length of a single-section pipe gallery),and the prefabricated pipe gallery structure in this area will appear stress concentration phenomenon,prone to transverse tensile failure.The obtained results provide the basis for the subsequent establishment of the structural mechanical model of the prefabricated pipe gallery under the two working conditions.(3)Based on the force characteristics and deformation mechanism of the prefabricated pipe gallery in the process of uneven settlement of the base,combined with the results of the model test,a calculation model of the internal force of the base full-width and half-width collapsible structure considering the variable foundation stiffness coefficient is proposed.The successive approximation method is used to solve the problem,and the bending moment and shear force at any point on the surface of the prefabricated pipe gallery structure are obtained.The theoretical model is compared with the model test results,and the results show that the calculation model is reasonable and effective.(4)Using this theoretical calculation model,the longitudinal internal force distribution of a prefabricated pipe gallery structure in Xi’an is obtained,and the processing range is optimized.Based on the research results of model tests and theoretical models,corresponding prevention measures and optimization suggestions are put forward from the aspects of structural strengthening,foundation strengthening and safe operation,which provide experimental and theoretical support for the structural design and strengthening of prefabricated pipe gallery in collapsible loess areas. |
