| The red layer soft rock is widely distributed in the southwestern region of China,and its unique engineering characteristics have a significant impact on railroad constructions in this region.Arching effect arch of soft rock basement due to deep excavation cutting is one of soft rock engineering diseases.Presently,there are few domestic and international studies on the mechanism of arching effect of soft rock bed in deep excavation.Most scholars focused on the summarization and deduction the causes of basement deformation base on examples analysis.However,robust experimental data and systematic analysis on the characteristics of stress changes,displacement deformation,and their interrelationships and influencing factors in deep-excavated cutting after excavation are lacking.Facing the situation,this paper focuses on the mechanism of arching effect of red-bed soft rock basement in deep excavation cutting.Neijiangbei Railway Station of the Chengdu-Chongqing High-Speed Railway and Qiuxi Station of the Chengdu-Zigong High-speed Railway are cited as examples.It clarifies the characteristics of upward arch deformation of two roadbeds and examines the factors affecting upward arch of soft rock basement based on an analysis of on-site geological investigation and monitoring data.By generalizing the physical model,this paper conducts the centrifugal model test on the soft rock basement of the cutting and initially analyzes the impact of the cutting excavation on the stress state of the basement.Based on the centrifugal model test,a numerical simulation study is conducted using the FLAC3 D software with the arched section of the Qiuxi station as the prototype.After excavation,the stress characteristics and displacement-deformation characteristics of the cutting basement are analyzed using elastic-plastic and creep calculations.Ultimately,after comparing the measured data to validate the validity of the numerical simulation,the single-factor numerical simulation affecting the upward arch of the basement is conducted,and the following conclusions are primarily drawn:(1)It is discovered by analyzing the monitoring data of the upward arch deformation of the roadbed of Neijiangbei Railway Station and Qiuxi Station that the excavation and unloading caused by the slope of the cutting affects the stress state of the basement,and that the excavation of the slope of the cutting as well as the horizontal stress of the basement affect the upward arch deformation of the soft rock basement.(2)The results of a centrifugal model test of a soft rock basement of a deep excavation cutting are examined in this paper,which reveals that the excavation and unloading of the slope of the cutting have an effect on the stress field and displacement field of the basement.The stress in the basement is redistributed,and the lateral pressure coefficient λ>1.0 in a certain depth h.Meanwhile,the lateral pressure coefficient λ as well as the vertical upward arch of the basement both decrease gradually as the depth of the basement increases.This indicates that the effect of slope excavation unloading gradually decreases with the depth of the basement,and the depth of its action area is h.In this model test,h is 27 cm.(3)Using simulation techniques,elastic-plasticity and creep calculations are performed on the soft rock basement of the cutting.The results of elastic-plastic numerical simulation indicate that the vertical displacement of soft rock basement increases linearly with the number of excavations of the upper geotechnical body,and that the amount of the upward arch is proportional to excavation h is the depth at which the horizontal stress of the basement is equal to the vertical stress h is 28 m after three excavation steps and 32 m after all five excavation steps are completed.Therefore,the greater the slope unloading volume,the greater the influence on the lower basement and the amount of basement upward arch.In the elastic-plastic calculation,the maximum upward arch deformation of the footing occurs in the center of the footing,which is approximately 29.2mm.The majority of the upward arch volume is concentrated in the 30 m depth of the footing.In the numerical calculation of creep,the amount of basement creep increases with time and decreases as basement depth increases.The creep deformation mainly occurs within the depth of 35 m of the basement,and the maximum amount of upward arch is about 23.6mm after 5 years of creep.(4)According to the results of a single-factor numerical simulation,when the excavation width-to-depth ratio of the cutting is less than 3,the deformation of the upward arch of the base increases with the width-to-depth ratio.When the width-to-depth ratio is greater than 3,the upward arch of the basement decreases.The upward arch deformation of the footing is proportional to its lateral pressure coefficient.The greater the initial lateral pressure coefficient,the greater the difference between horizontal stress and vertical stress after excavation of the slope and the greater the upward arch of the footing.The thickness of the basement mudstone layer also affects the amount of upward arch,and the thicker the basement mudstone,the less deformation of the upward arch after excavation.(5)The excavation of the cutting slope modifies the basement’s stress state,as determined by centrifugal model tests and numerical simulations.Therefore,the relative magnitude of horizontal and vertical stress is the primary factor affecting the upward arch of soft rock roadbeds.When line engineering construction is carried out in the southwest region of red-bed soft rock,a ground stress test should be conducted in the area.That is,choose an area with a small lateral pressure coefficient and a large thickness of basement mudstone,and design the engineering excavation with a reasonable excavation width and depth to reduce the deformation of the upward arch at the base of the cutting. |
PDF Full Text Request