Study On Environmental Effects Of Large-span Shallow-subsurface Excavation Station Construction In Soil-rock Assorted Area

With the expanding scale of urban construction, subway construction boom, the city subway notable feature is the buried depth, rock weakness, poor geological conditions, dense surface buildings and underground pipelines, etc., these features will determine the subway construction have a greater impact on the surrounding environment. Among them, the surface subsidence of the surrounding environment of the most prominent. In the subway excavation construction method, the shallow tunneling method has avoided a lot of demolition reconstruction of urban traffic characteristics of a small disturbance, it can develop rapidly. Related to this are the emergence of a large number of geotechnical engineering problems. Shallow ground stations such as the nature of which, Futuhoudu, construction methods, support method, form and size of the structure cross-section will have an impact on surface subsidence, or even cause serious consequences. Therefore, how to prevent collapse during subway construction, reliable and effective control of the city is expected to subway construction caused by ground subsidence, to protect the project along the buildings and underground pipeline safety, has become a subway construction project needs to address the important issue.Qingdao in the granitic area, cover thin, often encountered in the upper soil layer metro project, the lower strata of the typical geological conditions, the combination of soil and rock strata, therefore, it is difficult to design and construction, mining station’s depth, process, structure and mechanical construction characteristics ground deformation behavior, especially combination of geological conditions, soil and rock span a reasonable depth of tunneling and rock stations across less common than studies at home and abroad, including rock cross-over is not yet open for research, which is of great importance to study in the field of engineering geology.Supported by the subway engineering under construction in Qingdao, two typical stations of underground excavation were selected to study the influence of station construction of underground excavation on the suface settlement in the area characterized by the combination of soil and rock with emphasis in this paper, and the main reasearch content and obtained achievements were briefly demonstrated below.(1) The reasearch achievements of domestic and foreign on the surface settlement induced by subway construction was summerized, and the reasons, mechanism and main influencing factors of surface settlement caused by station construction in the area combined by soil and rock was studied. It is considered that surface settlement was mainly caused by construction disturbance, overexcavation, convergence of surrounding rock, lining deformation, and soil consolidation, which could lead to stress release of soil and rock and soil consolidation, and then induce significant surface settlement when the covering layer above the rock was consisted of underconsolidated soil.(2) Surface settlement caused by ground loss, excavation disturbance, consolidation under the construction of subway station of underground excavation was calculated using numerical simulation method, together with the system analysis to the simulated results, and the influence of different construction methods on the surface settlement in the area combined by soil and rock were proposed and verified. It is found that the self-stability of granite of different weathering degree in the stratum of Qingdao far better than that of the general stratum, and the optimized design of rock-thickness span ratio could efficiently take advantage of the depth into the rock, and then control the construction deformation of city subway in a better way.(3) The influence function and empirical formula on surface settlement unduced by subway station construction in the area characterized by the combination of soil and rock was studied and revised, and verified the in-situ monitoring results, through the study of weight assignation of various main influencing factors (e.g., buried depth, hole diameter, stratum parameters, and lining stiffness) on surface settlement induced by the subway station construction of underground excavation.(4) The characteristics of seismic propagation induced by the blasting in subway station and its influence on surface settlement in the combination strata of soil and rock was studied through numerical calculation and in-situ measurement. The study work showed that in the short time after the blasting, a repeat attenuation oscillation existed in the surface vertical deformation; blasting can cause a vibratory compaction to the rock body above the tunnels, on the other hand, have an impactive effect on the overlaying soil and then lead to an increasing of surface settlement with the maximum value of5～10mm. Therefore, it should be pay close attention to the the control of blasting vibration under construction.The study for the actual construction provides a theoretical basis and the guiding role of the "soil and rock mix," Formation of surface subsidence caused by construction-related research extends the scope of the study, filled under the conditions of the formation of surface subsidence caused by tunneling gap, the follow-up works has important reference value.