| In the construction of urban rail transit,there are obvious deficiencies in traditional geological prospecting methods,such as conventional drilling,traditional non-destructive detection and traditional seismic method,with many limited site conditions,poor anti-interference ability,prone to data distortion and insufficient detection accuracy.The resulting geological information blind area will cause a variety of safety problems,form groundwater pollution,underground holes and other diseases,and bring additional risks to the project.Micro dynamic detection as a new type of nondestructive detection technology,has the advantages of high efficiency,environmental protection,anti-interference ability,in the detection formation hole,fault,rock interface seriously affect the bad geological structure of engineering safety,with high accuracy and good geographical adaptability,can maximize the geological information blind area,reduce the shield interval of geological exploration construction cost,ensure the construction safety.In this paper,for the ground subsidence and subsidence caused by the loose structure of water-rich sand pebble formation in Chengdu area,the micro-motion detection method is introduced into the subway shield construction,and the key technology suitable for the micro-motion detection in this area is established.The spatial autocorrelation method(SPAC method)and spectral ratio method(H / V method)are collected and inverted to study the application of micro-destructive survey technology in the construction of subway shield tunnel under the condition of water-rich sand pebble complex formation.The study contents and main conclusions are as follows:(1)the new micro technology and traditional drilling technology,give full play to their respective advantages,the shield interval of high complex geological survey,get the high precision of transverse wave(S wave)velocity section,the section geological information rich,details reveal clear,can reflect the area within the complex geological situation,analyze the influence of engineering,to guide the subway shield construction.(2)Through the research on the shape of the platform array,the number of nodes,the radius of the array and the receiving conditions,provide a basis for the subsequent shield construction,and then develop a more scientific and reasonable construction organization mode.The test comparison shows that when the 7-node circular platform array,the radius of3 m and the rigid base of 3 contacts are coupled,the spatial autocorrelation coefficient curve,signal energy and waveform are relatively stable,which can provide guarantee for the subsequent study.(3)SPAC and H / V inversion methods are used to reconstruct the velocity structure,obtain the geological information in the survey area,investigate the formation cavity,and backfill the emergency drilling grouting in the high-risk area.Research found that micro dynamic detection technology not only flexible construction form,construction efficiency,and do not need artificial source,anti-interference ability,in complex formation hole,weak zone,soft hard interface survey,has high accuracy,can significantly reduce the process of shield construction collapse,surface subsidence,the risk of engineering accidents.(4)The micro-dynamic method is applied to locate the underground large concrete structure,and to evaluate the grouting and filling effect of the underground large concrete structure pipeline before the shield tunneling.Through the actual engineering comparison,it is found that the micro-motion detection technology is sensitive to the underground structures,and can locate the underground large concrete structures,evaluate the grouting and filling effect,and avoid the local tube cavity collapse caused by false filling in the process of shield cutting. |
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