A Study On The Disturbed Displacement Characetristic And Construction Safety Of Large-Sized Slurry Shield Tbm Which Crossing An Existing Subway Line At Close Range

Shield tunneling method has a history of more than 180 years and there are thousands of kinds of shields with different diameters in the world at present. In China, a variety of large-scale shields have been produced in Shanghai, Beijing, Guangzhou and Shenzhen and the technical level of shield construction improving constantly. Along with the quick development of underground pipe network construction and the expansion of city underground space, shield method is prevailing and developing at top speed, trend of which is towards high depth, sharp curve, long distance and big diameter. At the same time, more and more short-distance crossing in underground structure projects appears. Especially new tunnel construction will inevitably face the challenge of short-distance crossing of the subway tunnel which is operatingThis research focus on the key technology and theory problems of large-scale slurry shield short-distance crossing operating subway, by the means of laboratory experiment, numerical simulation, field experiment, in situ monitoring and theory analysis, systematically researched the physical and mechanical properties of synchronized grouting slurry and its influence on disturbed displacement, short-distance crossing soil displacement and effect of construction parameter, numerical solution of dynamic displacement increment field of operating subway train, stability of existed subway tunnel under short-distance crossing. Gained the innovative and engineering practical results:[1] By the means of laboratory experiment, systematically researched the influence of the type of cement, sodium silicate modulus and their mixture ratio on the physical and mechanical properties of synchronized grouting slurry. The research shows: i) the strength and elastic modulus of C-S grout with high labeling cement increased with the increase of the modulus and ratio of sodium silicate; the strength and elastic modulus of C-S grout with low labeling cement have a"best value"with the ratio of sodium silicate; ii) C-S grout with low labeling cement and 2.8 sodium silicate has high permeability and long curing time, is harmful on filling the shield void, decrease the soil loss and decrease the grouting amount. The result is instructive to the choose of the cement labeling, modulus of sodium silicate and mixture ratio.[2] Considering the influence of the character of shield segment and its producing accuracy, established the calculation method of effective thickness of tunnel structure by contact mechanics. The result showed: segment effective thickness has negative exponent relationship with ultimate machining error; the decrease of structure general rigidity do harm on the soil displacement field and structure deformation.[3] The deformation and displacement of tunnel under-construction and in-built could be effectively controlled by reasonable control on the parameter of shield cut water pressure and the synchronized grouting slurry pressure: i) to the neighboring tunnel structure, the soil loss existed a"best value", when soil loss is above the critical value, settlement of tunnel structure occurred, and the vertical displacement increased gradually; when soil loss is under the critical value, uplift of tunnel structure occurred. Surrounding structure vertical displacement could be effectively controlled by controlling the parameter to make the soil loss at the"best value". ii) During the construction of downline tunnel, no matter the value of soil loss, the roof settlement of upper existed tunnel is always big than floor settlement, which means the existed tunnel section turned"elliptical change". iii) During the crossing, upper tunnel segment beared tensile stress in different degree, which could cause leak of seam and local failure.[4] Aim at the complex and solution difficulty of coupling of crossing construction and operating subway train vibration during short-distance crossing, seriously considered the system structure character, based on the equivalent principle of mechanism, established a proper coupling dynamic model and segmentation solution method, adopted independently developed vehicle-bridge coupling numerical analysis software and ANSYS, researched dynamic influence of operating subway vibration on the short-distance tunnel construction. Result showed: During the lower tunnel crossing construction when upper tunnel was normal operating, because of the subway train vibration, the tunnel under construction and in-built both had large vertical vibration responding displacement increment. The result is adopted in the South Xizang Road tunnel construction, effectively avoided engineering risk, made sure the engineering safety.[5] By means of numerical simulation and field experiment, further systematically deepen the influence of excavation unloading (initial soil loss), pore water pressure, work face cut pressure and synchronized grouting pressure on the disturbed displacement field of shield tunnel excavation. Giving the summary: I) Synchronized grouting pressure (grouting amount) directly affected the soil layered settlement (especially the zone near grouting hole) and radial horizontal displacement, and had little influence on the soil axial horizontal displacement. II) The soil displacement before the working face was mainly affected by cut pressure, when cut pressure was smaller than the earth pressure, the soil before the working face was under active earth pressure, so occurred unloading displacement towards the working face, soil had opposite direction displacement with shield advancing; when cut pressure was equal to the earth pressure, the soil before working face was under earth pressure at rest, so occurred slight"push"displacement; when cut pressure was bigger than the earth pressure, the soil displacement before the working face increased further, direction was the same with the shield advancing. As a whole, soil displacement before working face showed out highly sensitivity and dependency on cut pressure. Further perfected theory results on this field. [6] Further clarified unsymmetry of vertical displacement field. That is: no matter the magnitude of synchronized grouting pressure, tunnel floor soil all showed"uplift", which means tunnel floor had irreversible"uplift"character; and the uplift or settlement of the proof was closely related to the grouting pressure: when synchronized grouting pressure P≤Ps, proof soil showed settlement; when synchronized grouting pressure P≥Ps, proof soil showed"uplift". The result further fulfilled the disturbed displacement filed of shield construction.In summary, this research further deepened and perfected related technology and theory of large-scale slurry shield short-distance crossing operating subway. Part of the achievements was adopted in 2010 Shanghai Expo matching project South Xizang Road tunnel, acquired fine technology economy benefit and social benefit.