| With the continuous deepening of city construction, development and utilization of underground space has become today’s city development needs to solve the city traffic congestion phenomenon. City subway tunnel is not the birth of a city planning, but with the gradual development of city, therefore, the Metro Planning and construction should not only ensure the safety of buildings, but also to ensure that no damage to underground pipeline construction. The subway is generally along the city road surface, on one hand it is to the passenger’s convenience, on the other hand it is to pile foundation, avoiding high-rise building basement. Therefore, in accordance with the " Design Code for Highway Tunnel " for neighborhood tunnel (in soft rock section of tunnel is less than 4B away from the other tunnel, B expresses for tunnel width), then the city subway mostly were neighborhood tunnel, but the new Austrian tunneling method construction machinery in mountain tunnel and shield construction cannot be mentioned in the same breath, and soil and rock properties are quite different。In Suzhou soft soil under these conditions, how is mutual influence between neighborhood shield tunnel construction and the soft soil? Based on this research, this paper presented the research from the macroscopic, microscopic and micro combination to explore the interaction effect of first hole and after the construction of the relationship, provides the reference for the similar engineering.In this paper, in the macroscopic aspect, through analyzed numerical simulation and field measurement of ground surface settlement, draw the interactive influence on macroscopic view, provided the ideas of design experiment scheme; in the microscopic analysis to segment, through numerical simulation and field measurement of segment of the stresses of three directions (radial, axial and ring direction) state, analyzed the interaction influence of first hole and the rear hole construction, one hand to verify the reliability influence rule of macro interaction, on the other hand to provide ideas for the design of soil mechanics test plan; at the microscopic aspect on soil mechanics test, and the experimental scheme was designed according to the macroscopic interaction laws and the segment stress analysis the soil stress, provided ideas for the design of micro test scheme; at the micro aspects of the comparative analysis of soil structure interaction effects were obtained, embodied in the aspects of micro soil. Through the above analysis, the main research results in this paper were:(1) Suzhou soft soil stratum has special geology environment. The soil is mainly the inland lake sediments, the layer thickness in 5-30m, uneven distribution, but the soil is homogeneous. Through the comparison of soil elsewhere, Suzhou soft soil layer has a relatively low water content, void ratio, angle of internal friction, high compression modulus and cohesion. Because the soil is different, the interaction law of the soft soil is also different from other regions.(2) From the macroscopic aspect, through the numerical simulation of different clear distance (0.25D,0.5D,0.75D, 1D,1.25D,1.5D, D is the outer diameter of shield machine) analysis of ground surface settlement, lateral and longitudinal interaction effects of settlement rules, got the following important conclusions; The interaction laws between first hole and the following tunnel construction, mainly in the following aspects:①The first tunnel construction produced disturbance on surrounding soil, making the following tunnel longitudinal and transverse settlement value increasing than the first hole.②The first hole construction process itself (along with the increase of construction steps), in its around formed the disturbance consolidation circle in different degree, in this paper attributed to the strong disturbance consolidation circle (range 0-0.25D), weak disturbance consolidation ring (0.25～0.75D), no disturbance consolidation (1D～1.5D). Consolidation ring formed by itself, so the following tunnel construction was affected by the disturbance consolidation circle,and the surrounding soil disturbance was reduced, it made the surface subsidence increased.The influence rules of construction on the first hole to the following tunnel, mainly manifested in the following aspects:①Influence of the following tunnel construction to the first hole was a process (arrival, passes through this process), manifested in the longitudinal and transverse settlement curve, the first cave settlement increased first and then decreased, that soil around of the first hole stress was also a process of quantity, that was the extrusion and extrusion process and shear coexist and tensile, forming the disturbance consolidation ring in their structure around, which made the surface soil mechanical performance for tensile and tensile, shear and extrusion process, settlement and increase and decrease.②In view of this process affects the following tunnel construction on the first hole (not arrived, passed through the comparison and after), longitudinal and transverse settlement, ground surface settlement value of first hole increase first and then decrease, that surface soil of first hole rebound phenomenon in the shield tunnel construction, and according to the rebound value is always less than the settlement after construction settlement value, that the following tunnel construction made disturbance consolidation circle to first hole has the tendency of increase.③The effect of the following tunnel construction to the first hole with the clear distance of different and different, when it was 0.25～0.75D (D is the diameter of the shield machine), ground surface settlement, lateral longitudinal hole in advance with the increase of amount of rear hole construction step, sedimentation value and decreases with the increase of distance, while in 1.0-1.5D. Sedimentation value increases with the increase of distance. That from the results of first hole construction, after formed the disturbance consolidation circle, the distance soft clay soil in the area within the uniform, and its engineering properties have changed for the better, made the following tunnel construction disturbance is smaller to the first hole, but the surface subsidence increases. According to this conclusion, proposed in the area of construction, shield the optimum spacing was about 0.75～1D.(3) In the segment of microscopic aspect, through the finite element numerical simulation and field monitoring to segment three (radial, axial and circumferential) direction stress analysis of characteristics, could draw the following conclusions:①Influence of shield construction on the first hole to the following hole construction, on the segment for the performance at the same monitoring section, first hole state stress of segment was different to the following tunnel segment, and the three direction stress of segment was different according to the monitoring position (the same section). Description of the first tunnel construction caused effects on the following hole segment stress.②Influence of shield construction on the first hole to the following hole construction segment, in the segment of the performance in the same monitoring section, was a dynamic process, namely the following hole shield construction did not reach, the monitoring section arrived and after, first hole segment received the corresponding disturbance, i.e. firstly compression, and then compression and shear, again pull process, such changes were reflected in the radial, axial and cyclic stress state to the. And the impact of construction on the first hole to the following hole, mainly the influence of tunnel lining structure arch waist in the left and right was larger, and the top of the arc and arc bottom less effect.③Through the segment of Suzhou Metro Line 4 subway shield construction of the first hole test measuring three direction to the stress state of the site design, namely with the radial pressure box measuring segment the back stress, using axial strain gauge measuring segment inside stress and circumferential stress, through the analysis of monitoring data, which could prove that the influence of the following tunnel construction to the first hole segment was a squeeze, shear, tensile process and extrusion, which proved the reliability of the result of numerical simulation.(4) In soil microscopic aspect, through indoor experiment, we could get the following conclusions:①Through the contrast of undisturbed soil and subjected to compression and consolidation test results, first hole construction disturbance of soft soil, deformation of soil, reduced the porosity ratio decreases and compression modulus increases, illustrated the properties of soil disturbance better, which could prove that the first hole construction in segment formed around disturbance consolidation ring.②Through the contrast of undisturbed soil and compressed-consolidation tests of first hole construction disturbance of soft soil, and analysis of the deformation rate of the soft soil decreases with the increase of load, that the consolidation of soil was influenced by the load and time. With respect to the shield construction, also the first hole construction on its surrounding soil impact was the biggest, the influence of the soil around the hole construction after the first hole was decreased.③Based on the direct shear test results, the comparison of undisturbed soil and soft soil’s cohesive force and internal friction angle which had disturbed by the first hole construction, internal friction angle and cohesion were found both increation with disturbance of shield construction, that perturbations in the process of construction, the shear strength of soil increases.④The comparison of compression-unloading-shear and pure shear test of cohesion and internal friction angle, internal friction angle and cohesion that was different between under compression and not compression. The sample which did the compression test, its cohesion and internal friction angle had increased obviously, that shield tunneling under squeeze pressure, had a consolidation phenomenon, that proved the existence of disturbance consolidation ring.⑤The research of forming condition of disturbance consolidation circle:a, the soil needed to be subjected to external loads; b, soil had a drainage channel in under the action of stress; c, soil deformation response in need under consolidation. For shield construction process, did not meet the monitoring sections provide that was extrusion and shear stress, so the soil loosen, provided drainage channel; when the tensile construction through monitoring section was provided when the soil, equivalent to the affected by the compression, thus forming the consolidation, but also by the surface deformation coordination.(5) At the micro level, through the observation of first hole before and after construction of undisturbed and after micro structural mechanics experiment of soil samples, the following conclusions could be obtained:①The undisturbed soil sample particles were scattered, and after compression stage, soil particles arranged closely and uniform; After we made the compressed-unloading-shear test, the soil had still closely arranged, but soil particle shearing edge happened deflection. Note in this process in the soil around the shield construction segment was to dense and uniform development.②Undisturbed soil sample by the construction disturbance of the particles toward the compacting direction, that disturbance of shield construction made the soil consolidation phenomenon.③The soil was shear extrusion process in the shield construction process perturbation, first, made the surrounding soil loose and permeability, but when the shield construction through, soil stress was quickly to the inside of the radial stress, at this time would form the disturbance consolidation effect, distributed around the shield support the supporting structure, after a period of time it had fomed the disturbance consolidation ring. |
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