| With the development of urban infrastructure construction, kinds of urban tunnels are springing up like mushrooms in urban underground engineering. However, kinds of the urban subsurface-excavated tunnels should pass underneath surface buildings due to the dense buildings in the city, which will have adverse effect on the safety and normal use of surface buildings, even lead to engineering accident. Among kinds of urban tunnels, double-arch tunnel without middle-wall is emerging as a new kind of double-arch tunnel, because it has not only the superior advantages of traditional double-arch tunnel, such as smooth line type, small occupied area, high space utilization, but also its unique advantages, such as the special structure form, good drainage performance and short construction period. Therefore, it is of great theoretical and practical significance to study the effect on surface buildings caused by subsurface-excavation construction of double-arch tunnel without middle-wall.On the basis of the project of Wucun tunnel in Xiamen Chenggong Avenue, theory analysis, construction monitoring and numerical simulation are adopt to systematically study the key problems about the effect on surface buildings caused by subsurface-excavation construction of double-arch tunnel without middle-wall. The main research and results are as follows:(1) Based on the research achievement of soil-structure interaction, impact of tunnel construction on surface buildings, interaction among tunnel, rock-soil and surface buildings which is made up of tunnel-rock&soil interaction, rock&soil-surface buildings interaction and tunnel-rock&soil-surface buildings interaction, is analyzed systematically. The research results show that:stratum movement and deformation is mainly caused by stratum loss, solidification of remoulded soil, lining deformation and stress relaxation of rock&soil; the value of stratum movement and deformation is mainly influenced by stratigraphic conditions, engineering factors and building parameters and so on; the fundamental principle of the interaction between surrounding rock and supporting structure is not only the force balance between surrounding rock pressure and resistance of supporting structure, but also the deformation compatibility between surrounding rock displacement and deformation of supporting structure; the main forms of foundation deformation include even settlement, inclination, bend, horizontal stretching and compression, which will cause different damage to superstructure correspondingly; compared to the surface settlement caused by single-hole tunnel excavation in natural stratum, surface settlement curve is smoother, but the influence scope is wider if there is a building above the tunnel; tunnel-rock&soil-surface buildings interaction has the characteristics of transmissibility, timeliness and spatiality.(2) According to the field monitoring data, thoroughly analysis has been done about the characteristics of stratum movement and deformation which is made up of stratum transverse settlement, stratum longitudinal settlement, stratum transverse horizontal displacement and stratum longitudinal horizontal displacement, caused by subsurface-excavation construction of double-arch tunnel without middle-wall. The research results show that:stratum transverse settlement at arbitrary depth caused by subsurface-excavation construction of tunnel shows normal distribution in any cross section of the soil, moreover the development the stratum transverse settlement develops gradually with time; stratum longitudinal settlement changed dynamically about10m(0.5times tunnel diameter) near the tunnel face; under the mainly influence of stratigraphic condition, distribution of ground water and excavation order of tunnel faces, both of the measured curve of stratum transverse horizontal displacement and stratum transverse longitudinal displacement changes complexly.(3) Effect of length, stiffness, load, floors of surface building, as well as the relative location of surface building and tunnel on surface settlement caused by subsurface-excavation construction of double-arch tunnel without middle-wall, are analyzed with3-D finite element model of "tunnel-rock&soil-surface buildings" which is set up by the commercial finite element software ABAQUS. The research results show that:if the building length is smaller than the width of subside caused by tunnel excavation in natural stratum, surface building can increase the maximum surface settlement, moreover the maximum surface settlement increases with the increase of building load and floors, and has no obvious change with the increase of building stiffness; if the building length is bigger than the width of subside, surface building can decrease the maximum surface settlement, moreover the maximum surface settlement decreases with the increase of building stiffness, increases with the increase of building load, and has no obvious change with the increase of building floors; the effect of surface building which lies above the existing tunnel on surface settlement is greater than that of the surface building which lies above the following tunnel.(4) On the basis of the field monitoring data of building settlement and crack of masonry and frame structure, thoroughly analysis has been done about the development and evolution law of building settlement and crack. The research results show that: excavation of tunnel face CRD1～CRD4of existing tunnel(left tunnel) has the most important influence on surface building settlement during the construction of double-arched tunnel with CRD method; excavation of tunnel face CRD5and CRD7of the following tunnel are the key construction sequences which should be paid more attention in the construction; the longer the construction period is, the greater building settlement and crack-width variation is, and vice versa; the ability to resist down concave deformation of surface building is stronger than that to resist upper convex deformation; crack width variation aggravates with the increase of uneven settlement of building, and vice versa, however crack width variation lags behind the variation of uneven settlement of building; building settlement can be effectively controlled or reduced by various measures of grouting, however the grouting pressure and grouting amount must be strictly controlled in tunnel construction; it is better to grouting slowly than fast, which ensures the uniform uplift of the whole building.(5) Based on the project of Wucun tunnel in Xiamen Chenggong Avenue, as well as the research results of the other tunnel projects, core problems about the requirements and methods of impact assessment and safety control of surface building in urban tunnel projects are analyzed. According to the research above, a systematic method of impact assessment and safety control of surface building is proposed, which includes assessment criteria and steps, monitor index, response measures. The assessment steps are as follows:①etermining the influence scope of tunnel construction,②investigating the present situation of surface buildings,③determining the calculating parameters for surface movement and deformation,④calculating the value of surface movement and deformation,⑤confirming the grade of surface building damage. Safety control measures of surface building include establishing control standards of building deformation, controlling stratum movement and displacement, building partition wall, reinforcing buildings, adjusting building settlement and incline, repairing buildings, etc.Finally, some suggestions about the further research of this topic are put forward on the basis of the thesis. |
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