| Nowadays, a great number of subway stations have been building in the cities. However, as a result of the limitation from ambient environment condition, the urban subway’s construction is performed under the complicated conditions. Especially, in some places, where there are plenty of tall buildings standing and underground pipelines covering densely, traditional excavation methods for metro station’s building are under restrictions. In this case, this dissertation put forward a new excavation method of metro station that is expanding excavation on the base of shield tunnel through the station. In this way, not only can it drastically reduce halt waiting time of shield machine and ensure construction security, but also solve a toughest problem existed for many years that is how to build a metro station and increase the efficiency of metro shield’s primary driving in some cities where there don’t meet the requirement of setting shaft out of complicated conditions.Taking Dong shankou station from the6th line of Guangzhou subway as engineering background,This dissertation synthetically adopts a variety of study means, such as theoretical analysis, numerical simulation,3-dimensional model tests and field monitoring etc. For the study of surrounding stratum and houses effect induced by the enlarging shield tunnels, this dissertation mainly relate and analyze from following parts and arrivals at some conclusions:1. In the process of enlarging shield tunnels, different surrounding rock grades have distinct influence on the surrounding stratum and houses, from which we can see:at the level of surrounding rock and houses safety, surrounding rock of Grade Ⅳ2is basically the critical range; in the case that surrounding rock grade is higher than IV2, it will remain as safe on the whole when the shield machine conducts expanding excavation and affects the surroundings; with the grade of surrounding rock continuously decreased,untill lower than IV2, the ground settlement increase rapidly; when the surrounding rock grade is V in some areas, whose whole stratum deformation is comparatively large, well then it is not rational to build the metro station through enlarging shield tunnels; Once this kind of strata happened to appear, it need to take some advance strengthening measures ahead of time, improve the strength of surrounding rock in the tunnel, and ensure construction and surrounding environment security.2. About the influence that houses have on the range and value of ground settlement, it mainly make some analysis from the buildings’weight and the relative position of houses to shield tunnel or enlarging shield tunnels, including the distance and angle. In terms with the different distance, if the distance is twice as long as the tunnel diameter, the growing trend about the whole settlement and the width of settling tank, namely the influence scope to the earth’s surface, will be slightly distinctive, only when the house is5tunnel diameters far away from the tunnel, will the influence that the house have on the earth surface have been very small. Regard the distance as constant, the more heavy the house’s dead weight is and the shorter the width to its influence direction, the greater the influence having on the earth surface’s settlement will be. To the situation that all is not clear, the value of ground settlement will have a positive correlation with the uniform force which the house dead load imposes on the foundation base, that is the bigger the uniform force is, the greater the value and range of the ground settlement will be and vice verse. The biggest influence width caused by the house is the house’s diagonal length, meanwhile the angle between the house and tunnel axis will be calculated by θ=90-arctan c/1.3. During the process of the enlarging shield tunnels, no matter which one will be firstly excavated between the left line and the right line, part of the settlement value caused by the shield approximately make up30%of the overall settlement. With the strength of surround rock decreasing, the rate of settlement that is caused by the left shield driving has little change, which is basically stable at30%. However, the rate of settlement that is caused by the right shield driving will be some higher along with the strength of surround rock increasing.4. On the whole, in the course of enlarging shield tunnels, the house’s relative deformation has a great effect on its own loads and safety factor. The jumping of house’s relative deformation must lead to its local stress increasing due to its structure own lagging in the adjustment, which is clearly demonstrated on the changes of house stress when the right expanding excavation is halfway. Therefore, the part that the house’s relative deformation gradually increasing has on the house stress is comparatively little, but the jumping of house’s relative deformation has a bigger influence on the house stress. So it should focus on controlling house’s value of local relative settlement.5. When the shield is ongoing expanding excavation, the house’s stress will increase gradually from top to bottom, moreover, its variety concentrate mainly on the ground floor. The security coefficient of wall,90degrees to the direction of house, is always smaller in the driving period. Specific to this working condition, it should take auxiliary construction method and reinforce the house and its foundation base in advance in order to protect it from crack destruction. The45degrees angle house requires focus on prevent crack destruction from the stage of the right shield working to the stage of connecting passage’s cutting through. It is necessary that the house that is parallel to the tunnel axis to control the stage between the left lines’s expanding excavation and the second connecting passage’s cutting through. 6. With the distance between the house and tunnel increasing, the house’s stress will rise at first and then descend, finally return to natural stress state under the action of deadweight in the stage of shield and expanding excavation. In the process of shield driving, the maximum of house stress approximately appear on the biggest curvatureof settlement trough, where the house’s horizontal deformation is the biggest and the stress state is the worst.7. At the part of engineering project, this dissertation makes a more comprehensive contrastive analysis from some aspects, including the construction period, economic benefit and cost of investment, to the traditional construction method and the new method of enlarging shield tunnels. It indicates that the new method not just reduce greatly the construction time, more than enormously lower capitalized cost of project and raise the economic benefit, which have a good role as reference of similar project in the future and worth to advocate.8. Through model tests and optimal computation, together with engineering geological condition and hydrogeology conditions in construction site area, this dissertation pro-pose an optimal process of shield under-passing buildings and ground consolidation scheme. In other words, it is double stratigraphic reinforcement measure that includes both setting long and large pipe shed or sleeve valve pipe and grouting reinforcement, which is applied to the actual projects.9. Based on the Peck formula and random medium theory, in the relatively safe stage of shield working, it could get the related corresponding parameter by inverse analysis, combining with the rate of settlement relation between the stage of shield and expanding excavation, in order to realize the transform of settlement parameters between the stage of shield and expanding excavation. By this way, it could take advantage of comparatively safe shield stage achieving an accurate forecast of ground settlement to the dangerous expanding excavation stage, which turn out that it has been made a good predictive effect and can have an important guiding significance to the working of expanding excavation stage. |
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