Predicting Methods Of Surrounding Rocks Deformation And Ground Surface Settlement Of Tunnel Expansion In-suit With Super Small Clear-distance

In recent years, tunnel expansion in-suit project is increasing day by dayboth at home and abroad. Tunnel expansion in-suit project turns out to besuper large span, super small clear-distance and flat section, and the existinglining always need to be demolished before the excavation of surroundingrocks and installation of lining. As a result, the bearing capacity of structureis easily reduced, the deformation of surrounding rocks is greater than expect.What’s more, it may cause collapse accident. Compare to a new tunnel, thedeformation of surrounding rocks and surface settlement caused by theexcavation of tunnel expansion in-suit is much more complex. However, howto predict it in a reliable way is still a serious and unsolved problem.Taking the uncommon two-to-four Damaoshan tunnel as background, theprediction methods of deformation of surrounding rocks and ground surfacesettlement are put forward by analytic solution, numerical simulation andempirical formula. Then the law of deformation of surrounding rocks andground surface settlement, the deformation characteristic and mechanicalresponse of surrounding rocks based on unloading effect and the sensitivityof mechanical parameters of surrounding rocks to surface settlement areresearched comprehensively, which provides reference to the surroundingrocks construction stability of tunnel expansion in-suit. The main work andachievements are as followed:1. Combined with the equivalent circle, the theory of complex function andSchwarz’s alternating method, the theoretical solution of surrounding rocksstress and deformation characteristics of non-circle cross section tunnel bylateral expansion is achieved. Taking two-to-four Damaoshan tunnel asexample, the preference width is analyzed.2. The unloading calculation method of tunnel expansion in-suit is carriedout based on the principles of unloading mechanical theory, then divide the surrounding rocks into three zones, namely, strongly disturbed zone, weaklydisturbed zone and non-disturbed zone.3. By programming APDL language, the various steps of unloadingcalculation method are imported into ANSYS. On the basis of it, thethree-dimensional finite element model of Damaoshan tunnel based onunloading effect is carried out.4. Based on the monitoring results, the deformation and mechanicalproperties of two-to-four tunnel by CD method under the consideration ofunloading effect are analyzed, as well as the distribution law of stronglydisturbed zone and weakly disturbed zone.5. The structure displacement of the existing four lane tunnel induced bytwo-to-four tunnel is as followed: the surrounding rocks on the left side ofthe existing four lane tunnel are within disturbed zone, therefore, the entiresection shows bias with deformation on left side greater than right side.6. The sequences of sensitivity of mechanical parameters to surfacesettlement are as followed: the elastic modulus, the Poisson’s ratio, cohesionforce and the friction angle.7. Based on the Peck formula and superposition principle, the simplefunction equation is put forward and the adaptability is verified.