| Drafty tunnel with ribbed arch beam is a new tunnel structure type which is half-embedded and half-uncovered. Its stress mode and load mechanism is still unknown and the design theory remains to be established. Thus studying on drafty tunnel with ribbed arch beam has a significant meaning.Relying on the Long-Pu tunnel engineering of Huang (shan)-Ta(ling)-Tao(lin) highway, the systemic research is done for the deformation law of tunnel with ribbed arch beam and the structural load mode by combining field investigation, laboratory test, theoretical analysis and numerical simulation. The deformation characters of tunnel with ribbed arch beam have been revealed and its simplified model of structural load has been put forward.The main content and results of this paper are listed as following:The site geological survey of Long-Pu tunnel engineering was completed, its engineering geological characteristic was evaluated comprehensively, and the basic information for construction of drafty tunnel with ribbed arch beam was obtained.According to the Long-Pu tunnel section of Huang(shan)-Ta(ling)-Tao(lin) highway, the structure types of tunnel are compared and selected. Compared with other schemes, tunnel with ribbed arch beam has many advantages such as small disturbance of slope, little environmental disruption, simple and lightness structure, nice shape, good drafty performance. Based on this, the scheme of drafty tunnel with ribbed arch beam is proposed.The deformation characters of tunnel with ribbed arch beam were analyzed briefly; the comparative study of forced deformation of tunnel and slope under different excavation methods was developed by finite element method. It is conclude that the excavation method has an obvious effect on deformation and stress of tunnel and a tiny effect on deformation and stress of slope. Comparing the results of scheme imposing ribbed beam later with those of scheme imposing ribbed beam first, it shows that: the force on ribbed beam of the former is about 50% of that of the latter. The forces on anti-slide pile and inside liner of tunnel have little difference for these two situations, and as well as the stress and the deformation of slope. Thus the effect of different excavation methods on slope can be ignored. Developing the numerical analysis of the Long-Pu tunnel of Huang-Ta-Tao highway and comparing it with the field monitoring data, it shows that: their deformation laws are basically identical with each other; the value and distribution of stress anatomize basically each other; and the simulation results can really reflect the stress states of tunnel.The comparative analysis of slope failure mode of tunnel with ribbed arch beam was developed. The results are listed as follows: for the case of homogeneous surrounding rock, the failure mode of tunnel starts from the area adjacent to skewback and a wedge body along a certain leaning line slips when the strength of surrounding rock is low; the failure mode of tunnel changes and the slip can not be considered as a wedge body slip when the strength of surrounding rock is high. For the case of heterogeneous surrounding rock, failure mode of tunnel is still the wedge body slip along a certain leaning line and the slip happens in the shallow rock stratum with a low strength. It means that structural load of shallow tunnel is mainly the loosening load of shallow rock stratum. According to the analysis of failure mode, it is concluded that: slope failure mode of tunnel with arch beam of costal type coincide with the assumption about failure mode of shallow tunnel in"Code for Design of Road Tunnel". So structural load model of tunnel with ribbed arch beam can be drawn lessons from the calculating method of load for shallow and bias tunnel in"Code for Design of Road Tunnel".A comparative analysis of the calculating methods for fracture angle of slope and tunnel was developed, the analysis shows that results using the method recommended in"Code for Design of Road Tunnel"accord with the numerical calculating results, for its considering factors are comprehensive and it introduces many influence parameters such as internal friction angle of surrounding rock, slope angle, frictional resistance of slip plane and so on. Thus this method is fit for calculating the fracture angle of slope of tunnel with ribbed arch beam.A suitable simplified model of structural load for tunnel with ribbed arch beam was proposed and the change laws of structural load model under different slope cutting depth and different surrounding rock were analyzed. Analysis shows that structural load model can basically reflect load change laws caused by the changes of slope cutting depth and surrounding rock properties. Comparing results show that because the slope surface is free surface, the inclined press load caused by excavation is more outstanding. So it is necessary to modify the horizontal load of simplified model of structural load. Change of properties of surrounding rock causes change of loosening failure area, while the simplified model of structural load is not sensitive to change of properties of surrounding rock. Thus the simplified model of structural load is improved. Using the measured data, the improved structural load model is verified. The related achievements have been applied to the Long-Pu tunnel engineering of Huang(shan)-Ta(ling)-Tao(lin) highway and give a direct guidance to the engineering construction. A good technical effect and social benefit has been obtained.
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