Study On Technology System Of Zero Cave-entrance And Its Application Of Large Cross-section Tunnel Under Complex Geological Conditions

With the development of high-grade expressway construction, people has paid more attention to the tunnel entrance's security, environment and economic .etc under complicated geological conditions of mountain areas, and taken higher requirements on the road landscape and environment. Stability of tunnel portal slope is better in natural state, while construction will destroy vegetation, and change hydro-geological conditions, the same to reduce support and maybe cause serious problem to effect construction safety. A large number practices shows that the deformation or damage on the tunnel entrance is related to environment damage and unreasonable method of excavating. So, the best way is to minimize the excavation and natural environment damage. This paper, taking Huang (Ta) Tao expressway as example and following the principle of engineering geological analysis, establishes a perfect engineering technology methods system on excavation of tunnel hole ,through slope geological condition, rock mass structure and slope structure features, deformation mechanism, hole-assisted method, hole digging method and feedback research of monitoring. The paper manly includes:The core is to control the slope above tunnel entrance and surrounding rock deformation, make sure its stability and environment protection, establish a technology system of zero cave-entrance about highway tunnel, the system describes the principle, process, techniques and construction of main points. At the same time, based on the concept of system, the paper studies the technology of digging hole on the typical slope at tunnel entrance in Huang (Ta) Tao highway.The paper sums up the slopes characteristics in detail, and analyses the two key factor including joints system and geological groups. Surveying the structure of slopes along line for Huang (Ta) Tao highway geological conditions, and making classification of geology, the slopes mainly divided into layered structure( ), like layered structure( ), soft interlayer structure( ), based slope structure( ), loose body structure( ) and massive structure( ).According to the above mentioned classification, making focus on the slope of tunnel entrance. Based on the survey of slope structure, analyzing the main impact factors on the slope stability of tunnel entrance, and according to structure geology, classifying the slope deformation including mainly collapse, landslide, block failure, bending .etc seven types.Analyzing the interaction mechanism between slope of tunnel entrance and surrounding rock, they are mutually respond to each other, the deformation of surrounding rock is the main factor causing slope failure, and excavation by backstroke will also cause slope deformation, therefore, the main measure is to control the deformation of surrounding rock in tunnel entrance.Based on rock stress, deformation features and force characteristic of support, and index of flat rate technical, analyzing the mechanical effects to large-section tunnel.Based on traditional method of digging hole, using the technology system of zero cave-entrance to the shallow slope with fracture entrance, and analyzing average pressure and bias pressure in terms of relation between slope strike and hole axis, mainly analysis on the mechanical effect of tunnel constriction-assisted, tress of surrounding rock and slope, deformation features, results show that: Compared to traditional method,"zero"system has an containment effect to the deformation toward slope orientation. For the above two types hole, significant stress concentration happens at sets of junction between arch and pipe shed, it shows these areas will be easy to produce damage deformation, so the connections should be welded effectively. For the bias type, the concentration stress happens from the sets of ear wall connecting with arch to the bottom of foundation, it indicates that the ear wall undertakes the push force from arch because of topography, also the ear wall plays a positive role to restrain slope deformation.According to the interaction relation between joint orientation and tunnel axis, analyzing separately on orthogonal and oblique types divided from digging hole system controlled by joints, results show that: This kind slope should use the idea"slope reinforced first, entering cave after", also can be indicated that analyzing slope structure and deformation mechanism before excavation, and based on the survey previous and geological conditions exposed in site, then, submitting the targeted program and taking optimal designing in accordance with the exposed information and monitoring feedback.Analyzing the characteristics of a new type drafty tunnel with ribbed arch beam, using the concept of the technology system of zero cave-entrance through the whole tunnel construction period, and with a focus to its mechanical features, surrounding rock and slope stress and deformation features.