| Red beds in Gansu Province is a regional special rock with distinctive engineering characteristics, which is the main building site of the Expressway.Along with the continued development of Gansu province Expressway to the red bed area,The deformation and failure of slope has become the main engineering geological problem in Expressway construction. However, the systematic study in the field of Expressway engineering in Gansu is still blank. In this paper, based on more than ten years of Gansu Expressway survey and design, construction and operation and maintenance practice, Using the basic theory of engineering geology, rock mechanics, soil mechanics and systems engineering, through geological mapping, laboratory and in situ tests, numerical simulation, theoretical calculation and typical engineering examples analysis, for the purpose of the research on engineering characteristics and slope stability of red beds, the following 7 aspects are studied:1. In order to clarify the importance of red beds in Gansu Expressway engineering, based on the results of previous studies, according to the results of 32 road of geological survey, the geologic features of red beds in Gansu Province is analyzed, universality and difference of the natural geological hazards in the red beds area in Gansu Province are discovered, the diseases of Expressway Engineering in red beds area are concealed and long term harm. complexity and long-term hazard of Expressway Engineering are also found.2. In view of the complexity of the physical and mechanical properties of red beds in Gansu Province, based on the statistics of the experiment results of 2000 groups of rocks, physical mechanics and water physical properties of red beds in Gansu Province are analyzed. There are obvious differences in the strength of rock in the two aspects of the distribution area and the lithologic classification.The correlation between physical and mechanical indexes of red beds in Gansu is detailed study, the recommended index system of physical mechanics for red beds of Gansu Expressway engineering is put forward.3.According to the test results of the typical tunnel drilling speed, The wave velocity characteristics of Cretaceous and Tertiary system are summarized. Relying on the comprehensive in-situ tests of the large rock mass of the Liujiaxia Bridge, the sandy mudstone of N ingxia group is found to belong to the plastic elastic rock mass. And it is found that the shear strength of rock / rock is larger t han that of concrete / rock contact surface. By Comparison of rock / rock shear test and rock block shear test results, rock cohesion is 66.7% of the rock, angle of internal friction is rock 63.46%. Comparison of cutting shear strength test of N ingxia group of sandy mudstone layer and layer conditions, it is found that the variation of the coefficient of internal friction in different shear directions is small, but the difference of cohesion is different, the anisotropy of shear strength of rock mass is obvious.4.From the need of slope support in Gansu Expressway, the major types of the red beds slope and rock slope in Gansu province are divided into two types: covered red beds slope and the rock slope, and the former is divided into 5 sub types: loess- red soil slope, cohesive soil- red soil slope, cohesive soil- red soil slope, gravel soil- red beds slope, sand- red beds slope, the latter is divided into 2 sub categories, such as homogeneous structure and layered structure, The deformation modes and failure mechanisms of various types of slope are analyzed.5.Combining construction practice of the Shiyan to Tin Shui expressway, through numerical simulations on progressive failure process of the cover type red beds slope and sheet pile wall deformation failure characteristic are analyzed. By establishing the geological model and model calculation of the covered red beds slope, Progressive deformation failure mechanism of the covered red beds slope described as Tension crack cut through the water bearing layer- tension crack water filling- hydrostatic pressure action- slope slip. the solution of fast estimation of slope stability coefficient based on tensile fracture site is presented. The shear strength and its influencing factors of the red layer cover are studied, and it is suggested that the residual strength is used to calculate the stability of the red bed slope.6.In view of the harmfulness of the bedding slide of the red bed slope,according to the basic principles of statics, the calculation formula of critical height of slope, critical slope and slope unloading platform critical width of bedding slope under the limit equilibrium state, and the calculation formula of the whole slip length of bedding slope with weak interlayer are derived. Relying on engineering examples of typical bedding slope failure during construction process in Lanzhou to Yongjing first grade Expressway, The effectiveness of the top unloading platform prevention bedding slope sliding is analyzed, and it is pointed out that the bedding sliding surface of slope with soft interlayer is located in the bottom of the weak interlayer, and these are verified by engineering examples.7.According to the complexity of factors affecting the stability of reservoir bank of abutment, relying on the Liujiaxia Bridge survey and design, the rock mass structure characteristics of abutment at reservoir bank in red beds area are studied. with stereographic projection, the stability of abutment bank under natural state is qualitatively analyzed. By using the limit equilibrium theory and Geo-slop software, considering 8 conditions combination by rainfall, earthquake, reservoir water level fluctuation, abutment loading and other factors, stability of natural slope abutment slope and excavation of the bridge is qualitatively analyzed. Base on the sensitivity analysis of parameters, the basic law that the slope stability increases with the internal friction angle and cohesion, and the lower the water level is, the lower the stability coefficient are discovered. by using the deformation theories, through the seven stages of FLAC simulation, it is not only found that the water rising process increase the vertical displacement of abutment slope, but also that the fluctuation of reservoir water level is not caused by the whole pore water pressure field, and the slope of the maximum vertical displacement 1.5mm, reservoir banks of the bridge on the whole are in steady state. The actual situation of the reservoir bank of abutment is consistent with the numerical simulation evaluation conclusion. |
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