| The landslides are common natural disasters in mountainous areas. The landslidesmay often cause great loss of life and property, and often threaten the people’s productionand living.The landslides cannot come into being without their own geological conditions androck soil structure conditions, weathering is the main factor in decrease of rock massstrength, and at the same time, the rainfall is the main induced factors of landslide. Sothere are important practical significances and engineering values to study rock massstrength development in weathering and slope stability under rainfall infiltration.The paper is based on the tunnel slope of Shiyan section coming from Fuzhou toYinchuan expressway, and focused on Yangnangou tunnel slope. The geologicalconditions and rock mass strength condition were mainly studied by indoor and outdoorphysical mechanics experiment on weathered rock mass, the strength-depth Boltzmannfunction was established. According to the characteristics of rainfall in Shiyan area, therainfall influence to the weathering slope is studied. Main results are as follows:（1）The lithology for the slope is serictie chlorite schist, which is soft rock, with thelow strength and Schistosity and fracture, and may easily weathered. The full weatheredrock residual soil is belong to gravel soil, the plasticity index of fine particle part soil is9.5, less than10, there is some property of silt. The direct shear test result of residual soilwas that the cohesive value was from13KPa to20KPa and friction angle value was about30degree, the value reduced when soil saturated. The large scale in-situ direct shear testwas carried out using the instrument developed by the Chinese academy of sciences,Wuhan rock mechanics research institute and Hong Kong University. The result of testshow that, the stress strain curve is the strain hardening type, the original rock structuralcharacteristics can be seen form the weathered rock residual soil.（2）Based on transversely isotropic model, anisotropic properties of serictie chloriteschist were studied, using rock mechanics test machine RMT-150C, developed byInstitute of Rock and Soil Mechanics, Chinese Academy of Sciences. The strength andelastic modulus parallel to foliations was higher than that vertical to foliations, The Ultimate compressive strength ratio (c/c’) was2.44, it showed great different withlayered rock for the ratio was usually about1.0. Five elastic constants of transverselyisotropic rocks showed obvious anisotropic property. The elastic modulus ratio (E/E ’)was3.86, the Pionsson’s ratio (v/v ’) was1.26. As the Poisson’s ratio v ’is usuallyabout0.2, so when E is more than three times of E ’, the Saint-Venant’s empiricalequation can be take place by a simple elastic equation G ’ E ’/2(1v’). Under parallelcompression, tension-split happened along foliations and rod press-bent failure was easilycaused by Poisson effect. Under vertical compression, tension-shear failure was easilycaused along lateral direction.（3）The strength of rock gradually changed under weathering, the weathering hasthe time and depth effect. The exploration research on weathering evolution process isvery lack, for weathering is caused by temperature and rainfall infiltration, rockweathering intensity decreased process was exploratory established using rainfallinfiltration for reference. It was verified by wetting-drying test of rock. Boltzmannfunction was used to express Weathering depth effect, and verified by test. Equations ofparameter selection were discussed.（4）According to rainfall characteristics in Shiyan area, two kinds of rainfall wereused for seepage analysis. The result is that, with rainfall infiltration water content willincrease, the matrix suction will decline, and water level will rise at the feet of slope.Pore water pressure, volatile water content and hydraulic conductivity gradually is risingwith elevation, there is hysteresis effect. The stability of the slope decrease with therainfall, and with hysteresis quality increase after the rain, heavy rainfall has greaterinfluence on the slope stability.The results eliminate the mutability of strength at the weathering boundary surface,which can be referenced for weathering effect, and can be useful for forecast of rainfalllandslide, making reasonable design and effective protection. |
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