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Weathering rates of rock and soil masses in Yen Bai City, Vietnam

Adetoro, adeyemi Ezekiel (2011) Weathering rates of rock and soil masses in Yen Bai City, Vietnam.

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Abstract:Weathering of rock masses, which start from the moment of exposure of a rock mass (e.g. through cutting of slopes) has a large influence on the geotechnical properties of a rock mass within the engineering timescales and is one of the main causes of slope failure, which is occurring presently in Yen Bai City in Vietnam. This called for the need to determine the rate of weathering of the mainly already deeply weathered tropical rock and soil masses of Yen Bai city area, which would allow better design of slopes. Fifteen cut slopes are selected out of inspected thirty – five cut slopes of AR?nc1 and AR?nc2 geological formations of the area and analyzed using Slope Stability Probability Classification (SSPC) and Colman‟s formula based methods. The SSPC method is used in acquiring the basic geotechnical parameters of the selected cut slopes and in analyzing them to determine their slope stability and other derived geotechnical parameters like cohesion and friction of the rock mass unit (i.e. SCOH and SFRI). The analyses using the two methods are carried out under two perspectives – rock mechanics and spatial analyses. Results show that SCOH and SFRI reduces as exposure time of cut slope increases, and the higher the SCOH and SFRI, the better the slope stability. There is also change in degree of weathering over some years of exposure of rock mass though might not be visible until after 20 years. It also shows that some materials are susceptible to weathering than others within the rock mass materials and between two geological formations. Generally, a comparison of weathering rate of rock mass between Yen Bai tropical and Mediterranean region (where SSPC was developed) shows that weathering rates are much higher in tropical than in the Mediterranean region as expected. A slope in the Yen Bai area is generally made at the maximum angle and slope height that can be sustained in the material at the time of exposure for the top soil layers. In the deeper layers, i.e. in slightly or moderately weathered material, the angle and slope height are not at the maximum at time of exposure, but progressive weathering due to exposure will weather these materials to highly or completely weathered in about 30 years. The slope angle and height cannot be sustained by highly or completely weathered material and the slope will fail.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
Link to this item:https://purl.utwente.nl/essays/92762
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