| Wen-ma highway, Ya-kang highway and G318(from Kangding to Zhubalong section),G317(from Maerkang to Dege section)is the vital traffic road to Tibet and Qinghai area. There are complex geological environment and intense tectonic activity in this region. These roads go through high mountains, canyons, plateaus, basins and other geomorphic patterns. Strong frost weathering caused a lot of geological disasters along the roads. Based on the field investigation, experiments which includes low temperature strain test, freeze-thaw cycle test, and uniaxial compression test with acoustic emission monitoring techniques of fissured rock mass, and theoretical calculation, studies results of the paper are as follows:(1) Characteristics of the distribution of geological disasters in the researched regionGeological environmental data and field investigation indicate that: Collapse is a major form of geological disasters along the roads, Characteristics of the distribution of geological disasters is mainly influenced by climate conditions, seismic, geomorphology, lithology, rock mass structure. Because of strong frost weathering, erosion, sliding is the main collapse pattern in high altitude area.(2) Influence factor and deformation characteristics of freeze-thaw in fissured rock massLithological, structure plane of rock mass, surface, moisture and temperature conditions are the main factors affecting the deformation of freeze-thaw damage of fissured rock mass. The low temperature strain test indicates that: the strain curves of fissured rock with different crevice in a cycle time are significant different. after several freeze-thaw cycles, Micro residual strain of the fissured rock mass tends to accumulated increasing.(3) Physical and mechanical characteristics of frozen-thawed rocks(1)Physical characteristics: The rock samples which whether dry or saturated through the different cycles of frozen- thawed cycle tests show no obvious signs of failure. Quality and wave velocity variation caused by freeze-thaw action, is quite small.(2)Mechanical characteristics: Phyllite and sandstone, varying levels of hardness, resulting in their destruction of the specimen under uniaxial compression forms, Phyllite occurred along phyllitic cleavage and sandstone dominated by shear failure. The uniaxial compressive strength of the rock samples with different moisture intends to decrease along with increase of cycles. and the uniaxial compressive strength ratio tends to increase. The tests also indicate that attenuation amplitude of saturated rock samples is obviously larger than dry samples’.(3)Acoustic emission(AE) characteristics: no frozen-thawed cycling test have least number of acoustic emission before failure, and acoustic emission signal is weaker.with the increase of number of freeze-thaw cycles, rock specimen in uniaxial compression of acoustic emission number is gradually increasing before the failure. Freeze-thaw cycles of increasing micro-fissures of rock, thus in uniaxial compression test of crack closing stage triggers a lot of acoustic emission signals.(4) Combining the existing calculation method of frost force and some assumptions to develop an expression that calculate the frost force of crack ice, thus introduce it to correct rock stability evaluation of the slip type dangerous rock.(5)Based on the experiments and theoretical calculations, Alpine area disaster-causing mechanism of rock slope summarized as follows:(1)Due to pore water and the rock mineralogical different thermodynamic characteristics of rocks, the effect of temperature difference leads to the two different deformation characteristics. Eventually,generate new micro-cracks and gradually surface of rock mass slope fragmentation and spalling;(2)Frost force increases the slope of dangerous rock fall,at the same time, Repeated freeze-thaw cycle of the rock deteriorate the strength parameters of discontinuities, reduces the shear strength of rock mass. Finally, Weaken the stability of rock, induced collapse disasters under the action of gravity. |
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