Study Of The Characteristics Of The Weathring Of Schist Under Freeze-Thaw Action Along Sichuan-Tibet Railway

In term of landform, Three Parallel Rivers Region (TPRR) along the Sichuan-Tibet Railway is in the alpine-gorge area of the Hengduan Mountains in Tibet southeast, with the characteristics of high altitude from 3000 to 6000m and high gap from1500 to 3000m. One of the typical rock and soil type in Three Parallel Rivers Region is the weathered deposit which consist in the environment of large temperature difference in alpine mountain regions. The special geological environment and the unique formation mechanism determines its special engineering geological characteristics. This paper selects schist Sichuan-Tibet Railway station controlling point, combined with engineering survey data and laboratory test by means of physical and mechanical properties of rocks and weathering mechanism under the conditions of freeze-thaw cycles, Combined with engineering survey data and laboratory tests, this paper selects the schist which collect from control point of the Sichuan-Tibet Railway, research physico-mechanical properties and weathering mechanism of the schist under freeze-thaw condition which provide a reference and guidance for railway engineering design,the choice of rock & soil mechanics parameters and railway maintenance.First of all, grasp the distribution of the climate, elevation, lithology and other factors by means of a review of the relevant literature, data and field investigation in the Three Parallel Rivers region of the Sichuan-Tibet Railway. Then the size of 025 x 50mm cylindrical rock samples are made from large in situ rock specimens and schist basic physical properties of indicators are obtained in the laboratory through performing physical properties test, hydrological properties test and acoustic wave velocity test. Conducting freeze-thaw cycles experiment of wide temperature range from -40 (±2℃) to+50 (±2℃) to simulate the effect of frost weathering in the Three Parallel Rivers Region environment (105 years),and freeze-thaw cycles experiment of temperature range from -20 (±2℃) to+ 20 (±2℃) were compared. During the experiment, loss of quality, change in velocity under different freeze-thaw cycles of rock samples are counted with observing deterioration in the appearance of rock samples, combining with uniaxial compression test.Then from the degradation of surface damage, mass loss, velocity, uniaxial compressive strength, uniaxial compressive stress-strain curve and other aspects, rock deterioration in the freezing and thawing cycles are analyzed respectively.Finally, based on the experimental data, rock joints spacing, broken rock shape, discontinuity surface rebound value, rock mass weathering characteristics are analyzed. Combined with the calculation of point load strength index、freeze-thaw weathering coefficient、velocity、velocity variation and with reference to other research the rate of rock freeze-thaw weathering are calculated. Compared with the analysis of rock freeze-thaw weathering and rock mass freeze-thaw weathering, the internal relation between them is explored.