| Under the influence of the transformation from permafrost region to seasonal permafrost region,geological disasters such as tunnel collapse and slope instability caused by freeze-thaw cycle frequently occur in the process of rock mass engineering construction in cold region,which have seriously affected the advancement of "One Belt And One Road" strategy in China.In this paper,the freeze-thaw damage characteristics and frost heave propagation mechanism of fractured rock mass were closely studied.Similar materials were used to prepare single-crack and double-crack rock samples with different fracture forms,and a series of freeze-thaw cycles and uniaxial compression tests were carried out.This paper analyzes the fracture characteristics and degradation of single fracture rock mass under the coupling action of freeze-thaw and load,explore double interference effect of fractured rock mass frost heaving extension and strength damage characteristics,and by using three dimensional crack extending simulation of freezing and thawing program TOUGH-FEMM analysis of test results,further reveals the low temperature of rock mass under different crack distribution form of frost heaving mechanism and the regularity of strength loss.The main research results are as follows:(1)Considering the real-time coupling of freeze-thaw and load,a unidirectional loading device suitable for high and low temperature freeze-thaw cycle test chamber was developed,and the freeze-thaw and load coupling test was conducted on single fractured rock mass.The results show that the single fractured rock mass at low temperature is subjected to pure I-type crack frost heave tensile stress under the action of no confining pressure.The frost heave crack will extend along the direction of the initial crack approximately.With the increasing of the unidirectional load(0 ? 9 MPa),the frost heaving crack will gradually turn to the direction of the maximum principal stress(compression direction).(2)Considering the influence of fracture morphology on frost heave propagation,the freeze-thaw cycle tests were carried out on the samples with different rock bridge dip angles(45° ? 180°)and different crack dip angles(0° ? 45°).It is found that under the action of low temperature freezing,the initial crack and its frost heave propagation crack will produce additional stress on the surrounding rock and adjacent cracks,and the stress field between the frost heave crack interferes with each other and superimposes each other,thus forming the stress shadow area similar to the hydraulic crack.With the increase of the dip Angle of the bridge and the crack Angle,the disturbance of the initial fracture by the induced stress becomes more intense,and the frost heaving crack at the end is more inclined to be overlapped with the adjacent crack and its propagation crack.(3)The strength damage and deformation characteristics of freeze-thaw rock mass were obtained by uniaxial compression tests of the two-crack samples before and after freeze-thaw.The results show that the frost heaving crack,as the dominant path,can provide a convenient channel for the accumulation and release of the loading energy,leading to different degrees of damage and deterioration of the UCS and elastic modulus of the freeze-thaw rock samples.Among them,the specimens with rock bridge angles of 90° ?135° are more likely to undergo shear slip failure along the path of frost heave crack,and the average decrease of compressive strength is more than 15%.(4)A double-crack model with different rock bridge inclination angles(45°,90° and135°)was established,and the swelling deformation and fracture process of double-crack rock mass under freeze-thaw action was simulated based on TOUGH-FEMM.The simulation results show that the discontinuous deformation such as crack propagation and coalescence can occur in the rock mass with double fracture after 1 ? 4 cycles of freeze-thaw,which is consistent with the experimental results. |
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