扰动后冻土抗压强度衰减规律及机理研究

ATTENUATION RULE AND MECHANISM OF COMPRESSIVE STRENGTH OF FROZEN SOILS SUBJECTED TO EXTERNAL DISTURBANCE

土体强度是冻结施工的关键技术指标,为研究外部扰动作用对冻土抗压强度的影响,采用室内试验方法对扰动后原状和重塑冻土无侧限抗压强度变化规律研究。研究表明原状冻土在扰动10次内,强度迅速衰减,之后降速放缓并稳定,残余强度与峰值强度比值约为0.3;重塑冻土强度随扰动次数呈弧形下降,残余强度与峰值强度比值小于0.1;冻土强度衰减原因可以从冰晶格断裂、土颗粒胶体断裂及温度升高三方面考虑;对于原状土,结构性破坏引起的强度衰减不可忽略,通过电镜试验发现,扰动后单位面积内土颗粒数量增加,有效粒径减小,颗粒形态更加规则,而重塑土颗粒形态未有明显变化,其强度损失主要是因为冰胶结力的丧失。结论可为冻结施工时外力扰动控制提供借鉴与参考。

The strength of soil is a key technical indicator during construction work in cold areas.The influence of external disturbance on the compressive strength of frozen soil is investigated,in which unconfined compressive strength of undisturbed and remolded frozen soil is measured in laboratory experiments.The results show that the strength of undisturbed frozen soil rapidly decreases within 10 disturbances and then stabilizes down with the residu⁃al strength ratio about 0.3.The strength of remolded frozen soil decreases in an arc type with the number of distur⁃bances,and the residual strength ratio is less than 0.1.The reasons for the strength attenuation of frozen soil are ice crystal lattice fracture,soil particle colloid fracture,and temperature rise.For undisturbed soil,the strength attenua⁃tion caused by structural failure cannot be ignored.Through electron microscopy experiments,the number of soil par⁃ticles per unit area increases after disturbance and the effective particle size decreases.Except those,the particle shape becomes regular and there is no significant change in the morphology of the reshaped soil particles.Finally,the strength loss mainly results from the loss of ice bonding force.