长时高压K_0固结再冻结黏土的卸围压强度特性

Strength properties of unloading confining pressure of long-term K_0-consolidated artifical frozen clay under high pressure

深厚表土层中立井井筒建设普遍采用冻结法,而深部冻土的原位力学特性是影响冻结壁力学特性及其安全稳定性的关键;现有的浅部冻土的试验方法,由于忽略了深、浅部土体固结、应力环境及形成工况的差异,已难以可靠地获得深部土的力学参数。基于"长时高压K_0固结—冻结—恒轴压卸围压"试验模式,通过三轴试验,研究了深部土重塑人工冻结黏土的强度与变形特征,以及固结时间、固结应力的影响规律。结果表明:卸围压路径下冻土试样呈现为黏–弹塑性破坏,固结时间为1~7 d时,其卸围压强度随固结时间的延长增长显著,而单位降温引起的强度增长速率受固结时间的影响不明显;随着固结时间延长至28 d,其卸围压强度受固结时间的影响不明显,但单位降温引起的强度增长速率增加显著;单位降温引起的冻土卸围压强度增长速率不受固结应力影响。

In most cases, the artificial ground freezing method has been applied to construction of vertical shaft in deep and thick alluvia. Thus the in-situ mechanical properties of deep frozen soils are the most pivotal influence factor to the stabilization of frozen wall. It is suspicious to acquire the mechanical parameters of deep soils by the methods which are suitable for shallow soils ignoring their engineering situation and origin. Therefore, based on the new test mode of ＂Long-term, K0 consolidated- freezing-constant axial pressure and unloading confining pressure＂, many triaxial unloading tests are conducted on remolded deep clay so as to study its strength and deformation properties and the influence laws of consolidation stress and consolidation time. The research results show that the failure mode of the frozen clay specimens under unloading path belongs to the viscoelastic-plastic one. The strength of the frozen clay consolidated for 1 to 7 days under unloading path increases evidently, however, the growth rate of strength is barely affected by the consolidation time while temperature decreases. Conversely, the strength increases inconspicuously when the consolidation time is expended to 28 days. In addition, there is significant increase of growth rate of strength relating to the descending temperature in the process of the long-term K0 consolidation. The influence of consolidated stress on the growth rate of strength hardly relates to the subzero temperature.