高温下饱和冻土一维融化热固结模型及解答

One-dimensional thaw thermo-consolidation model for saturated frozen soil under high temperature and its solution

冻结法应用及寒区施工中常采用高温热水强制融化冻土,针对饱和冻土在高温下的一维融化过程,建立了理论模型并给出了模型的解析解答。模型包含传热及热固结两部分,前者为全区域考虑未冻水的相变热传导过程,后者为融区内土体在温度、荷载及自重作用下的热固结过程。传热部分在文献中已有温度场、融化界面的解析解答,而融区内超静孔压的解析解答由本文推导获得。在忽略土颗粒、水的热膨胀作用后,模型和解答可以退化为Morgenstern和Nixon的经典冻土一维融化固结模型。利用模型解答对冻土在高温下一维融化过程中超静孔压、沉降进行了计算分析,结果表明:热压作用在热固结强度因子ε为正时会减小超静孔压,该效果随着ε增加而增强;减小融化固结比R或增大导温固结比F均扩大热压作用的相对影响范围,但前者使热压作用在融区内趋于均匀,后者会增加整体的热压作用;增加自重时间因子W_(r)几乎不改变热压作用强度及相对影响范围;高温的净效果使融土产生膨胀,但其影响小于普通固结沉降,因此总体效果仍表现为沉降。

During the application of artificial ground freezing technique and construction in cold regions,high-temperature hot water is often used to melt the frozen soil manually.For the one-dimensional thawing process of saturated frozen soil under high temperature,a theoretical model describing the process is established and an analytical solution is developed for the model.The model comprises a heat transfer part and a thermo-consolidation part.The former is a heat conduction process of frozen soil with phase change of pore ice considering the unfrozen water effect,while the latter is a thermo-consolidation process of soil in the thawed region under the effects of high temperature,external load and self-weight.The temperature field and the melting interface for the heat transfer part have already been deduced in the existing literatures,which are adopted directly.For the excessive pore water pressure in the thawed region,an analytical solution is developed.By neglecting the thermal expansion of soil grains and water,the proposed model and the developed solution may degenerate to those of the classical one-dimensional thaw consolidation model for frozen soil developed by Morgenstern and Nixon.The analytical solution is then used to analyze the excessive pore water pressure and the settlement for one-dimensional thawing process of frozen soil under high temperature.The results show that the effect of thermal pressure reduces the excessive pore water pressure if the thermo-consolidation intensity factorεis positive,and this effect increases with the increasingε.Reducing the thaw consolidation ratio R or increasing the diffusion consolidation ratio F will expand the relative influence zone of the thermal pressure.However,the former leads to a more uniform thermal pressure effect in the thawed region,while the latter generally increases the thermal pressure effect in the thawed region.Increasing the self-weight time factor W_(r) barely changes the intensity and the relative influence zone of the thermal pressure.The net effect of high temperature is to expand the thawed soil,but it is weaker than the effect of normal consolidation settlement,thus the general effect is still settlement.