One-dimensional thaw thermo-consolidation model for saturated frozen soil under high temperature and its solution
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摘要: 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Wr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。Abstract: 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 factor ε is positive, and this effect increases with the increasing ε. 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 Wr 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.
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[1] 李国玉, 马巍, 王学力, 等. 中俄原油管道漠大线运营后面临一些冻害问题及防治措施建议[J]. 岩土力学, 2015, 36(10): 2963-2973. https://www.cnki.com.cn/Article/CJFDTOTAL-YTLX201510034.htm LI Guo-yu, MA Wei, WANG Xue-li, et al. Frost hazards and mitigative measures following operation of Mohe-Daqing line of China-Russia crude oil pipeline[J]. Rock and Soil Mechanics, 2015, 36(10): 2963-2973. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTLX201510034.htm
[2] 牛富俊, 程国栋, 赖远明, 等. 青藏高原多年冻土区热融滑塌型斜坡失稳研究[J]. 岩土工程学报, 2004, 26(3): 402-406. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC200403024.htm NIU Fu-jun, CHENG Guo-dong, LAI Yuan-ming, et al. Instability study on thaw slumping in permafrost regions of Qinghai-Tibet Plateau[J]. Chinese Journal of Geotechnical Engineering, 2004, 26(3): 402-406. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC200403024.htm
[3] 陈瑞杰, 程国栋, 李述训, 等. 人工地层冻结应用研究进展和展望[J]. 岩土工程学报, 2000, 22(1): 40-44. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC200001006.htm CHEN Rui-jie, CHENG Guo-dong, LI Shu-xun, et al. Development and prospect of research on application of artificial ground freezing[J]. Chinese Journal of Geotechnical Engineering, 2000, 22(1): 40-44. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC200001006.htm
[4] 胡向东, 李忻轶, 吴元昊, 等. 拱北隧道管幕冻结法管间冻结封水效果实测研究[J]. 岩土工程学报, 2019, 41(12): 2207-2214. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201912008.htm HU Xiang-dong, LI Xin-yi, WU Yuan-hao, et al. Effect of water-proofing in Gongbei Tunnel by freeze-sealing pipe roof method with field temperature data[J]. Chinese Journal of Geotechnical Engineering, 2019, 41(12): 2207-2214. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201912008.htm
[5] 周洁, 李泽垚, 万鹏, 等. 组合地层渗流对人工地层冻结法及周围工程环境效应的影响[J]. 岩土工程学报, 2021, 43(3): 471-480. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC202103013.htm ZHOU Jie, LI Ze-yao, WAN Peng, et al. Effects of seepage in clay-sand composite strata on artificial ground freezing and surrounding engineering environment[J]. Chinese Journal of Geotechnical Engineering, 2021, 43(3): 471-480. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC202103013.htm
[6] 张升, 颜瀚, 滕继东, 等. 一个冻土的渗透系数模型及其验证[J]. 岩土工程学报, 2020, 42(11): 2146-2152. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC202011026.htm ZHANG Sheng, YAN Han, TENG Ji-dong, et al. New model for hydraulic conductivity of frozen soils[J]. Chinese Journal of Geotechnical Engineering, 2020, 42(11): 2146-2152. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC202011026.htm
[7] 程桦, 陈汉青, 曹广勇, 等. 冻土毛细-薄膜水分迁移机制及其试验验证[J]. 岩土工程学报, 2020, 42(10): 1790-1799. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC202010004.htm CHENG Hua, CHEN Han-qing, CAO Guang-yong, et al. Migration mechanism of capillary-film water in frozen soil and its experimental verification[J]. Chinese Journal of Geotechnical Engineering, 2020, 42(10): 1790-1799. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC202010004.htm
[8] 周扬, 周国庆, 周金生, 等. 饱和土冻结透镜体生长过程水热耦合分析[J]. 岩土工程学报, 2010, 32(4): 578-585. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201004018.htm ZHOU Yang, ZHOU Guo-qing, ZHOU Jin-sheng, et al. Ice lens growth process involving coupled moisture and heat transfer during freezing of saturated soil[J]. Chinese Journal of Geotechnical Engineering, 2010, 32(4): 578-585. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201004018.htm
[9] 周扬, 周国庆, 王义江. 饱和土水热耦合分离冰冻胀模型研究[J]. 岩土工程学报, 2010, 32(11): 1746-1751. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201011021.htm ZHOU Yang, ZHOU Guo-qing, WANG Yi-jiang. Separate ice frost heave model for coupled moisture and heat transfer in saturated soils[J]. Chinese Journal of Geotechnical Engineering, 2010, 32(11): 1746-1751. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201011021.htm
[10] ZHOU Y, ZHOU G Q. Intermittent freezing mode to reduce frost heave in freezing soils—experiments and mechanism analysis[J]. Canadian Geotechnical Journal, 2012, 49(6): 686-693. doi: 10.1139/t2012-028
[11] 梁波, 张贵生, 刘德仁. 冻融循环条件下土的融沉性质试验研究[J]. 岩土工程学报, 2006, 28(10): 1213-1217. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC200610006.htm LIANG Bo, ZHANG Gui-sheng, LIU De-ren. Experimental study on thawing subsidence characters of permafrost under frost heaving and thawing circulation[J]. Chinese Journal of Geotechnical Engineering, 2006, 28(10): 1213-1217. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC200610006.htm
[12] 王天亮, 卜建清, 王扬, 等. 多次冻融条件下土体的融沉性质研究[J]. 岩土工程学报, 2014, 36(4): 625-632. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201404006.htm WANG Tian-liang, BU Jian-qing, WANG Yang, et al. Thaw subsidence properties of soils under repeated freeze-thaw cycles[J]. Chinese Journal of Geotechnical Engineering, 2014, 36(4): 625-632. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201404006.htm
[13] 王效宾, 杨平, 张婷. 人工冻土融沉特性试验研究[J]. 南京林业大学学报(自然科学版), 2008, 32(4): 108-112. WANG Xiao-bin, YANG Ping, ZHANG Ting. Study on thaw settlement behaviour of artificial freezing soil[J]. Journal of Nanjing Forestry University (Natural Sciences Edition), 2008, 32(4): 108-112. (in Chinese)
[14] 赵贵涛, 韩仲, 邹维列, 等. 干湿、冻融循环对膨胀土土-水及收缩特征的影响[J]. 岩土工程学报, 2021, 43(6): 1139-1146. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC202106024.htm ZHAO Gui-tao, HAN Zhong, ZOU Wei-lie, et al. Influences of drying-wetting-freeze-thaw cycles on soil-water and shrinkage characteristics of expansive soil[J]. Chinese Journal of Geotechnical Engineering, 2021, 43(6): 1139-1146. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC202106024.htm
[15] MORGENSTERN N R, NIXON J F. One-dimensional consolidation of thawing soils[J]. Canadian Geotechnical Journal, 1971, 8(4): 558-565.
[16] MORGENSTERN N R, SMITH L B. Thaw-consolidation tests on remoulded clays[J]. Canadian Geotechnical Journal, 1973, 10(1): 25-40.
[17] NIXON J F, MORGENSTERN N R. Thaw-consolidation tests on undisturbed fine-grained permafrost[J]. Canadian Geotechnical Journal, 1974, 11(1): 202-214.
[18] ZHOU Y, ZHANG L Y, XU C, et al. Analytical solution for classical one-dimensional thaw consolidation model considering unfrozen water effect and time-varying load[J]. Computers and Geotechnics, 2020, 122: 103513.
[19] FORIERO A, LADANYI B. FEM assessment of large-strain thaw consolidation[J]. Journal of Geotechnical Engineering, 1995, 121(2): 126-138.
[20] GIBSON R E, SCHIFFMAN R L, CARGILL K W. The theory of one-dimensional consolidation of saturated clays. II. Finite nonlinear consolidation of thick homogeneous layers[J]. Canadian Geotechnical Journal, 1981, 18(2): 280-293.
[21] YAO X L, QI J L, WU W. Three dimensional analysis of large strain thaw consolidation in permafrost[J]. Acta Geotechnica, 2012, 7(3): 193-202.
[22] YAO X L, QI J L, LIU M X, et al. Pore water pressure distribution and dissipation during thaw consolidation[J]. Transport in porous media, 2017, 116(2): 435-451.
[23] QI J L, YAO X L, YU F, et al. Study on thaw consolidation of permafrost under roadway embankment[J]. Cold Regions Science and Technology, 2012, 81: 48-54.
[24] WANG S H, QI J L, YU F, et al. A novel method for estimating settlement of embankments in cold regions[J]. Cold Regions Science and Technology, 2013, 88: 50-58.
[25] WANG L M, WANG W L, YU F. Thaw consolidation behaviours of embankments in permafrost regions with periodical temperature boundaries[J]. Cold Regions Science and Technology, 2015, 109: 70-77.
[26] DUMAIS S, KONRAD J M. One-dimensional large-strain thaw consolidation using nonlinear effective stress-void ratio-hydraulic conductivity relationships[J]. Canadian Geotechnical Journal, 2018, 55(3): 414-426.
[27] 王涛, 岳丰田, 姜耀东, 等. 井筒冻结壁强制解冻技术的研究与实践[J]. 煤炭学报, 2010, 35(6): 918-922. https://www.cnki.com.cn/Article/CJFDTOTAL-MTXB201006012.htm WANG Tao, YUE Feng-tian, JIANG Yao-dong, et al. Research and practice on forced thaw technology applied to frozen wall of mine shaft[J]. Journal of China Coal Society, 2010, 35(6): 918-922. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-MTXB201006012.htm
[28] 袁云辉, 杨平, 王海波. 人工水平冻结冻土帷幕强制解冻温度场数值分析[J]. 南京林业大学学报(自然科学版), 2011, 35(4): 117-120. https://www.cnki.com.cn/Article/CJFDTOTAL-NJLY201104027.htm YUAN Yun-hui, YANG Ping, WANG Hai-bo. Thermal field numerical analysis of artificial thawing of horizontal freezing soil wall[J]. Journal of Nanjing Forestry University (Natural Sciences Edition), 2011, 35(4): 117-120. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-NJLY201104027.htm
[29] ZHOU Y, RAJAPAKSE R K N D, GRAHAM J. A coupled thermoporoelastic model with thermo-osmosis and thermal-filtration[J]. International Journal of Solids and Structures, 1998, 35(34/35): 4659-4683.
[30] 白冰. 岩土颗粒介质非等温一维热固结特性研究[J]. 工程力学, 2005, 22(5): 186-191. https://www.cnki.com.cn/Article/CJFDTOTAL-GCLX200505033.htm BAI Bing. One-dimensional thermal consolidation characteristics of geotechnical media under non-isothermal condition[J]. Engineering Mechanics, 2005, 22(5): 186-191. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-GCLX200505033.htm
[31] 吴瑞潜, 谢康和, 程永锋. 变荷载下饱和土一维热固结解析理论[J]. 浙江大学学报(工学版), 2009, 43(8): 1532-1537. https://www.cnki.com.cn/Article/CJFDTOTAL-ZDZC200908034.htm WU Rui-qian, XIE Kang-he, CHENG Yong-feng. Analytical theory for one-dimensional thermal consolidation of saturated soil under time-dependent loading[J]. Journal of Zhejiang University (Engineering Science), 2009, 43(8): 1532-1537. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-ZDZC200908034.htm
[32] 钮家军, 凌道盛, 王秀凯, 等. 饱和单层土体一维热固结精确解[J]. 岩土工程学报, 2019, 41(9): 1715-1723. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201909018.htm NIU Jia-jun, LING Dao-sheng, WANG Xiu-kai, et al. Exact solutions for one-dimensional thermal consolidation of single-layer saturated soil[J]. Chinese Journal of Geotechnical Engineering, 2019, 41(9): 1715-1723. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201909018.htm
[33] ZHOU Y, ZHOU J, SHI X Y, et al. Practical models describing hysteresis behavior of unfrozen water in frozen soil based on similarity analysis[J]. Cold Regions Science and Technology, 2019, 157: 215-223.
[34] ZHOU Y, WANG Y J, BU W K. Exact solution for a Stefan problem with latent heat a power function of position[J]. International Journal of Heat and Mass Transfer, 2014, 69: 451-454.
[35] ZHOU Y, HU X X, LI T, et al. Similarity type of general solution for one-dimensional heat conduction in the cylindrical coordinate[J]. International Journal of Heat and Mass Transfer, 2018, 119: 542-550.
[36] 涂新斌, 戴福初. 土体一维传热方程解析解及热扩散系数测定[J]. 岩土工程学报, 2008, 30(5): 652-657. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC200805007.htm TU Xin-bin, DAI Fu-chu. Analytical solution for one-dimensional heat transfer equation of soil and evaluation for thermal diffusivity[J]. Chinese Journal of Geotechnical Engineering, 2008, 30(5): 652-657. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC200805007.htm
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