Abstract：Under the condition of measuring suction，a series of three-dimensional swelling pressure tests，three-dimensional swelling pressure tests for controlling vertical deformation and three-dimensional swelling pressure tests of expansive soils after drying-wetting cycle were carried out on intact expansive soils by using an improved unsaturated soil true triaxial apparatus to investigate the variation characteristics of three-dimensional swelling pressure. The effects of matric suction，vertical deformation and drying-wetting cycle on the three-dimensional swelling pressure were studied. The results show that three-dimensional swelling pressure increases with a decrease in suction and gradually stabilizes. In this process，there is an obvious critical suction value ，and which increases with an increase in initial suction. When ，the growth rate of three-dimensional swelling pressures and the decrease speed of suction are faster，when ，the growth rate of three-dimensional swelling pressures and the decrease speed of suction are slower. Three-dimensional limit swelling pressures increase with an increase in initial suction，and the vertical limit swelling pressure increases faster with the initial suction. The small change of vertical strain will lead to the rapid decrease of three-dimensional swelling pressures. With the continuous development of vertical strain，the three-dimensional swelling pressures gradually decrease and tend to be stable. Under different vertical strain conditions，there is no significant difference in the attenuation of the two horizontal swelling pressures，but the attenuation of the vertical swelling pressure is always larger than that of the horizontal swelling pressures. When the vertical strain is constant，as the initial suction increases，the attenuation of the three-directional swelling pressures increase. After drying-wetting cycles，the moisture content and suction of expansive soils decrease with an increase in the number of cycles，and the three-dimensional limit swelling pressures of intact expansive soils increase with an increase in the number of drying-wetting cycles.
[1] DU J P，ZHOU A N，LIN X S，et al. Prediction of swelling pressure of expansive soil using an improved molecular dynamics approach combining diffuse double layer theory[J]. Applied Clay Science，2021，203：105998.
[2] MA T，YAO C，DONG Y，et al. Physicochemical approach to evaluating the swelling pressure of expansive soils[J]. Applied Clay Science，2019，172：85–95.
[3] REDDY P S，MOHANTY B，RAO B H. Investigations for chemical parameters effect on swelling characteristics of expansive soils[J]. KSCE Journal of Civil Engineering，2021，25：4 088–4 105.
[4] NAVARRO V，MORENA G D L，GONZÁLEZ-ARTEAGA J，et al. A microstructural effective stress definition for compacted active clays[J]. Geomechanics for Energy and the Environment，2018，15：47–53.
[5] MIAO L C，HOUSTON S L，CUI Y，et al. Relationship between soil structure and mechanical behavior for an expansive unsaturated clay[J]. Canadian Geotechnical Journal，2007，44(2)：126–137.
[6] 张振营. 关于“膨胀力在非饱和土强度理论中的应用”一文的探讨[J]. 岩土工程学报，1999，21(2)：248.(ZHANG Zhenying. Discussion on“Application of swelling pressure in strength theory of unsaturated soils”[J]. Chinese Journal of Geotechnical Engineering，1999，21(2)：248.(in Chinese))
[7] 卢肇钧，吴肖茗，孙玉珍，等. 膨胀力在非饱和土强度理论中的作用[J]. 岩土工程学报，1997，19(5)：20–27.(LU Zhaojun，WU Xiaoming，SUN Yuzhen，et al. The role of swelling pressure in the shear strength theory of unsaturated soils[J]. Chinese Journal of Geotechnical Engineering，1997，19(5)：20–27.(in Chinese))
[8] WAN L L，ZOU W L，WANG X Q，et al. Comparison of three inclusions in reducing lateral swelling pressure of expansive soils[J]. Geosynthetics International，2018，25(5)：481–493.
[9] 丁振洲，郑颖人，李利晟. 膨胀力变化规律试验研究[J]. 岩土力学，2007，28(7)：1 328–1 332.(DING Zhenzhou，ZHENG Yingren，LI Lishen. Trial study on variation regularity of swelling force[J]. Rock and Soil Mechanics，2007，28(7)：1 328–1 332.(in Chinese))
[10] JIA L Y，CHEN Y G，YE W M，et al. Effects of a simulated gap on anisotropic swelling pressure of compacted GMZ bentonite[J]. Engineering Geology，2019，248：155–163.
[11] 何芳婵，李宗坤. 南水北调南阳段弱膨胀土增湿膨胀与力学特性试验研究[J]. 岩土力学，2013，34(增2)：190–203.(HE Fangchan，LI Zongkun. Experimental study of wetting expansibility and mechanical properties of weak expansive soil in Nanyang section of South-to-North Water Diversion Project[J]. Rock and Soil Mechanics，2013，34 (Supp.2)：190–203.(in Chinese))
[12] 李献民，王永和，杨果林，等. 击实膨胀土工程变形特征的试验研究[J]. 岩土力学，2003，24(5)：826–830.(LI Xianmin，WANG Yonghe，YANG Guolin，et al. Test study on engineering deformation characteristics of compacted expansive soil[J]. Rock and Soil Mechanics，2003，24(5)：826–830.(in Chinese))
[13] AVSAR E，ULUSAY R，SONMEZ H. Assessments of swelling anisotropy of Ankara clay[J]. Engineering Geology，2009，105(1/2)：24–31.
[14] ABBAS M F，ELKADY T Y，AL-SHAMRANI M A. Evaluation of strain and stress states of a compacted highly expansive soil using a thin-walled oedometer[J]. Engineering Geology，2015，193：132–145.
[15] 刘洪伏，汪时机，李 贤，等. 邯郸强膨胀土三向膨胀力特性试验研究[J]. 岩土工程学报，2019，41(4)：789–796.(LIU Hongfu，WANG Shiji，LI Xian，et al. Experimental study on three-dimensional swelling pressure of highly expansive clay in Handan district of China[J]. Chinese Journal of Geotechnical Engineering，2019，41(4)：789–796.(in Chinese))
[16] 刘冬梅. 膨胀土的胀缩变形机制及其工程应用[J]. 南方冶金学院学报，1999，20(2)：69–73.(LIU Dongmei. Swelling shrinkage deformation mechanism of expansive soil and its engineering application[J]. Journal of Southern Institute of Metallurgy，1999，20(2)：69–73.(in Chinese))
[17] 谢 云，陈正汉，孙树国，等. 重塑膨胀土的三向膨胀力试验研究[J]. 岩土力学，2007，28(8)：1 636–1 642.(XIE Yun，CHEN Zhenghan，SUN Shuguo，et al. Test research on three-dimensional swelling pressure of remolded expansive clay[J]. Rock and Soil Mechanics，2007，28(8)：1 636–1 642.(in Chinese))
[18] CHEN Y G，DONG X X，ZHANG X D，et al. Cyclic thermal and saline effects on the swelling pressure of densely compacted Gaomiaozi bentonite[J]. Engineering Geology，2019，255：37–47.
[19] 方瑾瑾，邵生俊，李 荣，等. 真三轴条件下Q3黄土的屈服特性研究[J]. 岩石力学与工程学报，2016，35(9)：1 936–1 944.(FANG Jinjin，SHAO Shengjun，LI Rong，et al. Yield characteristics of Q3 loess in true triaxial tests[J]. Chinese Journal of Rock Mechanics and Engineering，2016，35(9)：1 936–1 944.(in Chinese))
[20] 方瑾瑾，冯以鑫，余永强，等. 真三轴条件下的原状黄土增湿变形特性[J]. 岩土力学，2020，41(4)：1 235–1 246.(FANG Jinjin，FENG Yixin，YU Yongqiang，et al. Wetting deformation characteristics of intact loess under true triaxial conditions[J]. Rock and Soil Mechanics，2020，41(4)：1 235–1 246.(in Chinese))
[21] 高国瑞. 膨胀土的微结构和膨胀势[J]. 岩土工程学报，1984，6(2)：40–48.(GAO Guorui. Microstructures of expansive soil and swelling potential[J]. Chinese Journal of Geotechnical Engineering，1984，6(2)：40–48.(in Chinese))
[22] 张颖钧. 裂土三向胀缩性的室内研究[J]. 大坝观测与土工测试，1991，15(1)：13–22.(ZHANG Yingjun. Laboratory investigations of three-dimensional swell-shrinking characteristics of expansive soils[J]. Dam Observation and Geotechnical Tests，1991，15(1)：13–22.(in Chinese))
2023, Vol. 42 
