目前，膨胀土在土木工程领域应用广泛，不仅涉及到地基、边坡等日常工程，也涉及到隧道开挖、核废料地下处置、垃圾填埋场等特殊工程，这些工程中膨胀土所受的环境错综复杂。膨胀土由于其活跃的水敏特性，对孔隙溶液极为敏感，不同试验环境(如温度等)和试验方法下得到的物理力学性质指标的差别较大。因此，有必要在不同孔隙溶液和试验环境以及试验方法下对膨胀土的力学特性进行详细的研究。 本文以膨胀土为研究对象，采用改变试验溶液温度和氯化钠溶液浓度来模拟不同孔隙溶液和试验环境，采用三种膨胀力测试方法，研究了膨胀土在不同试验环境和不同试验方法中的力学特性，具体的研究内容和成果如下： (1)采用三种不同的膨胀力测定方法对不同初始含水率和干密度的中膨胀土进行了试验研究。试验结果表明：初始含水率对膨胀力的影响相比初始干密度的影响微弱；相同初始条件的试样，三种试验方法测得的膨胀力区别显著，自由膨胀-压缩法测得的膨胀力最大，而加载膨胀法得到的膨胀力最小。通过核磁共振试验，对三种方法试验过试样的孔径分布进行了分析，由于自由膨胀-压缩法试样能够充分膨胀，试样中部分单元体孔隙消失，自由膨胀-压缩法试样的孔径较其他两种方法试样的孔径要大一些。 (2)利用恒温槽改造过的常规固结仪对强膨胀土进行了不同温度下的膨胀力和膨胀变形试验研究。在同一条件下，温度升高，水的粘滞系数减小，导致晶体内的部分水转化为孔隙中的水，这部分水不再对膨胀有贡献。因此，随着温度升高，膨胀土的膨胀力和膨胀变形均会降低。 (3)通过加载膨胀试验对中膨胀土进行不同浓度氯化钠溶液下的膨胀特性进行了探究，由于颗粒表面负电荷的影响，试样中形成了 Donnan渗透压，而Donnan渗透压随着浓度增加而降低，降低了试样的膨胀力，最终在相同垂直压力下，试样的饱和孔隙比随着浓度升高而降低。以蒸馏水饱和试样得到的结果作为基准，得到了不同浓度溶液下产生的化学力相对值，其主要影响因素为孔隙比和溶液浓度，建立了化学力与孔隙比和溶液浓度的关系。 (4)对中膨胀土在不同浓度氯化钠溶液中的无荷有侧限膨胀率进行了试验研究。结果表明：盐溶液对初始含水率较低的试样影响微弱，反之则影响强烈；核磁共振试验结果表明，试样的强结合水率是其分界点，当初始含水率小于该值时，试样基本不受氯化钠溶液影响，反之氯化钠溶液抑制试样的膨胀较为显著。试样的初始含水率高于强结合水率时，用盐溶液浸润试样时，试样的膨胀力随着盐溶液浓度升高而降低，而初始含水率低于强结合水率时，盐溶液浸入试样后会产生两方面相反的效应，中和了一部分影响。 (5)对不同浓度氯化钠溶液饱和的弱膨胀土剪切强度及剪切机理进行了研究。在剪切过程中，试样被动出现剪切面，试样阻止剪切面形成表现为试样剪切强度。核磁共振结果发现，用蒸馏水饱和试样的孔径较小，所用蒸馏水饱和后的试样阻碍剪切面形成更加剧烈，表现出了较高的剪切强度。因此，随着饱和溶液浓度增加，试样的剪切强度降低。 关键词：膨胀土；膨胀特性；剪切强度；温度；氯化钠溶液；核磁共振；孔径分布

 At present, expansive soil is widely used in engineering field, which not only involves the daily engineering of foundation and slope, but also special projects such as tunnel excavation, underground disposal of nuclear waste, landfill and so on. The chemical environment is very complex in these engineering. Expansive soil is very sensitive to the pore environment because of its water-sensitive properties. The physical and mechanical properties obtained in different test environments (such as temperature, etc.) and test methods are quite different. It is necessary to conduct detailed study on the mechanical properties of the expansive soil in different pore solution, test environments, and test methods. The expansive soil is as the test material in this paper. The mechanical behavior was investigated in sodium chloride solution with different concentration and in different test temperature. And different swelling pressure testing methods were used to measure the swelling pressure. The specific research content and results are as follows: (1)The experimental study on the middle expansive soil with different initial water content and dry density was carried out by using three different ways to determinating swelling pressure. The results show that the effect of initial water content on the swelling pressure is weaker than that of initial dry density. The swelling pressure is very different from the three test methods under the same condition. The maximum swelling pressure is obtained by the free expansion-compression method, and the swelling pressure of the loading-expansion method is the smallest. Finally, the difference of three methods is analyzed by NMR tests. The specimens can adequately expand, which results the disappearing of the intra-element pore by using the test method of free expansion-compression. The pore is the biggest in these specimens. (2)Tests on the strong expansive soil were conducted to investigate the swelling pressure and swelling deformation in different test temperature by using conventional consolidation modified by thermostatic. The viscosity coefficeient of water decrease as the increasing in temperature, which induce the water in crystal lattice flowing into pore. And thses water has no more contribution to swelling. So the swelling pressure and swelling deformation decrease with increasing the temperature. (3)The swelling characteristics of expansive soils in different sodium chloride concentrations were tested by loading-swelling test. There is Donnan osmotic pressure in specimens because of the negative charge on the surface of the particles. The Donnan osmotic pressure decrease with increasing the sodium chlorid solution concentration, which results in the decreasing of the swelling pressure. Under same vertical pressure, the saturated void ratio decarease with the increasing in sodium chlorid solution concentration. Based on the results obtained from the samples saturated by distilled water, the relative value of the chemical force produced by different concentration solution is obtained, which is mainly affected by void ratio and solution concentration. And the relationship among the chemical force, void ratio and solution concentration is established. (4)A series confined swelling tests with no vertical pressure were carried out on the middle expansive soil. The results show that the sodium chlorid solution affect weakly on the specimens with lower initial water content, oppositely, the effect is strong. The results of NMR tests show that the strong bound water content is the boundary point, and when the initial water content is less than that, the specimens is not affected by the sodium chloride solution. Conversely, the sodium chloride solution strongly inhibited the swelling of the specimen. When the initial water content larger than the strongly bound water content, swelling pressure decreas as the increasing in sodium chloride solution concentration. While, when the soil has only strongly bound water, the sodium chlorid solution has two inverse effects on the swelling pressure. (5)The direct shear test was carried out on the weak expansive soil saturated by sodium chloride solution with different concentrations in drainage consolidation. The specimens hinder from generating the shear surface in the shear procedure. The inhibition is the shear strength. The results of NMR tests show that the pore size of the specimen saturated by distilled water is smaller. The inhibition is the strongest in these specimens, thus the shear strength is higher. Keywords: expansive soil; swelling characteristic; shear strength; temperature; sodium chloride solution; nuclear magnetic resonance; pore-size distribution