【作者】 邓猛；

【导师】 赵成刚；

【作者基本信息】 北京交通大学 ， 岩土工程， 2012， 硕士

【摘要】 非饱和土是由固、液、气三相组成。目前大部分学者在研究非饱和土的时候都认为其中的气体是与大气相通,这样气体压力在土体变形过程中始终都不会发生变化（等于大气压）。已有研究表明气体的存在形态对非饱和土的性质有很大的影响,尤其是在气相内部连通或是存在较大封闭气泡的情形下,气压不再保持为常数,其变化必将对土的行为产生影响。但是目前人们对这一状态的研究并不多,在大多非饱和土的研究中,都认为气相是连续的,是和大气连通的。并且目前大部分的非饱和土试验都是在饱和度不太高的条件下进行的,而高饱和度的试验数据相对较少,气体测量也比较困难。目前对封闭气泡的研究,主要是针对大气泡的情况,而如何考虑土中的封闭气体气压变化对土体的影响,将是本文试验研究的一个重点。本文工作的目标是通过试验研究非饱和土中气相硬化对土体行为的影响,并对刘艳（2010年）[7]建立的固-液-气三相耦合的非饱和土本构模型（GAS模型）进行试验验证。不同于已有的试验方案,本文试验工作中分别进行高饱和度与低饱和度情况下的非饱和土试验,以此研究气相硬化对其行为的影响。研究中对取自北京某地区的粉质粘土进行固结排水剪切试验、非饱和土干湿循环试验、非饱和土等向固结排水试验。通过这些试验可以确定GAS模型参数：包括饱和模型参数λ, κ; LC屈服面参数km,θ；流体弹塑性参数λ_w, κ_w, λ_a；耦合系数k_sw, k_ws, k_sg, k_gs。利用所测参数,分别对高饱和度与低饱和度两种不同情况下的试验结果进行预测。试验结果研究表明,在高饱和度时,由于气相硬化的影响,需要考虑气相压力变化对非饱和土体变以及饱和度变化造成的影响；而在低饱和度时,则可以忽略气相硬化的作用。并将模型预测结果与试验结果进行对比,研究表明GAS模型能够较好的模拟高饱和度与低饱和度情况下的试验结果,从而通过试验验证了GAS模型的有效性,并揭示了高饱和度下气相硬化对土体力学行为的作用。更多还原

【Abstract】 An unsaturated soil is consisted of solid, liquid and gas. Most previous researchers presumed that gas is connected with the outside atmospheric pressure so that gas pressure keeps constant under the process of loading. Previous researches have showed that the form of gas has great role in mechanical behavior of unsaturated soils, especially to occluded gas or inner connected gas because of changes of gas pressure. But present studies of this state are little. Most researchers presume constant gas pressure, connected with each other. In addition, most experiments are conducted in low saturation, lacking of data in high saturation and existing difficulties in measuring gas pressure. Although this way has made problem simple, we must accept that there are occluded air in unsaturated soils. How to consider the influence of occluded gas bubbles on soils is an emphasis of this thesis through tests.The target of this thesis is to study the effect of gas hardening on soil behavior and make experimental verification for GAS model, a coupled solid-liquid-gas constitutive model of unsaturated soils. Different with existing test scheme, both high saturation tests and low saturation tests are done so as to the role of gas hardening on soil behavior. Studies has been conducted for silt clay from Beijing through consolidated drained triaxial tests of saturated soils, drying-wetting tests and isotropic consolidation tests of unsaturated soil tests. Parameters of the constitutive model of unsaturated soils considering the effect of gas hardening（GAS model）,proposed by Liu Yan, can be determined by these tests, including the parameters of saturated soils （λ, κ）; parameters of LC yielding surface （k_m, θ）; elastoplastic parameters of fluids （λ_w, λ_a, κ_a）; coupled parameters (k_sw, k_ws, k_sg, k_gs).According to the parameters measured by tests, we make prediction both on high saturation and low saturation. The results show that we should consider the effects of gas hardening on volumetric strain and saturation in high saturation and we can ignore these effects in low saturation. GAS model predicted results can correspond with the tests results both in high saturation and low saturation. So we can make a conclusion that GAS model is effective and show the role of gas hardening to mechanical behavior of soils.更多还原