【作者】 陈伟；

【导师】 孙德安；

【作者基本信息】 上海大学 ， 建筑与土木工程（专业学位）， 2021， 硕士

【摘要】 膨胀土是我国广泛存在的一种特殊土,在实际工程中弱膨胀土可用作路基填料,既充分利用当地土源又省时省力。但膨胀土存在吸水膨胀、失水收缩及反复变形的性质,因此对工程结构具有严重的隐患。为了预防膨胀土灾害以及在涉及膨胀土的工程中采取正确措施确保工程质量,有必要对膨胀土的各项力学性质进行研究。本文以南阳膨胀土为研究对象,通过各类室内试验对南阳膨胀土进行了基本物理特性以及渗透性、压缩变形特性、土水特性等方面的试验研究;同时利用饱和三轴仪-弯曲元测试系统,对干湿过程中非饱和膨胀土的最大剪切模量进行测试,并用非饱和土力学理论进行了预测,主要工作与研究成果如下:1、在脱湿过程中南阳膨胀土最大剪切模量与含水率关系曲线要高于吸湿过程的曲线,即最大剪切模量与含水率关系存在滞回特性,这与露点水势仪(WP4C)测量的膨胀土吸力与含水率间滞回特性相关。2、无论是竖向原状样或是横向原状样,在干密度和含水率相同条件下其最大剪切模量明显低于重塑样,经过对原状样和重塑样进行压汞试验,发现其原因在于原状样内部存在大孔隙。3、通过对竖向和横向的原状样进行先饱和、后经历干湿循环的弯曲元测试试验后发现,当孔隙比、含水率等控制一致时,不同取样方向的原状土最大剪切模量大小相近,即原状南阳膨胀土的最大剪切模量的各向异性程度较低。4、不同制样的制样方法会导致重塑样最大剪切模量的差异。无论是饱和状态下或是干湿过程中,相同状态下竖向压制的重塑样其最大剪切模量总小于横向压制的重塑样,其原因与土样中粘土叠片受制样压力而导致的定向排列有关。5、经历两次干湿作用的原状土最大剪切模量曲线始终位于经历一次干湿作用的曲线之下,证明干湿循环会降低土的动力模量,其原因在于膨胀土有较强的胀缩性,干湿作用次数增加会导致土体裂隙发育、结构性降低。6、在Hardin-Drnevich的最大剪切模量公式基础上提出了考虑吸力、饱和度、孔隙比的南阳膨胀土预测公式。先利用试验数据拟合了饱和原状土公式参数,然后代入非饱和土中进行验证,得到了较好的预测效果,并能同时适用于横竖不同方向的原状土。而对于重塑土,对于上述公式进行了适当修正,提出了新的孔隙比经验公式,发现能够较好地预测非饱和重塑土的最大剪切模量。更多还原

【Abstract】 Expansive soil is a kind of special soils widely existing in China.Weak expansive soils can be used as subgrade filler in practical projects,which not only makes full use of local soil sources,but also saves time and effort.However,the expansive soil has the properties of water absorption expansion,water loss shrinkage and repeated deformation,so it has serious hidden danger to the engineering structure.In order to prevent disasters of expansive soils and take correct action to ensure engineering quality in projects involving expansive soils,it is necessary to study various mechanical properties of expansive soils.In this paper,Nanyang expansive soil is taken as the testing specimens.The basic physical characteristics,permeability,compression deformation,soil-water characteristics and other aspects of Nanyang expansive soil are measured by various indoor tests.At the same time,the maximum shear modulus of unsaturated expansive soil during wetting-drying process was measured by using saturated triaxial apparatusbending element testing system and is predicted by the mechanics for unsaturated soils.The main research contents and conclusions are as follows:1.For the relationship between the maximum shear modulus and water content of Nanyang expansive soil,the drying curve is higher than the wetting one,i.e.,the relationship between the maximum shear modulus and water content also has hysteretic characteristics.This is related to the relationship between water content and suction measured by WP4 C.2.The maximum shear modulus of both vertical and transverse undisturbed samples is significantly lower than that of the remolded specimens under the same dry density and water content.After mercury intrusion tests on both specimens,it is found that the reason is that there are more pores in the undisturbed soil.3.Through making bending element test on vertical and transverse undisturbed specimens which saturated first and then experiencing wetting-drying cycle,it is found that the maximum shear modulus of undisturbed soils in different directions is similar when the porosity ratio and water content are uniformly controlled.It means there is no anisotropy in the maximum shear modulus of undisturbed Nanyang expansive soil.4.Different sample preparation methods lead to different maximum shear modulus of the remoulded specimens.The maximum shear modulus of vertically pressed samples under the same condition is always lower than that of transversely pressed samples either in saturated state or in wet-dry state,which is related to the orientation of montmorillonite stacks in soil samples due to sample pressure.5.The maximum shear modulus curve of undisturbed soil after twice wet-dry processes is always under the curve after once wet-dry process,which proves that the wetting-drying cycle will reduce the dynamic strength of soil.The reason is that the expansive soil has strong expansion and contraction.The increase of wetting-drying processes will lead to the full development of soil fissures and the reduction of structural properties.6.Based on Hardin-Drnevich’s maximum shear modulus formula,the Nanyang expansive soil prediction formula considering suction,saturation and pore ratio is proposed.First,the formula parameters of saturated undisturbed soil are fitted by test data,and then validated by substituting them into unsaturated soil.Good prediction results are obtained,which can also be applied to undisturbed soil in different directions.For remolded specimens,the above formula has been corrected appropriately and a new empirical formula of void ratio has been put forward.It is found that the maximum shear modulus of unsaturated remolded specimens can be predicted well.更多还原