【作者】 李鑫；

【导师】 雷华阳；

【作者基本信息】 天津大学 ， 土木工程， 2018， 硕士

【摘要】 当前我国面临着土地资源趋于恶化及严重紧缺的问题,这使得人们对我国沿海地区土地资源的需求量在不断增加,我国沿海地区软土分布广泛,表现为明显的“三高两低”特性,即:高含水率、高孔隙比、高压缩性、低渗透性、低强度。因此,如何有效加固软土成为软土地基处理过程中急需解决的工程技术问题。本文采用一种新型固化剂—聚丙烯酰胺,并对其加固软土的规律与机理进行探究。针对聚丙烯酰胺固化土,进行无侧限抗压强度试验、直接剪切试验以及压缩试验等宏观试验,分析聚丙烯酰胺加固软土的力学特性;并利用XRD试验、SEM扫描以及压汞试验等微观试验,探究聚丙烯酰胺加固软土的微观机理。同时,通过开展一系列真空预压联合聚丙烯酰胺模型试验,真实模拟现场真空预压地基处理方法,通过对比分析各组模型试验的参数与结果,探讨分析真空预压联合聚丙烯酰胺处理软土地基的加固效果,研究结果表明:(1)固化土在掺量为0.15%聚丙烯酰胺的作用下,其无侧限抗压强度、压缩模量以及黏聚力与内摩擦角得到了大幅度的提高,对于含水率为50%的软土来说,0.15%聚丙烯酰胺为固化土的最优掺量;在真空预压模型试验中,添加适量聚丙烯酰胺之后,真空度径向传递效率大大提高,孔隙水压力消散速率以及排水速率明显加快,固结加固时间大为缩短,加固后吹填土体的十字板强度整体提高70%左右。(2)聚丙烯酰胺具有双重作用,一方面适量聚丙烯酰胺可以有效增强土颗粒间的连接,形成更为紧密的纤维状、网状等空间结构;另一方面过量聚丙烯酰胺会抑制火山灰反应生成物的生成,促使土中部分自由水转变为结合水。因此针对不同区域、不同特性及不同含水率的软土要使用其对应的添加剂种类以及最优掺加量。更多还原

【Abstract】 The demand for land resources in the coastal areas of China continues to increase due to serious shortage and deterioration of land resources.At present,soft soil is widely distributed in these regions.However,the ultra-soft soil is characterized by a high water content,large void ratio,high compressibility,low permeability and low strength.Therefore,how to determine a proper method to effectively reinforce soft soil has been an intractable problem in soft soil foundation treatment.In the scope of this project,a newly proposed additive named Polyacrylamide(PAM)was applied to the reinforcement of soft soil.Subsequently,the reinforcement laws and mechanism of Polyacrylamide on soft soil were conducted.Two types of macroscopic and microscopic tests were carried out to evaluate the effectiveness of PAM on soft soil.In the macroscopic section,three geotechnical laboratory tests including the unconfined compressive strength tests(UCS),direct shear tests and compression tests were carried out to investigate the mechanical properties of solidified soil and microscopic mechanism of reinforced soil was analyzed using X-ray diffraction(XRD),scanning electron microscopy(SEM)and mercury intrusion porosimetry(MIP).In the meantime,a series of vacuum preloading model tests with varying content of PAM were conducted,stimulating field conditions.By comparing and analyzing the parameters and results of each model test,the reinforcement effect of vacuum preloading combined with Polyacrylamide on soft soil foundation is evaluated and discussed.(1)The test results indicated that the unconfined compressive strength,compression modulus,cohesion and the angle of internal friction of lime treated soft soil were improved significantly by the addition of 0.15% PAM;and an optimal dosage of PAM is 0.15% for the soft soil which had a water content of 50%;simultaneously,an optimal dosage of PAM can not only considerably shorten the consolidation time of the dredger fill but can also notably increase drainage efficiency,the rate of dissipation of excess pore pressure and the transmission of vacuum pressure.Besides,an approximately 70% increase in the vane shear strength was also observed.(2)Dual function of PAM was found by substantial microscopic tests;on the one hand,forces between soil particles could be enhanced significantly with the help of optimal dosage of PAM,forming more compact fibrous,reticulate,and other spatial structures;however,excessive dosage of PAM had an adverse impact on the pozzolanic reactions among soft soil.In the meantime,more bound water was generated and blocked by the additional PAM in the soil samples during vacuum preloading,thus obstructing the pore compression.Therefore,the appropriate additive and optimal dosage should be applied for specific soft soil.更多还原