以深圳市花岗岩残积土为研究对象,考虑氧化铁含量、含水率及干密度影响,对压实花岗岩残积土进行崩解试验研究。结果表明:压实花岗岩残积土遇水快速崩解,崩解过程中崩解物以小颗粒-碎屑-泥状形式逐渐剥离于土样,直至完全崩解。土的崩解过程主要受氧化铁含量影响,物理状态对其影响程度较小。土的崩解速率随时间的变化规律主要呈先迅速增大后快速减小、迅速增大后保持稳定和出现多个峰值3种模式;最大崩解速率随其氧化铁含量的增加而逐渐增大,随土样含水率和干密度的增大而减小;土样的完全崩解时间受其含水率的影响程度与其干密度有关,土样干密度较小时,其完全崩解时间变化范围较小,而当干密度>1.50 g/cm³时完全崩解时间随含水率的增大呈增大趋势;相同含水率时,土样的完全崩解时间随干密度的增大逐渐增大。

Disintegration test of compacted granite residual soil taken from Shenzhen was carried out in consideration of iron oxide content, water content, and dry density. Test results demonstrated that the compacted granite residual soil disintegrated quickly, during which the disintegrated materials gradually peeled off from the soil specimen from the form of small particles to debris and then to mud, until the soil sample completely disintegrated. The disintegration process of soil was mainly affected by the content of iron oxide rather than by the physical state of soil specimen. The disintegration rate of compacted granite residual soil changed with time in three modes: surged at first and then plummeted; surged at first and then stabilized; multiple peaks appeared. The maximum disintegration rate climbed with the expansion of iron oxide content but dropped with the increase of the water content and dry density. The degree of the impact of water content on complete disintegration time depended on dry density. In the presence of small dry density, the time required for complete disintegration changed within a small range; when dry density exceeded 1.50 g/cm³, the time required for complete disintegration elongated gently with the rise of water content. Given the same water content, the time required for complete disintegration gradually increased with the rising of dry density.

在华南地区循环湿热多雨气候的影响下,花岗岩残积土遇水极易崩解,诱发崩岗等地质灾害,对道路、桥梁等工程造成极大影响,因此常利用水泥、石灰和高岭土等固化剂对花岗岩残积土进行改良。为了进一步研究干湿循环条件下改良花岗岩残积土的崩解特性,采用自行设计的干湿循环崩解测试仪,开展华南地区干湿循环环境下改良花岗岩残积土的崩解试验,结合X射线衍射试验以及扫描电镜试验,研究固化剂对花岗岩残积土抗崩解性的改良效果,分析改良花岗岩残积土崩解机理。结果表明:干湿循环条件下,改良花岗岩残积土土样崩解过程可以分为4个阶段,即表层吸水剥落阶段、饱水软化阶段、饱和稳定阶段和完全解体阶段；干湿循环作用显著增大改良土崩解速率,部分试样崩解速率可达到原来的2~3倍,添加固化剂能有效增强花岗岩残积土的抗崩解性,完全崩解时长增加到素土的2~6倍；基于绿化角度,掺入高岭土对花岗岩残积土进行改良较为合适；素土以及改良土崩解过程中,土样黏土矿物(例如高岭石)含量减少,显著降低土样胶结作用,促进土样崩解的发生；花岗岩残积土内部孔隙大小分布不均匀的结构特征,使土样在崩解过程中产生吸力不平衡现象,较小的孔隙先被水填入,压缩土样孔隙内的空气,产生应力集中现象,这是土样崩解发生的内在驱动力。研究结果揭示了花岗岩残积土崩解机制,可为实际工程中对花岗岩残积土进行改良提供一定的参考。

Under the influence of the cyclic humid, hot, and rainy climate in South China, granite residual soil is easily disintegrated when it comes in contact with water. This induces geological disasters such as collapse and has a significant impact on roads, bridges, and other projects. Therefore, cement, lime, and kaolin are often used to improve the anti-disintegration property of residual soil. A self-designed dry-wet cycle disintegration tester was used to study the disintegration characteristics of improved granite residual soil in South China under dry-wet cycle conditions. The results show that the disintegration process of improved granite residual soil samples can be divided into four stages under dry-wet cycles: surface water absorption and spalling, saturating and softening, saturated stabilization, and complete disintegration. The dry-wet cycle significantly increases the disintegration rate of the improved soil, which can reach 2-3 times in some cases. The addition of curing agent can effectively enhance the anti-disintegration property of granite residual soil, and their total disintegration time increases to 2-6 times that of plain soil. From the perspective of greening, kaolinite is suitable for improving granite residual soil. The content of clay minerals (such as kaolinite) decreased during the disintegration of all the granite residual soil samples, which significantly reduced the cementation and enhanced the disintegration of the samples. The uneven distribution of pore size in the granite residual soil causes the unbalanced suction of the sample during disintegration. The smaller pores are first filled with water to compress the air in the pores of the sample, resulting in a stress concentration phenomenon, which is the internal driving force of disintegration. The results reveal the disintegration mechanism of granite residual soil and provide a reference for the improvement of granite residual soil in practical engineering.

为了探究微生物诱导碳酸钙沉淀(MICP)技术改良膨胀土膨胀特性的效果和作用机理,利用产脲酶菌CGMCC 1.368 7,开展了MICP拌和法处理膨胀土的膨胀特性试验。通过正交试验研究了反应液配比和Ca²⁺浓度对MICP拌和法处理膨胀土自由膨胀率、无荷膨胀率、CaCO₃百分生成量的影响及其变化规律,揭示了MICP改良膨胀土的微观机理。结果表明:经MICP拌和法处理后,膨胀土的膨胀特性得到显著改善;当反应液配比为1∶1、Ca²⁺浓度为2.0 mol/L时,膨胀土自由膨胀率最大降低了44.4%;当反应液配比为1∶3、Ca²⁺浓度为2.0 mol/L时,体膨胀率减小了92.2%,膨胀含水率降低了24.9%。MICP技术通过胶结土颗粒、充填土体孔隙和离子置换作用,降低膨胀土颗粒的亲水性,减小土颗粒间的排斥作用,减弱膨胀土的膨胀势。研究成果验证了基于MICP技术拌和法改良膨胀土膨胀特性的可行性。

The effectiveness and mechanism of MICP (Microbial Induced Calcium carbonate Precipitation) improving the expansion characteristics of expansive soil were investigated via test of expansive soil mixed with urease-producing bacteria CGMCC 1.368 7. The effects of reaction solution ratio and Ca²⁺ molar concentration on the free expansion rate, unloaded expansion rate, and percentage generation of CaCO₃ of expansive soil treated with MICP were studied by orthogonal experiments, and the microscopic properties of MICP-modified expansive soil were revealed. The swelling characteristics of expansive soil treated with MICP can be improved remarkably: when the ratio of reaction solution is 1∶1 and the concentration of Ca²⁺ is 2.0 mol/L, the free expansion rate of expansive soil is reduced by 44.4% at most; when the ratio of the reaction solution is 1∶3 and the concentration of Ca²⁺ is 2.0 mol/L, the volumetric expansion rate is reduced by 92.2%, and the expansion moisture content is reduced by 24.9%. MICP technology reduces the hydrophilicity of expansive soil particles, hinders the repulsion between soil particles, and weakens the expansion potential of expansive soil by cementing soil particles, filling soil pores and ion replacement. The research results verify the feasibility of improving the swelling properties of expansive soil by mixing based on MICP technology.