膨胀土具有吸水膨胀、失水收缩等不良工程性质,常采用石灰、水泥等土壤固化材料对其进行改良,但这些传统的土壤固化材料存在着污染环境、拌合不均匀等问题。以陕西省汉中市强膨胀土为研究对象,对仿岩溶碳酸氢钙改良膨胀土进行了自由膨胀率、无荷膨胀率、收缩、直接剪切、酸碱度和碳酸钙含量测定、粒度分析和扫描电镜试验等物理、力学、化学和微观结构试验。试验结果表明,仿岩溶碳酸氢钙可较好地降低膨胀土的胀缩性,并提高土体的抗剪强度,且仿岩溶碳酸氢钙与膨胀土的最优配比为6∶1;改良土中吸附的交换性Ca²⁺含量降低,碳酸钙含量增多,细粒含量降低,粗粒含量增多,内部孔隙减少;仿岩溶碳酸氢钙改良膨胀土的机理在于溶液中含有H⁺、Ca²⁺、HCO₃^-、CO₃^2-等离子,同时溶解有饱和的二氧化碳气体,通过离子交换作用,溶液中的H⁺置换了土颗粒吸附的Ca²⁺,减小了双电层厚度;通过岩溶作用,新形成的碳酸钙具有沉积胶结和填充作用,颗粒间联结强度和团粒化作用得到增强,从而降低了土体胀缩性。由此可见,仿岩溶碳酸氢钙对膨胀土具有良好的改良作用。

Lime and cement are widely used in engineering projects to modify the special engineering properties of expansive soil such as water swelling and dehydration shrinkage; but such traditional soil solidification materials are difficult to be well mixed, and also pollute the environment. The physical, mechanical, chemical and micro-structural properties of the typical strong expansive soil of Hanzhong stabilized by calcium bicarbonate from pseudo-karstification are studied by means of free swelling rate test, unloaded expansion rate test, shrinkage test, direct shear test, pH test, carbonic acid content determination test, particle size analysis test and scanning electron microscope test. Test results show that calcium bicarbonate from pseudo-karstification could reduce the swell-shrinking property of expensive soil and improve the soil's shear strength. The optimal mass ratio of calcium bicarbonate solution from pseudo-karstification to expansive soil is 6∶1. The content of exchangeable calcium ions, fine particles and interior pore decreased, while the content of calcium carbonate and coarse particles increased. The mechanism of solidifying expansive soil by calcium bicarbonate from pseudo-karstification can be explained as follows: given a large number of H⁺, Ca^{2 +}, HCO₃^-, CO₃² and excess carbon dioxide dissolved in solution, the Ca²⁺ adsorbed by soil particle are replaced by H⁺ through ion exchange reaction, hence reducing the thickness of electronic double layer. The newly formed calcium carbonate from karstification has effects of filling and reinforcing so that the connection between soil particles is enhanced and the swell-shrinking potential is reduced. In conclusion, calcium bicarbonate from pseudo-karstification has a good effect on reducing the swell-shrinking potential of expansive soil.