水泥土在侵蚀环境中的试验研究和等效分析

拱北隧道是港珠澳大桥连接线的重要组成部分，隧道基底采用水泥土加固体处理。在加固体所处的环境中，由于地下承压水与海水相连，海水中所含的侵蚀性离子易对加固体产生一定的影响。通过室内试验和理论推导，研究侵蚀环境下水泥土的力学性能和耐久性。自制水泥土试块并模拟侵蚀环境，水泥土试块在侵蚀环境中浸泡时间分别为90、180、270 d，对浸泡后的水泥土试块进行无侧限抗压试验。试验结果表明：在侵蚀环境的影响下，水泥土试块强度的最大值出现在90～ 270 d之间。浸泡时间超过90 d，氯化镁和氯化钠的混合溶液（MCN）使水泥土试块的抗压强度表现出明显的衰减响应。在低浓度（1.5 g/L和4.5 g/L）条件下，MSN中的硫酸镁与水泥土中的3CaO?2SiO2?3H2O充分反应，使水泥土的抗压强度达到最高值，同比情况下对水泥土的抗压强度损伤最小。在相同的浓度下，氯化镁对水泥土试块的抗压强度影响比硫酸镁大。从化学动力学基本原理出发，基于硫酸镁与水泥水化产物的化学反应过程，推导得出侵蚀性溶液浓度与侵蚀时间之间的关系式(C1/C2)β=t2/t1，即当水泥土被侵蚀后达到同等抗压强度时，侵蚀性物质浓度的反应级数次方与侵蚀时间成反比。根据公式，可以通过较高浓度的侵蚀性溶液对水泥土试样浸泡较短时间条件下的强度试验结果，预测分析较低浓度的侵蚀性溶液对水泥土试样浸泡较长时间条件下的水泥土强度。最后结合试验数据对理论结果进行了验证。

Experimental study and equivalent analysis of cemented soil under corrosion environment

Gongbei tunnel is an important part of Hong Kong-Zhuhai-Macao Bridge cable; its foundation pit bottom is dealt with cemented soil. The aggressive ions of the sea will easily have an effect on the cemented soil as the underground pressure water is connected to the brine. Through the laboratory experiment and theoretical deduction, the mechanical properties and durability of cemented soil in the corrosion environment are studied as follows. Laboratory cemented soil and corrosion environment are made to test the unconfined compression strength of the samples soaked at 90 d, 180 d and 270 d respectively. Result of this laboratory experiment indicates that: under the influence of erosion environment, the maximum value of uniaxial compressive strength of cement soil will be reached between 90 d and 270 d. After the soak period exceeds 90 d, the solution that contains MCN shows up an entirely negative effect on the compressive strength of cemented soil. Under low concentration (1.5 g/L and 4.5 g/L), the chemical reaction between MSN and cemented soil achieves an optimum value; in comparative conditions the compression strength damage of cement soil is minimal. The effect of magnesium chloride on compressive strength of the cemented soil samples is much larger than that of magnesium sulfate. Based on the principle of chemical kinetics and the chemical equation between magnesium sulfate and the cement hydration products, combined with the assumptions, the relationship between ion concentration and corrosion time is deduced as (C1/C2)β=t2/t1; that is, when the soil samples are eroded to equivalent compression strength, the reaction order of concentration is inversely proportional to corrosion time. According to the formula, the strength of cemented soil soaking in low concentration solution for a long time is predicted by the strength of cemented soil soaking in high concentration solution for a short time. At last, the theoretical results are verified by experimental data.