The disposal of soil containing humic acid (HA) poses an increasingly difficult problem for geotechnical environmental engineering. In this study, the unconfined compressive strength (UCS) test of cement-soil with different HA contents is conducted to analyze the effect of HA on the strength of cement-soil. Mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and X-ray diffraction (XRD) experiments reveal the effective mechanism of HA on the strength of cement-soil from the microscopic level. The results show that the strength of cement-soil decreases gradually with the increase of HA content. The failure mode of cement-soil slightly changed from brittle failure to plastic failure. The microscopic test shows that the incorporation of HA will lead to the apparent enlargement of the pores in the cement-soil. The large pores in the sample increase, the small micropores decrease, and the structure tends to be loose and overhead. The increased HA content added will significantly reduce the cement hydration products and destroy the cementation of the hydration products.

The effect and feasibility of peat soil environment (PSE) simulation pose a difficult problem for geotechnical environmental engineering. In this study, the actual content of humic group (HG) in peat soil of Dianchi Lake is determined, and the method of adding humic acid (HA) reagent into cohesive soil and soaking it in fulvic acid (FA) solution is used to simulate PSE of Dianchi Lake. By comparing the HG content of test samples and natural peat soil, the effect and feasibility of simulation test are studied. And the effects of HG on microstructure and material composition of PSE are analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The test results show that the content of HG and its components of PSE in seven sites of Dianchi Lake are quite different. The simulation method used in this study can simulate the PSE with different HA and FA contents, but the simulation method of soaking samples in FA solution cannot reach the actual effect. The SEM test confirm that the pore size and pore connectivity will increase with the HA reagent. However, FA is wrapped on the skeleton of soil through adsorption and fills some pores, which reduces the pore diameter and weakens pore connectivity. The XRD test shows that both HA and FA can reduce the diffraction peak of main substances in the samples, but not including SiO2. The reason is that HG and cohesive soil particles undergo coordination exchange and ion exchange; free HG combines with cohesive soil particles and transforms into bound HG, forming an organic-inorganic complex PSE.

The disposal of peat soil poses an increasingly difficult problem for actual engineering projects of Dianchi Lake area. This study obtains peat soil from seven areas around Dianchi Lake, and the content of humic acid (HA) in peat soil is between 2.36% and 28.13%. Then, this study simulates the peat soil by adding HA into the cohesive soil and uses cement to solidify it. The effect of cement and HA on the strength development of samples is examined by the unconfined compressive strength (UCS) test. Additionally, the microstructures of typical mixes are analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP). The results showed that HA will significantly reduce the UCS of cement soil. The SEM, XRD, and MIP confirmed that cement hydration reaction increases with cement ratio. In addition to the cementitious soil particles, hydration products gradually fill the pores of the soil and effectively reduce the number of large-size (6000∼40,000 nm) pores in cement soil, which makes the soil particle framework stronger. When the cement ratio increases from 15% to 25%, the diffraction peak of CAH and CSH increases faster. Combined with the results of the UCS test, it could be proved that cement ratio greater than 20% weakens the influence of HA on the strength development of cement soil sample.

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