# Study on Microstructure of Cemented Organic Soil in Dianchi Lake, China
###### Abstract  
The organic soil in the Dianchi Lake area contains much humic acid (HA), and the impact of HA on cemented soil has attracted much attention. In this study, test soil is prepared based on the actual HA content of the soil in Dianchi Lake, and cement is added to prepare samples. Unconfined compressive strength (UCS), scanning electron microscopy (SEM), energy-dispersive analysis (EDS), and X-ray diffraction (XRD) tests are conducted on the samples. The strength development and microstructure changes of cemented organic soil are studied. The results show that (1) cemented soil strength decreases with the increase in HA content and increases with the cement mixing ratio; (2) SEM and EDS tests show that with the increase in HA content, the connection between soil particles gradually changed from surface-surface to point-surface, point-edge, or point-point connection. A large overhead structure is inside the cemented soil, and its integrity weakens with increased HA content. However, elements such as Ca, Si, and Al exist in the pores of cemented soil, indicating that cement hydration products are cemented between soil particles. XRD testing shows that with the increase in HA content, the intensity of the diffraction peaks of hydration products in cemented soil gradually decrease. (3) In general, HA will gradually deteriorate the integrity of cemented soil and reduce its strength. When the HA content is more than 15%, the effect of HA on strength is more prominent. However, increasing the cement mixing ratio can effectively weaken HA's negative effect on cemented soil's strength. When the cement mixing ratio is between 15% and 25%, the strength of cemented soil with high HA content can be effectively increased. However, this approach is not conducive to the protection of the environment. Dianchi Lake; organic soil; humic acid; strength development; microstructure 2023138251382023313823  
or acidic solution, and occurs in soil as solid particles, which occur in the form of solid particles in the soil body and form the soil framework together with the soil particles [12]. With the prominence of fundamental engineering problems in peat soil environments, experts and scholars have gradually combined research on HG with engineering practices. In 1989, [PERSON] et al. [13] used cement to solidify fluid ooze and found that the strength of the solidified product decreased with the increase in HG. In contrast, the presence of ettrinigite would increase the strength of the solidified fluid ooze. In 2000, [PERSON] [14] found that the organic matter reacted with cement hydration products, weakening cement's reinforcement effect on organic soil. In 2002, [PERSON] et al. [15] found that organic matter would affect the hydration of cement by changing the pH value of the pore solution, thereby affecting the development of cemented soil strength. In the same year, [PERSON] [16] and other studies found that the organic matter in the soil is an acid body, which hinders the hydration reaction of cement. In 2003, [PERSON] et al. [17] found that when the soil organic matter content is high, the soil and surrounding solutions are acidic, with high water content and low permeability. In 2005, [PERSON] [18] found that HG had a corrosive effect on cemented soil. In 2009, [PERSON] et al. [19] used dredged sludge to explore the effect of HG on hydration products. The results show that HG reacts with the calcium hydroxide produced by cement hydration and generates soluble compounds, which affects the development of the strength of the cured product. In 2009, [PERSON] [20] studied the effect of HG on cemented soil strength through on-site sampling. The results showed that HG reacted with cement hydration products to form more complex compounds. The total amount of cement hydration products decreased, which changed the microstructure of the cemented soil, resulting in a decrease in the strength of the cemented soil. In 2017, [PERSON] [21] studied the effect of HG on the strength properties of cemented soil.