Most natural sedimentary clay contains organic matter, and even a small amount of organic matter will have a great impact on the physical and mechanical properties of clay. In order to clarify the influence of organic matter content on clay soil, the illite‐quartz mixture was mixed with natural amorphous peat soil (organic matter content is 50%) in different proportions for studying the influence of different organic matter contents on the physical properties (specific gravity, G_s; moisture content, w; void ratio, e; liquid limit, w_L; plastic limit, w_p; plasticity index, I_p) and shear characteristics (cohesion, c; friction angle, φ) of clay soil. The experimental results found that, with the change of organic matter content, the specific gravity and void ratio of clay changed linearly, while the water content, Atterberg limit, shear strength, cohesion, and friction angle changed nonlinearly with the increase of organic matter content. Moisture content and Atterberg limit have a turning point when OC = 7.5%. Shear strength, cohesion, and friction angle all have obvious turning points when OC = 7.5% and OC = 37.5%. The variation of moisture content and Atterberg limit with organic matter content indicates that OC = 7.5% may be the limit value for the different forms of organic matter in the clay. When OC ≤ 7.5%, the organic matter in clay is in the bound state; when OC > 7.5%, the bound organic matter reaches saturation; and the free organic matter gradually increases. The change law of shear strength characteristics with organic matter content shows that the interaction between minerals and organic matter exhibits different shear characteristics under different organic matter content. When OC ≤ 7.5%, clay shows mineral properties, when 7.5% < OC ≤ 37.5%, clay shows mineral‐free organic matter properties, and when OC > 37.5%, clay shows free organic matter properties.

Based on a long‐term comprehensive instrumentation program, the performance of an excavation pit constructed by the top‐down method in downtown Kunming was extensively examined. The measured excavation responses included the deflections of diaphragm wall, vertical column movement, slab axial force, building settlement caused by ground deformation, and the influence of pit excavation on the adjacent subway tunnel. This paper analyses the monitoring data of the existing construction stage. Based on the analyses on the data of field and numerical simulation, the following major findings were obtained: (1) the relationship between the measured maximum wall deflection, δ_hm, and excavation depth, H, in this study is δ_hm = 0.06%H ~ 0.27%H, which is quite different compared with the relationship of soft‐soil pit δ_hm = 0.02%H ~ 1.2%H, but closer to the normalized curve of rock‐socketed pile δ_hm = 0.01%H ~ 0.45%H and rock‐socketed diaphragm wall δ_hm = 0.031%H ~ 0.129%H. (2) The relationship between the maximum settlement of column (δ_p) and excavation depth (H) is δ_p = −0.09%∼0.04%H. The maximum distortion between the diaphragm wall and the column is less than 1/500 of the limit range proposed by Bjerrum. (3) The impact range caused by excavation is about 3.8 times the maximum excavation depth. The ground settlement around the foundation pit is groove type, and the maximum settlement point is located at 2.7 times the maximum excavation depth. (4) The excavation of the foundation pit leads to the maximum vertical settlement of 2 mm and maximum horizontal displacement of 5.2 mm in the subway tunnel; the maximum change of axial force and bending moment are 8.8 kN (the vertical direction) and 6.4 kN·m/m (the horizontal direction), respectively.

Activated cement with the characters of low water demand and high activity was made with Portland cement clinker and dehydrate-gypsum and liquid superplasticizer which were used as grinding additive in the grinding process. Three states of grinding effect exist with correspondence of different dosages of super-plasticizer: the optimal grinding aid dosage, the critical dosage, and the supercritical dosage. First, under the condition of the optimal grinding effect, the activated cement had the maximum strength with little dosage of super-plasticizer and small effect on the performance of activated cement; second, within the critical dosage, the strength of activated cement was similar to the common cement, more super-plasticizer were held and the performance of cement was obviously improved; third, within the supercritical dosage, the strength of activated cement was reduced, but it can accommodate much super-plasticizer, and had a remarkable influence on the performance of cement. The experiment also shows that different properties of low water demand activated cement can be made with admixture of different concentrations of super-plasticizer. Within the allowed limit, use more admixtures was in compile with green environmental protection concept, improve the durability of concrete, and resolve the problem of compatibility between common cement and super-plasticizer, and offered technical support in the produce of commercial concrete by directly use of Portland cement clinker.

With the acceleration of urbanization, clay with significant variations in organic matter content is commonly encountered in infrastructure construction. Its unique water retention capacity is crucial for engineering safety and stability. This study uses red clay as the matrix and incorporates peat to prepare soil samples with varying organic matter content. Soil–water characteristic tests were conducted using the pressure plate method, filter paper method, and vapor equilibrium method to obtain the soil–water characteristic curves across the entire suction range. Subsequently, scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were performed to analyze the mechanisms underlying the water retention characteristics. The experimental results indicate that the three different suction tests accurately reflect the soil–water characteristic curves of organic clay across the entire suction range. As the organic matter content in the soil increases, the air entry value and residual value of the soil samples exhibit a linear relationship with the organic matter content, enhancing the soil’s water retention capacity. The increase in organic matter content alters the microstructure of the clay, transforming the mineral–organic aggregates from ellipsoidal to plate-like shapes. While organic matter can influence the water retention of clay, within a certain suction range, the water retention capacity of organic clay is also related to the pore structure and the state of water within the pores. This is crucial for ensuring engineering safety and optimizing design solutions.