Blow-filled soil with high water content has poor engineering characteristics such as low strength, high water content and structural instability, etc. A new type of curing agent researched in-house was used to cure the blow-filled soil in the Binhai area of Tianjin, to achieve the properties of lightweight and high strength. In order to investigate the factors affecting the strength of blow-fill cured soil, the blow-fill cured soil was subjected to unconfined compression test, triaxial shear test and microstructure test. The results show that: The unconfined compressive strength of blow-fill cured lightweight soil is positively correlated with its density; The alkaline environment and salt content are favourable to the strength of blow-fill cured lightweight soil when the pH value is less than 11.4 and the salt content is lower than 1%, and the strength growth of cured soil is inhibited when the salt content is higher than this limit, respectively. When the salt content and pH value are low, the soil shows strain softening phenomenon, and the cohesion and internal friction angle of blow-fill cured lightweight soil gradually increase with the increase of salt content and pH value. The change mechanism of the strength of blow-fill cured lightweight soil with density, salt content and pH is explained from the microscopic level by nitrogen adsorption test and SEM scanning electron microscope test. The research results can provide a theoretical basis and reference for engineering practice.

Soft clay soils are generally structural in nature, and structural properties are an important factor influencing soil deformation characteristics. The soft clay soil of Tianjin Binhai was used as the raw material, and the structural soft clay soil was artificially prepared by mixing a small amount of cement with different contents to produce a nearly homogeneous soil with different structural properties. The test results show that the strain of the soil under lateral unloading conditions is related to the unloading rate, the structure of the soil itself and the consolidation envelope pressure. When the structural properties of the soil and the unloading rate are the same, the smaller the envelope pressure, the faster the strain growth rate of the specimen and the greater the strain during damage. When the structure of the soil is the same as the surrounding pressure, the strain at failure and the stress at failure both increase as the unloading rate increases. When the large principal strain ε₁ is less than the damage strain and the structural properties of the soil sample are not damaged, the slope of the ε₁-ε₃ relationship curve grows at a slower rate, and when the large principal strain ε₁ reaches its peak damage, the expansion rate in the direction of the small principal strain ε₃ accelerates until the sample is damaged. Under the same circumferential pressure, the initial unloading tangential modulus of the soil decreases with increasing unloading rate, and the unloading damage strength of the soil increases with increasing unloading rate. On this basis, the stress-strain relationship was analysed and a prediction formula for the unloading damage strength was established and validated, taking into account the effects of unloading rate and structural strength of the soil sample.