Foundation treatmentMedium expansive clay is a kind of structurally unstable high plastic clay with a particle size of0.002mm, mainly composed of strong hydrophilic minerals (such as montmorillonite and illite), It has great water absorption expansion, water loss and shrinkage properties and strength attenuation. Because of this special engineering characteristics, it is easy to appear in the foundation treatment, such as subsidence, mud-churning, longitudinal cracking, peeling, erosion, mud flow, shoulder collapse, slip collapse and other problems, which bring great harm to the project. In the process of engineering construction, it is necessary to accurately judge the expansion and contraction registration of expansive soil and the characteristics of engineering properties, and then choose the appropriate foundation treatment method. The treatment methods of expansive soil foundation are usually as follows:

1And in the soil

Non-expansive clay, sand, gravel and ash can be used to replace expansive soil to reduce the expansion and contraction of the foundation, and the thickness of soil exchange can be determined by deformation calculation. On a flat fieldI,IIIt is advisable to use sand, gravel cushion and cushion thickness for the foundation treatment of grade expansion soil≥300 mm, pad width should be greater than the width of the base, both sides appropriate and pad the same material backfill, and do waterproof treatment. The soil exchange method can get larger foundation bearing capacity than other treatment methods, fundamentally change the nature of the foundation soil, and the construction period is shorter.

2And improve the soil quality

Non-expansive materials such as lime and cement are added to expansive soil, or chemicals are added to make expansive soil lose its expansibility. The swelling property of expansive soil can be reduced or eliminated by mixing a certain amount of lime or cement in expansive soil;At the same time, organic and inorganic chemical agents have been applied in the improvement of expansive soil, which can reduce the plastic index and expansion potential of expansive soil.

3And pile foundation

When the expansive soil layer is thick or the atmospheric influence depth and the water table are deep, pile foundation can be used, and the pile tip is supported on the non-expansive soil layer or on the stable layer below the atmospheric influence layer.

4, pre-wet expansion

Before construction, make the soil wet and expand, and maintain a high moisture content in the soil, the soil will basically keep the same volume, so it will not lead to structural damage.

5, humidity control method

According to the characteristics of expansive soil, the change of soil water content is the fundamental condition of the damage of expansive soil, and the stability of the foundation can be ensured by cutting off the external seepage or evaporation conditions under the basement. At present, the successful methods of humidity control are: pre-immersion method, dark ditch moisture method, tent moisture method and total closure method.