Cement-soil deep mixing method by high pressure jet grouting or mixing machinery, special machinery, deep in the ground to curing agent (cement or cement powder, plus certain admixture) and force on the mixing of foundation soil, hardening of the wholeness, water stability and forms after a certain strength of cement-soil pile or cement clods, thus improve the strength of foundation, strengthen its deformation modulus method.
At present, according to the difference of construction method, cement-soil deep mixing method in our country can be divided into two kinds of spray deep mixing method and powder deep mixing method.
The basic principle of cement-soil reinforcement is that cement (or cement paste) and soil after mixing a series of physical and chemical reactions and gradually hardening. When reinforced with soil, calcium hydroxide, calcium hydrous silicate, calcium hydrous aluminate and calcium hydrous ferric aluminate are generated due to hydration and hydrolysis reaction. The equivalent adsorption and exchange of calcium ions with sodium and potassium ions in the soil can make the smaller clay particles become larger soil aggregates. The free calcium hydroxide in cement hydrate can absorb the calcium dioxide in the air in the water, and carbonation reaction occurs to produce calcium carbonate insoluble in water. Due to the above effects, the strength of cement soil is increased.
The properties of soil-cement are related to the soil itself, the amount of cement and the admixture. Generally used in engineeringC32.5Ordinary Portland cement and slag cement, incorporation7%~15%. The unconfined compressive strength of soil-cement increases with the increase of cement content, with the increase of cement grade, with the increase of age, and with the decrease of water content of the original natural soil.
The application of deep mixing technology in foundation pit supporting structure mainly has two aspects:
1, the formation of soil-cement seepage curtain
The permeability coefficient of soil-cement is smaller than that of natural soil, and it has good seepage control ability. In recent years, soil-cement has been widely used as seepage control curtain in foundation pit excavation project.
2, forming cement soil retaining structure
The excavation depth in soft soil foundation is4m~7mAround the foundation pit, the application of deep mixing method of soil-cement pile retaining wall can make full use of the strength of soil-cement to form the gravity support structure of soil-cement, and because of the seepage resistance of soil-cement, at the same time can also be used as seepage resistance curtain. Has been used in recent years4m~7mDeep foundation pit engineering.
3, the form of deep mixing cement soil pile wall
With the accumulation of practical engineering experience, the form of agitator support structure is constantly developing and optimizing, and there are many forms such as single type and compound type.
Cement-soil deep mixing technology is suitable for silt, silt soil with high water content and the bearing capacity of the foundation is not greater than120kPaThe soft soil containing clay minerals such as kaolinite, polyhydrous kaolinite and montmorillonite has better reinforcement effect.
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