1,Soil-cement gravity wallIntroduction to the
Cement-soil deep mixing method is through the special machinery - all kinds of deep mixer, along the depth of the curing agent (cement slurry or cement powder, plus a certain mixing agent) and the foundation soil forced in situ mixing to form cement-soil pile or cement soil block reinforcement foundation method.
At present, deep mixing method can be divided into two kinds of spray deep mixing method and powder deep mixing method. Deep cement mixing is a technique originally used to strengthen saturated soft clay foundations,20 century 80 In the middle of the decade, this method was introduced into foundation pit retaining engineering from strengthening soft soil foundation, and good social and economic benefits were obtained.
2And reinforcement mechanism of soil-cement
The basic principle of cement-soil reinforcement is that the cement and soil are gradually hardened by a series of chemical reactions after mixing. 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 soil itself, cement content and admixture. Generally used in engineering C32.5Ordinary Portland cement and slag cement, incorporation 7%～15％. Unconfined compressive strength of soil-cement q.It increases with the increase of cement incorporation, increases with the increase of cement grade, increases with the increase of age, and increases with the decrease of water content in the original natural soil.
3,Cement-soil mixing pileApplication in foundation pit support
The application of deep mixing technology in foundation pit supporting structure mainly has two aspects:
1) formed soil-cement impermeable curtain
The permeability coefficient of cement-soil is smaller than that of natural soil 10-7cm/sec Above, the permeability is very small, with good seepage ability, in recent years has been widely used in foundation pit excavation project seepage curtain.
2) to form soil-cement retaining structures
The excavation depth in soft soil foundation is 4m～7m Around 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 years 4m～7m Deep foundation pit engineering.
3) in the form of deep mixing soil-cement 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.
At present,Cement-soil mixing pileGravity retaining wall is often made of wall, grid form. This form of mixing retaining wall is generally only used for foundation pit excavation depth is not greater than7mWhen the ground is narrow or the excavation depth is very large, it is difficult to use gravity cement retaining wall.
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