Catchment Kang dewatering open channel plus sump dewatering has the characteristics of convenient construction and low cost, which is most widely used in the construction site.
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Its advantages are large drainage, large precipitation depth and large precipitation range..
In the foundation pit slope support engineering in high water level area, this method is often used as an auxiliary drainage measure of other precipitation methods.
common empirical parameters 1.
It has the characteristics of simple construction and large water output.
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when the permeability coefficient of the soil layer is too small, it is necessary to seal and fill the top of the well point pipe with clay, ensure that the connecting parts of the well point system have good air tightness, and enhance the water pumping and drainage capacity by improving the vacuum degree of the whole well point system.
Therefore, groundwater should be effectively treated in the engineering construction of deep foundation pit.
Precipitation method 1.
Electroosmosis well points electroosmosis well points are suitable for geological conditions with low permeability coefficient, such as clay, loam, silt and mucky clay with permeability coefficient less than 0.1m/d.
Light well point light well point is a widely used precipitation method in China.
Foundation pit dewatering is an important step to ensure foundation quality.
Tube well point tube well point is suitable for sand gravel layer with large permeability coefficient, stratum rich in groundwater and occasions where light well points are difficult to solve.
The construction of dewatering is an important link in the construction of deep foundation pit.
When the groundwater storage is small and the geological conditions are good, the ponding in the foundation pit can be removed by using open channels and water collecting wells.
It needs to be combined with light well points or jet well points.
It is simpler, faster, economical and safe than other well point systems, and is especially suitable for small precipitation area, The groundwater storage is small.
The water output of each tube well can reach 50 ~ 100m3 / h and reduce the depth of groundwater level by about 3 ~ 5m.
At the same time, due to the existence of seepage interception curtain wall, the influence of foundation pit dewatering on groundwater outside the curtain wall is greatly reduced, and the stability of surrounding buildings is effectively guaranteed.
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Foundation pit dewatering refers to the dewatering work done to ensure that the foundation pit can be constructed under dry conditions and prevent slope instability, foundation quicksand, pit bottom uplift, pit bottom piping and decline of foundation bearing capacity.
Seepage interception curtain wall seepage interception curtain wall can not be used as a precipitation scheme alone, and is generally used in combination with open channel or well point precipitation.
The common ones are seepage cut-off wall, curtain grouting, steel sheet pile, etc., which not only cut off the infiltration of groundwater into the foundation pit, but also play a certain role in supporting the slope of the foundation pit.
The punching depth shall be about 0.5m lower than the filter pipe.
Compared with other well point methods, it has the characteristics of large precipitation depth and high operation cost.
Methods of foundation pit dewatering: open ditch plus collecting well dewatering, light well point dewatering, jet well point dewatering, electroosmosis well point dewatering, deep well point dewatering, etc.
Most foundation pit accidents are related to groundwater.
Well points can be properly densified in special parts to ensure precipitation effect.
The jetting well point system can generate a vacuum of 250mm mercury column at the bottom of the well point, and its water level reduction depth is generally between 8 ~ 20m.
Generally, the groundwater level is required to be lowered to 0.5 ~ 1m below the bottom elevation of the foundation pit, so as to maintain the dry state of the foundation pit during excavation and ensure the stability of the foundation pit slope during excavation.
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Deep well point deep well point is a dewatering method widely used in foundation pit support.
When backfilling the well pipe, fill it with coarse sand to at least 1m above the filter pipe, and seal it with clay at least 0.5m from the surface.
The gradient of the precipitation funnel is about 1:10, that is, when the groundwater level at the well point drops by 1m and remains stable for a long time, the groundwater level within 10m away from the well point will be affected, and the farther away from the well point, the smaller the precipitation range.
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In the process of precipitation, the voltage, current density and power consumption should be measured and adjusted, which is cumbersome.
However, in areas with abundant groundwater, if only this method is used for precipitation, the foundation pit slope will have more water seepage and the working surface will be muddy, which is not conducive to the construction of structures.
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The pumping system and pipe fittings of jet well point jet well point are relatively complex, with relatively high failure rate and large energy loss during operation.
Therefore, this dewatering method is generally not applied to the foundation pit slope support in high water level areas alone, but usually combined with dewatering well points or seepage interception curtain wall.
Of course, the construction of seepage interception curtain wall requires a large site and will produce large noise, which will be subject to some restrictions during construction in densely populated areas and residential areas.
Seepage cut-off curtain wall is generally used when groundwater is very rich, groundwater supply is not fast, or it is necessary to control slope instability and uneven settlement of surrounding buildings.
The permeability coefficient of the soil layer applicable to the light well point is 0.1 ~ 50M / d.
This method is generally used for dewatering of phreatic layer, and the effect is the best when the permeability coefficient of soil is in the range of 20 ~ 200m / d.
Unilateral linear well points shall be arranged in the upstream direction of groundwater flow.
The spacing between well points can generally be 0.8m, 1.2m or 1.6m, depending on the groundwater level and the depth of the foundation pit.
The depth of lowering water level by this method is generally between 3 ~ 6m.
When the width of the foundation pit is less than 6m, one-sided linear well points can be arranged along the long side of the foundation pit, and if it is greater than 6m, two or circular well points are required.
Its applicable permeability coefficient of soil layer is the same as that of light well points, which is generally 0.1 ~ 50M / d.
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It mainly removes underground diving, construction water and falling rain.
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After the dewatering well operates for a period of time, the groundwater will form a stable dewatering funnel.
