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Vacuum drainage preloading method


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Vacuum drainage preloading method is a relatively new soft soil reinforcement technology, it is to belong to a kind of drainage consolidation method, level of it by laying drainage sand cushion and setting up the vertical row of water in the soft soil foundation, and laying on the sand cushion is not breathable film sealing device, with the aid of pipeline buried in the sand cushion, through vacuum device, negative pressure generated in the soil, The pore water in the soil is pumped out, so as to reduce the pore water pressure, increase the effective stress, so that the soil consolidation, reduce the late settlement, improve the bearing capacity of the foundation.
When vacuum is pumped, negative pressure gradually forms in the surface sand cushion and the vertical drainage channel successively, resulting in the pressure difference between the soil and the drainage channel and the cushion. Under the action of this pressure difference, the pore water in the soil is constantly discharged from the drainage channel, so that the soil is consolidated. It is mainly reflected in the following aspects:

1) The load on the film is equal to the pressure difference between inside and outside the film.

2) The groundwater level decreases and the additional stress increases accordingly.

3) The closed air bubbles are discharged, and the permeability of the soil is increased.
Layout of measurement line → laying of main branch filter and drainage pipe → laying of upper sand cushion → leveling of sand surface → laying of PVC film → construction of sealing ditch → setting of measurement marks → installation of vacuum pump → vacuum preloading and consolidation soil layer.

The construction content of vacuum drainage preloading method is mainly composed of four parts:

(1) the construction of a vertical and horizontal drainage channel, that is, the construction of plastic drainage plate and sand cushion;

(2) to the construction of a reinforced foundation and atmospheric isolation of the guarantee of an airtight sealing layer;

(3) to set up a set of high efficiency vacuum device. That is, in the sand cushion layer laid in the main and filter pipe network and the installation of vacuum pump and other equipment outside the sealing system;

(4) to set up a set of inspection system to ensure that the construction can be carried out according to the design requirements.
Vacuum preloading is to vacuum under the sealing membrane covering the ground, so that the pressure difference is formed inside and outside the membrane, so that the consolidation pressure of the clay layer is generated. That is, under the condition of constant total stress, the effective stress can be increased by reducing pore water pressure. Vacuum preloading and precipitation preloading are drainage consolidation under negative excess hydrostatic pressure, which is called negative pressure consolidation.

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