HomeVacuum Water Preloading
Release time：Apr 20,2023
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The purpose of the soft soil foundation treatment project is to reduce the settlement of the foundation after construction, and the vacuum preloading combined with water borne drainage consolidation method can be used for treatment. When there are existing buildings within the scope of influence of preloading soft foundation treatment in the project, necessary protective measures need to be taken.
The vacuum preloading combined with water borne drainage consolidation method treatment technology can generally use SPB100-C type plastic drainage boards made of raw materials for vertical drainage channels. The spacing between plastic drainage boards is 0.8m or 1.0m, and they are arranged in a square shape. The plastic drainage boards are installed through mechanical equipment of a inserting machine, with a depth of about 20-30m. The plastic drainage boards should not penetrate the silt layer and enter the sand layer. The bottom elevation of the plastic drainage board installation is about 2m from the sand layer.
The horizontal drainage system uses a non hydrophobic sand cushion to replace the traditional horizontal drainage sand layer, which can effectively reduce engineering costs. Horizontal drainage systems generally use PVC main pipes with corrugated filter pipes, while vacuum main pipes use Ф 75mm PVC pipe, laid around, with branch pipes Ф 40mm corrugated pipes with a spacing of 2.0m, plastic drainage plates and corrugated filter pipes are connected through dedicated connectors, and then connected to the main pipe; The main pipe is connected to the vacuum pump to form an overall horizontal drainage system network.
The sealing wall for soft foundation treatment adopts double row slurry mixing piles with a diameter of 700mm and a overlap of 200mm. The driving depth penetrates the fill and enters the impermeable layer by 2m. The horizontal sealing system uses sealing film with a surface water load of 100cm. The water covered cofferdam is formed by wrapping sand with Geotextile.
Clear and level the site, excavate stones, various debris, vegetation roots, etc., and do not contain sharp stones. After leveling, carry out subsequent vacuum preloading construction.
The vacuum pump is used to vacuum and perform vacuum preloading. In the early stage, a pressure of 25kPa is applied to check the integrity of the sealing film. If there are any leaks, they should be repaired in a timely manner. After the inspection is completed, the vacuum is loaded to 85kPa and the vacuum under the vacuum preloading film is ≥ 85kPa. The vacuum pumping and full load preloading time is 100-120 days.
After the vacuum preloading reaches constant load, the combined water load is 100cm; Then, monitor the vacuum degree under the membrane and monitor the ground settlement at any time. After the preloading meets the design requirements, stop the pump for unloading, remove the vacuum membrane and horizontal drainage pipeline system, and clean the site.
Vacuum water preloading process
(1) Surveying and setting out, laying main and branch filter drainage pipes;
(2) Laying the upper layer of sand cushion layer;
(3) Laying polyvinyl chloride film; Lay polyvinyl chloride film on the top surface of the sand cushion to isolate it from the atmosphere, and bury the film in the soil around it;
(4) Construction of sealing ditches and setting of measurement markers;
(5) Install a vacuum pump to vacuum and preload the soil layer for consolidation;
(6) Fill the cofferdam with high-quality cohesive soil on the membrane and pump water into the cofferdam for loading weight;
(7) Setting of settlement observation piles;
(8) Settlement observation analysis;
(9) Unloading of loaded water.
The vacuum water preloading method has been improved on the basis of the vacuum combined surcharge preloading method. The surcharge soil is replaced with water, which facilitates loading and unloading, improves the properties of soft soil, accelerates consolidation rate, saves construction period and costs, is convenient to obtain materials, saves time, and has high economic benefits.
