Soft Ground Improvement｜Full Standard Construction Procedures of Vacuum Preloading

On-site soft-ground improvement projects rely heavily on standardized workflows. This document sorts out the complete construction sequence of vacuum preloading, covering pre-construction preparation through to completion acceptance. It serves as a practical reference for technical staff and construction management personnel.

Overall Construction Sequence: 

Site clearance and leveling → Surveying and setting-out → Prefabricated vertical drain installation → Horizontal drainage network laying → Sealing system construction → Equipment installation and commissioning → Vacuum pumping and pressure stabilization → Full-process monitoring → Unloading and acceptance

Step 1: Site Clearance and Leveling 

Remove weeds, sludge and construction debris from the site. Level the ground and eliminate protrusions and depressions. Prevent sharp objects from piercing the sealing membrane and provide a flat base for subsequent operations.

Step 2: Surveying and Setting-out 

Carry out precise layout according to design drawings. Mark installation positions of prefabricated vertical drains, routes of drainage pipelines and boundaries of improvement zones. Set clear markers to ensure spacing and depth comply with design specifications.

Step 3: Prefabricated Vertical Drain Installation 

Use specialized drain insertion machines for positioning and installation. Strictly control installation depth, verticality and spacing. Avoid drain retraction, breakage and offset. Cut and fix drains upon completion to guarantee unobstructed drainage channels.

Step 4: Horizontal Drainage Network Laying 

Lay flexible filter hoses and main-branch pipe networks. Accurately connect vertical drains to branch pipes. Arrange pipelines evenly with reasonable gradients, free from kinks and blockages to form a fully connected drainage system.

Step 5: Sealing System Construction 

Lay base geotextile to protect the drainage system, followed by multi-layer sealing membranes. Weld membrane joints firmly by thermal fusion. Embed membrane edges into sealing trenches and compact for tight closure to eliminate air-leakage points.

Step 6: Equipment Installation and Commissioning 

Install vacuum pumps, water-gas separators and monitoring instruments. Connect pipeline systems and thoroughly inspect circuits and sealing performance. Perform no-load commissioning to verify normal equipment operation.

Step 7: Continuous Vacuum Pumping and Pressure Stabilization 

Start formal vacuum pumping and gradually raise vacuum pressure. Maintain stable negative pressure above 80 kPa with continuous operation; avoid arbitrary shutdowns. Take proper on-site protection measures.

Step 8: Full-Process Monitoring and Control 

Continuously monitor vacuum pressure under membranes, surface settlement, pore-water pressure and horizontal soil displacement. Record daily data and adjust construction conditions based on monitoring results.

Step 9: Unloading and Acceptance 

Unload and shut down equipment when consolidation degree, settlement and bearing capacity meet design requirements and remain stable for more than seven days. Dismantle facilities, compile documentation and complete completion acceptance.

Conclusion 

Vacuum preloading is a mainstream technique for large-area soft ground improvement. Every working procedure directly determines reinforcement performance. Strict implementation of standardized workflows and rigorous control over drainage, sealing, vacuum pumping and monitoring can effectively reduce quality risks and ensure soft-soil reinforcement meets design expectations.

Source: Guangzhou Sunzo Foundation Engineering Co., Ltd.

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