The vacuum preloading method is a soil improvement technique that utilizes atmospheric pressure as a temporary surcharge to accelerate soil settlement and enhance its characteristics. This process involves applying vacuum pressure to a separated mass of soil, which reduces atmospheric pressure and pore water pressure, resulting in soil consolidation. The method was first proposed by Kjellman in 1952 and is commonly used to improve the properties of fine-grained soils. It is suitable for various applications, including land reclamation and subgrade projects.
Figure-1: Vacuum Preloading System
A low-cost method that doesn’t require heavy machinery and can significantly reduce construction time has been developed. However, the main challenge in this process is maintaining sufficient vacuum pressure.
How to Improve Soil Properties by Vacuum Preloading Method?
Vacuum preloading is an effective soil consolidation technique that involves a drainage system, sealing or isolation system, and vacuum pumps. The drainage system comprises prefabricated vertical drains, horizontal filter pipes, and a sand layer, which channelize vacuum pressure and water flow. The thickness of the sand layer can range from 0.3 m to 0.8 m. A sealing system is used to prevent water and air leakage, while the isolation system consists of geomembrane, soft clay, and a cutoff wall. Vacuum pumps create a suction force that accelerates soil consolidation by removing water and air.
The area covered by one pump is determined by its power, with a pump of 7.5 kW used for an area larger than 1000m2. Vacuum suction decreases atmospheric and pore water pressure, creating a pressure difference that causes pore water to flow towards the vertical drain, leading to soil consolidation. The maximum surcharge pressure is 80 kPa. To monitor the vacuum degree, install vacuum gauges under the membrane.
Design parameters such as drainage spacing and depth, period of surcharge and vacuum pumping, sealing measures, and individual block area are controlled by soil properties, site conditions, vacuum, drainage system, and the purpose of soil improvement. Prefabricated vertical drain spacing can range from 0.7 m to 2.7 m, while the depth of the vertical drains depends on the soil profile. The termination depth of vertical drains is around 1 m above the bottom of the soft soil layer.
Vacuum pressure creates an inward force into the subsoil, but the influence on adjacent structures is low. Settlement plates are used to assess soil settlement and placed on the surface of a geotextile. Vacuum preloading is cost-effective and requires a short period to achieve a designated settlement. However, uneven settlement may occur. Vacuum preloading has been used for land reclamation and subgrade projects. In contaminated land, the system can collect water for later treatment. If there is a shortage of sand in land reclamation projects, vacuum preloading can consolidate excavated and dredged soil to be used instead of sand.
FAQs
What is the vacuum preloading method of soil improvement?
The vacuum preloading method is a technique that aims to expedite soil settlement and enhance its properties by utilizing atmospheric pressure as a temporary surcharge. The process involves introducing a vacuum pressure into a separate soil mass, which effectively reduces both atmospheric pressure and pore water pressure, leading to soil consolidation.
By decreasing the pore water pressure, the vacuum preloading method accelerates the consolidation process, which usually occurs gradually over time. This technique is commonly used in geotechnical engineering for soil improvement and stabilization.
The basic principle of vacuum preloading is to apply vacuum pressure to the soil mass and promote soil compaction through the application of external pressure. The resulting consolidation improves the soil’s characteristics, such as its bearing capacity and compressibility, making it suitable for various construction projects.
Overall, the vacuum preloading method is an effective and efficient approach to soil improvement and stabilization, particularly in areas with soft soil conditions. The technique allows for a more expedited consolidation process, resulting in enhanced soil properties that can withstand various loads and construction requirements.
What are the components of the vacuum preloading system?
The process of vacuum preloading entails the use of three key components: a drainage system, a sealing or isolation system, and vacuum pumps. These components work together to achieve the desired outcome of consolidating soil layers in a particular area.
The drainage system is responsible for removing excess water and promoting drainage of the soil. It is critical for this system to be effective in order to ensure the success of the overall process.
The sealing or isolation system is designed to prevent air from entering the vacuum zone, which would otherwise negatively impact the effectiveness of the vacuum pumps. This system is crucial to maintain the vacuum pressure required to consolidate the soil.
Finally, the vacuum pumps play a key role in creating the necessary vacuum pressure in the preloading zone. This pressure causes water to be drawn from the soil layers, which in turn leads to consolidation. It is essential to have reliable and efficient vacuum pumps in order to achieve the desired results.
What type of soil is suitable for vacuum preloading?
The method of vacuum preloading is effective for the consolidation and improvement of fine-grained soil.
What are the applications of the vacuum preloading method?
The versatility of this product makes it appropriate for a range of different uses, including land reclamation and subgrade projects. It is capable of performing well in a variety of environments and situations, making it a highly adaptable solution. Whether you need to reclaim land that has been damaged or you require a stable foundation for a construction project, this product can meet your needs. Its flexibility and durability ensure that it will perform reliably and consistently over time, delivering the results you require. With its many applications and benefits, it is a valuable resource for a wide range of industries and projects.
What are the advantages of the vacuum preloading method?
The ideal ground improvement technique is one that is efficient, machine-friendly, and does not require fill materials. Additionally, it should be able to achieve the desired consolidation within a short period of time. By meeting these criteria, a ground improvement technique can be considered highly effective and efficient. It is important to note that heavy machinery can often be costly and time-consuming, so a machine-friendly approach would be ideal. Moreover, the use of fill materials can also be a costly and time-consuming process, which can be avoided if the technique does not require them. Ultimately, a ground improvement technique that meets these criteria can save time and money while effectively improving the stability and strength of the soil.