Overview of preloading methods for soil improvement

2013

In this paper the analytical solutions for radial consolidation that include time dependent surcharge loading and vacuum pressure are proposed, whilst also considering the impact of the parabolic variation of permeability in the smear zone. The use of the spectral method for multilayered soil consolidation is introduced and verified. The Elliptical Cavity Expansion Theory is used to predict the extent of soil disturbance (smear zone) caused by the installation of mandrel driven vertical drains. The predicted smear zone is then compared to the data obtained from large-scale radial consolidation tests. Furthermore, the advantages and limitations of applying a vacuum through vertical drains are discussed using the proposed solutions. The vacuum pressure applied generates a negative pore water pressure that increases the effective stress within the soil, which leads to an accelerated consolidation. Vacuum pressure is modelled as a distributed negative pressure (suction) along the length of the drain and across the surface of the soil. Analytical and numerical analyses that incorporate the Authors' equivalent plane strain solution are conducted to predict the excess pore pressures, lateral and vertical displacement. The application of the theoretical models for selected case histories at the site of the 2nd Bangkok International Airport and the Port of Brisbane, are discussed and analysed. The predictions are compared with the available field data and show that the proposed model can be confidently used to predict the performance with acceptable accuracy through rigorous mathematical modelling and numerical analysis. The research findings verify that the role of the smear zone and vacuum distribution can significantly affect the consolidation of soil, but these aspects need to be modelled appropriately to obtain reliable.

Previously, because of availability of more sites, people used to choose the best one having geotechnical properties of soil favourable for construction of a project. Accordingly, people would choose the site requiring no ground improvement technique for construction of a project. In view of rapid urbanisation /industrialisation, people are getting limited options/alternatives to choose sites for new projects. In fact, many a time, it happens that people have no choice but to accept the only available site for construction, no matter how poor the soil properties it has. These types of sites with unfavourable geotechnical properties for projects need improvement of soil properties by any suitable and economically viable method. Preloading is a technique by which consolidation of soil can be achieved to a substantial amount before imposition of actual construction load. However, the preloading technique alone may not be found to be satisfactory in reduction of consolidation time to the desired extent. Installation of vertical drains, particularly prefabricated vertical drains, followed by preloading is one of the most acceptable and economical technique to consolidate poor soils within a limited period of desire, and are being used widely in our country now.

The International Conference on Civil and Architecture Engineering, 2014

The current research is concerned with a study on the effect of vacuum preloading conjunction with conventional surcharge loading for soft soil improvement experimental and numerical. Several experimental tests were performed by using a large-scale consolidometer were performed to examine the effect of vacuum and to determine parameters such as the extent of smear zone and the soil permeability characteristics. The experimental tests studied numerically using the method of finite elements. The settlement and excess pore pressure associated with a combined vacuum and surcharge load indicate that applying a vacuum has significant effect. The results indicated that the water content decreased with radial distance and the hydraulic conductivity in the smear zone of the PVD increased due to using vacuum pressure. Also, the time required to reach at certain degree of consolidation decreased with using vacuum preloading. Large-scale consolidometer and numerical simulation can be used in the preliminary design works which may reflect the influence on the cost estimate of the used of vacuum preloading technique.

EH Davis memorial lecture. Australian Geomechanics …, 2010

Recent advances in the application of vertical drains and vacuum Recent advances in the application of vertical drains and vacuum preloading in soft soil stabilisation preloading in soft soil stabilisation

Geo-Congress 2014 Technical Papers, 2014

Due to environmental concerns, sustainable ground improvement is considered a critical part of modern infrastructure development. Current policy on environmental sustainability often expects noise-free, chemical-free, and low carbon emission processes, while being economical. In this context, the application of prefabricated vertical drains (PVD) with vacuum preloading is regarded as one of the most sustainable ground improvement techniques. Compared with other ground improvement methods such as piling and chemical stabilization, this method will not only save a considerable cost in embankment construction, but will also improve the construction rate of coastal highways and rail tracks and their load-carrying capacity. The utilization of vacuum preloading will also minimize environmental impact by reducing greenhouse gas emissions and the need for mining natural surcharge fill. The FEM code ABAQUS with the equivalent approach is employed to study the performance of a full-scale test embankment constructed in Thailand. A comparison of the performance of the vacuum system with the standard surcharge fill is elucidated including its benefits and environmental impact.

Application of vacuum assisted preloading is an imperative method when a considerable load is required to meet the desired rate of settlement and an increase in the undrained shear strength upon consolidation. Moreover, where lateral displacements at the edge of a coastal embankment need to be controlled, application of vacuum pressure with a cut off offers the optimum solution. To facilitate vacuum propagation, vertical drains are usually employed in conjunction. The installation of vertical drains using a steel mandrel creates significant remoulding of the subsoil surrounding the drains thereby, reducing soil permeability and adversely affecting the soil consolidation process. In this paper, the simulation of vacuum assisted consolidation using the spectral method and finite element analysis is carried out. Subsequently, the 2D and 3D numerical multi-drain analyses are conducted to predict the excess pore pressures, lateral and vertical displacements. The performance of two selected case histories at the sites of Suvarnabhumi Airport, Thailand and Tianjin Port, China are discussed and analysed. The numerical predictions are then compared with the available field data. Finally, a procedure for the design of vertical drains is presented with a worked-out example.

This paper discusses the comparison of the effectiveness of using vacuum preloading to embankment preloading in accelerating consolidation process with prefabricated vertical drain (PVD). Sources for analysis were obtained from a full scale vacuum consolidation test data of Full Scale Test Geostructure Vacuum System Project in Pantai Indah Kapuk, Jakarta, conducted by PT. Geostructure Dynamics. The paper covers assessment of degree of consolidation and prediction of gain strength of soil due to dissipation of excess pore water pressure under vacuum preloading. The degree of consolidation and gain strength are calculated based on settlement data and pore water pressure data. The result from the analysis of consolidation with PVD-vacuum next is compared with the result of consolidation with PVD-embankment using PLAXIS 2D. In PLAXIS 2D, PVD is modeled in respect to geometric and permeability matching. Post test soil investigation data is also used to verify the analysis result. Comparison result for this location shows that with the same equivalent load and same spacing of PVD, vacuum method can reduce consolidation time up to 43% or accelerate consolidation process up to 1.7 times faster than conventional preloading method. Keywords: Consolidation, Prefabricated Vertical Drain (PVD), Vacuum Preloading

Geotextiles and Geomembranes, 2019

Vacuum consolidation of soils is a technology that, to date, has not been implemented in the Valley of Mexico, where clays are highly compressible and have very low shear resistance and low permeability. This paper describes the experience of a test embankment, in which the drain-to-drain vacuum preloading was assessed. The evaluation includes the description of the subsoil conditions, characteristics of the embankment, construction process and instrumentation that was installed. The test lasted approximately one year with a vacuum applied for six months. The monitoring results showed that the vacuum distributed along the vertical drains and on the surface soil layers accelerated the consolidation, reduced the lateral displacements toward the outside of the platform and increased the effective stress of the soil to a depth similar to the length of the drains. However, there were vacuum pressure losses of approximately 30% between the pumps and end of the horizontal flexible pipes that distribute the vacuum. These losses of vacuum pressure affected the soil consolidation process.

International Journal on Advanced Science, Engineering and Information Technology, 2020

The main issue of building constructions on soft soils is not a uniform settlement of soft ground, which has a slow process that effected construction failures and rising maintenance expenses. For many decades, to the improvement of ground soil stability, then applied using prefabricated vertical drain (PVD). Along the development of science and technologies, which followed by improvement of the soil stability method, that is called as Vacuum Consolidation Method (VCM). The objectives of this study are to determine how the effectiveness of vacuum consolidation with various patterns to soft soil settlement of constructions, and to find the right spacing of PVD installation due to un-uniform settlement of soft soils. The analysis of this study compared the numbers and rates of settlements in preloading, PVD, and VCM with various patterns, and to get a uniform settlement by two scenarios analysis, which are various spacing with single suction pressure (scenario 1) and single spacing with various suction pressures. Based on the result of analysis which showed the settlement of VCM in both patterns are 2.247 m in 105 days (square pattern) and 2.252 m in 90 days (triangular pattern). It means with a triangular pattern has 70.2 more effective than others in the rate of the settlement period. It also showed the VCM has larger than others in volume settlements. The results of 2 scenarios analysis showed that the implementation of scenario one was difficult due to various spacing, while scenario two can be implemented because numbers of settlements depend on suction pressure of the vacuum.

MSc Eng Thesis- Universerty of Peradeniya, 2019

Performance of the ground improvement can be evaluated in terms of degree of consolidation, creep settlement, volume reduction for soft soil layer and in terms of improvement of the preconsolidation pressure and the strength gain for the peaty soil. Above factors were evaluated using field monitoring data as well as the finite element model developed by using the 'Sigma/W' computer software. Then the obtained results were compared to find out the suitability of vacuum consolidation method to improve peaty soil.