Vacuum Consolidation Method Research Articles

Study on Pile Bearing Capacity Improvement in Soft Soil After Vacuum Consolidation

The main problem in developing property over soft soil is significant settlement due to the consolidation process. The soil settlement, which will occur gradually throughout the years, will disrupt existing infrastructures, in this case bridges. To mitigate this issue, the common method is by speeding up the consolidation. The consolidation process must be sped up to avoid the differential settlement problem at the bridge abutments. Due to the limited supply of fill material, a vacuum consolidation method is adopted. In this method, a Prefabricated Vertical Drain (PVD) is installed, and a vacuum is applied to impose pressure as preloading. Because of the consolidation process, theoretically, the effective stress of the consolidated soil increases, and the soil shear strength does as well. Increasing the shear strength of the soils will increases the pile capacity. However, the interesting question is how much the shear strength of the soil can increase and impacts the pile capacity. In this paper, the shear strength improvement of the consolidated soil and the effect on pile bearing capacity is evaluated. This study used a series of in-situ tests that were carried out before and after the vacuum consolidation. A pile loading test using the Pile Dynamic Analyzer (PDA) method was carried out to verify the pile bearing capacity improvements. From the comparison result, it is shown that the theoretical capacity of the piles after consolidation were close to the pile test results.

A Case Study of Peat Ground Improvement by Vacuum Consolidation in Hokkaido, Japan

This paper presents the field performance of vacuum consolidation method on peat ground and some technical learning from the field trial. Peat is well known to be a soft soil which has particular characteristics, including extremely high compressibility and greatly low undrained shear strength. In case of an embankment building over peat ground, sliding failure and large settlement often occur due to the particular characteristics. For actual construction sites on peat ground, therefore, some kinds of ground improvement methods are commonly used. One of the methods is the vacuum consolidation method which can load vacuum pressure with the soft ground by vacuum pumps and prefabricated vertical drains to accelerate the consolidation and increases the strength of soft ground. Peat ground distributed widely in Hokkaido, the northernmost land of Japan. A full-scale trial construction of vacuum consolidation was conducted in a highway project over peat deposit in Hokkaido of Japan to reveal its performance. Although the undrained shear strength of peat ground at the trial construction site was approximately 10 kN/m2 and extremely low, a 10.7 m high embankment was successfully built in only 45 days. This experimental fact implies that the vacuum consolidation method has extremely high effects in improving the stability of peat ground. Based on a result of the trial construction, it also revealed that the increase of undrained shear strength of the peat ground using vacuum consolidation and the suitable spacing of prefabricated vertical drains for peat ground.

Calculation for soft soil improvement by vacuum consolidation method combined with PVDs

This paper presents a method of soft soil improvement by vacuum consolidation method combined with PVDs. One of the effective methods of soft soil improvement compared to the traditional preloading method, which consumes a lot of embankment materials, Extending construction time, and also causes the risk of slope instability due to the height of the embankment. The method of soft soil improvement by vacuum is a method of creating negative pressure in groundwater by vacuum pump and that negative pressure is maintained by an airtight geo-membrane system, thus increasing the effective pressureof soil by reducing excess pore water pressure while the total pressure remains unchanged. When using the vacuum compression method combined with PVDs, the surrounding soil tends to move into the vacuum area, thus minimizing the risk of slope instability. And the time to apply vacuum pressure is much faster than preloading method to create equivalent pressure. Specific application for the soil improvement of a factory in Cai Mep industrial zone will show the effectiveness of this method.

Kontribusi Tol (Tax On Location) Dalam Pembangunan Ekonomi di Palembang

This study examines the contribution of the Toll Road to Palindra's economic development. The Palindra Toll Road, which has an investment value of 3.3 trillion, is mostly built in swampy areas and difficult terrain, so a special construction method is needed, namely by using the Vacuum Consolidation Method (VCM) technology. Roads were conducted to collect data, followed by validation and reliability tests, Critical Performance Analysis (IPA). The construction of the toll road over the swamp resulted in some agricultural land in the Pemulutan area being displaced. This certainly has an impact on the income of farmers whose daily work is farming. In addition, there are many other positive impacts that can be utilized until now, such as toll roads that facilitate access to connect from one area to another, as well as stabilizing traffic that usually occurs in the Palembang- Indralaya area.

SOIL SUBSTANCE ANALYSIS USING PVD WITH VACUUM CONSOLIDATION METHOD (VCM)

The construction of toll roads on soft clay has the main problems of the relatively low bearing capacity of the subgrade and the relatively large and long duration of subgrade compression. The infrastructure built on the subgrade could be damaged before it reaches its planned age if the subgrade not repaired first. The selection of the soft clay soil handling method considers the cost and time at the time of construction in the field. For this reason, alternative methods needed that are cost and time efficient and have minimal risk to environmental impacts. The vacuum consolidation method (VCM) is an alternative to improve water saturated soft clay. Soil improvement using the vacuum consolidation method is intended to accelerate the settlement and increase the bearing capacity of the soft native soil by vacuum pumping the soil to reduce the moisture content and air content of the soil grains to accelerate long-term settlement and differential settlement. This study aimed to analyze the soil settlement using PVD with the vacuum consolidation method (VCM). The analysis conducted showed that to achieve 90% consolidation without PVD, it would take 13,922 years and using PVD, it would take 18 months, and using PVD and the vacuum consolidation method (VCM), it would take 4,8 months. The use of PVD with the vacuum consolidation method (VCM) can speed up the consolidation process compared to using PVD or only using PVD. The total decrease that occurred was 2,043 m.

Observations from Ground Improvement Using Vacuum Consolidation Method

In the modern world of Civil Engineering, challenges arise during the various phases of construction, starting from the project development phase to the completion of the project. One of the main factors to be considered before commencing any infrastructure project is the foundation of where it is to be built. Without a strong foundation, it's not possible to proceed further to subsequent stages and in some cases, significant improvements may be required before starting the construction process. Although there are several different available methods for soil improvement in Civil Engineering, preloading using vacuum pressure with prefabricated vertical drains (Vacuum Consolidation Method) is one of the commonly applied techniques. Nowadays, it is widely used in countries having soft soil settlement problems. This paper presents the observations made from a soil improvement project using VCM including the site conditions and methodologies adopted during the process. The field data related to parameters such as pore pressure, settlement and shear strength improvement in natural soft clay have been presented and discussed. The degree of consolidation in the field has been back-calculated from settlement data and compared with values obtained from the 1-D consolidation equation. Field investigation tests, such as borehole tests and field vane shear tests, were performed before and after the soil improvement and it was found that the soft soil properties can be enhanced using vacuum consolidation without the use of any surcharge loading as well.

Determination of the affected area of vacuum consolidation method for roadbed ground improvement to adjacent works

Vacuum Consolidation Method (VCM) is one of the effective ground improvement treatments applied in construction works in Viet Nam recently. However, its affected area impacts to the adjacent works has not been studied in detail and standarised, leading to unexpected incidents. This paper proposes a method to determine the affected area of vacuum consolidation method then propose solutions to protect works. The result was demonstrated at approach road of Vam Sat 2 bridge project, located in Can Gio district, Ho Chi Minh city and shows high efficiency, ensuring economic-technical factor.

Centrifuge-model tests on pore water pressure combined with vacuum and embankment loading

Vacuum consolidation is a ground-improvement method in which negative pressure is applied to drain materials placed in a soft ground to consolidate the ground. Using the vacuum consolidation method, a soft ground can be consolidated without the shear deformation of the ground, and the combination of this method along with embankment loading enables the stable construction of the embankment and the suppression of the displacement of the surrounding ground. In this study, centrifuge-model experiments were conducted under a gravitational acceleration of 50g for the purpose of investigating the pore water pressure of the ground during both vacuum consolidation and embankment loading. Embankment loading was reproduced by a loading device consisting of an air cylinder and a loading plate, and vacuum consolidation was reproduced by depressurising the inside of a model drain using a vacuum pump. Three experimental cases were conducted: one case with only embankment loading and two cases with a combination of vacuum consolidation and embankment loading. From the experimental results, it was confirmed that in the ground where vacuum consolidation was applied, large negative pressure propagated near the drain material, and the increase in pore water pressure due to embankment loading was suppressed.

The Effectiveness of Vacuum Consolidation to Soft Soil Settlement

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.

Study of VCM Improved Soft Soil Properties Using Non-Destructive and Destructive Techniques

In Bangkok, the demand for housing is extensively high due to the city growing rapidly, so some swampy areas are filled with soil. A Prefabricated Vertical Drain (PVD) with the Vacuum Consolidation Method (VCM) is required to make the soil applicable for construction. However, it is difficult to monitor the soil strength during the process because the airtight sheet will be broken. This research aims to study the possibility of using the Spectral Analysis of Surface Waves (SASW) test to monitor the effectiveness of the VCM method and to study the development of shear-wave velocity over the consolidation period. Multiple instruments were installed on site, namely, vacuum gauges, settlement plates, and a piezometer, as well as a borehole to monitor the pump pressure, settlement, porewater pressure, and soil properties. Ten SASW tests were taken to measure the change in shear-wave velocity (Vs) over 7 months. The results showed an increment in the Vs along with increments in the settlement and undrained shear strength (Su), as well as a decrement in pore pressure during the consolidation period. The correlation between Vs and soil settlement was developed to predict the amount of settlement using Vs. These all indicated the potential of using the SASW method for soil improvement monitoring purposes.

Analytical study on suppression effect of pore water pressure and displacement of surrounding ground by vacuum consolidation method

Analytical study on suppression effect of pore water pressure and displacement of surrounding ground by vacuum consolidation method

An Improved Method for Dewatering Sewage Sludge Using Intermittent Vacuum Loading with Wheat Straw as Vertical Drains

This paper presents an experimental investigation on the feasibility and effectiveness of an improved method for dewatering sewage sludge (SS) in landfills. Compared with traditional vacuum preloading with prefabricated vertical drains (PVDs), an improved intermittent vacuum loading with wheat straw vertical drains (WSVDs) was developed and a series of laboratory tests were conducted to evaluate the effects of WSVD type and intermittent loading period on the dewatering properties of SS. Tests results showed that the WSVD has a good elastic deformation characteristic during vacuum loading and unloading over PVD. The vacuum degree transmission tests on three types of WSVD showed that 5 cm crushed wheat straw is the optimum one. The surface settlement and water content of SS after the model test are similar for WSVD and PVD in the traditional vacuum consolidation method. There was a significant improvement when applying intermittent vacuum and optimum daily loading time of 10 hours was obtained. The cracks found in the sludge cake around the drainage body using improved method are suggested as the key factor since they are able to improve the vacuum transmission capacity and the permeability of SS. The improved method is expected to offer a feasible and cost-effective way to deal with high water content SS in landfills.

Vacuum consolidation for construction of motor road embankments in peat soil

One of the efficient methods to accelerate primary filtration consolidation of peat is vertical draining combined with vacuuming.This article presents the results of laboratory analysis of vacuuming impact onto the peat deformation rate in the bases of motor road embankments. It demonstrates that the duration of peat vacuuming increases and its efficiency decreases with the increase of pressure exerted by surcharge sand layer.The results of compression tests have shown that relative peat deformation after vacuum consolidation is 0.24…0.37; this means the deformation rate of the road base in the course of operation will be significantly lower.The effect of vacuum consolidation on peat settlement rate during motor road embankment construction was assessed by numerical simulation in PLAXIS software, which enables accounting for consolidation and creep processes in motor road base courses. The results of numerical simulation were used to compare the efficiency of preloading the peat using surcharge sand with the efficiency of vertical draining combined with vacuuming, considering the allowable embankment settlement rate during motor road operation. Due to a low settlement rate, the vacuum consolidation method ensures normal road operation and allows increasing the maintenance interval.

Reducing the secondary consolidation of peat ground using vacuum consolidation

This paper discusses secondary consolidation of peat ground improved by vacuum consolidation method, and quantitatively presents the degree of reduction of the secondary consolidation. When an embankment is constructed for roads, river dykes or other purposes on peat ground, settlement after the construction due to remarkable secondary consolidation of peat ground is a serious problem. Therefore, to clarify the reduction effect on secondary consolidation obtained by using the vacuum consolidation method for peat ground, a trial embankment and elasto-viscoplastic finite-element (FE) analysis were performed. It was proved, with the trial embankment, that the surcharge effect by unloading vacuum pressure reduces the secondary consolidation. The coefficient of secondary consolidation (Cα) of peat ground improved by vacuum consolidation was approximately 30−50% that of non-improved peat ground. The trial embankment and the FE analysis revealed that the reduction effect could be expressed quantitatively in relation to the over-consolidation ratio (OCR), and Cα decreases hyperbolically with an increase of the OCR with the maximum curvature near an OCR of 1·3.

Influence of vertical drains on improving dredged mud by vacuum consolidation method

Vacuum consolidation preloading method (VCM) has been widely adopted as an effective solution for soft soil improvement over the world. Recently, VCM has been successfully applied for improving the geotechnical properties of dredged mud, which is normally dumped at reclamation area by hydraulic pumping. However, it has been also reported that application of VCM for treatment of the dredged mud has been failed in some particular cases. The failures are mainly caused by clogging problem in vertical drains due to fine-grained soils that reduces the drainage efficiency of drainage system. To address this issue, a series of model tests have been conducted to investigate the performances of vertical drains among prefabricated vertical drain, sand drain and filter pipe. As the goal, the performances of types of the vertical drain solutions are analyzed based on the monitoring data of settlement, influencing zone surrounding the vertical drains. The test results reveal that sand drain shows the best performance among the others. In addition, the clogging problem is clearly shown in case of PVD.
 Keywords: dredging slurry; vacuum consolidation method; model test; PVD; filter pipe; sand drain.

ANALISA PENURUNAN TANAH LUNAK DENGAN BEBERAPA METODE KONSOLIDASI PADA PROYEK JALAN TOL PALINDRA

Based on Daily Traffic Average of Palembang - Inderalaya in 2007, traffic volume of 2 ways of Palembang City for traffic capacity had been reach at 19900 vehicles/2 ways/day. Therefore, in order to decrease traffics jamthen government has built Palembang – Inderalaya Highway (Palindra). According to topography of Palembang City, it has lying on lowland areas with soft soils type which has high compressibility. The objectives of this study are to estimate soft soils settlement with various method of consolidation which are oedometer test, pre-fabricated vertical drain (PVD), and vacuum consolidation method (VCM). The results of this study showed the numbers of settlement of soft soils 1,479 m for 17,24 years in oedometer test, 1,342 m for 105 days in PVD with square pattern, and 1,354 m for 90 days in PVD with triangular pattern. Meanwhile, the numbers of settlement with VCM method have 2,250 m for 105 days with PVD square pattern, and 2,251 m for 90 days with PVD triangular pattern. Based on those results, it can be concluded that VCM triangular pattern more effective than others.

Feasibility of vacuum consolidation in managing dredged slurries with wheat straw as drainage channels

It is suggested to use wheat straw as both vertical and horizontal drainage materials when using vacuum consolidation method to process dredged slurry in this paper. To verify the feasibility of this proposal, compression and hydrulic conductivity test on wheat straw and vacuum consolidation tests on slurry using wheat straw as drainage materials were conducted. The results show that the compression process of wheat straw is composed of instantaneous settlement and creep. The density of wheat straw changes from 20 kg/m3 to 200 kg/m3 as vertical stress varies from 5 kPa to 100 kPa. The creep rate increases to maximum when vertical stress reaches 60 kPa and then decreases with as vertical stress further increases. The hydrulic conductivity coefficient of wheat straw is changed between 104 cm/s and 101 cm/s, which decreases linearly as density increases in semi-logarithmic coordinates (hydraulic conductivity in log scale). In vacuum consolidation tests, the settlement, water content, and undrained shear strength of slurry proceeded by vacuum consolidation with wheat straw as drainage materials are similar to those obtained by using PVD and sand as drainage materials. All the results obtained by this paper show that it is feasibility to use wheat straw as vertical and horizontal drainage materials in vacuum consolidation.

Macro-element method with water absorption and discharge functions for vertical drains

When simulating the vertical drain method using a soil–water coupled finite element analysis, a macro-element method can be used as a means of approximately applying the water absorption function of drains to individual elements. In this paper, the discharge function of vertical drains was added to the method by treating the water pressure in the drain as an unknown and adding a continuity equation for the drains to the governing equations. By extending the method in this way, the analytical results came to exhibit the well-resistance phenomenon automatically, depending on the analytical conditions. Numerical analyses were conducted after incorporating the proposed macro-element method into a quasi-static soil–water coupled elasto-plastic finite element method based on the finite deformation theory. The main conclusions are as follows: (1) the proposed method enables highly accurate approximations for problems involving material and/or geometrical nonlinearity and multilayered grounds; (2) the proposed macro-element method is capable of reproducing various phenomena that occur when the vacuum consolidation method is applied to a clayey ground containing a middle sand layer; (3) by following the formulation used in this paper, it is unnecessary to match the mesh division width to the drain arrangement and spacing. In addition, it is possible to obtain solutions that are minimally affected by the mesh size.

真空圧密工法を施工した超軟弱地盤の長期沈下予測

真空圧密工法を施工した超軟弱地盤の長期沈下予測

Prediction of embankment behavior of regulating reservoir with foundation improved by vacuum consolidation method

The present paper addresses the numerical prediction of the behavior of a ground and a reservoir dyke with a retaining wall at the site of a regulating reservoir whose soft soil foundation is improved by using both the usual embankment preloading and vacuum consolidation. To evaluate the settlement, the lateral deformation, and the dissipation of pore pressure during vacuum preloading, a numerical analysis using an elasto-plastic FEM for soil–water coupled problems, incorporating the SYS Cam-clay model, is carried out in two dimensions. However, a change in the soil parameters during the vacuum preloading leads to a less accurate computation. To account for the uncertainties in the input parameters of the constitutive model for the improved ground, an inverse analysis approach is adopted. The particle filter is used to identify the compression index of the clay layers and the coefficient of permeability of the organic soil layer based on the measured settlement at the bottom of the preloading embankment during the vacuum consolidation. The reservoir dyke with a retaining wall is constructed on an improved foundation after removing the preloading embankment, and an attempt is made to predict its performance after construction by an elasto-plastic FEM for soil–water coupled problems using the identified parameters.