Prefabricated Vertical Drains Research Articles

Analysis of Soil Improvement Through PVD and Vacuum Preloading with Several Equivalent Permeability Methods

Vacuum preloading combined with prefabricated vertical drain (PVD) is one of the common soft soil improvement methods. Soft soils often pose significant problems in construction projects due to their low shear strength and high compressibility, leading to settlement issues and potential structural instability. The PVD combined with vacuum preloading method addresses these problems by accelerating the consolidation process and minimizing settlement during service period. The acceleration occurs due to the presence of PVD, allowing dissipation of excess pore water in horizontal direction towards the PVD. Thereafter, the water in the PVD is drained to the surface. When modelled in 2D, PVD behaves as a continuous drain in the plane strain direction, causing the flow conditions to deviate from the actual conditions. To address this issue, equivalent soil permeability values is required, allowing the 2D model to produce results closely resembling the actual conditions. This research explores the improvement of PVD vacuum preloading through three equivalent permeability approaches. Utilizing field monitoring data, which includes settlement measurements from settlement plates, changes in pore water pressure recorded by piezometers, and lateral deformation data captured by inclinometers, the study evaluates the effectiveness of these approaches. Comparative analyses with field monitoring data reveal that Indraratna equivalent permeability method has the best fit. The integration of PVD and vacuum preloading, coupled with the refinement of equivalent permeability methodologies, offers a promising solution for addressing soft soil problems in geotechnical engineering. This research contributes to the practical application of these methods in construction projects, emphasizing their potential to enhance soil stabilization and reduce settlement-related risks.

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.

Vacuum consolidation of dredged slurry improved by horizontal drainage-enhanced geotextile

The vacuum consolidation behavior of dredged slurry improved by horizontal drainage-enhanced geotextile (HDeG) application was investigated. For comparison, vacuum consolidation tests using a prefabricated vertical drain (PVD) and layered prefabricated horizontal drains (PHDs) were conducted. Based on the test results, it was found that by using HDeG, the consolidation rate of the dredged slurry was significantly increased. Thus, the effectiveness of the HDeG method was verified. The nonwoven geotextile sheet of HDeG could provide a sufficient vacuum pressure and drainage and therefore greatly shorten the drainage path. The HDeG-induced consolidation settlement generally matched the calculated 1D consolidation settlement well using a representative coefficient of consolidation. The analysis of scanning electron microscopy images shows that after the vacuum consolidation test, the porosity of the PHD filter (vacuum PHD treatment) was only 11% (21.1% of the initial porosity), while the porosity of the PHD filter of the HDeG was 22.16% (42.6% of the initial porosity), suggesting that the geotextile effectively reduced the apparent clogging of the drains.

Finite strain elastic visco-plastic consolidation model for layered soils with vertical drain considering self-weight loading and nonlinear creep

Prefabricated vertical drains (PVDs) combined with vacuum and/or surcharge loading have been widely adopted to improve the strength of soft soils. Precise consolidation analysis is the theoretical basis for the design of preloading method with PVD. Current consolidation theories for layered soils with PVD seldom consider the influence of large strain, nonlinear creep, and self-weight loading simultaneously. This paper, thus, presents a finite strain elastic visco-plastic consolidation model, called RCS-EVP, for radial consolidation of layered soils with PVD. RCS-EVP is developed based on the piecewise-linear method. It takes into account nonlinear creep with limit creep strain, variable boundary conditions, anisotropy of soil hydraulic conductivity, and variable compressibility and hydraulic conductivity during the consolidation under self-weight, time-dependent surcharge and/or vacuum loading. The performance of RCS-EVP is evaluated by comparing with the results from finite element simulations and a laboratory physical model test. The variations of settlement and pore pressure of a soft soil ground improved by vacuum preloading with PVD are estimated using RCS-EVP. The results indicate that RCS-EVP provides good estimates of long-term consolidation of layered soils with PVD under both laboratory and in-situ conditions.

Analyzing Embankment Displacement: PVD and Vacuum Consolidation with Sheet Pile Protection

The global widespread adoption of Prefabricated Vertical Drains (PVD) in conjunction with vacuum consolidation is driven by its robust and cost-efficient attributes. However, this construction method is not without challenges, as it has been linked to substantial displacements, posing risks to adjacent structures. Addressing such concerns in a Vietnamese road construction project, this study focuses on the innovative contribution of sheet pile protection as a highly effective solution. Utilizing numerical analysis with an anisotropic model, we examine the impact of sheet pile protection on embankment displacement. Through comparative analysis with field data, our study demonstrates the remarkable efficacy of the sheet pile method in significantly reducing both vertical and lateral settlements. Acting as a protective membrane, it effectively counters suction from the PVD vacuum zone. These findings make a substantial contribution to the field, providing engineers handling similar structural protection scenarios with invaluable insights and a novel approach to mitigating displacements associated with PVD and vacuum consolidation.

Effects of Filter Material on the Permeability of Sapric Peat in Flexible Wall Permeability Tests

Introduction Installation of Prefabricated Vertical Drains (PVDs) is one of the alternatives for ground improvement used in peatland deposits. However, filter paper is commonly used as standard filter material to determine the permeability of peat rather than the PVD material itself. Aims This paper presents preliminary data on the effect of using two different filter materials on the permeability behavior of Sapric peat. Methods A series of flexible wall permeability tests (FWPTs) was conducted to evaluate the peat permeability behavior under compression using two filter materials. This study compared Whatman standard filter paper and Prefabricated Vertical Drain (PVD), which is a non-woven geotextile filter material. Results The results showed that both tests using filter paper and a PVD filter exhibited a high initial coefficient of permeability, which depends on the hydraulic gradient. The coefficient of permeability significantly decreased until a certain period and then diminished with time. The coefficient of permeability from PVD filter tests was found to be approximately 2.6 times higher than that of the standard filter paper under the same compression. The duration required to reach a semi-steady state flow condition from the PVD test was 0.9 times faster than the standard filter paper. The random error of the coefficient of permeability data from the tests using the PVD filter was lower than the data of the standard filter paper. Conclusion This preliminary result suggests that standard filter material might not represent the actual coefficient of permeability of Sapric peat. The coefficient of permeability value was less consistent compared to the PVD filter. The selection of filter material plays a crucial role in ensuring accurate and reliable results, especially when dealing with PVD construction in peat. Using the PVD filter in FWPT appears to be suitable for the design of PVD in peat. The findings of this study contribute to evaluating the correct parameters for engineers to design and analyze the effectiveness of the ground treatment method using PVD in peat.

Vacuum consolidation theory of dredged slurry considering nonlinear clogging behaviors

Clogging in the prefabricated vertical drains (PVDs) and soils is an inherent feature associated with vacuum treatment of slurry ground. The clogging column is characterized by nonlinear growth of volume over time and nonlinear permeability distribution along the radial direction. This study aims to develop a drain-well consolidation model for vacuum treatment of dredged slurry, with specific considerations of the nonlinear behaviors of the clogging column and PVD drainage capacity. The constitutive compression and permeation behaviors of the dredged slurry are described by extended power functions, which avoids the singularities associated with the conventional logarithmic constitutive equations when the effective consolidation stress approaches zero. Parametric studies were conducted to explore the consolidation effects while considering different combinations of parameters that govern the nonlinear behaviors of the clogging column and PVD-drainage capacity. The significance of considering the abovementioned nonlinear behaviors was demonstrated by comparing the field test results on a dredged slurry ground. Results indicate that clogging primarily affects consolidation by causing a nonlinear permeability distribution along the radial direction of the clogging column and nonlinear attenuation of PVD-drainage capacity.

A Novel Approach to Determine the Treatment Range of Prefabricated Vertical Drains and Cement‐Soil Mixing Piles for Wide and High Embankment on Soft Ground

AbstractWide embankments with a width of tens or even hundreds of meters change the settlement distribution mode of soft ground. At the same time, the influence of embankment height on the stability and settlement of soft ground is quite significant. For the wide and high embankments, when the prefabricated vertical drain (PVD) is applied in the middle of the embankment and the cement‐soil mixing pile (CSMP) is implemented on both sides of the embankment, a novel determination approach of the reasonable proportion of the suitable treatment range of the PVD and the CSMP is proposed in this study. Combined with the engineering example of the Sanya Station yard of Hainan East Ring Railway, the Plaxis 2D finite element program is used to carry out the parameter analysis on the different proportions of PVD and CSMP in treatment ranges. It is confirmed that the proportion of the PVD and the CSMP in this project is between 2:3 and 4:1, which is consistent with the final design scheme provided by the design company. The on‐site monitoring results of this site show the effectiveness of the determination approach proposed in this paper.

Consolidation analysis for soft soil with non‐Darcian flow considering variable discharge capacity of prefabricated vertical drain

AbstractGround improvement is a complex issue, and accurately predicting the consolidation and settlement of soft soil with prefabricated vertical drain (PVD) presents a significant challenge. Recent laboratory and field tests have highlighted the influence of the variable discharge capacity of PVD and the non‐Darcian flow behavior of soft soil on consolidation. However, existing theories have not yet considered these two factors simultaneously. To address this gap, a numerical solution for consolidation analysis incorporating non‐Darcian flow and variable discharge capacity of PVD was developed and applied in a test area. The results of this study demonstrate the significant impact of both non‐Darcian flow and variable discharge capacity on the consolidation rate. A comprehensive comparison between the findings of this numerical solution, the degenerate solution, and monitored data reveals clear differences. Notably, the non‐Darcian exponent (s) and discharge capacity parameters (A3) were found to exert a greater influence on consolidation behavior compared to other factors. These findings provide valuable guidance for the design and implementation of following airport ground improvement strategies.

Clogging Behaviors in PVD and Their Evaluation Criteria for Dredged Mud Slurry

During the consolidation period of vacuum preloading drainage of dredged mud slurry, the clogging behaviors of the filter drainage structural layers and the core boards of prefabricated vertical drains (PVD) determine the drainage capacities of PVD. However, currently, there is a lack of comprehensive research on the evaluation criteria for these two clogging behaviors. Therefore, based on typical dredged mud slurry, typical geomembranes, and raw material core boards with different bending forms, relevant macro and micro-scale experimental studies have been carried out in this study. The research results show that (1) with the application of the gradient ratio test method, the clogging behaviors of filter membranes of PVD under graded vacuum preloading can be effectively simulated. Also, in the design of graded vacuum preloading, characteristics of equivalent pore sizes and pore structures should be emphasized to investigate the suitability of filtration and drainage performance of PVD filter membranes. (2) The compressive yield strength of core board grooves is a key factor influencing the reduction rate of flow capacity. The reduction rate of flow capacity and well resistance increment can be used as comprehensive indicators reflecting the clogging behaviors of core boards, while the bending angles and bending rates of core boards can be used as specific technical indicators. (3) The proposed clogging evaluation criteria for PVD are as follows: a filter membrane gradient ratio (GR) > 4.0, a core board bending rate >60% and a core board bending angle < 45°, or a reduction rate of flow capacity of bending drainage board > 90% or well-resistance increment > 9. Also, these criteria can be incorporated into the control indicators for drainage performance of PVD used in such types of foundations.

Analytical models for consolidation of unsaturated composite foundation improved by impermeable columns and PVDs

In this study, two equal-strain consolidation models centred on an impermeable column and a prefabricated vertical drain (PVD), respectively, are developed for the study of unsaturated composite foundations reinforced by impermeable columns and PVDs. The analytical solutions, accounting for the smear effect, well resistance, and time-dependent loading, are obtained through the application of the constant of variation method, Fourier series expansion, and decoupling technique. The validity of the proposed solutions for both distribution modes is then verified by comparing it with the analytical solution for the consolidation of PVD-improved composite foundations. Finally, the analyses are conducted to examine the effects of loading rate, smear parameter, well resistance factor, and distribution pattern on consolidation behaviors during multi-stage loading. Notably, it is observed that the consolidation completion time is unaffected by the loading rate, instead relying on the magnitude of the loading values. The presence of multiple smear zones, resulting from the installation of impermeable columns and PVDs, amplifies the smear effect on consolidation. Additionally, increasing the number of PVDs is found to have a notable effect on accelerating the consolidation rate; however, it is crucial to consider the accompanying increase in well resistance.

Penerapan Soil Preloading, PVD, dan PHD untuk Analisis Penurunan Konsolidasi Tanah

Soft clay has a low bearing capacity, high compressibility and low permeability. This condition causes soft clay soil to have a long settlement time. To overcome this soft soil condition, soil improvement methods are needed. One of the efforts is to use a combination of soil preloading methods, Prefabricated Vertical Drain (PVD), and Prefabricated Horizontal Drain (PHD) methods. Calculating soil settlement with soil improvement is carried out using the Asaoka method, which is a field observation method, and the theoretical method using the Terzaghi method. Based on the calculation results of field observations using the Asaoka method, the average degree of soil settlement is 93.5%. The calculation results of the Asaoka method are recalculated using a back calculation to produce a new parameter value, namely the horizontal consolidation (Ch) value, which is then compared with the Ch value in the previous plan. In the Terzaghi method, the average soil settlement value is 1.205 meters. The results of soil settlement value are used to analyze the height of the embankment based on the load ratio requirement in SNI 8460: 2017, where the load ratio on the ground is ≥ 1.3 times the planned load under service conditions. Based on the monitoring results, a load ratio value of 0.875 was obtained so that the SNI requirements carried out a re-planning of the landfill. Then, proceed with the design of PVD and PHD. The results obtained in planning use triangular PVD patterns with a distance between PVDs of 1 meter.

Analisis Penurunan Gabungan Prefabricated Vertical Drain dan Stone Column Untuk Perbaikan Tanah Lunak

Soft soil is inevitable in the construction, be it road construction or building construction. Soil improvement is needed to overcome the problem of soft soil, soil improvement methods are growing and diverse. This research is focused on studying the interaction behavior of combination two soil improvement methods, namely Prefabricated Vertical Drain (PVD) and Stone Column (SC). This research was conducted using PLAXIS 2D with Mohr-Coulomb (MC) and Soft Soil (SS) material models. The results showed that the combination of PVD and SC methods provides the advantage that PVD can accelerate the consolidation time and SC can reduce the settlement that occurs in the soil. The use of SS model is greater settlement compared to using Mohr-Coulomb material model with a settlement of 1,641 m for Soft Soil and 0.463 m for Mohr-Coulomb. SC depth variation affects the settlement and settlement time, the longer the SC the smaller settlement and the shorter time, while PVD only affects the time. Combining PVD and SC results in better settlement and settlement time compared to PVD or SC alone. Variations in construction methods result in slight differences for MC material models, whereas for SS material models, construction methods 2 are greater in settlement and shorter time.

Study Of Various Types Of Pvd And Ph.D. Joints On Vertical Drainage Performance

An important factor for increasing the effectiveness of the PVD (Prefabricated Vertical Drains) is the value of sufficient discharge capacity so that the PVD can work optimally. The use of PVD is usually accompanied by the use of PHD (Prefabricated Horizontal Drains) as horizontal drainage and combined with preloading. In the field, the connection is made by winding the PVD to the PHD and then tying it with cable ties. The connection system can cause deformation at the top of the PVD thereby reducing the effectiveness of the PVD discharge capacity. This study aims to find the optimal PVD-PHD connection system for the discharge capacity which is affected by confinement pressure, overburden pressure, and hydraulic gradient with a PVD-PHD connection system discharge capacity tester. The test specimens used were PVD (5mm thick; 100mm wide) and Ph.D. (20 mm thick; wide: 100 mm, 200mm, and 300mm). 4 types of connection systems have been tried, namely connections A1 and A2 where the PHD is connected in a horizontal position, and connections B1 and B2 where the PHD is connected in a vertical position. Of the four connection systems B1, the connection system has the largest discharge capacity value and a significant increase in PHD width from 100 mm to 300 mm with an increase of 7.694% at 50 kPa overburden pressure and 1.0 hydraulic gradient the highest compared to other connection types

Analisis Proses Konsolidasi Dengan PVD Pada Proyek Reklamasi di Samping Tangki CPO Antar Pulau Belawan Berdasarkan Bore Log BH-1

In the planning of civil building, construction problems are often encountered in soft soil types, including low soil carrying capacity and large settlements (settlements) when given a load. Soil improvement is needed to speed up the consolidation settlement time. One method that can be applied to speed up the consolidation settlement time is to use a pre-fabricated vertical drain (PVD) and this preloading method is able to increase the shear strength of soft soils and remove pore water in the soil. This research aims to determine the magnitude of settlement of soft soil consolidation using the 1-dimensional Terzaghi consolidation formula and analysis using the finite element method with PLAXIS 2D modeling, comparing the results of PLAXIS 2D modeling with actual data, the effect of the smear zone effect on the settlement of soil consolidation in the embankment area and to determine the difference in the decrease in preloading methods combined with PVD and preloading without PVD based on point bore log BH-1. From the results of the analysis, it is found that the consolidation settlement by analytical method using the 1-dimensional Terzaghi consolidation formula was 0.858 meters. The amount of settlement that occurs in the consolidation process using PLAXIS 2D modeling taking into account the smear zone effect is 0.786 meters and 0.852 meters without taking into account the smear zone effect. Meanwhile, the actual settlement that occurred in the field based on settlement plate (SP-01) was 0.867 meters and the magnitude of the preloading settlement without PVD was 0.512 meters. It can be concluded that the PVD combination preloading method is proven to accelerate consolidation time, while the improvement with the preloading method alone produces a relatively small decrease.

Analysis of long-term settlement of road embankment on peat ground during its service period

Roads on peat grounds are subject to stringent requirements in terms of controlling the residual settlement during their service period in order to minimize the post-construction maintenance work. This paper addresses the applicability of the Finite Element Method (FEM) by incorporating a time-dependent model for peats to an evaluation of the residual settlement. The applicability of isotach viscoplasticity, used to describe the peats’ behavior under variable-rate compression, was confirmed in laboratory tests. Long-term consolidation test results and a model simulation revealed the particular importance of two mechanisms in the residual settlement in peat grounds, namely, the stress-dependency of the coefficient of consolidation, cv, and the viscosity-induced secondary consolidation. A model peat ground, capturing these mechanisms, was implemented for the FEM and applied to a case history of a high-standard road construction in Hokkaido, Japan. The viscoplastic parameters determined from standard oedometer tests successfully reproduced the observed long-term settlement in a peat-dominated section of the expressway. The analysis was extended to address the settlement in the peat ground with the installation of prefabricated vertical drains (PVDs). The results indicate that the delayed primary consolidation due to the stress-induced cv reduction can be significantly alleviated, while the settlement arising from the secondary consolidation over a longer term is little affected by the PVDs. These insights point to the importance of untangling the two mechanisms of long-term settlement for the sake of making accurate predictions of the residual settlement in different time scales.

Deformation and Strength Characteristics of Marine Soft Soil Treated by Prefabricated Vertical Drain-Assisted Staged Riprap under Seawall Construction

Prefabricated vertical drains (PVDs) with staged riprap preloading have been widely used in soft soil ground improvement and embankment construction. However, ground treatment effectiveness evaluation is still a difficult problem due to multiple factors. Considering this, in situ monitoring and numerical simulation were conducted to study the deformation and strength characteristics of marine soft soil ground treated by PVD-assisted staged riprap under the Lingni Seawall construction in China. Monitoring and analysis of results showed that use of PVD-assisted staged riprap resulted in a good improvement effect. In particular, in the PVD-treated zone within 10 m in depth, corresponding to a half-length of the PVD, the average radial degree of consolidation reached up to 75–100%, and the soil strength increased significantly by 200–700%. Moreover, numerical simulation showed that the linear 1-dimensional drain element of PVD closely met the engineering accuracy requirements with good consistency with the monitoring data. Compared with a totally solid element model, the numbers of elements and nodes were reduced and the calculating efficiency and model accuracy were increased by using a PVD linear element, which provides a basis for building large complex finite element models.

Prediction Analysis on Coefficient of Consolidation Values in Improved Soft Clays

Consolidation is a phenomenon in soil mechanics that often causes geotechnical problems. One solution to overcome consolidation phenomena is by speeding up process of pore water pressure dissipation. The type of soil improvement to upgrade the performance of soft clay is by applying pre-fabricated vertical drain (PVD) and pre-compression simultaneously. Geotechnical instrumentations such as settlement plates, piezometers, and inclinometers were installed at the field of study to monitor magnitude of settlement during consolidation process. After the final settlement was achieved, the consolidation parameters such as coefficient of consolidation, and rate of settlement, were back calculated. Prediction analysis of consolidations parameters was performed by means of Asaoka method. The results of this study is very interesting and provide useful engineering information. It is interesting to note that this case study may be beneficial use to practicing engineers and researchers.

THE BEHAVIOR OF FLOW CONDITION IN PREFABRICATED VERTICAL DRAINS DUE TO INCREMENTAL CONFINING PRESSURE

Prefabricated Vertical Drains (PVDs) are commonly used in geotechnical engineering to speed the consolidation of soft and compressible soils. Understanding the behavior of PVDs under various load conditions is essential for their efficient design and implementation. This research aims to improve the performance and efficacy of PVD systems in geotechnical engineering applications by investigating and comprehending the behavior of flow conditions in PVDs under incremental confining pressure. Three PVD samples varying in thicknesses have been evaluated in the laboratory to determine their discharge capacity and transmissivity under various hydraulic gradients. The PVD was subjected to incremental confining pressures between 50 and 200 kPa. The apparatus utilized in this study was designed by following ASTM D4716. The flow condition was determined by limiting the hydraulic gradients and calculating the turbulence degree of the flow. The analysis results showed that the flow inside PVD is non-laminar, and the PVD with the larger cross-section is more resilient to deviations in the hydraulic gradient. The proposed equations accurately predicted the discharge capacity of PVDs under increasing confinement pressures, and a comparison with experimental results revealed a high level of concordance. Particularly for PVDs with larger cross-sectional areas, the hydraulic gradient significantly affected the discharge capacity.

Analisis Pengaruh Preloading Kombinasi Prefabricated Vertical Drain pada Proses Konsolidasi di Proyek Reklamasi di Samping Tangki Cpo Antar Pulau Belawan Berdasarkan Bore Log Bh-2)

To carry out construction on soft soil, cases of land subsidence are often encountered. This is due to the low bearing capacity and small shear force, large compression, and very small permeability. To address this problem, one method that can be implemented is soil improvement using preloading and Prefabricated Vertical Drain (PVD). The aim of this research is to find out the magnitude of consolidation settlement by using analytical methods and by using PLAXIS 2D modeling at reclamation project locations besides CPO tanks between Belawan Islands based on Bore Log BH-02 data. It is also to compare coarse mesh, medium mesh, and fine mesh in PLAXIS 2D modeling, and to obtain the amount of land subsidence using preloading only and preloading with a combination of preloading and Prefabricated Vertical Drain (PVD) based on Bore Log BH-02 points. From the analytical results obtained a decrease of 1.254 meters. While the PLAXIS 2D modeling uses a medium mesh that has been combined with a PVD of 1.268 meters. This means that the results of the settlement by modeling using PLAXIS 2D are closer to the SP-02 settlement plate data of 1.270 meters. The settlement uses PLAXIS 2D with a coarse mesh of 1,266 meters and a fine mesh of 1,282 meters. While modeling using preloading only obtained a decrease of 0.340 meters. It can be concluded that the results of modeling using PLAXIS 2D in using medium mesh that has been combined with PVD are relatively closer to settlement data in the field with a percentage difference of 0.142% settlement plate SP-02 settlement.