Prefabricated Vertical Drains Research Articles

Application and design method of dredging sludge ground treated via prefabricated radiant drain vacuum preloading

The high-water-content sludge produced through dredging seriously restricts marine ecological environments. Vacuum preloading methods (involving prefabricated vertical drains (PVDs)) are widely used to dewater and consolidate sludge ground, but these methods require long treatment periods and have deprived reinforcement effects. To overcome the limitations of PVD vacuum preloading, a prefabricated radiant drain (PRD) vacuum preloading method is proposed is this study by adding a prefabricated horizontal drain (PHD) to the PVD framework. Physical model tests are conducted under PVD and PRD vacuum preloading conditions, and a large-strain three-dimensional finite element (FE) model is established and validated against the physical model test data. FE parametric analyses are also conducted to evaluate the key factors influencing the PRD, i.e., the PHD length and spacing. The results show that the reinforcement effect of PRD vacuum preloading is better than that of PVD vacuum preloading. The ground settlement effect increases as the PHD length increases and the PHD spacing decreases. The settlement and pore water pressure metrics show elliptical distributions with an increasing PHD length. Through this work, an applicable sludge ground treatment design procedure is suggested based on parametric analyses; these findings can provide a reference for designing sludge ground treatments in the future.

Dewatering of dredged slurry by horizontal drain assisted with vacuum and flocculation

This study proposes a new method using the combination of flocculation and prefabricated horizontal drain (PHD) assisted with vacuum pressure for rapid dewatering of high-water-content dredged slurry. First, to demonstrate the superiority of using PHD over the more commonly used prefabricated vertical drain (PVD), experiments were conducted to compare the dewatering performance between the PHD and the PVD. Then six model tests with the proposed dewatering method were performed with various contents of flocculant (anionic polyacrylamide (APAM)) to investigate the effect of APAM content on the dewatering process and soil properties (i.e. undrained shear strength, permeability and compressibility). Furthermore, particle size distributions of the slurry before and after model tests were measured to analyze the dewatering behavior and changes in material properties. Finally, particle loss during vacuum consolidation for various APAM contents were compared to study the flocculation effect on clogging problem. Results indicate that the proposed method can prevent significant bending deformation of the drain board and mitigate clogging of the drain filter and, thus, can significantly accelerate the dewatering process of high-water-content dredged slurry.

An analytical solution for contaminant extraction from multilayered soil using PVD-enhanced system

Prefabricated vertical drains (PVDs) have been employed to enhance the in situ remediation of contaminated fine-grained soils. Subsurface heterogeneity can interfere with the distribution and extraction of contaminants during the remediation process. In the present study, an analytical solution for contaminant extraction from multilayered soil using a PVD-enhanced system is developed based on an equivalent planar two-dimensional model. The analytical solution is derived using a procedure that combines the Laplace transform, eigenfunction method and numerical Laplace inversion. The validity and accuracy of the solution are verified by comparison with an existing analytical solution and the results obtained using a numerical model. The effects of several key parameters on the performance of a PVD remediation system in a triple-layered contaminated soil are evaluated. The results indicate that the remediation efficiency for clay layers decreases with increasing hydraulic conductivity or thickness of the sand layer. The PVD remediation system may be unfeasible for contaminated sites with high subsurface heterogeneity caused by permeability contrast. The remediation process for clay layers can be accelerated by increasing the clay vertical dispersivity.

Effectiveness of a Geocomposite-PVD system in preventing subgrade instability and fluidisation under cyclic loading

Instability of subgrade soil sometimes associated with soil fluidisation can lead to uncontrollable deformation and failure at a critical number of loading cycles for a given cyclic deviator stress and frequency. Although numerous laboratory experiments on the performance of Prefabricated Vertical Drains (PVDs) and geocomposites have already been carried out in the past, how effectively this combination can mitigate the potential for subgrade fluidisation under repeated (cyclic) loading is still not properly understood. The primary objective of this paper is to evaluate the integrated role of PVDs and geocomposite in preventing subgrade fluidisation using Dynamic Filtration Apparatus (DFA). Laboratory experiments show that the continuous dissipation of EPWP and the substantial reduction in drainage path lengths by PVDs can prevent subgrade fluidisation at shallow depths, while geocomposite can provide adequate surficial drainage and effective confinement at the ballast/subgrade interface. By measuring the Excess Pore Pressure Gradients (EPPGs) during cyclic loading, the test results convincingly reveal the promising performance of PVD-geocomposite combination under different loading conditions.

Analysis of the Effect of Smear Zone on Consolidation Decline in the Tebing Tinggi-Kisaran Toll Road Project (Phase 1) Tebing Tinggi – Indrapura STA 102+700 Toll Road Project with 3D PLAXIS Modeling

Repairing of soft clay Embankment loading method with PVD is a soil improvement system consisting of Embankment loading work, installation PVD, installation PHD, and geotechnical instruments. Preload serves to compress the subgrade. PVD serves to speed up the process of soil compaction. Horizontal drains serves to drain pore water taken from the PVD in a horizontal direction to the outside of the location that improved. Geotechnical instruments function to monitor and record the process and determine the performance of the result improving soil that have been carried out. Embankment loading and PVD (Prefabricated Vertical Drain) are technologies that are often used in the construction world to increase shear strength and speed up consolidation time of soft soils. However, during the installation of PVD using a mandrel it can affected the surrounding soil, causing the soil to become disturbed. The disturbed area is called by Smearzone. Due to the presence of a smear area, analysis and calculations are needed to obtain a consolidation time that is in accordance with field conditions. This analysis aims to compare the decrease of displacement in the settlement plate (SP-124) with modeling in PLAXIS 3D considering using with or without taking into account the effect of the smearzone. The method used in this thesis is the analytical method using Terzaghi theory and the finite element method using PLAXIS 3D. From the results obtained analytically the magnitude of the decrease is 15.252 cm while the results from the PLAXIS 3D analysis without the effect of the smear zone is 15.15 cm and with the effect of the smear zone being, 2 times the dimensions of the mandrel the results obtained are 15.131 cm, 15.133 cm and 15.134 cm, with 3 times the dimensions of the mandrel the results obtained are 15,142 cm, 15,141 cm and 15,14 cm and with 4 times the dimensions of the mandrel the results obtained are 15,144 cm, 15,143 cm and 15,143 cm. The decrease that occurs in the settlement plate 124 in the field is 15.10 cm. So it can be concluded that the calculation of consolidation decrease using analytical theory is relatively close to the decrease in actual results in the field with a percentage difference of 1% decrease. There are differences in settlement due to laboratory data not representing the entire soil layer. Due to the decrease that occurred 15.10 cm, the result of the effect of the smear effect 2 times the mandrel dimension and half of the coefficient of permeability of the original soil with a reduction ratio of 0.2% is the result that is closest to the results of field observations compared to without a smear effect of 0.331%.

Studying the soil column formation in soft soil improved by vacuum preloading via coupled scale‐up CFD‐DEM simulations

AbstractIn many large‐scale land reclamation projects, vacuum preloading combined with a prefabricated vertical drain (PVD) system has been utilized successfully to improve the slurry with extremely high water content. However, in the use of PVD systems for soft soil with high fine contents, a dense “soil column” forms around the drainage board, which dramatically impedes the drainage and compromises the improvement level. To understand the soil column formation mechanism, coupled computational fluid dynamics‐discrete element method (CFD‐DEM) and scale‐up strategy were employed in this work to study microsized soil particle movements. The results showed that the soil particles driven by the fluid gradually clogged the PVD board filter and then piled up. Under vacuum preloading, seepage occurred in the soil column, causing vacuum pressure loss and reducing the drainage velocity. As the permeability of the micron‐sized soil column is exponentially related to the particle size, the drainage velocity through the soil column with high fine content was low. With the development of the soil column, the drainage velocity decreased, slowing the subsequent soil column development, and changing the packing structure of the soil column. In addition, the vacuum pressure, opening size of the drainage board filter, and cohesion among soil particles influenced the soil column formation. The effects of these aspects are discussed in this work to provide ideas for improving the drainage efficiencies of PVD systems.

Analysis of prefabricated vertical drains with surcharge preloading of Hiep Phuoc clay

Finite-difference analysis of soft ground treatment with prefabricated vertical drains (PVDs) was performed using a newly developed consolidation model. The model uses the concept of multi-compression indices and coefficients of consolidation (CoCs) to investigate the behaviour of a soft ground deposit (pore water pressure dissipation, surface settlement and sub-layer ground settlement) and to validate the newly developed Consopro finite-difference procedure. The pre-consolidation pressures of the soft ground deposit were characterised using a combination of piezocone penetration profiling and constant rate-of-strain (CRS) consolidation tests (0.02%/min) on undisturbed samples that were retrieved from the Saigon premier container terminal in the south of Vietnam. After comparison of the back-calculated results with field-observed data, a correlation between the CoCs determined by CRS consolidation tests and the CoCs from piezocone dissipation tests, which were carried out after soil improvement, was determined.

Analysis of ground deformation development and settlement prediction by air-boosted vacuum preloading

Vacuum preloading has been widely used to improve soft soils in coastal areas of China. An increasing amount of evidence from field operations has shown that conventional vacuum preloading is prone to clogging in prefabricated vertical drains (PVDs) and demands a large volume of sand fills. In recent years, air-boosted vacuum preloading has been developed to overcome these limitations; however, this method still requires more data to verify its performance. In this study, a field test for air-boosted vacuum preloading was conducted, and a large-strain two-dimensional (2D) finite element (FE) model was developed and validated against the field test data. Then, a series of FE parametric analyses was performed to assess key factors, i.e. the air injection pressure, the injection spacing, and the characteristics of cyclic injection, which affect the performance of the air-boosted vacuum preloading. The results showed that the ground settlement and lateral displacement of the soils increased due to an increase in the injection pressure, a decrease in the injection spacing, or increases in the number and duration of the injection cycles. Based on the parametric analyses, an empirical formula for ground settlement prediction was proposed and compared with a case history reported in the literature, showing good agreement.

Consolidation mechanism of high-water-content slurry during vacuum preloading with prefabricated vertical drains

Vacuum preloading combined with prefabricated vertical drains (PVDs) has been widely used to improve soft clayey soil deposits. However, the consolidation deformation of high-water-content slurry under vacuum pressure is still not fully understood. In this study, the displacement field of the slurry during vacuum preloading was directly observed using the particle image velocimetry (PIV) technique. The test results showed that the displacement field of the slurry could be divided into three different zones that reflect distinct consolidation patterns. In zones I and III, the slurry was predominantly compressed along the horizontal and vertical directions, respectively, whereas in zone II, compression occurred in both vertical and horizontal directions. In particular, the slurry elements in zones I and II underwent horizontal extension prior to horizontal compression. The study also visualized the boundary of the soil column and provided an equation for the relation between soil column thickness and consolidation time, which could provide a reference for the theoretical consolidation calculations related to soil columns.

Analysis of a Prefabricated Vertical Drain (PVD) Soil Improvement Project

A settlement analysis has been carried out for several sectors of a rail station yard improved with prefabricated vertical drains (PVD) in Istanbul, Turkey, that exhibited prolonged consolidation beyond the predicted values in certain sectors of the treated zone. Final settlement and End of Primary (EOP) settlement times have been estimated theoretically as well as using the Asaoka graphical procedure. The compliance of settlement-time curves with in-situ measurements and Asaoka solution has been investigated. A geotechnical model was developed for finite element and three-dimensional consolidation analyses. The settlement curves obtained by varying horizontal-vertical permeability coefficient ratio (kh/kv) and in-situ measurements have been compared, and kh/kv values corresponding to 90% degree of consolidation has been computed for all sectors. The effect of drain spacing (sdrain) as well as drain length (Ldrain) on the rate of consolidation have been examined for each sector, keeping the specified ratios constant. The times corresponding to 95% degree of consolidation (t95) have been calculated using the theoretical solution and compared to in-situ measurements. Calculated t95‘s have also been compared to their estimated values by varying the spacing (sdrain) and the length (Ldrain). Additionally, the required intervals of sdrain and Ldrain have been obtained corresponding to the calculated t95 times.

Investigation of the Consolidation Behavior of Soft Soil Improved with Vertical Drains by Finite Element Method

The primary consolidation may take long time due to the low permeability of clay soils in such cases soil improvement may be required to shorten the consolidation time, increase shear strength, and therefore bearing capacity. Preloading is one of the commonly used methods to consolidate soils before actual load and to strengthen weak compressible soils. In cases with time problems, the use of prefabricated vertical drains (PVD) with pre-loading shortens the drainage path and reduces the consolidation time by taking advantage of the horizontal permeability of the soils is generally higher. In this study, an embankment constructed at different load rates with constant accelerates and analyzes were performed for the non-drained and drained conditions of clay soils with PVDs are in 2m, 1m, and 0.5m intervals. In this way, the effect of load rate and PVD usage on consolidation settlement and excess pore pressures in underlying low permeable clayey soil was investigated.

Finite Element Analysis of Vertical and Horizontal Drainage Structures under Vacuum Combined Surcharge Preloading

Combined vacuum and surcharge preloading has gradually been widely used because of its advantages of low cost, green environmental protection, and good treatment effect. The conventional prefabricated vertical drain presents obvious defects in vacuum preloading treatment, such as obvious silting, serious bending of the drainage board, large attenuation of vacuum degree of drainage board along the depth, long construction period, and so on, which affect the final reinforcement effect. In this paper, the MIDAS finite element simulation of combined vacuum and surcharge preloading of prefabricated vertical drains (PVDs) and prefabricated horizontal drains (PHDs) is established through the comparative experiment of the engineering field. The comparative experimental study is carried out from the aspects of the vertical settlement, horizontal displacement, and pore water pressure. The results show that under combined vacuum and surcharge preloading, the consolidation effect of soft soil with PHDs is better than that with PVDs. When PHDs are used, the vertical settlement increases by 7.2% compared with PVDs; the horizontal displacement is larger; and the pore water pressure dissipates faster. This is because when the PHDs are adopted, the consolidation direction of the soil is consistent with the direction of the vacuum suction, which is mainly caused by vertical settlement. With the consolidation, the spacing between PHDs is gradually shortened, and the drainage distance is reduced, which can effectively reduce the consolidation time and improve the reinforcement effect of the soil. In addition, the PHDs can move downward uniformly with the soil during the consolidation process and have almost no bending deformation, which makes the vacuum transfer more uniform and effective.

Consolidation in Soft Soil – Case Study on Prefabricated Vertical Drains (PVDs)

Background: Constructing on soft ground is one of the challenges of geotechnical engineering. The unpredictable behaviour and characteristics of soft soil can cause much damage resulting in high maintenance costs in the post-construction phase. Objective: The purpose of this study is to analyse the consolidation process and ground improvement method using surcharge and a prefabricated vertical drain by measuring the accuracy of the prediction settlement value with the actual site settlement results. Methods: An effective ground improvement method is the application of a surcharge and prefabricated vertical drains (PVDs). Various methods can be used to predict the settlement effectively, one such method being PLAXIS 3D simulation. A case study on ground improvement works was selected for this research, where PVDs were constructed and implemented at the site. A few undisturbed samples were collected from the site to generate the parameters based on the lab test conducted in the simulation process. This parameter was carefully studied and representing the principal input for the 3D model, which is generated and represents the actual ground improvement method for the selected case study. The analysis was performed using a borehole and soft soil model to generate the diagram. The prediction settlement value was generated from the PLAXIS 3D analysis as the baseline comparing to the actual results. The factors that influence the settlement value, such as the length and spacing of the prefabricated vertical drain, construction method, and soil characteristics, are also discussed. Results: A predicted settlement of 2553 mm was generated by the simulation, while the actual settlement outcome at the site was 2096 mm, a difference of 457 mm, and a prediction accuracy of 82.1%. Conclusion: The study found that the combination of surcharge and prefabricated vertical drain in the ground improvement worked well. Also, discussed were the factors that influenced the accuracy of the prediction and the site results.

ALTERNATIVE IMPROVEMENT OF SUBGRADE AND REINFORCEMENT OF EMBANKMENT ON PELABUHAN KUALA TANJUNG TOLL ROAD, INDERAPURA - KUALA TANJUNG SECTION IN NORTH SUMATRA (STA 0+000 S/D STA 3+500)

Planning the Kuala Tanjung Ruas Port of Inderapura - Kuala Tanjung Toll Road is one of the efforts to support economic growth in North Sumatra. The toll road will be built on a pile with a height of 2 ms / 9 m at STA 0 + 000 to STA 3 + 500. Due to limited land, the toll road section must be built on the poor subgrade. Based on the N-SPT test results, it is known that the subsoil consists of a clay layer with a thickness reaching 36 meters and a layer of sand at the top and bottom with a low N-SPT value. If the soft subgrade is burdened with a high heap, it is estimated that the subgrade will experience landslides, so it is necessary to plan the improvement of the subgrade and reinforcement of the pile.The soil improvement method chosen is the pre-loading method with a combination of the prefabricated vertical drain (PVD). Pre-loading method aims to spend the compression that occurs on the subgrade so that there is no compression during the service life of the road. The combination with PVD is intended to speed up the compression time in thick clay layers. The stability of the embankment will be calculated using a computer-assisted program, and geotextile reinforcement planning will be carried out if the value of the safety factor does not meet the requirements.Based on the analysis of compression computation will be divided into five zones. The amount of compression obtained under various piles of 2 ms / d 9 m was 2.25 m, 1.49 m, 1.75 m, 2.57 m, 3.65 m, 4.3 m, 4.69 m, and 5.06 m with an initial heap height of 5.02 m, 5.26 m, 6.51 m, 8.34 m, 10.41 m, 12.07 m, 13.46 m, and 14.83 m. Compression time required for subgrade is relatively long with a period of more than five years so that the planned acceleration with PVD. To accelerate the compression time to 5-6 weeks, a triangular PVD installation pattern is used with a spacing between PVD of 1.5 m and a depth of PVD installation as thick as a soft soil layer. From the results of the pile stability control, it is predicted that the pile will experience slides so that the reinforcement is installed with geotextile.Rp1.598,213,522,582.08.

PLANNING TO REPAIR THE APPROACH SLABS BRIDGE MUARA TABIRAI, RANTAU – KANDANGAN

Muara Tabirai Bridge is on the border between Rantau and Kandangan District ,which is precisely is on the street of Kalumpang-Margasari, the village of Paci, Kalumpang subdistrict. Increasing economic growth has led to the economy of the population being affected by the development of the city, gradually increasing in economic sectors as a result of global economic growth. The increase in this economy is due to the growing industry in the area. This is accompanied by the increase and needs of the population in the area that resides in the region. Unfortunately, after one year of construction of Muara Tabirai Bridge, the approach slabs bridge in the direction Kandangan on the right side suffered a decrease in the soil to damage the asphalt, due to the possibility of a landslide on the side of the road, then the implementers make alternative repairs by using a bronjong which makes the load heavier than before so that the ground that supports the burden of the heap, bronjong and traffic load can not withstand and So in this final task is done repair on the ground soil and design a retaining wall that is more suitable for the condition of the landThe basic soil repair method used is by a phased heap (Preloading) combined with the Prefabricated Vertical Drain (PVD) ,which serves as a water and air release on the soil, thus experiencing a consolidated degree of 90%. And for retaining wall against the side of the heap is used sheet pile with the type of free-standing ,which is suitable for the location of the pile located in the river. After that, the calculation of budget plan (RAB) on the Land, improvement Project,From the result of calculation obtained, a gradual heap (Preloading) carried out 0.2 m/week ,and ,a high critical heap (HCR) obtained on the high end of the plan (HR) 3.14 m obtained a security figure (SF) of 1.148 so that the heap used the soil reinforcement that is Mini pile erection so that the safety number (SF) reaches more than equal to 1.5 Prefabricated Vertical Drain (PVD) is used specification of the product PT. Teknindo Superior System installed when before done the filling is on the ground ground, planning Prefabricated Vertical Drain (PVD) using a triangular mounting pattern with a distance between PVD 1.25 m, depth 28 m and the time required is 21 weeks. Planning of soil retaining structure used is cantilever sheet pile type, obtained a total length of sheet pile of 20.938 m at STA 0 + 275 on the left and right side of the bridge. The budget plan for this basic land improvement project is Rp. 30,886,527,167

Formation mechanism of clogging of dredge slurry under vacuum preloading visualized using digital image technology

Vacuum preloading combined with prefabricated vertical drains (PVDs) system has been widely used to improve the soft clay with high water content. Clogging is usually formed around the PVDs during the vacuum preloading, impeding the propagation of the vacuum pressure and slowing down the consolidation process. To understand the forming mechanism of the clogging, particle image velocimetry (PIV) technique and particle tracking velocimetry (PTV) technique were adopted in the model test of vacuum preloading test. Through this study, three stages can be identified from the results of water volume discharge rate and maximum displacements versus time. In the first stage, the soil around the PVD is horizontally consolidated, which leads to the rapid formation of clogging. In the second stage, the formation of clogging slows down due to the loss of vacuum pressure, which further reduces the drainage. In the third stage, the clogging tends to be stable, and the drainage consolidation rate is significantly reduced. PTV results show that there is a difference in the displacement of large and small particles during improvement. Two methods were proposed to estimate the thickness of clogging zone, reflecting a growing layer of clogging zone compressed around the PVD. This study provides new insights to investigate the formation mechanism of clogging during vacuum preloading test.

Ventilated Well Method for Efficient Dewatering of Soft Soils: Experimental Investigations

AbstractTwo of the conventional methods to improve soft soil deposits are evaporative dewatering and accelerated consolidation of the deposits using prefabricated vertical drains (PVDs). Evaporativ...

Numerical Investigating on Representativeness of Tracers in PIV Model Test of Dredged Slurry Treated by Vacuum Preloading

The vacuum preloading method is commonly adopted for improving the soft ground that the embankment of the railway line is laid on. The PIV (Particle Image Velocimetry) technique is a powerful tool in observing the formation of the soil column, a phenomenon that is unique to the dredged slurry when treated by vacuum preloading. However, it is not clear to what extent the motions of the slurry particles can be represented by the PIV tracers. In this paper, a mesoscopic model has been established by using the CFD-DEM method to reproduce the vacuum consolidation process of the slurry, in which the PVD (Prefabricated Vertical Drain) membrane, the slurry particles, and the tracers are described by the DEM, and the pore water is governed by the CFD method. Eight computational cases that can cover a broad range of material parameters governing the PIV model tests on the dredged slurry have been designed and studied by the established model. The representativeness of the PIV tracer is evaluated by comparing the statistic displacement of the tracer to that of the slurry particles. It is found that for the commonly used tracer, the carbon powder, can reliably represent the particle motions of the slurry since the difference in displacements of the tracer and the slurry particles is smaller than 6.5% if the diameter ratio between the tracer and the slurry particle is within 1.8.

Analytical Solutions for the Radial Consolidation of Unsaturated Foundation with Prefabricated Vertical Drain Based on Fourier Series Expansion Theory

This paper presents the analytical solution of the radial consolidation of a prefabricated vertical drain (PVD) foundation under the unsaturated condition. In the proposed modeling, air and water phases in the foundation are thought to dissipate horizontally toward to the drain, and the smear effect, drain resistance and external time-dependent loading are fully considered. The analytical mathematical tools, namely the general integration method, Fourier series expansion method, decoupling method and the constant variation method, are utilized to solve the partial differential equations. Moreover, the current solutions are verified with existing solutions in the literature. Finally, a case study considering the ramp loading and exponential loading is conducted to investigate the consolidation patterns under various loading parameters. The results show that smear effect and drain resistance can significantly hinder the dissipation process of excess pore pressures, and different external loading types will lead to various dissipation characteristics (i.e., peak values).

The reinforcement analysis of soft ground treated by thermal consolidation vacuum preloading

Vacuum preloading technology can effectively reinforce the soft ground in coastal areas of China, which provides support for the safe construction and normal operation of transportation engineering. However, the conventional vacuum preloading technology has the limitations of ground reinforcement due to the clogging of the prefabricated vertical drain (PVD). This paper was based on the fact that elevated temperature could improve soil permeability and shear strength. Thermal consolidation vacuum preloading technology was proposed to analyze the ground reinforcement effect. To understand the reinforcement effect, the model experimental case of thermal consolidation vacuum preloading was designed to compare and analyze the temperature distribution, the development of water discharge, surface settlement, average consolidation degree, pore water pressure, water content and undrained shear strength at 25 °C, 50 °C and 70 °C in the laboratory-scale investigation. The research results presented that thermal consolidation vacuum preloading technology could significantly improve water discharge, surface settlement, average consolidation degree, undrained shear strength and reduce pore water pressure, water content, which illustrated that this technology was capable of significantly improving the effectiveness of soft ground. The research results could provide a reference for the soft ground treated by novel vacuum preloading technology to accumulate data.