Installation Of Vertical Drains Research Articles

Study comparison of ground subsidence due to preloading installation of egg tray triangular vertical drains with distance variations on a small laboratory scale

Abstract The approach to infrastructure development is conducted on soft clay soil, which introduces the threat of consolidation-induced subsidence. The construction soil must possess adequate bearing capacity and shear strength to withstand the loads imposed on it throughout the construction process. Soil with low shear strength necessitates reinforcement to enhance its bearing capacity. This study aims to investigate the effects of preloading on the settlement behavior of soft soil. Applying clay-filled test containers, the laboratory implements the method through a small-scale model approach. As preloading, an embankment load is applied to the soil. The supplementary weight was incrementally increased by 1 kg, 2 kg, 4 kg, 8 kg, and 16 kg for five days. The sample experiments that were conducted were EgVD-0, EgVD S-17, and EgVd S-29. Consolidation was observed in the outcomes of the EgVD S-17 and EgVD s-29 investigations, surpassing EgVD-0 by 53.69% and 57.19%, respectively. EgVD S-17 of 3.56 cm and EgVD S-29 of 3.92 cm were present along with an EgVD-0 decrease of 1.65 cm.

An analytical solution for nonlinear consolidation of composite foundations improved by stone columns and vertical drains

The nonlinear compressibility and permeability of soft soils is a key factor in the consolidation of both composite and natural foundations. However, there are few corresponding consolidation theories for vertical drain-stone column composite foundations in which the nonlinear consolidation characteristics of soils can be taken into account. In this study, a nonlinear consolidation model is established to describe the seepage relations between soft soils, vertical drains and stone columns. Then, a consolidation governing equation is derived, where the total excess pore water pressure (EPWP), u¯, is a variable, and the average consolidation degree defined by strain and stress of the composite foundation is obtained, respectively. Numerous calculations are performed to analyze the consolidation behaviors of such composite foundations. The results show that the installation of vertical drains can enhance the consolidation rate effectively; the external load and the initial modulus ratio of column to soil have an influence on the stress concentration effect of stone columns. Finally, the proposed analytical solution is applied to the settlement calculation for an actual project, and the calculated results are in good agreement with the measured data in the early and late stages of consolidation.

Improved Mandrel System for Prefabricated Vertical Drain Installation: A Macro to Micro Analysis

Increasing development of infrastructure in Indonesia has driven the need for effective ground improvement methods to accelerate the consolidation of soft soil, which is estimated to occupy around 10% of the country’s land area. A prefabricated vertical drain combined with vacuum preloading is among the most effective methods for this purpose. However, the prefabricated vertical drain creates a smear zone in the surrounding soil area during installation. This study examines the effectiveness of a newly developed mandrel system in reducing the smear zone during prefabricated vertical drain installation. Large-scale consolidation tests at a macro level and microstructure analysis using scanning electron microscopy at a micro level were employed to investigate the effect of soil water content and shear strength. The results show that the water content and shear strength of the soft soil gradually increased in the inner smear zone and transition zone, while both decreased in the radial distance. Furthermore, the soil structure underwent a transformation in which the particle area and pore area became a closed flake structure, and apparent agglomeration occurred. The test results indicate that the newly developed mandrel system can effectively reduce the smear zone. The macro to micro test results demonstrated that the mandrel system is successful in reducing the smear zone effect.

A semi‐analytical solution for displacement‐controlled elliptical cavity expansion in undrained MCC soil

AbstractConventional cavity expansion theory is a one‐dimensional problem and is not applicable for the two‐dimensional cavity expansion issue, which is also required for geotechnical problems. This paper proposes a novel semi‐analytical solution for displacement‐controlled elliptical cavity expansion (DC‐ECE) in undrained soil. The displacement and strain fields for DC‐ECE are obtained from the strain path method (SPM) with the aid of conformal mapping theory. The effective stress can be subsequently obtained by the incremental stress‐strain calculation using a suitable constitutive model such as the MCC model. Then, the computed effective stress results are substituted into the stress equilibrium equation to give the pore pressure solution. The new semi‐analytical solution reveals the non‐axisymmetric characteristics of DC‐ECE and allows the elastic‐plastic (EP) boundary, excess pore pressure, stress, and displacement to be calculated. The proposed method provides a solution to non‐axisymmetric cavity expansion issues and it can be applied to geotechnical engineering problems, including vertical drain installation, flat dilatometer tests and noncylindrical pile penetration in clay.

Analisis Perbaikan Tanah Lunak dengan Kombinasi Preloading dan Prefabricated Vertical Drain pada Pembangunan Jalan Tol Pematang Panggang – Kayu Agung, Sumatera Selatan

The construction project of Pematang Panggang - Kayu Agung Toll Road, Section 4 is located in Ogan Komering Ilir Regency, South Sumatra. This project area has a soft clay soil type. With the condition of the soft soil, soft soil repairs need to be done at the project site. The soil improvement used is the Preloading Method combination of Prefabricated Vertical Drain (PVD) and Prefabricated Horizontal Drain (PHD). This method of repair is done by comparing the time of soil consolidation before and after using the Preloading combination of Prefabricated Vertical Drain (PVD) and Prefabricated Horizontal Drain (PHD) by measuring the time needed to achieve consolidation of 90% and the effectiveness of the Prefabricated Vertical Drain (PVD) installation pattern. With the installation of Prefabricated Vertical Drain on the pattern of installation of rectangles / rectangles with a distance of 0.8 m, it can accelerate consolidation to 19 weeks from the time before PVD is installed. It takes 130 years. Then hoarding with Hinisial = 11 meters is carried out, for the first stage of hoarding with a value of Hcr = 4.375 m carried out up to 4 m, the decrease that occurs is 1.0735 m so that the remaining stock is 2.9265 m. After the value of Cu (Undrained cohesion) has increased, for the second stage of stockpiling, the value of Hcr = 13,526 m. The decrease that occurred in the second stage was 1.6634 m with the rest of the embankment 5.3366 m. So the total embankment height that has been compressed is 8.2631 m. and to reach the Hfinal the next hoarding stage is carried out to reach 8.69 m

Combined Effects of Vertical Drain and Pre-loading to Reduce The Number Of Geotextile Reinforcement For Road Embankment Design

The study of the behavior of embankments reinforced by geosynthetic construction on soft clay soil with and without a prefabricated vertical drain is described. The effect of a pre-loading with stage construction method to construct the embankment, the gain of bearing capacity, as well as the depth of compressible soil was also considered in this study. The limit equilibrium using Bishop and Fellenius methods was used in this study to determine the stability of the embankment. Vertical drain installation, combined with the stage construction method, substantially reduces the number of geotextile reinforcements needed. The number of geotextiles can be reduced by up to twice that compared with foundation soil without PVD. Furthermore, the combined use of geotextile and PVD can improve the performance of embankment height as well as increase the critical height of the embankment with geotextile reinforcements. Without PVD, the embankment will be safe against landslides (without geotextile) of less than 3.5 meters. When using PVD, the embankment critical height can increase by up to 7 meters. This condition occurs when the embankment is constructed using the stage construction method, geotextile reinforcement, as well as PVD installation for soil improvement.

EXPERIENCE OF SEALING WEAK WATER-SATURATED LOESS SOILS WITH VERTICAL SAND DRAINS IN SEISMIC REGIONS

The article presents the results of studies relating to compaction of weak water-saturated forest soils and vertical sandy drains under static and seismic effects in the conditions of the Central Asian region. Considering the absence of any experimental and theoretical studies of the application of this parameter, field (in-situ) experimental studies were carried out to identify the possibilities and effectiveness of its use in conditions of weak water-rich loess soils of the Republic of Tajikistan. The article discusses changes in the basic physical and mechanical characteristics of soils and experimental structures. At the experimental site, three plots with a size of 10·10 m were prepared, where the plot was loaded without the installation of vertical sand drains; 3·3 m to a depth of 6.0 m. Static loading of experimental plots by a derivative by layer-by-layer dumping of ground material with measurement of total and layer-by-layer deformations of the packed thickness. Imitation of seismic impact with an intensity of 8 points was carried out using short-delayed explosions of explosive charges. Studies have shown the effectiveness of the use of vertical sandy drains for compaction of weak water-saturated loess soils. Recommendations are given on the use of explosion energy to improve the quality of soil compaction.

An analytical solution for consolidation of PVD-installed deposit considering nonlinear distribution of hydraulic conductivity and compressibility

PurposeIt is well known that the prefabricated vertical drain (PVD) installation process generates a significant soil disturbance around PVD. This disturbed zone significantly affects the rate of settlement and excess pore pressure dissipation. However, the characteristics of these zones were still uncertain and difficult to quantify; there remains large discrepancy among researchers. This study aims to develop a simple analytical solution for radial consolidation analysis of PVD-installed deposit considering mandrel-induced disturbance.Design/methodology/approachThe proposed solution takes into account the nonlinear distributions of both horizontal hydraulic conductivity and compressibility toward the drain. The proposed solution was applied to analyze field behavior of test embankment in New South Wales, Australia.FindingsBoth effects significantly increased the time required to achieve a certain degree of consolidation. The effect of hydraulic conductivity on the consolidation rate was more significant than the effect of compressibility variation. And, the increased compressibility in the soil-disturbed zone due to mandrel installation significantly increased vertical strain of the PVD-improved soil deposit. The predicted results using the proposed analytical solution were in good agreement with the field measurements.Practical implicationsA geotechnical engineer could use the proposed analytical solution to predict consolidation behavior of drainage-installed ground.Originality/valueConsolidation behavior of PVD-installed ground could be reasonably predicted by using the proposed solution with considering variations of both hydraulic conductivity and compressibility due to PVD installation.

A novel analytical approach for predicting the noncylindrical pile penetration‐induced soil displacement in undrained soil by combining use of cavity expansion and strain path methods

SummarySince development of cavity expansion theory and strain path method, almost all the conventional analyses of pile penetration problem have been based on circular cross section penetrometer. However, noncylindrical pile (with noncircular cross section) is also required in geotechnical engineering such as rectangular cross‐sectional pile, X‐sectional cast‐in‐place concrete pile, H‐shaped steel pile, prefabricated vertical drains, and flat dilatometer. This paper presents a novel and general analytical approach for capturing the soil deformation mechanism around the pile with arbitrary cross section. The penetration problem is simulated by a new 2‐dimensional (radial and circumferential) cavity expansion model. Based on the theoretical framework of strain path method, the kinematics (velocity field) of the noncylindrical cavity expansion is reduced to solve the Laplace equation with arbitrary velocity boundary conditions by using the conformal mapping technique. Then, solutions for the strain and displacement, which could consider the large deformation effect, are obtained by the integration of the strain rate and velocity along the streamline. The analytical solution is validated by comparing the degenerate solution of this study with conventional circular (cylindrical) cavity expansion theory. Subsequently, typical numerical examples for the deformation mechanism of elliptical and rectangular cavity expansion are presented to prove the advantage of the proposed new solution particularly in capturing the noncylindrical symmetric displacement field. A brief application of the proposed new analytical solution to the interpretation of the smear effect of prefabricated vertical drain installation confirms its useful in geotechnical engineering.

Laboratory determination of smear and transition zones due to prefabricated vertical drain installation

ABSTRACTThe smear zone, which develops during the placement of the prefabricated vertical drain (PVD) in the ground using a steel mandrel, is a significant factor that influences the performance of PVDs. The determination of the width and hydraulic conductivity of smear zone is an important consideration in designing ground improvement by preloading with PVDs. Thus, the extent and hydraulic conductivity of the PVD smear zone have received significant attention; however, there is still uncertainty and the topic remains discrepant among investigators. There is limited or no smear zone hydraulic conductivity data that is directly produced by laboratory or field tests. In this study, a laboratory smear zone model experiment that was developed as a performance test for determining the extent of the smear zone and measuring directly its hydraulic conductivity was used. Based on the findings obtained from two different materials (Craney Island dredgings and Hydrite R kaolinite soil), it is indicated that the disturbed zone is made up of two areas, namely smear zone and transition zone, and that the hydraulic conductivity in these areas is lower than the undisturbed soil. The ratio of the hydraulic conductivity of the smear and transition zones to that of the undisturbed soil was found to vary between 0.32 and 0.50 and between 0.57 and 0.82, respectively in different soils. The diameter of the smear zone was found to be 2.3–3.3 times higher than the equivalent diameter of the mandrel depending on the soil. The diameter of the transition zone extended 5.2–7.3 times the equivalent diameter of mandrel again depending on the soil. These directly measured values, in general, are supportive of the published values based on indirect means and the test device can be used to study the impact of mandrels of different size and shape and other factors by minor modification.

Stability of an Embankment on Soft Consolidating Soil with Vertical Drains

Stability of an embankment constructed on soft consolidating soil improved with pre-fabricated vertical drains is investigated. The factor of safety of the embankment is obtained at various time intervals from the end of construction till the end of consolidation in order to check the embankment stability. Finite element method is used to obtain the effective stresses at required points in soil at various time intervals. Critical slip surface is obtained using two methods. In the first method, the critical slip surface is assumed as an arc of a circle selected among various probable slip circles with minimum factor of safety whereas, in the second method, a random walking type Monte Carlo technique is used to predict the critical slip surface. The effects of providing vertical drains on stability of an embankment is investigated by comparing the factor of safety of slope with vertical drains to the factor of safety of slope without vertical drains. It is concluded from the study that the installation of vertical drains enhances the factor of safety of the embankment from the end of construction till the end of consolidation.

Effects of vertical drains on settlement and load carrying capacity of a footing on soft soil

Effectiveness of providing vertical drains on the settlement and load carrying capacity of a footing on soft consolidating soil is investigated. Numerical model based on finite element method is used to formulate the consolidation problem. Axi-symmetric three-dimensional problem for the flow of water in soil mass is converted into an equivalent plane strain model. Modified Cam-Clay model is used to represent the behavior of soil. The settlement and pore pressure predicted by various matching approaches to model the vertical drains in plane strain analysis is also compared. It is concluded from the study that the settlement of the footing after construction reduces and the load carrying capacity of the soil increases due to installation of vertical drains.

Prediction of the stress state and deformation of soil deposit under vacuum pressure

Stress state and deformation of a clayey deposit under vacuum pressure has been investigated using field data as well as laboratory vacuum consolidation test results. The field vacuum consolidation project was conducted in Saga, Japan for a clayey deposit with prefabricated vertical drain (PVD) installation. Laboratory tests were conducted under triaxial condition using undisturbed soil specimen with a mini-vertical drain inserted in the center to simulate PVD induced consolidation. By comparing the field and laboratory test results, it has been found that the effective confinement from the surrounding soils to the vacuum treated area is close to active earth pressure for a zone about 5 m depth from the ground surface, and below it is between active and at-rest states. A scaling factor has been derived to convert consolidation time in laboratory to the field case. It has been shown that with the scaling factor, the results of laboratory vacuum consolidation test under triaxial condition can be used to predict field settlement curves for vacuum loading.

Soil disturbance analysis due to vertical drain installation

The installation of drains creates a disturbed region known as a smear zone where the change in the clay structure affects the horizontal permeability and compressibility. The parameters required to characterise the smear effect are the extent of the smear zone and the ratio of the horizontal coefficient of permeability in the undisturbed zone and in the smear zone. Only limited studies have been carried out on different aspects of soil disturbance due to driving vertical drains and its effects on the subsequent consolidation. In this paper the disturbed zone around a rectangular mandrel was characterised using soil samples obtained from the soft clay layer at various locations beneath an embankment built at Ballina, Australia, where vertical drains were installed. By determining the change in the coefficient of permeability, the water content and volume compressibility across the smear zone, the effects of soil disturbance on consolidation due to the installation of drains can be quantified using the available numerical model.

REVIEW ON “ EFFECT OF SMEAR ON CONSOLIDATION BY RADIAL SEEPAGE FLOW USING PVD”

The installation of vertical drains with a mandrel causes significant disturbance of the subsoil surrounding the mandrel, resulting in a smear zone. The smear zone affects the consolidation of the soil. This paper presents a new analytical solution for the consolidation analysis of soil with a vertical drain. this zone retards the horizontal consolidation of soft clays in the vicinity of PVD. The characteristics of the smear zone, such as its extent and hydraulic conductivity remain discrepant among investigators. This study attempts to determine the extent of the smear zone and to measure the hydraulic conductivity of the smear zone directly by laboratory tests.

Assessment of the Elastic-Viscoplastic Behavior of Soft Soils Improved with Vertical Drains Capturing Reduced Shear Strength of a Disturbed Zone

AbstractSoil disturbance induced by the installation of vertical drains reduces the horizontal soil permeability and shear strength in the disturbed zone. Thus, the soil disturbance contributes to the reduced overconsolidation ratio (OCR) of the soil in the vicinity of drains, influencing soil deformation. Although a significant amount of research has been conducted on the effect of permeability variations in the smear zone, the influence of the reduced shear strength in the smear zone on the ground behavior has not been investigated. In this study, a numerical solution adopting an elastic-viscoplastic model with nonlinear creep function in combination with the consolidation equations has been developed. Moreover, the effects of shear strength variation in the disturbed zone on the time-dependent behavior of soft soil deposits improved with vertical drains and preloading have been studied. The applied elastic-viscoplastic model is based on the framework of the modified Cam-clay model, capturing soil creep...

Analyzing consolidation data to predict smear zone characteristics induced by vertical drain installation for soft soil improvement

In this paper, the effects of variability of smear zone characteristics induced by installation of prefabricated vertical drains on the preloading design are investigated employing analytical and numerical approaches. Conventional radial consolidation theory has been adopted to conduct analytical parametric studies considering variations of smear zone permeability and extent. FLAC 2D finite difference software has been employed to conduct the numerical simulations. The finite difference analyses have been verified using three case studies including two embankments and a large-scale laboratory consolidometer with a central geosynthetic vertical drain. A comprehensive numerical parametric study is conducted to investigate the influence of smear zone permeability and extent on the model predictions. Furthermore, the construction of the trial embankment is recommended as a reliable solution to estimate accurate smear zone properties and minimise the post construction settlement. A back-calculation procedure is employed to determine the minimum required waiting time after construction of the trial embankment to predict the smear zone characteristics precisely. Results of this study indicate that the accurate smear zone permeability and extent can be back-calculated when 30% degree of consolidation is obtained after construction of the trial embankment.

Analytical Solution for Contaminant Extraction Using Well Injection Depth Extraction Technology Considering the Effect of Smear Zone

The smear zones are usually caused by the installation of vertical drains in fine-grained soil. An analytical solution for contaminant extraction using well injection depth extraction (WIDE) system considering the smear effect was developed. The injection rate was assumed to be equal to the retrieval rate to maintain full saturation and steady-state seepage flow. The results obtained by the proposed analytical solution agree well with those obtained from the finite element method. An illustrative example was presented to show the influence of the smear zones and results reveal that the smear zone can have a great influence on the contaminant extraction from soils. The 500-hour base concentration of acetone in the middle of the contaminated soil increases by a factor of approximately 1.9 when the effect of the smear zone is considered in the model.

Trial Embankment Analysis to Predict Smear Zone Characteristics Induced by Prefabricated Vertical Drain Installation

In this study, FLAC finite difference software has been adopted to simulate the performance of the ground improved using prefabricated vertical drains assisted preloading, considering smear zone characteristics. The numerical code has been applied to predict smear zone properties employing a back calculation procedure using the results of several case studies. The construction of a trial embankment is proposed as a reliable method to predict the smear zone characteristics. The proposed back calculation method is applied to estimate the minimum required degree of consolidation and consequently the minimum required preloading time, resulting in a reliable estimation of the smear zone permeability and extent. Three preloading case studies considering both conventional preloading and vacuum assisted preloading have been simulated to verify the numerical code and to conduct the parametric study using the back calculation procedure. According to the results, the properties of the smear zone can be back-calculated reliably, when at least 33 % degree of consolidation due to trial embankment construction is achieved.

Modified Analytical Solution to Radial Consolidation with Soil Characteristics in a Disturbed Zone

An analytical solution modified from Hansbo's equation is suggested to evaluate the degree of radial consolidation, considering the consolidation characteristics of remolded clay and variation of soil properties within the disturbed zone. With increasing k h /k s , the time factor T h for a certain degree of radial consolidation continuously increases, while the time factor T hs slightly decreases and finally converges to the almost identical relation. Under the assumption that the settlement occurred between the prefabricated vertical drain (PVD) installation and the surcharge load application is resulted from the reduction of void ratio within the disturbed zone, the radius of the disturbed zone is estimated to be 2.675 r m for a disturbed zone of constant permeability or void ratio, while radii of the transition zone and fully disturbed zone are found to be 4.1 r m and 1.0 r m , respectively, for a disturbed zone with linear variation in the void ratio. The settlement vs. time relation predicted by the suggested solution is in good agreement with the settlement measured at Busan Newport site when k h /k f values of 2.5 and 5.0 are used for clay layers located above and below EL - 30 m, respectively, and linear variation of the void ratio within the disturbed zone is assumed.