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

2021 ◽  
Author(s):  
Honglei Sun ◽  
Zili He ◽  
Xueyu Geng ◽  
Mengfen Shen ◽  
Yuanqiang Cai ◽  
...  
Keyword(s):  
Formation Mechanism ◽  
Discharge Rate ◽  
Soft Clay ◽  
Vacuum Pressure ◽  
Water Volume ◽  
High Water Content ◽  
Volume Discharge ◽  
Vacuum Preloading ◽  
Consolidation Process ◽  
Prefabricated Vertical Drains

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. In order 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 horizontal 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 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.

scholarly journals Ultrasoft Ground Treatment of Vacuum Preloading Combined with Calcium-Based Flocculants

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Jin-Kai Yan ◽  
Feng Ji ◽  
Xia Bian ◽  
Gui-Zhong Xu ◽  
Lei Liu ◽  
...  
Keyword(s):  
Transmission Rate ◽  
Threshold Value ◽  
High Water ◽  
Soil Strength ◽  
Frame Structure ◽  
Vacuum Pressure ◽  
Engineering Properties ◽  
High Water Content ◽  
Vacuum Preloading ◽  
Prefabricated Vertical Drains

Vacuum preloading is one of the popular methods improving the engineering properties of slurry ground with high water content. Commonly, the efficiency of vacuum preloading gradually decreased due to the clogging of prefabricated vertical drains (PVDs) and the low-vacuum transmission rate inside slurry. Thus, the calcium-based flocculants were used to accelerate the dewater capacity and enhance the soil strength during vacuum preloading. This paper performed a series of model tests to investigate the effect of calcium-based flocculants on the efficiency of vacuum preloading. It is found that the vacuum transmission rate was significantly improved by flocculants in comparison with raw slurry. Accordingly, the after-treatment undrained shear strength increased with the vacuum pressure, while the after-treatment water showed a decrease trend. This suggests that the increase of vacuum transmission rate inside the slurry due to the calcium-based flocculants was the main reason for the improvement of efficiency of vacuum preloading. In addition, there existed an optimal flocculants amount, where the vacuum pressure increased with flocculants’ amount up to this threshold value, followed by a decrease in vacuum pressure. This means that, at lower flocculants amount, the increase in soil flocs due to flocculation effect tended to refine the net-frame structure and water flow path, leading to an increase in the efficiency of vacuum preloading. When exceeding the optimal amount, overdosage of flocculants resulted in the clogging of PVDs due to large cemented soil particles, reducing the vacuum transmission rate inside the slurry. Hence, the after-treatment soil strength decreased with flocculants’ amount when it is higher than the optimal value.

scholarly journals Analisis Alternatif Perbaikan Tanah Lunak dan Sangat Lunak pada Jalan Tol

2020 ◽  
Vol 3 (4) ◽  
pp. 1137
Author(s):  
Christian Eka Putra ◽  
Chaidir Anwar Makarim
Keyword(s):  
Bearing Capacity ◽  
Soft Soil ◽  
Soft Clay ◽  
Soil Improvement ◽  
High Water Content ◽  
Vacuum Preloading ◽  
Consolidation Process ◽  
Toll Road ◽  
Vertical Drain ◽  
Prefabricated Vertical Drain

The existence of soft soil is one of the problems in the field of construction. Soft soil is soil that has high water content and low carrying capacity. In the case of this toll road, soil investigation at the site shows that the subgrade in the toll road planning is soft clay soil to a depth of 32 meters so that soil improvement is needed. High landfill built on soft subgrade without reinforcement will experience landslides. So it is necessary to strengthen the landfill and repair the subgrade to prevent road slides. The soil improvement methods in use are vacuum preloading and Prefabricated Vertical Drain with the vacuum functioning as an additional load. In addition to accelerating the consolidation process, the vacuum can also reduce the height of the embankment needed to achieve the desired planned road elevation. Strengthening with geotextile is also carried out on the landfill with a height of 5.94 meters so that there is no landslide on the fill. Using soil improvement methods such as vacuum preloading and prefabricated vertical drain will increase the bearing capacity of the soil so that differences in bearing capacity occur before and after repair. AbstrakKeberadaan tanah lunak menjadi salah satu masalah dalam bidang konstruksi. Tanah lunak adalah tanah yang memiliki kadar air yang tinggi dan daya dukung yang rendah. Pada kasus jalan tol ini, penyelidikan tanah di lokasi menunjukan bahwa tanah dasar pada perencanaan jalan tol merupakan tanah lempung lunak hingga kedalaman 32 meter sehingga dibutuhkan perbaikan tanah dasar. Timbunan tinggi yang dibangun di atas tanah dasar lunak tanpa perkuatan akan mengalami kelongsoran. Sehingga diperlukan perkuatan timbunan dan perbaikan tanah dasar untuk mencegah kelongsoran jalan. Metode perbaikan tanah yang digunakan adalah vacuum preloading dan Prefabricated Vertical Drain dengan vacuum berfungsi sebagai beban tambahan. Selain mempercepat proses penurunan, vacuum juga dapat mengurangi tinggi timbunan yang dibutuhkan untuk mencapai elevasi jalan rencana yang diinginkan. Perkuatan dengan geotextile juga dilakukan pada timbunan dengan tinggi yang mencapai 5.94 meter supaya tidak terjadi kelongsoran pada timbunan tersebut. Dengan menggunakan metode perbaikan tanah berupa vacuum preloading dan prefabricated vertical drain akan meningkatkan daya dukung tanah sehingga akan diketahui perbedaan daya dukung yang terjadi sebelum dan sesudah diperbaiki.

Effectiveness of partially penetrating vertical drains under a combined surcharge and vacuum preloading

2011 ◽  
Vol 48 (6) ◽  
pp. 970-983 ◽  
Author(s):  
Xueyu Geng ◽  
Buddhima Indraratna ◽  
Cholachat Rujikiatkamjorn
Keyword(s):  
Analytical Solutions ◽  
Soft Clay ◽  
Three Dimensional ◽  
Vacuum Pressure ◽  
Vacuum Preloading ◽  
Prefabricated Vertical Drains ◽  
Vertical Drains ◽  
Vertical Drain ◽  
Degree Of Consolidation ◽  
Pressure Suction

This paper considers the consolidation of a layer of clay in which partially penetrating prefabricated vertical drains (PVDs) are used in conjunction with a combined surcharge and vacuum preloading. Analytical solutions for partially penetrating PVDs are derived by considering vacuum pressure (suction), time-dependent embankment surcharge, well resistance, and smear zone. Three-dimensional seepage with a virtual vertical drain is assumed to reflect real seepage into the soil beneath the tip of a PVD. Analytical solutions were then used to examine the length of the vertical drain and vacuum pressure on soft clay to determine the consolidation time and degree of consolidation, associated settlement, and distribution of suction along the drain. The proposed solutions are then employed to analyse a case history. Finally, an appropriate PVD length in relation to clay thickness and drain spacing is recommended for various loading patterns.

scholarly journals Compression and consolidation behaviors of lime-treated dredging slurry under vacuum pressure

2021 ◽  
Author(s):  
Xueyu Geng
Keyword(s):  
Mechanical Characteristics ◽  
Vacuum Pressure ◽  
Laboratory Model ◽  
Log P ◽  
Soil Permeability ◽  
Lime Treatment ◽  
Vacuum Preloading ◽  
Prefabricated Vertical Drains ◽  
Vertical Drains ◽  
Oedometer Tests

Dredging slurry is treated by a combination of lime treatment and vacuum preloading. However, the mechanical characteristics and consolidation mechanics of lime-treated slurry under vacuum loading is not fully understood, making it difficult to predict slurry settlement. In this study, we develop a laboratory model of lime-treated slurry and subject it to vacuum preloading to investigate the compression and consolidation behaviors. The results demonstrate the reduction of the risk of clogging around the prefabricated vertical drains, the increase in soil permeability, and the improvement of vacuum preloading upon lime treatment. log (1 + e)-log p curves for soils with different percentages of lime content are obtained through a series of modified oedometer tests. Based on these curves, an analytical solution for lime-treated slurry settlement under vacuum preloading was derived and validated through laboratory tests. The solution can be used to predict lime-treated slurry settlement under vacuum pressure effectively.

scholarly journals Analytical and numerical solutions for a single vertical drain including the effects of vacuum preloading

2005 ◽  
Vol 42 (4) ◽  
pp. 994-1014 ◽  
Author(s):  
Buddhima Indraratna ◽  
Cholachat Rujikiatkamjorn ◽  
Iyathurai Sathananthan
Keyword(s):  
Finite Element ◽  
Plane Strain ◽  
Numerical Solutions ◽  
Soft Clay ◽  
Vacuum Pressure ◽  
Excess Pore Pressure ◽  
Soil Consolidation ◽  
Vacuum Preloading ◽  
Element Analysis ◽  
Vertical Drains

A system of vertical drains combined with vacuum preloading is an effective method to accelerate soil consolidation by promoting radial flow. This study presents the analytical modeling of vertical drains incorporating vacuum preloading in both axisymmetric and plane strain conditions. The effectiveness of the applied vacuum pressure along the drain length is considered. The exact solutions applied on the basis of the unit cell theory are supported by finite element analysis using ABAQUS software. Subsequently, the details of an appropriate matching procedure by transforming permeability and vacuum pressure between axisymmetric and equivalent plane strain conditions are described through analytical and numerical schemes. The effects of the magnitude and distribution of vacuum pressure on soft clay consolidation are examined through average excess pore pressure, consolidation settlement, and time analyses. Lastly, the practical implications of this study are discussed.Key words: consolidation, finite element method, soft clay, vacuum preloading, vertical drains.

scholarly journals Studi Aplikasi Vacuum Preloading Sebagai Metode Alternatif Percepatan Proses Konsolidasi pada Tanah Lempung Lunak Jenuh Air: Trial GVS pada Perumahan Pantai Indah Kapuk, Jakarta

2011 ◽  
Vol 2 (2) ◽  
pp. 1055 ◽  
Author(s):  
Andryan Suhendra ◽  
Masyhur Irsyam
Keyword(s):  
Soft Clay ◽  
Vacuum Preloading ◽  
Consolidation Process ◽  
Software Application ◽  
Alternative Method ◽  
Pump Pressure ◽  
Water Saturated ◽  
Reliability Monitoring ◽  
Water Tension ◽  
Saturated Soft Clay

Vacuum preloading is an alternative method to improve water-saturated soft clay by accelerating the consolidation process. A trial using GVS system was done at Pantai Indah Kapuk residence, Jakarta to investigate the system reliability. Monitoring equipments used include settlement plate to measure the consolidation decrease, piezometer to measure pore water tension, inklinometer to identify the soil direction and lateral movement during the vacuum preloading process, and manometer to measure the vacuum pump pressure. Analytical calculations to estimate the consolidation decrease is done using one-dimensional consolidation theory of Terzaghi. Besides, a numerical analysis is performed by element method up to Plaxis software application. Meanwhile, the monitoring results are achieved using Asaoka theory that estimates the achieved degree of reduction and consolidation. The monitoring results and theoretical analysis indicate that the GVS system included in the vacuum preloading method is quite reliable as an alternative method of consolidation acceleration of water-saturated soft clay. 

Research on Surface-Layer Improvement Technology for Dredger Fill by Vacuum Preloading

2012 ◽  
Vol 256-259 ◽  
pp. 1703-1706
Author(s):  
Yan Hua Yang ◽  
Fu Quan Ji ◽  
Zhao Yang
Keyword(s):  
Large Scale ◽  
Soft Soil ◽  
Soft Clay ◽  
Drainage System ◽  
High Water ◽  
Soil Improvement ◽  
High Water Content ◽  
Construction Technology ◽  
Vacuum Preloading ◽  
Reclaimed Land

The surface-layers have very high water content and low bearing capacity, so far to be the very soft clay foundation, which come from the reclaimed land in project of reclamation. It is difficult to improve the very soft clay foundation by traditional vacuum preloading. A new method named surface soft soil improvement is presented in this paper, which can make the soft clay foundation to be improved in preliminary. Once forming the hard coat layer, the foundation may reach the needs of further construction. In the construction technology, the horizontal filter pipe net is used to instead of the sand bedding course. By laying of woven cloth and non-woven geotextile over the surface of reclaimed silt, installing PVDs by manpower becomes possible. Besides, the vertical PVDs all are connected with the horizontal filter pipe net directly, that makes a whole spatial drainage system. The loss of the degree of vacuum is decreased, and the improvement is increased. Thus, this construction technology is as a reference to the large scale engineering construction and similar projects.

scholarly journals Numerical Investigation to the Effect of Suction-Induced Seepage on the Settlement in the Underwater Vacuum Preloading with Prefabricated Vertical Drains

2021 ◽  
Vol 9 (8) ◽  
pp. 797
Author(s):  
Shu Lin ◽  
Dengfeng Fu ◽  
Zefeng Zhou ◽  
Yue Yan ◽  
Shuwang Yan
Keyword(s):  
Practical Implication ◽  
Soil Surface ◽  
Small Strain ◽  
Seepage Flow ◽  
Excess Pore Pressure ◽  
Combined Effects ◽  
Vacuum Preloading ◽  
Prefabricated Vertical Drains ◽  
Vertical Drains ◽  
The Difference

Vacuum preloading combined with prefabricated vertical drains (PVDs) has the potential to improve the soft sediments under water, however, its development is partly limited by the unclear understanding of the mechanism. This paper aims to extend the comprehension of the influential mechanism of overlapping water in the scenario of underwater vacuum preloading with PVDs. The systematic investigations were conducted by small strain finite element drained analyses, with the separated analysis schemes considering suction-induced consolidation, seepage and their combination. The development of settlement in the improved soil region and the evolution of seepage flow from the overlapping water through the non-improved soil region into improved zone are examined in terms of the build-up of excess pore pressure. Based on the results of numerical analyses, a theoretical approach was set out. It was capable to estimate the time-dependent non-uniform settlement along the improved soil surface in response to the combined effects of suction-induced consolidation and seepage. The difference of underwater and onshore vacuum preloading with PVDs is discussed with some practical implication and suggestion provided.

Laboratory Model Tests on Dredger Fills by Vacuum Preloading with No Sand Cushion

2012 ◽  
Vol 170-173 ◽  
pp. 655-660
Author(s):  
Ya Jun Wu ◽  
Jian Bo Yang
Keyword(s):  
Fine Particles ◽  
Soil Strength ◽  
Plasticity Index ◽  
Laboratory Model ◽  
Soil Parameters ◽  
Grain Composition ◽  
Vacuum Preloading ◽  
Prefabricated Vertical Drains ◽  
Water Contents ◽  
Sand Cushion

It is difficult to operate on the hydraulic-filled mucky soil foundation which the water content is high, so the vacuum preloading method with no sand cushion is used to deal with the foundation in some areas in China. Although there are still many problems in it’s application, such as, the effective range of the prefabricated vertical drains(PVDs) is small, the surrounding soil is easy to be accumulated and the soil strength increases little. For these problems, a laboratory model test on dredger fills made from the 4th layer of the Shanghai mucky soil by vacuum preloading with no sand cushion is performed. The changes and distributions in the settlement, water contents, permeability, plasticity index and grain composition of the dredger fill are studied in the process of the vacuum preloading. It is found that the water contents and permeability of the soft clay near the PVD (the diameter is about 40 to 50cm) are much lower than the outside, while the content of fine particles, plasticity index and soil strength near the PVD is much higher than the others. The measured data shows that the fine particles gather to a soil column at the center of the PVD under the action of vacuum negative pressure, then the permeability and the grain composition of the soil around the PVD is changed. As a result, soil parameters are not evenly distributed. Finally, some suggestions about how to reduce the non-uniformity are proposed.

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