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.

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 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 Consolidation Effect of Prefabricated Vertical Drains with Different Lengths for Soft Subsoil under Vacuum Preloading

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Chenhui Lou ◽  
Junfeng Ni ◽  
Jingchun Chai ◽  
Hongtao Fu ◽  
Xiuqing Hu ◽  
...  
Keyword(s):  
Laboratory Model ◽  
Vacuum Preloading ◽  
Prefabricated Vertical Drains ◽  
Vertical Drains ◽  
Shallow Layer ◽  
Pore Water Pressures ◽  
Practical Engineering ◽  
Different Depths ◽  
Degree Of Consolidation ◽  
Consolidation Effect

The application of vacuum preloading to prefabricated vertical drains (PVDs) with different lengths is widely used in practical engineering to investigate their consolidation at the same depths of even and multilayer subsoils from the seabed. In a laboratory, model experiment was conducted using even subsoil and embedded PVDs with lengths of 0.6 and 1.2 m. The obtained results showed that in the even subsoil, the 1.2 m PVDs maintained a higher vacuum pressure in the shallow layer and demonstrated better consolidation behavior as compared to those of the 0.6 m PVDs. In the upper subsoil layer, the average vane shear strengths of these two systems increased to 18.2 and 22.6 kPa, respectively. The degree of consolidation of the upper subsoil layers in the two model experiments calculated from the pore water pressures under boundary drainage conditions were 51% and 68%, respectively. For practical verification purposes, similar experiments were conducted for multilayer subsoil by inserting PVDs with lengths of 6 and 15 m into different test sites. As a result, the vane shear strengths of the upper 6 m subsoil layers increased to 26.3 and 33 kPa, while the degree of consolidation were 72.1% and 80.9%, respectively, although some irregularities were observed at different depths.

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.

Measured and predicted performance of prefabricated vertical drains (PVDs) with and without vacuum preloading

2010 ◽  
Vol 28 (1) ◽  
pp. 1-11 ◽  
Author(s):  
J. Saowapakpiboon ◽  
D.T. Bergado ◽  
S. Youwai ◽  
J.C. Chai ◽  
P. Wanthong ◽  
...  
Keyword(s):  
Vacuum Preloading ◽  
Prefabricated Vertical Drains ◽  
Vertical Drains

Characterization of a smear zone around vertical drains by large-scale laboratory tests

2000 ◽  
Vol 37 (6) ◽  
pp. 1265-1271 ◽  
Author(s):  
J S Sharma ◽  
D Xiao
Keyword(s):  
Large Scale ◽  
Soft Clay ◽  
Excess Pore Pressure ◽  
Laboratory Model ◽  
Clay Layer ◽  
Prefabricated Vertical Drains ◽  
Vertical Drains ◽  
Undisturbed Samples ◽  
Oedometer Tests ◽  
Excess Pore

Installation of prefabricated vertical drains using a mandrel causes disturbance of clay surrounding the drain, resulting in a "smear" zone of reduced permeability. In this paper, an attempt is made to characterize the smear zone using large-scale laboratory model tests. Two tests, simulating the cases of "no smear" and "with smear," were conducted. Excess pore-water pressures were monitored at seven different locations along the radial direction. In addition, undisturbed samples were collected at various locations in the clay layer for conducting oedometer tests. The distribution of excess pore pressure due to drain installation gave a clear indication of the extent of the smear zone. The effect of reconsolidation on the properties of clay was found to be much greater than that of the remoulding of the clay. The extent of the smear zone was also confirmed from the change in permeability of the clay layer in the smear zone obtained from oedometer tests. The radius of the smear zone is about four times that of the mandrel, and the horizontal permeability of the clay layer in the smear zone is approximately 1.3 times smaller than that in the intact zone.Key words: consolidation, permeability, smear zone, soft clay, vertical drains.

Vacuum preloading consolidation of reclaimed land: a case study

1998 ◽  
Vol 35 (5) ◽  
pp. 740-749 ◽  
Author(s):  
J Q Shang ◽  
M Tang ◽  
Z Miao
Keyword(s):  
Land Reclamation ◽  
Soil Improvement ◽  
Large Area ◽  
Vacuum Preloading ◽  
Reclaimed Land ◽  
Improvement Project ◽  
Prefabricated Vertical Drains ◽  
Vertical Drains ◽  
Soft Clays

This case study presents the design, operation, and results of a soil improvement project using the vacuum preloading method on 480 000 m2 of reclaimed land in Xingang Port, Tianjing, China. The areas treated with vacuum ranged from 5000 to 30 000 m2. The effects of soil improvement are demonstrated through the average consolidation settlement of 2.0 m and increases in undrained shear strengths by a factor of two to four or more. The study shows that the vacuum method is an effective tool for the consolidation of very soft, highly compressive clayey soils over a large area. The technique is especially feasible in cases where there is a lack of surcharge loading fills, extremely low shear strength, soft ground adjacent to critical slopes, and access to a power supply.Key words: vacuum preloading consolidation, soil improvement, soft clays, land reclamation, prefabricated vertical drains.

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