Effects of soil spatial variability on axisymmetric versus plane strain analyses of ground improvement by prefabricated vertical drains

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.

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Modelling of a vacuum consolidation project in Vietnam

ENGINEERING AND TECHNOLOGY ◽

10.46223/hcmcoujs.tech.en.9.1.354.2019 ◽

2020 ◽

Vol 9 (1) ◽

pp. 78-101

Author(s):

Nguyen Trong Nghia

Keyword(s):

Analytical Solution ◽

Numerical Modelling ◽

Plane Strain ◽

Ground Improvement ◽

Soft Soil ◽

Design Tool ◽

In Situ Monitoring ◽

Improvement Project ◽

Prefabricated Vertical Drains ◽

Prefabricated Vertical Drain

Ground improvement technique by prefabricated vertical drain (PVD) in combination with vacuum preloading is widely used to facilitate consolidation process and reduce residual settlement. However, this technique seem hardly be estimated by both analytical method and numerical method because it has complex boundary conditions (such as vacuum pressure changing with time). Moreover, lateral displacements caused by this technique are also significant problem. Numerical modelling may be an effective design tool to estimate behavior of soft soil treated by this method, however it needs to have a proper calibration of input parameters. This paper introduces a matching scheme for selection of soil/drain properties in analytical solution and numerical modelling (axisymmetric and plane strain conditions) of a ground improvement project by using Prefabricated Vertical Drains (PVD) in combination with vacuum and surcharge preloading. In-situ monitoring data from a case history of a road construction project in Vietnam was adopted in the back-analysis. Analytical solution and axisymmetric analysis can approximate well the field data meanwhile the horizontal permeability need to be adjusted in plane strain scenario to achieve good agreement. In addition, the influence zone of the ground treatment was examined. The residual settlement was investigated to justify the long-term settlement in compliance with the design code. Moreover, the degree of consolidation of non-PVD sub-layers was also studied by means of two different approaches.

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Application of Depth-Measurable Prefabricated Vertical Drains for Soft Ground Improvement

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.405-408.466 ◽

2013 ◽

Vol 405-408 ◽

pp. 466-469

Author(s):

Yong Hua Cao ◽

Jian Yu

Keyword(s):

Ground Improvement ◽

Measuring Method ◽

Soft Ground ◽

Prefabricated Vertical Drains ◽

Vertical Drains ◽

Impulse Method ◽

Installation Depth ◽

Soft Ground Improvement

A kind of depth-measurable prefabricated vertical drains (PVD) was applied for soft ground improvement in Tianjin, China. Test was conducted to check the effectiveness of impulse method for detection of installation depth of PVD. The PVD were set into two groups in length: 20 m and 8 m. The installation depth of PVD was checked in 24 hours since they were installed. The tests result revealed that the measuring precision of impulse method is fairly good but it can be effect by the installation depth. The measuring precision can be controlled in 2% for most PVD when the installation depth was about 20 m. There is a fall down of precision when the installation depth was about 8 m. There is no need for additional construction measures when the PVD for impulse method are installed. All of the PVD installed can be checked for installation depth easily, so the apparatus and measuring method are good in operability and stability.

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A Case Study of Combined Drainage Consolidation-Preloading Methods for a Highway Subgrade on Peat Soils

Advances in Civil Engineering ◽

10.1155/2020/8816619 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10

Author(s):

Yue Gui ◽

Shengjun Liu ◽

Xiaqiang Qin ◽

Jianfei Wang

Keyword(s):

Ground Improvement ◽

Sri Lankan ◽

Peat Soils ◽

Prefabricated Vertical Drains ◽

Vertical Drains ◽

Consolidation Coefficient ◽

Gravel Pile ◽

Insight Into

A highway project of up to 100 km/h is currently being constructed between Colombo and Katunayake International Airport across a Sri Lankan muskeg area. At this site, peat deposit was initially 0.8∼15.3 m thick and was underlain by sand, clay, or gneiss. The ground improvement methods adopted in the project were combined drainage consolidation-preloading methods, pipe pile foundation, and geogrids. This paper provides a detailed insight into the implementation of combined drainage consolidation-preloading methods used in the project, including sand pile, gravel pile, and plastic drainage plate as the prefabricated vertical drains. Periodical field-level observations were taken during the ten years, including the construction and postconstruction periods. The results show that peat soils’ consolidation coefficient has been increased several times to tens of times due to ground improvement. After removing the temporary surcharge, the highway embankments did not heave and was followed by long-term settlements totaling 1.3∼7.4 cm over the following seven years of observations. Analysis of the settlement records shows that combined drainage consolidation-preloading methods have helped accelerate drainage consolidation and reduce postconstruction settlement.

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The Experimental Research of Slurry Improvement with Different Kinds of Vertical Drains under New Vacuum Conditions

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.405-408.396 ◽

2013 ◽

Vol 405-408 ◽

pp. 396-401

Author(s):

Jian Chen ◽

Qiao Liang Tang ◽

Shi Jing Liu

Keyword(s):

Experimental Research ◽

Ground Improvement ◽

Soil Improvement ◽

Vacuum Preloading ◽

Prefabricated Vertical Drains ◽

Vertical Drains ◽

Drain Spacing ◽

Soil Zone ◽

Reclaimed Soil ◽

Improvement Effect

The results of experimental research are presented and discussed with focus on the ground improvement effect of slurry with different kinds of vertical drains under new vacuum conditions. In these conditions, horizontal sand cushion, which is requested in regular vacuum preloading method, is cancelled. Vertical drains are connected with sealed pipes, so the vacuum head can be transmitted into vertical drains without decreasing. For the experimental research, slurry taken from reclaimed soil zone is placed into six model casing boxes. Different kinds of vertical drains (prefabricated vertical drains (PVDs) and sand drains) are installed into the soil with different spacing (0.4 m and 0.8 m). A vacuum pressure of 80 kPa was applied continuously for 90 days. The effect of filter type of PVD, type of vertical drain and drain spacing under new vacuum preloading condition to slurry soil improvement is examined. Test results show that this new vacuum preloading condition can transmit vacuum head into vertical drains efficiently and the effect of drain filter to slurry improvement is affected by the drain spacing.

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