scholarly journals Visualization and Quantification of the Penetration Behavior of Bentonite Suspensions into the Pore Network of non-cohesive Media by using μ-CT Imaging

2016 ◽  
Author(s):  
Britta Schoesser ◽  
Atefeh Ghorbanpour ◽  
Matthias Halisch ◽  
Markus Thewes
Keyword(s):  
Filter Cake ◽  
Pore Space ◽  
Water Pressure ◽  
Soft Soil ◽  
Theoretical Models ◽  
Bored Pile ◽  
Soil Skeleton ◽  
Bentonite Suspension ◽  
Penetration Behavior ◽  
Drill Holes

Abstract. Bentonite suspensions are an essential tool for different construction techniques in horizontal and vertical drilling, in diaphragm and bored pile walls as well as in pipe jacking and tunneling. One of the main tasks of the suspension is to prevent the surrounding ground from collapsing during the excavation process of trenches, drill holes or tunnels. In order to maintain the soil stability close to the excavation, the bentonite suspension has to counteract against the earth and water pressure. Therefore, the pressure acting in the suspension has to counter the groundwater pressure and to be transferred into an effective stress to support the soil skeleton. The creation of a pressure transfer mechanism can be achieved in two ways. A direct relation exists between the mechanism of the pressure transfer and the penetration behavior of the bentonite suspension in the subsoil. The relation of the size of the bentonite particles in the suspension and the size of the pores in soft soil is decisive. In addition, the yield strength of the bentonite suspension is a determining factor. Concerning the penetration behavior two theoretical models exist actually: formation of a filter cake and entire penetration into the pore space. If the pore space is smaller than the size of the bentonite particles, a filtration process takes place. Here, the bentonite particles agglomerate gradually at the entrance of the pore space and create a thin nearly impermeable layer. This membrane is named filter cake. If the pore space is larger than the size of the bentonite particles, the suspension penetrates into the subsoil up to a certain depth. These models have a more theoretical character due to missing visual evidence concerning the interaction of the bentonite suspension in the pore space. Here, the micro CT technique delivers a valuable contribution to this research.

Pore-morphology-based simulations of drainage and wetting processes in porous media

2011 ◽  
Vol 42 (2-3) ◽  
pp. 128-149 ◽  
Author(s):  
T. P. Chan ◽  
Rao S. Govindaraju
Keyword(s):  
Porous Media ◽  
Hydraulic Properties ◽  
Pore Space ◽  
Water Pressure ◽  
Theoretical Models ◽  
Hysteretic Behavior ◽  
Water Retention Curve ◽  
Pore Morphology ◽  
Soil Hydraulic Properties ◽  
Soil Hydraulic

Soil hydraulic properties relating saturation, water pressure, and hydraulic conductivity are known to exhibit hysteresis. In this paper, we focus on the determination of the water retention curve for a porous medium through a novel pore-scale simulation technique that is based on mathematical morphology. We develop an algorithm that allows for the representation of three-dimensional randomly packed porous media of any geometry (i.e. not restricted to idealized geometries such as spherical or ellipsoidal particles/pore space) so that the connectivity-, tortuosity-, and hysteresis-causing mechanisms are represented in both drainage and wetting processes, and their role in determining macroscopic fluid behavior is made explicit. Using this method, we present simulation results that demonstrate hysteretic behavior of wetting and non-wetting phases during both drainage and wetting cycles. A new method for computing interfacial surface areas is developed. The pore-morphology-based method is critically evaluated for accuracy, sample size effects, and resolution effects. It is found that the method computes interfacial areas more accurately than existing methods and allows for (i) examination of relationships between water pressure, saturation and interfacial area for hysteretic soils, and (ii) comparisons with previously developed theoretical models of soil hydraulic properties. The pore-morphology-based method shows promise for applications in vadose zone hydrology.

Geosynthetic Encased Column: comparison between numerical and experimental results

2021 ◽  
Vol 44 (4) ◽  
pp. 1-12
Author(s):  
Nima Alkhorshid ◽  
Gregório Araújo ◽  
Ennio Palmeira
Keyword(s):  
Pore Water Pressure ◽  
Water Pressure ◽  
Ground Improvement ◽  
Soft Soil ◽  
Experimental Tests ◽  
High Permeability ◽  
Soft Soils ◽  
Column Comparison ◽  
Surrounding Soil ◽  
Granular Column

The use of granular column is one of the ground improvement methods used for soft soils. This method improves the foundation soils mechanical properties by displacing the soft soil with the compacted granular columns. The columns have high permeability that can accelerate the excess pore water pressure produced in soft soils and increase the undrained shear strength. When it comes to very soft soils, the use of granular columns is not of interest since these soils present no significant confinement to the columns. Here comes the encased columns that receive the confinement from the encasement materials. In this study, the influence of the column installation method on the surrounding soil and the encasement effect on the granular column performance were investigated using numerical analyses and experimental tests. The results show that numerical simulations can reasonably predict the behavior of both the encased column and the surrounding soil.

scholarly journals Perbandingan Pengujian Konsolidasi Menggunakan Alat Rowe Cell dan Oedometer pada Tanah Lanau Lunak

2020 ◽  
Vol 22 (2) ◽  
pp. 149-155
Author(s):  
Iskandar ◽  
Rabiya
Keyword(s):  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Soil Samples ◽  
Soil Parameters ◽  
Soil Consolidation ◽  
Test Results ◽  
Soft Soils ◽  
Better Than ◽  
Rowe Cell

Soil consolidation testing using an oedometer and rowe cell. Oedometers are often used on clay and soft soils. However, in the development of the rowe cell device, the results of lowering soft soil were better than the oedometer. The advantage of this rowe cell is that it can determine the saturation value of the soil samples tested. The rowe cell tester can measure the pore water pressure at the beginning and end of each consolidation stage. This rowe cell can provide suitable settlement for soft soils. This consolidation test to obtain soil parameters such as Cv and Cc by using the rowe cell tool. After that, from the test results, the two tools were compared.

Study on Artificial Island Ground Improvement Method and Effect

2014 ◽  
Vol 1030-1032 ◽  
pp. 1037-1040
Author(s):  
Jin Fang Hou ◽  
Ju Chen ◽  
Jian Yu
Keyword(s):  
Pore Water Pressure ◽  
Water Pressure ◽  
Ground Improvement ◽  
Soft Soil ◽  
Horizontal Displacement ◽  
Treatment Method ◽  
Surcharge Preloading ◽  
Porosity Ratio ◽  
Improvement Method ◽  
Consolidation Degree

The artificial island ground on an open sea is covered by thick soft soil. It must be improved before using. In accordance with a designing scheme, the ground treatment method is inserting drain boards on land and jointed dewatering surcharge preloading, the residual settlement is not more than 30cm after improvement and the average consolidation degree is more than 85%. In order to estimate ground improvement effect and construction safety, instruments are buried to monitor the whole ground improving processes. By monitoring settlement and pore water pressure, it is shown that the total ground settlement in construction is 2234mm, its final settlement is 2464mm, and consolidation degree and residual settlement respectively satisfy requirements. In ground improvement, horizontal displacement is small and construction is safe. Meanwhile, the results of soil properties and vane shear strength detection tests show the soft soil ground is greatly reduced in water content and porosity ratio, and improved in strength. It is named that the ground improvement method is reasonable and reaches expected effect.

scholarly journals Experimental Study on the Variation Law of Excess Pore Water Pressure at the Bottom of the Foundation Pit for Excavation

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Qizhi Hu ◽  
Qiang Zou ◽  
Zhigang Ding ◽  
Zhaodong Xu
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Confining Pressure ◽  
Deep Foundation ◽  
Foundation Pit ◽  
Excess Pore Water Pressure ◽  
Accurate Expression ◽  
Excess Pore

The excavation unloading of deep foundation pits in soft soil areas often produces negative excess pore water pressure. The rebound deformation of soil on the excavation surface of the foundation pit can be predicted reliably through the accurate expression of relevant variation laws. In combination with the principle of effective stress and the general equation of unidirectional seepage consolidation, an equation for calculating the rebound deformation from the bottom in the process of foundation pit excavation unloading was obtained. Additionally, a triaxial unloading test was adopted to simulate the excavation unloading processes for actual foundation pit engineering. After studying the variation law of the excess pore water pressure generated by excavation unloading, it was found that the negative excess pore water pressure increased with increasing unloading rate, while the corresponding peak value decreased with increasing confining pressure. The equation for rebound calculation was verified through a comparison with relevant measured data from actual engineering. Therefore, it is considered that the equation can reliably describe the rebound deformation law of the base. This paper aims to guide the design and construction of deep foundation pits in soft soil areas.

scholarly journals Water Transport in Unsaturated Cracked Concrete under Pressure

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Yuanzhu Zhang ◽  
Siming Zhang ◽  
Gang Wei ◽  
Xinjiang Wei ◽  
Liqiao Jin ◽  
...  
Keyword(s):  
Water Transport ◽  
Driving Force ◽  
Crack Width ◽  
Water Pressure ◽  
Theoretical Models ◽  
Double Porosity ◽  
Hydraulic Pressure ◽  
Pressure Potential ◽  
Cracked Concrete ◽  
Concrete Permeability

In order to analyze the process of hydraulic water infiltrating cracked concrete of underwater tunnels, the equation of water transport in unsaturated cracked concrete under pressure was proposed according to the double-porosity medium model. Penetration tests on prefabricated cracked concrete blocks were conducted, and then the influence of hydraulic pressure, initial saturation, and crack width on water transport was studied. The results show that the larger the water pressure, the lower the initial saturation, and the wider the crack width, then the greater the penetration depth, which can be reasonably explained according to water motion theoretical models in this study. Moreover, the TOUGH2 software was used to simulate the change and distribution of saturation, driving potential, and water velocity of unsaturated cracked concrete, which further proved the experimental results and theoretical analysis. It reflects that both pressure potential and matric potential are the driving force of water transport in underwater cracked concrete, and the driving force will be converted with the change of concrete saturation. In addition, crack width is positively correlated with concrete permeability.

scholarly journals Experiment Study of Lateral Unloading Stress Path and Excess Pore Water Pressure on Creep Behavior of Soft Soil

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Wei Huang ◽  
Kejun Wen ◽  
Dongsheng Li ◽  
Xiaojia Deng ◽  
Lin Li ◽  
...  
Keyword(s):  
Pore Water ◽  
Creep Behavior ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Stress Path ◽  
Deviatoric Stress ◽  
Excess Pore Water Pressure ◽  
Pore Water Pressures ◽  
Excess Pore

The unloading creep behavior of soft soil under lateral unloading stress path and excess pore water pressure is the core problem of time-dependent analysis of surrounding rock deformation under excavation of soft soil. The soft soil in Shenzhen, China, was selected in this study. The triaxial unloading creep tests of soft soil under different initial excess pore water pressures (0, 20, 40, and 60 kPa) were conducted with the K0 consolidation and lateral unloading stress paths. The results show that the unloading creep of soft soil was divided into three stages: attenuation creep, constant velocity creep, and accelerated creep. The duration of creep failure is approximately 5 to 30 mins. The unloading creep behavior of soft soil is significantly affected by the deviatoric stress and time. The nonlinearity of unloading creep of soft soil is gradually enhanced with the increase of the deviatoric stress and time. The initial excess pore water pressure has an obvious weakening effect on the unloading creep of soft soil. Under the same deviatoric stress, the unloading creep of soft soil is more significant with the increase of initial excess pore water pressure. Under undrained conditions, the excess pore water pressure generally decreases during the lateral unloading process and drops sharply at the moment of unloading creep damage. The pore water pressure coefficients during the unloading process were 0.73–1.16, 0.26–1.08, and 0.35–0.96, respectively, corresponding to the initial excess pore water pressures of 20, 40, and 60 kPa.

scholarly journals Influence of Soil Structure on the Mechanical Response of Soft Soil

2018 ◽  
Vol 38 ◽  
pp. 03027
Author(s):  
Bin Bin Xu
Keyword(s):  
Yield Stress ◽  
Pore Water ◽  
Soil Structure ◽  
Mechanical Response ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Before And After ◽  
Strain Relationship ◽  
Consolidation Behavior

Usually the natural sedimentary soils possess structure more or less, which makes their mechanical response much different from the fully remolded soils. In this paper, the influence of soil structure on the mechanical response such as compressibility, shear, permeability is literately reviewed. It is found that the compressibility and consolidation behavior of structured and remolded soils can be divided clearly before or after the structural yield stress. The stress-strain relationship can be divided into two segments before and after the structural yield stress. Before the yield stress, the curve is elevating and after the yield stress the curve is decreasing. The increasing rate of pore water pressure increases after the soil reached yield stress.

scholarly journals Numerical Modelling of Prefabricated Vertical Drain for Soft Clay Using ABAQUS

2015 ◽  
Vol 773-774 ◽  
pp. 1502-1507
Author(s):  
Saiful Azhar Ahmad Tajudin ◽  
Mohd Fairus Yusof ◽  
I. Bakar ◽  
Aminaton Marto ◽  
Muhammad Nizam Zakaria ◽  
...  
Keyword(s):  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Soft Clay ◽  
Elastic Model ◽  
Clay Layer ◽  
Soil Consolidation ◽  
Consolidation Process ◽  
Vertical Drain ◽  
Prefabricated Vertical Drain

Construction, buildings and infrastructure founded on soft clays are often affected by settlement problem. Therefore, Prefabricated Vertical Drain (PVD) is one of the best solutions to accelerate soil consolidation by shortening the drainage path. In this study, numerical investigation was carried out to pursue a better understanding of the consolidation behavior of soft clay improved with PVD. The consolidation process accelerated by PVD with surcharge of 50 kPa was analysed using the ABAQUS software by adopting an elastic model. The aim of this study is to compare the settlement and the required time to fully consolidate the soft soil at different drain spacings (1.0 m, 1.5 m and 2.0 m) for two different thickness of the clay layer. The results shows that the time required to completely consolidate the soft soil for 12 m and 20 m thickness of clay layer with different spacings are in the range of 3 months to 66 months. The settlement rate and excess pore water pressure dissipation are increased when the spacing of the drain closer.

scholarly journals New approach of vacuum preloading with booster prefabricated vertical drains (PVDs) to improve deep marine clay strata

2018 ◽  
Vol 55 (10) ◽  
pp. 1359-1371 ◽  
Author(s):  
Yuanqiang Cai ◽  
Zhiwei Xie ◽  
Jun Wang ◽  
Peng Wang ◽  
Xueyu Geng
Keyword(s):  
Lateral Displacement ◽  
Water Pressure ◽  
Ground Improvement ◽  
Soft Soil ◽  
Marine Clay ◽  
Vacuum Preloading ◽  
Prefabricated Vertical Drains ◽  
New Approach ◽  
Study Results ◽  
Prefabricated Vertical Drain

This paper presented a new approach for ground improvement of deep marine clay in which the conventional booster tube in the current air booster vacuum preloading technology was replaced by a booster prefabricated vertical drain (PVD). In comparison to the ordinary PVD, the booster PVD could provide inflow channels for the compressed air when the booster pump was in operation. To examine the performance of this new air booster vacuum preloading technology, in situ field tests were conducted at Oufei sluice project in Wenzhou, China, where the thickness of the soft soil layers (i.e., marine clay) was more than 20 m. An extensive monitoring system was implemented to measure the vacuum pressure, pore-water pressure, settlement, and lateral displacement at this reclamation site. With the collected field monitoring data, a comprehensive data analysis was carried out to evaluate the extent of ground improvement. The study results depicted that this new air booster vacuum preloading technology was more effective for the ground improvement of the deep marine clay layers, in comparison to the conventional vacuum preloading technology.

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