Field study of pile – prefabricated vertical drain (PVD) interaction in soft clay

2020 ◽  
Vol 57 (3) ◽  
pp. 377-390
Author(s):  
Dongli Zhu ◽  
Buddhima Indraratna ◽  
Harry Poulos ◽  
Cholachat Rujikiatkamjorn
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Negative Skin Friction ◽  
Excess Pore Water Pressure ◽  
Soil Movement ◽  
Lateral Soil Movement ◽  
Compressible Soil ◽  
Excess Pore

Piles and prefabricated vertical drains (PVDs) are two well-established inclusions used by geotechnical practitioners when dealing with soft compressible foundations. Induced movements in highly compressible soil can adversely influence the pile response by inducing additional movements and stresses in the piles. Especially, undesirable soil–pile interaction often leads to the development of excess pore-water pressure during pile installation and negative skin friction caused by the settlement of compressible soil surrounding the piles. Additional drainage by PVDs prior to the installation of a pile could reduce excess pore-water pressure, lateral soil movement, and negative skin friction on the pile. In this paper, full-scale field testing on two trial embankments built on soft soil is reported and the relative behaviour of these two embankments is compared and discussed. Soft soil underneath both embankments was consolidated before one pile was installed at the centre of each embankment. The pore-water pressure, lateral soil movement, surface settlement, and associated strain at the pile shaft were recorded. The pile capacity was tested immediately and 3 h after pile installation. The monitoring and testing results indicated that preconsolidation with PVDs before piling can effectively reduce the excess pore-water pressure, lateral soil movement, and downdrag on the pile.

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 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 Constitutive Model of Lateral Unloading Creep of Soft Soil under Excess Pore Water Pressure

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Wei Huang ◽  
Kejun Wen ◽  
Xiaojia Deng ◽  
Junjie Li ◽  
Zhijian Jiang ◽  
...  
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Creep Model ◽  
Creep Tests ◽  
Excess Pore Water Pressure ◽  
Model Research ◽  
Creep Time ◽  
Excess Pore

Presented in this paper is a study on the lateral unloading creep tests under different excess pore water pressures. The marine sedimentary soft soil in Shenzhen, China, was selected in this study. The results show that the excess pore water pressure plays a significant role in enhancing the unloading creep of soft soil. Higher excess pore water pressure brings more obvious creep deformation of soft soil and lower ultimate failure load. Meanwhile, the viscoelastic and the viscoplastic modulus of soft soil were found to exponentially decline with creep time. A modified merchant model and a combined model of the modified merchant model and plastic elements are used to simulate the viscoelastic and the viscoplastic deformation, respectively. Therefore, a lateral unloading creep model of soft soil is developed based on the modified merchant model. The accuracy and applicability of this model were verified through identifying the parameters in the model. Research results are of particular significance to the numerical simulation of underground space excavation in soft soil areas which considers the effects of excess pore water pressure.

Finite Element Analysis for Subgrade Consolidation Settlement in Soft Soil

2013 ◽  
Vol 448-453 ◽  
pp. 1256-1259
Author(s):  
Feng Tan ◽  
Tai Quan Zhou
Keyword(s):  
Finite Element ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Soil Depth ◽  
Water Pressure ◽  
Soft Soil ◽  
Excess Pore Pressure ◽  
Excess Pore Water Pressure ◽  
Consolidation Settlement ◽  
Excess Pore

The two-dimensional finite element model for subgrade consolidation settlement analysis within soft soil pile is developed using ABAQUS. The numerical simulation on a highway subgrade deformation is performed to study the variation of consolidation settlement and the excess pore water pressure distribution in the central location and the part under centerline of the embankment. The results show that settlement develops gradually with the increasing period of soil consolidation. The excess pore water pressure of deep subgrade soils under embankment centerline rise due to the increased load. After each soil layer was filled, the excess pore water pressure increased in the first and was stable later along with the increase of soil depth. After the embankment soil was filled completely, excess pore pressure dissipated with time developing until the completion of consolidation.

scholarly journals Post-Cyclic Mechanical Behaviors of Undisturbed Soft Clay with Different Degrees of Reconsolidation

2021 ◽  
Vol 11 (16) ◽  
pp. 7612
Author(s):  
Yuan Lu ◽  
Jian Chen ◽  
Juehao Huang ◽  
Libo Feng ◽  
Song Yu ◽  
...  
Keyword(s):  
Shear Strength ◽  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Undrained Shear Strength ◽  
Excess Pore Water Pressure ◽  
Undrained Shear ◽  
Excess Pore

Soft soil is often subjected to cyclic loading such as that imposed during storms, under traffic, or in an earthquake. Furthermore, the cyclic-loading-induced excess pore water pressure can be partially dissipated after cyclic loading. Thus, different reconsolidation processes should be considered. A series of static and dynamic triaxial tests were conducted on undisturbed soft soil to determine the post-cyclic mechanical behavior thereof, such as the variation of undrained shear strength, the development of excess pore water pressure, and the evolution of effective stress path. The effects of consolidated confining pressure, cyclic stress ratio, and degree of reconsolidation were analyzed. Results show that the trend of all stress–strain curves is similar under different conditions. The effect of the degree of reconsolidation is such that, with increasing the degree of reconsolidation, the shear strength is enhanced. Meanwhile, compared with undrained shear strength without cyclic loading, the shear strength after cyclic loading with full reconsolidation is increased. These factors also have a significant effect on the undrained shear strength: the greater both the confining pressure and cyclic stress ratio are, the higher the undrained shear strength. A positive excess pore water pressure is always observed during post-cyclic shearing process, irrespective of different factors. The S-shaped effective stress paths under different test conditions are observed and cross the critical state line. The microstructures of undisturbed soil and post-cyclic specimens with different degrees of reconsolidation were quantitatively investigated. Besides that, the degree of influence of different factors on the post-cyclic undrained strength was analyzed. Based on the test results, the undrained shear strength with cyclic load-history was well predicted by existing models.

Analysis on Excess Pore Water Pressure Caused by Prestressed Concrete Pipes Construction in Saturated Clay Ground

2010 ◽  
Vol 168-170 ◽  
pp. 1238-1244
Author(s):  
Gui Hai Fu ◽  
Li Min Wei ◽  
Hui Zhou
Keyword(s):  
Pore Water ◽  
Prestressed Concrete ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Excess Pore Water Pressure ◽  
Concrete Pipes ◽  
Saturated Clay ◽  
Clay Ground ◽  
Excess Pore

Prestressed concrete pipes construction by hammer cause high excess pore water pressure in deep soft soils because Soil disturbance by violent and poor permeability of soft soil. Taking the typical soft ground in passenger special line from Hang Zhou to Ning Bo as the engineering example, the in-situ measuring of the excess pore water pressure in saturated clay ground during the construction of the piles was carried out, and the comparison analysis with the solutions from Vesic theory was also done. The changing rules of excess pore water pressure and its influence range during the sinking of the piles were studied, which would provide an important basis for the design and construction of the similar projects.

Experimental Study on Dynamic Compaction-Plastics Drain Board Method in Backfill Subgrade Reinforcement

2011 ◽  
Vol 474-476 ◽  
pp. 2032-2036
Author(s):  
Yong Ma ◽  
Mao Tian Luan ◽  
Zhong Chang Wang
Keyword(s):  
Experimental Study ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Time Effect ◽  
Dynamic Compaction ◽  
Excess Pore Water Pressure ◽  
Compaction Method ◽  
Excess Pore

Plastics drain board method is one of the most effective ways of reducing excess pore water pressure during the process of dynamic compaction in soft soil subgrade reinforcement. Based on field test in neritic backfilled area of Jinzhou Port 207B berth, the pore water pressure, groundwater level, subgrade bearing capacity and time effect of deformation have been measured and analyzed. The application of dynamic compaction-PDB method makes a mighty advance of the dynamic compaction method, which provides a new way for soft soil treatment in coastal areas.

Study of Fast Drained Consolidation of Silt

2011 ◽  
Vol 90-93 ◽  
pp. 422-425 ◽  
Author(s):  
Qing He Huang
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Low Cost ◽  
Water Pressure ◽  
Soft Soil ◽  
Acceptance Test ◽  
Construction Period ◽  
Excess Pore Water Pressure ◽  
Horizontal Drain ◽  
Excess Pore

The silt has the properties, such as low strength and slow drainage; so it is usually treated by precompression method. For short construction period and low cost , a new drained consolidation method-drainage consolidation due to excessive pore water pressure for silt is tested: fist, the sand is replaced in the surface of silt for horizontal drain; and then, the plastic drain boards is applied for vertical drain; finally, the excess pore water pressure is generated by surcharge loads and dynamic consolidation and the drainage consolidation is fast under the excess pore water pressure. The result of the settlement observation and acceptance test shows that the result of drainage consolidation due to excessive pore water pressure for silt soft soil is remarkable.

Parameters Analysis on Construction Control of Precast Piles in Soft Soil Ground

2012 ◽  
Vol 616-618 ◽  
pp. 326-331
Author(s):  
Xiang Qian Hu ◽  
Xue Tun Zhao ◽  
Hong Gang Huang ◽  
Jun Ting Long
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Influence Factors ◽  
Control Parameters ◽  
Excess Pore Water Pressure ◽  
Parameters Analysis ◽  
Driven Pile ◽  
Excess Pore

Based on the precast pile foundation field test of the power plant, the distribution and dissipation of the excess pore water pressure induced by the construction of the precast pile are first analyzed after the plastic drain board driven in the soft ground. Then the influence factors of the distribution and dissipation of the excess pore water pressure are presented. Subsequently the quality problem of the pre-date driven pile caused by the construction of the precast pile is studied. The main control parameters of the precast pile construction under the complicated condition are provided, which will provide a reference for such similar projects.

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