Experimental Study on the Time Effect of the Jacked Pile

2013 ◽  
Vol 353-356 ◽  
pp. 125-129
Author(s):  
Rui Cai Wang ◽  
Jian Yong Shi ◽  
Sheng Chen ◽  
Hua Jie Chen
Keyword(s):  
Initial Stress ◽  
Pore Water ◽  
Effective Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Stress Path ◽  
Test Results ◽  
Stress Increment ◽  
Excess Pore Water Pressure ◽  
Triaxial Apparatus

Based on the strain-holding test by using GDS stress path triaxial apparatus, the changes of pore water pressure and stress of soil around the pile were simulated during and after pile jacking. Test results show as follows: excess pore water pressure and effective stress increment increase with strain and initial stress rising at the stage of strain applied. And at the stage of strain holding, effective stress increment increases with rising of strain and initial stress. For the total effective stress increment, the proportion of effective stress increment is large at the stage of strain applied. And at the stage of strain holding, the proportion of effective stress increment is small.

Effective stress paths and yielding in soft clays below embankments

1985 ◽  
Vol 22 (3) ◽  
pp. 357-374 ◽  
Author(s):  
D. J. Folkes ◽  
J. H. A. Crooks
Keyword(s):  
Pore Water ◽  
Effective Stress ◽  
Strain Softening ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Clay ◽  
Stress Path ◽  
Excess Pore Water Pressure ◽  
Soft Clays ◽  
Effective Stress Path

Current methods of predicting the response of soft clays to surface loading are often unsuccessful because the assumed constitutive relationships, including effective stress path behaviour, are incorrect. In particular, the transition from small-strain to large-strain behaviour (i.e. yielding) is frequently not taken into account. Recent laboratory testing has demonstrated that the behaviour of soft clays is largely controlled by yielding. The locus of effective stress states causing yield is known as the yield envelope (YE).The effective stress paths (ESP's) in soft clay foundations below the centre of six fills were determined from computed total stresses and measured pore-water pressures. Yield behaviour is clearly indicated by ESP shapes. The yield envelopes inferred from analyses of field data are similar to those obtained from laboratory testing. Effective stress path shapes vary widely, depending on a variety of factors, including imposed stress level, rate of construction, and boundary drainage conditions. This finding contradicts an earlier conclusion that soft clay behaviour can be characterized by a single ESP. Because of the wide range of possible ESP shapes, the parameters [Formula: see text] does not provide an adequate basis for determining the effective stress state in a soft clay.The ESP/YE analyses indicate that yield can occur either during loading or during excess pore-water pressure dissipation following completion of loading. Yield of sensitive soils during loading is usually followed by strain softening. However, in some soils, dilatant behaviour appears to occur. Yield during dissipation of excess pore-water pressure is characterized by a dramatic change in cv and increased compressibility. Key words: soft clay, yield, effective stress paths, field behaviour, strain softening, rate of consolidation.

Security Control Method of Loading for Surcharge Preloading Based on the Stress Path

2011 ◽  
Vol 368-373 ◽  
pp. 2795-2803
Author(s):  
Heng Hu ◽  
Yan Li ◽  
Zhi Liang Dong ◽  
Yan Luo ◽  
Gong Xin Zhang
Keyword(s):  
Pore Water ◽  
Safety Factor ◽  
Control Method ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Stress Path ◽  
Excess Pore Water Pressure ◽  
Surcharge Preloading ◽  
Security Control ◽  
Excess Pore

All the time, security control method of loading is an important research part in the surcharge preloading, which is directly related to safety of the construction process. Starting from the stress path, discussing the variation of excess pore water pressure and relationship between stress path and security, and bringing forward the control method with a safety factor Fs based on the stress path. By measuring the change of excess pore water pressure, the control method with a safety factor Fs can reflect quantitatively the security status of soil and achieve the purpose of the process control, finally the security control method including the safety factor of loading and speed control is put forward to monitor construction safety. The safety factor of loading Fs is verified and back analyzed with the finite-element software, getting the correction factor from 0.90 to 1.20.

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 Drained volumetric behaviour and static liquefaction of very loose sand reinforced with synthetic fibres

2019 ◽  
Vol 92 ◽  
pp. 12001
Author(s):  
Xidong Zhang ◽  
Adrian R Russell
Keyword(s):  
Pore Water ◽  
Effective Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Fibre Reinforcement ◽  
Loose Sand ◽  
Confining Stress ◽  
Excess Pore Water Pressure ◽  
Static Liquefaction ◽  
Excess Pore

Synthetic fibres may be used to reinforce soils. Fibre reinforcement may, for example, improve the mechanical behaviour of very loose sand which is usually susceptible to static liquefaction. In this study, two types of polypropylene fibres are mixed into sand to explore the effect of fibre reinforcement on drained volumetric behaviour and undrained static liquefaction. Drained and undrained stress-controlled triaxial compression tests are conducted on both unreinforced and fibre reinforced samples which are in very loose states. It is observed that, under drained compression, both unreinforced and fibre reinforced samples show volumetric contraction. In undrained compression the excess pore water pressure eventually becomes almost equal to the initial confining stress in all samples. This represents a state of liquefaction in unreinforced samples, and they become fluidised indicating the effective stress has become zero. However, in reinforced samples, the fluidised condition is absent, indicating that a conventional type of liquefaction has not occurred. It is concluded that static liquefaction in very loose sand can be prevented by fibre reinforcement, as the induced tensile stress in fibres makes the effective stress (that is the stress carried by the soil skeleton) remain above zero even when the excess pore water pressure is equal to the confining stress.

scholarly journals Experimental Study on Undrained Shear Properties of Saline Soil under Freeze-Thaw Cycles

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Shukai Cheng ◽  
Qing Wang ◽  
Jiaqi Wang ◽  
Yan Han
Keyword(s):  
Pore Water ◽  
Effective Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Stress Path ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
Freeze Thaw Cycle ◽  
Effective Stress Path ◽  
Strain Relationship

The freeze-thaw cycle is an important external factor affecting the hydromechanical characteristics of saline soil in cold regions. Due to the presence of water and salt, it has a greater impact on stability. The construction of various projects, such as ditch fills and road subgrades, has mostly used disturbed soils. Therefore, this article takes remolded saline soil in Qian’an, Jilin Province, China, as the research object to evaluate the action of freeze-thaw cycles on the critical state line, effective stress path, pore water pressure-strain relationship, stress-strain relationship, shear strength index, and other mechanical properties via a freeze-thaw cycle test and a consolidated undrained triaxial shear test (CU). The experimental results show that regardless of whether the soil specimen undergoes a freeze-thaw cycle, its stress-strain relationship shows characteristics of strain hardening, while, as the number of freeze-thaw cycles increases, the shear strength gradually decreases. As both the confining pressure and number of freeze-thaw cycles increase, the pore water pressure increases, as does the pore water pressure coefficient in shear failure. Under the action of freeze-thaw cycles, on the p ′ − q plane of the stress space, the effective stress path gradually moves to the lower left side. Both the effective stress path and the pore water pressure characteristics indicate that the degree of consolidation of the soil specimens continuously decreases as the number of freeze-thaw cycles increases. The position of the critical state line gradually lowers, and the critical state stress ratio decreases. The effective stress strength index can more accurately reflect the comprehensive influence of freeze-thaw cycles and confining pressure on the mechanical characteristics of soils than the total stress strength index. Logistic functions can be used to fit and predict the degradation law of the internal friction angle and cohesion.

scholarly journals Identification of hydrogeological evolution using hydrogeology-seismology analysis of groundwater head fluctuation related to the 1999 MW = 7.5 Chi-Chi earthquake

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Chien-Lin Huang ◽  
Nien-Sheng Hsu ◽  
Chun-Hao Yao ◽  
Gene J.-Y. You
Keyword(s):  
Pore Water ◽  
Effective Stress ◽  
Principal Components ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Stress Relief ◽  
Pumping Test ◽  
Excess Pore Water Pressure ◽  
Pressure Release ◽  
Excess Pore

Abstract At 1:47 a.m. on September 21, 1999, the Mw 7.5 Chi-Chi earthquake struck Taiwan. The purpose of this study is to (1) apply multiple spatiotemporal-frequency analysis to filter the post-seismic change in groundwater head to explore the implicit drawdown associated with excess pore-water pressure release and effective stress relief during post-seismic evolution and (2) establish a stochastic experimental optimization model for identifying the hydrogeological evolution. The approaches used for post-seismic drawdown filtration include multi-rank principal components decomposition, multi-frequent wavelet transforms decomposition, and multi-level wavelet de-noising. This study especially evaluates the following advanced post-seismic evolving parameters: (1) harmonic average leaking/injecting rate, (2) distance between the acting position and monitoring well, (3) storage coefficient under effective stress relief and formation compression, and (4) transmissivity for excess-pore-water pressure release. This study applies the integrated methodology on 179 monitoring wells in the Chou-Shui River alluvial fan. Results show that the overlying principal components PCs and low-level wavelet de-noising can filter additional sources/sinks, in which the extracted drawdown from PC1+PC3 was related to the excess pore-water pressure relaxation process, that from PC2+PC5+PC6+PC7 and high-frequency wavelet de-noised detail cD2 related to the earth tidal fluctuation effect, and that from PC4+PC9 and cD3 related to the barometric effect. According to the Riemann integral and an objective function value duration curve, calculated occurrence probability from the stochastic optimization for SC2, the storage coefficient was reduced from pre-seismic pumping test value 0.00107, post-seismic 27th hour evolving value 0.000826 to post-seismic pumping test value 0.000578 in 2004, and the transmissivity increased from pre-seismic test value 92.4 m2/h, post-seismic 27th hour evolving value 98.6 m2/h to post-seismic test value 147.6 m2/h. The results demonstrate that the SC2 and GH3 zones suffer from crustal compression and the permeability was increased to dissipate excess pore-water pressure and effective stress.

scholarly journals Dynamic Behavior of Quay Walls According to N-values of Backfill and Amplitude of Seismic Accelerations

2021 ◽  
Vol 21 (1) ◽  
pp. 207-217
Author(s):  
Seong-Kyu Yun ◽  
Seungjong Kim ◽  
Jiseong Kim ◽  
Gichun Kang
Keyword(s):  
Pore Water ◽  
Effective Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Wall Structure ◽  
Sand Soil ◽  
Excess Pore Water Pressure ◽  
Quay Wall ◽  
Seismic Accelerations ◽  
Excess Pore

Sand soil discharge, which seemed to be the liquefaction damage, was observed in the backfill of a quay wall structure during the Pohang earthquake in 2017. This discharge occurred because the bearing capacity decreased owing to the loss of effective stress, which was caused by the increase in the excess pore-water pressure with the dynamic loads from the earthquake. In this study, the effects of the variations in the N-value of the backfill of the quay structure and the seismic acceleration coefficient were investigated for increasing excess pore-water pressure and decreasing effective stress, owing to the dynamic load from earthquakes.

Stress–strain pattern–based criterion to assess cyclic shear resistance of soil from laboratory element tests

2016 ◽  
Vol 53 (9) ◽  
pp. 1460-1473 ◽  
Author(s):  
Dharma Wijewickreme ◽  
Achala Soysa
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Shear Stiffness ◽  
Large Strains ◽  
Fundamental Parameter ◽  
Stress Strain ◽  
Cyclic Shear ◽  
Excess Pore Water Pressure ◽  
Excess Pore

The cyclic shear response of soils is commonly examined using undrained (or constant-volume) laboratory element tests conducted using triaxial and direct simple shear (DSS) devices. The cyclic resistance ratio (CRR) from these tests is expressed in terms of the number of cycles of loading to reach unacceptable performance that is defined in terms of the attainment of a certain excess pore-water pressure and (or) strain level. While strain accumulation is generally commensurate with excess pore-water pressure, the definition of unacceptable performance in laboratory tests based purely on cyclic strain criteria is not robust. The shear stiffness is a more fundamental parameter in describing engineering performance than the excess pore-water pressure alone or shear strain alone; so far, no criterion has considered shear stiffness to determine CRR. Data from cyclic DSS tests indicate consistent differences inherent in the patterns between the stress–strain loops at initial and later stages of cyclic loading; instead of relatively “smooth” stress–strain loops in the initial parts of loading, nonsmooth changes in incremental stiffness showing “kinks” are notable in the stress–strain loops at large strains. The point of pattern change in a stress–strain loop provides a meaningful basis to determine the CRR (based on unacceptable performance) in cyclic shear tests.

Consolidation Theory for Composite Ground with Granular Columns Based on Different Calculation Models

2011 ◽  
Vol 261-263 ◽  
pp. 1534-1538
Author(s):  
Yu Guo Zhang ◽  
Ya Dong Bian ◽  
Kang He Xie
Keyword(s):  
Pore Water ◽  
Analytical Solutions ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Vertical Flow ◽  
Excess Pore Water Pressure ◽  
Consolidation Theory ◽  
Composite Ground ◽  
Granular Column ◽  
Excess Pore

The consolidation of the composite ground under non-uniformly distributed initial excess pore water pressure along depth was studied in two models which respectively considering both the radial and vertical flows in granular column and the vertical flow only in granular column, and the corresponding analytical solutions of the two models were presented and compared with each other. It shows that the distribution of initial excess pore water pressure has obvious influence on the consolidation of the composite ground with single drainage boundary, and the rate of consolidation considering the radial-vertical flow in granular column is faster than that considering the vertical flow only in granular column.

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