Investigation on the Effects of Freeze-Thaw Action on the Pore Water Pressure Variations of Soils

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Lianhai Zhang ◽  
Wei Ma ◽  
Chengsong Yang
Keyword(s):  
Pore Water ◽  
Soil Type ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Great Influence ◽  
Frozen Soil ◽  
Silty Clay ◽  
Freeze Thaw ◽  
Soil Microstructure ◽  
Thaw Cycle

Freeze-thaw action changes soil microstructure and thus has a great influence on physical and mechanical properties of soils, which is closely correlated to pore water pressure (PWP). Herein, the PWPs of sandy soil and silty clay were measured in laboratory during freeze-thaw cycles (FTC). Experimental results showed that PWP was influenced by temperature, freeze-thaw history (i.e., number of freeze-thaw cycle), soil type and others. The PWP experienced a periodical change as temperatures periodically changes during the FTC testing, the PWP decreased during freezing and increased during thawing. Soil type has a slight influence on the variation of PWP, both in character and extent. A theoretical analysis of PWP in frozen soil was given to explain the PWP changes. In addition, the PWP depression during freezing was a major driving force for water migration. The PWP variations are highly relevant to the changes in soil microstructure such as soil particle (grain size composition and mineral composition), pore structure, and particle arrangement, which will be the focus of further research.

scholarly journals Ageing deformation of tailings dams in seasonally frozen soil areas under freeze-thaw cycles

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Jiaxu Jin ◽  
Shiwang Li ◽  
Chenguang Song ◽  
Xinlei Zhang ◽  
Xiangfeng Lv
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Frozen Soil ◽  
Practical Significance ◽  
Permafrost Region ◽  
Tailings Dam ◽  
Freeze Thaw ◽  
Tailings Dams ◽  
Thaw Cycle

Abstract The freeze-thaw cycle is one of the important factors in inducing a dam-break in the permafrost region, so it is of great practical significance to study the mechanism of the failure deformation of tailings dams under freeze-thaw cycles. In this paper, the water-heat-force coupling model of a tailings dam considering frost-thaw damage is established, and the freeze-thaw cyclic ageing deformation of a tailings dam in a seasonally frozen soil area is studied. The correctness of the model is validated by numerical calculation. The research shows under the same water content, the compressive strength and modulus of deformation decrease with an increase in the number of freeze-thaw cycles, the cohesion and internal friction angle decrease, and the amplitude gradually decreases before becoming stable. In the process of cooling, the pore water pressure first increases and then decreases, and the pore water pressure first decreases and then increases during the heating process. The research results can provide a theoretical basis and reference values for the stability analysis of tailings dams in seasonally frozen soil areas.

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.

Theoretical prediction of rutting in flexible pavement subgrades

1992 ◽  
Vol 29 (5) ◽  
pp. 765-778 ◽  
Author(s):  
D. V. Ramsamooj ◽  
R. Piper
Keyword(s):  
Pore Water ◽  
Critical State ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Permanent Deformation ◽  
Flexible Pavement ◽  
Load Test ◽  
Model Parameters ◽  
Silty Clay ◽  
Rate Of Development

The theoretical model for predicting the cyclic response of soils is extended to handle the generation and dissipation of pore-water pressures and to predict the rutting of the subgrade of a flexible pavement. The model utilizes multiyield surfaces and the concepts of critical state mechanics to predict the permanent deformation of the subgrade under vehicular loading. The theoretical solution also considers the effects of the drainage characteristics of the subgrade soil on the rate of development of the permanent deformation. Experimental verification of the model concepts are presented for a drained cyclic load test on Ottawa sand and for undrained cyclic loading on Newfield clay using published experimental data. An illustrative example is given for the prediction of rutting in a silty clay subgrade. The model parameters for the silty clay are obtained from triaxial and consolidation tests. These parameters are then put into a computer program that determines the rut depth, pore-water pressure, and the ratio of the vertical deformation and the rut depth as functions of the number of vehicular loads for a flexible pavement for various conditions of drainage ranging from undrained to fully drained. The role of the coefficient of consolidation of the subgrade in controlling the rate of development of the rut depth is highlighted. Key words : critical state soil mechanics, multiyield surfaces, rutting, silty clay subgrade, drainage, vehicular loading.

scholarly journals Numerical Simulation of Seepage and Deformation in Excavation of a Deep Foundation Pit under Water-Rich Fractured Intrusive Rock

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Changfeng Yuan ◽  
Zhenhui Hu ◽  
Zhen Zhu ◽  
Zijin Yuan ◽  
Yanxiang Fan ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Water Inrush ◽  
Risk Level ◽  
Silty Clay ◽  
Deep Foundation ◽  
Foundation Pit ◽  
Deep Foundation Pit

Water is one of the major risk sources in the excavation of deep-large foundation pits in a water-rich area. The presence of intrusive broken diorite porphyrite in the stratum aggravates the risk level of deep foundation pits. Based on a geological survey report and design documents of parameter information, MIDAS/GTS software was used to perform the numerical simulation of an engineering example of a deep foundation pit project of ultradeep and water-rich intrusion into the broken rock station of subway line 4 in a city. The simulation results show the characteristics of seepage path evolution, seepage aggregation areas and points, and the effect of seepage on the deformation of a deep foundation pit during the whole construction of this deep foundation pit. The results show that with the precipitation-excavation of the deep foundation pit, the pore water pressure at the bottom of the foundation pit follows a distribution of three “concave” shapes. High-permeability pressure zones are found around the foundation pit, intruding broken diorite porphyrite zones, and middle coarse sand zones. With further excavation of the foundation pit, the seepage pressure in the middle part of the foundation pit gradually decreases, and the two “concave” distributions in the middle gradually merge together. After excavation to the bottom of the pit, the pore water pressure at the bottom is distributed in two asymmetrical “concave” shapes, and the maximum peak of pore water pressure is found at the intrusion of fractured porphyrites prone to water inrush. The four corners of the foundation pit are prone to form seepage accumulation zones; therefore, suffosion and piping zones are formed. The surface settlement caused by excavation is found to be the largest along the longitudinal axis of the deep foundation pit, whereas the largest deformation is found near the foundation pit side in the horizontal axis direction of the foundation pit. With the excavation of the deep foundation pit, the diaphragm wall converges to the foundation pit with the maximum deformation reaching about 25 mm. After the first precipitation-excavation of the deep foundation pit to the silty clay and the bottom of the pit with the largest uplift, with further precipitation-excavation of the deep foundation pit, the uplift at the bottom of the deep foundation pit changes only slightly.

scholarly journals Pore water pressure responses of saturated sand and clay under undrained cyclic shearing

2021 ◽  
Author(s):  
An ◽  
Hiroshi ◽  
Nhan ◽  
Nhan ◽  
Tien ◽  
...  
Keyword(s):  
Shear Strain ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Silty Clay ◽  
Shear Tests ◽  
Sand Liquefaction ◽  
Cyclic Shear ◽  
Wide Range ◽  
Number Of Cycles

In this study, changes in the pore water pressure were observed for saturated specimens of a loose fined-grain sand (Nam O sand) and a soft silty clay (Hue clay) subjected to undrained cyclic shearing with different testing conditions. The cyclic shear tests were run for relatively wide range of shear strain amplitude (g = 0.05%-2%), different cycle numbers (n = 10, 50, 150 and 200) and various shear directions (uni-direction and two-direction with phase difference of q = 0o, 45o and 90o). It is indicated from the experimental results that under the same cyclic shearing condition, the pore water pressure accumulation in Hue clay is at a slower rate, suggesting a higher cyclic shear resistance of Hue clay than that of Nam O sand. Liquefaction is reached easily in nominally 50% relative density specimens of Nam O sand when g ³ 0.4%, meanwhile soft specimen of Hue clay is not liquefied regardless of the cyclic shearing conditions used in this study. The threshold number of cycles for the pore water pressure generation generally decreases with g meanwhile, the threshold cumulative shear strain for such a property mostly approaches 0.1%. In addition, by using this new strain path parameter, it becomes more advantageous when evaluating the pore water pressure accumulation in Nam O sand and Hue clay subjected to undrained uni-directional and two-directional cyclic shears.

Variation behavior of pore-water pressure in warm frozen soil under load and its relation to deformation

2018 ◽  
Vol 15 (3) ◽  
pp. 603-614 ◽  
Author(s):  
Hu Zhang ◽  
Jianming Zhang ◽  
Ze Zhang ◽  
Mingyi Zhang ◽  
Wei Cao
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Frozen Soil

Test Study of Pore Water Pressure during Dynamic Compaction at the Subgrade of Highway in the Yellow River Flood Area

2011 ◽  
Vol 374-377 ◽  
pp. 436-439
Author(s):  
Kai Yao ◽  
Zhan Yong Yao ◽  
Xiu Guang Song ◽  
Qing Sen Shang
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Yellow River ◽  
Water Pressure ◽  
Dynamic Compaction ◽  
The Yellow River ◽  
Silty Clay ◽  
Excess Pore Water Pressure ◽  
River Flood ◽  
Excess Pore

The Yellow River flood area mainly consisted of silt and silty clay. Water level observing holes and pore water pressure gauges were embedded in the test section. The observation results showed that: The pore water pressure of 3m and 5m grew slowly at the beginning. With the increase of ramming strike and the total ramming strike energy, the fourth hit pore water pressure mutated and then grew slowly. The pore water pressure of 7m and 9m grew slowly all the time. Because of the well point dewatering, the excess pore water pressure dissipated very soon. 70~75% of the excess pore water pressure of the first pass dissipated 3 hours after ramming strike, then the excess pore water pressure dissipated slowly. The excess pore water pressure of 3m and 5m grew significantly, so the effective reinforcing depth of dynamic compaction was 5m.

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