Influence of Soil Fabrics and Stress State on the Undrained Instability of Overconsolidated Binary Granular Assemblies

AbstractThe instability of saturated granular soils in field conditions generates drastic collapse in terms of runoff deformation because of its failing to sustain naturally applied loading conditions such as earthquakes, wave actions and vibrations. The objective of this laboratory investigation is to study the effects of the depositional methods, overconsolidation ratio (OCR) and confining pressure on the undrained instability shear strength of medium dense (Dr = 52%) sand–silt mixtures under static loading conditions. For this purpose, a series of undrained monotonic triaxial tests were carried out on reconstituted saturated silty sand samples with fines content ranging from 0% to 40%. Three confining pressures were used (P’c = 100, 200 and 300 kPa) in this research. The sand–silt mixture samples were prepared using two depositional methods, dry funnel pluviation (DFP) and wet deposition (WD), and subjected to two OCRs (1 and 2). The obtained instability lines and friction angles indicate that the funnel pluviated samples exhibit strain hardening compared to the wet deposited samples and that normally consolidated and overconsolidated wet deposited clean sandy samples were very sensitive to static liquefaction. The test results also indicate that the instability friction angle increases with the increase in the OCR expressing soil dilative character tendency increase. The instability friction angle decreases with the increase in the fines content for DFP and the inverse tendency was observed in the case of WD.

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Experimental study on the thermal damage characteristics of cement stone

Thermal Science ◽

10.2298/tsci200618317x ◽

2020 ◽

pp. 317-317

Author(s):

Feng Xu ◽

Bowen Qian ◽

Ling Tan ◽

Jianqiang Xu ◽

Shengchuan Tang ◽

...

Keyword(s):

Strain Curve ◽

Horizontal Wells ◽

Friction Angle ◽

Confining Pressure ◽

Triaxial Tests ◽

Cement Stone ◽

Different Temperatures ◽

Confining Pressures ◽

Southwest Region ◽

Sealing Failure

Aiming at the problem of cement ring sealing failure during deep high-temperature shale gas exploitation, comprehensively considering the influence of the characteristics of multi-cluster fracturing of multiple horizontal wells and formation temperature, the cementing cement the southwest region is taken as the research object. After exposure to different temperatures (95?C and 135?C) and for different times (5, 10 and 20 times), axial and triaxial tests with different confining pressures (0, 5 MPa, 15 MPa and 30 MPa) were carried out. The research shows that: (1) the stress-strain curve of cement stone after heat treatment can be divided into four stages: compaction, elastic, yield and post-peak stage. As the confining pressure increases, the compaction phase disappears, the yield phase increases, and we see the transition from brittle to ideal plasticity after the peak; (2) as the temperature and number of thermal cycles increase, the cohesive force decreases significantly, and the internal friction angle shows a slight increase. The elastic modulus and the peak strength decreased.

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Study on some fundamental factors affecting the static liquefaction of sand

Journal of Mining and Earth Sciences ◽

10.46326/jmes.htcs2020.06 ◽

2020 ◽

Vol 61 (HTCS6) ◽

pp. 40-47

Author(s):

Kien Trung Nguyen ◽

Thang Kim Nguyen ◽

Ha Quang Ta ◽

Huy Quang Dang ◽

Keyword(s):

Significant Influence ◽

Confining Pressure ◽

Triaxial Tests ◽

Liquefaction Resistance ◽

Factors Affecting ◽

Static Liquefaction ◽

The World ◽

Long Time ◽

Confining Pressures ◽

Undrained Conditions

Static liquefaction of soil is a hazard that has caused a lot of damage to humans. Therefore, this phenomenon has been studied for a long time over the world, nevertheless, research on this issue in Vietnam is still limited. This paper presents the results of several triaxial tests under undrained conditions to evaluate the influence of some fundamental factors on the static liquefaction of Fontainebleau sand. The results show that the relative density and the confining pressure have a significant influence on the static liquefaction of the sand. When the density of the sand increases, the liquefaction resistance of the sand increases, until a certain limit, the sand changes from liquefaction behavior to dilatancybehavior with a decrease in pore pressure and an increase in mean effective stress. When the test is carried out at different confining pressures, the greater the confining pressure, the higher the liquefaction resistance.

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Experimental Study of Stress-Seepage Coupling Properties of Sandstone under Different Loading Paths

Geofluids ◽

10.1155/2021/4955017 ◽

2021 ◽

Vol 2021 ◽

pp. 1-21

Author(s):

Xi Chen ◽

Wei Wang ◽

Yajun Cao ◽

Qizhi Zhu ◽

Weiya Xu ◽

...

Keyword(s):

Elastic Modulus ◽

Pore Pressure ◽

Complex Loading ◽

Friction Angle ◽

Confining Pressure ◽

Triaxial Tests ◽

Compression Tests ◽

Biot Coefficient ◽

Cyclic Loading And Unloading ◽

Loading And Unloading

The study on hydromechanical coupling properties of rocks is of great importance for rock engineering. It is closely related to the stability analysis of structures in rocks under seepage condition. In this study, a series of conventional triaxial tests under drained condition and hydrostatic compression tests under drained or undrained condition on sandstones were conducted. Moreover, complex cyclic loading and unloading tests were also carried out. Based on the experimental results, the following conclusions were obtained. For conventional triaxial tests, the elastic modulus, peak strength, crack initiation stress, and expansion stress increase with increased confining pressure. Pore pressure weakened the effect of the confining pressure under drained condition, which led to a decline in rock mechanical properties. It appeared that cohesion was more sensitive to pore pressure than to the internal friction angle. For complex loading and unloading cyclic tests, in deviatoric stress loading and unloading cycles, elastic modulus increased obviously in first loading stage and increased slowly in next stages. In confining pressure loading and unloading cycles, the Biot coefficient decreased first and then increased, which indicates that damage has a great impact on the Biot coefficient.

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Experimental Study on Mechanical Property of Thermo-Mechanical and Hydro-Mechanical Coupling Condition for a Sandstone

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.326-328.1797 ◽

2006 ◽

Vol 326-328 ◽

pp. 1797-1800 ◽

Cited By ~ 1

Author(s):

Qing Chun Zhou ◽

Hai Bo Li ◽

Chun He Yang ◽

Chao Wen Luo

Keyword(s):

Pore Pressure ◽

Deformation Modulus ◽

Confining Pressure ◽

Triaxial Tests ◽

Underground Engineering ◽

Coupling Condition ◽

West China ◽

Mechanical Coupling ◽

North Water ◽

Confining Pressures

The mechanical properties of rock under high temperature, high geostress and high pore pressure are the basic and important information to assess the safety of underground engineering in west China. Based on the environmental conditions of the west route of south-to-north water transfer project in west China, a series of triaxial tests at confining pressures (0 to 60MPa) and temperatures (25°C to 70°C) as well as pore pressure (0 to 10MPa) have been conducted for a sandstone. It is reported that under the temperatures varying from 25°C to 70°C, the strength of the rock increases with the increment of confining pressure, while the deformation modulus of the rock doesn’t change distinctly with the increment of confining pressures. It is also indicated under the temperatures condition in the experiments, when the confining pressure is lower than 40MPa, the strength of the rock increases with the increment of temperature, whereas when the confining pressure is higher than 40MPa, the strength of rock tend to decrease with increment of temperature. It is further shown that the strength decreases with increasing pore pressure, and the decreasing rates tend to decrease with the increment of confining pressures.

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Physical and Mechanical Properties of a Bulk Lightweight Concrete with Expanded Polystyrene (EPS) Beads and Soft Marine Clay

Materials ◽

10.3390/ma12101662 ◽

2019 ◽

Vol 12 (10) ◽

pp. 1662 ◽

Cited By ~ 4

Author(s):

Jianguo Wang ◽

Bowen Hu ◽

Jia Hwei Soon

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Cement Content ◽

Mass Density ◽

Physical And Mechanical Properties ◽

Confining Pressure ◽

Expanded Polystyrene ◽

Triaxial Tests ◽

Filling Material ◽

Confining Pressures

The variation of physical and mechanical properties of the lightweight bulk filling material with cement and expanded polystyrene (EPS) beads contents under different confining pressures is important to construction and geotechnical applications. In this study, a lightweight bulk filling material was firstly fabricated with Singapore marine clay, ordinary Portland cement and EPS. Then, the influences of EPS beads content, cement content, curing time and confining pressure on the mass density, stress–strain behavior and compressive strength of this lightweight bulk filling material were investigated by unconsolidated and undrained (UU) triaxial tests. In these tests, the mass ratios of EPS beads to dry clay (E/S) were 0%, 0.5%, 1%, 2%, and 4% and the mass ratios of cement to dry clay (C/S) were 10% and 15%. Thirdly, a series of UU triaxial tests were performed at a confining pressure of 0 kPa, 50 kPa, 100 kPa, and 150 kPa after three curing days, seven curing days, and 28 curing days. The results show that the mass density of this lightweight bulk filling material was mainly controlled by the E/S ratio. Its mass density decreased by 55.6% for the C/S ratio 10% and 54.9% for the C/S ratio 15% when the E/S ratio increased from 0% to 4% after three curing days. Shear failure more easily occurred in the specimens with higher cement content and lower confining pressure. The relationships between compressive strength and mass density or failure strain could be quantified by the power function. Increasing cement content and reducing EPS beads content will increase mass density and compressive strength of this lightweight bulk filling material. The compressive strength with curing time can be expressed by a logarithmic function with fitting correlation coefficient ranging from 0.83 to 0.97 for five confining pressures. These empirical formulae will be useful for the estimation of physical and mechanical properties of lightweight concretes in engineering application.

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Internal Erosion Failure of Uniform Sands under Confinement and Constricted Seepage Exit

Water ◽

10.3390/w12092417 ◽

2020 ◽

Vol 12 (9) ◽

pp. 2417

Author(s):

Kuang-Tsung Chang ◽

Kevin Zeh-Zon Lee ◽

Han-Yu Wu

Keyword(s):

Particle Size ◽

Critical Velocity ◽

Friction Angle ◽

Confining Pressure ◽

Internal Erosion ◽

Seepage Water ◽

Field Investigations ◽

Mechanical Models ◽

Confining Pressures ◽

Experimental Findings

Seepage water may move soil particles and cause internal erosion of soils, leading to sinkholes and the collapse of embankments and slopes. To account for the effects of confinement and constricted seepage exit, a test apparatus was developed to study the internal erosion of granular soils under various confining pressures, particle sizes, and sizes of the seepage exit opening. As indicated in the literature, the behavior of internal erosion has been largely studied by laboratory experiments and field investigations, and mechanical models that help describe the failure mechanism of internal erosion are less prevalent. A hydro-mechanical model that incorporates the fluid drag force and the shear strength of soil was therefore developed for quantifying the internal erosion experiments conducted in this study. The experimental results showed that the greater the confining pressure or the particle size, the greater the critical velocity; the greater the seepage exit opening, the smaller the critical velocity. The critical velocity predicted by the proposed hydro-mechanic model compares reasonably well with the experimental data. In addition to the confining pressure, particle size, and size of the seepage exit opening, the proposed model also showed that the friction angle and porosity of the soil are factors influencing the critical velocity, which is consistent with the experimental findings of this study.

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Laboratory study on subgrade fluidization under undrained cyclic triaxial loading

Canadian Geotechnical Journal ◽

10.1139/cgj-2019-0350 ◽

2020 ◽

Vol 57 (11) ◽

pp. 1767-1779 ◽

Cited By ~ 4

Author(s):

Buddhima Indraratna ◽

Mandeep Singh ◽

Thanh Trung Nguyen ◽

Serge Leroueil ◽

Aruni Abeywickrama ◽

...

Keyword(s):

Stress Ratio ◽

Confining Pressure ◽

Cyclic Stress ◽

Triaxial Tests ◽

Loading Conditions ◽

Cyclic Triaxial ◽

Cyclic Stress Ratio ◽

Upward Migration ◽

Efficient Operation ◽

Mud Pumping

A long-term issue that has hampered the efficient operation of heavy-haul tracks is the migration of fluidized fines from the shallow soft subgrade to the overlying ballast, i.e., mud pumping. This paper presents a series of undrained cyclic triaxial tests where realistic cyclic loading conditions were simulated at low confining pressure that is typical of shallow subgrade beneath a ballast track. Subgrade soil specimens with a low-plasticity index collected from a field site with recent history of mud pumping were tested at frequencies from 1.0 to 5.0 Hz and a cyclic stress ratio (CSR) from 0.1 to 1.0. The experimental results indicate that under adverse loading conditions of critical cyclic stress ratio (CSRc) and frequency, there is upward migration of moisture and the finest particles towards the specimen top and this causes the uppermost part of the soil specimen to soften and fluidize. Conversely, a smaller value of CSR tends to maintain stability of the specimen despite the increasing number of loading cycles. It is noteworthy that for any given combination of CSR and frequency, the relative compaction has a significant influence on the cyclic behaviour of the soil and its potential for fluidization.

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The Choice of Basic Pillar Design Theory for Locked Sand Condition

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.256-259.354 ◽

2012 ◽

Vol 256-259 ◽

pp. 354-357

Author(s):

Zi Wei Ding ◽

Amirhossein Bagherieh ◽

Rui Min Feng ◽

Xing Xing Wen

Keyword(s):

Design Theory ◽

Design Method ◽

Friction Angle ◽

Confining Pressure ◽

Triaxial Tests ◽

Pillar Design ◽

Design Theories ◽

Locked Sand ◽

Unconfined Strength ◽

Very High

Because of unique properties of locked sand (very high friction angle and very low cohesion), a new pillar design method based on present basic pillar design theories must be developed. Wilson theory puts its focus on confining pressure, which is related to friction angle and cohesion. Triaxial tests results show that locked sand at Pattison mine has an average friction angle of 57°, which means the strength of the material increases rapidly with the confining pressure, and average cohesion of 2.6 MPa. Results show that choosing Wilson theory as basic pillar design theory not only considers the high friction angle of locked sand, but also minimizes the effects of Wilson’s hypothesis of neglecting the unconfined strength.

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Experimental Study of Rockfill Particle Breakage

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.900.445 ◽

2014 ◽

Vol 900 ◽

pp. 445-448

Author(s):

Zhi Hua Xu ◽

Da Wei Sun

Keyword(s):

Internal Friction ◽

Large Scale ◽

Reference Value ◽

Friction Angle ◽

Confining Pressure ◽

Particle Breakage ◽

Internal Friction Angle ◽

Dam Construction ◽

Confining Pressures ◽

The Relationship

As the high concrete faced rockfill dams construction, grain breakage gradually become the factors that influence the high dam construction which can not be ignored. This text based on the master of rockfill of shuibuya dam as the experimental material, getting and analyzing the particle breakage data under different confining pressure through the large-scale triaxial test, and the results show that the particle breakage index increases with the increase of confining pressures. The relationship between particle breakage index and confining pressure can be expressed by formula;Particle breakage increase leading to reduced internal friction angle and the shear strength of rockfill, and the author newly introduced two broken variable to describe the relationship which can be expressed by the formula between the particle breakage and internal friction angle, it has certain reference value for establishing constitutive model considering particle breakage.

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Investigation on the relationship between CT numbers and marble failure under different confining pressures

REVIEWS ON ADVANCED MATERIALS SCIENCE ◽

10.1515/rams-2021-0070 ◽

2021 ◽

Vol 60 (1) ◽

pp. 846-852

Author(s):

Yang Yan-Shuang ◽

Li Kai-Yue ◽

Zhou Hui ◽

Tian Hao-Yuan ◽

Cheng Wei ◽

...

Keyword(s):

Damage Mechanics ◽

Triaxial Compression ◽

Ct Scanning ◽

Confining Pressure ◽

Triaxial Tests ◽

Compression Tests ◽

Ct Number ◽

Confining Pressures ◽

Loading Tests ◽

Rock Specimens

Abstract Computed tomography (CT) scanning technology is helpful in investigating rock materials as it can demonstrate the micro structure of rock clearly. Conventional triaxial compression tests and the corresponding graded triaxial loading tests were carried out to investigate the complex failure mechanism of the marble at the Jinping Hydropower Station. After that CT-scanning tests were done on the loaded marble specimens. The test results show that (1) the CT numbers of the specimens have a certain statistical regularity, that is, the CT numbers of the specimens under different confining pressures satisfy the Weibull distribution, as the confining pressure increases, the mean values rise while variances decrease; (2) in the two groups of tests, the average CT numbers corresponding to the conventional triaxial tests are higher than those corresponding to the graded loading tests, but the CT number variances are lower than those of the graded loading tests; and (3) according to meso-damage mechanics, the damage variables of the rock specimens were established based on the definition of CT numbers. The calculation results show that the damage variables decrease with the increase in confining pressure, the damage variables of the rock specimens in the graded loading tests are higher than those in the conventional triaxial test, and the differences between the two loading tests have grown with the increase in confining pressure.

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