The Effect of Sampling on the Undrained Soil Properties of a Leda Soil

1971 ◽  
Vol 8 (4) ◽  
pp. 546-557 ◽  
Author(s):  
Gerald P. Raymond ◽  
David L. Townsend ◽  
Miroslav J Lojkasek
Keyword(s):  
Sampling Method ◽  
Sampling Methods ◽  
Axial Stress ◽  
Pressure Coefficient ◽  
Confining Pressure ◽  
Stress Difference ◽  
Consolidation Pressure ◽  
Failure Index ◽  
Confining Pressures ◽  
Leda Clay

The comparison of consolidated undrained triaxial results on sensitive Leda clay sampled by six different sampling methods is presented. The results indicate that the failure index, represented by the axial stress difference as a fraction of the axial failure stress difference against strain plots, are widely different at very low consolidation pressures, but are similar and approximate to the results from block samples as the consolidation pressure is increased. The pore pressure coefficient A appears to be independent of the sampling method and remains remarkably consistent throughout any test (up to failure) except where the confining pressure is very low or above the preconsolidation pressure.Routine commercial sampling methods (including laboratory preparation) using 50-mm diameter samples were found to partially destroy the cementation bonds, causing a decrease in strength at low confining pressures and an unsafe increase in strength at medium confining pressures. This trend is decreased by better sampling.

scholarly journals The meso-fracturing mechanism of marble under unloading confining pressure paths and constant axial stress

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Linna Sun ◽  
Liming Zhang ◽  
Yu Cong ◽  
Yaduo Song ◽  
Keqiang He
Keyword(s):  
Shear Failure ◽  
Axial Stress ◽  
Confining Pressure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Confining Pressures ◽  
Tension Cracks ◽  
Trial And Error Method ◽  
Unloading Confining Pressure ◽  
Fracturing Mechanism

AbstractFailure tests on marble during unloading confining-pressure under constant axial stress and simulations with the particle flow code were performed. The influence mechanism of the unloading rate of the confining pressure, initial unloading stress, and confining pressure on the failure characteristics of, and crack propagation in, marble was studied. By using the trial-and-error method, the conversion relationship between the unloading rates of confining pressures in laboratory tests and numerical simulations was ascertained. Micro-cracks formed in the unloading process of confining pressure are dominated by tension cracks, accompanied by shear cracks. The propagation of shear cracks lags that of tension cracks. As the confining pressure is increased, more cracks occur upon failure of the samples. The proportion of shear cracks increases while that of tension cracks decreases. The failure mode of samples undergoes a transition from shear-dominated failure to conjugated shear failure.

Prefabricated Structures Surface Marble Rheological Tests and Constitutive Model Analysis

2014 ◽  
Vol 501-504 ◽  
pp. 419-425
Author(s):  
Qing Xu ◽  
Jiang Da He ◽  
Hong Qiang Xie ◽  
Ming Li Xiao ◽  
Jian Feng Liu
Keyword(s):  
Mechanical Properties ◽  
Rheological Properties ◽  
Flow Rate ◽  
Axial Stress ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Rheological Parameters ◽  
Structural Plane ◽  
High Confining Pressure ◽  
Confining Pressures

The mechanical properties of intact rock and rock containing structural plane are very different. From the diversion tunnel of Jinping deep rock site to retrieve the complete block of marble, after a high confining pressure triaxial compression simulation tectonic movements, the formation of structural plane, it represents the mechanical properties of the original rock. On the surface of the marble structure containing triaxial compression creep tests, the results showed: at low confining pressure, the weak marble surface as micro-damage accumulation, the emergence of non-uniform partial destruction, while at high confining pressure, creep curve better continuity and integrity; different confining pressures, marble initial rheology and stability both appear rheological phase, accelerated phase rheological obvious; different confining pressures, the same stage of the axial stress steady flow rate compared with the confining pressure increases, the axial steady state flow rate becomes smaller; marble under test showed the rheological properties, the use of Nishihara model can better demonstrate the rheological properties and determine the rheological parameters for other practical engineering reference.

scholarly journals Dilatancy behaviour and permeability evolution of sandstone subjected to initial confining pressures and unloading rates

2021 ◽  
Vol 8 (1) ◽  
pp. 201792
Author(s):  
Honggang Zhao ◽  
Chao Liu ◽  
Gun Huang
Keyword(s):  
Mechanical Response ◽  
Axial Stress ◽  
Deformation Behaviour ◽  
Crack Density ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Permeability Evolution ◽  
Confining Pressures ◽  
Sandstone Permeability ◽  
Shear Dilatancy

Mechanical response, deformation behaviour and permeability evolution of surrounding rock under unloading conditions are of significant importance in rock engineering activities. In this research, triaxial experiments of sandstone subjected to different initial confining pressures and unloading rates under fixed axial stress were conducted. The results showed that sandstones experienced shear dilatancy before failure. However, the dilatancy factor did not decrease with increasing confining pressure, i.e. the dilatancy behaviour was not suppressed, which contradicted the phenomenon under increasing axial stress. The crack density also increased with increasing initial confining pressure. Furthermore, the normalized permeability was positively correlated with unloading rates. The sandstone permeability was closely related to the shear dilatancy behaviour. In the accelerated dilatancy stage, the relationship between normalized permeability and volumetric strain was linear at low unloading rates and nonlinear at high unloading rates. The linear/nonlinear relationship between them can directly affect the temporality of respective mutation, so as to guide the prevention of geological disasters at different excavations rates.

scholarly journals Surface microstructures developed on polished quartz crystals embedded in wet quartz sand compacted under hydrothermal conditions

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Peter M. Schutjens ◽  
Christopher J. Spiers ◽  
André Rik Niemeijer
Keyword(s):  
Quartz Sand ◽  
Axial Stress ◽  
Dissolution Kinetics ◽  
Confining Pressure ◽  
Pressure Solution ◽  
Hydrothermal Conditions ◽  
Quartz Crystals ◽  
Surface Microstructures ◽  
Quartz Aggregates ◽  
Intergranular Pressure

AbstractIntergranular pressure solution plays a key role as a deformation mechanism during diagenesis and in fault sealing and healing. Here, we present microstructural observations following experiments conducted on quartz aggregates under conditions known to favor pressure solution. We conducted two long term experiments in which a quartz crystal with polished faces of known crystallographic orientation was embedded in a matrix of randomly oriented quartz sand grains. For about two months an effective axial stress of 15 MPa was applied in one experiment, and an effective confining pressure of 28 MPa in the second. Loading occurred at 350 °C in the presence of a silica-saturated aqueous solution. In the first experiment, quartz sand grains in contact with polished quartz prism ($$\overline10{1 }0$$ 1 ¯ 010 ) faces became ubiquitously truncated against these faces, without indenting or pitting them. By contrast, numerous sand-grain-shaped pits formed in polished pyramidal ($$17\overline{6 }3$$ 17 6 ¯ 3 ) and ($$\overline{4 }134$$ 4 ¯ 134 ) crystal faces in the second experiment. In addition, four-leaved and (in some cases) three-leafed clover-shaped zones of precipitation formed on these prism faces, in a consistent orientation and pattern around individual pits. The microstructures observed in both experiments were interpreted as evidence for the operation of intergranular pressure solution. The dependence of the observed indentation/truncation microstructures on crystal face orientation can be explained by crystallographic control of stress-induced quartz dissolution kinetics, in line with previously published experimental and petrographic data, or possibly by an effect of contact orientation on the stress-induced driving force for pressure solution. This should be investigated in future experiments, providing data and microstructures which enable further mechanism-based analysis of deformation by pressure solution and the effect of crystallographic control on its kinetics in quartz-rich sands and sandstones.

Design Research of Steel Pipe Combination of Angle Steel Tower of XiYue 220kV Cross Section

2013 ◽  
Vol 470 ◽  
pp. 408-411 ◽  
Author(s):  
Yan Zhong Ju ◽  
Xiao Xu Fu ◽  
Neng Xian Zeng
Keyword(s):  
Finite Element Analysis ◽  
Cross Section ◽  
Design Research ◽  
Axial Stress ◽  
Steel Pipe ◽  
Stress Difference ◽  
Analysis Software ◽  
Element Analysis ◽  
The Finite Element Analysis ◽  
Angle Steel

Given the path situation of Xiyue substation 220kV four outlets project crossing Shunde waterway section,this article applies of Dao Heng tower full stress analysis software and the finite element analysis software ANSYS to two steel pipe combination of angle steel towers to carry on design research,contrast axial stress of two kinds of software,analyse the reasons of axial stress difference.

Mechanical behaviour of powders using a medium pressure flexible boundary cubical triaxial tester

2003 ◽  
Vol 217 (3) ◽  
pp. 233-241 ◽  
Author(s):  
F Li ◽  
V M Puri
Keyword(s):  
Shear Modulus ◽  
Mechanical Behaviour ◽  
Triaxial Compression ◽  
Three Dimensional ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Alumina Powder ◽  
Medium Pressure ◽  
Mean Pressure ◽  
Confining Pressures

A medium pressure (<21 MPa) flexible boundary cubical triaxial tester was designed to measure the true three-dimensional response of powders. In this study, compression behaviour and strength of a microcrystalline cellulose powder (Avicel® PH102), a spray-dried alumina powder (A16SG), and a fluid-bed-granulated silicon nitride based powder (KY3500) were measured. To characterize the mechanical behaviour, three types of triaxial stress paths, that is, the hydrostatic triaxial compression (HTC), the conventional triaxial compression (CTC), and the constant mean pressure triaxial compression (CMPTC) tests were performed. The HTC test measured the volumetric response of the test powders under isostatic pressure from 0 to 13.79MPa, during which the three powders underwent a maximum volumetric strain of 40.8 per cent for Avicel® PH102, 30.5 per cent for A16SG, and 33.0 per cent for KY3500. The bulk modulus values increased 6.4-fold from 57 to 367MPa for Avicel® PH102, 3.7-fold from 174 to 637 MPa for A16SG, and 8.1-fold from 74 to 597MPa for KY3500, when the isotropic stress increased from 0.69 to 13.79 MPa. The CTC and CMPTC tests measured the shear response of the three powders. From 0.035 to 3.45MPa confining pressure, the shear modulus increased 28.7-fold from 1.6 to 45.9MPa for Avicel® PH102, 35-fold from 1.7 to 60.5MPa for A16SG, and 28.5-fold from 1.5 to 42.8MPa for KY3500. In addition, the failure stresses of the three powders increased from 0.129 to 4.41 MPa for Avicel® PH102, 0.082 to 3.62 MPa for A16SG, and 0.090 to 4.66MPa for KY3500, respectively, when consolidation pressure increased from 0.035 to 3.45MPa. In addition, the shear modulus and failure stress values determined from the CTC test at 2.07, 2.76, and 3.45MPa confining pressures are consistently greater than those from the CMPTC test at the same constant mean pressures. This observation demonstrates the influence of stress paths on material properties. The CTT is a useful tool for characterizing the three-dimensional response of powders and powder mixtures.

scholarly journals Research on Microscopic Evolution Laws of Sandstone Deformation and Failure Based on the Particle Discrete Element Method

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Zhiwei Cai ◽  
Tongqing Wu ◽  
Jian Lu ◽  
Yue Wu ◽  
Nianchun Xu
Keyword(s):  
Shear Crack ◽  
Rock Fracture ◽  
Confining Pressure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Deformation And Failure ◽  
Fracture Development ◽  
Confining Pressures ◽  
The Law ◽  
Microcrack Growth

The fracture of sandstone is closely related to the condition of internal microcracks and the fabric of micrograin. The macroscopic mechanical property depends on its microscopic structures. However, it is difficult to obtain the law of the microcrack growth under loading by experiments. A series of microscopic sandstone models were established with particle flow code 3D (PFC3D) and based on the triaxial experiment results on sandstones. The experimental and numerical simulations of natural and saturated sandstones under different confining pressures were implemented. We analyzed the evolution of rock deformation and the rock fracture development from a microscopic view. Results show that although the sandstones are under different confining pressures, the law of microcrack growth is the same. That is, the number of the microcracks increases slowly in the initial stage and then increases exponentially. The number of shear cracks is more than the tensile cracks, and the proportion of the shear cracks increases with the increase of confining pressure. The cracking strength of natural and saturated sandstones is 26% and 27% of the peak strength, respectively. Under low confining pressure, the total number of cracks in the saturated sample is 20% more than that of the natural sample and the strongly scattered chain is barely seen. With the increase of the confining pressure, the effect of water on the total number of cracks is reduced and the distribution of the strong chain is even more uniform. In other words, it is the confining pressure that mainly affects the distribution of the force chain, irrespective of the state of the rock, natural or saturated. The research results reveal that the control mechanism of shear crack friction under the different stress states of a rock slope in the reservoir area provides a basis for evaluating the stability of rock mass and predicting the occurrence of geological disasters.

Uplift behaviour of tapered piles established from model tests

2000 ◽  
Vol 37 (1) ◽  
pp. 56-74 ◽  
Author(s):  
M Hesham El Naggar ◽  
Jin Qi Wei
Keyword(s):  
Load Transfer ◽  
Compressive Loading ◽  
Compressive Load ◽  
Tensile Load ◽  
Confining Pressure ◽  
Cohesionless Soil ◽  
Uplift Capacity ◽  
Experimental Modelling ◽  
Confining Pressures ◽  
Load Tests

Tapered piles have a substantial advantage with regard to their load-carrying capacity in the downward frictional mode. The uplift performance of tapered piles, however, has not been fully understood. This paper describes the results of an experimental investigation into the characteristics of the uplift performance of tapered piles. Three instrumented steel piles with different degrees of taper were installed in cohesionless soil and subjected to compressive and tensile load tests. The soil was contained in a steel soil chamber and pressurized using an air bladder to facilitate modelling the confining pressures pertinent to larger embedment depths. The results of this study indicated that the pile axial uplift capacity increased with an increase in the confining pressure for all piles examined in this study. The ratios of uplift to compressive load for tapered piles were less than those for straight piles of the same length and average embedded diameter. The uplift capacity of tapered piles was found to be comparable to that of straight-sided wall piles at higher confining pressure values, suggesting that the performance of actual tapered piles (with greater length) would be comparable to that of straight-sided wall piles. Also, the results indicated that residual stresses developed during the compressive loading phase and their effect were more significant on the initial uplift capacity of piles, and this effect was more pronounced for tapered piles in medium-dense sand.Key words: tapered piles, uplift, axial response, load transfer, experimental modelling.

Non-Probabilistic Sampling in Quantitative Clinical Research

2022 ◽  
Vol 7 (1) ◽  
pp. 0-0
Keyword(s):  
Best Practices ◽  
Quantitative Research ◽  
Sampling Method ◽  
Sampling Methods ◽  
Early Career ◽  
Probability Sampling ◽  
Probabilistic Sampling ◽  
Quantitative Studies ◽  
Health Studies ◽  
Probabilistic Sample

Quantitative researchers need a probabilistic sample to generalise their findings, but research constraints often compel them to use non-probabilistic samples. The use of non-probability sampling methods in quantitative studies has therefore become a norm. Interestingly, even studies published in top-quality journals compromise best practices that the use of non-probabilistic samples requires. Based on a thorough review of relevant studies, we developed a typology of non-probability sampling methods used in quantitative health studies. An attempt was made to discuss the limit of inference under each type of non-probability sampling method. Non-probability sampling in quantitative research was also delineated as a way to maximise response rate. This study is expected to guide students and early career epidemiologists to understand how to apply non-probabilistic sampling methods in quantitative approaches and plausibly document or report their chosen methods.

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