Comparison of two fine sands under torsional loading

2008 ◽  
Vol 45 (12) ◽  
pp. 1659-1672 ◽  
Author(s):  
V. N. Georgiannou ◽  
A. Tsomokos
Keyword(s):  
Phase Transformation ◽  
Cyclic Loading ◽  
Hollow Cylinder ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Strength Reduction ◽  
Monotonic Loading ◽  
Sudden Increase ◽  
Loading Conditions ◽  
Continuous Increase

In this paper the behaviour of two “standard research sands”, widely used for experimental purposes, is compared in a torsional hollow cylinder apparatus under monotonic and cyclic loading conditions. Both sands are fine and uniform with D50 = 0.22 and 0.29 mm, respectively. However, their response to undrained monotonic loading at similar void ratios is dramatically different, with the finer sand showing strength reduction after peak and the coarser sand showing continuous increase in strength with torsional shear. The difference in response is mainly attributed to grain angularity and to a lesser degree to their grading. The results of drained torsional hollow cylinder tests show initial contraction followed by dilation. The stress ratio at phase transformation is uniquely defined by both drained and undrained tests for each sand. Cyclic loading instability is manifested by a sudden increase in shear strain and excess pore-water pressure leading to initial liquefaction. The instability initiates across the instability line for the sand showing strength reduction and across the phase transformation line for the sand showing continuous increase in strength with shearing. Both lines are defined under monotonic loading conditions. The liquefaction, stiffness, and damping characteristics of the sands are given in this paper.

Determination of the Cyclic Properties of Silty Sands

2018 ◽  
pp. 416-445
Author(s):  
Eyyüb Karakan ◽  
Selim Altun
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Triaxial Tests ◽  
Loading Conditions ◽  
Systematic Testing ◽  
Geotechnical Problems ◽  
Insight Into

Liquefaction may be triggered by cyclic loading on saturated silty sands, which is responsible of severe geotechnical problems. Development of excess pore water pressure in soil results in a liquid-like behavior and may be the reason of unavoidable superstructural damage. In this study, in order to investigate the behavior of saturated silty sands exposed to cyclic loading under undrained conditions, a systematic testing program of stress-controlled cyclic triaxial tests was performed on specimens of different silt contents, under different loading conditions and environment. The effect of parameters such as silt content on the liquefaction behavior of specimens was studied. Pore water pressure and shear strain curves were obtained for the silty sands. Furthermore, the boundaries existing in the literature on sands are compared with the results current research, on silty sands. Conclusively, the outcomes of this study were useful to develop insight into the behavior of clean and silty sands under seismic loading conditions.

TIME TO THE END OF PRIMARY CONSOLIDATION (EOP) OF SOFT CLAYEY SOILS: CONCERNING THE EFFECT OF ATTERBERG’S LIMIT AND CYCLIC LOADING HISTORY

2019 ◽  
Vol 128 (2B) ◽  
pp. 29-41
Author(s):  
Trần Thanh Nhàn
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Clayey Soils ◽  
Loading History ◽  
Cyclic Shear ◽  
Wide Range ◽  
Primary Consolidation ◽  
Time Required

In order to observe the end of primary consolidation (EOP) of cohesive soils with and without subjecting to cyclic loading, reconstituted specimens of clayey soils at various Atterberg’s limits were used for oedometer test at different loading increments and undrained cyclic shear test followed by drainage with various cyclic shear directions and a wide range of shear strain amplitudes. The pore water pressure and settlement of the soils were measured with time and the time to EOP was then determined by different methods. It is shown from observed results that the time to EOP determined by 3-t method agrees well with the time required for full dissipation of the pore water pressure and being considerably larger than those determined by Log Time method. These observations were then further evaluated in connection with effects of the Atterberg’s limit and the cyclic loading history.

Type of Slope Failure Identified from Pore Water Pressure and Moisture Content Measurements

2015 ◽  
Vol 744-746 ◽  
pp. 690-694
Author(s):  
Muhammad Rehan Hakro ◽  
Indra Sati Hamonangan Harahap
Keyword(s):  
Moisture Content ◽  
Pore Pressure ◽  
Slope Failure ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Failure Process ◽  
Small Scale ◽  
Content Increase ◽  
Sudden Increase ◽  
Model Slope

Rainfall-induced landslides occur in many parts of the world and causing a lot of the damages. For effective prediction of rainfall-induced landslides the comprehensive understanding of the failure process is necessary. Under different soil and hydrological conditions experiments were conducted to investigate and clarify the mechanism of slope failure. The failure in model slope was induced by sprinkling the rainfall on slope composed of sandy soil in small flume. Series of tests were conducted in small scale flume to better understand the failure process in sandy slopes. The moisture content was measured with advanced Imko TDR (Time Domain Reflectrometry) moisture sensors in addition to measurements of pore pressure with piezometers. The moisture content increase rapidly to reach the maximum possible water content in case of higher intensity of rainfall, and higher intensity of the rainfall causes higher erosion as compared to smaller intensity of the rainfall. The controlling factor for rainfall-induced flowslides was density of the slope, rather than intensity of the rainfall and during the flowslide the sudden increase in pore pressure was observed. Higher pore pressure was observed at the toe of the slope as compared to upper part of the slope.

scholarly journals Mechanical response and pore pressure generation in granular filters subjected to uniaxial cyclic loading

2018 ◽  
Vol 55 (12) ◽  
pp. 1756-1768
Author(s):  
Jahanzaib Israr ◽  
Buddhima Indraratna
Keyword(s):  
Cyclic Loading ◽  
Pore Pressure ◽  
Pore Water ◽  
Mechanical Response ◽  
Pore Water Pressure ◽  
Axial Strain ◽  
Water Pressure ◽  
Internal Erosion ◽  
Excess Pore Water Pressure ◽  
Excess Pore

This paper presents results from a series of piping tests carried out on a selected range of granular filters under static and cyclic loading conditions. The mechanical response of filters subjected to cyclic loading could be characterized in three distinct phases; namely, (I) pre-shakedown, (II) post-shakedown, and (III) post-critical (i.e., the occurrence of internal erosion). All the permanent geomechanical changes such, as erosion, permeability variations, and axial strain developments, took place during phases I and III, while the specimen response remained purely elastic during phase II. The post-critical occurrence of erosion incurred significant settlement that may not be tolerable for high-speed railway substructures. The analysis revealed that a cyclic load would induce excess pore-water pressure, which, in corroboration with steady seepage forces and agitation due to dynamic loading, could then cause internal erosion of fines from the specimens. The resulting excess pore pressure is a direct function of the axial strain due to cyclic densification, as well as the loading frequency and reduction in permeability. A model based on strain energy is proposed to quantify the excess pore-water pressure, and subsequently validated using current and existing test results from published studies.

scholarly journals Evaluation of local friction and pore-water pressure evolution along instrumented probes in saturated clay for large numbers of cycles

2019 ◽  
Vol 56 (12) ◽  
pp. 1953-1967
Author(s):  
Rawaz Dlawar Muhammed ◽  
Jean Canou ◽  
Jean-Claude Dupla ◽  
Alain Tabbagh
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Static Friction ◽  
Good Picture ◽  
Friction Resistance ◽  
Saturated Clay ◽  
Tip Resistance ◽  
Number Of Cycles

To investigate local friction mobilization along piles subjected to cyclic axial loadings, a calibration chamber experiment is presented based on the implementation of instrumented probes in specimens of saturated clay. Typical results obtained with a piezo-probe are presented, allowing not only tip resistance and local friction to be measured, but also the local pore-water pressure developed on the probe shaft. In addition, specific piezometers installed in the clay specimen allow a good picture to be obtained of the pore-water pressure field around the probe during installation and loading. After installation of the probe, a succession of monotonic and cyclic displacement-controlled loading phases is applied. Upon displacement-controlled cyclic loading of the piezo-probe up to a very large number of cycles (105 cycles), an initial degradation of local friction is observed followed by a subsequent reinforcement, which continues until the end of the cyclic sequence. The friction evolution is related to the evolution of the pore-water pressure measured during cyclic loading. In particular, the influence of the cyclic loading sequence on the post-cyclic static friction resistance is evaluated. A comparison is finally made with the results obtained with another type of probe, showing a good consistency between both types of results.

Membrane filter properties and application of the filter to undrained cyclic triaxial test of unsaturated materials

2017 ◽  
Vol 54 (8) ◽  
pp. 1196-1202 ◽  
Author(s):  
Hailong Wang ◽  
Junichi Koseki ◽  
Tomoyoshi Nishimura ◽  
Yukika Miyashita
Keyword(s):  
Hydraulic Conductivity ◽  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Membrane Filter ◽  
Water Pressure ◽  
Characteristic Curve ◽  
Loading Frequency ◽  
Loading Test ◽  
Pressure Plate

Properties of the membrane filter recently introduced as an alternative to the ceramic disk are revealed through diffusion and hydraulic conductivity tests. It is shown that diffusion of air through the membrane filter is significantly affected by suction magnitude and that hydraulic conductivity of the membrane filter can easily be affected by the quality of water used in the test. The application of the membrane filter to the soil-water characteristic curve tests (SWCC tests) shows that similar SWCCs can be obtained by employing pressure plate apparatuses with either the ceramic disks or the membrane filter installed, and that repeatability of the SWCC by using the membrane filter pressure plate apparatus is reasonably good. The application of the membrane filter to the undrained cyclic loading test of unsaturated sandy materials shows that the response (the duration to measure the equilibrated pore-water pressure of unsaturated materials) of the membrane filter pedestal in a modified triaxial system may be as short as ∼2 s in certain test conditions, and fairly good pore-water pressure and air pressure measurements can be obtained during undrained cyclic loading with a loading frequency of 0.1 Hz.

J-R Fracture Toughness of Nuclear Piping Materials Under Excessive Seismic Loading Condition

2016 ◽  
Author(s):  
Jin Weon Kim ◽  
Myung Rak Choi ◽  
Sang Bong Lee ◽  
Yun Jae Kim
Keyword(s):  
Fracture Toughness ◽  
Cyclic Loading ◽  
Fracture Resistance ◽  
Cyclic Load ◽  
Fracture Behavior ◽  
Loading Rate ◽  
Seismic Loading ◽  
Monotonic Loading ◽  
Rate Effect ◽  
Loading Conditions

This study investigated the loading rate effect on the fracture resistance under cyclic loading conditions to clearly understand the fracture behavior of piping materials under excessive seismic conditions. J-R fracture toughness tests were conducted under monotonic and cyclic loading conditions at various displacement rates at room temperature (RT) and the operating temperature of nuclear power plants (NPPs), i.e., 316°C. SA508 Gr. 1a lo w-alloy steel (LAS) and SA312 TP316 stainless steel (SS) piping materials were used for the tests. The fracture resistance under a reversible cyclic load was considerably lower than that under monotonic load regardless of test temperature, material, and loading rate. Under both cyclic and monotonic loading conditions, the fracture behavior of SA312 TP316 SS was independent of the loading rate at both RT and 316°C. For SA508 Gr. 1a LAS, the loading rate effect on the fracture behavior was appreciable at 316°C under both cyclic and monotonic loading conditions. However, the loading rate effect diminished when the cyclic load ratio (R) was −1. Thus, it was recognized that the fracture behavior of piping materials, including seismic loading characteristics, can be evaluated when tested under a cyclic load of R = −1 at a quasi-static loading rate.

Pore-Pressure Accumulation and Soil Softening Around Pile Foundations for Offshore Wind Turbines

2012 ◽  
Author(s):  
Pablo Cuéllar ◽  
Matthias Baeßler ◽  
Werner Rücker
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Wind Turbines ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Large Diameter ◽  
Constitutive Law ◽  
Offshore Wind ◽  
External Loading ◽  
Offshore Wind Turbines

The foundation of offshore wind turbines usually involves the installation of large-diameter steel piles in the seabed, either in monopile or multi-pile configurations (jacket, tripod, etc…), which have to ensure a proper fixity of the turbine during its whole service life-time. However, such foundations raise several challenges and novel questions, partly due to the special characteristics of the offshore environment (for instance, the large numbers of load cycles from wind and waves and the possible influence of transient changes of pore water pressure around the pile) and aggravated by their large diameter, reduced slenderness and elevated ratio of lateral to vertical loads (see Fig. 1). This paper studies the effects of cyclic lateral loading on the offshore piles focusing on the possibility of a progressive accumulation of residual pore water pressure within the saturated embedding soil. As it will be shown, this can lead to significant changes of their behaviour under external loading, which can potentially compromise the foundation’s stability or serviceability. The paper will also analyse some singular effects of an irregular loading (e.g. cyclic loading with variable amplitude), in particular the so-called “order effects” and the phenomena arising during a realistic storm of moderate magnitude, and discuss their potential for transient damages to the foundation’s stiffness. All these phenomena, which can lead to a loss of serviceability of the structure, have been investigated by the authors by means of a coupled bi-phasic analytical model of the offshore foundation featuring a versatile constitutive law suitable for the soil. The constitutive model, in the frame of the theory of Generalized Plasticity, can reproduce some complex features of cyclic soil behaviour such as the tendency for a progressive densification under cyclic loading, which is responsible for the soil liquefaction phenomena in undrained conditions. Finally, some implications of these issues for the practical design of offshore monopiles will be discussed and some specific recommendations for the design procedures will be outlined.

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