Effective stress regime around a jacked steel pile during installation ageing and load testing in chalk

This paper reports experiments with 102 mm diameter closed-ended instrumented Imperial College piles (ICPs) jacked into low- to medium-density chalk at a well-characterized UK test site. The “ICP” instruments allowed the effective stress regime surrounding the pile shaft to be tracked during pile installation, equalization periods of up to 2.5 months, and load testing under static tension and one-way axial cyclic loading. Installation resistances are shown to be dominated by the pile tip loads. Low installation shaft stresses and radial effective stresses were measured that correlated with local cone penetration test (CPT) tip resistances. Marked shaft total stress reductions and steep stress gradients are demonstrated in the vicinity of the pile tip. The local interface shaft effective stress paths developed during static and cyclic loading displayed trends that resemble those seen in comparable tests in sands. Shaft failure followed the Coulomb law and constrained interface dilation was apparent as the pile experienced drained loading to failure, although with a lesser degree of radial expansion than with sands. Radial effective stresses were also found to fall with time after installation, leading to reductions in shaft capacity as proven by subsequent static tension testing. The jacked, closed-ended, piles’ ageing trends contrast sharply with those found with open piles driven at the same site, indicating that ageing is affected by pile tip geometry and (or) installation method.

Download Full-text

Stability and load-displacement behaviour of axially cyclic loaded displacement piles in sands

Canadian Geotechnical Journal ◽

10.1139/cgj-2020-0738 ◽

2022 ◽

Author(s):

Siya Rimoy ◽

Matias Silva ◽

Richard J. Jardine

Keyword(s):

Cyclic Loading ◽

Effective Stress ◽

Fine Sand ◽

Diameter Ratio ◽

Stress Regime ◽

Cyclic Behaviour ◽

Pile Diameter ◽

Calibration Chamber ◽

High Level ◽

Cyclic Damage

Uncertainties regarding the axial cyclic behaviour of piles driven in sands led to an extended programme of calibration chamber instrumented pile experiments. Broad trends are identified and interpreted with reference to normalised cyclic loading parameters Qcyclic/QT, Qmean/QT and N. Cyclic damage is shown to be related to changes in the radial effective stress regime close to the shaft. While stable loading leads to little or no change as cycling continues in the sand masses’ effective stress regime, high-level cyclic loading can affect stresses far out into the sand mass. The test systems’ chamber-to-pile diameter ratio has a significant impact on outcomes. Piles installed in loose, fine, sand are far more susceptible to cyclic loading than in denser, coarser sand. Little or no change in pile stiffness was seen in tests that remained within the stable cyclic region, even over 10,000 or more cycles. Unstable tests lost their stiffness rapidly and metastable cases showed intermediate behaviours. The permanent deflections developed under cycling depend on the combined influence of Qcyclic/QT, Qmean/QT and N. While model tests provide many valuable insights into the behaviour of piles driven in sand, they are unable to capture some key features observed in the field.

Download Full-text

MODELING OF DEGRADATION OF THE COMPOSITE PROPERTIES ON CRACKING AND DELAMINATION WHEN SUBJECTED TO STATIC AND CYCLIC LOADING

Composites Mechanics Computations Applications An International Journal ◽

10.1615/compmechcomputapplintj.v1.i4.20 ◽

2010 ◽

Vol 1 (4) ◽

pp. 315-331 ◽

Cited By ~ 1

Author(s):

Doan Chuck Luat ◽

S. A. Lurie ◽

A. A. Dudchenko

Keyword(s):

Cyclic Loading ◽

Static And Cyclic Loading ◽

Composite Properties

Download Full-text

Experimental study of the influence of sand base reinforcement on the development of deformations under static and cyclic loading

IOP Conference Series Materials Science and Engineering ◽

10.1088/1757-899x/918/1/012008 ◽

2020 ◽

Vol 918 ◽

pp. 012008

Author(s):

V M Antonov ◽

I A Al-Naqdi

Keyword(s):

Experimental Study ◽

Cyclic Loading ◽

Sand Base ◽

Static And Cyclic Loading

Download Full-text

A comparative study on methods for determining the hydraulic properties of a clay shale

Geophysical Journal International ◽

10.1093/gji/ggaa532 ◽

2020 ◽

Vol 224 (3) ◽

pp. 1523-1539

Author(s):

Lisa Winhausen ◽

Alexandra Amann-Hildenbrand ◽

Reinhard Fink ◽

Mohammadreza Jalali ◽

Kavan Khaledi ◽

...

Keyword(s):

Pore Pressure ◽

Effective Stress ◽

Ion Beam ◽

Applied Pressure ◽

Pressure Oscillation ◽

Stress Conditions ◽

Data Set ◽

Clay Shale ◽

Permeability Coefficients ◽

Effective Stresses

SUMMARY A comprehensive characterization of clay shale behavior requires quantifying both geomechanical and hydromechanical characteristics. This paper presents a comparative laboratory study of different methods to determine the water permeability of saturated Opalinus Clay: (i) pore pressure oscillation, (ii) pressure pulse decay and (iii) pore pressure equilibration. Based on a comprehensive data set obtained on one sample under well-defined temperature and isostatic effective stress conditions, we discuss the sensitivity of permeability and storativity on the experimental boundary conditions (oscillation frequency, pore pressure amplitudes and effective stress). The results show that permeability coefficients obtained by all three methods differ less than 15 per cent at a constant effective stress of 24 MPa (kmean = 6.6E-21 to 7.5E-21 m2). The pore pressure transmission technique tends towards lower permeability coefficients, whereas the pulse decay and pressure oscillation techniques result in slightly higher values. The discrepancies are considered minor and experimental times of the techniques are similar in the range of 1–2 d for this sample. We found that permeability coefficients determined by the pore pressure oscillation technique increase with higher frequencies, that is oscillation periods shorter than 2 hr. No dependence is found for the applied pressure amplitudes (5, 10 and 25 per cent of the mean pore pressure). By means of experimental handling and data density, the pore pressure oscillation technique appears to be the most efficient. Data can be recorded continuously over a user-defined period of time and yield information on both, permeability and storativity. Furthermore, effective stress conditions can be held constant during the test and pressure equilibration prior to testing is not necessary. Electron microscopic imaging of ion-beam polished surfaces before and after testing suggests that testing at effective stresses higher than in situ did not lead to pore significant collapse or other irreversible damage in the samples. The study also shows that unloading during the experiment did not result in a permeability increase, which is associated to the persistent closure of microcracks at effective stresses between 24 and 6 MPa.

Download Full-text

A Finite Element Study on Compressive Resistance Degradation of Square and Circular Steel Braces under Axial Cyclic Loading

Applied Sciences ◽

10.3390/app11136094 ◽

2021 ◽

Vol 11 (13) ◽

pp. 6094

Author(s):

Hubdar Hussain ◽

Xiangyu Gao ◽

Anqi Shi

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Cyclic Loading ◽

Slenderness Ratio ◽

Hysteretic Behavior ◽

Element Analysis ◽

Section Shape ◽

Axial Cyclic Loading ◽

Global Buckling ◽

Parametric Studies

In this study, detailed finite element analysis was conducted to examine the seismic performance of square and circular hollow steel braces under axial cyclic loading. Finite element models of braces were constructed using ABAQUS finite element analysis (FEA) software and validated with experimental results from previous papers to expand the specimen’s matrix. The influences of cross-section shape, slenderness ratio, and width/diameter-to-thickness ratio on hysteretic behavior and compressive-tensile strength degradation were studied. Simulation results of parametric studies show that both square and circular hollow braces have a better cyclic performance with smaller slenderness and width/diameter-to-thickness ratios, and their compressive-tensile resistances ratio significantly decreases from cycle to cycle after the occurrence of the global buckling of braces.

Download Full-text

Behaviour of RC beam repaired using alkali activated slag-based agent under static and cyclic loading

Structures ◽

10.1016/j.istruc.2021.02.039 ◽

2021 ◽

Vol 31 ◽

pp. 761-768

Author(s):

Sulaem Musaddiq Laskar ◽

Ruhul Amin Mozumder ◽

Aminul Islam Laskar

Keyword(s):

Cyclic Loading ◽

Rc Beam ◽

Alkali Activated Slag ◽

Activated Slag ◽

Static And Cyclic Loading ◽

Alkali Activated

Download Full-text

Stress sensitivity of porosity and permeability under varying hydrostatic stress conditions for different carbonate rock types of the geothermal Malm reservoir in Southern Germany

Geothermal Energy ◽

10.1186/s40517-021-00197-w ◽

2021 ◽

Vol 9 (1) ◽

Author(s):

Daniel Bohnsack ◽

Martin Potten ◽

Simon Freitag ◽

Florian Einsiedl ◽

Kai Zosseder

Keyword(s):

Effective Stress ◽

Hydraulic Properties ◽

Rock Strength ◽

Pore Network ◽

Stress Sensitivity ◽

Stress Conditions ◽

Rock Matrix ◽

Effective Stresses ◽

Rock Types ◽

Porosity And Permeability

AbstractIn geothermal reservoir systems, changes in pore pressure due to production (depletion), injection or temperature changes result in a displacement of the effective stresses acting on the rock matrix of the aquifer. To compensate for these intrinsic stress changes, the rock matrix is subjected to poroelastic deformation through changes in rock and pore volume. This in turn may induce changes in the effective pore network and thus in the hydraulic properties of the aquifer. Therefore, for the conception of precise reservoir models and for long-term simulations, stress sensitivity of porosity and permeability is required for parametrization. Stress sensitivity was measured in hydrostatic compression tests on 14 samples of rock cores stemming from two boreholes of the Upper Jurassic Malm aquifer of the Bavarian Molasse Basin. To account for the heterogeneity of this carbonate sequence, typical rock and facies types representing the productive zones within the thermal reservoir were used. Prior to hydrostatic investigations, the hydraulic (effective porosity, permeability) and geomechanical (rock strength, dynamic, and static moduli) parameters as well as the microstructure (pore and pore throat size) of each rock sample were studied for thorough sample characterization. Subsequently, the samples were tested in a triaxial test setup with effective stresses of up to 28 MPa (hydrostatic) to simulate in-situ stress conditions for depths up to 2000 m. It was shown that stress sensitivity of the porosity was comparably low, resulting in a relative reduction of 0.7–2.1% at maximum effective stress. In contrast, relative permeability losses were observed in the range of 17.3–56.7% compared to the initial permeability at low effective stresses. Stress sensitivity coefficients for porosity and permeability were derived for characterization of each sample and the different rock types. For the stress sensitivity of porosity, a negative correlation with rock strength and a positive correlation with initial porosity was observed. The stress sensitivity of permeability is probably controlled by more complex processes than that of porosity, where the latter is mainly controlled by the compressibility of the pore space. It may depend more on the compaction of precedented flow paths and the geometry of pores and pore throats controlling the connectivity within the rock matrix. In general, limestone samples showed a higher stress sensitivity than dolomitic limestone or dolostones, because dolomitization of the rock matrix may lead to an increasing stiffness of the rock. Furthermore, the stress sensitivity is related to the history of burial diagenesis, during which changes in the pore network (dissolution, precipitation, and replacement of minerals and cements) as well as compaction and microcrack formation may occur. This study, in addition to improving the quality of input parameters for hydraulic–mechanical modeling, shows that hydraulic properties in flow zones largely characterized by less stiff, porous limestones can deteriorate significantly with increasing effective stress.

Download Full-text