Lateral Stress Measurements Research Articles

Thermo-hydro-mechanical behaviour of deep Ypresian clays

Investigating the thermo-hydro-mechanical behaviour of deep Ypresian clays (300 to 400 m below ground) is crucial since they are one of Belgium’s potential host rock formations for deep geological disposal of radioactive waste. To this aim, a newly designed and fully instrumented thermal oedometer cell with lateral stress measurement was used to determine the stress state accurately. First, well-preserved core samples were loaded to bring them to the large in situ stresses and reduce the induced matric suction on deep water-undrained sampling. The remaining matric suction was then reduced by soaking with synthetic water of the formation. Next, drained loading and unloading paths were followed to attain different vertical effective stresses at varying overconsolidation ratios (OCRs) before the drained thermal paths (heating and cooling). The results indicated a systematic increase in the horizontal effective stress on heating at constant vertical effective stress. In addition, thermal-induced volume changes in heating/cooling at different OCRs were studied. Test results were finally interpreted within a thermo-mechanical elastoplastic framework.

Effectiveness of self-sealing after gas transport in Boom Clay

The study of gas transport in low permeable materials is becoming a significant focus in energy-related geotechnics, particularly for managing deep geological disposal of long-lived and heat-emitting radioactive waste. Argillaceous rocks, studied to host the disposal, may present induced fractures caused by the excavation activities that increase the permeability to liquid and gas. The generation of gases can also lead to an excessive pressure build-up in these saturated media resulting in the development or reactivation of fractures/fissures creating preferential pathways for the gas flow [1]. Nevertheless, these rocks present the advantage of self-seal (via swelling of clay minerals due to re-saturation, consolidation or creep), reducing fissure permeability and potentially restoring the barrier function [2].
 This study focuses on Boom Clay, a Cenozoic clay candidate for hosting the repository in the Belgian programme, aiming at characterising the effectiveness of its self-sealing process after gas injection/dissipation tests due to the swelling of clay minerals during re-saturation. This poorly indurated rock presents sedimentary bedding planes that can act as preferential pathways during the gas invasion. In a previous experimental campaign, samples at two bedding orientations (parallel and orthogonal to the flow) were tested under oedometer conditions [3, 4]. The results indicate that gas transport induced slight expansion of the samples in both orientations, increasing their intrinsic permeability, which suggested the opening of preferential paths. Furthermore, the analyses of the pore network using mercury intrusion porosimetry (MIP) and micro-focus X-ray computed tomography (µ-CT) confirmed the development of gas pathways following the bedding direction or interconnecting bedding planes [4, 5].
 To assess the self-sealing capacity, oedometer tests were carried out at two bedding directions using an oedometer cell with lateral stress measurement to comprehensively understand the stress state and ensure that gas flow occurred through the sample rather than between the sample-ring interface. Prior to the gas injection stage, water permeability was measured. Subsequently, a gas injection/dissipation stage was performed at constant vertical stress. Immediately after, the sample was placed in contact with synthetic water to allow re-saturation. Finally, the water permeability was measured again. The self-sealing capacity of the clay was assessed by comparing the water permeability at both stages. If the obtained values are similar, the barrier function has been restored. Some tests also included a second gas injection to evaluate the potential pathway reopening. MIP and µ-CT data allowed for evaluating microstructural changes due to these processes.
 The experimental results demonstrate that gas can flow at pressures lower than the minor lateral stress, and the computed effective gas permeability is always higher than the initial intrinsic water permeability, pointing to the opening of preferential pathways (Figure 1a). Water permeability after re-saturation showed values comparable to the initial intrinsic permeability, recovering the hydraulic barrier function thanks to the clay minerals’ swelling (Figure 1a). This indicates the good self-sealing capacity of the Boom Clay. The gas permeability calculated during a second injection/dissipation stage is slightly higher than the initial one, suggesting some memory of the previously opened path (Figure 1a). The self-sealing effect was also observed in the CT images performed under unstressed conditions after water-undrained unloading of the tested samples. The fissures detected after the gas injection (Figure 1b left) are no longer visible after re-saturation within the technique resolution (fissures > 40µm) (Figure 1b middle). However, a small proportion of large and disconnected pores were identified in CT images, likely due to some gas exsolution. Regarding the subsequent gas injection, it again led to the development of fissures following the bedding direction detected with microstructural techniques (Figure 1b right).

The laterally confined consolidation of initially compacted and wetted swelling clay

This paper describes the laterally confined consolidation of an Israeli clay following compaction and swelling on wetting, including the measurement of lateral stresses. The results of the tests are compared to those obtained during consolidation of the clay from an initially slurried condition. In comparing the compression and expansion indices relative to vertical, lateral and mean stress, it was found that they varied, depending on the initial, preparation conditions; the values approached the slurried values with decreasing initial dry density. During unloading, the expansion indices were found to be independent of initial conditions, and essentially the same as those of the slurried soil. The coefficient of lateral earth pressure at rest during loading, K0, of the compacted and then wetted specimens was found to be reasonably constant regardless of initial soil conditions, but significantly higher than the value of the slurried soil. However, during unloading, the relationship between the normalized coefficients of lateral earth pressure at rest, K0'/K0, and the overconsolidation ratio, OCR, was found to be essentially the same as that obtained for the slurried soil.

Simultaneous measurement of axial strain and lateral stress based on cascaded interference structure.

To solve the cross-sensitivity problem in the dual-parameter optical fiber system, a new type of sensor based on cascaded interference structure is proposed without cross-sensitivity. The design consists of a Michelson interferometer and a Sagnac interferometer based on a high-birefringence suspended core fiber segment. After calculating by the analogous Fast Fourier Transformation (FFT) and filtering by FFT filter, the spectrum of the sensor responds linearly to the change of axial strain and lateral stress. The sensitivity to lateral stress is 3.13 nm/(kPa) in the range from 0 to 1200 Pa and the axial strain is 1.846e-4 (nm·µɛ)-1 from 0 to 4000 µɛ. The capability of the proposed sensor for dual-parameter sensing is also experimentally demonstrated. The precision rate for dual-parameter sensing is as high as 66.7%, reflecting the sensor's usability for simultaneous measurement of axial strain and lateral stress.

Measurement of Lateral Stress and Friction in Rockfill Oedometer Tests Enabling the Analysis of the Experimental Results in the p′-q Space

Abstract The oedometer is one of the simplest and most reliable laboratory tests. Its main drawback is that stress state is not fully known. Over the years, a number of enhancements were intended to overcome this limitation. This work presents the development of a large size oedometer for testing gravels made of crushed rock under varying moisture conditions. Load application is done by air pressure acting on the upper end of the specimen (Rowe type oedometer), and the lateral stress is measured using a strain-gage-instrumented oedometer ring. Special features were included in the ring geometry for enhancing the lateral stress measurement signal, while keeping the deformation of the ring to acceptably low levels. The lateral friction between specimen and oedometer wall is computed as the difference between the applied load and the reaction force at the specimen base, measured by means of three load cells. The performance of the oedometer is studied by means of a finite element model of the oedometer ring. The deformability of the ring and the production of spurious readings of lateral stress due to varying operation conditions are evaluated and found to be satisfactorily low. Some experimental results on a rockfill type material are presented. The lateral stress and friction data are analysed in terms of the lateral stress ratio and in the p′-q space. The observed behavior is found to be stress– and suction–dependent. The results are consistent with triaxial tests of the same material published elsewhere.

Lateral Stress Sensor Based on an In-Fiber Mach–Zehnder Interferometer and Fourier Analysis

A novel lateral stress sensor based on a compact in-fiber Mach–Zehnder interferometer (MZI) and Fourier analysis is proposed and demonstrated. The in-fiber MZI is formed by cascading two offset splicing joints. The interference occurs between the copropagating fundamental core and cladding modes. The influence of offset value on the performance of modal interferometer, including the extinction ratio and insertion loss, has been experimentally investigated. The spatial spectra of the proposed in-fiber interferometers with different interference lengths are analyzed by Fourier transform. An in-fiber interferometer with an interference length of 30 mm has been fabricated for lateral stress measurement. The performance of the lateral stress sensor is investigated in a spatial frequency domain by Fourier transform of the corresponding transmission wavelength spectra. The responses of intensity peaks to different lateral stresses are analyzed in the spatial frequency domain. The sensitivity of the in-fiber MZI-based lateral stress sensor is as high as 0.00455/ $\mu\text{m}$ . The proposed lateral stress sensor possesses the advantages of simple and compact structure, high sensitivity, ease of manufacture, and low cost, and it will provide a simple and effective method for detecting the slight fiber deformation induced by lateral stress.

Spatial identification of traps in AlGaN/GaN heterostructures by the combination of lateral and vertical electrical stress measurements

We present a methodology and the corresponding experimental results to identify the exact location of the traps that induce hot electron trapping in AlGaN/GaN heterostructures grown on Si substrates. The methodology is based on a combination of lateral and vertical electrical stress measurements employing three ohmic terminals on the test sample structure with different GaN buffer designs. By monitoring the evolution of the lateral current during lateral as well as vertical stress application, we investigate the trapping/detrapping behaviors of the hot electrons and identify that the traps correlated with current degradation are in fact located in the GaN buffer layers. The trap activation energies (0.38–0.39 eV and 0.57–0.59 eV) extracted from either lateral or vertical stress measurements are in good agreement with each other, also confirming the identification. By further comparing the trapping behaviors in two samples with different growth conditions of an unintentionally doped GaN layer, we conclude that the traps are most likely in the unintentionally doped GaN layer but of different origins. It is suggested that the 0.38–0.39 eV trap is related to residual carbon incorporation while the 0.57–0.59 eV trap is correlated with native defects or complexes.

Cascaded interferometers structure based on dual-pass Mach-Zehnder interferometer and Sagnac interferometer for dual-parameter sensing.

In this article, we propose and demonstrate a cascaded interferometers structure based on a dual-pass Mach-Zehnder interferometer (DP-MZI) and a Sagnac interferometer (SI) for simultaneous measurement of strain and lateral stress. The cascaded interferometers configuration consists of a SI structure following with a MZI setup. By inserting a section of polarization-maintaining photonic crystal fiber (PM-PCF) in the sensing loop of the SI structure, an inline interference between the two orthogonal polarization modes of PM-PCF, as well as the interference between the sensing arm and the reference arm of the DP-MZI, i.e., the cascaded interferometers with dual interference, are realized. Theoretical study shows that the reflection spectrum of such cascaded interferometers is consisted of two parts: the big spectrum envelope owing to the SI and the fine interference fringes as a result of the DP-MZI. Experimental results show that the SI achieves the sensitivity of lateral stress and strain 1.28 nm/kPa, 0.78 pm/µε, respectively, while the DP-MZI achieves -0.009 nm/kPa and 5.65 pm/µε, demonstrating the ability for dual parameters measurement with high accuracy.

Revisiting the calibration of manganin gauges for lateral stress measurements in shock-loaded solids

The calibration of manganin gauges for lateral stress measurements, in shock loaded specimens, is revisited through a simplified analysis, which is based on the dependence of the gauge's strength on shock amplitude. This dependence is derived from the measured resistive hysteresis of the gauge, as obtained in shock and release experiments. The resulting values for the gauge's strength, as a function of shock amplitude, are about half the values which were obtained previously by a different analysis. With the revised strength values, a new calibration curve is derived for the commercial grid-like gauges, as lateral stress transducers in planar impact experiments.

Effect of particle fabric on the coefficient of lateral earth pressure observed during one-dimensional compression of sand

The effect of initial particle fabric on the one-dimensional compression response of Fraser River sand was investigated. One-dimensional compression with lateral stress measurement was carried out on reconstituted Fraser River sand specimens using an instrumented oedometer. Laboratory specimens were reconstituted by air pluviation, tamping, and vibration and were prepared with an initial relative density ranging from medium loose to very dense. For Fraser River sand in one-dimensional compression, air-pluviated specimens yielded the highest values for the coefficient of lateral earth pressure at rest (Ko), tamped specimens produced the lowest Kovalues, and vibrated specimens produced intermediate Kovalues. The results from the present study demonstrate that specimens resulting from different laboratory reconstitution methods (i.e., different initial particle fabrics) exhibit different one-dimensional compression responses and produce different Kovalues. A “fabric factor” was introduced to account for the effect of the initial particle fabric on the measured coefficient of lateral earth pressure at rest. Using the fabric factor, the constant volume friction angle, and the specimen relative density, a new empirical equation defining the coefficient of lateral earth pressure at rest during normally consolidated loading is proposed.

Liquefaction, Lateral Stress, Consolidation State, and Aging

In 1986–1989, Jackson Lake Dam, Wyoming, was removed after standard penetration tests indicated that the foundation soil was subject to liquefaction. Part of a subsequent research program involved measuring lateral in situ stresses at various depths in the foundation soil by use of the Ko Stepped Blade, a device that introduces a stepwise lateral displacement of soil so contact pressures can be extrapolated to give the hypothetical pressure on a zero-thickness step. The foundation soil was cohesionless mix of alluvial and deltaic silts and sands with some sharp-edged gravel. The lateral stress measurements established relationships between the four topics in the title of this paper. A normal consolidation state, meaning that a soil is in equilibrium with its own weight, can be established when Ko is constant with depth and lateral effective stresses extrapolate to zero at the ground surface. On this basis, three stress zones were identified: (1) Based on limited data, an uppermost zone, to a depth of 4 m (13 ft) underneath the dam, was identified as being normally consolidated under the weight of the dam. This is as expected and probably occurred during construction. Underneath the upper zone was (2) a transition zone, 4 to 5.5 m (13 to18 ft) in depth, and under that (3) a lower zone, 5.5 to 10 m (18 to 33 ft) in depth. The lower zone was determined to be normally consolidated without the weight of the dam. Ko without the weight from the dam was determined to be 0.5, and lateral effective stresses extrapolate to zero at the predam ground surface. Note that the value of Ko was measured and not derived from empirical correlations. Nevertheless, it is consistent with normal consolidation and a friction angle of 30 degrees reported for this deposit. Despite having been characterized as cohesionless, the soil deep underneath the dam had resisted consolidation for over 60 years, and the depth to the underconsolidated layer is consistent with observations that liquefaction can be deep-seated. The existence of such a layer calls into question the use of a temporary surcharge for site preparation for cohesionless soils, or a reliance on measurements that settlement has stopped. A similar situation can be anticipated under existing structures such as dams and highway embankments that are located on the geologically young but historically old granular soil deposits of floodplains and deltas. The weight of the dam reduced Ko in the lower zone soil from 0.5 to 0.35. This can happen only if the soil has developed sufficient strength to resist consolidation and can be attributed to aging. Mohr circles drawn from the lateral stress measurements indicate a gain in cohesion of the order of 34 kPa (4.9 psi or 700 psf) from aging. The gain also may be explained by an increase in the friction angle from dilatancy attributed to cementation rims at grain contacts. The site was treated by deep dynamic compaction that increased Ko to 1.0, but with considerable variability. That value indicates a temporary liquid condition, and may have been preserved by seepage forces when pore water pressure supported the entire weight of the soil column. The replacement dam reduced the average Ko from 1.0 to about 0.5, which should be sufficient prevent future liquefaction. However, the cap on Ko of 1.0 during ramming can restrict the amount of additional load if the final Ko is to be no lower than the normal consolidation value.

Shock and mechanical response of 2139-T8 aluminum

Planar shock wave experiments were performed on 2139-T8 aluminum to determine its response to dynamic loading. A Hugoniot was determined to 12 GPa. Lateral stress measurements along with a study of the release behavior indicate that this material retains its shear strength to at least 8 GPa. Spall strength was measured for ∼1 μs compressive pulse durations and found to be approximately constant at 1.45 GPa up to shock stresses of 10 GPa. Beyond 10 GPa, spall strength decreases considerably. Uniaxial stress compression tests were conducted with a servo-hydraulic load frame and the Kolsky bar method to obtain stress-strain curves at strain-rates from 0.001/s to 85k/s. This data shows the material is rate independent. The shock experiments were simulated using a Lagrangian finite element code using a polynomial equation of state, the Johnson-Cook strength law, and the Cochran and Banner spall model. The ability of the simulations to reproduce the experimentally measured data is mixed, with significant deviations in modeling the plastic wave front, plastic release, and the spall pull-back signals.

Lateral soil stiffness adjacent to deep integral bridge abutments

Our understanding of the performance of integral bridge abutments subjected to cyclic loading has been improved using well-designed laboratory experiments, and by observation of abutment performance in the field. However, there remains significant uncertainty on how the increase in lateral stress that arises due to cycling of the backfill may be assessed for abutment design. Such uncertainty is addressed in this paper by drawing on results from a series of experiments performed using the University of Western Australia (UWA) beam centrifuge. The experimental results shed light on the effects, for granular backfill, of initial density, retained height, cyclic history and particle shape. These results, as well as observations made from tests involving overconsolidated clays, are used in conjunction with the existing database of lateral stress measurements to assist in the development of recommendations for assessment of design lateral stresses on deep integral bridge abutments.

Shock wave propagation in dense particle suspensions

Shock wave propagation in a multiphase suspension is studied experimentally. Particle suspensions are used as a means of obtaining a system in which there is limited initial interparticle contacts with a large degree of parametric variability. Suspensions were created in ethylene glycol at several volume fractions (41%, 48%, and 54%) of silicon carbide particles. Plate impact experiments are conducted to obtain the shock Hugoniots of the various suspensions at particle velocities in the range of 200–900 m/s. Transitions are shown to exist in the Us-up Hugoniots of the suspensions. In situ longitudinal and lateral stress measurements are made in the 48% suspension at two different impact velocities demonstrating a deviatoric stress component to the stress state in the suspension. The results are discussed in terms of the development of extensive interparticle contacts in a mechanism analogous to classical shear thickening in dense suspensions.

Tacticity in shocked polymer hydrocarbons

There is a recent interest in the response of thermoplastics to shock. Previous work on three simple hydrocarbons has indicated that the shear strength increases with the complexity of the side group. Strength values have been calculated using lateral stress measurements with manganin gauges that have been recalibrated for use in the low stress regime. The present work aims to investigate the effect of the configuration of the thermoplastic’s chain when side groups are added. In particular, whether steric effects are present when the groups become larger. Results show that whilst polyethylene has the lowest shear strength, polypropylene and polystyrene have similar values. In all cases the strength of polymer increases with time after the shock has passed. As the applied stress increases, polystyrene and polypropylene strengthen to a higher degree when compared with polyethylene. Explanations are offered in terms of microstructure and tacticity of the chain.

Note on the interpretation of powder shear test data

Powder shear testing has been used to assess flowability of powders for at least 48 years [A.W. Jenike, Storage and Flow of Solids, Bull., Eng. Exp. Station, Univ. Utah, vol. 123, 1964]. A fundamental part of the data interpretation involves construction of Mohr’s circles such that they are tangent to the experimental locus; a set of powder shear strengths, τ m, measured at variable applied compressive normal stresses, σ N. Despite the customary application of this tangency criterion, we have found justifications for it to be scant. In this work, we revisit the Mohr’s circle construction and find that proper construction would require measurement of reactionary lateral powder stresses, σ r. We further provide reasoning to support placement of the experimental locus passing through the apex (top) of Mohr’s circles for isotropic or orthotropic powders and not tangentially to them. This placement is not unexpectedly in agreement with the results of a recent numerical simulation [C. Thornton, L. Zhang, Numerical simulations of the direct shear test, Chem. Eng. Technol. 26 (2) (2003) 153–156], and reveals errors in subsequently calculated constants on the order of 20%.

The shock Hugoniot of Tuffisitic Kimberlite Breccia

The Hugoniot of a material represents the response to high-rate loading at pressures associated with those produced by blasting charges. The shock Hugoniot curve of a kimberlite, Tuffisitic Kimberlite Breccia (TKB), has been determined between 0.3 and 8.4 GPa using plate impact experiments. The dynamic shear response of TKB is reported for impact stresses between 1.1 and 3.2 GPa. Longitudinal and lateral stress measurements were made using embedded manganin gauges and VISAR in material shocked to a state of uniaxial strain. The shock response of TKB reveals a relatively weak material with no clear Hugoniot Elastic Limit (HEL) in the longitudinal stress measurements. The lateral stress measurements suggest an HEL between 0.6 and 0.9 GPa. Inelastic deformation is observed at all stresses due to a combination of volume compaction and brittle failure. The current data have been compared with similar reports in the literature and theory in order to accurately describe the response of this inhomogeneous geological material.

The inelastic behavior and failure of dense glass under shock loading to 15GPa

The in-material longitudinal and lateral stress histories in an extra-dense, silica-based glass have been measured at impact pressures well above the Hugoniot elastic limit using embedded manganin stress gauges during plate impact experiments. The measurements of longitudinal stress extend the current data and are used to provide an extensive principal Hugoniot for the material. The lateral stress measurements obtained at high impact pressures show the pressure-dependent nature of the failure process, consistent with previous studies on dense glasses. The longitudinal and lateral data obtained are used to determine the shear strength versus time history during high-pressure loading. These data in conjunction with high-speed photographic records provide insight into the inelastic response and evolution of failure in brittle materials during shock loading.

Lateral stress measurements and shear strength in shock loaded tungsten carbide

The shear strength of a monolithic tungsten carbide has been measured as a function of impact stress. Results show that it increases with stress, in agreement with the work of others. Interestingly, it has also been shown that lateral stress increases, and thus shear strength decreases behind the shock front. Potential mechanisms are discussed, including cracking within the shock front itself, and stress relaxation due to high velocity dislocation motion within the shock front, followed by dislocation multiplication behind it.

Car Stability Detection from Tyre Stresses

In the framework of on-board active systems to control vehicle dynamics, a new approach is presented here. The study and developed application are dedicated to Electronic Stability Program field. This paper gives a feasibility study of the detection and quantification of the trajectory stability via stresses generated in the wheel-road interface. The approach chosen is based on fault diagnosis tools and fuzzy logic due to strong non-linear and coupling aspects. Finally a "detector" of stability (potential dangerous situation), essentially based on the measurement of lateral stresses, is given and tested on real measurements.