Triaxial Cyclic Loading Tests Research Articles

Mechanical Behavior of Polyurethane Polymer Materials under Triaxial Cyclic Loading: A Particle Flow Code Approach

Polyurethane polymer grouting materials were studied with conventional triaxial tests via the particle flow code in two dimensions (PFC2D) method, and the simulation results agreed with the experimental data. The particle flow code method can simulate the mechanical properties of the polymer. The triaxial cyclic loading tests of the polymer material under different confining pressures were carried out via PFC2D to analyze its mechanical performance. The PFC2D simulation results show that the value of the elastic modulus of the polymer decreases slowly at first and fluctuated within a narrow range near the value of the peak strength; the cumulative plastic strain increases slowly at first and then increases rapidly; the peak strength and elastic modulus of polymer increase with the confining pressure; the PFC2D method can be used to quantitatively evaluate the damage behavior of the polymer material and estimate the fatigue life of the materials under fatigue load based on the number and the location of micro-cracks. Thus, the PFC2D method is an effective tool to study polymers.

Strain-Softening Model for Marble Considering the Degradation of Elastic Modulus

Rocks encountered in deep underground engineering, such as coal mining and tunnel excavating applications, are usually in states of failure. It is of great engineering significance to study the post-peak strength behavior of rock. A strain-softening model that considers the degradation of elastic modulus was suggested in this article. The strain-softening characteristics and degradation law of the elastic modulus for marble were first obtained based on triaxial cyclic loading tests. A strain-softening model was then suggested by considering the degradation of the elastic modulus. Finally, the suggested model was embedded in the finite difference software (FLAC), and the conventional triaxial compression tests for marble were simulated. The results showed that the stress–strain curves simulated using the suggested model were in agreement with the contour curves of cyclic loading. The results may serve as a reference for the strain-softening characteristics of the Jinping marble studied in this paper.

Site response analysis for the seismic improvement of a historical and monumental building: the case study of Augusta Hangar

Eastern Sicily is very rich of historical buildings, but at the same time is one of the most seismically active areas of Italy. In particular, the city of Augusta was damaged by the January 11, 1693 Val di Noto Earthquake, as well as some others Sicilian cities. Afterwards, the strongest earthquake, about 300 years later, was the Sicilian Earthquake of December 13, 1990, with an epicenter close to Augusta and maximum intensity of VII–VIII MCS. In order to study the geotechnical dynamic characteristics of the foundation soil of the Augusta Hangar, in situ investigations and laboratory tests have been carried out. Among in situ investigations, borings, standard penetration tests (SPT), field vane tests (FVT), Menard pressure meter tests (MPT), down-hole tests (DHT) have been carried out. Among laboratory tests oedometer tests, direct shear tests (DST), consolidated drained triaxial tests (CDTXT), n. 6 undrained triaxial tests (UTXT), cyclic loading torsional shear tests (CLTST), resonant column tests (RCT) have been carried out. Special attention has been devoted to the variation of the Young modulus non-linearity, shear modulus G, and damping ratio D by cyclic loading triaxial tests and resonant column tests. This paper tries to summarize this information in a comprehensive way in order to provide a representative geotechnical model of the site where an important historical building is located. Processing of all these data also allowed the ground response analysis at the surface, in terms of time history and response spectra, using as input in the linear-equivalent codes EERA, STRATA, and DEEPSOIL both synthetic seismograms and recorded accelerograms. The results of the ground response analyses represent useful tools for the safeguard of historical buildings and have been used for the planning of the seismic improvement interventions.

Constitutive model for cyclic behaviour of cohesionless sands

ABSTRACTThis paper presents a constitutive model for describing the stress-strain response of sands under cyclic loading. The model, formulated using the critical state theory within the bounding surface plasticity framework, is an upgraded version of an existing model developed for monotonic behaviour of cohesionless sands. With modification of the hardening law, plastic volumetric strain increment and unloading plastic modulus, the original model was modified to simulate cyclic loading. The proposed model was validated against triaxial cyclic loading tests for Fuji River sand, Toyoura sand and Nigata sand. Comparison between the measured and predicted results suggests that the proposed modified model can capture the main features of cohesionless sands under drained and undrained cyclic loading.

A Geotechnical Engineering Study for the Safeguard, Restoration and Strengthening of Historical Heritage

Eastern Sicily is very rich of monuments and historical buildings, but at the same time is one of the most seismically active areas of Italy. In particular the city of Noto, which is now considered the capital of Baroque in Sicily, was destroyed by the 1693 Val di Noto Earthquake and rebuilt in another site, as in the case of some others cities. In order to study the geotechnical dynamic characteristics of the foundation soil of monuments, in situ investigations and laboratory tests have been carried out. Among in situ investigations, Borings, SPT, CPT, D-H, C-H and DMT have been carried out. Among laboratory tests, special attention has been devoted to the variation of the Young modulus non linearity, shear modulus G and damping ratio D by Cyclic Loading Triaxial tests and Resonant Column tests. This paper tries to summarize this information in a comprehensive way in order to provide a representative geotechnical model of the sites where important monuments are located.

Dynamic Strength and Accumulated Plastic Strain Development Laws and Models of the Remolded Red Clay under Long-Term Cyclic Loads: Laboratory Test Results

Abstract The dynamic strength and accumulated plastic strain are two important parameters for evaluating the dynamic response of soil. As a special clay, the remolded red clay is often used as the high speed railway subgrade filling, but studies on its dynamic characteristics are few. For a thorough analysis of the suitability of the remolded red clay as the subgrade filling, a series of long-term cyclic load triaxial test under different load histories are carried out. Considering the influence of compactness, confining pressure, consolidation ratio, vibration frequency and dynamic load to the remolded red clay dynamic property, the tests obtain the development curves of the dynamic strength and accumulated plastic strain under different test conditions. Then, through curve fitting method, two different hyperbolic models respectively for the dynamic strength and accumulated plastic strain are built, which can match the test datum well. By applying the dynamic strength model, the critical dynamic strength of the remolded red clay are gained. Meanwhile, for providing basic datum and reference for relevant projects, all key parameters for the dynamic strength and accumulated plastic strain of the remolded red clay are given in the paper.

Experimental investigation on mechanical damage characteristics of sandstone under triaxial cyclic loading

The mechanical damage characteristics of sandstone subjected to cyclic loading is very significant to evaluate the stability and safety of deep excavation damage zones. However to date, there are very few triaxial experimental studies of sandstone under cyclic loading. Moreover, few X-ray micro-computed tomography (micro-CT) observations have been adopted to reveal the damage mechanism of sandstone under triaxial cyclic loading. Therefore, in this research, a series of triaxial cyclic loading tests and X-ray micro-CT observations were conducted to analyse the mechanical damage characteristics of sandstone with respect to different confining pressures. The results indicated that at lower confining pressures, the triaxial strength of sandstone specimens under cyclic loading is higher than that under monotonic loading; whereas at confining pressures above 20 MPa, the triaxial strength of sandstone under cyclic loading is approximately equal to that under monotonic loading. With the increase of cycle number, the crack damage threshold of sandstone first increases, and then significantly decreases and finally remains constant. Based on the damage evolution of irreversible deformation, it appears that the axial damage value of sandstone is all higher than the radial damage value before the peak strength; whereas the radial damage value is higher than the axial damage value after the peak strength. The evolution of Young's modulus and Poisson's ratio of sandstone can be characterized as having four stages: (i) Stage I: material strengthening; (ii) Stage II: material degradation; (iii) Stage III: material failure and (iv) Stage IV: structure slippage. X-ray micro-CT observations demonstrated that the CT scanning surface images of sandstone specimens are consistent with actual surface crack photographs. The analysis of the cross-sections of sandstone supports that the system of crack planes under triaxial cyclic loading is much more complicated than that under triaxial monotonic loading. More axial and lateral tensile cracks were observed in the specimens under cyclic loading than under monotonic loading.

순환골재를 포함한 입상재료의 특성에 관한 실험적 연구

PURPOSES : In Korea, most designs of pavement had been mainly performed by considering CBR of granular materials before KPRP(Korea Pavement Research Program) and 86 AASHTO design method were introduced. Since then, the trend of the pavement designs gradually have moved to using mechanical characteristics throughout the resilient modulus based on the test results up to recently. In this study, we should like to research the mechanical characteristics of paving materials containing Recycled aggregates through the cyclic loading triaxial compression tests. METHODS : The kinds of materials were tested; coarse grained subbase materials, refining aggregates base materials and recycled aggregates. RESULTS : The present study aims to figure out the resilient modulus of paving materials containing Recycled aggregates through the cyclic loading triaxial compression tests. CONCLUSIONS : The test results revealed that the engineering properties of the recycled aggregates were more excellent than the those of others.

Effects of axial cyclic loading at constant confining pressures on deformational characteristics of anisotropic argillite

Triaxial cyclic loading tests have been performed to assess the influence of plastic deformation on inelastic deformational properties of anisotropic argillite with bedding planes which is regarded as a kind of transversely isotropic media. Considering argillite’s anisotropy and inelastic deformational properties, theoretical formulae for calculating oriented elastic parameters were deduced by the unloading curves, which can be better fitted for the description of its elasticity than loading curves. Test results indicate that with the growth of accumulated plastic, strain, the apparent elastic modulus of argillite decreases in a form of exponential decay function, whereas the apparent Poisson ratio increase in a form of power equation. A ratio of unloading recoverable strain to the total strain increment occurred during a loading cycle is defined to illustrate the characteristic relations between anisotropic coupled elasto-plastic deformation and plastic strain. It is significant to observe that high stress level and plastic history have an inhibiting effect on argillite anisotropy.

Investigation of the resilient behavior of granular base materials with simple test apparatus

In many developing countries, where resources are at premium, thin asphalt layers or chip seals are widely used to provide a durable all weather pavement surfacing. In such pavements the role of granular layers is very important in the general performance of the structure. Pavement designs in these countries are empirical in nature and rely on simple input parameters like California Bearing Ratio (CBR) values. Although widely applicable the traditional CBR test does not provide the mechanical properties such as resilient and permanent deformation characteristics of granular road materials. This paper documents the characterization technique developed to determine the mechanical behavior of granular (sub-) base materials based on CBR test using repeated load cycles. The confining pressure developed in the complex CBR stress state is estimated using strain gauges. Finite Element analysis has been attempted to model the repeated load CBR (RL-CBR) and derive an equivalent resilient modulus. Furthermore, a large scale cyclic load triaxial test was carried out on coarse unbound granular materials (UGMs) to validate the result of the RL-CBR. The RL-CBR test reasonably estimates the resilient modulus of UGMs which can be used as an input in mechanistic pavement design analysis in the absence of triaxial testing facilities.

Mechanical Behavior of Natural and Recycled Granular Materials for Roads

Abstract This paper presents a study on resilient and permanent strains measured with the precision cyclic load triaxial test on a limestone aggregate (reference material) commonly used in subbase or capping layers in Belgium and on two recycled materials (steel slag and crushed concrete aggregate) also used in subbase or capping layers. The influence of stress level, water content, density, and compaction method (vibrating hammer or vibrocompaction) was analyzed. Tests with one cyclic stress level on one specimen (single stage loading) and tests with several cyclic stress levels on the same specimen (multi-stage loading) were performed, in order to evaluate the prediction capability of the multi-stage loading test. The latter test procedure is quicker and more practical. Although the permanent strains obtained by the two test procedures were different, the multi-stage loading method did indicate the trend of the long-term behavior of the material. The test results showed that in comparison with the reference material, the recycled materials, particularly the steel slag, exhibited good mechanical behavior (high stiffness, high strength, and good resistance to permanent strains) under-well controlled conditions of water content.

Unified description of sand behavior

In this paper, the mechanical behavior of sand, was systematically described and modeled with a elasto-plastic model proposed by Zhang et al. [1]. Without losing the generality of the sand, a specific sand called as Toyoura sand, a typical clean sand found in Japan, has been discussed in detail. In the model, the results of conventional triaxial tests of the sand under different loading and drainage conditions were simulated with a fixed set of material parameters. The model only employs eight parameters among which five parameters are the same as those used in Cam-clay model. Once the parameters are determined with the conventional drained triaxial compression tests and undrained triaxial cyclic loading tests, then they are fixed to uniquely describe the overall mechanical behaviors of the Toyoura sand, without changing the values of the eight parameters irrespective of what kind of the loadings or the drainage conditions may be. The capability of the model is discussed in a theoretical way.

Analysis of the mechanisms of slope failures triggered by the 2007 Chuetsu Oki earthquake

The 2007 Chuetsu Oki earthquake (MJMA = 6.6) triggered more than one hundred slope failures in the northwest part of Niigata prefecture, Japan. A reconnaissance survey conducted by the authors revealed that although most of the failures were only a few meters deep, they still caused significant damage to roads, railways, and houses. It was also found that a vast number of shallow slides were concentrated along the coastal line of the Japan Sea, while only few, but relatively larger failures occurred in a mountainous part of the study area, which is located in a considerable distance from the earthquake’s epicenter. This paper summarizes the reconnaissance observations, describes the geologic characteristics of the area covered by landslides, provides characterization of major types of the landslides, and examines the causes and mechanisms of typical failures. In addition, this paper seeks to investigate the mechanism of the Ohzumi landslide, the largest slide triggered by the Chuetsu Oki earthquake. For this purpose, a comprehensive analysis that included field investigation and laboratory testing of soils samples was performed. Results of field investigation suggested that the failure plane of the Ohzumi landslide formed in a saturated layer of sandy soil near a boundary with bedrock. Data from undrained cyclic loading triaxial compression tests indicated that the sandy material was highly susceptible to generation of high excess pore-water pressures during earthquake loading. On the basis of the obtained results and the outcome of seismic response and slope stability analyses, the authors posited an explanation on the mechanism of the Ohzumi landslide.

Case Study: Dynamic Modulus Characterization of Naturally Occurring Bituminous Sands for Sustainable Pavement Applications

──────────────── ─────── Abstract: Oil sand is a generic name given to naturally occurring deposits of bituminous sand materials that are mined for crude oil production. These materials are currently used as subgrade materials of temporary and permanent roads in oil sand fields. The presence of high bitumen content makes oil sand materials problematic for field operations of off-road haul trucks and shovels during the warm spring and summer months. The behavior of oil sand materials is primarily dependent upon stress states, temperature, and the rate of loading or frequency. To effectively account for temperature and loading frequency, dynamic modulus is the preferred material property to characterize bituminous materials. In this paper, dynamic modulus is determined for three types of oil sand materials with natural bitumen contents of 8.5, 13.3, and 14.5% by weight using cyclic load triaxial test procedure. All the three oil sand samples were compacted close-to-field densities and then tested at two temperatures and three loading frequencies (related to field trafficking speeds) at different stress states. Based on the test results, dynamic modulus was modeled as a power function of the applied stress states and temperature. Using all the test data obtained from the three oil sand samples, unified dynamic modulus characterization models were successfully developed to account for stress state, bitumen content, and temperature. The proposed model can be calibrated for field practical use to estimate modulus and deformation behavior of these oil sand materials for their sustainable use in pavement applications. 2 Oil sands, sometimes called as tar sands, are natural deposits of bituminous sand materials that are rich in bitumen content to the extent that oil can be extracted from these deposits. Oil sands are found worldwide. The largest and most thoroughly studied deposits are located in Canada, United States, and Venezuela. The Alberta Province in Canada has the world's largest deposit of oil sands. Oil sand surface mining involves excavation to remove the overburden and providing access to the mineral sands below it using haul trucks and shovels. In situ, the oil sand deposits are predominantly quartz sand surrounded by a thin film of water and fines, with bitumen filling the pore spaces between the sand grains. The quartz sand, silt, and clay, i.e., inorganic materials of the oil sand composition normally constitutes about 80% by weight, with bitumen and water constituting about 15 and 5%, respectively (1). Oil sand materials are currently used as construction materials of temporary and permanent roads in oil sand fields for operating large capacity haul trucks and shovels. These materials often exhibit stress dependent, viscoelastic, and plastic behavior under off-road construction and mining equipment. Field studies have shown that the modulus and deformation behavior of oil sands are primarily dependent upon the

Large-Scale Triaxial Tests to Study Effects of Compaction Energy and Large Cyclic Loading History on Shear Behavior of Gravel

This study examines the effects of compaction on peak strength and small strain stiffness of large prismatic specimens of gravel by conducting monotonic and large cyclic loading triaxial compression tests. The specimens were prepared using an automatic compaction system while measuring quantitatively the compaction energy. For the evaluation of small strain stiffness, a static technique using small cyclic vertical loading with local strain measurement and a dynamic technique using P-wave measurement were employed. It was revealed that the peak strength of compacted gravel increased in a non-linear manner with the increase in the compaction energy. On the other hand, the difference between statically and dynamically measured small strain Young's moduli was reduced as a result of increase in the compaction energy. The peak strengths of three almost equally dense specimens were found similar to each other irrespective of the difference in the loading histories with/without large cyclic loading. However, the values of the axial strain at the peak stress state were different among the three specimens, affected by the different loading histories.

A Try to Give a Unified Description of Toyoura Sand

In this paper, based on the model proposed by Zhang et al., 2007, a miner modification for the evolution equation of overconsolidation is carried out at first and then a unique description of the overall mechanical behaviors of Toyoura Standard Sand (TSS), a typical clean sand, was conducted, in which the eight parameters for describing TSS is kept constant no matter what kind of loadings or drainage conditions may be. In the theoretical simulation, based on conventional drained triaxial compression tests and undrained triaxial cyclic loading tests. the material parameters of TSS are determined. By using the uniquely determined material parameters, other tests under different loadings and drainage conditions are simulated by the constitutive model. The capability of the model to describe uniquely the overall behaviors of the sand under different drainage conditions and different loadings with one set of fixed parameters is verified.

Investigation on effectiveness of a prefabricated vertical drain during cyclic loading

The effectiveness of prefabricated vertical drains (PVDs) in enhancing the stability of soft soils during cyclic loading was investigated using triaxial cyclic loading tests. Both undrained and with PVD tests were employed to study the associated excess pore pressure and accumulated strain under the repeated loading condition. The loading frequency and cyclic stress ratio have been chosen to be the variables which influence the performance of soft clays. The experimental results illustrate that with PVDs, the excess pore water pressure generation during cyclic loading decreases significantly. It is found that the excess pore water pressure build up depends on both loading frequency and cyclic stress ratio. The excess pore water pressure will increase when each of them is increased. Furthermore, when the loading frequency is 0.1 Hz, the ratio of coefficient of consolidation under cyclic loading to that under static loading is almost one. With the increasing loading frequency, this ratio increases accordingly.

Geotechnical characteristics of volcanic soil from seismically induced Aratozawa landslide, Japan

This paper seeks to investigate the properties of volcanic soil from the Aratozawa landslide, the largest failure triggered by the 2008 Iwate-Miyagi Nairiku earthquake, Japan. The Aratozawa landslide, which extended about 1,200 m long and 800 m wide, consisted of a complex system of ridges and depressions, including a number of smaller failures that occurred within the slide body. Field investigation was carried out to study the geotechnical properties of pumice that was exposed at the scarp of two smaller slides. The pumice was found to be heavily weathered, having low dry density and high moisture content. Portable cone penetration tests were performed to evaluate the in situ properties of soil as well as to determine the thickness of the weathered zone. Laboratory examination included slake-durability tests, grain-size distribution analysis, and a series of cyclic loading triaxial compression tests conducted on undisturbed and reconstituted samples. Laboratory test data indicated that the soil had a high potential for generation of excess pore-water pressures, suggesting that liquefaction might have occurred in the weathered mass of pumice during the earthquake.

Development of residual strain in cyclic and creep loading triaxial tests on sand

Development of residual strain in cyclic and creep loading triaxial tests on sand

Laboratory Testing of Suction and Deformation Properties of Base Course Aggregates

The most significant problem related to base course aggregates in Finland and in many other countries affected by seasonal frost is the development of permanent deformations, especially during the frost-thawing period. From 1996 to 2000, a series of research projects was carried out to examine the mechanical, thermodynamic, electrical, and chemical factors that affect the seasonal variation of strength and deformation behavior of base course aggregates. The test series included frost heave tests and normal as well as long-lasting cyclic-loading triaxial tests performed in situations simulating seasonal conditions of dryness, moisture, and the period following a freeze—thaw cycle. Also, chemical and suction properties of the selected aggregates were examined. Results show clearly that even though the aggregates were reflecting significantly different permanent deformation behavior, the resilient deformation properties of all tested aggregates were relatively good, and their resilient modulus values were not significantly lowered even during the thawing phase. Meanwhile, the suction properties of aggregates appeared to have a significant effect on the deformation behavior. Suction properties, in turn, result foremost from the fines content but also from chemical properties of the aggregate. A fairly simple tube suction test proved to function well in identifying the problematic aggregates and in defining appropriate binder types and their required amounts. Further, the results suggest that the properties of aggregates bound with emulsified bitumen are not necessarily improved when binder content is increased.