Cyclic Shear Tests and DEM Analysis of Soil-Rock Mixture-Concrete Interfaces with Different Fine Contents

Geosynthetics are being widely used as a reinforcement material in the construction of mechanically stabilized earth (MSE) walls. The strength and stability of these walls are depending upon the interface behavior between soil and reinforcement material. It is understood from the literature review that the dynamic interface properties of soil and geosynthetics are not well explored yet, as in the case of static loading conditions. The present study investigates the cyclic behavior of the interface between sand and non-woven geotextile material. The objective was achieved by simulating the cyclic direct shear test using finite element-based package PLAXIS2D. The behavior of interface shear stiffness, and damping ratio were studied with increase in number of cycles and displacement amplitude. In addition, the interface behavior of geotextile with the sand having different fines content was also studied. The results revealed that the increase in the fines content causes the reduction in the interface shear stiffness. The interface shear strength properties obtained from the cyclic direct shear test were compared with the static shear test. The friction angle obtained from the cyclic shear test was 6% higher than that obtained from the static direct shear test.

The suitability of strength parameters for stability calculation is very much important in evaluating landslide slope stability. A new cyclic direct shear apparatus which can be brought in the field was designed for the purpose of quick and rational determination of strength parameters. The features of this apparatus are: 1) the apparatus can be brought in the field due to its compactness and light weight, 2) cyclic shear test with any cycle and amount of shear displacement can be performed automatically, 3) since normal force is controlled by high accuracy digital servo motor system, both constant pressure test and constant volume test can easily be performed, and 4) friction force between sliding surface of the specimen and the surfaces of the upper and lower boxes can be measured by the load cells installed inside the shear boxes.Residual strength parameters can be obtained from the cyclic shear test with this apparatus and using intact specimen sampled from the site. Strength parameters corresponding to fully softened state can also be obtained by the specimen which is made by fully remolding the specimen after cyclic shear test and preconsolidating it from the state of slurry. The two sets of strength parameters (cr, φr) for residual state and (cs, φs) for fully softened state, respectively obtained from the tests mentioned above, can be used for the method of determination of design strength parameters proposed by the present authors.Case studies for two sites of landslide proved the suitability of the strength parameters determined from the method based on the experimental data obtained by new designed cyclic direct shear test apparatus.

With the rapid increase in global waste generation, waste management has become an urgent global issue. This thesis begins with a scientometric analysis of solid waste research (SWR) trends, examining over 17,000 related publications to explore the evolving trends and influencing factors. The current focus of SWR is shifting towards biological treatment, waste source reduction, waste recycling, and the properties and reutilization of byproducts. Despite the growing interest in emerging technologies like “biogas”, established methods including “landfilling” and “incineration”, handle over 80% of the world's waste disposal needs. Given Singapore's imperative need to extend the lifespan of its only operational landfill, landfill mining and waste reuse present viable solutions. Therefore, a thorough investigation of different types of waste under the unique conditions of the offshore landfill is essential and fundamental to all subsequent efforts. This thesis explores the application of machine learning-enhanced multi-geophysical site investigation methods at Semakau Landfill (SL). The study employs Electrical Resistivity Tomography (ERT), Induced Polarization (IP), Multichannel Analysis of Surface Waves (MASW), and Microtremor Array Measurement (MAM) to investigate waste layers in SL, validated by geotechnical and geochemical test results. To accurately describe the heterogeneity of the landfill, unsupervised machine learning clustering methods are used to stratify the wastes based on geophysical investigation results, providing explicit classification criteria. This approach performs well in long-term cells, yielding a 3D stratified model consistent with borehole records. Geophysical results indicate that wastes with a high proportion of unincinerated materials have higher resistivity and chargeability than marine clay, which can be used to accurately determine the waste boundary. Low resistivity usually indicates higher saturation or concentrated leachate. High polarization areas may contain more metallic waste or active biodegradation reactions. Shear wave velocity (Vs) can be used to distinguish embankment boundaries and assess the consolidation degree of wastes. Despite the significant variability in the properties of mixed waste materials (MM), the trend of averaged geophysical parameters across different depth levels can be used to reasonably estimate waste depth, water table, and the distribution of stiff layers. The relationship between Vs and Standard Penetration Test (SPT) obtained through regression analysis allows for reasonable predictions of the stiffness of MM based on surface wave survey results. Using SPT and Igeo (Geochemical index) as labels, training geophysical results with the Artificial neural network (ANN) method provides reliable predictions of SPT and Igeo for areas without drilling and sampling. This method, combined with a set of geotechnical and geochemical data, enables a reasonable estimation and description of the stiffness and contamination levels across the entire area. To verify the feasibility of reusing waste materials, this thesis employs cyclic simple shear tests and shear wave velocity measurements to analyze the static and dynamic shear properties of incinerator bottom ash (IBA). The friction angle of IBA varies from 38.3 to 42.5° as density increases, while it consistently exhibits strain-hardening behavior. IBA tends to liquefy under unidirectional cyclic test conditions with lower cyclic stress ratio (CSR) and consolidation stress, while cyclic mobility failure is more common for multi-directional cyclic tests with higher CSR and consolidation stress. The cyclic resistance ratio reduction factor (RFCRR) for IBA ranges from 0.70 to 0.73, which can be used to correct the overestimation of cyclic shear resistance obtained from unidirectional cyclic shear tests. The cyclic stress ratio – normalized shear wave velocity (CSR – Vs1) plot shows that the liquefaction behavior of IBA under cyclic shear loading is similar to that of natural sand with 5% fine content, suggesting that fine content might be a factor controlling the liquefaction behavior of IBA.

During earthquake, soil deposits are subjected to cyclic loading. Under undrained conditions, cyclic shear stress causes transient disturbance and gives rise to an increase in excess pore water pressure leading to loss of shear strength in saturated soil deposits, there will be excessive strains with continued loss of shear strength resulting in liquefaction. Researchers have identified a significant number of cases where ground failure took place during earthquake in soil deposits containing fines leading to considerable damage to buildings. Some studies show a decrease in liquefaction resistance and others show an increase in liquefaction resistance with an increase in fines content in soil deposit. There is no clarity regarding the effect of fines. In view of this, an experimental investigation has been carried out to evaluate the liquefaction potential of sand-clay mixtures. A series of undrained stress-controlled cyclic triaxial shear tests were performed on reconstituted samples obtained from Cauvery River sand and sand mixtures containing different percentages of plastic fines up to 30%. This paper reports the results of stress-controlled cyclic triaxial shear tests under undrained conditions at 100 kPa confining pressure at a frequency of 0.1 Hz. The results show that the cyclic strength decrease with an increase in fines content upto 20% beyond which it increases. In the present investigation, the limiting fines content is 20%. The results of CRR were analyzed in terms of relative density, fines content, and plasticity characteristics. The results indicate that flow liquefaction depends on the acceleration (CSR) and initial state (void ratio).

When loose, saturated sands and non-plastic silts are subjected to undrained cyclic loading, they will generate positive pore pressures. This increase in pore pressures leads to a decrease in effective stress with a corresponding decrease in shear strength and increase in liquefaction susceptibility. For combinations of sand and non-plastic silt, the threshold fines content can be defined as the non-plastic silt fines content at which the soil changes from sand-like behavior to silt-like behavior. Soils below the threshold fines content behave like sands and soils above the threshold fines content behave like silts. During cyclic triaxial and cyclic direct simple shear tests performed on specimens of sand and silt prepared to the same relative density but different fines contents, two rates of pore pressure generation were observed. When compared at five cycles of loading, soils with silt contents above the threshold fines content were found to produce pore pressure ratios as much as 50% higher than those observed for soils with silt contents below the threshold fines content. When evaluated in terms of cycles, cycle ratio, and dissipated energy ratio, the rate of pore pressure generation was found to be more rapid for soils above the threshold fines content than for soils below the threshold fines content.

In order to investigate the failure mechanism of rock joint, a series of laboratory tests including cyclic direct shear tests under constant normal load(CNL) conditions were conducted. Morphology parameters of the rock joint surface were precisely calculated by means of a three-dimensional laser scanning machine. All test results were analyzed to investigate the shear behavior and normal displacement behavior of rock joints under CNL conditions. Degradation of rock joint surface during cyclic shear tests was also analyzed. The comparison results of the height parameters and the hybrid parameters of the joint surface during cyclic tests show that the degradation of the surface mostly happens in the first shear and the constant normal loads imposed on the joints have significant promotion effects on the morphology degradation. During cyclic shear tests, joints surfaces evolve from rough state to smooth state but keep an overall undulation. Dilatancy of rock joints degrades with the degradation of joint surface and the increase of normal loads. The closure deformation of joint is larger than that of the intact rock, and the normal stiffness increases with the increase of shearing times.

Pre-shear effect on liquefaction resistance of a Fujian sand

Pre-shear history has been proven to be a critical factor in the liquefaction resistance of sand. In contrast to prior experimental studies in which triaxial shear tests were used to examine the effect of pre-shear on the liquefaction resistance of sand, hollow cylinder torsional shear tests were used in this study, to avoid the influence of inherent anisotropy that is inevitably produced during the sample preparation process due to gravitational deposition. A series of cyclic undrained shear tests were carried out on sand samples that had experienced different degrees of pre-shear loading. The test results showed that the liquefaction resistance of sand is greatly reduced by its pre-shear history, and a small pre-shear strain can cause sand to be much more prone to liquefaction. During the cyclic shear tests, the samples that had experienced pre-shear loading exhibited different behaviors when cyclic shear loading started in different directions, i.e. the clockwise direction and the counterclockwise direction.

An experimental investigation of the dynamic internal shear behavior of a hydrated needle-punched geosynthetic clay liner is presented. Monotonic and cyclic displacement-controlled shear tests were conducted at a single normal stress to investigate the effects of displacement rate, displacement amplitude, number of cycles, frequency, and motion waveform on material response. Monotonic shear tests indicate that peak shear strength first increased and then decreased with increasing displacement rate. Cyclic shear tests indicate that cyclic response was primarily controlled by displacement amplitude. Excitation frequency and waveform had little effect on cyclic shear behavior or postcyclic static shear strength. Number of cycles (greater than or equal to 10) also had little effect on postcyclic static shear strength. Shear stress versus shear displacement diagrams displayed hysteresis loops that are broadly similar to those for natural soils with some important differences due to the presence of needle-punched reinforcement. Secant shear stiffness displayed strong reduction with increasing displacement amplitude and degradation with continued cycling. Values of damping ratio were significantly higher than those typical of natural clays at lower shear strain levels. Finally, cyclic tests with increasing displacement amplitude yielded progressively lower postcyclic static peak strengths due to greater levels of reinforcement damage. Postcyclic static residual strengths were unaffected by prior cyclic loading.

Liquefaction resistance of Christchurch sandy soils from direct simple shear tests

Undrained cyclic response of silty sands improved by microbial induced calcium carbonate precipitation

Earthquake-induced large deformations and failure mechanisms of silty sands in sloped ground conditions

Combined effect of fines content and uniformity coefficient on cyclic liquefaction resistance of silty sands

An extensive experimental program of constant-volume (undrained) cyclic simple shear tests was undertaken on Ticino, Italy, sand with different contents of nonplastic fines, ranging from 0% to 40%. The samples were reconstituted by moist tamping and tested with different initial states, including void ratios and effective vertical stresses. Test results confirmed that the concept of equivalent granular void ratio e* is appropriate for the interpretation of the undrained cyclic behavior of sand with different amounts of fines up to the limiting fines content. Because a single trend for critical state (CS) data points was observed in the e*-log(p′) plane (EG-CSL) for different amounts of fines, the cyclic simple shear test results were analyzed within a unified critical state soil mechanics (CSSM) framework in terms of an alternative state parameter, Ψ*. A unique correlation between undrained cyclic strength (CRR) and Ψ* was found, irrespective of the fines content and initial state. Although a correlation between the cyclic resistance ratio and the conventional state parameter Ψ works as well, the procedure based on Ψ* has the advantage that the cyclic behavior of a certain sand with different contents of non plastic fines is described by a single reference curve (EG-CSL). In contrast to previous investigations in the literature, which mainly used triaxial tests, the CRR-Ψ* correlation proposed in the present study is based on cyclic simple shear tests, which better represent the real ground conditions under seismic loading.

The SHS-Multirisk Project proposes a residence model that is simultaneously resistant to earthquakes and hurricanes within a specific range of magnitude to be defined in the project. It uses simple, low-cost, and environmentally friendly construction technologies compared with traditional alternatives or more technological, but less accessible ones. To reach the SHS-Multirisk objectives, an experimental campaign to carry on cyclic shear tests involved a set of 15 reinforced soil-cement compressed earth block walls. Within this program, a particular test system was developed, conditioned by the guidelines: simplicity, availability of resources (especially components, equipment, and workmanship), rationalization of the available space, and scalability of the tests. Considering the short time available for designing and manufacturing the test system and for carrying out the shear tests, it was decided to adopt a project management framework in Scrum mode. This article presents the system developed to conduct full-scale cyclic shear (combined with bending) tests on walls, exploring its characteristics, the development process, the experiment execution process, and a basic analysis of the main test outputs.