Soil Specimens Research Articles

Small-strain stiffness of liquefiable sands: A comparison between bender elements and resonant-column tests

Soil stiffness can be estimated by geophysical and dynamic testing methods. In the laboratory, the most common methods to measure the small-strain stiffness are the bender elements (BE) and resonant-column (RC) tests. This paper focuses on the comparison between the results of the small-strain stiffness of sands by BE and RC tests. For this purpose, an experimental program involving three liquefiable sandy soils (i.e., NB, TP-Lisbon and Toyoura sands) was carried out. Such program covered the measurement of the small-strain stiffness of these soils by BE in triaxial and RC apparatuses for different mean effective stress conditions. All tests were carried out on saturated soil specimens, which were remoulded using the air pluviation method for various relative densities. The experimental results were interpreted in terms of shear-wave velocity (Vs) and maximum shear modulus (Gmax) to derive the stress-dependency laws of these parameters. The experimental results revealed differences between Vs obtained from BE and RC tests, evidencing a clear effect of relative density on the shear-wave propagation. However, such a variation may be significantly reduced when a normalisation of Gmax in terms of a void ratio function F(e) is applied. As a result, this study demonstrated and validated the importance of accounting for the soil state conditions, for adequate compatibility of BE and RC tests in the estimate of the small-strain stiffness of liquefiable sands.

Evaluation of soil texture classification from orthodox interpolation and machine learning techniques

The current investigation examines the effectiveness of various approaches in predicting the soil texture class (clay, silt, and sand contents) of the Rawalpindi district, Punjab province, Pakistan. The employed techniques included artificial neural networks (ANNs), kriging, co-kriging, and inverse distance weighting (IDW). A total of 44 soil specimens from depths of 10–15 cm were gathered, and then the hydrometer method was adopted to measure their texture. The map of soil grain sets was formulated in the ArcGIS environment, utilizing distinct interpolation approaches. The MATLAB software was used to evaluate soil texture. The gradient fraction, latitude and longitude, elevation, and soil texture fragments of points were proposed to an ANN. Several statistical values, such as correlation coefficient (R), geometric mean error ratios (GMER), and root mean square error (RMSE), were utilized to evaluate the precision of the intended techniques. In assessing grain size and spatial dissemination of clay, silt, and sand, the effectiveness and precision of ANN were superior compared to kriging, co-kriging, and inverse distance weighting. Still, less than a 50% correlation was observed using the ANN. In this examination, the IDW had inferior precision compared to the other approaches. The results demonstrated that the practices produced acceptable results and can be used for future research. Soil texture is among the most central variables that can manipulate agriculture plans. The prepared maps exhibiting the soil texture groups are imperative for crop yield and pastoral scheduling.

Landslide Risk Assessment and Preventive Measures of Selected Locations in the Rangamati District, Bangladesh

Detecting landslides and unstable slopes is one of the most crucial responsibilities in the emergency response to resist landslides. Having a wide range of hilly terrines in the southeast region of Bangladesh, the risk of landslide disasters is becoming a critical issue. In Chittagong, especially in the Rangamati hill tracts, there have been several losses of life and property due to landslides in the recent past. This research attempts to evaluate the landslide risk in Rangamati hill tracts and provide suggestions to mitigate the landslide hazard by modifying the hill slope. Soil specimens from different hill locations were collected from three areas in the Rangamati district. Several laboratory experiments were conducted to determine the soil properties, and 2D slope stability analysis using Bishop's simplified method was used to evaluate the landslide potential. Different preventative measures, for example, soil nailing, anchors, and cutting slopes like stairs, are also implemented to mitigate the landslide potential by increasing the slope stability was assessed and suggested. Weighted Overlay Model (W.O.M.) was implemented for the Landslide Susceptibility Analysis in ArcGIS to confirm the potential hazard in the study areas, and hazard maps were suggested based on the slope stability results and current slopes in Rangamati. The slope stability analysis of the three spots showed that spot 3 is the most vulnerable spot, which had a low factor of safety value. Even with different mitigation techniques, spot 3 showed a lower factor of safety value, which was verified with the Weighted Overlay Method. It was also seen that among the mitigation techniques, anchoring the slopes is the most effective one that drastically increases the factor of safety value.

Possible remediation of impact-loading debris avalanches via fine long rooted grass: an experimental and material point method (MPM) analysis

Debris avalanches often originate along steep unsaturated slopes and have catastrophic consequences. However, their forecast and mitigation still pose relevant scientific challenges. This is also due to the variety of mechanisms observed near high sub-vertical bedrock outcrops, such as the impact loading of soil failed upslope the outcrop, the build-up of pore water pressures in the inception zone, and the bed entrainment along the landslide propagation path. At the University of Salerno, an experimental and numerical investigation campaign started some years ago to explore the feasibility of using long-root grass to mitigate or even inhibit the inception of debris avalanches. Previous laboratory results were achieved through two twin 2-m-long columns (one bare, one vegetated), where the change in soil retention curve and soil mechanical response was assessed. As follow-up, an experimental field setup was installed in 2020 first, and in an improved configuration in 2021. Here, three different species of long-root grass were grown. In situ soil suction and water content measurements were periodically collected in the vegetated and in the original soils. In both cases, soil specimens were also collected, and laboratory geotechnical tests were performed to individuate the changes in both the water retention and strength response. Increased values of soil suction and shear strength were outlined, despite some differences, for all the grown species compared to the original soil. Using these novel experimental data, advanced large-deformation stress–strain hydro-mechanically coupled analyses were recently performed through a material point method (MPM) approach. The original slope conditions were compared to various slope configurations engineered via long-root grass. The benefits and the open issues related to this novel green technology for landslide mitigation are discussed. Some insights are outlined for the possible reduction of the soil volumes mobilized inside the inception zone of debris avalanches.

Utilization of Coffee Husk Ash on the Geotechnical Properties of Gypsum-Stabilized Expansive Clayey Soil

Expansive clayey soils (CSs) expand and become softer as moisture content increases, but they get harder and stronger as they dry out. The earth’s swelling and shrinkage characteristics under varying moisture conditions make roads built on expansive CS, in particular, vulnerable to early degradation. In this investigation, coffee husk ash (CHA), gypsum, and a blend of the two additives (G-CHA) were used in experimental tests to treat expansive CS. This study aims to evaluate experimentally the potential of expansive soil stabilization using different additives: CHA, gypsum, and a combination of gypsum and CHA. Five different percentages of CHA (5%, 10%, 15%, 20%, and 25%), three percentages of gypsum (3%, 6%, and 9%), and variable percentages of their combinations were used to stabilize the soil for pavement subgrade application. Atterberg limits, compaction, linear shrinkage (LS), swelling, unconfined compressive strength (UCS), and California bearing ratio (CBR) tests were performed on treated and virgin soil specimens at 3, 7, 14, 28, and 56-day curing times. Results showed that CHA additives effectively reduced the plasticity, LS, and swell potential in addition to increasing the maximum dry unit weight, UCS, and CBR. It was determined that the UCS and CBR values for the 6% stabilized gypsum soil increased by 28.95% and 19.54%, respectively, and reduced by 41% of the plastic index parameter after the addition of 15% CHA. Based on the evaluation of the results, an optimum mixture of 6% gypsum and 15% CHA (SG6C15) stabilized soil can be used in pavement subgrade applications as it achieved the minimum strength target. The performance of CHA-treated samples as subgrade material is superior to that of untreated virgin soil. Because of the stronger subgrade, smaller pavement layers result in a thinner pavement structure.

Behavior of clayey soil treated with nano magnesium oxide material

Clayey soils are spread in many countries and require significant improvement. Recently, nanomaterial have been entered to the geotechnical research as a treatment material. Current study utilized magnesium oxide (MgO) as an additive to enhance swelling potential, compressibility characteristics, and index properties of clayey soil from Mosul city using different content of nano-MgO and under varies curing periods. The results showed that the free swell and swell pressure of the soil specimens have been reduced by 25%, and 19%, respectively for 0.25, and 0.75% content of nano material under 3 days of curing time at 25C. Results also showed that the compressibility characteristic represented by the compression index parameter has been reduced by 20.3% for 0.75% of nano-MgO material. Moreover, the soil plasticity index exhibited a maximum increase at 0.75% of nano content. Moreover, results showed that the pH value increased while the electrical conductivity (EC) decreased with the nano-MgO content. To evaluate the curing time effect, specimens were cured for varies curing time under curing temperature of 25 ºC. Then, the free swell, swell pressure, compression index, and Atterberg limits were measured. The results revealed that the free swell and swell pressure for both untreated and treated specimens were reduced during different periods of curing time. Furthermore, the compression index of treated soil was reduced by approximately half for curing time of 28 days. In sum, the swelling and consolidation reduction with curing brought significant improvement and promising results for the treated samples.

Effects of pre-shearing stress ratio on the mechanical behaviours of gap-graded soils subjected to internal erosion

Internal erosion can induce significant changes in the mechanical properties of soils, posing various hazards to dam and dike structures. Despite its importance, our current understanding of this phenomenon remains incomplete. The influence of pre-shearing stress conditions on the mechanical behaviours of soils during the internal erosion process is particularly challenging, as existing experiments have not been able to maintain the constant pre-shearing stress ratios. To bridge this gap in knowledge, this paper presents a series of discrete element method (DEM) simulations focused on gap-graded cohesionless soil. The primary objective of these simulations is to investigate two specific cases of internal erosion: suffusion and suffosion processes. Soil specimens are subjected to different pre-shearing stress ratios in the standard triaxial tests before being submitted to different levels of erosion to study their constitutive responses. The results show that erosion-induced deformation (i.e. suffosion) only starts after a specific amount of mass loss. This mass loss and the pre-shearing stress ratio form a well-defined criterion for triggering suffosion, which is named “suffosion surface”. The volumetric strain is shown to be a better indicator to describe the suffosion process than the commonly used void ratio. The pre-shearing stress ratio significantly influences the suffosion response of the soil sample, with a higher pre-shearing stress ratio facilitating soil failure. Furthermore, soil specimens undergo both deviatoric and volumetric responses during the suffosion process. To this end, new DEM-based statistical equations were proposed to describe the observed mechanisms, which are helpful for the future development of constitutive models to describe internal soil erosion.

Fibre optic sensing for strain-field measurement in geotechnical laboratory experiments

Strain measurement inside the soil body in three-dimensional (3D) experiments is a real challenge for physical modellers in geotechnics. The use of fibre optic sensing offers the possibility of continuous measurement of the strain at depth with high spatial and temporal resolution in small-scale laboratory experiments. Despite the technology not being fully ready yet for centrifuge experiments, this is an important development in geotechnics. This paper explores the capacities of distributed fibre optic sensing (DFOS) as a solution for direct soil strain profile measurement at depth. A series of small-scale plane-strain experiments is used to simulate the simple case of the formation of a downwards subsidence. DFOS cables are laid in the soil specimen, and strains are directly compared with the soil movement, recorded with cameras through particle image velocimetry. Results indicate the ability of DFOS in detecting soil movements and underline the typical signature strain profile expected during this type of experiments. Finite-element analyses are carried out to further underpin the consequences of performing these tests at 1g and extend the findings to potential applications in 3D and on the geotechnical centrifuge. This shows promising results for detection of soil strain profiles inside the soil body in 3D.

Insight on characterization through porosity-to-lime index of a stabilized soil for the long-term

The strength of lime-cemented soils has received significant attention in previous studies. However, limited research has focused on studying soil mixtures for extended durations beyond 365 days, which is essential for understanding shear strength, microstructure, unconfined compressive, and matric suction. Consequently, there is a need to explore the long-term behavior and unsaturated properties of soil specimens cured for up to 500 days using appropriately hydrated lime, considering the semi-empirical porosity/lime index. By investigating various curing times ranging from 15 to 500 days, as well as employing different compaction energies (standard, intermediate, and modified) and lime content ranging from 3% to 9% by weight, this study aims to characterize the evolution of resistance and unsaturated properties of lime-cemented soils. The semi-empirical porosity/lime index is employed to guide the characterization and analysis of the mixtures' resistance properties. By developing equations to estimate the resistance of these mixtures, the study contributes to reducing lime consumption (and reducing CO2 emissions during its production) and optimizing curing time, leading to environmentally friendly geotechnical projects. Due to the utilization of the porosity/lime ratio, lime consumption can be minimized, and curing time can be fixed, resulting in a significant reduction in energy requirements, which is beneficial for the environment. The outcomes of this research have profound implications for the design and construction of sustainable structures such as dams, pavements, and slope protection systems, ensuring their long-term stability, resilience, and ecological balance.

The influence of soil fabric on the monotonic and cyclic shear behaviour of consolidated and compacted specimens

While the fabric of soil can significantly influence its behaviour, the effect of varying fabric parameters on the subgrade shear response is still not well understood. This study creates soil specimens with different fabrics which are then captured through X-ray microscopic-computed tomography scanning and quantified by image processing techniques. A comprehensive laboratory investigation is conducted to understand how the soil fabric affects its monotonic and cyclic shear behaviour. The results indicate that the consolidation method creates a more homogeneous fabric with mainly small-to-medium interconnected pores, whereas the compaction technique creates significantly large and mostly inter-aggregate pores with lower connectivity. In this regard, the consolidated specimens exhibit an elastic-perfectly plastic behaviour, while the compacted specimens show strain-hardening transformation during isotropic monotonic shearing. Under anisotropic conditions, the compacted specimens exhibit a greater strain softening response and excess pore pressure than the consolidated specimens because they have a weaker fabric. Furthermore, the compacted specimens show a smaller threshold strain at a lower critical number of cycles due to the collapse of large pores. These current findings prove the decisive role that soil fabric plays in determining the shear response and failure of subgrade soils.

Experimental Wave-Based Assessment of Liquefaction Resistance for Different Degrees of Saturation

Abstract This paper presents the results of an experimental program carried out in the laboratory aimed at assessing the liquefaction resistance by correlations between longitudinal wave (P-wave) and shear wave (S-wave) velocities (VP and VS) and cyclic stress ratio from triaxial testing (CSRCTx) for different degrees of saturation (Sr). The liquefaction resistance was assessed using a cyclic triaxial apparatus equipped with Hall-effect transducers and bender elements, combining stress-based (large-strain level) and wave-based (small-strain level) approaches. These tests were carried out in soil specimens at relatively high degrees of saturation, which were estimated during testing by VP measurements interpreted using Biot’s theory. The results revealed that, for the same relative density and confinement stress, the S-wave-based approach did not predict the liquefaction resistance well because of the negligible variation in the stress state and soil stiffness for the assessed Sr values, which were above the air-entry value. In turn, the P-wave-based approach effectively predicted the liquefaction resistance increment of the TP-Lisbon sand for different Sr conditions because of the strong dependency of P-wave propagation on the degree of saturation in granular media. This is a consequence of the most relevant factor conditioning the pore pressure buildup in partially saturated sands, e.g., the compressibility of the occluded air bubbles, which can be detected by VP but not by VS.

Heavy metal(loid)s contamination and ecotoxicological hazards in coal, dust, and soil adjacent to coal mining operations, Northwest Pakistan

Heavy metal(loid)s (HM) are ascertained hazardous to the environment due to their toxic, bioaccumulative, and persistent nature. Coal, dust, and surrounding soil near coal mines (n = 21) in each specimen were examined for HM in the districts of Hangu and Kurram. Samples were investigated for HM using the atomic absorption spectrophotometer. Iron (Fe) exhibited the highest mean concentrations, whilst molybdenum (Mo) showed the lowest in the selected coal, dust, and soil specimens were 62,100 and 1.14, 52,610 and 0.9, and 45,300 and 2.0 mg/kg, respectively. HM in studied media was evaluated for ecotoxicological factors, namely contamination factor (CF), potential-ecological risk index (PERI), hazard index (HI), and cancer risk. CF values of dust were very-high and considerable due cadmium (Cd) in the districts of Hangu and Kurram, while that of soil were considerable in both districts. The ecological-risks (190 < PERI<380) were “considerable” due to dust and soil of the Hangu district, while the “moderate” ecological-risk (95 < PERI<190) was noted for the Kurram district. The HI values surpassed the limit of 1 for children due to soil and dust exposures. Higher HI values may pose chronic health risks to the locals. Among exposure routes, oral ingestion was noted as the primary pathway's. CR values were noted as less than the threshold set by the US EPA. This study recommended that HM contaminations be monitored periodically on a priority basis to develop strategies for combating the problem of health concerns.

Experimental Study on the Synergistic Solidification of Soft Soil with Ceramic Powder–Slag–Phosphorus Slag

The bearing capacity of silt soft soil is poor, making it difficult for it to be used as a subgrade material in foundation engineering, and the use of traditional Portland cement curing agents causes environmental pollution. In this study, a new soft soil curing agent, CSP (ceramic powder–slag–phosphorus slag), was prepared using ceramic powder, slag, and phosphorus slag. The unconfined compressive strength of 7-day was determined via an orthogonal test, and the optimal ratio of the curing agent was determined. The effects of the initial water content, curing agent content, admixture type, and admixture content on the mechanical properties of solidified soil were investigated via a uniaxial compression test. The microstructure characteristics of the solidified soil were analyzed via XRD and SEM-EDS, and the mechanism by which ceramic powder–slag–phosphorus slag acted as a curing agent to increase the strength of the soft soil was explored. The results show that the optimal ratio of the curing agent for the inorganic binder is ceramic powder/slag/phosphorus slag = 3:2:1, the best water glass modulus is 1 mold, the best water glass content is 26%, and the 7-day compressive strength can reach 2.382 MPa; the strength of the solidified soil decreases with an increase in the water content and increases with an increase in the curing agent content. When the water content is 35% and the curing agent content is 14%, the strength of the solidified soil can meet the requirements of relevant specifications. When the content of triisopropanolamine was 2.0% and 1.5%, the compressive strength of the 7-day and 28-day solidified soil specimens increased most significantly. The ceramic powder–slag–phosphorus slag can promote the formation of aggregates and amorphous hydration products (C-S-H, C-A-H), be distributed on the surface of the soil and fill the pores, and enhance the cementation between the particles, improving the compactness of the soil structure. In terms of the macroscopic performance, the mechanical properties of the solidified soil were significantly improved. Therefore, CSP curing agents can be promoted and applied as green, economical, environmentally friendly, and low-carbon curing materials in soft soil roadbed engineering.

Mechanical and deformation behavior of clay reinforced by discarded mask fibers

The outbreak and spread of the new coronavirus epidemic has caused a large number of using masks, which leads to a huge amount of discarded masks that may have serious effects on the ecological environment. To further verify the feasibility of the discarded masks for soil reinforcement and quantify its reinforcing effects, the tensile property tests of masks, the triaxial tests of mask fiber reinforced soil and the scanning electron microscope tests were carried out. The test results showed that the tensile strength of the discarded mask was about 15% lower than that of the new mask. Mask fiber reinforcement could improve the shear strength of clay and effectively restrain the bulging deformation of the soil specimen. At the optimum fiber content of 0.1%, the peak deviatoric stress was increased by around 20%. The reinforcing effect of discarded mask fibers for the same type of soil reached approximately 85% of that reinforced by polypropylene fibers. At a certain fiber content, the shear strength of the soil specimen was relatively high when the water content was low. The soil specimen showed a characteristic of brittle failure. With increasing water content, the shear strength of the soil specimen decreased and the plasticity gradually increased. It could be seen from the SEM images that the bonding and friction between the fibers and soil particles as well as the constraint behavior caused by the fiber webs were the main reasons for the strength improvement of the soil specimens. However, the reinforcing effect of polypropylene fiber was better because of its uniform distribution in the soil. The investigation results of this study can provide guidance for the application of discarded masks in geotechnical engineering.

Effects of fir-wood biochar on CH4 oxidation rates and methanotrophs in landfill cover soils packed at three different proctor compaction levels

Application of biochar to landfill cover soils can purportedly improve methane (CH4) oxidation rates, but understanding the combined effects of soil texture, compaction, and biochar on the activity and composition of the methanotrophs is limited. The amendment of wood biochar on two differently textured landfill cover soils at three compaction levels of the Proctor density was explored by analyzing changes in soil physical properties relevant to methane oxidation, the effects on CH4 oxidation rates, and the composition of the methanotrophic community. Loose soils with and without biochar were pre-incubated to equally elevate the CH4 oxidation rates. Hereafter, soils were compacted and re-incubated. Methane oxidation rates, gas diffusivity, water retention characteristics, and pore size distribution were analyzed on the compacted soils. The relative abundance of methanotrophic bacteria (MOB) was determined at the end of both the pre-incubation and incubation tests of the packed samples. Biochar significantly increased porosity at all compaction levels, enhancing diffusion coefficients. Also, a re-distribution in pore sizes was observed. Increased gas diffusivity from low compaction and amendment of biochar, though, did not reflect higher methane oxidation rates due to high diffusive oxygen fluxes over the limited height of the compacted soil specimens. All soils, with and without biochar, were strongly dominated by Type II methanotrophs. In the sandy soil, biochar amendment strongly increased MOB abundance, which could be attributed to a corresponding increase in the relative abundance of Methylocystis species, while no such response was observed in the clayey soil. Compaction did not change the community composition in either soil. Fir-wood biochar addition to landfill cover soils may not always enhance methanotrophic activity and hence reduce fugitive methane emissions, with the effect being soil-specific. However, especially in finer and more compacted soils, biochar amendment can maintain soil diffusivity above a critical level, preventing the collapse of methanotrophy.

Exploring the combination of biochar‐amended soil and automated irrigation technology for water regulation and preservation in green infrastructure

AbstractBiochar is a carbon sink material with the potential to improve water retention in various soils. However, for the long‐term maintenance of green infrastructure, there is an additional need to regulate the water contents in the covers to maintain vegetation growth in semiarid conditions. In this study, biochar‐amended soil was combined with subsurface drip irrigation, and the water preservation characteristics of this treatment were investigated through a series of one‐dimensional soil column tests. To ascertain the best treatment method specific to semiarid climatic conditions, the test soil was amended with 0%, 1%, 3%, and 5% biochar. Automatic irrigation devices equipped with soil moisture sensors were used to control the subsurface water content with the aim of enhancing vegetation growth. Each soil column test lasted 150 h, during which the volumetric water contents and soil suction data were recorded. The experimental results reveal that the soil specimen amended with 3% biochar is the most water‐saving regardless of the time cost. Soil with a higher biochar content (e.g., 5%) consumes a more significant amount of water due to the enhancement of the water‐holding capacity. Based on the experimental results, it can be concluded that the appropriate ratio can be determined within 1%–3%, which can reduce not only the amount of irrigated/used water but also the time cost. Such technology can be explored for water content regulation in green infrastructure and the development of barriers for protecting the environment around deep underground waste containment.

Improving soil resilience to drought climate by an eco-friendly approach

With the intensification of global warming, the increasing extreme drought climate has seriously threatened the stability of critical geotechnical infrastructure. This study proposes a novel, eco-friendly approach to improve soil resilience to drought climate. In order to verify the feasibility and durability of the proposed approach, a series of simulated climatic wetting-drying (WD) cycles were carried out using four sets of soil specimens treated with different W-OH (an eco-friendly polymer) concentrations. During this period, the water evaporation history, desiccation cracking process, WD cycle durability and microstructure evolution of soil specimens treated with different W-OH concentrations were investigated. The results reveal that the W-OH modification has a significant suppression effect on the whole process of soil evaporation, which can effectively prolong the soil evaporation time of constant rate stage and falling rate stage. The addition of W-OH not only significantly reduces crack ratio, total crack length, and average crack width, but also slows down the crack growth rate. Compared with untreated soil specimen, the treatment with low concentration of W-OH (2% and 4%) can effectively mitigate the formation of desiccation cracks, while the treatment of higher concentration of W-OH (6%) can directly prevent the occurrence of such cracks. The microstructure analysis results indicate that the W-OH can transform the soil structure into a denser state through two ways of bridging and encapsulation, which significantly increases the migration resistance of pore water and improves soil strength properties. This investigation is expected to improve fundamental understanding of soil-atmosphere interactions under eco-friendly polymer modification and provides insights into the potential application of eco-friendly polymer modification in enhancing soil resilience to extreme drought climate.

An Experimental Analysis of Precipitated Silica in Petroleum-Contaminated Clay for the Strengthening of Soil Characteristics

In recent times, the environmental impacts of petroleum-contaminated clay (PC clay) have intensified, leading to more severe detrimental effects. To address this issue, the use of precipitated silica (P silica) has proven to be an effective solution. P silica offers improved treatment for the contaminated clay and enhances the engineering properties of the soil. A series of experiments such as pH test, electrical conductivity test, unconfined compressive strength (UCS) test, California bearing ratio (CBR) test, free swell index (FSI) test, compaction test and Atterberg limit tests were conducted to compare the soil characteristics of the PC clay with and without the treatment of P silica. The PC clay soil specimens were tested after the inclusion of P silica with varying dosages of 0%, 3%, 6%, 9% and 12% by dry weight of clay soil. The inclusion of P silica at a dosage of 6% resulted in the optimum strength of 275.12 kPa. This dosage also led to a reduction in free swell index (FSI) and maximum dry density (MDD), indicating a flocculation mechanism caused by the presence of P silica. Additionally, there was an improvement in stiffness and strength parameters, as evidenced by the enhancement in CBR (California bearing ratio). Therefore, the effective utilization of P silica in contaminated clay soil provides a variety of applications in the geotechnical field.

A new empirical model for the undrained shear strength of undisturbed marine fine-grained soil based on piezocone penetration tests

Simple, precise, and economical evaluation of the undrained shear strength Su of undisturbed marine soil can facilitate the construction of offshore projects. In this study, piezocone penetration tests (CPTu) were conducted at the site of a wind power project, and consolidated undrained triaxial tests were performed on specimens of undisturbed marine fine-grained soil taken from the site. Analysis shows that the Eslami–Fellenius and Chinese soil classification methods based on CPTu data are more applicable for marine soils. The test results indicate that the stress–strain curve exhibits strain softening if the clay content is less than 30 %, otherwise it exhibits either strain hardening or strain stability. Furthermore, the specimens exhibit two deformation failure modes: softening contraction and hardening dilatancy. From the correlation between the consolidated undrained triaxial test data and the CPTu data, Su can be determined simply via an explicit expression involving the measured pore pressure behind the cone (u2), the corrected cone tip resistance (qt), and the soil depth H, and this expression is significantly more precise than the existing empirical formulas. The proposed method offers a sound basis for designing the foundations of marine engineering and infrastructure projects in different sea region.

Modernized Resonant Column and Torsional Shearing Apparatus With Multipoint Contactless Displacement Detection System

Abstract In this study, a modification of resonant column/torsional shearing (RC/TS) apparatus was proposed to perform a qualitative analysis of a noncohesive soil specimen vibration during RC tests. An additional multipoint displacement detection system was installed in the RC/TS WF8500 device. In the new measuring system, 48 mini-magnets are attached to the side surface of a cylindrical soil specimen, creating a regular grid of measuring points. Around 48 Hall sensors (Honeywell SS495A1) are used to measure changes in the magnetic field strength due to the movement of the corresponding magnets on the surface of the specimen subjected to dynamic torque. The Hall sensor generates an analog signal that is proportional to the change in the magnetic field. The measurements are collected with a newly developed data acquisition system that consists of a set of analog-to-digital converters and a set of ARM (Advanced RISC (Reduced Instruction Sets Computing) Machine) microcontrollers. The measurement system is controlled with a dedicated software, ControlRec, developed by the authors. The measurements are taken synchronically with and independently from the standard RC test procedure. The new measuring technique allows to observe displacements of the 48 points on the specimens’ surface with over 4 times higher sampling rate than in the original measuring system. As a result, additional effects related to the mechanical wave propagation through soil specimen were observed (local disturbances in distribution of vibration amplitudes or significant displacements near the bottom end of the specimen, which is assumed to be fixed in the standard RC/TS results analysis), that could not be identified using the standard equipment of the device.