High Void Ratio Research Articles

Estimating radial attenuation of vacuum pressure for dredged clays

The radial attenuation of vacuum pressure in dredged clays limits the effectiveness of vacuum consolidation. In this study, a series of model tests were conducted on five dredged clays with varying initial water contents to investigate this radial attenuation. The significant radial attenuation can be divided into two stages: the increasing and stabilization stages. In the stabilization stage, exponential radial attenuation is observed. Lower initial void ratio (e 0) and higher void ratio at liquid limit (e L) lead to a decrease in radial attenuation. Additionally, higher applied vacuum pressure (p v) results in a greater reduction in the magnitude of the radial vacuum pressure. In the increasing stage, the radial vacuum pressure increases exponentially to a stable state after start-up. The radial attenuation is attributed to the differential start-up time (i.e., initial time-point at which the increase begins) and varying increase rates. Lower e 0, higher e L, and higher p v values reduce the start-up time and raise the increase rate. A changing pattern is proposed to describe the exponential radial attenuation using three parameters: radial attenuation coefficient (k 2), increasing coefficient (k 3), and time-delay coefficient (D t). Furthermore, an empirical estimation for the radial attenuation is also suggested without relying on time-consuming tests

Enhancing Dynamic Shear Resistance and Efficient Micro-Void Reduction of Expansive Soil Using Activated Nano-Desilicated Fly Ash

Excessive swelling and high compressibility of soil have posed countless challenges such as poor dynamic shear strength for engineers dealing with cyclic loading in pavement structure. To address this challenge, the durability and mechanical properties of the investigated subgrade were treated with 10%, 20%, and 30% of activated nano-disilicate fly ash (NDFA) to the dry mass of the subgrade soil. A series of swelling pressure tests, One-dimensional compression tests, and dynamic triaxial (DT) tests were conducted on the samples fabricated using altered moisture content. The findings demonstrated that the swelling pressure and compressibility of the NDFA-treated specimens significantly decreased to an average of 15.3% and 18.4% respectively upon 20% inclusion of NDFA beyond which the swelling stress and compressibility values further decreased signifying the impact of NDFA on the expansive subgrade. The consolidation results also revealed that the treated soil’s consolidation parameters greatly decreased compared to the untreated soil with a high void ratio and compression index (Cc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${C}_{c}$$\\end{document}). The dynamic shear resistance of the subgrade soil increased by 36% upon the addition of 10% NDFA content compared to the untreated soil which portrayed a very low resistance against dynamic shear modulus (Gmax\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${G}_{max}$$\\end{document}) with a corresponding high damping ratio. The investigation revealed a strong correlation between Cc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${C}_{c}$$\\end{document} and dynamic shear modulus which is closely correlated to a coefficient determination of 0.99 due to the parameter’s dependency on porosity, particle shape, and stiffness.

Thermomechanical Vibration Response of Solid and Foam FGM Nano Actuator/Sensor Plates

Abstract Purpose In this study, the effect of foam structure on the thermomechanical behaviour of high void ratio porous FGM piezoelectric smart nanoplates is investigated. Method The material of the smart nanoplate consists of PZT-4 on the bottom surface and BaTiO3 on the top surface and is formed by functional grading of these two materials along the thickness of the plate. Four different foam distribution models are modelled to examine the foam structure of the highly porous smart nanoplate, which has become widespread in biosensor applications. For this reason, uniform, symmetrical, top symmetrical and bottom symmetrical foam distribution models are created up to 75% void ratio. To determine the nano size, equations of motion are obtained by using nonlocal strain gradient elasticity and sinusoidal shear deformation theories together, and these equations are solved by the Navier method according to general boundary conditions. Result and Conclusions As a result of the analysis, it is observed that the applied external electric potential creates a softening effect on the plates with the piezoelectric elasticity effect and therefore reduces the thermal buckling temperatures. It is observed that the presence of the foam structure significantly improves the thermal resistance of the material and increases the buckling temperatures. It is also observed that the foam distribution model has significant effects on the thermomechanical behaviour.

Study on the propagation characteristics of gas explosions disturbed by crushed rock in tunnels through gas-containing stratum

Gas explosions pose a serious risk to tunnel construction when through a gas-containing stratum. The crushed rock accumulated in tunnel could have a significant impact on explosion. To understand the mechanism of crushed rock influence on gas explosion, methane/air explosion experiments under the crushed rock with different blockage ratios and void ratios were carried out using an independently designed experimental system. The results show that the crushed rock can significantly affect the explosion intensity, and the various blockage ratios show a higher degree of influence than the void ratio. The crushed rock has the combined effect of accelerating and quenching on the flame, and there has an optimum blockage that dramatically accelerates the flame propagation. The needle-shaped, divergent and reversed flames appeared with high blockage ratio and void ratio conditions. The velocity ratio (ratio of the flame front velocities upstream and downstream of the crushed rock) has an exponential function relationship with the blockage ratio. Under certain void ratio conditions, the maximum explosion overpressure shows a parabolic trend with increasing blockage ratio. This study is helpful to guide the understanding of the explosion characteristics under practical tunnel conditions and the change law of flame structure with crushed rock obstruction.

Effect of carbonation on development of reactive MgO-based pervious concrete

Pervious concrete, developed to solve urban flooding and overloaded drainage issues, has limited strength due to its large void ratio. Reactive MgO cement (RMC) is a sustainable cement gaining strength through carbonation, which can have a more pronounced carbonation-induced enhancement in mechanical properties compared with Portland cement. However, its carbonation degree was limited due to the dense microstructure. To address both issues, pervious concrete using RMC was developed, and its void ratios were leveraged to facilitate the carbonation of RMC. Experimental results revealed that compared with that of samples cured under ambient environment (i.e. 4.7–15.7 MPa), the compressive strength of RMC-based pervious concrete cured under accelerated carbonation (11.2–39.7 MPa) and water/CO2 cycles (10.3–29.6 MPa) was enhanced by 77–278%. As the design void ratio increased from 0.15 to 0.30, the permeability coefficient of pervious concrete increased from 0.1 to 2.3 mm/s, while the carbonation of RMC-based pervious concrete also benefited from high void ratio, with the highest 28-day carbon sequestration ratio reaching 12.7%, as indicated by XRD, TGA tests and SEM observations. Furthermore, a mathematical model was established to estimate the thickness of cement paste on aggregates in pervious concrete, which was less than 1 mm and decreased as the design void ratio increased.

Failure of Gravel Compaction Pile (GCP) Improved Embankment – Case Study

Due to the scarcity of suitable land, it becomes necessary to utilize marshy lands consisting of soft soil for infrastructure development. Soft soil has a problematic nature due to its high moisture content, high compressibility, high void ratio and very low shear strength. Hence, it is a responsibility of the geotechnical engineers to overcome these issues by adopting suitable ground improvement techniques. Gravel Compaction Pile (GCP) is one of the most popular soft ground improvement techniques used in the field. This technique has been successfully applied during the construction of the Colombo-Katunayake Expressway project and the Outer Circular Highway project. However, GCP technique has failed in the Southern Expressway Extension Project from Matara to Beliatta section. Therefore, in this study, the causes of the failure of the GCP improved embankment section were studied based on the field records. The slope stability of the embankment during construction was analysed using Matsuo and Kawamura's method. Back analysis revealed that once shear failure occurred in the subsurface, the shear strength of the soft soil reduces to its residual value and it takes longer time to regain its original strength. Further, it was noted that when the soft soil thickness is greater than 10 - 12 m, it becomes extremely challenging to improve the soft ground without any reinforcement. Therefore, it is strongly recommended to accurately interpret the subsurface characteristics in order to select the most suitable ground improvement technique.

Influence of time on the small strain shear modulus of an allophanic volcanic ash

The small strain shear modulus is an important parameter in the assessment of soil dynamics problems. Studies on the small strain shear stiffness of volcanic ash remain rare probably because globally they cover just under 1% of the land surface. However, on a regional scale, this figure may be consequential as in the case of Japan, where about one third of its total land surface is covered by andosols. In this research, we aimed at understanding the influence of confinement time, a non-negligible parameter, contingent on the soil type, which needs to be accounted for when assessing the shear modulus. Bender element tests were conducted on allophanic volcanic ash, kuroboku soil sampled from the southern island of Kyushu in Japan. The allophanic ashes present all the characteristics of a non-textbook soil, notably high natural water content, high liquid and plastic limits and high void ratios. From the micrographic images, it was observed that the soil structure consisted of different types of porous particles (allophane, imogolite, volcanic glass and so on) at different internal spatial scales. Strong electrostatic bonding between the allophane particles means that in normal conditions the soil material exist as aggregates. The consequence is that the end of the consolidation stage is reached within a few minutes. Thus, the threshold demarcating the onset of the creep stage is different compared to sedimentary materials or other clayey soils. Based on the test results, empirical equations for predicting the time-dependent behaviour of the shear modulus were proposed.

An experimental study of stress-dependent water retention behaviour of two lateritic clays with different minerals

Lateritic soils are associated with a high content of sesquioxides, which enhance the aggregation of fine particles. The formation of aggregates can induce significant changes in the pore size distribution (PSD) and consequently affect the hydro-mechanical behaviour of lateritic soils. The influence of mineral types on the extent of aggregation and the stress-dependent water retention behaviour of lateritic clays is not well understood. In this study, the stress-dependent water retention curves (SDSWRCs) of a compacted lateritic sandy fat clay with halloysite (i.e., GLH) obtained from Ghana were measured at different net vertical stresses using an improved stress-controlled pressure plate apparatus. The results were then compared with those of another lateritic sandy lean clay with goethite (NLG) obtained from Nigeria. Additionally, scanning electron microscopy (SEM) was employed to examine the microstructure associated with these soils. The experimental results show that GLH has a higher ability to retain water than NLG at any given suction, even though the former has a higher void ratio than the latter prior to the drying-wetting cycle. This is because of the presence of relatively small aggregates and small-size macropores in GLH, as revealed by SEM images. On the other hand, the water retention capacity of both soils reduces with elevated stress levels, except at net vertical stress of 120 kPa for GLH, with a corresponding decrease in the rate of desorption. Furthermore, the overall increase in the total degree of hysteresis measured is almost 2 times higher for NLG (i.e., 116%) than GLH (i.e., 72%) in the stress and suction range considered, contrary to the decreasing trends commonly reported in the literature. It was found that the sizes of aggregates in GLH reduced (‘finer soil’) as stress level increased and caused more water to be retained. Conversely to GLH, the aggregate size remained unchanged for NLG, as revealed by aggregate size analysis. This is mainly because of the differences in the strengths provided by the unique minerals in the two soils (i.e., halloysite for GLH and goethite for NLG) to the aggregates, due to the different parent rocks from which the soils were formed.

Verification of The Possibility of Air-void Recovery in RSBS Double-Layer Low-Noise Porous Asphalt Pavement

Radial type styrene-butadiene-styrene double-layer low-noise porous asphalt (RSBS DLPA) pavement is a type of porous asphalt pavement which had high air-void ratio, and well-known to absorb tyre/pavement noise and the rain through the pavement's layer. According to the Korea Meteorological Administration, from July to August in 2022, the daily rain precipitation was more than 100 mm per day and categorized as heavy rain. Due to the high air void ratio in RSBS DLPA pavement, the rainwater will be transferred through the pavement layer. The heavy rain splashing onto the surface pavement is similar to the method using the low water pressure and low-vacuum that our company developed which helps to recover the low-noise porous asphalt pavement. In this study, the CPX method was used to measure the noise level before and after heavy rain to differentiate the noise level. The results showed that the heavy rain had an effect on reducing the noise level. Before heavy rain, the noise level was up to 89.9 dB, while the noise level was decreased to 87.7 dB after heavy rain. It is shown that our cleaning method able to recover the air-void content as same as heavy rain.

Laboratory Modelling and Analysis of Displacement Pile in Different Geometries on Alluvial Soils

Alluvial soils are weak soils require precautions, which have disadvantageous engineering characteristics such as low shear strength and bearing capacity, high void ratio and settlement potential. Different foundation systems are preferred for structures built on these soils to transfer the load effects safely. Pile foundations as a deep foundation is classified depending on various parameters such as; material property, application method, load-bearing method. In this study, cylindrical and square concrete piles with different cross-sections and lateral areas placed in the alluvial soil. The natural alluvial soil taken from İzmir province, Balatcik location was placed in displacement-controlled pile model unit with a unit weight of ≈ 17 kN/m3. The manufactured concrete piles were driven into soil with Standard Proctor hammer. Tensile effects were applied at different time intervals to examine long-term and short-term behavior. As result of experiments, load-displacement (p-y) and displacement-time (y-t) graphs were drawn. When the displacement piles were examined under long-term tension, it was seen that the cylindrical piles displaced most. Square piles with same cross-sectional area with cylindrical piles made less displacement. All studies were modeled 1:1 as numerical and compared with experimental results. Studies showed that the experimental and numerical results for pile behavior were compatible.

Numerical simulation of biaxial undrained shear test based on fluid–solid coupling DEM method

The undrained shear test plays a crucial role in comprehending the deformation and failure mechanisms inherent in rock and soil. While the test offers a macroscopic perspective, numerical simulations can delve into the microscopic aspects of sample behavior, thereby compensating for this limitation. Drawing inspiration from the measurement sphere fluid–solid coupling method and the discrete element method, this paper proposes a tailored numerical simulation approach for the biaxial undrained shear test. This approach is implemented in the high-performance discrete element software MatDEM. In this study, a rapid division method for the fluid network is presented, along with a detailed explanation of the control equation governing excess pore water pressure and fluid–solid interaction during shear. Subsequently, A custom flexible boundary with a relatively smooth surface is introduced to simulate the constraint of the rubber membrane, which helps reduce simulation errors. Furthermore, the specific process of the numerical simulation is introduced, and an effective method for generating samples with high void ratios is proposed. Finally, three different cases are presented, involving varying confining pressures, different void ratios, and specific shear paths, respectively. The results indicate that the proposed method can effectively simulate the process of undrained shear tests and accurately capture the excess pore water pressure responses, and lateral deformation of the samples during shearing.

Predictive Modelling of Land Subsidence Due to Groundwater Level Decline in Gedebage District, Bandung, Indonesia

The Gedebage district in Bandung city has experienced a vast physical development in recent years. Previous geodetic studies showed that the area undergoes high-rate land subsidence. The subsurface soil of the Gedebage area has remarkably high compressibility, void ratio, and water content. A thick sequence of soft organic clay of 20-27 m exists, making the area prone to subside. As the district continues to develop, it is important to predict the future rate of land subsidence in the area. This paper aims to analyze the contribution of groundwater exploitation to the land subsidence rate. A combination of 1-dimensional Terzaghi consolidation analytical analysis and numerical modeling was employed in this study. Groundwater level data up to 2015 was used, and hydrostatic condition was assumed to occur in 1986. Results show that the Gedebage area has subsided as much as 161 cm since 1986. Modeling results are consistent with geodetic survey results. It is predicted that the land subsidence will slow down in the next 40 years, provided that the groundwater level remains stable.

Engineering Properties of Novel Vertical Cutoff Wall Backfills Composed of Alkali-Activated Slag, Polymer-Amended Bentonite and Sand.

The workability, hydraulic conductivity, and mechanical properties are essential to contaminant containment performance of cementitious backfills in vertical cutoff walls at contaminated sites. This study aims to investigate the engineering properties of a novel vertical cutoff wall backfill composed of reactive magnesia (MgO)-activated ground granulated blast furnace slag (GGBS), sodium-activated calcium bentonite amended with polyacrylamide cellulose (PAC), and clean sand (referred to as MSBS-PAC). Backfills composed of MgO-activated GGBS, sodium-activated calcium bentonite, and clean sand (referred to as MSBS) were also tested for comparison purposes. A series of tests were conducted which included slump test, flexible-wall hydraulic conductivity test, and unconfined compression test. The pore size distributions of two types of backfills were investigated via the nuclear magnetic resonance (NMR) technique. The results showed the moisture content corresponding to the target slump height was higher for MSBS-PAC backfill than that for MSBS backfill. The MSBS-PAC backfill possessed lower pH, dry density, and higher void ratio at different standard curing times as compared to MSBS backfill. The unconfined compressive strength and strain at failure of the MSBS-PAC backfill were noticeable lower than those of the MSBS backfill. In contrast, the hydraulic conductivity of MSBS-PAC backfill was approximately one order of magnitude lower than that of the MSBS backfill, which was less than 10-9 m/s after 28-day and 90-day curing. Lower hydraulic conductivity of MSBS-PAC backfill was attributed to the improvement of pore structure and pore fluid environment by PAC amendment.

Experimental study on the behavior of single pile foundation under vertical cyclic load in coral sand

The bearing behaviors of piles in coral sand are critical for project safety due to the unique physical and mechanical properties of coral sand, such as high void ratio, high compressibility, high friction angle and easy to break. A series of model experiments were carried out in this study to evaluate the vertical behavior of single pile in coral sand foundation under cyclic dynamic load with the consideration of the influence of the amplitude of cyclic load, the static biased load and the number of cyclic. Load-settlement relationships, settlement-cyclic number relationships, pile tip and pile side resistances have been thoroughly investigated. Results showed that the load in coral sand foundation will transfer to the pile tip more obviously compared with the pile foundation in quartz sand. Therefore, the pile side resistance will be reduced while the corresponding pile tip resistance will be increased. Particularly, the weakening of side resistance mainly occurs in the first 500 cycles. The development of cyclic cumulative settlement is affected by the combination of the magnitude of static biased load and cyclic amplitude. The existence of static biased load is conducive to restrain the cyclic cumulative settlement when the amplitude of cyclic load is less than static load.

Characterization of engineering properties of deep-water soils in the South China Sea

The characterization of the geological and geotechnical properties of marine sediments is crucial for the exploration of subsea oil and gas resources. In this study, the engineering properties of deep-water soils recovered from the South China Sea (SCS) were in detail characterized via a series of laboratory tests to explore their physical, mechanical, mineralogical and microstructural behaviors. The results show that the index properties of deep-water soils are characterized by high natural water content, high void ratio, high Atterberg limits, but low density. The sensitivity of these soils is higher than 10, indicating their strong natural structure, which significantly controls the shear behavior and failure model. The intact samples show strain-softening to strain-hardening behavior with an increase in the confining pressure, while reconsolidated samples consistently show strain-hardening phenomenon under any level of confining pressure. The cyclic T-bar penetration tests show a dramatic strength degradation behavior of the intact samples. The compression curves of the intact samples always lie above the remoulded ones, and there is an obvious yielding phenomenon for the intact samples. The deep-water soils exhibit high thixotropy, as proposed by a criterion to evaluate the thixotropic capacity of soils. The mineralogy and microstructure analysis indicate that biogenic silica and an open flocculated structure might be the underlying reasons for the unique physical and mechanical properties of deep-water soils. The findings through this study provide essential parameters for related engineering applications and a deeper insight into understanding the unique properties of deep-water soils.

Compressibility, permeability and microstructure of fine-grained soils containing diatom microfossils

Fine-grained soils containing diatom microfossils of biological origin are found worldwide. However, although these soils are acknowledged to have unique physical and mechanical properties, the exact role of diatoms in determining their compression and hydraulic behaviours remains unclear, especially when high effective stress is involved, and the underlying micromechanism is yet to be revealed. This study investigated the compression and permeability of diatomaceous soils prepared by mixing pure diatom and kaolin powders through one-dimensional constant rate of strain compression tests with a maximum vertical stress of 10 MPa. The microstructure of the soils studied was observed by atomic force microscopy, scanning electron microscopy and mercury intrusion porosimetry, and the microstructural evolution during compression was traced. The results indicate that the special hollow structure of diatom particles with internal pores contributes significantly to the high void ratio, compressibility and permeability of diatomaceous soils, and increasing the diatom content improves the pore distribution non-uniformity of the diatom–kaolin mixtures. In addition, the diatom particles have high brittleness and breakage potential, leading to microstructural rearrangement during compression, especially pore-structure adjustment. Lower compressive stress deforms the inter- and intra-aggregate pores, but higher vertical stress damages the diatoms’ hollow structure, which changes the compression and hydraulic parameters in a different manner from the case of conventional clay. This paper enriches the knowledge concerning the multilevel behaviour of fine-grained soils containing diatom microfossils and provides a fundamental dataset.

Swelling–shrinkage mechanisms of diatomaceous soil and its geohazard implication

Current understanding of soil behaviors from classic soil mechanics is constantly challenged by a variety of unusual soils, one of which is diatomaceous soils (DSs). It is well understood that this biological-origin soil has fundamentally different geotechnical features from that of common fine-grained soils because of the presence of diatom fossils. Recently, increasing geohazards and engineering disasters associated with DS swelling–shrinkage are reported but the exact role of diatoms in determining soil swelling–shrinkage, the underlying mechanisms, and the geohazard implications, have not yet been revealed. This study systematically investigates the swelling–shrinkage behavior of natural DS as well as artificial mixture of diatoms and clay minerals (kaolinite and montmorillonite). The swelling–shrinkage behaviors are explained from the perspectives of mineralogy and microstructure as revealed through X-ray diffraction, scanning electronic microscopy, and transmission electron microscopy. Diatoms have a special microstructure with inter-frustule pores, and the intra-skeletal and skeletal pores in DS make the soil characterized by a high void ratio and water content. In addition, the presence of diatoms curbs the swelling–shrinkage of DS but this may be overwhelmed by the high stress generated due to the swelling of montmorillonite. The wetting–drying cycles subjected to DS result in fissure development, a higher level of swelling–shrinkage behavior, and ultimately in related geohazards such as landslides. The distinct swelling–shrinkage behavior of DS makes the previous classification inapplicable; thus, more rational classification methods are adopted. This study enhances the understanding of the swelling–shrinkage behavior of DS and the control of related geohazards.

Reinforcement of Calcareous Sands by Stimulation of Native Microorganisms Induced Mineralization

Calcareous sand is a special soil formed by the accumulation of carbonate fragments. Its compressibility is caused by a high void ratio and breakable particles. Because of its high carbonate content and weak cementation, its load-bearing capacity is limited. In this study, the optimal stimulation solution was obtained with response surface methodology. Then, the effect of reinforcing calcareous sand was analysed with unconfined compressive strength (UCS) tests, calcium carbonate content tests, microscopy and microbial community analyses. The components and concentrations of the optimal stimulation solution were as follows: sodium acetate (38.00 mM), ammonium chloride (124.24 mM), yeast extract (0.46 g/L), urea (333 mM), and nickel chloride (0.01 mM), and the pH was 8.75. After the calcareous sand was treated with the optimal stimulation scheme, the urease activity was 6.1891 mM urea/min, the calcium carbonate production was 8.40%, and the UCS was 770 kPa, which constituted increases of 71.41%, 35.40%, and 83.33%, respectively, compared with the initial scheme. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses showed that calcium carbonate crystals were formed between the particles of the calcareous sand after the reaction, and the calcium carbonate crystals were mainly calcite. Urease-producing microorganisms became the dominant species in calcareous sand after treatment. This study showed that biostimulation-induced mineralization is feasible for reinforcing calcareous sand.

Investigation of the Impact of Tropical Red Clay Soils' Mineralogical Composition on their Physical and Mechanical Properties– a Case Study Ruaka – Kenya

Introduction: Residual soils covering large areas of the earth have been chiefly discovered in the last 30 years in most volcanic tropical and subtropical countries. Understanding their behaviour is essential for various infrastructure developments. Methods: The physical and mechanical properties of the soils are affected by their mineralogical composition. There is a need to determine the mineralogical composition of the soils and investigate the impact on properties. This paper presents the results of a laboratory study conducted on red clay soil from Ruaka, a suburb in Kenya, to investigate the effect of mineral and chemical composition on the soil’s physical and mechanical properties. Disturbed and undisturbed samples were subjected to different tests such as Atterberg limits, soil classification, consolidation test, X-ray fluorescence, X-ray diffraction and petrology test based on the British Standard soil classification system (1377-1994). The soils were classified as clay with high plasticity, and high clay content varied between 59-79% resulting in mechanical instability of the soil in this site. Results: The mineral and chemical analysis indicated the formation of unique minerals like Halloysite, Quartz, Kaolinite, and Mica, which influenced the geotechnical properties of clay. The index properties of clay recorded high values; the moisture content and plastic limit varied between 37- 46% with a slight increase as depth increased; the liquid limit varied between 63-68% with increased depth. Conclusion: The average value of maximum dry density was reported as around 1247 kg/m3 with high optimum moisture content, reaching 35.5%. Besides that, the soil had a high void ratio of 1.145 to 1.63, which increased the permeability of the clay to 1.223E-5 cm/s. The properties of red clay soils in more than ten tropical regions in Kenya compared with the soil under study are also presented in this paper.

Mechanical properties of unbound granular materials reinforced with nanosilica

The development of new technologies for soil improvement has been a hot research topic in the fields of geological engineering, geotechnical engineering, and road engineering. Nanomaterials have been proven to offer significant advantages in the field of geotechnical material enhancement due to their unique structures and excellent properties. The effect of nanosilica amount on the stress-strain behavior, elastic modulus, shear strength, and shear parameters of unbound granular materials was investigated, and its potential enhancement mechanism was discussed in this research. Treated samples with nanosilica contents (by weight) of 0,1%, 2%, 3%, 3.5%, 4%, and 4.5% were prepared and rigorously examined through unconsolidated undrained (UU) triaxial tests under different confining pressures. Also, the intrinsic mechanism and variations in the microstructure of the specimens were investigated by the computed tomography (CT) and scanning electronic microscope (SEM). Testing results showed that with the addition of more nanosilica, the elastic modulus and shear strength of the specimens increased and the ductility decreased. The apparent cohesion of the treated specimens increased approximately linearly and had almost as little effect on the internal friction angle. The maximum improvement rate was obtained at 3.5% of nanosilica content. The CT and SEM scanning results indicated that the control specimen has a higher void ratio than the treated specimens, and the filling and nucleation effects of nanomaterials may be the intrinsic mechanism to improve the mechanical properties of unbound particulate materials. The experimental results contribute to enriching the application of nanomaterials in geotechnical engineering, guiding the optimization of mechanical properties of unbound granular materials.