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To investigate the effect of in-pit vehicle load on the stability of the pit against overturning, a long tunnel foundation pit project in Suzhou is used as a case. In-pit vehicle load effects are modelled using the improved equivalent soil thickness method. Through the utilization of the upper limit theory of limit analysis of finite soils and considering the spatial distribution of suction force in the matrix of unsaturated soils, a deduced method for calculating the stability coefficient of the unsaturated finite soil pit against overturning under vehicle load is established. The results indicate that in-pit vehicle load favours pit stability against overturning relative to conventional outside-pit vehicle load. The change in pit stability is more significant when the soil rupture angle is corrected by using the improved equivalent soil thickness method. The increased suction in the unsaturated soil matrix contributes to the pit's stability against overturning. When calculating the stability coefficient against overturning, the finite earth pressure theory proves to be more realistic than the classical earth pressure theory. The results of this study can provide a valuable reference for similar types of pits to prevent overturning. [ABSTRACT FROM AUTHOR]

Nano-SiO2, a highly acclaimed nanomaterial for enhancing cemented soil, has shown remarkable improvements in the physical properties and microstructure of cemented soil. The organic matter content in soil plays a crucial role in determining the engineering quality of cemented soil, regardless of whether it is in a freshwater or seawater environment. Therefore, when employing Nano-SiO2 as an amendment for cemented soil, it is crucial to consider the influence of different soil types and environmental conditions on the effectiveness of the enhancement. This study presents a scientific approach for enhancing the consolidation of cemented soil by incorporating Nano-SiO2 as an additive in both freshwater and seawater environments. To ensure consistency with practical construction practices, the experiments were divided into freshwater preparation and curing groups, as well as seawater preparation and curing groups. In soils with distinct characteristics, we utilized five different gradient levels of Nano-SiO2 additives and subjected the cemented soil specimens to a 60-day immersion curing process. Subsequently, unconfined compressive strength (UCS) tests were performed on samples that had reached the specified curing age to investigate the alterations in the mechanical properties of cemented soil caused by Nano-SiO2. The internal microstructure and chemical composition of the cemented soil were analyzed utilizing scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The UCS and deformation modulus of cement soil composed of silty clay A and silty clay D with low organic matter content in fresh water environment increased by 109%, 24.7% and 117%, 43% respectively after adding 3.2% Nano-SiO2; In freshwater environments, the cemented soil composed of high-organic-matter content mucky silty clay B, muddy soil C, and dredged silt E experienced respective increases of 16% and − 27%, 2% and 42%, 6% and − 6% in UCS and deformation modulus after adding 3.2% Nano-SiO2; The UCS and deformation modulus of cemented soil with high organic matter content in seawater and freshwater environment increased by 3% and 6% (Soil B), 12% and 67% (Soil C), 23% and 27% (Soil E), respectively, after adding 3.2% Nano-SiO2; The increase of UCS and deformation modulus of cement soil by adding Nano-SiO2 is negatively correlated with the content of organic matter. in the case of cemented soil with high organic matter content in a seawater environment, the specific type of soil not only impacts UCS and deformation modulus of the soil but also influences the effectiveness of enhancement. Due to the organic matter, the rate of hydration reaction in cemented soil is reduced, resulting in a decrease in the formation of pozzolanic reaction products with SiO2. As a result, the improvement in Nano-SiO2 effectiveness is diminished. [ABSTRACT FROM AUTHOR]

Due to the twofold influence of irregular excavation and geometric effect, the deformation mechanism of foundation pits is complicated. To investigate the impact of uneven excavation and geometric differences on the deformation characteristics of deep foundation pits, a long tunnel Phase IV deep foundation pit project in Suzhou is used as a case. Through the field measured data, the special effects of inclined pit bottom and rectangular shape are analyzed, and the deformation characteristics of the pit are summarized, as well as compared against the statistical data. The results indicate that the overall deformation of the pit is small since the pit is in a semi-excavated state. The excavation depth has a significant impact on pit deformation, and irregular excavation will cause the distribution of pit deformation to be skewed towards the deeper side of the excavation depth. As a result of the uneven excavation, the actual working condition of each portion of the foundation trench is inconsistent, causing the unexcavated portion to disturb the excavated portion, resulting in an ongoing process of cumulative deformation. Under the influence of the geometric effect of the rectangular pit, the deformation distribution pattern along the longitudinal section of the pit is parabolic with peaks at the centre and minimal towards the ends. The results of this study can provide a reference for the excavation design of the same type of pit and the study of pit deformation characteristics. [ABSTRACT FROM AUTHOR]

An analytical approach for quantitatively estimating the behavior of existing pile due to adjacent pile driving in slope, which is crucial to evaluate the potential risk of existing pile-based buildings. In this study, a two-stage method is utilized for analyzing the behavior of an existing pile to adjacent pile driving. First, a simplified model for deriving the free-field lateral slope displacement due to pile driving is proposed. In this model, a group of single spherical cavities expansion is utilized to simulate the process of pile penetration, and the stress function is used to account for the influence of the slope surface boundary condition. Validity and precision of this approach are determined by comparing it to previously published studies. To analyze pile-soil interaction, secondly, the Pasternak foundation model and the soil lateral displacement generated by nearby pile driving in the first stage are introduced. The suggested model's validity and correctness in the second stage is confirmed by comparing it to the finite element model. Finally, a variety of distinct parameters are done for an adequate discussion of the variance about the existing pile's behavior resulting from nearby driving. [ABSTRACT FROM AUTHOR]

The major drawbacks of a railway track include noise, vibration, and aggravated track degradation. Resilient mats and asphalt have been increasingly used in recent years to mitigate this noise and vibration. However, these materials are quite expensive. Conventional asphalt is very stiff and brittle, making it more prone to cracking. The present work aims to develop a novel material that can be used as a base layer in ballasted and slab tracks. The current research proposes a sustainable and resilient base course layer comprising ground rubber (GR) and polyurethane foam adhesive (PFA). In this study, the performance of GR embedded in the sand is investigated. The use of PFA-treated sand with and without GR is then explored. The optimum dosage of PFA for soil and GR for treated and untreated soil is recommended based on static direct simple shear (SDSS) and cyclic direct simple shear (CDSS) tests. SDSS tests were performed to evaluate the monotonic performance of all mixtures. CDSS tests were performed to assess the long-term performance of these different mixes under repeated cyclic loading (50,000 load cycles) and varying cyclic shear stress amplitude. It is shown that PFA helps reduce the settlement and enhance soil shear strength, while GR increases the damping ratio of the soil. The optimum dosage of PFA is recommended 10%. The optimum GR content for untreated and PFA-treated soil is recommended 5 and 10%, respectively. [ABSTRACT FROM AUTHOR]

The present research focuses on developing alternate sustainable base materials for a high-speed slab track. In this study, a series of monotonic triaxial, cyclic triaxial and permeability tests were conducted on four types of materials, viz. mix-A (gravel soil), mix-B (soil mixed with rubber), mix-C (polyurethane foam adhesive (PFA)-treated soil), and mix-D (PFA-treated soil–rubber mixture). The influence of cyclic loading frequency, effective confining pressure, drainage condition and relative density on the deformation, excess pore water pressure, resilient modulus and damping ratio of these different mixes is evaluated. The monotonic triaxial test results indicate that the PFA treatment of mix-A and mix-B increased their shear strength and critical state strength. In contrast, incorporating rubber into mix-A and mix-C helped enhance their ductility. The cyclic triaxial test results show that the PFA treatment of mix-A and mix-B significantly reduced the magnitude of deformation and generation of excess pore water pressure, which caused these untreated mixes to fail prematurely under lower confinement to which a typical base layer is subjected. The influence of cyclic loading frequency and effective confining pressure on the material's response differed for untreated and treated soil. The permeability test results indicate good drainage for mix-D comparable to mix-A. [ABSTRACT FROM AUTHOR]

The landfill liner is the last line of defense to protect the soil from damage, but it is difficult to satisfy both impermeability and crack resistance requirements with conventionally compacted clay. This paper proposes a new composite material to enhance the anti-seepage and anti-cracking properties of clay as a solution to this problem. In this Study, the effects of two single amendment materials, Nano-SiO2 (6 dopings) and sisal fiber (SF) (4 dopings), and a composite amendment material (Nano-SiO2+SF), on the permeability and cracking resistance of the improved clay were investigated by infiltration tests and dry-wet cycle tests, respectively. The nuclear magnetic resonance test (NMR) test reveals the microscopic pore changes of soil and explore the reinforcement mechanism. The findings of penetration experiments demonstrate that Nano-SiO2 and SF, both single and composite components, can increase the modified clay's impermeability. The optimum content of Nano-SiO2 is 3%, and its permeability coefficient is 5.09 × 10−8 cm·s−1, which is two orders of magnitude lesser than that of virgin soil. The results of three dry and wet cycle tests showed that the overall trend of fracture length and cracking factor (CIF) increased with the increase of the number of de-wetting. After the third de-wetting of the modified clay, 0.75% Nano-SiO2 + 0.3% SF is the optimal dose, which reduces the fissure length by 19.94 times and CIF by 27.25 times compared with the three de-wetting of the plain clay. As a whole, the data demonstrates that the composite Nano-SiO2 and SF are able to make up for the shortcomings of each component. It can simultaneously improve the anti-seepage and anti-cracking properties of the enhanced clay. The test results provide a certain benchmark for the impermeability and anti-cracking of landfill liners. [ABSTRACT FROM AUTHOR]

The poor performance of critical zones along a railway line has long been a subject of concern for rail infrastructure managers. The rapid deterioration of track geometry in these zones is primarily ascribed to limited understanding of the underlying mechanism and scarcity of adequate tools to assess the severity of the potential issue. Therefore, a comprehensive evaluation of their behaviour is paramount to improve the design and ensure adequate service quality. With this objective, a novel methodology is introduced, which can predict the differential plastic deformations at the critical zones and assess the suitability of different countermeasures in improving the track performance. The proposed technique employs a three-dimensional geotechnical rheological track model that considers varied support conditions of the critical zone. The approach is successfully validated with published field data and predictions from finite element analysis. This methodology is then applied to a bridge-open track transition zone, where it is observed that an increase in axle load exacerbates the track geometry degradation problem. The results show that the performance of critical zones with weak subgrade can be improved by increasing the granular layer thickness. Interpretation of the predicted differential settlement for different countermeasures exemplifies the practical significance of the proposed methodology. [ABSTRACT FROM AUTHOR]

This study presents a computational analysis of pipeline failure and soil penetration when struck by lightning. A numerical method based on an electro-thermal coupled model is proposed for this purpose. The electric disruption of soil and the thermal damage of pipelines are used to represent engineering failures and calamities. The heterogeneity of the soil and the temporal-spatial distribution of lightning are considered when modelling natural lightning and the ground. Innovative numerical simulations illuminate the mechanisms and processes underlying electrical disasters and pipeline failure. The simulation results indicate that lightning strikes can induce electric penetration in soils and damage underground pipelines. Under the calculative conditions of this article, a cloud-to-ground lightning strike with a voltage of 10 kV can cause a thermal breakdown hole in an underground conduit with a wall thickness of 0.05 m and a depth of 1 m. At the same time, the temperature rises to 500 °C at the location of the pipe perforation opening and 200 °C at the location of the unperforated pipe. The novel numerical method may reveal the mechanism of pipeline failure and the electric penetration of soil during lightning impacts. [ABSTRACT FROM AUTHOR]

This paper presents a computational analysis of the evolution of mechanical characteristics in natural rock formations under the combined action of high-voltage electro-pulse and fluid injection. To solve the combined problem, a numerical solution based on a hydromechanical model is proposed. A system of anisotropic damage model is applied to capture tensile and shear damage. Innovative numerical simulations reveal that high-voltage electro-pulse can significantly enhance the effectiveness of rock-breaking in fluid injection. The simulation consists of two primary phases. First, high-voltage electro-pulse causes pre-damage and radial fissures in the rock formation, which creates a more favorable environment for subsequent fluid injection. The fluid flux is then conducted in the pre-damaged hole to fracture the rock formation further. The unique numerical method may have consequences for optimizing the rock-breaking strategy in geoengineering applications, such as the development of geothermal systems and the exploitation of oil/gas resources. Highlights: Presenting a novel method for rock-fracturing, high-voltage electropulse-assisted fluid injection. The hydro-mechanical coupled model is employed in the stage of electropulse and fluid injection. A system of tensile–shear mixed damage model is demonstrated and utilized to capture the tensile and shear damage. The in situ stress field and heterogeneity are considered to model natural rock formation. [ABSTRACT FROM AUTHOR]

Cemented soil structures are frequently exposed to the corrosive environment of seawater for an extended period, severely affecting their interior structure and mechanical qualities. This study presents laboratory-based approach to investigate the effect of nano-SiO2 on the structural and mechanical properties of cemented soil in a simulated seawater environment. The unconfined compressive strength (UCS), elastic modulus and other mechanical properties of cemented soil mixed with nano-SiO2 and ordinary silicate cemented soil were evaluated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to deduce the crystalline composition and microstructure characteristics of the modified cemented soil. The results show that the addition of nano-SiO2 greatly increased the compressive strength and corrosion resistance of the cemented soil. In a 3C (105% salinity) simulated saltwater curing environment, the compressive strength of the cemented soil containing 2% nano-SiO2 increased by 86% and 158% at 30days and 60days, respectively. XRD and SEM showed that nano-SiO2 enhanced the interface structure of cemented soil and increased the compactness of the cement-soil system. The current study demonstrates that nano-SiO2 could considerably improve the mechanical characteristics and corrosion resistance of cemented soil when exposed to simulated seawater. [ABSTRACT FROM AUTHOR]

Cemented soils are subjected to a variety of adverse environmental conditions in the marine environment, including corrosive seawater exposure, the dry–wet cycle, and temperature variations. These environmental conditions significantly jeopardize the reliability and durability of foundations built on these types of engineered soil. The addition of nanoparticles to this cement treated soils is offered as an engineering solution for extending their service life. Four different nanomaterials that have been extensively studied in the literature are employed as admixtures in the cemented soil. Appropriate dosages of these nanomaterials are determined based on the data from unconfined compressive strength test (UCS) and the scanning electron microscopy (SEM). Wet–dry cycles are applied on the cement treated soil samples to simulate the tidal rise and fall relevant to the marine environment. Nuclear magnetic resonance tests (NMR) are also performed to complement the SEM study. Incorporating Nano-SiO2 into soft soil cured with cement in marine environment improved the mechanical strength and stiffness of the cement soils. It also decayed the corrosion rate of the cemented soils in ocean, and the improvement in mechanical stability was also quite remarkable. After 60 cycles of seawater exposure, the strength of Nano-SiO2 cement soils increased by 3.4 times that of conventional cemented soils, while the corrosion rate decreased by 85%. The improved durability of Nano-SiO2 cemented soils is a function of their structural filling tropism and distribution tropisms. The improved durability of Nano-SiO2 is a result of the combined effect of particle effect, volcanic ash effect and nucleation effect. [ABSTRACT FROM AUTHOR]

This article presents a mathematical model for simulating the mechanical behaviour of lightning strikes and analysing the resulting damage to the soil. This article focuses on the electro-thermal effect and seepage caused by lightning strikes in particular. Then, a numerical model based on the conservation laws of momentum, mass and energy is developed for soil subjected to lightning strikes. Comparisons to field observations and theoretical calculations are used to demonstrate the efficacy and accuracy of numerical simulations. The findings demonstrate that lightning strikes can cause soils to experience both seepage force and heat stress. Under the calculative condition of this article: by increasing the intrinsic permeability of the soil, kp (≥10−10 m2), the seepage force can be effectively reduced, hence reducing the risk of lightning strikes; improving the electrical conductivity of the soil β (≥10−1 S/m) and lowering its thermal expansion coefficient (≤10−6 K−1) can greatly reduce the damage caused by lightning strikes to the soil. The preceding investigations demonstrate that the suggested model is capable of evaluating mechanical damage caused by lightning in the soil, and the findings contribute to a better understanding of soil mechanical response to lightning strikes [ABSTRACT FROM AUTHOR]

In order to examine the thermal effect of lightning currents on sandstone, an electro-thermal coupling model based on electromagnetic field and heat transfer theory was constructed. This model considers the spatial Gaussian distribution of lightning current. The model is validated by comparing field observations and theoretical analyses from the previously published studies. The transient calculation is performed to investigate the dynamic change process within the sandstone during lightning strikes, and the effects of related factors such as the peak current of the lightning current, waveform parameters, and electrothermal parameters of the sandstone on the model results are analysed. The results indicate that a lightning strike generates a large amount of electromagnetic heat in the sandstone, causing it to heat up and melt or even vaporize. The entire dynamic process exhibits a logarithmic growth tendency, with rapid development of temperature and phase change areas during the early stages of lightning current, followed by gradual increases until constant. The temperature varies most dramatically around the lightning strike point, and the area affected by lightning strikes decreases as the horizontal plane deepens. Within the sandstone, both the temperature isosurface and phase transition area show a hemispherical distribution. When the peak current is greater, the wave front time is shorter, the half-value time is longer, the resistivity is greater, or the specific heat is more, the overall temperature in the sandstone is greater, and the phase change region is larger under the same conditions. [ABSTRACT FROM AUTHOR]

The stress–dilatancy relation is of critical importance for constitutive modelling of geomaterial. A novel fractional-order stress–dilatancy equation had been developed for granular soil, where a nonlinear stress–dilatancy response was always predicted. However, it was experimentally observed that after a certain extent of shearing, an almost linear response between the stress ratio and the dilatancy ratio, rather than the nonlinear response, usually existed. To capture such stress–dilatancy behaviour, a new fractional stress–dilatancy model is developed in this study, where an apparent linear response of the stress–dilatancy behaviour of soil after sufficient shearing is obtained via analytical solution. As the fractional order varies, the derived stress–dilatancy curve and the associated phase transformation state stress ratio keep changing. But, unlike existing researches, no other specific parameters, except the parameter related to fractional order, concerning such shift are required. Then, the developed stress–dilatancy model is applied to constitutive modelling of granular soil and soil–structure interface, for further validation. A series of test results of different granular soils and soil–structure interfaces under different loading conditions are simulated and compared, where a good model performance is observed. [ABSTRACT FROM AUTHOR]

The three-dimensional analysis of slope stability with cracks is crucial to investigate the mechanism of slope landslides to achieve desired accuracy. In the frame of limit analysis, the kinematic approach is adopted to evaluate the three-dimensional slope stability with cracks, based on a modified 3D horn-like rotation mechanism including below-toe failure. The effect of pore water pressure is considered using a commonly adopted coefficient ru. Stability charts are presented for convenience in the form of the dimensionless critical height γH/c as well as the factor of safety without iterations. The results indicate that the presence of pore water pressure decreases the stability of slopes and increases the depth of the crack. Gentle slopes with large values of ru are found to be more prone to below-toe failure. [ABSTRACT FROM AUTHOR]

Calcareous sand is widely distributed in the islands of the South China Sea, which could be promisingly used as the construction materials. However, particle breakage commonly occurs in calcareous sands, which may significantly influence their mechanical characteristics. To address these issues, an eco-friendly agent, i.e., polyurethane foam adhesive (PFA) is proposed to improve the engineering properties of calcareous sands, compared to the commonly used alkaline stabilizing agents (e.g., lime, cement). The objective of this work is to examine the effectiveness of using PFA in improving the strength-deformation properties of calcareous sand. A series of laboratory tests including direct shear tests, unconfined compression tests, and oedometer tests were performed on the calcareous sands improved by PFA. In addition, A scanning electron microscope (SEM) was conducted to reveal microstructural analysis of using PFA for calcareous sand. The experimental results provided insights into the shear strength, deformation modulus, as well as the micro-structural characteristics of improved calcareous sands with various PFA contents and particle size distributions. [ABSTRACT FROM AUTHOR]

A new method is proposed to evaluate the seismic stability of a rigid retaining wall undergoing translation or rotational failure. In the present method, strain-dependent dynamic properties are used to assess the seismic stability of rigid retaining walls against sliding and overturning failure conditions. The effect of foundation soil properties on the stability of retaining walls is also considered. From the parametric study, it is observed that the foundation soil properties have a significant effect on both sliding and rotational stability of rigid retaining walls. This can be attributed to the use of strain-dependent dynamic properties and the consideration of foundation soil properties. The predictions of the proposed method are compared and verified against the results from other methods proposed in the past. The percentage increase in the results compared to the existing literature is a maximum of 10 and 28% for rigid (bedrock) and flexible (sand deposit) foundation, respectively. [ABSTRACT FROM AUTHOR]

The average salinity of seawater is 3.5%, with a significant presence of corrosive ions, primarily Cl− and SO42−. In contrast to cement engineering in terrestrial natural environments, cement-reinforced structures exposed to corrosive marine environments not only endure ion erosion but also undergo periodic desiccation due to tidal variations in seawater. The coupling of these effects results in a reduction in the mechanical properties of cemented soil, inevitably leading to the degradation of cemented foundations, posing a serious threat to their safety and normal functionality. Investigating the improvement of the mechanical properties of cemented soil in corrosive coastal environments is a crucial engineering challenge in current coastal construction projects. To address this engineering challenge, this study proposes the use of Nano-SiO2 to enhance the mechanical characteristics of cemented soil, aiming to improve the strength and durability of cement-reinforced structures. Simulating the main corrosive ions in seawater by using different concentrations of SO42− ions, the study subjected cemented soil samples to dry–wet cycles to simulate the desiccation caused by tidal changes in seawater. Unconfined compressive strength tests were conducted on cemented soil and nano-cemented soil samples under coupled conditions, revealing that the incorporation of Nano-SiO2 increased the strength of cemented soil and slowed down the corrosion rate. With an ion concentration of 12.3 g/L, after 60 dry and wet cycles, the compressive strength of nano-cemented soil increased by 90% compared to conventional cemented soil, with a mass loss only half that of conventional cemented soil. XRD, SEM, and NMR tests on various cemented soil samples indicated that the addition of Nano-SiO2 filled small pores, suppressed pore development, and interacted with cement hydration products, forming a gel-like structure that improved the compactness of cemented soil. This, in turn, mitigated ion corrosion and the degradation of cemented soil under dry–wet cycles. [ABSTRACT FROM AUTHOR]