Unconsolidated Research Articles

Integrated Geotechnical Analysis of Allophanic Volcanic Ash Soils: SDMT and Laboratory Perspectives

The geological study area is volcano-tectonic in nature. Microscopic observations and mineralogical analyses revealed the presence of allophane and diatom clusters whose mineral compositions coincided with weathered andesites and dacites. Edometric consolidation tests showed a high porosity and a reduction in the void ratio by up to five times. These are highly compressible soils with a Cc/Cs ratio of 12 to 15 and a specific gravity (Gs) of 2.4. Low initial bulk density (1.10 Mg/m³), high plasticity, and SUCS (OH) classification are typical of soft soils, with an effective friction angle (ɸ’CD) of 25.5° to 30° and effective cohesion (c’CD) of 11.90 to 47.27 KPa. The shear wave velocity for the first 10 m (Vs10) on average ranged from 78 m/s to 120 m/s, whereas that for the first 30 m (Vs30) was 169 m/s. The permeability, which was calculated indirectly, was between 2 × 10−7 and 3 × 10−8 m/s. With an organic matter content between 5% and 25%, the Caupicho soil is an organic mineral sediment that is not considered peat (non-peat). The results of this study serve as a basis for future analyses of soil dynamics, bearing capacity, and consolidation settlements in the medium and long term in an area of high urban growth in southern Quito, Ecuador.

Study on the Influence of Heat Exchange of Static Drill Rooted Energy Pile on the Consolidation of Coastal Soft Soil Site

ABSTRACTThe use of static drill‐rooted energy piles in deep soft soil foundations causes thermal exchange between the piles and the surrounding soil, resulting in excess pore pressure and consolidation settlement in the soft soil layer around the piles, which affects the long‐term deformation of the site. To investigate the impact of the operation of this novel energy pile on the consolidation of the soil around the pile, a simulation analysis was conducted using the ABAQUS software to assess the soil temperature, pore pressure, and consolidation settlement around the static drill rooted energy pile group under a 120‐day heating and cooling cycle. The research findings indicated that the temperature change decreased as the distance between the soil and the pile increased, resulting in less thermal consolidation settlement and pore pressure variations. Heating conditions (ΔT = 18.7°C) resulted in a 17°C increase in the soil temperature below the center of the pile group, with temperature changes becoming negligible beyond 8D. The maximum pore pressure variations in the soil occurred at 2D and 6D distances from the pile, with values of 1.24 and 1.12 kPa, respectively. Under heating conditions, the surface settlement at a 2D distance from the pile group was 6.19 mm, which increased to about 10 mm under heating–cooling cycles. These research findings provide a foundation for analyzing the environmental impact of novel energy piles in coastal areas.

Poromechanical analysis of regional frozen ground responses under heat exchanger operations

The permafrost of the northern hemisphere is under threat of degradation due to increasing global temperatures resulting from climate change. Thawing permafrost exhibits lower strength and increased permeability, leading to soil instability and subsidence beneath structures. To mitigate the effects of permafrost thaw, heat extraction is utilized to cool the frozen soil bodies. Ground heat exchangers (GHE) are geo-structures that exchange heat with the ground and can be used for heat extraction. In this work, Thermo-Hydro-Mechanical modeling is employed to simulate the state of a saturated soil body during freezing and thawing in Umiujaq, Quebec, Canada. An initially frozen soil body is analyzed under seasonal temperature variations and GHE operations. The pore pressure development and ground deformation are well quantified. It is shown that GHE operations can effectively mitigate the risks associated with talik formation, with group-GHE formations being more effective in this regard. Additionally, it is demonstrated that group-GHE operations are effective in mitigating excessive thawing settlement. Furthermore, the shortcomings of single-GHE operations, such as limited radius of effect and differential settlement, can be improved by group-GHE formations through a confinement effect.

Experimental Study on the Symmetry of the Soil-Arching Effect of a Pile Foundation in a Reinforced High-Fill Area

In addition to the vertical external load and soil settlement load, the pile foundation in reinforced high-fill areas is also affected by the horizontal load caused by the rear stacking load, and pile stress is affected by the soil-arching effect in reinforced areas that have typical passive pile characteristics. In order to study the symmetry of the soil-arching effect of pile foundations in a reinforced-fill area, indoor model tests were designed and the relevant data for the pile foundation and reinforced soil under surcharge were obtained. Through the analysis, the following conclusions were drawn: the peak bending moment of the pile body is basically consistent with the position of the potential sliding surface of reinforced soil; the maximum shear force of the pile body appears about 150 mm below the embedding point; with an increase in depth, the soil-arching effect becomes obvious. There are two different forms of friction, soil-arching and direct soil-arching between piles and behind piles, and the soil between single-row piles has a symmetrical distribution. In addition to the vertical external load and soil settlement load, the pile foundation in reinforced high-fill areas will also be affected by the horizontal load caused by the rear stacking load, and pile stress will be affected by the soil-arching effect in reinforced areas, which has typical passive pile characteristics. In order to study the symmetry of the soil-arching effect of pile foundations in a reinforced-fill area, indoor model tests were designed, and the relevant data for pile foundation and reinforced soil under surcharge were obtained. Through analysis, the following conclusions were drawn: (1) the peak bending moment of the pile body is basically consistent with the position of the potential sliding surface of reinforced soil; the maximum shear force of the pile body appears about 150 mm below the embedding point; with an increase in depth, the soil-arching effect becomes obvious. There are two different forms of friction, soil-arching and direct soil-arching between piles and behind piles, and the soil between single-row piles has a symmetrical distribution.

Behavior of Micropile (Type D) Subjected to Vertical Load: Parametric Numerical Studies

Micropiles, small-diameter-drilled and grouted piles, are often used to provide foundation support in challenging ground conditions. This research seeks to understand the behavior of Type D micropiles (pressure-grouted) within layered soil profiles. Layered soils frequently create complexity because of differences in stiffness, strength, and permeability, which impact load transfer and the interaction between the micropiles and the surrounding soil. Type D micropiles use pressure injection, which results in enhanced skin friction, better grout–soil contact, and a greater capacity to carry loads. A set of numerical simulations was conducted to analyze the behavior of the micropile Type D under axial loading, which was evaluated by considering factors such as micropile diameter, spacing, and inclination. The results indicated that increasing the diameter of a micropile significantly improves its performance by enhancing load transfer and structural stiffness, as well as reducing soil deformation and settlement. In addition, for vertical micropiles and those with inclination angles of 10° and 20°, stiffness increased with diameter, while axial displacement remained constant at a 45° inclination. Furthermore, larger diameters reduced lateral displacements up to 20° inclination angles by increasing stiffness, but lateral deflection increased at 45° due to greater lateral load components. The bending moment increased with inclination angle, driven by higher horizontal loads and increased eccentricity, while spacing had little effect for angles greater than 20° due to effective load redistribution.

Numerical Simulation Study on Settlement of Surrounding Soil Caused by Sink Construction in Soft Ground Layer

Numerical Simulation Study on Settlement of Surrounding Soil Caused by Sink Construction in Soft Ground Layer

Plant Adaptation and Soil Shear Strength: Unraveling the Drought Legacy in Amorpha fruticosa.

Climate change has led to an increasing frequency of droughts, potentially undermining soil stability. In such a changing environment, the shallow reinforcement effect of plant roots often fails to meet expectations. This study aims to explore whether this is associated with the alteration of plant traits as a response to environmental change. Focusing on Amorpha fruticosa, a species known for its robust root system that plays a crucial role in soil consolidation and slope stabilization, thereby reducing soil and water erosion, we simulated a drought-rewetting event to assess the legacy effects of drought on the soil shear strength and the mechanical and hydrological traits associated with the reinforcement provided by A. fruticosa. The results show that the legacy effect of drought significantly diminishes the soil shear strength. Pretreated with drought, plant roots undergo morphological alterations such as deeper growth, yet the underground root biomass and diameter decline, thereby influencing mechanical reinforcement. Chemical composition analysis indicates that the plant's adaptation to drought modifies the intrinsic properties of the roots, with varying impacts on different root types and overall reinforcement. Concurrently, the stomatal conductance and transpiration rate of leaves decrease, weakening the capacity to augment soil matric suction through transpiration and potentially reducing hydrological reinforcement. Although rewetting treatments aid in recovery, drought legacy effects persist and impact plant functional attributes. This study emphasizes that, beyond soil matric suction, plant adaptive mechanisms in response to environmental changes may also contribute significantly to reduced soil shear strength. Consequently, ecological restoration strategies should consider plant trait adaptations to drought, enhancing root systems for soil conservation and climate resilience.

Seismic Resilience of Geogrid Reinforced Concrete Earth-Retaining Wall of Various Incremental Panels Based on Physical and Numerical Modelling

The dynamic response for different earth-retaining walls having geogrid as a reinforcement, combined with cohesionless granular material for backfill to mitigate earth pressure, has been examined through scale-down shaking table experiments and full-scale 3D FE analysis, utilizing ABAQUS as the finite element software. The scale factor is 1/4th for scaled-down. This study included various physical modelling experiments using different geogrid-reinforced earth retaining (GRER) walls (1m height, 7.5cm, thickness, and length 1m). Additionally, comprehensive 3D finite element analysis were conducted with the configurations measuring (4m, height 0.3m, thickness, and length 4m). This study examines hollow prefabricated concrete panels with shear key (PC-W), stone masonry walls of gravity type (GM-W), and traditional reinforced concrete (RC-W) walls. It also presents comparative investigations, such as lateral horizontal displacement of the wall, lateral pressure to the backfill, backfill soil settlement, and settlement of the wall foundation of various (GRER) walls. The accuracy of the Finite Element simulation framework has also been assessed in the shaking table experiment, as well as the FE analyses. According to the results, a PC-W wall with a shear key is the most effective type because it shows more resistance toward displacement. As per the comparison of the test models, GRER walls’ seismic response was more affected by the earthquake waves from the far field having long-term high acceleration values. In contrast, seismic waves from the close field had a smaller impact on the walls’ seismic response. However, the geogrid could improve the GRER seismic resilience deformation. Geogrid layers may reduce backfill pressures and backfill settlements. The geogrids located in the central portion within the reinforced soil and the geogrid roots connected to the walls were essential to the seismic design of the geogrid-reinforced earth retaining wall. To evaluate the reliability of the findings, the models have a predicted R2 variance below 0.1, indicating a consistent relationship between these two variables.

Influence of particle size on soil consolidation processes

Settlements in infrastructure works such as roads, bridges and highways are often underestimated due to a lack of understanding of the phenomena associated with volumetric deformations of soils. This can lead to significant damage to the structures built on them and in some cases it will be necessary to demolish them or render them useless. This study shows the difference in longterm deformations that occur between two types of soil depending on their particle sizes. The study shows the results of two soil samples subject to consolidation, with identical initial moisture content, but with a different particle size distribution. It also shows how the consolidation process occurs and the direct influence of particle size on the long-term volumetric reduction process of soils.

How A Study of Soil Dynamic Properties on the Stability of Building Structures in Foundation and Foundation Engineering

In the context of the increasingly widespread application of high-rise buildings, the selection of foundation base forms with appropriate materials is of great practical significance. The article takes the student teaching building of a college in city A as an example, with the help of the eigenvalue buckling analysis method provided by ANSYS, the three-dimensional finite element model is used to analyze the foundation pit building support structure from the soil moisture content, seismic action and the influence of different clay soil quality. Meanwhile, the feasibility of adopting foundation for buildings with clay1 as the main holding layer is verified from both energetic and dynamic aspects. After the foundation pit building construction, the lateral displacement is overall small, and the maximum lateral displacement is controlled within 4mm. With the increase of soil moisture content, the lateral displacement of the supporting structure gradually increased, and when the moisture content increased to 7 ml and 8 ml, the cumulative values of lateral displacement were 4.4 mm and 5.5 mm, which increased by 1.2 mm and 2.3 mm, respectively, with an increase of 37.50% and 71.88%, which indicated that the building construction should avoid the effect of the rainy season on the soil moisture content. With the analysis under the coaction model, the results show that the rate of foundation soil subsidence is increasing with the increase of floor loading. Under the analysis of the effects of different earthquake levels on different soil qualities, the interlayer displacement of clay 1 under 8 ∘ multiple and 8 ∘ rare earthquakes meets the requirements, so clay 1 meets the feasibility of building foundation engineering.

Theoretical and experimental study on the consolidation of soil with continuous drainage boundary under electroosmosis–surcharge preloading

Electroosmosis and surcharge preloading represent two effective soil consolidation methodologies. Their combined application has been proven to be effective in shortening the consolidation period and mitigating the degradation of electroosmotic consolidation performance due to crack generation. In this study, an axisymmetric free-strain consolidation analytical model incorporating a continuous drainage top boundary was established. A semi-analytical solution was then derived utilizing Laplace–Hankel transform and boundary condition homogenization. The validity of the proposed solution was confirmed by comparing it with three cases documented in the existing literature. Additionally, a comparison with indoor model box test results demonstrated the rationality of setting the top boundary as a continuous drainage boundary. Parameter analysis revealed several key insights: firstly, under the free strain assumption, the spatiotemporal distribution of excess pore water pressure aptly captured the coupled effects of the radial electric field. Secondly, the combination of electro-osmosis and preloading technology significantly improved consolidation efficiency, with this effect becoming more pronounced as the applied voltage increased. Lastly, the general solution based on the continuous drainage boundary proved to be suitable for addressing the consolidation of soft soils enhanced by vertical drainage, applicable to real foundation consolidation problems with top boundaries exhibiting different permeabilities.

Estimation of the wetting induced settlement of loess soils from the wetting soil-water characteristic curve

Collapsible loess soils, known for their significant volume reduction upon the wetting, pose critical challenges in the geotechnical engineering. The estimation of the wetting-induced settlement is crucial for the foundation design and the determination of the negative skin friction on the pile. In this paper, a new method is proposed to estimate the wetting induced collapse from the wetting soil-water characteristic curve (SWCC) and the index properties of the loess soils. In the proposed model, both the water-entry value (WEV) and constant water content suction (ψwc) were adopted for the quantification of the volume change with respect to the reduction in soil suction. The proposed method is verified against the experimental data from published literature. Subsequently, the ground settlement of the loess soil in the inundated condition was calculated by adopting the proposed method and comparing the results with the field measurement data. The results of study indicated that the performance of the proposed method is better than the conventional method in predicting the ground settlement by using the local code in China.

РЕЗУЛЬТАТЫ ХИРУРГИЧЕСКОГО ЛЕЧЕНИЯ ОПУХОЛЕЙ СПИННОГО МОЗГА И ПОЗВОНОЧНИКА С КОМПРЕССИЕЙ НЕВРАЛЬНЫХ СТРУКТУР

Spinal cord tumors, differing in their histostructure, the nature of growth and the ratio to the diameter of the spinal cord, continue to be a difficult problem, both in terms of choosing the optimal treatment tactics and results. We present the results of surgical treatment of the most common spinal chord neoplasms in 2022, conducted in the Alexandro-Mariinskaya Regional Clinical Hospita. The purpose of the study – to present the results of surgical treat-ment of spinal cord and spine tumors with secondary compression of neural structures that differ in histostructure, de-gree of malignancy and level of lesion. In 2022, 19 patients were operated on by various methods in the Alexandro-Mariinskaya Regional Clinical Hospita. 3 clinical cases with different histostructure and topographic-anatomical level of lesion are presented. Surgical treatment of spinal cord tumors was performed in 19 patients with different histostruc-ture and topographic and anatomical lesion levels. Using the example of three clinical cases, the choice of various sur-gical treatment tactics that are most optimal for maintaining the patient's quality of life is demonstrated. The analysis of the surgical manual, its relationship with the prognostic trend, which affect the overall survival of patients with tu-mors of the spinal cord and spine. The dependence of a number of factors was revealed: the histological structure, the degree of “aggressiveness” of the oncological process, the possible spread of metastatic foci in the body. This, in turn, is interconnected with modern methods of diagnosis, surgical and adjuvant treatment, neurological and somatic compen-sation of the patient, which will allow to determine and transfer the aggressiveness of the indicated treatment method. The available modern equipment, accumulated surgical experience and the chosen active tactics for the maximum total removal of the lesion justified themselves, allowing to achieve a good functional result in 18 of the 19 operated patients.

DETERMINATION OF PARAMETERS OF AN EXPERIMENTAL MODEL OF A MULTI-STOREY STEEL FRAME

: The load-bearing capacity of the structure can be accurately determined on large models made from the same material (or a material with similar elastic properties) as the actual structure. The scale of the model can be 1/5-1/6. This depends not only on the actual dimensions of the structure but also on the material of the model. Experience shows that for metal and concrete models, it is reasonable to adopt a scale of 1/5-1/15. Previous studies show that analysis based on the calculation of an idealized multi-story steel frame structure without considering imperfections does not fully reflect the actual performance of the steel frame and may not always ensure the load-bearing capacity of the building and the operational requirements for permissible frame displacements. It is interesting to compare some approximate data on the cost of testing in kind with the cost of testing the model. Thus, full-scale tests of large-panel buildings erected on subsidence soils ac-count for 10 to 30% of the cost of the buildings themselves. The cost of such tests on models would be 2-3%, that is, 5-10 times cheaper. The provided data indicates the feasibility of using modeling in the design of structures. The research results can be used to refine and develop building codes and standards, enabling the calculation and design of multi-story buildings that account for the actual performance of the steel frame-work.

Research on consolidation and settlement characteristics of soft soil with high initial water content

Research on consolidation and settlement characteristics of soft soil with high initial water content

ON IDENTIFICATION OF PARAMETERS OF A NONLINEAR CONSOLIDATION MODEL OF SANDY SOIL

Previously, the authors of this article formulated a physically and geometrically nonlinear formulation of the problem of porous fluid-saturated medium deformation during fluid filtration (consolidation problem) in terms of the rate of solid phase displacement and the change in pore pressure in differential and variational forms. The developed consolidation model takes into account changes in the porosity and permeability of the medium during deformation. Deformation-type constitutive relations are used in the model. The developed consolidation model can be used to simulate non-stationary processes in the soil, for example, the formation of ruts and unevenness of dirt roads, as well as to calculate the uneven settlement of engineering structures. This work is devoted to the experimental determination of the deformation and strength properties of water-saturated sandy soils, which is the next stage in the consolidation process simulation. The results of the experimental determination of the bulk and shear properties of sandy soil using the ASIS automated complex (OOO NPP “Geotek”) are presented. The studies were carried out on three quartz sands of various grain sizes. To determine the volumetric moduli of dry and water-saturated sandy soils, compression tests were carried out under a continuously growing vertical load at a constant strain rate. The experiments were carried out for various strain rates in the range from 3·10–6 to 3·10–3 s–1. According to the experimental results, the bulk properties do not depend on the strain rate in the specified range. Deformation and strength shear characteristics of sandy soils were determined by the method of multiplanar shear, approximating a simple shear. The tests were carried out under a kinematically applied shear load with a given constant strain rate according to the scheme of consolidated-drained shear. The dependences of the deformation and strength properties of coarse and fine quartz sands on the shear strain rate in the range from 2·10–4 tо 4·10–3 s–1 were studied. Increasing, decreasing and nonmonotonic dependences of the internal friction angle on the shear strain rate were obtained for dry and water-saturated sands of various grain sizes. For water-saturated sands, the maximum spread in the values of the internal friction angle for different strain rates does not exceed 7 %. A technique has been developed for recalculating the obtained properties and experimental dependences into the parameters of the proposed sandy soil consolidation model.

Re-examination and analysis of test data on consolidation of soft soils exhibiting creep with different thicknesses

Accurate prediction regarding the long-term settlements of soft soils is challenging. One of the reasons for this is time-dependent soil behaviours. How to extrapolate such behaviours from thin laboratory testing with limited timescales to an in situ thick soil layer with large timescales is still an ongoing debate, which can be dated back to the work of Ladd and co-workers in 1977. Many experimental results that were previously used to advocate hypothesis A have been re-analysed and found to align with hypothesis B. However, discrepancies remain in some historical data, particularly in the case of Osaka clay retrieved from the seabed under the Kansai international airport islands. This study begins by introducing the main implications and selected existing models for the time-dependent behaviours of soft soil. It then focuses on the re-examination of selected test results from the work of Watabe and co-workers in 2008, supplemented by numerical simulation using isotache models. The analysis emphasises the importance of considering equal initial conditions when comparing data from samples with varying thicknesses. Furthermore, the good agreement observed between measured data and the simulation results using hypothesis B methods demonstrates the validity of hypothesis B for predicting the long-term consolidation behaviour of soft soil both in the laboratory and at field scales.

Semi‐Analytical Study of Pile–Soil Interaction on a Permeable Pipe Pile Subjected to Rheological Consolidation of Clayey Soils

Semi‐Analytical Study of Pile–Soil Interaction on a Permeable Pipe Pile Subjected to Rheological Consolidation of Clayey Soils

Theoretical Study on Consolidation of Slurry Treated by PHDs‐VP Considering Clogging Effect and Vacuum Preloading Process

ABSTRACTPrefabricated horizontal drains combined with vacuum preloading (PHDs‐VP) have addressed the shortcomings of prefabricated vertical drains combined with vacuum preloading (PVDs‐VP), beginning to emerge as a popular method for dredged slurry treatment. However, theoretical research on PHDs‐VP consolidation is relatively scarce. This study proposes a novel analytical model for predicting the consolidation behavior of the slurry treated by PHDs‐VP. This model treats the PHDs layer as a continuous drainage layer. Analytical solutions considering the clogging effect and the vacuum preloading process have been derived. The correctness and applicability of the proposed model have been verified through degeneration analysis and comparison with laboratory experimental data. Subsequently, an in‐depth sensitivity analysis of parameters has been conducted to assess the influence on consolidation. The research findings indicate that the clogging effect significantly reduces the consolidation rate, while the influence of the increasing rate in vacuum pressure is relatively minor. Additionally, increasing the slurry filling rate and the PHDs layout density can both accelerate soil consolidation. These findings offer significant guidance for the implementation of PHDs‐VP method in engineering.

One-dimensional consolidation analysis of layered foundations with continuous drainage boundaries considering soil structure and physical properties

IntroductionMany theories of consolidation for soils have been proposed in the past, but most of them have ignored the structural characteristics of clay, yet the natural layered soils are widely distributed around the world.MethodsA theoretical model is established to analyze the one-dimensional consolidation behavior of layered soils, in which a time-dependent drainage boundary and the structural characteristics of the soil are taken into account. Using the integral transform and characteristic function methods, the analytical solution is derived, the effectiveness of which is evaluated against the degradation of solutions and the numerical results calculated using the finite element method.Results and discussionFinally, the influences of interface parameter, soil permeability coefficient and soil compressibility on consolidation behaviors are discussed. Results show that in structured soils, early dissipation of excess pore water pressure and consolidation rates are predominantly influenced by interface parameters, permeability, and volume compression coefficients. Higher values of these parameters accelerate early stages of consolidation, which is especially evident in the upper soil layers. Over time, the distinct effects of interface and permeability coefficients on consolidation diminish. Higher volume compression coefficients, while initially beneficial, eventually slow down the consolidation process, indicating an interaction with the ongoing soil structural changes.