Unconsolidated Research Articles

A hydro-mechanical coupled contact method for two-phase geotechnical large deformation problems within the SNS-PFEM framework

This paper proposes a novel numerical algorithm to solve frictional contact problems in two-phase porous media, accounting for the large deformation and interface fluid flow, within the framework of the Stable Node-based Smoothed Particle Finite Element Method (SNS-PFEM). The proposed approach builds on our previous work that was only designed for single-phase large deformation contact problems. Within this work, the hydro-mechanical coupling system is discretized using equal-order interpolation, with a polynomial pressure projection method to eliminate the pore pressure instability. Surface-to-surface discretization is then applied to formulate the contact constraint of the two-phase porous medium. Using the dual Lagrange multiplier approach, a coordinate transformation is introduced to enforce the contact constraint of the solid phase. This transformation is subsequently utilized to develop a new interface fluid element, which serves as a tool to model the fluid exchange behaviour between porous media and contact gaps. Different from existing interface fluid elements, the proposed element is constructed based on the contact algorithm, thereby enabling it to handle non-conforming interfaces and tackle challenges associated with large sliding problems. Furthermore, the proposed method can maintain a well-conditioned system matrix throughout the computation process. These distinctive attributes significantly enhance the flexibility of numerical modelling. Finally, the accuracy and performance of our method are verified through four numerical examples. The results show that the proposed method can effectively simulate various geotechnical problems, including multi-layer soil consolidation, fluid-soil-structure interaction, and geological interface-controlled slope failure.

Numerical Investigation of Two Methods to Reduce the Settlement of a Light-Weight Highway Embankment on Soft Soils

The development of road and highway networks sometimes involves passing through compressible soils of poor quality. Given their mechanical properties as foundation soils, these soils are characterized by low short-term shear strength, expressed by undrained cohesion, which increases during soil consolidation, and are also characterized by significant compressibility, resulting in large-scale settlements when a load is applied to them. Nowadays, there are reinforcement methods that make it possible to execute these structures while limiting the risks of instability. This study consists of the numerical analysis of a light-weight embankment of a highway section built on soft soils. Two reinforcement methods are investigated to support the embankment layers and reduce settlement. Interest is given to the behavior of the soils in place before and after the installation of the adopted reinforcement. The analysis is carried out in such a way as to show the importance of the complete consolidation of the soils in place in the long term, which makes it possible to take into account the dissipation of the pore pressures.

Co-simulation for optimal working parameter selection during soil vibratory compaction process

The working parameters of vibratory rollers have an important effect on the compaction quality. The traditional method of obtaining the best working parameters through field tests is time-consuming and laborious. In order to determine the best working parameters more conveniently and accurately, a mechanical-hydraulic-finite element co-simulation method is proposed in this paper. This method considers the effect of the hydraulic system on vibration compaction and makes the simulation result as close to the actual condition as possible. By analyzing the change of soil stress and settlement, the effect regulation of working parameters on compaction quality is obtained. The results show that the proposed co-simulation method can accurately reflect the real conditions, and the best compaction quality can be achieved when the walking speed is 3 km/h, the vibration frequency is 24 Hz, and the amplitude is 2.5 mm. The research provides a reference for improving the compaction quality and compacting-related simulation.

Hydrate reservoir deformation under multi-well strategies based on the dynamic elastic modulus relationship

In order to demonstrate the safety of the multi-well mining method, stratum deformation using multi-well systems is discussed. Firstly, ultrasonic experiments and triaxial tests of hydrate-bearing sediments under different confining pressure and hydrate saturation conditions were carried out. The soil static elastic modulus was compared with the dynamic elastic modulus relationship. Then the dynamic elastic modulus relations were applied to the multi-field coupling model to simulate the hydrate mining process in reservoirs by multi-well strategies. The experimental results show that hydrate saturation impacts the elastic modulus more than the effective confining pressure. In the simulation results, with the increase of the reservoir depth, the soil settlement shows a trend from small to large and then to small. The maximum soil displacement is located at the junction between the hydrate and the overlying layers, regarded as the weak point. In addition, increasing the well branches, expanding the well spacing, and increasing the wellhead radius can increase gas production. However, at the same time, it will also increase the reservoir deformation, thus posing risks to the stability of the formation and extraction wells. On this basis, the efficiency-safety factor was set, and the best mining scheme was determined.

Design and Experiment of Adaptive Profiling Header Based on Multi-Body Dynamics–Discrete Element Method Coupling

To promote the germination of rice panicles during the regeneration season, it is necessary to ensure a stubble height of 300–450 mm when mechanically harvesting the first-season rice. However, due to variations in the depth of the paddy soil and fluctuations in the height of the header during harvesting, maintaining the desired stubble height becomes challenging, resulting in a significant impact on the yield during the regeneration season. This study presents the design of an adaptive profiling header capable of adjusting the height and level of the header adaptively. Based on the theoretical analysis of the profiling mechanism, a quadratic regression orthogonal rotation combination experiment is designed. Considering the actual field conditions, the range of each factor is determined, and simulation experiments are conducted based on the MBD-DEM coupling to establish a mathematical regression model between each factor and indicator. In the case of the profiling wheel linkage length of 562 mm, profiling wheel width of 20 mm, and profiling wheel mass of 3.6 kg, the supporting force of the header on the profiling wheel would be greater than zero, the supporting force of soil on the profiling wheel and the depth of soil subsidence represent the smallest values, and the highest sensitivity and accuracy of the profiling wheel are achieved. Bench tests demonstrated that the header exerts a force on the profiling wheel, confirming the normal functioning of the profiling. The average magnitudes of forces exerted by the soil on the profiling wheel are obtained to be 31.98 N, 31.63 N, and 30.86 N, whereas the corresponding average soil subsidence depths are obtained as 3.4 mm, 5.6 mm, and 8.3 mm, aligning closely with the simulation values. The results indicate that the profiling mechanism achieves high accuracy in ground profiling and that the structural design is reasonable. By employing fuzzy PID control to adjust the height of the header, the average error in adjustment is obtained as 6.75 mm, while the average error in the horizontal adjustment is derived as 0.64°. The header adjustment is fast, offering high positioning accuracy, thereby meeting the harvesting requirements of the first season of ratooning rice.

Multi-data settlement prediction along a road section integrating InSAR and coastal subsurface information with data assimilation

This paper presents a novel approach to examining the impact of soil settlement and its spatial distribution on infrastructure. The study focuses on a specific road section in the Friesland coastal plain in the north of the Netherlands, investigating how the Holocene coastal subsurface architecture influences settlement patterns. Our study underscores the importance of integrating multiple datasets, providing data at varying resolutions. The road segment traverses lithostratigraphical units, which include tidal channel and tidal flat deposits, overlaying an older tidal basin system and intercalated peat beds. Through data assimilation of a settlement model optimized with InSAR measurements, we have identified settlement heterogeneities that can be explained by combining high-resolution variations in lithology with gradual changes in lithostratigraphy. This was accomplished by utilizing a medium-resolution model (MRM) based on borehole descriptions and a high-resolution data (HRD) approach based on cone penetration tests along the road. The HRD method proved more effective in capturing abrupt changes in lithology between channel structures, while the MRM provided a continuous representation of the lithostratigraphic setting of the area. Our study demonstrates that subsurface heterogeneities have significant implications for subsidence along roads. Settlement rates increase from 2–4 mm/year towards 9 mm/year along the road section, resulting in a differential settlement of more than 5 mm/year over a distance of less than a kilometer. This is primarily attributed to variations in lithostratigraphy. Overall, this new innovative approach offers a practical and cost-effective solution for predicting subsidence due to settlement, eliminating the need for expensive laboratory tests. By integrating lithology and lithostratigraphy, more efficient road maintenance and management become possible.

Soil liquefaction and subsidence disaster in İskenderun related to the 6 February 2023 Pazarcık (Mw: 7.7) and 20 February Defne (Mw: 6.4) earthquakes, Türkiye

Soil liquefaction and subsidence disaster in İskenderun related to the 6 February 2023 Pazarcık (Mw: 7.7) and 20 February Defne (Mw: 6.4) earthquakes, Türkiye

Thermal consolidation of layered saturated soil under time‐dependent loadings and heating considering interfacial flow contact resistance effect

AbstractDue to the presence of tiny gaps at the interface of two layers of saturated soil, water seepage occurs at a slower rate within these gaps, resulting in laminar flow at the interface. Based on the Hagen‐Poiseuille law, a general imperfect flow contact model was established for layered saturated soil interfaces by introducing the flow contact transfer coefficient Rω and the flow partition coefficient ηω. The investigation focused on the thermal consolidation behavior of layered saturated soil foundations under variable loadings considering the flow contact resistance effect at the interface. By employing the Laplace transform and its inverse transform, a semi‐analytical solution for the thermal consolidation of layered saturated soil foundations was derived. In the context of a two‐layer soil system, the effects of Rω, ηω, and permeability coefficient k on the consolidation process were examined. The obtained results were then compared with three other interfacial contact models, thereby confirming the rationality of the presented model. The study findings revealed that the flow contact resistance effect leads to a clear jump in the pore water pressure. Furthermore, an increase in Rω and a decrease in ηω were found to significantly enhance displacement and pore water pressure, while having minimal impact on the temperature increment. These insights contribute to a more comprehensive understanding of the thermal consolidation behavior of layered saturated soil foundations and underscore the significance of accounting for the flow contact resistance effect in such analyses.

Multivariate probabilistic assessment of a regional database in Copenhagen

Extensive research has been carried out to establish empirical equations between two geotechnical properties and in spite of the increase in correlation studies, a construction of a multivariate distribution function of more than two parameters is still rare. The objective of this study is to investigate the possibility of constructing two multivariate distribution functions, each consisting of 5 geotechnical parameters based on a) triaxial and soil classification tests and b) oedometer and soil classification tests in stiff over-consolidated clay till from Copenhagen. For this purpose, laboratory measurements from twenty-six sites in Copenhagen are utilized and two multivariate databases are constructed. The correlations among the ratio of deviatoric and mean effective stresses (q/p´), over-consolidation ratio (OCR), secant modulus at reference stress 100 kPa (E50ref), initial void ratio (eo) and liquid limit (LL) are investigated in multivariate model A, while multivariate model B demonstrates the correlations among oedometer modulus at 100 kPa reference stress (Eoed(ur)ref), over-consolidation ratio (OCR), permeability change index (Ck), initial void ratio (eo) and liquid limit (LL). The Nataf transformation model is used for the construction of the multivariate distributions, which are then used to simulate the correlations between geotechnical properties by generating artificial samples. Finally, the artificial samples are compared with the original database for an initial validation of the model. The constructed multivariate models obtained as a result of this study can act as prior for Bayesian updating in multivariate distribution functions when additional geotechnical tests are carried out.

Thermo-hydro-mechanical behaviour of deep Ypresian clays

Investigating the thermo-hydro-mechanical behaviour of deep Ypresian clays (300 to 400 m below ground) is crucial since they are one of Belgium’s potential host rock formations for deep geological disposal of radioactive waste. To this aim, a newly designed and fully instrumented thermal oedometer cell with lateral stress measurement was used to determine the stress state accurately. First, well-preserved core samples were loaded to bring them to the large in situ stresses and reduce the induced matric suction on deep water-undrained sampling. The remaining matric suction was then reduced by soaking with synthetic water of the formation. Next, drained loading and unloading paths were followed to attain different vertical effective stresses at varying overconsolidation ratios (OCRs) before the drained thermal paths (heating and cooling). The results indicated a systematic increase in the horizontal effective stress on heating at constant vertical effective stress. In addition, thermal-induced volume changes in heating/cooling at different OCRs were studied. Test results were finally interpreted within a thermo-mechanical elastoplastic framework.

Modeling of the accurate application of the Kernel Efficiency Method in the proportioning process of shield tunnel construction

Abstract The existing control strategies for subway construction struggle to address the challenges posed by the impact of large-diameter shield-driven underpass subway tunnels on soil settlement. In this paper, based on the mechanism of ground settlement of the shield tunnel under the KNX method, the influence of the underpass tunnel on the existing tunnel and its surrounding soil stress-strain characteristics is calculated by the Peck superposition method. The KNX method is optimized by optimizing the ratio of KNX slurry and the grouting pressure to control the existing tunnel and the ground settlement. The geotechnical general finite element analysis software is being introduced to conduct numerical simulation and engineering application experiments to verify its effectiveness. The results show that when the bonding force of the grouting material is 350Pa-s, the maximum value of the variation is 3.91mm, and the mobility is more suitable, which can effectively fill the void of the shield machine and reduce the settlement of the foundation. When the grouting pressure is 280kN/m2, the maximum contraction of the tunnel is 6.25mm, which can ensure the safety of the existing tunnel on the basis of the tunnel so that the actual settlement of the soil in the tunnel is minimized. Comprehensively, the optimization of the ratio of the KNP method in the control of the deformation characteristics of the soil and structures under the shield tunnel has effectiveness and can effectively provide theoretical and technical guidance for the construction of subway tunnels under the large-diameter shield under the subway.

Field test of compactability of soaked subsidence soil using heavy tamper

Dynamic compaction, including heavy compaction, is a widespread method throughout the world for improving the physical and mechanical characteristics of subsidence and low-density soils. The results of theoretical and experimental studies have established that the depth of compaction and the density of compacted soils depend on the weight, shape of the bottom, the height of the tamper and humidity, the type of structural connection, and the granulometric composition of the compacted soil. This article discusses the results of compaction with a heavy tamper when soaking loess-like subsidence soil, widespread in the city of Darkhan, Mongolia, to optimal moisture.

Technology for reducing the risk of landslides by unloading the landslide mass

The work has developed measures to reduce the risk of a landslide in the area near the village of Toktogul, Uzgen district of the Kyrgyz Republic. This landslide area was studied on the basis of field research on the ground and the results of desk work. The sliding of soil masses in the area can cause destruction and debris of residential and administrative buildings, roads and power lines, as well as injury and death. Considering the equilibrium of the system of forces acting on the mass of filler soil of the slope section and analyzing them, measures for unloading the landslide body in this section are proposed. The proposed longitudinal profiles of drainage channels to reduce the moisture content of subsidence soil and transverse profiles of developed soil to reduce the weight of subsidence soil are presented. Based on the results of processing research data and analysis, it is recommended to reduce the weight of unstable (subsidence) soil by stepwise development along the slope of the site and transporting it up to 5 km for subsequent brick production. It is also recommended to protect subsidence soil from waterlogging by installing drainage channels. Based on the results of the research, a real project was developed to protect the site from landslides near the village of Toktogul. The proposed measures make it possible to reduce the risk of a landslide in the area under consideration using methods and technical means that are inexpensive and accessible to government agencies and local administrations.

Study on the influence of structural spacing on the deformation caused by the excavation of shield underpass socket pipe gallery

In a prefabricated composite pipe gallery with socket joints, the repeated loading and unloading effect of shield construction on the overlying soil and the existing pipe gallery may cause considerable deformations to the pipe gallery at the joint while ensuring its own bearing capacity. The shield tunnelling underneath the existing pipe gallery project of the Fuzhou Metro was used as a basis to model the socket pipe gallery on ABAQUS finite element software. The influence of changes in the pipe-tunnel spacing on the deformation and displacement of the pipe gallery and stratum were investigated. It was found that when the shield passes through the pipe gallery with 0.25 times the tunnel diameter, in addition to the settlement area of the disturbance centre, uplift areas are created on both sides of the pipe gallery and the surface. Meanwhile, because of the socket structure of the pipe gallery, the vertical displacement of the pipe gallery is not synchronized with the settlement of the lower soil. Furthermore, with the increase in the pipe-tunnel spacing, the settlement trough of the vertical displacement curve of the pipe gallery and the stratum are gradually broadened, and the peak settlement gradually increases.

Different Design Aspects of L-Shaped Earth Retaining Structures

The L-shaped retaining walls (L-SRWs) are considered one of the important earth retaining structures (ERSs). The investigation of L-SRWs mainly depends on factors directly related to the design process. Reviewing these factors represents the key matter in the design of ERSs, and this is the main purpose of this paper. This review showed that, in the design of L-SRWs, there are important issues to be considered. Some of them are related to the backfill and foundation soils e.g. the dependency of soil stiffness on the state of stresses, information related to soil behavior, inclination and quality of backfill, and settlement of foundation soil. Other issues are related to the wall itself such as the wall dimensions, failure mechanism, and flexural failure mode. In the design processes of L-SRWs, structural and geotechnical design requirements should be considered. L-SRWs should be designed to be proportional in their dimensions, the width of the wall base and its height should be designed to meet a specific ratio. Considerations related to the "conjugate rupture planes", the displacement pattern, and flexural failure mode should be included in the design process of L-SRWs.

Medusa SDMT testing at the Onsøy Geo-Test Site, Norway

The Medusa SDMT is the last-generation, fully automated version of the seismic dilatometer (SDMT). An extensive in situ testing campaign with the Medusa SDMT was carried out in June 2022 in different soil types at four well-known benchmark test sites in Norway, part of the Geo-Test Sites (NGTS) research infrastructure managed by the Norwegian Geotechnical Institute. The experimental campaign was conducted as part of the Transnational Access project – JELLYFISh funded by H2020-GEOLAB. This paper presents a preliminary assessment of significant results obtained by Medusa SDMT at the Onsoy test site, a soft marine clay. The data is compared to available in situ and laboratory data previously published at the Onsøy test site. The results show that the Medusa SDMT data are consistent with traditional (pneumatic) SDMT results. Furthermore, the parameters obtained from the interpretation of Medusa SDMT data, in particular the overconsolidation ratio OCR, the coefficient of earth pressure at rest K0, and the undrained shear strength su agree generally well with the corresponding parameters obtained in past investigations from other in situ and laboratory tests.

Analytical solution for one-dimensional consolidation of structured soft soils with continuous drainage boundary

A closed form analytical solution is proposed to analyze the one-dimensional consolidation behavior of structured saturated clay soils under continuous drainage boundary. Firstly, the soil structural properties and arbitrary loading conditions are taken into account in the established mathematical model. Using the finite sine Fourier transform and characteristic function methods, analytical calculation is conducted, and the solution effectiveness is evaluated against the degradation of solutions and the results of finite difference analysis. Finally, the influences of interface parameter, properties of soil structure and structural yield stress on consolidation behaviors are discussed. Results show that the larger the interface parameter is, the easier the soil structure enters the failure stage, and the smaller the consolidation degree is. Furthermore, the time for initiating the failure stage does not change, when the interface parameter and structural yield stress keep unchanged; in the meanwhile, the greater the consolidation coefficient is, the greater the consolidation degree of foundation becomes when the soil structure begins to fail, and the earlier the soil enters the complete failure stage. When the interface parameter is determined, the ratio of structural yield stress to load can accelerate the soil consolidation rate, but all consolidation curves coincide for the same ratio.

REMOTE IDENTIFICATION OF MICROSEDIMENTAL RELIEF FORMS AND SOIL SECTIONS OF AGROLANDSCAPES OF THE FORESTS OF UKRAINE WITH SIGNS OF HYDROMORPHISM

Background. Agricultural lands play a key role in ensuring the food security of the population and the development of the country's economy. However, excessive wetting poses a significant threat to these lands, as a result of which the conditions for the formation of soils with signs of glaciation and low fertility are formed within the lower relief elements, which significantly reduces their potential. In order to highlight the problems of geospatial identification of micro-recessed landforms (MRLF) on agricultural lands, the article uses spectral indices based on the data of RSE. Methods. 6 spectral indices were selected for the research. They were used to obtain data on areas of soil subsidence on arable lands, namely: NDWI, NWI, NDMI, NDVI, OSAVI, WRI. Solving research tasks involved the use of data from the Sentinel-2A satellite system. In order to visualize the spread of MRLF on the research territory, a high-resolution image (0.2 m per 1 pixel) obtained in the "Digitals Professional 5.0" software was used. Processing and geospatial visualization of the RSE data were performed in the Arc Map environment of the Arc GIS 10.8 program using the raster calculator tool. Results. Within the reference fields, the dynamics of the values of water and vegetation indices were constructed and analyzed, and the identification ability for the geospatial separation of soil areas with signs of hydromorphism was evaluated. It is shown that the identification capacity of the indices depends not only on the level of soil moisture, but also on the biomass of vegetation (scales of crop damage), which is indicated by the high information capacity of the traditional vegetation index NDVI. The most informative index ranges were established: for NDVI, the range is from -0.117 to -0.024 with an identification percentage of 98.0 %; for OSAVI – 78.0 % with a range of 0.255–0.313; for NDMI with a range variation of -0.041 to -0.149 and an identification percentage of 56.0. Сonclusions. The results of remote identification of the areas of the MRLF enabled to obtain information about the moisture content of the soils of the arable lands of the research area. The ability of the specified indices during the geospatial identification of microrecessed landforms (MRLF) and soil areas within them with signs of hydromorphism was evaluated. It is demonstrated that the use of orthophotos with a resolution of 0.2 m per 1 pixel serves as important supporting aids of successful completion of the specified tasks. It was found that the identification ability of water indices on test fields without existing vegetation is too low. On the other hand, the shielding of the soil surface by vegetation with areas of damaged crops makes it possible to isolate MRLF. The obtained information can be used during the development of the methodology of soil science surveying and planning of largescale soil survey activities

Carbon stock changes of drained nutrient-rich organic forest soils in Latvia

Impact of drainage of organic soils in forest land on soil carbon (C) stock changes is of high interest not only to accurately estimate soil C stock changes, but also to provide scientifically based recommendations for forest land management in context of climate change mitigation. To improve knowledge about long-term impact of drainage on nutrient-rich organic soils in hemiboreal forests in Latvia, 50 research sites representing drained conditions (Oxalidosa turf. mel. (Kp) and Myrtillosa turf. mel. (Ks) forest site types) and undrained conditions as control areas (Caricoso-phragmitosa, Dryopterioso-caricosa and Filipendulosa forest site types) were selected. Soil C stock changes after drainage was evaluated by comparing current C stock in drained organic soils to theoretical C stock before drainage considering impact of soil subsidence. During the 53-years period after drainage, the peat subsidence was higher in nutrient-rich Kp forest site type compared to moderate nutrient-rich Ks forest site type (peat subsided by 37.0 ± 4.8 and 23.3 ± 4.8 cm, respectively). In nutrient-rich Kp forest site type, soil C stock decreased by 4.98 ± 1.58 Mg C ha–1 yr–1 after drainage, while no statistically significant changes in soil C stock (0.19 ± 1.31 Mg C ha–1 yr–1) were observed in moderate nutrient-rich soils in Ks forest site type. Thus, in Ks forest site type, the main driver of the peat subsidence was the physical compaction, while in Kp forest site type contribution of organic matter decomposition and consequent soil C losses to subsidence of the peat was significant.

Research on Engineering Characteristics of Cement Mixing Piles Strengthening Steel Sheet Pile Structure Wharf

In order to solve the technical problem of using steel sheet piles in soft soil foundations of deep water docks, the use of grid type cement mixing pile walls to reinforce the in-situ soft soil behind steel sheet pile docks is a new type of composite structure attempt. This paper combines practical engineering and uses finite element analysis software to study the vertical displacement, vertical stress, and horizontal displacement changes of reinforced soil in three layout forms: non-mixing pile structure, grid type cement mixing structure, and dispersed mixing pile structure. The results show that the grid type cement mixing pile structure can reduce soil settlement, improve the stability of reinforced soil, and reduce lateral soil pressure on steel sheet piles compared to the non-mixing pile structure and the dispersed mixing pile structure. In the practical application of steel sheet pile wharf engineering, the use of grid type cement mixing piles can improve the stability and engineering benefits of the wharf structure.