Soft Soil Model Research Articles

Enhancing Deep Excavation Optimization: Selection of an Appropriate Constitutive Model

To minimize the impact on nearby structures during deep excavations, choosing an appropriate soil constitutive model for analysis holds significant importance. This study aims to conduct a comparative analysis of various constitutive soil models—namely, the Mohr–Coulomb (MC) model, the hardening soil (HS) model, the hardening soil small strain (HSS) model, and the soft soil (SS) model—to identify the most suitable model for the lacustrine deposit. To implement these models, the soil’s index properties and mechanical behavior were evaluated from undisturbed soil samples. The numerical simulation and verification of these properties were carried out by comparing the laboratory test results with the outcome of the finite element method; the most suitable constitutive soil model for the soil was identified as the HSS model. Upon analyzing the wall deflection and ground settlement profiles obtained from respective constitutive models, it was observed that the HS and HSS models exhibit similar characteristics and are well-suited for analyzing typical lacustrine soil. In contrast, the MC and SS models yield overly optimistic results with lower wall deflection and ground settlement and fail to predict realistic soil behavior. As a result, this research highlights the significance of selecting the appropriate constitutive soil model and refining the parameters. This optimization process contributes significantly to the design of support systems, enhancing construction efficiency and ensuring overall safety in deep excavation projects.

Laboratory investigations of coupled polyethylene–sand–soft soil shallow foundations

This study investigates clayey soil from a road project situated in the district of Lodhran, Punjab, Pakistan. The subgrade prepared with the soil distorted due to heaving after a certain period of its construction. First, laboratory tests were conducted to explore the reason for this problem, examining the fundamental engineering properties of soil. The test results show that the soil acts as a soft material when water content reaches 30%, significantly reducing its strength. The soft soil is generally considered unsuitable for civil work due to its poor performance behaviour. So, the performance of clayey soil was examined in the study at its soft state by coupling it with stronger materials, such as polyethylene polymeric reinforcement and sand, developing laboratory-scale foundation models. Based on the model studies, the study proposes a sustainable polyethylene–sand–soft soil model, which shows 155 and 56% higher ultimate bearing capacity (BC) than soft soil and sand-reinforced soft soil foundations. The changes in BC occur due to the reinforcement action of the polyethylene reinforcement, which is associated with its tensile membrane action effects and interlock bonding at the soil-reinforcement interface. Practically, the study can reduce the dependency of industry practitioners on sand materials. Using polyethylene in civil work is viable for environmental sustainability.

Using soft soil models in geotechnical engineering: a review paper

Soil is considered a complicated material as, in general, the behavior under loading is non-linear in addition it is anisotropic material and its behavior is time-dependent. Various models were developed in the method of finite element for modeling the behavior of soil under different loading cases, and it must be known that no constitutive model is available that can simulate completely the actual soil behavior under all conditions. This paper attempts to investigate the soft soil model and present a discussion about the advantages and disadvantages for the purpose of giving an overview, and discussing the main finding of the previous studies regarding using the Soft Soil model in the numerical analysis of geotechnical engineering problems and applications. In this research, it was observed from the previous studies that the relation between the modified compression index (λ*) and unloading index (κ*) is from (5 to 10). The Soft Soil model gives a stiffer stress-strain behavior compared to Hardening model. Using this model for compressible soils needs a longer calculation time than other models as the material stiffness matrix was included in each calculation step. It shows satisfactory results in the analysis of the settlement of immediate and consolidation cases of foundation in clayey soil than the model of Mohr-Coulomb.

Analisis Penurunan Gabungan Prefabricated Vertical Drain dan Stone Column Untuk Perbaikan Tanah Lunak

Soft soil is inevitable in the construction, be it road construction or building construction. Soil improvement is needed to overcome the problem of soft soil, soil improvement methods are growing and diverse. This research is focused on studying the interaction behavior of combination two soil improvement methods, namely Prefabricated Vertical Drain (PVD) and Stone Column (SC). This research was conducted using PLAXIS 2D with Mohr-Coulomb (MC) and Soft Soil (SS) material models. The results showed that the combination of PVD and SC methods provides the advantage that PVD can accelerate the consolidation time and SC can reduce the settlement that occurs in the soil. The use of SS model is greater settlement compared to using Mohr-Coulomb material model with a settlement of 1,641 m for Soft Soil and 0.463 m for Mohr-Coulomb. SC depth variation affects the settlement and settlement time, the longer the SC the smaller settlement and the shorter time, while PVD only affects the time. Combining PVD and SC results in better settlement and settlement time compared to PVD or SC alone. Variations in construction methods result in slight differences for MC material models, whereas for SS material models, construction methods 2 are greater in settlement and shorter time.

BEHAVIOR OF AIRPORT FLEXIBLE PAVEMENT OVER SWELLING SOIL REINFORCED BY NEW ASPHALT LAYERS

Longitudinal fractures are a common occurrence in runway pavements built on expansive soil subgrades. Such soil behavior leads to a reduction in the carrying capacity and lifespan of runways, as variations in water content accelerate cracking and deformations in the various pavement construction layers. To examine the behavior of reinforced runway flexible pavement over expanding subgrade soil, this study uses experimental and numerical analyses. Non-destructive deflection test is used to assess static behavior, measuring deformations and stresses in various runway profiles both before and after reinforcing with new asphalt layers created using the ACN-PCN process. Using the software program PLAXIS 3D, a three-dimensional (3D) finite element model (FEM) was designed to anticipate pavement distortions resulting from sudden, high-pressure movements caused by the expansion of soil. The materials were simulated using a soft-soil model (SSM) for the expanding subgrade and nonlinear behavior for the pavement layers. The experimental results and computer analyses were compared, and it was discovered that the measured and calculated deflection curves generally match very well

Numerical Analysis of Soft Soils Reinforced with Deep Mixing Column

The deep mixing method is an in-situ soil improvement method in which the soil is mixed with cement and other binding materials. Within the scope of this study, two-dimensional numerical analyzes of a reinforced soil by deep mixing columns were carried out. Two different soft clay soil properties (Model 1 and Model 2) were used in the analyses. Analysis of two-dimensional models was done with PLAXIS 2D finite element program. The deformations, consolidation and compression obtained from Mohr-Coulomb and soft soil models were compared. The effects of soil properties and the length of the column, modulus of elasticity, diameter and distance between them were investigated for two models. As a result, it is thought that two-dimensional analyzes together with the modeling that will reflect the current site conditions can give reasonably realistic results if the soil properties are selected well and correctly before the construction phase.

Adaptive-passive tuned mass damper for structural aseismic protection including soil–structure interaction

As one of the most traditional vibration mitigation devices, tuned mass dampers (TMDs) are applied widely in aseismic protection of building structures. The control effect of a passive TMD is depended on its parameters, especially the frequency ratio. Nevertheless, passive TMDs are high sensitive to the frequency detuning issue, and a mistuned TMD will lose its aseismic protection. Soil-structure interaction (SSI) will deviate the structural frequency and lead to a mistuned TMD. Besides, different soil conditions will lead to different frequency deviations of the primary structure. However, it may be difficult to obtain parameters of the soil exactly. To solve this problem, a recently developed adaptive-passive eddy current pendulum TMD (APEC-PTMD) is applied to a benchmark 40-story tall building including SSI in this study, and four different soil conditions are considered. The APEC-PTMD can identify the optimal TMD frequency in the building with different soil types, and then retune itself through adjusting the pendulum length, and also the air gap between the conduct plate and permanent magnets to reset its damping ratio. Therefore, no prior knowledge of the soil condition is needed for the APEC-PTMD. To verify the aseismic protection effect, 44 far-field earthquake excitations are chosen, and two passive TMDs are used for comparison, while one is optimized for the base-fixed structure and the other is optimized based on the dense-soil model. The passive TMD will become mistuned when SSI is considered or soil parameters are changed, while APEC-PTMD can adapt to the structural dominant frequency with different SSI. Therefore, it always works as a passive TMD with well-tuned parameters. Results show that the APEC-PTMD has a better aseismic protection than the passive TMD, especially in the soft-soil model, and it has an excellent control effect compared to the without TMD case at the same time.

Numerical Modeling of Shallow Foundation Behavior Using Soft Soil Model

This study discusses the results of simulation a finite element analysis of the load-settlement curve using soft soil model of shallow foundation subjected to axial load rested on three different types of clayey soils, it was considered different shear strength parameters (C=16, C=25, and C=70). It was concluded for clayey soil of C=16, there was a match to the experimental load – settlement curve using the soft soil model. It was also observed increase in the foundation width led to an increase in bearing capacity, however, bearing capacity increased by around (79 %) for an increase in footing width of (6.25), so it was about (144%) for (12.5).

О применении моделей грунта Soft Soil и Hardening Soil Small-Strain в рамках задачи фильтрационной консолидации на различных этапах возведения и эксплуатации здания в условиях слабых грунтов

The article considers the problem of stage-by-stage construction of a framed structure building on a slab foundation in conditions of soft soils. The calculation was carried out within the frame of the filtration consolidation problem in the numerical formulation. A comparative analysis is submitted (within the frame of Soft Soil model and Hardening Soil Small-Strain model) for the resulting deformations of the base and the slab, the forces in the nodal structural elements, and the distribution of pore pressure in the base at various stages of the building`s construction and operation.

ANALYSIS OF THE COMBINATION OF METHODS OF FASTENING THE JUNCTION POINT OF A HORIZONTAL TUNNEL WITH A VERTICAL SHAFT IN CONDITIONS OF DENSE URBAN DEVELOPMENT

Purpose. The problem of compares the long-term behavior of a tunnel-well taking into account the rigid and flexible couplings in the projected structures in Ukraine with 3d digital modeling using the three-dimensional finite element method. A refined geotechnical model has also been developed, taking into account the nature of the piezometric starting conditions and the proposed piezometric conditions for assessing the long-term condition as well as a summary of the properties and dimensions of the tunnel and the shaft. Methodology. Analysis of structural connections based on the experience of building shallow subways in dense urban development on the example of construction projects in China and Mexico. Search for the optimal combination of implemented methods to achieve the optimal result. Problems of a choice of a mode with 3d digital modeling using the three-dimensional finite element method based on two assumptions; the first assumption considers the rigid connection as a monolithic concrete structure between the shaft wall and the tunnel body, and the second assumption considers a material with elastic behavior between the two structures, which in turn leads to a flexible connection. The main parameters that must be clarified and corrected by the designer of the system during commissioning are determined. Next, the soft soil model was used to perform the analyzes with end elements for compressible layers. Findings. Simulation in the application, the Plaxis software environment obtained graphs of transients for the most important operating parameters, such as the geometry of the tunnel and the indicated lining, the flotation pool, three-dimensional clusters. Originality. Scientific interest in advancing technologies used in combination. Development of an algorithm for the optimal selection of the parameters of flexibility and durability in specific conditions, to save time and simplify the calculation forms. Practical value. The analysis of the obtained results is carried out, the main focus was on the relative loads and stress concentrations in the connecting elements, namely the stresses that occur in the transverse direction of the joint. Also in articles were determined some of the advantages and disadvantages of the different connection alternatives are discussed in order to neutralize the impact of the case in the future.

Applicability of Constitutive Models to Describing the Compressibility of Mining Backfill: A Comparative Study

The compressibility of mining backfill governs its resistance to the closure of surrounding rock mass, which should be well reflected in numerical modeling. In most numerical simulations of backfill, the Mohr–Coulomb elasto-plastic model is used, but is constantly criticized for its poor representativeness to the mechanical response of geomaterials. Finding an appropriate constitutive model to better represent the compressibility of mining backfill is critical and necessary. In this paper, Mohr–Coulomb elasto-plastic model, double-yield model, and Soft Soil model are briefly recalled. Their applicability to describing the backfill compressibility is then assessed by comparing numerical and experimental results of one-dimensional consolidation and consolidated drained triaxial compression tests made on lowly cemented backfills available in the literature. The comparisons show that the Soft Soil model can be used to properly describe the experimental results while the application of the Mohr–Coulomb model and double-yield model shows poor description on the compressibility of the backfill submitted to large and cycle loading. A further application of the Soft Soil model to the case of a backfilled stope overlying a sill mat shows stress distributions close to those obtained by applying the Mohr–Coulomb model when rock wall closure is absent. After excavating the underlying stope, rock wall closure is generated and exercises compression on the overlying backfill. Compared to the results obtained by applying the Soft Soil model, an application of the Mohr–Coulomb model tends to overestimate the stresses in the backfill when the mine depth is small and underestimate the stresses when the mine depth is large due to the poor description of fill compressibility. The Soft Soil model is recommended to describe the compressibility of uncemented or lightly cemented backfill with small cohesions under external compressions associated with rock wall closure.

Material Models to Study the Effect of Fines in Sandy Soils Based on Experimental and Numerical Results

Choosing and calibrating a robust and accurate soil material model (constitutive model) is the first important step in geotechnical numerical modelling. A less accurate model leads to poor results and more difficulty estimating true behaviour in the field. Subsequent design work is compromised and may lead to dangerous and costly mistakes. In this research, laboratory experimental results were used as a basis to evaluate several soil material models offered in Plaxis2D software. The deciding feature of the soil model was how well it could represent effects of percentage of fine material within sandy soils to simulate its behaviour. Results indicate that the Hardening Soil (HS) model works well when the percentage of fine (soft) materials is less than 10%. Above that level, the Soft Soil model (SS) becomes the most suitable. Finally, some important conclusions about this research and recommendations for future research are highlighted.

Consolidation in Soft Soil – Case Study on Prefabricated Vertical Drains (PVDs)

Background: Constructing on soft ground is one of the challenges of geotechnical engineering. The unpredictable behaviour and characteristics of soft soil can cause much damage resulting in high maintenance costs in the post-construction phase. Objective: The purpose of this study is to analyse the consolidation process and ground improvement method using surcharge and a prefabricated vertical drain by measuring the accuracy of the prediction settlement value with the actual site settlement results. Methods: An effective ground improvement method is the application of a surcharge and prefabricated vertical drains (PVDs). Various methods can be used to predict the settlement effectively, one such method being PLAXIS 3D simulation. A case study on ground improvement works was selected for this research, where PVDs were constructed and implemented at the site. A few undisturbed samples were collected from the site to generate the parameters based on the lab test conducted in the simulation process. This parameter was carefully studied and representing the principal input for the 3D model, which is generated and represents the actual ground improvement method for the selected case study. The analysis was performed using a borehole and soft soil model to generate the diagram. The prediction settlement value was generated from the PLAXIS 3D analysis as the baseline comparing to the actual results. The factors that influence the settlement value, such as the length and spacing of the prefabricated vertical drain, construction method, and soil characteristics, are also discussed. Results: A predicted settlement of 2553 mm was generated by the simulation, while the actual settlement outcome at the site was 2096 mm, a difference of 457 mm, and a prediction accuracy of 82.1%. Conclusion: The study found that the combination of surcharge and prefabricated vertical drain in the ground improvement worked well. Also, discussed were the factors that influenced the accuracy of the prediction and the site results.

Evaluation of Lateral and Axial Deformation for Earth Pressure Balance (EPB) Tunnel Construction Using 3 Dimension Finite Element Method

Mass Rapid Transit Jakarta (MRTJ) phase 1 tunnel construction using the earth pressure balance method has been completed and surface settlement and lateral displacement data according to elevation and inclinometer readings has been collected to evaluate the effect of tunnel’s construction on surrounding infrastructure. Soil stratification along the research area, defined according to boring logs and soil parameters for the hardening soil model (HSM) and the soft soil model (SSM), was determined by optimization of stress-strain curve fitting between CU triaxial test, consolidation test and soil test models in the Plaxis 3D software. Evaluation of the result of surface settlement measurements using an automatic digital level combined with geodetic GPS for elevation and position control points showed that the displacement behavior was affected by vehicle load and stiffness of the pavement. Lateral displacement measurements using inclinometers give a more accurate result since they are placed on the soil and external influences are smaller than surface settlement measurement. The result of 3D finite element modeling showed that surface settlement and lateral displacement during TBM construction can be predicted using HSM with 2% contraction. SSM and the closed-form solutions of Loganathan and Poulos are unable to provide a good result compared to the actual displacement from measurements.

Geotechnical engineering analysis of material modeling and earthquake coefficient effect on NMR mine area

Waste management issue in mining industry has become increasingly important. In this regard, construction of tailings embankment or dams play an important role. Most of the tailings dams require some kinds of remedial actions during their operational life time, wherein PT Newmont Minahasa Raya (NMR), a mine company in North Sulawesi, Indonesia, has established a new forest covering 215 ha aimed at functioning as a rainwater catchment area to recharge associated groundwater systems. Two different material models were utilized during the finite element computations, comparing the performance of the more advanced constitutive Soft Soil material model, (Soft Soil Model, SSM) against the Mohr-Coulomb material model (Mohr-Coulomb Model, MCM) commonly used today. Practical geotechnical analysis of the stability of embankment construction is done by using a program Plaxis calculations based on the Finite Element Method for analyzing the value of deformation with Earthquake Coefficient obtained value safety factor 1.9085 as MCM and 1.9078 as SSM.

Seismic damage assessment of a historical masonry minaret considering soil-structure interaction

Historical structures should be carefully preserved and transferred to the next generations. Therefore, their seismic performances should be investigated in detail. In the finite element method, many parameters affect the seismic behaviour and damage distribution in the structures. One of the most significant parameters is the Soil-Structure Interaction effect. In finite element analyses, the soil medium is generally neglected, and the structures' base is restrained by fixed supports. In this study, seismic response of a historical masonry minaret is investigated by considering the Soil-Structure Interaction and Operational Modal Analysis methods. To determine the effect of Soil-Structure Interaction on structural behaviour, the fixed supports, hard and soft soil mediums at the base of the structure are modelled. The material and failure behaviours are defined with the Concrete Damage Plasticity model. Displacements, principal stresses, damage rates, and damage distribution of models are obtained with nonlinear time history analyses. According to the results, the interstory drift increases due to the decrease in the stiffness of the soil media. In addition, the fixed supports model was damaged more tensile stress damage than the other models. The least occurred in the soft soil model. It is concluded that the Soil-Structure Interaction effect significantly affects structural behaviour, especially the damage rate and distribution.

Case study on soft soil improvement using vertical drains—field measurements and numerical studies

This paper presents an interesting case study for a very large ground improvement project in north Egypt using prefabricated vertical drains (PVD) and surcharge. The first 15m of soil at this site is soft silty clay to silty sand over 35m layer of very soft clay. To build a trustable numerical model that can predict the behaviour of the complex situation, a trial area was built, including several types of instrumentations for intensive monitoring of deformations and excess pore water pressures over time. Undisturbed samples were collected all over the soil profile and tested in the lab to determine the soil parameters to be used in the numerical model. An axisymmetric numerical model was built and calibrated using the collected data to predict the soil behaviour and the development of settlements due to the construction works. The analyses were performed using the soft soil model and the soft soil creep model; thus, the numerical investigations allow an evaluation of the long-term effects. The comparisons of the finite element analysis with the measured deformations presented in this paper show a very good match. Moreover, pre and post in situ measurements of standard cone penetration tests with sensors for the measurement of the pore water pressures (CPTu) have been used to calibrate the numerical model. These CPTu tests were used additionally to verify the improvement of the soil shear parameters over the preloading duration. It is shown that a combination of surcharge and vertical drains can be successfully used to improve the soft soil conditions present at the discussed project.

Numerical Modelling of Oedometer Test

Abstract The oedometric test is a test widely used in civil engineering. The main objective of this article has been to investigate the primary consolidation behaviour of the intact soil samples by comparing the results obtained from finite element analysis computations in PlAXIS2D with the experimental result of the soil samples obtained from the site of the Al-Ahdab oil field in the east of Iraq. Three different material models were utilized during the finite element analysis, comparing the performance of the more advanced constitutive Soft Soil material model against the modified Cam Clay and Mohr-Coulomb material models. Numerical results of Oedomter test show that the Soft Soil model behaviour is the most appropriate model to describe the observed behaviour.

Numerical Analysis of One-Dimensional Consolidation in Fine-Grained Soils

The purpose of this study is to discuss which constitutive law can describes at best the observed behavior of Silt and Gravelly Clay on the basis of experimental and analytical results. To find numerical solution for saturated soils in oedometer test Plaxis 2D the finite element software was used. In order to obtain the compressibility, excess pore pressure and degree of consolidation curves; two constitutive laws were used in this work: the Soft Soil Model ‘SSM’ and the Modified Cam Clay Model ‘MCC’. Predicted results were found in good agreement with measurements obtained from experimental test and analytical solutions. The Soft Soil is in good agreement with experimental results in the compressibility curve; however the Modified Cam Clay Model is the most appropriate if compared with the analytical solution.

Assessment of Stiffness and Strength Parameters for the Soft Soil Model of Clays of Cameroon

This paper focuses on the advanced modelling of soft Cameroon clays for the global prediction of the behaviour of geotechnical structures. A comprehensive set of experimental data on Cameroon subsoils from the oedometer and triaxial tests are analyzed in this paper in order to determine the stiffness and strength parameters for the Soft Soil model. It is based on 71 soil samples taken from both sides of the construction sites of several major structures across the territory. At the first approach, the soil samples taken were analyzed in a geotechnical laboratory to obtain physical and mechanical identification parameters specific to each soil type. The results obtained reveal that the analyzed soils are generally compressible clays. In the second phase, the law of behaviour of the Soft Soil model was used to characterize these Cameroon soils. Its parameters were obtained after calibration of the results of the laboratory tests obtained in first approach. The results obtained in this article can be compared to the different models obtained on clays soils around the world. The parameters are of the same order of magnitude as other clays modelled around the world.