Soil Creep Model Research Articles

Behaviour of 60-year-old trial embankments on peat

The search for low cost solutions for roads on peatlands inspired the construction of four full scale trial embankments at two sites in Norway in the early 1960's. The embankments are still accessible and this work was motivated by present day needs to develop environmentally sustainable solutions to such problems. The embankments were constructed using locally sourced sand and sawdust and have behaved very well with the sawdust settling beneath the water table as designed and remaining in perfect condition some 60 years later. A detailed characterisation of the distinctly different peat at the two sites is presented and it is shown that the peat properties are as expected from local and international experience. Laboratory work on the sawdust showed that it behaves like a highly compressible fibrous peat. Short-term embankment settlement behaviour was controlled by the level of applied load whereas long-term creep settlements were governed by the peat consolidation properties. Pore water pressures dissipated unexpectedly quickly. Modelling using the Soft Soil Creep model in PLAXIS captured both short- and long-term settlements and the pore pressure dissipation well.

The role of creep deformation in pit lake slope stability

Large-scale open-pit mining activities have profound impacts on the surrounding landscape and environment. At the cessation of open-pit mining, the rehabilitation of large void spaces can be achieved by pit-lake filling, where the water body provides a confining pressure on surrounding mine surfaces, reducing both the likelihood of slope failure and the need for ongoing slope maintenance. Although pit-lakes present a range of long-term benefits, the geotechnical performance of mines containing soft soils that are susceptible to creep under increasing loads due to pit-lake filling is seldom considered. From a geotechnical standpoint, creep induced failure is commonly associated with slow, downslope movements, prior to critical slope failure events. In this research, time-dependent slope stability analyses based on creep-sensitive materials are presented for an open-cut mine undergoing pit-lake filling. Numerical simulation provides a mechanism for the assessment of materials exhibiting soft soil creep constitutive behaviour under various loading conditions due to pit-lake filling. The response of mine surfaces is investigated for various filling regimes, highlighting location-dependent deformation rates, pore pressures and slope Factors of Safety for a large Australian open-pit brown coal mine. Results are presented for two separate creep-sensitive materials, identifying the ability to achieve final, stable landforms for a range of long-term pit-lake conditions.Article HighlightsTime-dependent creep deformation behaviour is investigated for a large Victorian open-pit brown coal mine undergoing pit-lake rehabilitation.The soft soil creep model is implemented for a large open-pit rehabilitation model, to assess long-lasting creep movements of a specific mine slope.Mine void filling rates are simulated for a range of rehabilitation scenarios over a 5 to 40 year period, identifying the excess pore water pressure distributions in addition to vertical and horizontal deformations rates.The long-term behaviour of 8 cross-section profiles is presented, identifying the effect of pit-lake filling for silt and clay interseam materials.

The finite element modeling of rigid inclusion-supported embankment

Abstract The design of supported embankments on soft soil is a common challenge for civil engineers. This article aims to evaluate the performance of three advanced constitutive models for predicting the behavior of soft soils, i.e., hardening soil, hardening soil model with small-strain stiffness, and soft soil creep. A case study of a rigid inclusion-supported embankment is used for this purpose. Plaxis 3D program was adopted to predict the settlements in subsoil layers and vertical stresses in the load transfer platform. Comparison between field measurements and result of Plaxis 3D modeling was performed. Results demonstrate that soft soil creep model yields predictions in a good agreement with the field measurements, while hardening soil small strain model gives slightly worst predictions.

Soil Parameters of Kallang Formation and Old Alluvium in Singapore for Excavation Study with Plaxis

Plaxis is a software program widely used in Singapore for the analysis of excavation problems in the Kallang Formation and the Old Alluvium. The present study showed that the soft soil creep model was the most appropriate for excavation study of a retaining wall with a stabilizing berm in the estuarine deposit and the upper and lower marine clays of the Kallang Formation, and the hardening soil model was the most appropriate for the fill, fluvial deposits, and Old Alluvium in Singapore using Plaxis. The appropriate values of soil parameters of the estuarine deposits, fluvial deposits, Kallang Formation, and Old Alluvium for excavation study required by the hardening soil and the soft soil creep models will be summarized based on the summary of design parameters of a detailed geotechnical study and a literature review of the appropriate values reported in the literature for each soil layer. The validity of using such values for Plaxis analysis will be confirmed by a comparison of the predicted deflection of a diaphragm wall with the field measurement. The appropriate values of soil parameters of the estuarine deposits, fluvial deposits, Kallang Formation, and Old Alluvium for excavation study required by the hardening soil and the soft soil creep models will be very useful for practicing engineers.

Performance analysis of a jacked-in single pile and pile group in saturated clay ground

When a pile is installed into saturated clay ground, the “setup” effect may occur due to ground consolidation, which changes pile performance. Although this phenomenon has been observed both in the field and laboratory, its numerical simulation is still challenging. In this work, pile installation effects on the behaviors of jacked-in piles were investigated through three simulation techniques by a three-dimensional finite element analysis program, PLAXIS 3D. A constitutive model called the soft soil creep model was used to describe the soil behavior based on soil parameters obtained from laboratory tests. The behaviors of single piles were first investigated with or without the consolidation process after pile installation to evaluate the pile setup effect. Then, a pile group comprising 4 piles was analyzed using the consolidation process to verify the applicability of the three simulation techniques. The calculated results were compared with the corresponding experimental results. The calculated results using three techniques generally agreed well with the experimental results in terms of initial stiffness and pile shaft resistance. Both the measured and calculated results indicate that ground consolidation caused by pile installation significantly increases the pile bearing capacity and especially, the pile shaft resistance. Therefore, the pile setup effect can be reasonably simulated by the three proposed techniques.

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.

Consolidation settlement of soil foundations containing organic matters subjected to embankment load

Peatland is distributed in China widely, and organic matters in soil frequently induce problems in the construction and maintenance of highway engineering due to the high permeability and compressibility. In this paper, a selected site of Dali-Lijiang expressway was surveyed in China. A numerical model was built to predict the settlement of the foundation of the selected section employing the soft soil creep (SSC) model in PLAXIS 8.2. The model was subsequently verified by the result of field observance. Consequently, the parameters of 17 types of soils from different regions in China with organic contents varying from 1.1–74.9% were assigned to the numerical model to study the settlement characteristics. The calculated results showed that the duration of primary consolidation and proportion of primary settlement in the total settlement decreased with increasing organic content. Two empirical equations, for total consolidation settlement and secondary settlement, were proposed using multiple linear regression based on the calculated results from the numerical models. The analysis results of the significances of certain soil parameters demonstrated that the natural compression index, secondary compression index, cohesion and friction angle have significant linear relevance with both the total settlement and secondary settlement, while the initial coefficient of permeability exerts significant influence on the secondary settlement only.

Simulation of the influence of dynamic loading on the stress-strain state of the natural and geoengineering environment

The paper provides numerical simulation of the influence of dynamic loading on the stress-strain state of the natural and geoengineering technogenic environment taking into account the soil basis for forecasting its use as the basis of the structure. Paper demonstrates the impact of static and dynamic loading on the subsidence of the landfill. To take into account the liquid phase of the waste and the viscoplastic medium, Darcy's law is used as an equation of balance of forces. The body of the landfill is modeled by weak soil taking into account the creep, using the Soft Soil Creep model. The covering and underlying soil layers are described by the Coulomb – Mohr model. An effective method for calculating the sedimentation of natural and geoengineering environment on the example of a solid waste landfill, based on numerical modeling of the stress-strain state of the landfill and underlying soil using finite elements is developed. It is demonstrated that the largest subsidence is experienced by the landfill with sand, as the base soil, but in percentage terms the amount of subsidence with the maximum load relative to the initial subsidence without loading is the largest in clay (33.7%). The obtained results must be taken into account when using landfills as a basis for buildings, structures, routes, recreational areas, etc.

Prediction of embankment settlement on Swedish peat using the Soft Soil Creep model

Despite the prevalence of peat in northern areas of Europe and elsewhere, there are comparatively few case histories of carefully monitored embankments constructed directly on peat. In addition the...

Modeling elasto-visco-bio-plastic mechanical behavior of municipal solid waste in landfills

This paper presents a mechanical model for the prediction of short-term and long-term settlement of municipal solid waste in landfills. The load-induced volumetric compression, shear behavior, tensile behavior, and the time-dependent creep compression behavior of the waste are modeled using the soft soil creep model. The compression induced by decomposition of waste is modeled based on the phenomenon of wetting-induced strains observed in compacted fills with expansive soils. The proposed model is validated using benchmark datasets obtained from two long-term laboratory experiments performed on waste samples obtained from a landfill in UK. Two additional numerical simulation cases (CONV—without leachate injection and BIOR—with leachate injection) were examined by application of the proposed mechanical model on a typical full-scale landfill cell geometry to determine the spatial and temporal variation in the short-term and long-term settlement characteristics of waste in the simulated landfill cell. The settlement of waste predicted by the model could capture the key mechanisms of short- and long-term waste settlement in landfills. The leachate injection in BIOR simulation enhanced the rate of depletion of the degradable solids resulting in a significant increase in the waste settlement. For the simulated landfill and waste conditions, the biodegradation-induced settlement contributed to more than 90% of the settlement of the waste in both CONV and BIOR simulations. The distribution of the injected leachate had a considerable influence on the settlement profiles observed within the waste.

Settlement of a railway embankment on PVD-improved Karakore soft alluvial soil

This paper presents a case history of the settlement performance of a railway embankment built on a Prefabricated Vertical Drain (PVD) improved soft alluvial soil of Karakore area, Wollo province, north-east of Ethiopia. The embankment was constructed on Awash - Kombolcha - Haragebaya (AKH) railway project for the purpose of preloading so as to facilitate the consolidation settlement in a short period of time; and it was monitored for more than 750 days. Numerical predictions of Class A and Class C (based on back-calculation procedure) were performed using Plaxis 2D. The soft soil creep (SSC) model was employed for the soft soil layers, while the Mohr-Coulomb (MC) model was used for the drainage and fill layers. The predictions were compared with the field monitoring settlement data. Quite a reasonable agreement was achieved from the finite element modelling of Class C prediction when the prediction was compared with the actual field settlement values. Parametric sensitivity studies were carried out to examine the influence of parameters on the rate and magnitude of settlements. The results of the numerical predictions and parametric studies have been discussed in detail. The soil on the flood plain area of Karakore is found to be very soft to soft alluvial deposit and formed over Tertiary Eocene stiff clay. The variable conditions of the soil formation and deposition highly dictated the deformation and excess pore water pressure behaviour of the soft subsoil sediment. The parametric sensitivity study showed that, following the compression index, the initial void ratio, the hydraulic conductivity, and the OCR highly influenced the settlement responses of PVD-improved soft alluvium soil respectively.

Case study on long-term ground settlement of reclamation project on clay deposits in Nansha of China

In the design of reclamation, long-term settlement is seriously concerned. This paper presents a case study on the ground settlement of a reclamation project in Nansha, China. Fourteen undisturbed soil samples were taken at different depths from this site. Both oedometer tests on fourteen specimens and triaxial hydraulic conductivity tests on nine specimens were conducted. Finite element (FE) modelings using soft soil creep (SSC) model or soft soil (SS) model for modeling clayey soils with or without creep and the calculation using a new simplified method were performed to analyze the consolidation settlement of clay deposits subjected to filled loadings. The FE simulated results and calculated results from the new simplified method were compared with the monitored data in the field. Results show that the curves of the FE modeling using SSC model and the calculation from new simplified method have the same trends as those of the measured settlements. The creep contributes to excess pore pressure dissipation during the consolidation. Furthermore, ground settlements of the reclamation are predicted with the aid of the FE and new simplified method analysis. These predictions can provide the essential information for engineers to control or reduce the settlement in future.

ВЫДАВЛИВАНИЕ СЛАБОГО СЛОЯ ГРУНТА ИЗ СЖИМАЕМОЙ ТОЛЩИ ОСНОВАНИЯ ФУНДАМЕНТОВ КОНЕЧНОЙ ШИРИНЫ

The paper provides a quantitative assessment of the deflected mode of foundation stratum of finite width foundation, in the compressible thickness of which there is a slack clay soil layer. A number of criteria for assessing the possibility or impossibility of extruding a slack layer depending on its strength and rheological properties, as well as the relative thickness of the layer to its length (h/l) and the relative depth of the layer (h/d) have been given. Closed analytical solutions are given to determine the rate of Foundation precipitation depending on the rate of extrusion of the weak layer, including taking into account the damped and undamped creep. The analytical solutions in the article are supported by the graphical part made with the help of the Mathcad program. Plots of changes in shear stresses in the layer along the x axis at different distances from the axis and at different values 0, contours of horizontal displacement velocities in the weak layer at different distances from the x axis, plots of horizontal displacement velocities in the middle of the weak layer and plots of horizontal displacement velocities in the weak layer at different distances from the x axis are given. As a calculation model for describing the creep of a slack layer, rheological ones of the soil using power and hyperbolic functions and their modifications have been considered. In addition, most modern rheological models that take into account soil hardening during creep have been considered. Based on these models, the problem is solved by means analytical and numerical methods using the Mathcad PC and the PLAXIS PC according to the Soft Soil Creep model. The graphical part shows the isofields of horizontal displacements for 300 days and 600 days and the corresponding contours of horizontal displacements.

Precision of the Creep Coefficient and Secondary Consolidation of Water-Saturated Viscous Soil

Patterns of soil consolidation with significant filtration and viscous resistance to volumetric deformation are considered. Joint models were characterized, issues identified and practical calculations of the consolidation of water-saturated boggy soils were presented. The conceptual contradictions for the viscous-elastic-plastic model were analyzed using the Bingham nonlinear water-saturated body model of the KONSO program and the Plaxis Soft soil creep model. The method of the correct determination of creep and nonlinear viscosity parameters during the compression-consolidation testing was presented.

Finite element analysis of time-dependent behavior in deep excavations

This study investigated the time-dependent behavior of a diaphragm wall and ground surface for a typical excavation in soft clay using two-dimensional finite element analysis. During excavation, deformations normally increase with time, both in the soil excavation time and the elapsed time between excavation stages. The increase may be due to consolidation and/or creep but the mechanism has never been studied comprehensively before. The hardening soil, hardening soil small strain, soft soil, and soft soil creep model were used depending on analysis requirements. Compared to the measurement, the soft soil creep model could simulate the time-dependent wall deflection and maximum ground settlement properly. Creep had a significant contribution to increasing the wall deflection while consolidation had little effect. Creep also caused a significant increase in the ground settlement both in excavation stages and elapsed times while consolidation caused the ground settlement to rebound slightly during elapsed times. The maximum wall deflection and ground settlement induced by the bottom-up method were 0.79 and 0.80 times as large as those by the top-down method, respectively. This was a contribution of a three times smaller support stiffness, elapsed time and unsupported length of the bottom-up method compared to those of the top-down method.

Creep characteristics and pore water pressure changes during loading of water storage tank on soft organic soil

ABSTRACT Peat ground is widely distributed throughout the southern part of Iraq. Peat contains a large amount of organic matter and has a very high natural water content. This study discusses results of settlement of water storage tank constructed in southern oilfield of Iraq. The first part of this study deals with field experimental works, which included drilling boreholes and evaluating the mechanical soil properties. The second part is conducted using finite element method through the 3D software, adopting the Soft Soil Creep Model and Soft Soil Model. Results showed that the secondary settlement has greatly affected the behaviour and final settlement of the tank, and the Soft Soil Creep Model is a better representative to the field settlement than Soft Soil Model. The results of Soft Soil Creep model are greater than those of Soft Soil Model for vertical displacement, horizontal displacement and pore water pressure because of secondary compression effect.

Three-dimensional numerical study of long-term settlement induced in shield tunneling

The objective of this study is to examine the mechanism of the long-term settlement induced in shield tunneling. A series of finite element analysis were conducted using PLAXIS 3D on a well document shield tunneling case in Taipei Mass Rapid Transit System. Various simulation were executed assessing the impact of consolidation on long-term settlement using Soft Soil and Hardening Soil with Small-strain models. Simulation to assess the impact of the creep behavior of the soil on the long-term settlement was also executed using the Soft Soil Creep model. The computed surface settlements were compared to the field measurements. It was found from this study that the computed settlement matched the field measurement when creep behavior of the soft soil was considered but if creep was not accounted for, the computed settlement undervalued the field measurements. Finally, a series of parametric study was executed to examine the influence of various parameters on the long-term settlement. The results obtained from the parametric study of shield tunneling in thick clay clearly distinguished that mechanism of long-term settlement in shield tunneling is predominantly due to creep behavior of the soft soil since consolidation constitutes 5% of the total settlement while creep accounts for 80% of the total settlement.

Stability Analysis of Colombo–Katunayake Expressway (CKE) Using Finite Element and Limit Equilibrium Methods

Colombo–Katunayake Expressway (CKE) is the second major highway in Sri Lanka connecting the International Airport at Katunayake to Colombo, and this expressway is constructed over soft soils, predominantly peat. A research study was conducted to analyse the stability of two critical sections of the CKE project using finite element method (FEM), limit equilibrium method (LEM) and Matsuo chart. In the FEM, PLAXIS 2D package was used to simulate the behaviour by using four different types of analyses: (1) Mohr–Coulomb (MC) analysis: MC model for all soil layers; (2) MC-SS 1 analysis: soft soil (SS) model for peat and MC model for remaining soil layers; (3) MC-SS 2 analysis: SS model for peat and soft clay layers and MC model for remaining soil layers; and (4) MC-SS-SSC analysis: soft soil creep (SSC) model for peat, SS model for soft clay and MC model for remaining soil layers. Further, LEM analysis was carried out using SLOPE/W and obtained factor of safety (FOS) values were compared with the FEM analysis. In addition, effect of geotextile on the long-term stability was analysed in FEM. Based on the outcome of the FEM analysis, it was noticed that MC-SS 2 model is the best model to predict the actual field condition for soft soil with high overconsolidation ratio values. In addition, FOS values obtained from PLAXIS were in very good agreement with those obtained from SLOPE/W. Incorporation of geotextile improves the stability of the embankment, and the optimum stiffness of the geotextile should be selected for practical applications.

Study of long-termed displacements of a tunnel boring machine during its stoppage

This paper studies the long-termed displacement of a tunnel boring machine (TBM) resting on soft clay during its unscheduled stoppage for 100 days. It is based on a real case of tunneling in a coastal city of Ningbo in China. The numerical prediction is carried out by using different soil models in the software PLAXIS, and the prediction is compared with on-site measurement of the displacement. Different factors are considered in the prediction, including soil creeping and the disturbance to the soft clay during the tunneling. The study indicates that the consideration of disturbance is essential to the accurate prediction. While advanced soil models including the soft soil model and soft soil creep model are not able to accurately predict the TBM displacement, the consideration of soil disturbance leads to a very good agreement with the measurement. The accurate prediction of ground settlements also justifies consideration of the disturbance in the study of tunneling.

Evaluation of creep models for frozen soils

To model the creep behavior of frozen soils, three creep stages have to be reasonably described(i.e., primary, secondary and tertiary stages). Based on a series of uniaxial creep test results, three creep models were evaluated. It was shown that hypoplastic creep model has high prediction accuracy for both creep strain and strain rate in a wide stress range. The elementary rheological creep model can only be used for creep strains at low stress levels, because of the restraints of its mathematical construction. For the soft soil creep model, the progressive change from the primary to secondary and tertiary stages cannot be captured at high stress levels. Therefore, the elementary rheological and soft soil creep models can only be used for low stress levels without a tertiary stage; while the hypoplastic creep model is applicable at high stress levels with the three creep stages.