• Geomechanics and Engineering
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• v.32 no.1
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• pp.21-34
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• 2023

In order to analyze the effect of the cyclic lateral loading on the response of a pile-soil system, a full-scale single steel pile was subjected to one-way cyclic loading. The test pile was driven into a bi-layered soil consisting of a normally consolidated saturated clay overlying a silty sandy layer, the site being submerged by water up to one meter above the mudline in order to reproduce the conditions of an offshore pile foundation. The aim of this paper is to present the main results of interpretation of the cyclic lateral tests in terms of pile deflections, bending moment, and cyclic P-Y curves. From these latter an absolute secant reaction modulus E_AS,N was derived and a simple calculation model of the test single pile is proposed based on this modulus. Two applications of the proposed model are carried out, one with a 2D finite element modelling, and the second with a load transfer curves-based method.

• Geomechanics and Engineering
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• v.25 no.2
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• pp.75-87
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• 2021

Because the hydraulic/mechanical behaviour of unsaturated soil is more complicated than that of saturated soil, one of the most important issues in modelling unsaturated soil is to properly couple its stress-strain relationship with its water retention characteristics. Based on the results of a series of tests, the stress-strain relationship and the changes in suction and saturation of unsaturated completely decomposed granite (CDG, also called Masado) vary substantially under different loading/hydraulic conditions. To precisely model the hydraulic/mechanical behaviour of unsaturated Masado, in this study, the superloading concept was firstly introduced into an existing saturated/unsaturated constitutive model to consider the structural influences. Then a water retention curve (WRC) model considering the volumetric change in the soil, in which the skeleton and scanning curves of the water retention characteristics were assumed to shift in parallel in accordance with the change in the void ratio, was proposed. The proposed WRC model was incorporated into the constitutive model, and the validity of the newly proposed model was verified using the results of tests conducted on unsaturated Masado, including water retention, oedometer and triaxial tests. The accuracy of the proposed model in describing the stress-strain relationship and the variations in suction and saturation of unsaturated Masado is satisfactory.

• Geomechanics and Engineering
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• v.3 no.1
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• pp.1-16
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• 2011

Piles passing through sloping liquefiable deposits are prone to lateral loading if these deposits liquefy and flow during earthquakes. These lateral loads caused by the relative soil-pile movement will induce bending in the piles and may result in failure of the piles or excessive pile-head displacement. Whilst the weak nature of the flowing liquefied soil would suggest that only small loads would be exerted on the piles, it is known from case histories that piles do fail owing to the influence of laterally spreading soils. It will be shown, based on dynamic centrifuge test data, that dilatant behaviour of soil close to the pile is the major cause of these considerable transient lateral loads which are transferred to the pile. This paper reports the results of geotechnical centrifuge tests in which models of gently sloping liquefiable sand with pile foundations passing through them were subjected to earthquake excitation. The soil close to the pile was instrumented with pore-pressure transducers and contact stress cells in order to monitor the interaction between soil and pile and to track the soil stress state both upslope and downslope of the pile. The presence of instrumentation measuring pore-pressure and lateral stress close to the pile in the research described in this paper gives the opportunity to better study the soil stress state close to the pile and to compare the loads measured as being applied to the piles by the laterally spreading soils with those suggested by the JRA design code. This test data shows that lateral stresses much greater than one might expect from calculations based on the residual strength of liquefied soil may be applied to piles in flowing liquefied slopes owing to the dilative behaviour of the liquefied soil. It is shown at least for the particular geometry studied that the current JRA design code can be un-conservative by a factor of three for these dilation-affected transient lateral loads.

• Korean Journal of Soil Science and Fertilizer
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• v.47 no.6
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• pp.443-450
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• 2014

To determine Pb species in soils following the immobilization process, sequential extraction has been used despite the possibility of overestimating Pb species from unintended reactions during chemical extraction. Meanwhile, the application of extended X-ray absorption fine structure (EXAFS) has been shown to provide a more precise result than chemical extraction. In this study, the immobilization of Pb in contaminated soils treated with liming materials such as oyster shell (OS) or eggshell (ES) was evaluated with thermodynamic modelling and EXAFS analysis. Thermodynamic modelling by visual MINTEQ predicted the precipitation of $Pb(OH)_2$ in OS and ES treated soils. In particular, the values of saturation index (SI) for $Pb(OH)_2$ in OS (SI=0.286) and ES (SI=0.453) treated soils were greater than in the control soil (SI=0.281). Linear combination fitting (LCF) analysis confirmed the presence of $C_{12}H_{10}O_{14}Pb_3$ (lead citrate, 44.7%) by citric acid from plant root, Pb-gibbsite (Pb adsorbed gibbsite, 26.4%), and Pb-kaolinite (Pb adsorbed kaolinite, 20.3%) in the control soil. On the other hand, $Pb(OH)_2$ (16.8%), Pb-gibbsite (39.3%), and Pb-kaolinite (25.6%) were observed in the OS treated soil and $Pb(OH)_2$ (55.2%) and Pb-gibbsite (33.8%) were also confirmed in the ES treated soil. Our results indicate that the treatment with OS and ES immobilizes Pb by adsorption of Pb onto the soil minerals as a result of the increase in soil negative charge and the formation of stable $Pb(OH)_2$ under high pH condition of soils.

• Journal of Korea Soil Environment Society
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• v.4 no.2
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• pp.55-62
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• 1999

The solvent flushing apparatus for soil remediation was designed. After the soil around nuclear facilities was sampled and compulsorily contaminated by Co, the characteristics remediated by solvent flushing were analyzed. Meanwhile, the nonequilibrium sorption code was developed for modelling of the soil remediation by solvent flushing, input parameters needed for modelling were measured by laboratory experiment. Experimental results are as follows : The soil around nuclear facilities belongs to Silt Loam including a lot of silt and sand. When water was used as a solvent, the higher was the hydraulic conductivity. the higher the efficiency of soil remediation was. The values calculated by the nonequilibrium sorption code agreed with experimental values more exactly than the values calculated by the equilibrium sorption code. When EDTA solution was used as a solvent. the soil remediation efficiency by EDTA solution showed higher than that by water.

• Geomechanics and Engineering
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• v.11 no.4
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• pp.471-492
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• 2016

Underground tunnelling is one of the sustainable construction methods which can facilitate the increasing passenger transportation in the urban areas and benefit the community in the long term. Tunnelling in various ground conditions requires careful consideration of the stability factor. This paper investigates three dimensional stability of a shallow circular tunnel in a layered soil. Upper bound theorem of limit analysis was utilised to solve the tunnel face stability problem. A three dimensional kinematic admissible failure mechanism was improved to model a layered soil and limiting assumptions of the previous studies were resolved. The study includes calculation of the minimum support pressure acting on the face of the excavation in closed-face excavations. The effects of the characteristics of the layers on the minimum support pressure were examined. It was found that the ratio of the thickness of cover layers particularly when a weak layer is overlying a stronger layer, has the most significant influence on the minimum tunnel support pressure. Comparisons have been made with the results of the numerical modelling using FLAC3D software. Results of the current study were in a remarkable agreement with those of numerical modelling.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1260-1268
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• 2008

In case of deep excavation analysis, the theory of beam on elasto-plastic geo-material (elasto-plastic theory) can not consider the inclined ground layers appropriately. It is frequently assumed that the soil layers are parallel to the surface. However, the soil layers are generally inclined and even asymmetric. The common modelling of the asymmetric half section of the excavation system using the elasto-plastic theory, can lead differences from the real behaviour of ground, which has critical significance in case of deep excavation in urban area. In this study, an attempt to find appropriate modelling methods was made by carrying out a comparative study between the FEM and the elasto-plastic analyses. It is shown that in case of the upward-inclined soil profile the elasto-plastic theory may underestimate the performance of retaining structures.

• Journal of the Korean Geosynthetics Society
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• v.10 no.4
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• pp.105-112
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• 2011

This paper presents the numerical modelling technique for modeling the time-dependent behavior of geosynthetic reinforced soil wall under a sustained load. The applicability of power law-based creep models for modeling the creep deformations of geogrid and reinforced soil was first examined. The modeling approach was then used to simulate the long-term performance of a geosynthetic reinforced soil wall used in a bridge abutment. The results indicated that the power law-based models can be effectively used for modelling the long term behavior of geosynthetic reinforced walls under sustained loading. In addition, it was shown that, when using creep deformation susceptible backfill soils, the abutment wall and the sill beam may experience deformations exceeding allowable limits. Practical implications of the findings from this study are discussed in great detail.

• Geomechanics and Engineering
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• v.17 no.1
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• pp.1-9
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• 2019

This paper proposes a new numerical approach to model geocell reinforced soils, where the geocell is described as membrane elements and the complex interaction between geocell and soil is realized by coupling their degrees of freedom. The effectiveness and robustness of this approach are demonstrated using two examples, i.e., a geocell-reinforced foundation and a large scale retaining wall project. The first example validates the approach against established solutions through a comprehensive parametrical study to understand the influence of geocell on the improvement of bearing capacity of foundations. The study results show that reducing the geocell pocket size has a strong effect on improving the bearing capacity. In addition, when the aspect ratio maintains the same value, the bearing capacity improvement with increasing geocell height is insignificant. Comparing with the field monitoring and measurement in the project, the second example investigates the application of the approach to practical engineering projects. This paper provides a practically feasible and efficient modelling approach, where no explicit interface or contact is required. This allows geocell reinforced soils in large scale project can be effectively modelled where the mechanism for complex geocell-soil interaction can be explicitly observed.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1991.04a
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• pp.29-33
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• 1991

This paper reports the application study of the ground reinforement under a buried pipeline subjected to differential settlement via a finite element modelling. The Soil-reinforrement interaction helps to mimimize the differential settlement between the adjoining pipe segments. The settlement pattern and deformation slope of a pipeline have been evaluated for a boundary condition at the joint between a rigid structure and apipeline. The analysis results are compared for both non-reinforied and reinforced cases to measure the effectiveness of the soil reinforcement for restraining the settlement of the pipeline.