• Journal of the Korean Geotechnical Society
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• v.30 no.1
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• pp.17-25
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• 2014

Offshore wind turbine foundations are subjected to wind, current and wave loadings. Hence, both static and cyclic behaviors of foundation's soil are important for the design of offshore wind turbine foundation. Undrained cyclic behaviors of soils depend upon the number of loading cycles, vertical effective stress, cyclic shear strain, relative density, and the combination of cyclic and average shear stresses. In order to evaluate the effect of average and cyclic shear stresses on the undrained cyclic behavior of marine silty sand, cyclic direct simple shear (CDSS) tests are performed with relative density of 85%, vertical effective stress of 200 and 300 kPa, and failure criteria of either 15% double amplitude cyclic shear strain (${\gamma}_{cyc}$) or permanent shear strain (${\gamma}_{p}$). The results are presented in the form of design graphs or contour diagrams. The undrained cyclic behavior of marine silty sand is found to be dependent on cyclic and average shear stresses and/or the combination of both shear stresses. It is found that when significant average shear stress exists the permanent or progressive shear strain is the govering failure criteria instead of cyclic shear strain.

• Geomechanics and Engineering
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• v.11 no.3
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• pp.325-343
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• 2016

A total stress-based bounding surface model is developed to predict the undrained behaviour of saturated soft clays under cyclic loads based on the anisotropic hardening modulus field and bounding-surface theories. A new hardening rule is developed based on a new interpolation function of the hardening modulus that has simple mathematic expression and fewer model parameters. The evolution of hardening modulus field is described in the deviatoric stress space. It is assumed that the stress reverse points are the mapping centre points and the mapping centre moves with the variation of loading and unloading paths to describe the cyclic stress-strain hysteresis curve. In addition, by introducing a model parameter that reflects the accumulation rate and level of shear strain to the interpolation function, the cyclic shakedown and failure behaviour of soil elements with different combinations of initial and cyclic stresses can be captured. The methods to determine the model parameters using cyclic triaxial compression tests are also studied. Finally, the cyclic triaxial extension and torsional shear tests are performed. By comparing the predictions with the test results, the model can be used to describe undrained cyclic stress-strain responses of elements with different stress states for the tested clays.

• Journal of the Earthquake Engineering Society of Korea
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• v.28 no.1
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• pp.33-39
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• 2024

Understanding the behavior of soil under cyclic loading conditions is essential for assessing its response to seismic events and potential liquefaction. This study investigates the effect of non-plastic fines content (FC) on excess pore pressure generation in medium-density sand-silt mixtures subjected to strain-controlled cyclic direct simple shear (CDSS) tests. The investigation is conducted by analyzing excess pore pressure (EPP) ratios and the number of cycles to liquefaction (Ncyc-liq) under varying shear strain levels and FC values. The study uses Jumunjin sand and silica silt with FC values ranging from 0% to 40% and shear strain levels of 0.1%, 0.2%, 0.5%, and 1.0%. The findings indicate that the EPP ratio increases rapidly during loading cycles, with higher shear strain levels generating more EPP and requiring fewer cycles to reach liquefaction. At 1.0% and 0.5% shear strain levels, FC has a limited effect on Ncyc-liq. However, at a lower shear strain level of 0.2%, increasing FC from 0 to 10% reduces Ncyc-liq from 42 to 27, and as FC increases further, Ncyc-liq also increases. In summary, this study provides valuable insights into the behavior of soil under cyclic loading conditions. It highlights the significance of shear strain levels and FC values in excess pore pressure generation and liquefaction susceptibility.

• Journal of the Korean Geotechnical Society
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• v.31 no.4
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• pp.5-12
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• 2015

The construction of waste landfill sites has been increased due to recent expansion of various waste. Geotextiles are widely used for the purpose of reinforcement and protection of waste inside the landfill. Geotextile affects the shear behavior of waste landfill which forms the contact surface with soil. In this study, the effect of acidic and alkaline components in leachate has been analyzed through the laboratory experiment on the shear stress reduction of the contact surface of ground-geotextile under the cyclic load. For this purpose, a dynamic contact surface shear tester has been manufactured, and cyclic simple shear tests have been performed using geotextile and soil specimen which were immersed in chemical solutions for 60 and 840 days, respectively. Based on the Disturbed State Concept, the characteristics of shear stress on the contact surface of ground-geotextile due to chemical factors have been identified by the disturbance function.

• Journal of the Korean GEO-environmental Society
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• v.23 no.12
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• pp.25-31
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• 2022

Unlike structures installed on land, the structures installed on the offshore ground must consider long-term cyclic loads such as wave loads, wind loads and tidal loads at sea. Therefore, it is important to analyze the behavior of the ground subjected to long-term cyclic loads in order to design a structure installed on the ocean ground. In this paper, cyclic simple shear tests were performed to analyze the ground behavior for long-term cyclic loads according to the confining pressure, and a three-dimensional design failure curve was prepared that can easily check the failure characteristics according to the confining pressure. As a result of the analysis, it was confirmed that the position of the design failure curve is different depending on the confining pressure even under the same conditions of the cyclic shear stress ratio and the average shear stress ratio, and the number of cyclic loads reaching failure is affected by the confining pressure. From the created 3-D design failure curve under different confining pressure, the tendency and approximate value of the design failure curve according to the confining pressure can be estimated.

• Journal of the Korean GEO-environmental Society
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• v.8 no.6
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• pp.69-76
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• 2007

The sands which use for soil improvement of soft ground at coastal area contain more or less amount of shells. In this research the effects of shell contents on the liquefaction resistance of the shelly sand were studied. NGI cyclic simple shear tests were performed for the shell-sands with shell contents of 0%, 5%, 10%, 20%, 30% under the effective vertical stress of 50kPa, 100kPa and 150kPa for 40% and 55% of relative density, respectively. Cyclic simple shear test results showed that for the low effective vertical stress, the liquefaction resistance increased rapidly with increase of shell contents in both 40% and 55% relative density. On the other hand, for the high effective vertical stress, the liquefaction resistance increased slightly in 40% relative density and was almost same in 55% relative density. Liquefaction resistance decreased with increasing effective vertical stress for both 40% and 55% relative density. In the same effective vertical stress and shell contents, liquefaction resistance increased with the increase of relative density.

• Journal of the Korean Geotechnical Society
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• v.22 no.12
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• pp.89-98
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• 2006

In this paper the behavior of saturated sand deposits where liquefaction occurred before is studied for successive earthquakes. The relationship between past pore pressure generation and reliquefaction resistance is examined by using cyclic direct simple shear tests. If the soil sample in direct simple shear produced nearly 90% of excess pore pressure during first time loading, its liquefaction resistance increased during following cyclic loading after consolidation. However, a fully liquefied soil during first time loading has a densely packed condition but shows less liquefaction resistance for the following cyclic loading. UBCSAND model that can account for pore pressure change and stiffness loss of soil during shaking is used to analyze the centrifuge test simulating reliquefaction. The pore pressure rise during first time cyclic loading controls liquefaction resistance. The measurements from reliquefaction centrifuge test are compared with numerical predictions. By considering frequent earthquakes having occurred at the Southern Korea near Japan, such effective stress approach is necessary for reliquefaction study.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.243-252
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• 1993

Undrained cyclic simple shear tests and undrained cyclic triaxial tests were performed on silt containing sand in order to investigate the effects of silt contents on the liquefaction strength and shear characteristics of the sand. From the view that the difference of liquefaction strength for different content of silt stems from dilatancy characteristics of the sand, stress-dilatancy relation of the sand was obtained from drained triaxial test in which the mean stress was kept constant. Considerations on liquefaction behaviors were made by comparing the drained and undrained behaviors of sands during static shear test. It is concluded that ${\lambda}$-value of the stress-dilatancy relation will be closely related to the liquefaction strength.

• Structural Engineering and Mechanics
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• v.53 no.2
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• pp.189-204
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• 2015

After the large destruction of Lisbon due to the 1755 earthquake, the city had to be almost completely rebuilt. In this context, an innovative structural solution was implemented in new buildings, comprising internal timber framed walls which, together with the floors timber elements, constituted a 3-D framing system, known as "cage", providing resistance and deformation capacity for seismic loading. The internal timber framed masonry walls, in elevated floors, are constituted by a timber frame with vertical and horizontal elements, braced with diagonal elements, known as Saint Andrew's crosses, with masonry infill. This paper describes an experimental campaign to assess the in-plane cyclic behaviour of those so called "frontal" walls. A total series of 4 tests were conducted in 4 real size walls. Two models consist of the simple timber frames without masonry infill, and the other two specimens have identical timber frames but present masonry infill. Experimental characterization of the in-plane behaviour was carried out by static cyclic shear testing with controlled displacements. The loading protocol used was the CUREE for ordinary ground motions. The hysteretic behaviour main parameters of such walls subjected to cyclic loading were computed namely the initial stiffness, ductility and energy dissipation capacity.

• Steel and Composite Structures
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• v.28 no.2
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• pp.123-138
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• 2018

Eccentrically braced frames (EBF) represent an optimal structural solution for seismic prone areas, being able to provide high dissipative capacity and good elastic stiffness, to withstand strong seismic events without significant loss of bearing capacity and to avoid damage to non-structural elements in case of low and moderate earthquakes. The accurate knowledge of the cyclic behaviour of the dissipative links, characterizing the whole performance of EBFs, is required to optimize the structural properties and to refine the design techniques adopted for multi-storey buildings' analysis. Reliable numerical models for the links, at the same time requiring a limited computational effort, are then needed. The present work shows the results of a wide experimental test campaign executed on real-scale one storey/one bay frames with horizontal and vertical links, together with the elaboration of a simple semi-analytical model for the quick representation of the cyclic behaviour of shear links.