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Large soil movements arising from the installation of jack-up spudcan foundations may induce detrimental effects on piles supporting adjacent permanent jacket platforms. Particularly, in a dense sand-over-clay profile, there is a risk of spudcan rapid penetration due to underlying clay bearing capacity failure, known as spudcan punch-through failure, which can cause further damage to piles in the proximity. This study investigates the foundation interaction between the spudcan and adjacent pile in a sand-overlying-clay soil profile by way of centrifuge modelling. Issues investigated include thickness of the upper sand layer with incidence of sand plug beneath the spudcan and spudcan–pile clearance. The experimental findings reveal that spudcan punch-through hazard and the magnitude of induced pile moments amplifies primarily due to the increase in the thickness of the upper sand. In addition, the magnitude of induced pile moment in a sand-over-clay profile is significantly higher than that in a single clay profile because of the post-peak bearing behaviour observed in stratified soil, yielding to a greater risk to pile integrity. Soil pressure profiles on the piles are also back-analysed. Two generalised induced soil pressure profiles are deduced, with the first profile representing the onset of spudcan punch-through and the second profile denoting the situation of post-punch-through failure.

Piles installed to increase bearing capacities of super structures in soft soil layers are vulnerable to horizontal loads such as seismic loads. This study aims to verify the stability of piles used for a pile supported slab track system using dynamic centrifuge test and numerical analysis. First of all, validation of the numerical analysis method was performed by comparing the seismic response from the two methods: dynamic centrifuge test and its numerical model. Verifications were also obtained for four different centrifuge test model setups. Numerical models were designed similar to the physical models on a prototype scale. The numerical method solves the dynamic problem by an explicit method in the time-integration stage. The acceleration response of the slab track and bending moment of the pile show good agreement between the two methods. Based on the verified numerical analysis model, the parametric studies for embankment thickness and soft ground stiffness were performed, in addition, the seismic stability of pile supported slab track was evaluated.

Gyeongju bentonite is a Ca-bentonite and a highly compacted buffer material primarily considered in Korea, as a part of an engineered barrier system (EBS) of high-level radioactive waste (HLW) repository. During the repository lifetime, the buffer material should guarantee the safe disposal of HLW against any external mechanical impact, including seismic activity. Therefore, the dynamic deformation properties of buffer material is crucial to validate its lifetime effectiveness and performance. Even though there are some researches to investigate the dynamic properties of the bentonite buffer, there has been no researches for the Korean bentonite buffer. For this reason, the paper aims to evaluate the dynamic properties at small-strain of Gyeongju bentonite and correlate the small-strain deformation properties with unconfined compressive strength using seismic and static laboratory tests. Three sets of compacted cylindrical bentonite specimens with varying dry densities (1.50 g/cm3 to 1.77 g/cm3) were produced using a cold isostatic pressing technique under three different pressing loads. Free-free resonant column (FFRC) tests and unconfined compressive (UC) tests were performed. The FFRC tests measured deformation properties at small strain, including unconstrained and constrained compression velocities, Young’s modulus (Emax), constrained modulus (Max), material damping ratio (Dmin), and Poisson’s ratio. The UC tests evaluated the compressive strength and secant modulus (E50) at large-strain. In this study, it was found that the deformation properties (Emax and Mmax) and unconfined compressive strength increase with the increase in a design rage of dry density. Poisson’s ratio measured at constrained boundary yields relatively constant value close to 0.4 for specimens at a range of dry density higher than 1.5 g/cm3. In addition, it was found that the elastic moduli have an almost linear relationship with the unconfined compressive strength. Finally, empirical equations between elastic moduli and unconfined compressive strength for Gyeongju compacted bentonite are proposed for a Koeran design guideline.

Undrained shear strength is a key parameter of clay and is popularly determined by penetrometers. Miniature penetrometers are preferred to estimate the undrained shear strength of clay for small-size model tests. In order to estimate undrained shear strength, an empirical factor should be established to correlate the tip resistance to the undrained shear strength. However, published data on miniature penetrometers are limited. This paper aims to evaluate empirical factors on miniature cone and T-bar penetrometers using a cylindrical chamber. Kaolin clay specimens were prepared in the chamber under five pre-consolidation pressures to control their undrained shear strength. Two miniature cones with diameters of 10 mm and 16 mm and a T-bar penetrometer with 10-mm diameter and 40-mm length were used to investigate penetration rate, boundary, and empirical factor. Unconsolidated-undrained triaxial tests and vane shear tests were carried out to measure undrained shear strength. Finally, empirical factors for the penetrometers were constructed to correlate tip resistance to undrained shear strength. The empirical factors established at 20 mm/s of a penetration rate for 10-mm-diameter cone, 16-mm-diameter cone and T-bar penetrometer are 18.33, 13.09 and 12.5, respectively.

This study investigates the soil-structure interaction of a piled Gravity Base Foundation (piled GBF) supporting an offshore wind turbine tower. The piled GBF is a gravity base foundation supported by five piles with one center and four outer piles. A series of three-dimensional finite element analyses were performed to investigate p-y characteristics in the piled GBF. The results were validated against centrifuge test data prior to undertaking a detailed parametric study, exploring the relevant range of parameters in terms of foundation type, vertical load due to the gravity base self-weight, loading height, undrained shear strength, and the pile bearing condition. Overall, the center pile of the piled GBF showed the highest ultimate soil reaction force, while the leading pile indicated the lowest value. Due to the rotation of mat and self-weight of GBF, significant shear failure was mobilized near the leading pile, which reduced the ultimate soil reaction force. This was also confirmed through the comparison studies with group pile (no mat), piled raft (low self-weight of mat) and rock-socketed piled GBF (no rotation of mat).

Korea has started to build wind farms in the Yellow Sea, with the seabed consisting of a thick silty sand deposit. It is therefore important to understand the behavior of potential foundati...

Bucket foundations have been increasingly used to support offshore wind turbines as alternatives to monopiles and can be classified into two types: monopod and tripod/jacket supported on multiple shallow foundations. Despite the recent research on the bearing capacity and stiffness of skirted foundations, knowledge regarding the monotonic and cyclic responses of multiple bucket foundation systems in saturated sand is scarce. In this study, the angular rotation of mono-bucket and tripod foundation systems in dense sand due to drained monotonic and cyclic loading was analyzed by performing a series of three-dimensional finite element (FE) analyses. The Hardening Soil Model with Small Strain Stiffness (HS small) and the UBC3D-PLM soil model were employed to analyze the moment response of offshore foundations subjected to wind and wave loading. The procedures were validated against a database of well-documented centrifuge tests. Calibration was carried out based on the monotonic and cyclic model tests, in-situ shear wave velocity measurements, and empirical relationships for shear moduli. Long-term deformations and the resulting decreasing trend in accumulated rotation, which is a unique feature of tripod suction caisson foundations (the so-called “self-healing’’ mechanism), uncertainties, and nonlinearities in centrifuge tests and numerical predictions involving different alternative calibration scenarios of the models are discussed. Based on the numerical results, a closed-form expression is proposed that enables the prediction of drained bearing capacity of multiple caissons under combined loading. This expression was validated for a range of embedment ratios.

Flexibility of underground structures relative to the surrounding medium, referred to as the flexibility ratio, is an important factor that influences their dynamic interaction. This study investigates the flexibility effect of a box-shaped subway tunnel, resting directly on bedrock, on the ground surface acceleration response using a numerical model verified against dynamic centrifuge test results. A comparison of the ground surface acceleration response for tunnel models with different flexibility ratios revealed that the tunnels with different flexibility ratios influence the acceleration response at the ground surface in different ways. Tunnels with lower flexibility ratios have higher acceleration responses at short periods, whereas tunnels with higher flexibility ratios have higher acceleration responses at longer periods. The effect of the flexibility ratio on ground surface acceleration is more prominent in the high range of frequencies. Furthermore, as the flexibility ratio of the tunnel system increases, the acceleration response moves away from the free field response and shifts towards the longer periods. Therefore, the flexibility ratio of the underground tunnels influences the peak ground acceleration (PGA) at the ground surface, and may need to be considered in the seismic zonation of urban areas.

The Philippines is a naturally water-rich archipelago capable of sustaining its ecological goods and providing services and needs of its people. Several waterbodies have been declared as natural wetlands in the country supporting the needs of community like water and food. In this study, 65 natural wetlands were considered including six sites that were identified as ‘Wetlands of International Importance’ such as Naujan Lake National Park, Agusan Marsh Wildlife Sanctuary, Olango Island Wildlife Sanctuary, Tubbataha Reefs Natural Park, Las Pinas-Paranaque Critical Habitat and Ecotourism Area and Puerto Princesa Subterranean River National Park. There are 22 wetland types presented in this research categorizing the Philippine wetlands. Philippine wetlands are now facing tremendous challenges such as land use conversion, abuse of resources, pollution coming from domestic, industrial and agricultural activities, and climate change. This paper provides an overview of Philippine wetlands in terms of their characteristics and components, impacts in the ecosystem, and the challenges they are dealing with. Moreover, the preservation measures that the government and private agencies implements to these wetlands were discussed and assessed. The enforcement of local and national laws concerning wetlands is found to be inadequate resulting in poor quality wetlands. The preservation and utilization of these wetlands can be maximized with a voluntary participation of whole Philippine community.

This study aims to investigate seismic response of bucket foundations for the support of offshore wind tower. The prototype design of the bucket foundation was scaled down with a scaling number of 1/240 to manufacture the model. An additional gravity base foundation (GBF) model was prepared and its diameter is same with the bucket. The dynamic centrifuge tests for both models installed in sandy soil were carried out at 60 G resulting in the 1/4 scale prototype. Two real earthquake motions, Kobe and El Centro earthquakes were applied to the models. The earthquake motion scaled with peak accelerations from 0.02 G to 0.2 G was excited at the base of the soil container. The acceleration at the platform level (i.e. the connection of the tower and foundation) for the bucket foundation is lower than that of the GBF. The types of earthquake affected the responses at the platform. The displacement at the platform level of the bucket was also lower than the GBF. The contact pressure was at the bottom invert of both models and skirt surface of the bucket. The contact pressure at the bottom invert of the GBF significantly increases with increasing excitation while that of the bucket is negligible. The contact pressure at the skirt surface of the bucket significantly increases due to seismic loading.

This study investigates the performance of group suction anchors installed in silty sand and subjected to horizontal pullout loading. The group anchors in this study consist of two or three unit suction anchors rigidly connected to each other in parallel array to improve the pullout resistance. The performance of these group anchors was studied extensively using centrifuge model tests and numerical simulations. The pullout resistances of the group anchors were compared with that of a single anchor. To quantify the improvement, the efficiency of a group anchor was defined as the ratio of the pullout resistance of a group anchor to that of a single anchor multiplied by the number of the unit anchors, and the improvements are discussed. Additional parametric studies were performed using numerical models to study the effect of the physical conditions of the group anchor. The parameters include the L / D ratio of a unit suction anchor, and the spacing between unit suction anchors.

This study aims to investigate a hybrid gravity base foundation to support offshore wind tower. A new hybrid gravity base foundation considered in this study has five component piles, referred to as ‘piled gravity base foundation’. The three-dimensional finite element analyses were carried out for the piled gravity base foundation subjected to a combined load with a lateral load and overturning moment. The parametric analyses were undertaken varying the loading height and direction, the rigidity of the piled gravity base foundation, the field soil layers, and the clay strength. Overall, the response of the piled gravity base foundation was significantly influenced by the interaction between the cone base piles and the surrounding soil. The increased strength of the soil led to a significant reduction of the pile and gravity base foundation responses, in terms of the bending moments, axial forces, lateral displacements, and rotations.

Centrifuge tests were performed to investigate the effect of the relative density of the sandy layer on the lateral response of 6-m-diameter offshore monopiles. The end tips of the monopiles are socketed into rock-bearing layers. For the simulation of the rock-socketed monopiles in sands with different relative densities (dense and medium dense sand layers), centrifuge tests at an acceleration of 60 g were conducted using well-instrumented model monopiles under significant lateral loads and bending moments. Based on the centrifuge test results, the p–y relationship and the initial stiffness (initial gradient of a p–y curve) changed with an increasing depth for both dense and medium dense sand layers. As a result, the newly developed p–y curves for rock-socketed large-diameter monopiles in this study were quite different from the existing API (American Petroleum Institute) p–y curves, which were developed based on relatively small-diameter driven piles. It was found that the initial stiffness for the medium dense sand layer was significantly lower than that for the dense sand layer at a shallow depth; however, the ratio of initial stiffness of the medium dense sand layer to that of the dense sand layer decreases significantly as the depth increases and approaches the stiff rock-bearing layer.

To investigate the behavior of dredged-sea-sand fill compacted inside tide embankments with a damaged geosynthetic mat, centrifugal model tests and numerical simulation were conducted, both considering variations in sea level. The results from the three centrifugal model tests demonstrate that the subsidence of the dredged-sea-sand fill inside tide embankments with a damaged geosynthetic mat was strongly affected by the loss of dredged-sea-sand into the filter layers with large particles and a decrease in the bearing capacity of the filter layers with small particles. In addition, a comparison of the test and simulation results confirms that the loss of sand into the filter layer and the subsidence of the dredged-sea-sand fill were well reproduced by the numerical simulation.

Verification of nonlinear dynamic numerical analysis was performed using dynamic centrifuge test results for pile supported track under seismic loadings. The numerical analysis models were constructed in the same dimensions with the centrifuge tests in prototype scale. Verification was conducted by comparing the measurement data obtained from the centrifuge test and numerical analysis output directly. Total 4 different numerical models corresponding centrifuge test are verified with changing thickness of soft soil layer, embankment, input motion intensity and history. Numerical analyses were conducted in time domain by an explicit time integration method. Dynamic hysteretic damping model was adopted for nonlinearity behavior of soil under seismic excitation. The piles were modeled with shell element that can show interface behavior with surrounding soils. The other structural members are modeled in a hexahedron solid element that has an interface. Seismic responses of the pile supported track were quite similar for both numerical analysis and centrifuge test.

Penetration resistance of bucket foundations with skirt wall in the silty sand of the western coast of Korea was analyzed by centrifuge modelling. The penetration resistance is induced when the bucket foundations are jacked into the soil without suction, and is directly related to the self-weight penetration depth. The procedure by Houlsby and Byrne (2005), which takes into account the effect of stress increase by frictional resistance of skirt wall, was utilized to generate the penetration resistance similar to the experimental results. This paper describes the methods by which major parameters such as lateral earth pressure coefficient and friction angle between the skirt wall and the soil are evaluated. The effect of changes in these parameters on the predictions is analyzed. Also, observed soil behaviour during jacking penetration is investigated.

In centrifuge modeling, it is important to evaluate the in-flight strength and stiffness parameters of the soil model to understand soil behavior. Both the shear-wave velocity (Vs) and cone...

Current floating structures require more reliable and higher anchoring capacities because of their increased size. A suction anchor is one of the most popular anchors for a floating system. In this study, the behavior of a suction anchor installed in cohesionless soil was investigated when the anchor was subjected to mainly a horizontal load. Three-dimensional finite element numerical analyses were carried out using ABAQUS, and three centrifuge tests were performed to calibrate the numerical analyses. A parametric study with different dimensions and loading points for the suction anchor was conducted. The horizontal capacity of the suction anchor was estimated, and the soil reaction distribution was analyzed when the load was applied at the optimal point. Based on the results, an analytical equation for calculating the horizontal capacity of a suction anchor was proposed that can be easily adopted for design.

A series of dynamic centrifuge tests was designed and conducted to study the seismic behavior of buried box tunnels. In this study, numerical simulations of the same tests were also performed using a finite difference software. The simulation results were in very good agreement with the results observed in the centrifuge tests. Subsequently, verified numerical model was used to perform parametric studies on the effect of an underground box tunnel on the ground surface acceleration. The results of parametric studies revealed that an underground tunnel could have either positive or negative effect on the ground surface acceleration. Presence of the tunnel amplifies long periods and deamplifies short periods of the motion. Therefore, it is concluded that the effect of an underground structure on the acceleration at the ground surface may be significant and hence, should be taken into account for seismic zonation of urban areas.

Understanding the soil–structure interaction (SSI) mechanism is crucial in the seismic design of nuclear power plant (NPP) containment systems. Although the numerical analysis method is generally used in seismic design, there is a need for experimental verification for the reliable estimation of SSI behavior. In this study a dynamic centrifuge test was performed to simulate the SSI behavior of a Hualien large-scale seismic test (LSST) during the Chi-Chi earthquake. To simulate the soil profile and dynamic soil properties of the Hualien site, a series of resonant column (RC) tests was performed to determine the model soil preparation conditions, such as the compaction density and the ratio of soil–gravel contents. The variations in the shear wave velocity (VS) profiles of the sand, gravel, and backfill layers in the model were estimated using the RC test results. During the centrifuge test, the VS profiles of the model were evaluated using in-flight bender element tests and compared with the in-situ VS profile at Hualien. The containment building model was modeled using aluminum and the proper scaling laws. A series of dynamic centrifuge tests was performed with a 1/50 scale model using the base motion recorded during the Chi-Chi-earthquake. In the soil layer and foundation level, the centrifuge test results were similar to the LSST data in both the time and frequency domains, but there were differences in the structure owing to the complex structural response as well as the material damping difference between the concrete in the prototype and aluminum in the model. In addition, as the input base motion amplitude was increased to a maximum value of 0.4g (prototype scale), the responses of the soil and containment model were measured. This study shows the potential of utilizing dynamic centrifuge tests as an experimental modeling tool for site specific SSI analyses of soil–foundation–NPP containment system.

The importance of levee stability is increasingly being recognized due to critical failures of river embankments and levees worldwide. On the basis of centrifuge tests and numerical analysis, this study presents seepage characteristics of embankments with buttressed slopes on low permeable, thick clay foundations. Two models of embankments having reinforcement placed on opposite slopes and constructed on a low permeable foundation were designed for centrifuge tests. Seepage centrifuge tests were performed at a high water level and beyond a high water level. Seepage characteristics of the embankment and foundation were analyzed by means of embedded pore water transducers. Moreover, numerical analysis results under various conditions simulated by SEEP/W were compared with the test results. Safety factors simulated by SLOPE/W were also compared with both models under the same water levels. The results show that the low permeable foundation above groundwater level presented a high degree of saturation before submerging, and the river-side buttressed slope embankment is safer than the land-side buttressed slope embankment. The conditions of the foundation and the reinforcement direction of the embankment should be considered when the seepage behavior and stability of an embankment are determined.

Many old levees along major rivers in South Korea have been reinforced by enlargement construction. Conventionally, the design settlement is simply estimated without considering variations in the material properties of the foundation layer underneath existing and enlarged embankments. A case study on an actual enlarged embankment located near Buyeo along the Kum River was performed using centrifuge tests. First, construction of the existing part on a soft foundation layer of kaolin clay was simulated. Second, enlargement of the existing embankment was simulated. The deformation pattern and differential settlement were then observed. After the enlargement simulation, block samples were extracted from the foundation layer for consolidation tests. The deformation pattern of the embankment was analyzed using GeoPIV. Clear differential settlement occurred and caused a tension crack in the enlarged embankment simulation test. The conventional method estimated a design settlement that was different from the measured settlement, and the differential settlement between foundations under the existing and enlarged embankments could not be estimated. Material properties from the consolidation tests differed depending on the location, and the foundation settlement differed according to the acquiring method. Based on these findings, design settlement should be estimated by considering the differential conditions of an actual field.

For circular rigid footings with a rough base on sand, combined vertical - horizontal loading capacity was studied by three-dimensional numerical modelling. A numerical model was implemented to simulate the swipe loading and the probe loading methods and an interpretation procedure was devised in order to eliminate the numerical error from the restricted mesh density. Using the Mohr-Coulomb plasticity model, the effect of friction angle was studied under the associated flow-rule condition. The swipe loading method, which is efficient in that the interaction diagram can be drawn with smaller number of analyses, was confirmed to give similar results with the probe loading method, which follows closely the load-paths applied to real structures. For circular footings with a rough base, the interaction diagram for combined vertical (V) - horizontal (H) loading and the inclination factor were barely affected by the friction angle. It was found that the inclination factors for strip and rectangular footings are applicable to circular footings. For high H/V ratios, the results by numerical modelling of this study were smaller than the results of previous studies. Discussions are made on the factors affecting the numerical results and the areas for further researches.

This study attempts to propose dynamic centrifuge model tests as a method of seismic risk assessment in order to discover how stone architectural heritages with masonry structures have endured seismic load, and whether there is any possibility of future earthquake damage. Dynamic centrifuge tests have been conducted for one fifteenth scale models of Seok-ga-tap and the five-storey stone pagoda of Jeongnimsa temple site, which are Korean representative stone pagodas. In order to make input motions of the earthquake simulator, site investigation and site-specific response analysis have been performed. The models of two stone pagodas, which have the same number of pieces with the real structures, have been produced and the dynamic centrifuge tests have been conducted for the model pagodas. Accelerometers were attached at different heights of the pagoda. The measured acceleration records and frequency responses were analysed during dynamic centrifuge test. Two real earthquake records, Hachinohe and Ofunato earthquakes and a sweeping signal with ranged frequency were utilised for input motions of dynamic centrifuge tests to evaluate the behaviour of the stone pagodas. For Seok-ga-tap models, it was observed that acceleration tends to be amplified with height. The third floor body shows at most 2.5 amplification of acceleration in comparison to the surface ground. The amplification was at a frequency of 3.83 Hz and it was considered as the natural frequency of the pagoda. For the five-storey stone pagoda, the seismic wave energy significantly reduced while it passed the first body floor, and then the peak acceleration was gradually amplified upwards. It was found that the pagodas did not collapse when the peak acceleration of ground surface was raised to 0.4 g. Given that the maximum design seismic acceleration specified in Korean seismic design guide is 0.22 g and the amplification ratio of peak acceleration in the supporting ground of the pagodas ranges from 1.45 to 1.74, it can be shown that the two pagodas are stable against 2400-year return period earthquake level, and have excellent seismic performance.

In the design procedure for a retaining wall, the pseudo-static method has been widely used and dynamic earth pressure is calculated by the Mononobe–Okabe method, which is an extension of Coulomb’s earth pressure theory computed by force equilibrium. However, there is no clear empirical basis for treating the seismic force as a static force, and recent experimental research has shown that the Mononobe–Okabe method is quite conservative, and there exists a discrepancy between the assumed conditions and real seismic behavior during an earthquake. Two dynamic centrifuge tests were designed and conducted to reexamine the Mononobe–Okabe method and to evaluate the seismic lateral earth pressure on an inverted T-shape flexible retaining wall with a dry medium sand backfill. Results from two sets of dynamic centrifuge experiments show that inertial force has a significant impact on the seismic behavior on the flexible retaining wall. The dynamic earth pressure at the time of maximum moment during the earthquake was not synchronized and almost zero. The relationship between the back-calculated dynamic earth pressure coefficient at the time of maximum dynamic wall moment and the peak ground acceleration obtained from the wall base peak ground acceleration indicates that the seismic earth pressure on flexible cantilever retaining walls can be neglected at accelerations below 0.4 g. These results suggest that a wall designed with a static factor of safety should be able to resist seismic loads up to 0.3–0.4 g.

The geomechanical and thermal responses of sediments can be significantly affected by the dissociation of gas hydrates via various emergent phenomena such as fluid volume expansion, free gas generation, gas migration, and sediment softening. This study explores the geomechanical and thermal responses of hydrate-bearing sediments subjected to thermal stimulation, using physical modeling with a geotechnical centrifuge that enables the simulation of near-seafloor sediment conditions. A water-saturated and CO2 hydrate-bearing sand column was prepared in a large cylindrical pressure vessel, and a linear stress gradient for a near-seafloor condition was created by increasing centrifugal acceleration. The hydrate-bearing sand column was subjected to thermal stimulation, and changes in temperature, pressure, compressional wave velocity (VP), shear wave velocity (VS), and electrical resistance were monitored at various locations across the column. It was found that VP and electrical resistance were good indicators...

Sandy gravel materials have recently been utilized in place of crushed rock materials as the main rockfill materials in Concrete Faced Rockfill Dams (CRFD) to address geological and environmental problems. In this paper, an experimental scheme for centrifuge modeling was developed to simulate a Concrete Faced Gravel-fill Dam (CFGD). The dam considered in this study was designed to implement a drainage zone of high permeability in the main gravel-fill zone to enhance safety against accidental water infiltration into the dam. Two centrifuge tests were performed and compared to investigate the performance of the drainage zone. The first test was done with the drainage zone and the second without the drainage zone. In the centrifuge tests, water infiltration was simulated by raising the water table over pre-implemented cracks on the model face slab. The infiltration behaviors were monitored by pore water pressure transducers. The centrifuge tests showed that the drainage zone of the CFGD effectively drains infiltrating water out of the dam body in a short time. Numerical modeling was also performed to help understand the process of seepage through cracks.

This study investigates the kinematic behavior of a clay-mandrel-anchor system during the driving-retrieval process and its influence on the installation of prefabricated vertical drains and clay disturbance. In addition, a new anchor plate with an asymmetric shape is proposed as an alternative for improved anchoring performance and clay disturbance mitigation. To investigate the behavior of the clay-mandrel-anchor system, two-dimensional centrifuge model tests were developed and successfully performed to visualize anchoring kinematics and deformation of the clay layer. The tests demonstrated that the asymmetric anchor plate effectively provides an anchoring mechanism and reduces the degree of disturbance. The conventional anchor has potential risk of delayed anchoring and thus unsuccessful installation. While the amount and extent of clay deformation are obviously affected by the protruding length of the anchor plates into the clay, the protrusion length has less influence on the range of the sme...

This paper describes some details of a self-balanced earthquake simulator on the centrifuge in KAIST and results of a series of proof tests for verifying its dynamic performance and excitation capacity. The main feature of the earthquake simulator is the dynamic self-balancing technique adopted to eliminate a large portion of the undesired reaction forces and vibrations transmitted to the centrifuge main body. This feature is achieved by embarking counter-weight platform and two back-to-back hydraulic bearings. The maximum base shaking acceleration of the earthquake simulator is 20 g in horizontal direction under 40 g of centrifuge acceleration with a maximum payload of 700 kg, corresponding to 0.5 g of horizontal shaking acceleration in the prototype scale. The loading frequency ranges from 40 Hz to 200 Hz (300 Hz) for sinusoidal (real earthquake) inputs. The dimension of slip table is 670 mm × 670 m in length and width. The proof test results show that the earthquake simulator can reproduce mono-frequency sinusoidal inputs in a wide band of frequencies as well as multi-frequency real earthquake inputs at the bottom of soil models with satisfactory fidelity, and the dynamic self-balancing contributes to the safety of the centrifuge structure.

Mononobe-Okabe (M-O) theory is widely used for evaluating seismic earth pressure of retaining wall. It was originally developed for gravity walls, which have rigid behavior, retaining cohesionless backfill materials. However, it is used for cantilever retaining wall on the various foundation conditions. Considering only inertial force of the soil wedge as a dynamic force in the M-O method, inertial force of the wall does not take into account the effect on the dynamic earth pressure. This paper presents the theoretical background for the calculation of the dynamic earth pressure of retaining wall during earthquakes, and the current research trends are organized. Besides, the discrepancies between real seismic behavior and M-O method for inverted T-shape retaining wall with 5.4m height subjected to earthquake motions were evaluated using dynamic centrifuge test. From previous studies, it was found that application point, distribution of dynamic earth pressure and M-O method are needed to be re-examined. Test results show that real behavior of retaining wall during an earthquake has a different phase between dynamic earth pressure and inertial force of retaining wall. Moreover, when bending moments of retaining wall reach maximum values, the measured earth pressures are lower than static earth pressures and it is considered due to inertial effects of retaining wall.

In order to evaluate the bearing capacity behaviour of a monopod suction bucket foundation for an offshore wind tower at the western sea of Korea, a centrifuge load test and numerical analyses were performed. The monopod bucket foundation was designed to be installed in a silty sand layer. The model soil was prepared to simulate a target site by using soil samples having similar properties and controlling relative density. In-flight miniature cone penetration test and bender element array were used to confirm that the model soil had represented the target site conditions. The load - rotation curve of the centrifuge load test was analysed. A series of numerical analyses were performed to validate the experimental conditions. Self-weight of the model, distance to the boundary and elastic modulus of the soil layer were varied to study their effects on the load - rotation curves.

The standard CPT(Cone Penetration Test), which can be easily performed to investigate in-situ soil engineering properties, has been widely used. CPT are also widely being utilized in centrifuge model tests. In this study, a miniature cone with 10mm diameter was developed and its applicability in the centrifuge was evaluated. The developed miniature cone was equipped with a four degree-of-freedom in-flight robot. A series of cone penetration tests was performed under four centrifuge acceleration levels. As results, the cone resistances measured at the same confining stress within shallow penetration depth were affected by the centrifugal accelerations. The critical depth was proportional to the cone diameter and relative density. Cone resistances results below the critical depth and soil parameters obtained from the laboratory tests were compared with those by previously proposed empirical relations.

In this study, the failure behavior of a levee under overflow conditions was investigated by conducting centrifuge tests on a small scale model for the Janghyun levee in Kangrung, Kangwon-do, and based on the test results a levee protection method using waterproof mat was proposed. The model levees were constructed by scaling down the prototype levee to 1:50, where LVDT and pore-pressure sensors were installed to monitor the behavior of the levees during overflow. Overflow tests were carried out in three different conditions depending on where the waterproof mat was installed; 1) no waterproof mat, 2) installed in upper slope and crest of the levee, 3) installed in the entire levee. The centrifuge test results indicated that the application of the waterproof mat reduced erosion and soil loss in the levee. Especially, it was found that under overflow, the levee breach could be avoided with the waterproof mat installed in upper slope and crest only, although soil loss occurred in downstream slope inevitably. It is expected that levee failures occurred frequently in rainy season may be effectively prevented by using waterproof mat if overflow of levee due to heavy rains is well predicted in advance.

A suction anchor is one of the most popular anchors for deepsea floating systems. An anchor used for catenary mooring is predominantly under a horizontal load. In this study, the behavior of a suction anchor installed in cohesionless soil was investigated when the anchor was mainly subjected to a horizontal load induced by a catenary line. In order to study the behavior of the suction anchor, 3D FEM analysis models were developed and analyzed. Depending on the location of the load (padeye), the ultimate horizontal load was monitored. The distributions of the reaction forces around the anchor induced by the seabed were analyzed using the circumferential stress to understand the behavior of the suction anchor under a horizontal load.

In dynamic centrifuge tests, appropriate boundary conditions are required in order to simulate the seismic semi-infinite soil layer responses within the confines of a finite size model container. An ESB (equivalent shear beam) model container first designed at the University of Cambridge was built with a stack of light-weight aluminum frames separated by rubber to experimentally achieve this goal. In this paper, a significant number of dynamic centrifuge tests and the corresponding seismic response analyses were performed to evaluate the dynamic performance of a newly constructed ESB model container and to shed light on the range of testable soil conditions. In the set of conducted tests, it appears that the end walls of the ESB model container behave in accordance with the dynamic response of the soil deposit, despite a difference in the natural period depending on the relative density of the sand deposit. This is attributed to the differences in mass and stiffness of the end walls compared to those of the contained soil model. For partially filled model container, significant differences in seismic responses are observed in the end walls and in the soil deposit due to seismic interaction caused by the upper unfilled frames of the container. These findings suggest that dynamic model tests using this ESB model container should be conducted with the container completely filled. In addition, on the basis of a comparison with the seismic soil behavior inside a rigid-walled model container, it is clear that the ESB model container can provide a more representative lateral boundary configuration for dynamic site response studies.