Bearing capacity analysis of open-ended piles considering the degree of soil plugging

Jeong, S.,Ko, J.,Won, J.,Lee, K. Japanese Society of Soil Mechanics and Foundation 2015 Soils and foundations Vol.55 No.5

This paper presents a new design approach for predicting the degree of soil plugging and the inner skin friction of axial-loaded open-ended piles. The main objective of this study was to propose the SPT-based design method considering the plugging effect, since the SPT test is commonly used to identify the subsoil condition in sandy soils. The plugging effect for open-ended piles was quantified using field plugging measurements and the results of three full-scale field pile load tests. Based on the plugging measurements, the relationship of the plug length ratio (PLR) with the soil properties, pile geometry and pile driving condition was established. Additionally, a linear relationship between the PLR and incremental filling ratio (IFR) was proposed. Full-scale tests were performed on three instrumented piles with different diameters (508.0, 711.2 and 914.4mm). An instrumented double-walled pile system was used to measure the outer and inner skin friction along the pile shaft. Based on the results of the full-scale field pile load tests, the inner skin friction of the open-ended piles was proposed as a function of the IFR and pile diameter. The predicted values were consistent with the measured values, such as the IFR and inner skin friction. The proposed method can predict the degree of soil plugging and the inner skin friction of open-ended piles and be selected as convenient option in engineering field.

Load-carrying behavior of tranmission-tower connected foundations subjected to different load directions

Kyung, D.,Lee, J. Japanese Society of Soil Mechanics and Foundation 2015 Soils and foundations Vol.55 No.3

Connected foundations comprise an effective option for improving the mechanical performance of transmission tower foundations. In this study, the load-carrying behavior of connected foundations for transmission tower structures was investigated focusing on the effect of the load direction based on the field experimental testing program. Improved performances of connected foundations were observed for load directions of both θ=0<SUP>o</SUP> and 45<SUP>o</SUP> considered in this study. The downward settlements at the compressive side for θ=45<SUP>o</SUP> were larger than those for θ=0<SUP>o</SUP>, while the upward displacements were similar. For both vertical and lateral displacements, the use of connected foundations was more effective for θ=45<SUP>o</SUP>, and the effectiveness became more pronounced as the connection-beam stiffness increased. However, the lateral load-carrying capacities for θ=0<SUP>o</SUP> and 45<SUP>o</SUP> were not significantly different for all connection-beam conditions. From the prototype-scaled model load tests, it was confirmed that the use of connected foundations for transmission tower structures is similarly effective for different load directions. Based on the test results, it was suggested that a unified design methodology is applicable for the stability analysis of transmission tower structures subjected to different load directions.

Effective installation of micropiles to enhance bearing capacity of micropiled raft

Hwang, T.H.,Kim, K.H.,Shin, J.H. Japanese Society of Soil Mechanics and Foundation 2017 Soils and foundations Vol.57 No.1

<P>While micropiles are used in many geotechnical projects, as ground reinforcement rather than as structural elements, field engineers have reported that the bearing capacity of micropiled rafts greatly exceeds the range of common ground reinforcement. This is known to be due to the confining effects of micropiles from the interaction between the ground and the micropiles, which extends the failure area of the ground significantly. Utilizing micropiles as ground reinforcement can excessively underestimate the structural contribution of the footing in a micropiled-raft system to the bearing capacity. This study investigates the support characteristics of a micropiled raft through model tests and a numerical analysis. The support behavior of the micropiled raft is evaluated for various conditions, such as soil type, pile length, and installation angle. It is found that the micropiles modify the failure behavior of the ground considerably, and that the bearing resistance can be enhanced by considering the appropriate failure mode, installation angle, and pile length. (C) 2017 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.</P>

Probabilistic analysis of consolidation that considers spatial variability using the stochastic response surface method

Bong, T.,Son, Y.,Noh, S.,Park, J. Japanese Society of Soil Mechanics and Foundation 2014 Soils and foundations Vol.54 No.5

To obtain more accurate and reasonable results in the analyses of soil consolidation, the spatial variability of the soil properties should be considered. In this study, we analyzed the consolidation by vertical drains for soil improvement considering the spatial variability of the coefficients of consolidation. The coefficients for the variation in the vertical and horizontal coefficients of consolidation in Yeonjongdo, South Korea were evaluated, and the probability density function (PDF) was assumed by the Anderson-Darling goodness-of-fit test. Standard Gaussian random fields were generated based on a Karhunen-Loeve expansion, and then transformed using Hermite polynomials in the random field with the log-Gaussian PDF of the coefficient of consolidation. The average degree of consolidation was subsequently calculated using the finite difference method coupled with log-Gaussian random fields. In addition, the stochastic response surface method (SRSM) was applied for the efficient probabilistic uncertainty propagation. A sensitivity analysis was performed for the input parameters of the random field, and the spatial variability was considered using random variables from the Karhunen-Loeve expansion as the input data for the SRSM. The results indicated that when considering the spatial variability of soil properties, the probability of failure for the target degree of consolidation was smaller when the correlation distance was taken into account than when it was not. Additionally, the probability of failure decreased when the correlation distance decreased. Compared with the Monte Carlo simulation (MCS) results, the SRSM analysis can achieve results of similar accuracy to those obtained using the MCS analysis with a sample size of 100,000 (numerical runs), and a third-order SRSM expansion with only 333 numerical runs is sufficient for obtaining the probability with errors less than 0.01.

Evaluation of disturbance function for geosynthetic-soil interface considering chemical reactions based on cyclic direct shear tests

Kwak, C.W.,Park, I.J.,Park, J.B. Japanese Society of Soil Mechanics and Foundation 2013 Soils and foundations Vol.53 No.5

Various geosynthetics for reinforcement, protection and encapsulation are widely applied to civil structures and waste landfill sites. The use of geosynthetics inevitably involves the coupled behaviors of different materials which include large displacement and strain-softening behaviors, etc. Current research indicates that the behavior of geosynthetic-soil systems depend on the shear strength of the interface governed by several intrinsic and environmental factors, such as moisture, normal stress, chemical conditions, and thermal components, etc. In this study, the effects of acidity and basicity from leachate and waste are intensively considered in order to build up the chemical reaction mechanism of the shear strength of the interface under cyclic loading based on an experimental inspection. The Multi-Purpose Interface Apparatus (M-PIA) has been newly manufactured, and cyclic direct shear tests for submerged geosynthetic-soil specimens under different chemical conditions have been performed. A Focused Ion Beam (FIB) analysis has also been performed to induce the reason for the variation in the disturbance function and to verify the hypothesis on the decay-proof ability of geosynthetics. Consequently, a new approach to reflect the chemical effect of geosynthetics has been applied by suggesting the use of new disturbance function parameters in the Disturbed State Concept. The basic schematic of the Disturbed State Concept (DSC) constitutive model is employed; then, new disturbance function parameters are proposed to describe the chemical degradation of the geosynthetic-soil interface under dynamic conditions. Furthermore, based on the FIB results, it is be deduced that the variation in the disturbance function mainly results from the different types of decay in the soil minerals.

Closure to ''Assessment of K₀ correlation to strength for granular materials'' by Junhwan Lee, Tae Sup Yun, Dongyeol Lee, and Junghwoon Lee

Lee, J.,Yun, T.S.,Lee, D. Japanese Society of Soil Mechanics and Foundation 2014 Soils and foundations Vol.54 No.2

Proposed point bearing load transfer function in jointed rock-socketed drilled shafts

Lee, J.,You, K.,Jeong, S.,Kim, J. Japanese Society of Soil Mechanics and Foundation 2013 Soils and foundations Vol.53 No.4

The point bearing behavior of rock-socketed drilled shafts under axial loading is investigated by numerical analysis and a load transfer approach (q-w). A numerical analysis using the distinct element method (DEM) is carried out to investigate the effects of pile diameter and the elastic modulus, discontinuity spacing and the inclination of rock mass on the point bearing behavior. The emphasis is quantifying the point bearing mechanism by taking rock discontinuity into consideration based on field loading tests performed on 39 instrumented piles. A new hyperbolic q-w function is proposed considering the point bearing resistance influence factors, including rock mass discontinuity. Through comparisons with other field data, the proposed q-w function represents a significant improvement in the prediction of the point bearing load transfer characteristics of jointed rock-socketed drilled shafts.