1,720,966 research outputs found
Numerical analysis of offshore monopile during repetitive lateral loading
No full textRenewed interest in the long-term pile foundations has been driven by the increase in offshore wind turbine installation to generate renewable energy. A monopile subjected to repetitive loads experiences an evolution of displacements, pile rotation, and stress redistribution along the embedded portion of the pile. However, it is not fully understood how the embedded pile interacts with the surrounding soil elements based on different pile geometries. This study investigates the long-term soil response around offshore monopiles using finite element method. The semi-empirical numerical approach is adopted to account for the fundamental features of volumetric strain (terminal void ratio) and shear strain (shakedown and ratcheting), the strain accumulation rate, and stress obliquity. The model is tested with different strain boundary conditions and stress obliquity by relaxing four model parameters. The parametric study includes pile diameter, embedded length, and moment arm distance from the surface. Numerical results indicate that different pile geometries produce a distinct evolution of lateral displacement and stress. In particular, the repetitive lateral load increases the global lateral load resistance. Further analysis provides insight into the propagation of the shear localization from the pile tip to the ground surface.
Theoretical Study on Geometries of Electrodes in Laboratory Electrical Resistivity Measurement
Full text linkElectrical resistivity tests have been widely conducted in multiple scales, from a few centimeters to kilometers. While electrode spacing is used to define field resistance, laboratory measurements in a limited space need to consider electrode geometry. However, there are no studies that theoretically explore the effects of the geometries of electrodes and container size on laboratory electrical resistivity measurements. This study formulates a theoretical electrical resistance for the geometry of cylindrical electrodes and the size of a non-conductive container with the method of image charges. As a complementary study, experimental tests were conducted to verify the derived equations. The discussion includes the concepts of the spherical equivalent electrodes and a simple design method for container size
Full-scale test of Direct-buried Cable in Sand under Repetitive Loading
No full textDirect-buried cable construction can minimize cumbersome processes, thereby decreasing construction time and cost. However, there is no regulation on burial depth that consider the long-term performance of backfilling soil for direct-buried cables. This study examines the mechanical response of direct-buried cables subjected to re-petitive loads. This experimental study uses a full-scale chamber to replicate field construction. The stress on the cable, vertical displacement on the surface, and shear wave velocity between loading plate and cable are continuously monitored during 10,000 repetitive loading cycles. A miniature electrical cone is used to indirectly quantify the initial relative compaction. Repetitive loading densifies the soil around the cable, increasing stress on the cable and accumulating vertical strain. The trends are more pronounced with lower initial relative compaction. The shear wave velocity increases during repetitive loading, suggesting a change in the earth pressure coefficient. Applied stress - vertical strain allows the estimation of resilient modulus. These observations will provide a better understanding of the mechanical response of backfilling soil. Additionally, the uniaxial compression test of the underground power cable made for direct burial is conducted to measure the displace-ment of the cable insulator under the field condition obtained from the full-scale test. Then mechanical stability of the cable is investigated based on the axial displacement of the cable insulator.
Effect of soil type on effective soil thermal conductivity for the full range of water saturation
No full textAccurate estimation of effective soil thermal conductivity is crucial for designing and managing geosystems such as underground power cables, thermally active geostructures, and nuclear waste repositories. Previous studies have examined the soil thermal response by varying soil properties and water saturation for specific soil types. However, the applicability of these methods in capturing the evolution of effective soil thermal conductivity across different soil types and fundamental soil properties is limited. This study investigates the effect of soil type and fundamental soil properties on effective soil thermal conductivity across the full range of water saturation. A predictive model is developed to describe the evolution of normalized thermal conductivity with saturation, incorporating two physically meaningful parameters that characterize the initial and intermediate thermal response with increasing water saturation. This model adequately fits the effective soil thermal conductivity data collected from the literature. Using an extensive dataset of various soil types, soils are classified into three major texture groups: coarse-textured, moderately coarse-to medium-textured, and moderately fine-to fine-textured soils. These groups exhibit distinct trends in thermal conductivity evolution with water saturation, as reflected in their model parameters. Further analysis explores the key soil properties that govern these model parameters, providing a comprehensive understanding of the mechanisms controlling thermal conductivity variation. As an engineering application, a practical reference is proposed to categorize soils based on key parameters such as the saturated and dry thermal conductivity, initial porosity, and average thermal conductivity of soil particles.
Sands subjected to repetitive vertical loading under zero lateral strain: accumulation models, terminal densities, and settlement
No full textGeosystems often experience numerous loading cycles. Plastic strain accumulation during repetitive mechanical loads can lead to shear shakedown or continued shear ratcheting; in all cases, volumetric strains diminish as the specimen evolves towards terminal density. Previously suggested models and new functions are identified to fit plastic strain accumulation data. All accumulation models are formulated to capture terminal density (volumetric strain) and either shakedown or ratcheting (shear strain). Repetitive vertical loading tests under zero lateral strain conditions are conducted using three different sands packed at initially low and high densities. Test results show that plastic strain accumulation for all sands and density conditions can be captured in the same dimensionless plot defined in terms of the initial relative density, terminal density, and ratio between the amplitude of the repetitive load and the initial static load. This observation allows us to advance a simple but robust procedure to estimate the maximum one-dimensional settlement that a foundation could experience if subjected to repetitive loads. © 2016, Canadian Science Publishing. All rights reserved.This research was conducted by the authors while at the Georgia Institute of Technology. Support for this research was provided by the Goizueta Foundation and the KAUST endowment
Dynamic Properties of Grouted Granitic Rocks
No full textGrouting is an empirical constructional technique aimed at improving poor ground
conditions prior to construction of underground structures through the injection of
cementitious, resinous or chemical grouts. For rock grouting, microcements are often
used as a grout material due to their higher strength gain and lower bleeding potential
compared to Type I ordinary Portland cement. The injected microcement grout flows
through the innate discontinuities present in rock masses and contribute significantly to
their mechanical behavior. The deformational characteristics of geological media are
affected by the subjected strain levels and state of stress and for jointed rocks, the
state of joints (roughness, filling material etc.) also have a significant effect. In this
study, the dynamic properties of microcement grouted granitic rocks were analyzed
using the rock mass dynamic test (RMDT) apparatus. Resonant column tests were
conducted on a regularly spaced, planar jointed granitic rock specimen before and after
grouting to analyze the effects of grouting on the strain-dependent shear modulus and
damping ratio
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
