Taesik Kim

Anisotropy Evolution and Irrecoverable Deformation in Triaxial Stress Probes

This paper presents the results and analysis of experimental investigations of compressible Chicago clays with regard to the evolution of stiffness anisotropy. The experimental program was conducted on high-quality block samples obtained from the excavation for the Block 37 project in Chicago. The specimens were consolidated to in situ stresses via a recompression technique and then were subjected to directional stress probes. On-specimen LVDTs and an internal load cell with high accuracy were used for stress-strain response of the specimen. The stiffness and stiffness anisotropy ratio at very small strains were obtained synchronously from bender element tests during the consolidation and stress probes. The structural change as anisotropy evolves within a specimen is discussed. The results of the experimental program showed that compressible Chicago clay is an initially cross-anisotropic material under the in situ stresses. This anisotropy changes at the onset of irrecoverable deformation at stresses defined by previously established Y2 yield surfaces. DOI: 10.1061/(ASCE)GT.1943-5606.0000575.

Effects of Stress Path Rotation Angle on Small Strain Responses

AbstractThe results of experimental studies on the stress-strain behavior of Chicago glacial clays are presented and discussed. This paper describes small strain responses as a function of stress path rotation angle. Undrained compression and extension tests with three different preshear stress paths were conducted on high quality, hand-cut block samples obtained at two different depths from the excavation for the Block 37 project in Chicago. One preshear stress path was applied to investigate the stress-strain response representative of the in situ conditions via a recompression technique. The other two preshear stress paths were selected to isolate the effects of recent stress history such that the only difference between the two sets of paths was the direction of loading to a common effective stress condition. A period of drained creep at constant effective stress was imposed on all specimens prior to shearing to negate the possible effects of creep on the small strain responses. The results are discus...

Gmax of Reclaimed Ground on the Western Coast of Korea Using Various Field and Laboratory Measurements

The maximum shear modulus of soil is a principal parameter for the design of earth structures under static and dynamic loads. In this study, the statistical data of the maximum shear moduli of reclaimed ground in the Songdo area on the western coast of Korea were evaluated using various field and laboratory tests, including the standard penetration test (SPT), piezocone penetration test (CPTu), self-boring pressure meter test (SBPT), down-hole seismic test (DHT), seismic piezocone penetration test (SCPTu) and resonant column test (RCT). Soils were classified variously by using a conventional unified soil classification system and classification charts for CPTu data. For the soils containing mostly sand and silt, the soil classifications using the classification charts for CPTu data show good agreement with the unified soil classification. Based on the statistical analysis on various maximum shear moduli, new site-specific empirical correlations between the shear moduli and SPT and CPTu values were proposed. Predictions of the maximum shear moduli using the proposed correlations were compared with the data obtained from the DHT, which is comparatively exact in evaluating the maximum stiffness of soils. The good agreement confirmed that the proposed correlations reasonably predicted the maximum shear moduli of soils in western coastal area of Korea.

Elastic cross-anisotropy of chicago glacial clays from field and laboratory data

The initial anisotropy of natural clays can be characterized by the elastic shear moduli measured by wave propagation techniques both in situ and in the laboratory. This paper summarizes results of studies of the initial anisotropy of fresh water glacial clays from two sites in the Chicago area. Advanced cross-hole seismic tests which measure both horizontally propagating and vertically- and horizontallypolarized shear wave velocities and seismic cone penetration tests (sCPT) were performed in situ. Bender elements were used to measure propagation velocities on laboratory specimens cut from high quality block samples of soft to medium clays obtained from the excavation for the Ford Design Center project. These clays are lightly overconsolidated, supraglacial tills. Laboratory specimens of hard clay from the One Museum Park West site were obtained with a Pitcher barrel sampler; these clays are overconsolidated, basal tills. Both in situ and laboratory results for the soft to medium clays indicate that the magnitude of the shear moduli are the same in each polarized direction. These clays are slightly cross anisotropic. For the harder clays, the in situ shear moduli are larger than those measured in the laboratory, presumably as a result of the sample disturbance arising from Pitcher barrel sampling.

A Mobility-Aware Adaptive Duty Cycling Mechanism for Tracking Objects during Tunnel Excavation

Tunnel construction workers face many dangers while working under dark conditions, with difficult access and egress, and many potential hazards. To enhance safety at tunnel construction sites, low latency tracking of mobile objects (e.g., heavy-duty equipment) and construction workers is critical for managing the dangerous construction environment. Wireless Sensor Networks (WSNs) are the basis for a widely used technology for monitoring the environment because of their energy-efficiency and scalability. However, their use involves an inherent point-to-point delay caused by duty cycling mechanisms that can result in a significant rise in the delivery latency for tracking mobile objects. To overcome this issue, we proposed a mobility-aware adaptive duty cycling mechanism for the WSNs based on object mobility. For the evaluation, we tested this mechanism for mobile object tracking at a tunnel excavation site. The evaluation results showed that the proposed mechanism could track mobile objects with low latency while they were moving, and could reduce energy consumption by increasing sleep time while the objects were immobile.

Pattern Matching Based Sensor Identification Layer for an Android Platform

As sensor-related technologies have been developed, smartphones obtain more information from internal and external sensors. This interaction accelerates the development of applications in the Internet of Things environment. Due to many attributes that may vary the quality of the IoT system, sensor manufacturers provide their own data format and application even if there is a well-defined standard, such as ISO/IEEE 11073 for personal health devices. In this paper, we propose a client-server-based sensor adaptation layer for an Android platform to improve interoperability among nonstandard sensors. Interoperability is an important quality aspect for the IoT that may have a strong impact on the system especially when the sensors are coming from different sources. Here, the server compares profiles that have clues to identify the sensor device with a data packet stream based on a modified Boyer-Moore-Horspool algorithm. Our matching model considers features of the sensor data packet. To verify the operability, we have implemented a prototype of this proposed system. The evaluation results show that the start and end pattern of the data packet are more efficient when the length of the data packet is longer.

Vehicular datacenter modeling for cloud computing: Considering capacity and leave rate of vehicles

Abstract In this paper, we propose a vehicular datacenter model in a parking lot, where vehicles can be considered as a resource for cloud computing. One of the crucial issues facing the vehicular datacenter is failures caused by arrival and departure of dynamic resources. These failures result in performance degradation of the execution time because the task must be restarted. In order to reduce execution time and mitigate the effects of uncertainty, we propose a vehicular datacenter model that makes use of a checkpoint mechanism. We first characterize the dynamic vehicles in parking lots considering each vehicle’s capacity and leave rate. We derive the expected execution time to analyze the characteristics of vehicles and propose a resource selection strategy based on that time. We also derive the optimal number of checkpoints for each vehicle that maximizes the efficiency of the checkpoint. We demonstrate the results of our analysis through various evaluations.

Hydraulic Conductivity Variation of Coarse-Fine Soil Mixture upon Mixing Ratio

This paper presents the theoretical and experimental investigations of the hydraulic conductivity variation of the soil mixture that contains two distinct particle size distributions, coarse and fine soils. A new model for the hydraulic conductivity is introduced that focuses on the relationship between the coarse-fine soil mixing ratio and the hydraulic conductivity of the mixture. For the model verification, permeability tests were conducted. The glass beads and quality-controlled standard sand and soils obtained from fields were used for the specimen. The experiment results showed that the hydraulic conductivity of the soil mixture strongly depends on the mixing ratio. As the amount of the coarse soil contained in the fine soil increased, the hydraulic conductivity of the mixture decreased from that for the fine soil until the critical mixing ratio. This ratio is defined as the fine soils perfectly fill the voids between the coarse soils without remains. When the ratio is greater than the critical mixing ratio, the hydraulic conductivity is drastically increased with the mixing ratio up to that of the coarse soil. The comparison between the computed values and the test results shows that the introduced model successfully describes the measurements.

A Rendezvous Point Replacement Scheme for Efficient Drone-based Data Collection in Construction Sites

The present invention relates to a rendezvous point replacement method for efficient drone-based data collection at a construction site. According to an embodiment of the present invention, the rendezvous point replacement method for drone-based data collection comprises: a first step of allowing a drone to broadcast a first message to surroundings to inform a location of the drone; a second step of allowing a plurality of sensors to collect information related to surroundings and measure the remaining energy amount and a received signal strength indication (RSSI) for the first message in response to the first message; a third step of allowing the plurality of sensors to transmit a second message including the remaining energy amount and the RSSI value to the drone; a fourth step of allowing the drone to designate one rendezvous point of one of the plurality of sensors using the remaining energy amount and the RSSI value; a fifth step of allowing the drone to transmit a third message to the designated rendezvous point to inform a fact that the rendezvous point has been designated; a sixth step of allowing the rendezvous point to collect information sensed by a sensor other than the sensor of the rendezvous point among the plurality of sensors; and a seventh step of allowing the rendezvous point to transmit the collected information to the drone.

Numerical simulation of triaxial stress probes and recent stress-history effects of compressible Chicago glacial clays

AbstractNumerical simulations and calibration of hypoplasticity constitutive parameters for Chicago clays are presented based on laboratory tests conducted on high-quality block samples and field t...