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CONTENTS
Volume 7, Number 4, April 2011
 

Abstract
Cast iron pipe has been used as a water distribution technology in North America since the early nineteenth century. The first cast iron pipes were made of grey cast iron which was succeeded by ductile iron as a pipe material in the 1940s. These different iron alloys have significantly different microstructures which give rise to distinct mechanical properties. Insight into the non destructive structural condition assessment of aging pipes can be advantageous in developing mitigation strategies for pipe failures. This paper examines the relationship between the small-strain and large-strain properties of exhumed cast iron water pipes. Nondestructive and destructive testing programs were performed on eight pipes varying in age from 40 to 130 years. The experimental program included microstructure evaluation and ultrasonic, tensile, and flexural testing. New applications of frequency domain analysis techniques including Fourier and wavelet transforms of ultrasonic pulse velocity measurements are presented. A low correlation between wave propagation and large-strain measurements was observed. However, the wave velocities were consistently different between ductile and grey cast iron pipes (14% to 18% difference); the ductile iron pipes showed the smaller variation in wave velocities. Thus, the variation of elastic properties for ductile iron was not enough to define a linear correlation because all the measurements were practically concentrated in single cluster of points. The cross-sectional areas of the specimens tested varied as a result of minor manufacturing defects and levels of corrosion. These variations affect the large strain testing results; but, surface defects have limited effect on wave velocities and may also contribute to the low correlations observed. Lamb waves are typically not considered in the evaluation of ultrasonic pulse velocity. However, Lamb waves were found to contribute significantly to the frequency content of the ultrasonic signals possibly resulting in the poor correlations observed. Therefore, correlations between wave velocities and large strain properties obtained using specimens manufactured in the laboratory must be used with caution in the condition assessment of aged water pipes especially for grey cast iron pipes.

Key Words
cast iron pipes; ductile iron pipes; ultrasonic; wave velocity; non-destructive evaluation.

Address
Paul Groves, Giovanni Cascante, and Mark Knight : Department of Civil and Environmental Engineering, University of Waterloo, Waterloo,ON, Canada N2L 3G1

Abstract
A reliability-based slope stability assessment method considering fluctuations in the monitored matric suction was proposed for real-time identification of slope risk. The assessment model was based on the limit equilibrium model for infinite slope failure. The first-order reliability method (FORM) was adopted to calculate the probability of slope failure, and results of the model were compared with Monte-Carlo Simulation (MCS) results to validate the accuracy and efficiency of the model. The analysis shows that a model based on Advanced First-Order Reliability Method (AFORM) generates results that are in relatively good agreement with those of the MCS, using a relatively small number of function calls. The contribution of random variables to the slope reliability index was also examined using sensitivity analysis. The results of sensitivity analysis indicate that the effective cohesion c\' is a significant variable at low values of mean matric suction, whereasmatric suction (ua-uw) is the most influential factor at high mean suction values. Finally, the reliability indices of an unsaturated model soil slope, which was monitored by a wireless matric suction measurement system, were illustrated as 2D images using the suggested probabilistic model.

Key Words
unsaturated soil slope; reliability analysis; real-time monitoring.

Address
Jung Chan Choi and Seung Rae Lee : Department of Civil and Environmental Engineering, KAIST, Daejeon 305-701, Republic of Korea
Yunki Kim : Civil ENG Team, Samsung C&T Corp. 137-857, Republic of Korea
Young Hoon Song : Hyundai Engineering & Construction Co., LTD. Gyeonggi-Do 446-716, Republic of Korea

Abstract
The behaviors of saturated soils such as compressibility and permeability are distinguished by preconsolidation stress. Preconsolidation stress becomes an important design parameter in geotechnical structures. The goal of this study is to introduce a new method for the evaluation of preconsolidation stress based on the shear wave velocity at small strain, using Busan, Incheon, and Gwangyang clays in Korea. Standard consolidation tests are conducted by using an oedometer cell equipped with bender elements. The preconsolidation stresses estimated by shear wave velocity are compared with those evaluated by the Casagrande, constrained modulus, work, and logarithmic methods. The preconsolidation stresses estimated by the shear wave velocity produce very similar values to those evaluated by the Onitsuka method (one of the logarithmic methods), which yields an almost real preconsolidation stress. This study shows that the shear wave velocity method provides a reliable method for evaluating preconsolidation stress and can be used as a complementary method.

Key Words
compressibility; consolidation; fabric change; preconsolidation stress; shear wave velocity; void ratio.

Address
Hyung-Koo Yoon, Changho Lee and Jong-Sub Lee : School of Civil, Environmental and Architectural Engineering, Korea University, Seoul 136-701, Korea
Hyun-Ki Kim : School of Civil and Environmental Engineering, Kookmin University, Seoul 136-702, Korea

Abstract
In marine clay deposits, naturally formed or artificially reclaimed, the evaluation and monitoring of the consolidation process has been a critical issue in civil engineering practices due to the time frame required for completing the consolidation process, which range from several days to several years. While complementing the conventional iconographic method suggested by Casagrande and recently developed in-situ techniques that measure the shear wave, this study suggests an alternative experimental procedure that can be used to evaluate the consolidation state of marine clay deposits using the shear wave velocity. A laboratory consolidation testing apparatus was implemented with bimorph-type piezoelectric bender elements to determine the effective stress-shear wave velocity (

Key Words
bender element; consolidation state; effective stress; marine clay; shear wave velocity; under-consolidation.

Address
Ilhan Chang : Department of Civil and Environmental Engineering, KAIST, 291 Daehak-no,Yuseong-gu, Daejeon 305-701, Korea
Tae-Hyuk Kwon : Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley CA 94720, USA
Gye-Chun Cho : Department of Civil and Environmental Engineering, KAIST, 291 Daehak-no,Yuseong-gu, Daejeon 305-701, Korea

Abstract
A specially designed tendon, which is proposed by embedding an FBG sensor into the center king cable of a 7-wire strand tendon, was applied to monitor the prestress force and load transfer of ground anchor. A series of tensile tests and a model pullout test were performed to verify the feasibility of the proposed smart tendon as a measuring sensor of tension force and load transfer along the tendon. The smart tendon has proven to be very effective for monitoring prestress force and load transfer by measuring the strain change of the tendon at the free part and the fixed part of ground anchor, respectively. Two 11.5 m long proto-type ground anchors were made simply by replacing a tendon with the proposed smart tendon and prestress forces of each anchor were monitored during the loading-unloading step using both FBG sensor embedded in the smart tendon and the conventional load cell. By comparing the prestress forces measured by the smart tendon and load cell, it was found that the prestress force monitored from the FBG sensor located at the free part is comparable to that measured from the conventional load cell. Furthermore, the load transfer of prestressing force at the tendon-grout interface was clearly measured from the FBGs distributed along the fixed part. From these pullout tests, the proposed smart tendon is not only expected to be an alternative monitoring tool for measuring prestress force from the introducing stage to the long-term period for health monitoring of the ground anchor but also can be used to improve design practice through determining the economic fixed length by practically measuring the load transfer depth.

Key Words
ground anchor; prestressing force; load transfer; Fiber Bragg Grating (FBG); smart tendon; pullout test.

Address
Young-Sang Kim, Hyun-Jong sung, Hyun-Woo Kim and Jae-Min Kim :Department of Marine & Civil Engineering, Chonnam National University, Yeosu 550-749, Korea

Abstract
In this study, the measurements of the dielectric constants of soil at 900 MHz and 1 GHz were made to relate those properties to the moisture content of the soil. This study

Key Words
dielectric constant; electromagnetic; soil; open-ended probe; radar; landslide; moisture.

Address
Hong Chul Rhim : Department of Architectural Engineering, Yonsei University, Seoul, Korea


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