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Abstract This paper presents a non-destructive method for detecting necking defects in bored piles using electromagnetic waves. Small-scale laboratory experiments are conducted with a defective model pile with diameter of 0.6 m and length of 1.0 m. Four artificial necking defects are introduced on three different sides of the model pile. One necking defect is introduced at the upper position on one side of the model pile, another one is introduced at the lower position on other side of the model pile, and the other two are introduced at both the upper and lower positions on the same side of the model pile. Electrical wires are installed alongside the main rebars of a reinforcement cage to configure a two-conductor transmission line. Electromagnetic waves are generated and detected using a time domain reflectometer. The experimental results indicate clear detection of the reflected electromagnetic waves at the necking defects and pile end. In addition, the calculated defect locations are similar to the actual locations. This study demonstrates that electromagnetic waves can be effective in detecting necking defects at various positions in bored piles. [ABSTRACT FROM AUTHOR]

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• Electromagnetic characteristics of five cement-slime mixtures using two TDR sensors are investigated. • Conventional probes struggle with the early conductivity of cement-slime mixtures. • Insulated wires detect signals across all slime ratios. • Dielectric constant drop indicates increased compressive strength. This study explores the electromagnetic characteristics of five cement–slime mixtures using two types of time domain reflectometry sensors. For 28 days of curing, compressive strength tests are conducted and electromagnetic signals are measured. The electromagnetic wave velocity and corresponding apparent permittivity are calculated, and the relationships between these properties and the compressive strengths of the mixtures are established. Results show that in the initial curing period, capturing the apparent permittivity using a conventional probe proves difficult due to the high electrical conductivity of the mixtures. In contrast, an insulated electrical wire can detect reflected signals across all slime ratios, but it exhibits less sensitivity to changes in the electromagnetic signal. The apparent permittivity decreases exponentially over the curing time, influenced by the hydration process. Strong correlations are found between the apparent permittivities derived from both sensors and between decreasing apparent permittivity and increasing compressive strength. [ABSTRACT FROM AUTHOR]

This study investigates variations in the velocity and sensitivity of electromagnetic waves in transmission lines configured in defective model piles for the detection of necking defects containing soil. Experiments are performed with model piles containing defects filled with different materials, such as air, sands, and clay. Five different types of transmission lines are configured in model piles. The electromagnetic waves are generated and detected using a time domain reflectometer. The velocity of electromagnetic waves is highest when the defect is filled with air, and it decreases with an increase in the water content. The velocity is lowest when the defect is filled with clay. The sensitivity of transmission lines for detecting defects decreases with an increase in soil water contents. The transmission line with a single electrical wire and epoxy-coated rebar exhibits the highest sensitivity, followed by that with three and two parallel electrical wires. Transmission lines with a single electrical wire and uncoated rebar and those with two parallel electrical wires wrapped with a sheath exhibit poor sensitivity when the defect is filled with clay. This study demonstrates that electromagnetic waves can be effective tools for detecting necking defects with wet and conductive soils in bored piles. [ABSTRACT FROM AUTHOR]

The stability of tunnels and rock slopes is adversely affected by defects in rock bolts. This study investigates the suitability of the smart sensing method using electromagnetic waves for inspecting defects in rock bolts. Experiments were performed with one fully grouted and eight defective rock bolts, out of which five have non-grouted parts at the ends with different non-grouted ratios, and three have different types of voids. Electromagnetic waves were generated and detected using a time domain reflectometer by configuring two-conductor transmission lines in the rock bolts. Results show that electromagnetic waves are reflected both at defects and ends of rock bolts. The electromagnetic wave velocity increases with an increase in the non-grouted ratio and decreases when rock bolts are embedded in a concrete block simulating rock mass. The estimated locations of defects found by electromagnetic waves are in good agreement with actual defect locations. This study demonstrates that smart sensing using electromagnetic waves is an effective method for inspecting and determining defect locations and the non-grouted ratio of rock bolts. [ABSTRACT FROM AUTHOR]