PURPOSES : This study aims to evaluate the applicability of ground penetrating radar (GPR) for surveying utility pipes under sidewalks made of concrete brick and plate-stone block pavements.
METHODS : GPR tests were conducted at two test sections to detect layer boundary and utility pipes under the pavements. The central frequency of the single-channel GPR was 800, 500, 250, and 100 MHz, and the central frequency of multi-channel (8) GPR was 450 MHz. GPR signals were analyzed in terms of 1-D (A-scan) and 2-D (B-scan) profiles.
RESULTS: From the A-scan data analysis, the vertical resolution of the GPR ranged from 7.3 cm for 800 MHz to 133.1 cm for 100 MHz in the concrete brick block pavement and 13.9 cm for 800 MHz to 144.2 cm for 100 MHz in plate stone block pavement. From the B-scan data analysis, 250 MHz to 500 MHz GPR was sufficient to differentiate the layer boundary at a depth of 1.0~1.5 m to detect utility pipes at a depth of 0.5~2.0 m in both block pavements. In the plate-stone block pavement, GPR signal attenuation was greater because of the wire mesh in the concrete layer. Thus, the penetration depth was approximately 80% of the concrete brick-block pavement.
CONCLUSIONS : The penetration depth and vertical resolution of GPR in the sidewalk paved with blocks were comparable to those of roadway pavement. Among the GPR evaluated, the 250 MHz GPR was the most desirable, and the 500 MHz GPR was affordable for the investigation of underground pipes situated up to 2.0~3.0 m under sidewalks.

ABSTRACT
 1. 서론
 2. GPR 탐사 기본 원리
  2.1. GPR 탐사 개요
  2.2. GPR 탐사 원리
  2.3. GPR 탐사 방법
 3. GPR 시험 조건
  3.1. GPR 장비
  3.2. 보도블록 포장 GPR 조사 방법
 4. GPR 시험 결과 분석
  4.1. 시멘트벽돌 포장 구간
  4.2. 판석 포장 구간
  4.3. 보도블록 포장 시험 조사 결과 비교
 5. 결론
 REFERENCES

• 이창민(서울특별시 품질시험소 도로포장연구센터) | Lee Chang Min
• 윤진성(서울특별시 품질시험소 도로포장연구센터) | Yoon Jin-sung
• 백종은(서울특별시 품질시험소 도로포장연구센터) | Baek Jongeun (The Pavement Research Center, Quality Inspection Office Division, Seoul Metropolitan Government) 교신저자
• 김순태((주)지오레이다) | Kim Soontae