A study on the field application of high strength steel pipe reinforcement grouting

고강도 강관 보강 그라우팅의 현장 적용성에 관한 연구

Abstract

In this paper, we conducted experimental investigation on the field applicability through the verification of reinforcement effect of the steel pipe reinforcement grouting using high strength steel pipe. SGT275 (formerly known as STK400) steel pipe is generally applied to the traditional steel pipe reinforcement grouting method. However, the analysis of tunnel collapse cases applying the steel pipe reinforcement grouting shows that there are cases where the excessive bending and breakage of steel pipe occur. One of the reasons causing these collapses is the lack of steel pipe stiffness responding to the loosening load of tunnels caused by excavation. The strength of steel pipe has increased due to the recent development of high strength steel pipe (SGT550). However, since research on the reinforcement method considering strength increase is insufficient, there is a need for research on this. Therefore, in this study, we conducted experiments on the tensile and bending strength based on various conditions between high strength steel pipe, and carried out basic research on effective field application depending on the strength difference of steel pipe through the conventional design method. In particular, we verified the reinforcement effect of high strength steel pipe through the measurement results of deformed shape and stress of steel pipe arising from excavation after constructing high strength steel pipe and general steel pipe at actual sites. The research results show that high strength steel pipe has excellent bending strength and the reinforcement effect of reinforced grouting. Further, it is expected that high strength steel pipe will have an arching effect thanks to strength increase.

본 논문에서는 고강도 강관을 이용한 강관 보강 그라우팅의 보강 효과 검증을 통해 현장 적용성에 관한 실험적 내용을 다루었다. 기존 강관보강 그라우팅 공법에는 SGT275 (구 STK400) 강관을 일반적으로 적용하고 있으나, 강관 보강 그라우팅이 적용된 터널의 붕락사례를 보면 강관의 과도한 꺾임, 파단 등의 사례가 발생되고 있다. 이러한 사례가 발생하는 여러 원인 중 굴착에 따른 터널의 이완하중에 대응하는 강관의 강성 부족이 그 원인이 될 수 있다. 최근 들어 고강도 강관(SGT550)의 개발로 강관의 강도가 증가했으나, 강도 증대를 고려한 보강방안에 대한 연구가 미흡하므로 이에 대한 연구가 필요한 실정이다. 따라서 본 연구에서는 고강도 강관과 일반 강관의 이음 유무, 주입재의 충전 여부 등 다양한 조건에 대해 인장강도 및 휨 전단력 실험을 수행하고, 기존 제시된 설계법을 통해 강관의 강도 차이에 따른 효율적인 현장 적용성에 대한 기초 연구를 수행하였다. 특히, 실제 현장에 고강도 강관과 일반 강관을 시공하고 굴착에 따른 강관의 변위형상과 응력에 대한 계측 결과를 통해 고강도 강관의 보강 효과를 검증하였다. 연구결과 고강도 강관은 휨 강도가 우수하여 보강효과가 우수한 것으로 나타났으며, 강도 증진효과로 인해 아칭효과도 기대된다.

Fig. 1. Examples of steel pipe damage (KICT, 2008)

Fig. 2. Examples of steel pipe using steel pipe reinforcement grouting

Fig. 3. Types of steel pipes for testing

Fig. 4. Production process of test steel pipe

Fig. 5. Tensile strength test

Fig. 6. Tensile strength test results

Fig. 7. Bending shear force tests (by type of steel pipe and whether joint etc.)

Fig. 8. Bending shear force test results

Fig. 9. Load concept acting on steel pipe (Kim et al., 2003)

Fig. 10. Vertical load and horizontal load acting on steel pipe (Kim et al., 2003)

Fig. 11. Stress of steel pipe according to excavation distance and relaxed loads

Fig. 12. Summary of field test construction

Fig. 13. Results of measurement

Fig. 14. Stress comparison of steel pipes by theoretical and measured stress

Table 1. Comparison of mechanical properties and chemical composition of steel pipes

Table 2. Comparison of steel pipe specifications

Table 3. Tensile strength test cases of steel pipes

Table 4. Shear force test cases of steel pipes

Table 5. Tensile strength test result of steel pipes

Table 6. Bending shear force test result of steel pipes

Table 7. Conditions for calculation of stress in steel pipe

Table 8. Stress of small diameter steel pipe according to excavation distance and relaxed loads (MPa)

Table 9. Stress of large diameter steel pipe according to excavation distance and relaxed loads (MPa)

Table 10. Stress comparison of steel pipes

Table 11. Stress comparison of steel pipe after 1 m excavation

Table 12. Stress comparison of steel pipe after 2 m excavation

Table 13. Stress comparison of steel pipe after 3 m excavation

Table 14. Stress comparison of steel pipe after 4 m excavation

Table 15. Stress comparison of steel pipe after 5 m excavation

Table 16. Stress comparison of steel pipe after 6 m excavation