Numerical Analysis for Optimum Reinforcement Length Ratio of Reinforced Earth Retaining Wall

보강토옹벽의 최적 보강길이비 산정을 위한 수치해석적 연구

Abstract

Recently, method of reinforced earth retaining wall have been proposed according to the material of facing, geosynthetic, construction method, and facing slope. However, the regulations such as the design method and detailed review items according to each construction method are not clear, and collapse due to heavy rainfall frequently occurs. In this study, to obtain a more stable technical approach in the design of reinforced earth retaining wall, the combination of the pullout failure of reinforced earth retaining wall and the optimal reinforcement ratio of height using reinforced earth retaining wall using a single strength reinforcement is assumed, optimum design of stiffener, optimal design of superimposed wall and optimum length ratio of reinforcement material of geosynthetics are proposed through safety factor according to reinforcement length ratio (L/H).

최근 국내에 사용되고 있는 보강토옹벽 공법은 전면체의 재질, 보강재, 축조방법, 축조경사에 따라 수많은 종류가 제안되었으나 각 공법에 따른 설계방법이나 상세검토항목 등의 규정이 명확하지 않으며 집중호우에 따른 붕괴도 빈번하게 발생하고 있는 실정이다. 본 연구에서는 이러한 보강토옹벽의 설계에 있어서 좀 더 안정된 기술적 접근을 위해 설치높이별 단면을 가정하고 단일 강도의 보강재를 사용한 보강토옹벽의 인발파괴와 높이별 최적의 보강재 조합을 산정하고 산정된 각 단면에 대해서 보강길이비(L/H)에 따른 안전율 변화를 통하여 보강재의 최적 설계와 다단식 보강토옹벽의 최적 설계 그리고 보강재인 토목섬유의 재질에 따른 최적 길이비를 산정하여 제시하였다.

Fig. 1. Process flow chart

Fig. 2. Section S1 (Facing slope=1:0.05)

Fig. 3. Section S2 (Facing slope=1:0.2)

Fig. 4. Section S3 (Facing slope=1:0.3)

Fig. 5. Optimum geotextile combination of facing slope S1

Fig. 6. Optimum geotextile combination of facing slope S2

Fig. 7. Optimum geotextile combination of facing slope S3

Fig. 8. Change in safety factor according to reinforcement length ratio (L/H) of S1 (MSEW)

Fig. 9. Change in safety factor according to reinforcement length ratio (L/H) of S1 (SLOPE/W)

Fig. 10. Change in safety factor according to reinforcement length ratio (L/H) of S2 (MSEW)

Fig. 11. Change in safety factor according to reinforcement length ratio (L/H) of S1 (SLOPE/W)

Fig. 12. Change in safety factor according to reinforcement length ratio (L/H) of S2 (MSEW)

Fig. 13. Change in safety factor according to reinforcement length ratio (L/H) of S1 (SLOPE/W)

Fig. 14. Section and condition of superimposed wall

Fig. 15. Strain-tensile strength curve by type of geogrids (Han et al., 2012)

Fig. 16. Calculation overburden load of superimposed wall (NCMA, 1998)

Fig. 17. Change in safety factor according to reinforcement length ratio (L/H) of superimposed wall

Fig. 18. Geosynthetics fracture ratio of PET geogrid

Fig. 19. Optimum geogrid combination (H=6.0m, L=4.2m)

Fig. 20. Optimum geogrid combination (H=7.0m, L=4.6m)

Fig. 21. Optimum geogrid combination (H=8.0m, L=5.2m)

Fig. 22. Optimum geogrid combination (H=9.0m, L=5.9m)

Fig. 23. Optimum geogrid combination (H=10.0m, L=6.2m)

Table 1. Properties of geosynthetics

Table 2. Geosynthetics fracture ratio of facing slope S1

Table 3. Geosynthetics fracture ratio of facing slope S2

Table 4. Geosynthetics fracture ratio of facing slope S3

Table 5. Layout optimum geotextile combination of facing slope S1

Table 6. Layout optimum geotextile combination of facing slope S2

Table 7. Layout optimum geotextile combination of facing slope S3

Table 8. Length/Height (L/H) for optimal design of geosynthetics

Table 9. Design of superimposed MSE wall (FHWA, 1997)

Table 10. Safety factor according to Length/Height ratio (L/H)

Table 11. Length/Height (L/H) for optimal design of superimposed wall