Journal of the Korean Geosynthetics Society (한국지반신소재학회논문집)

Korean Geosynthetics Society (한국지반신소재학회)
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Evaluation of Performance of Expansive Material for Restoration of Underground Cavity and Stress Release Zone

지하공동 및 이완영역 복구를 위한 팽창성 재료의 성능 평가

  • Lee, Kicheol (Dept of Civil and Environmental Engineering, Incheon National University) ;
  • Choi, Byeong-Hyun (Dept of Civil and Environmental Engineering, Incheon National University) ;
  • Bak, Jongho (Dept of Civil and Environmental Engineering, Incheon National University) ;
  • Kim, Dongwook (Dept of Civil and Environmental Engineering, Incheon National University)
  • Received : 2018.11.20
  • Accepted : 2018.12.04
  • Published : 2018.12.30
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Abstract

Recently, the number of ground subsidence resulting from underground cavity has been increased. Accordingly, the importance of restoration of stress release zone around the underground cavity has been emphasized. The stress release zone is composed of low density soils having extremely low stiffness and degree of compaction, which can lead to additional cavity expansion and collapse of overlying ground. Therefore, in this study, the suitability of restoration method of underground cavity using expansive material for reinforcement of stress release zone around the cavity is verified. The basic physical properties and expansion characteristics of the expansive material were examined. The experiment equipment capable simulating of stress release zone was developed and is used to investigate the effect of expanding material on stress release zone. The stress release zone was simulated using the spring in numerical analysis. The factors of the volume ratio of the underground cavity to the expansion material, the degree of stress relaxation, and the shape of the cavity were varied in numerical simulations, and the behavior of stress release zone was analyzed based on the numerical analysis results. Analysis variables are factors that affect each other. Also, filling of underground cavity and capacity of restoration of stress release zone were confirmed when the expansive material was inserted into underground cavity.

최근 국내외적으로 지하공동과 더불어 지반함몰발생 빈도수가 높아지고 있다. 따라서 지하 공동 주변부 응력이완영역의 복구에 대한 관심도 높아지고 있다. 이완영역은 지반 내에서 빈공간이 발생함에 따라 빈 공간 주변부의 지반이 원지반의 강성 및 다짐도를 잃고 느슨해진 상태로 추가적인 공동 확장 및 붕괴를 유발 할 수 있다. 따라서 본 연구에서는 공동 주변부 지반 이완영역을 보강하기 위해 팽창성 재료를 활용한 지반함몰 복구공법을 적용하고 이를 검증하고자 한다. 우선적으로 팽창성 재료의 기본 물리적 특성 및 팽창 특성을 파악하였고, 이완영역 모사 실험 장비를 제작하여 팽창성 재료의 팽창 시 이완영역에 미치는 영향을 파악하였다. 이완영역은 수치해석상 스프링계수로 모사하였다. 수치해석 변수로는 공동 체적에 대한 투입된 팽창성 재료의 부피비, 이완영역의 이완정도, 공동의 형상을 설정하였고, 이에 따른 이완영역의 전반적인 거동을 수치해석적으로 분석하였다. 해석 결과 해석 변수들은 서로 영향을 주는 인자들이였으며, 팽창성 재료가 지하공동에 삽입되었을 경우 지하공동 채움 및 이완영역 복구 정도를 확인하였다.

Keywords

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Fig. 1. Illustration of stress release zone during tunnel excavation and stress release zone determination (modified after Xu et al., 2018)

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Fig. 2. Mechanism of restoration for ground cavity with inserting of expansive material

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Fig. 4. Laboratory tests of expansive material; (a) uniaxial compression, (b) expansion ratio, (c) temperature effect and (d) expansion pressure test

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Fig. 3. Brief chemical equation of urethane reaction process (modified after Kim and Youn, 2009)

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Fig. 5. Assumption of stress release zone when cavity was occurred in this study

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Fig. 6. Composition of experiment equipment capable simulating of stress release zone; (a) combination with each part (b) mold, (c) load cell attached spring and (d) frame for fixing

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Fig. 7. Principle of experiment equipment capable simulating of stress release zone

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Fig. 8. Experiment procedure: (a) Pour the half of sands, (b) insertion of expansive material into equipment, (c) installation of part containing load cell and spring after pour of the remaining half of the sands, and (d) measurement of sand-expensive material mixture

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Fig. 9. Results of experiment: Variation of average expansion pressure with (a) time and (b) displacement (spring coefficient = 148.764 kN/m)

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Fig. 10. Relationship between thermal strain and temperature given in ABAQUS/CAE (modified after SIMULIA, 2014)

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Fig. 11. Result of thermal expansion analysis: (a) Numerical model and (b) Ratio of expanded-to-initial volume with increasing thermal expansion coefficient

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Fig. 12. Result of uniaxial compression analysis: (a) Numerical model and (b) uniaxial compression strength with increasing elastic modulus (Poisson's ratio = 0.3)

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Fig. 14. Modeling of experiment equipment capable simulating of stress release zone

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Fig. 15. Displacement field of soil and expansive material after expansion based on the model represented in Fig. 14

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Fig. 16. Behavior after expansion according to the volume ratio of the expansion material to the cavity: Increased volume in percentile : (a) 1.7%, (b) 10.5%, (c) 23.6% and (d) 41.9%

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Fig. 17. Variation of (a) maximum expansion pressure and (b) average compressive strain with increasing spring coefficient

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Fig. 18. Variation of (a) maximum expansion pressure and (b) average compressive strain with ratio of width and height (W/H)

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Fig. 13. (a) boundary condition of experiment capable simulating of stress release zone: (a) Numerical modeling and (b) result and plot after numerical analysis

Table 1. Laboratory test for expansion material

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Table 2. Results with volume ratio of the expansion material to the cavity

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