1. 서울대학교 Geotechnical and Geoenvironmental Engineering Laboratory

2. 서울대학교 Wednesday Seminar Geotechnical & Geoenvorinmental Engineering Lab. CONTENTS -2--2- Introduction 1 Literature Review 2 Research Plan 3 Summary 4

3. 서울대학교 Wednesday Seminar Geotechnical & Geoenvorinmental Engineering Lab. Introduction -3--3-

4. 서울대학교 Geotechnical & Geoenvorinmental Engineering Lab. Wednesday Seminar -4--4- Introduction Background Seoul, 2014 - Length 8m - Width 2.5m - Depth 5m Guatemala, 2010 - Diameter 20m - Depth 30m

5. 서울대학교 Geotechnical & Geoenvorinmental Engineering Lab. Wednesday Seminar -5--5- Introduction Background - Annual occurrences of ground cave-ins have increased. - Research for ground cave-ins needed. - Annual occurrences of ground cave-ins have increased. - Research for ground cave-ins needed. (September, 2014, ‘Sink Hole Assessment and Countermeasures‘, Policy forum) 435 573 689 854

6. 서울대학교 Geotechnical & Geoenvorinmental Engineering Lab. Wednesday Seminar -6--6- Introduction Ground Cave-ins and Subsidence (Sink Hole) : Depression or hole in the ground caused by some form of collapse of the surface layer

7. 서울대학교 Geotechnical & Geoenvorinmental Engineering Lab. Wednesday Seminar -7--7- Introduction Ground cave-ins and subsidence are induced by groundwater seepage and soil leaking through damaged sewer pipelines (September, 2014, ‘Sink Hole Assessment and Countermeasures‘, Policy forum) 1. Inherent ground cave-ins : Development of cavities by dissolution of limestone by groundwater 2. Artificial ground cave-ins : Development of cavities by 1) Ground excavation, 2) Damaged pipelines Types of Ground cave-ins and subsidence

8. 서울대학교 Wednesday Seminar Geotechnical & Geoenvorinmental Engineering Lab. Literature Review -8--8-

9. 서울대학교 Geotechnical & Geoenvorinmental Engineering Lab. Wednesday Seminar Nakai et al. (1997) : Comparison between model tests and numerical analyses by evaluating the surface settlement - Type of soils (Dry toyoura sand & Kaolin clay) - Height of tunnel (D/B) -9--9- Literature Review Ground Cave-ins and Subsidence by Excavation

10. 서울대학교 Geotechnical & Geoenvorinmental Engineering Lab. Wednesday Seminar -10- Literature Review Ground Cave-ins and Subsidence by Excavation Lee et al. (2006) : Comparison between centrifuge tests and numerical analyses by evaluating the surface settlement - Number of tunnels (Single-tunnel / Parallel-tunnel) - Center to center distance (d) - Cover to diameter ratio (C/D)

11. 서울대학교 Geotechnical & Geoenvorinmental Engineering Lab. Wednesday Seminar -11- Literature Review Ground Cave-ins and Subsidence by Excavation Coudron et al. (2006) : Comparison between model tests and numerical analyses by evaluating the surface settlement - Width of cavity - Height of cavity - Structure above soils

12. 서울대학교 Geotechnical & Geoenvorinmental Engineering Lab. Wednesday Seminar -12- Literature Review Ground Cave-ins and Subsidence by Damaged Sewer Pipelines Water Research Center (England) : Explanation on development of underground cavities by poor connections of sewer pipelines Limitations of WRC - Explanation limited to the phenomena of cavity development - No explanation given on mechanism of ground cave-ins and subsidence induced by damaged sewer pipelines

13. 서울대학교 Geotechnical & Geoenvorinmental Engineering Lab. Wednesday Seminar -13- Literature Review Ground Cave-ins and Subsidence by Damaged Sewer Pipeline Higashi et al. (2003), Kuwano et al.(2009), Mukunoki et al.(2009) : Simulation of ground cave-ins and subsidence by damaged sewer pipelines (By naked eye or X-ray Computed Tomography (CT))

14. 서울대학교 Geotechnical & Geoenvorinmental Engineering Lab. Wednesday Seminar -14- Literature Review Ground Cave-ins and Subsidence by Damaged Sewer Pipeline Higashi et al. (2003), Kuwano et al.(2009), Mukunoki et al.(2009) : Some limitations existing in researches performed in Japan (1) No consideration on the soils at site - Used typical soils (ex. Toyoura sands) (2) No consideration on the seepage pressure at site - Used arbitrary differential heads (3) No investigation on the mechanism of ground cave-ins and subsidence - Evaluated only the cavities and loosening sections of soils - Evaluated cavities and loosening sections of soils only at specific times

15. 서울대학교 Wednesday Seminar Geotechnical & Geoenvorinmental Engineering Lab. Research Plan -15-

16. 서울대학교 Geotechnical & Geoenvorinmental Engineering Lab. Wednesday Seminar -16- Research Plan Steps of Research - Establishment of plan for model tests - Development of testing apparatus - Verification of digital image analysis - Evaluation of external deformation by model tests - Evaluation of internal deformation by DIA - Investigation on the mechanism of ground cave-ins - Establishment and verification of prevention methods/countermeasures

17. 서울대학교 Wednesday Seminar Geotechnical & Geoenvorinmental Engineering Lab. Summary -17-

18. 서울대학교 Geotechnical & Geoenvorinmental Engineering Lab. Wednesday Seminar -18- Summary I. Annual occurrences of ground cave-ins (Sink holes) have been increasing recently. Consequently, research of ground cave-ins is needed. II. Most of artificial ground cave-ins are induced by groundwater seepage and soil leaking through damaged sewer pipelines. III. Many researches have performed the evaluation of ground cave-ins and subsidence by model tests and numerical analyses. However, they do not properly investigate the overall mechanism of the development of ground cave-ins and subsidence. IV. Evaluation of external deformation by model tests and internal deformation by DIA will be performed. ⇒ The mechanism of ground cave-ins will be investigated, and the prevention methods will be established and verified.

19. 서울대학교 Any question? Geotechnical and Geoenvironmental Engineering Laboratory