Analysis of NATM Tunnel Responses due to Earthquake Loading in Various Soils

Transcription

1 Analysis of NATM Tunnel Responses due to Earthquake Loading in Various Soils Presented by by Zaneta G. G. Adme Florida Florida State State University University Advisor Makola M. Abdullah, Ph.D.

2 Outline Background Objective Methodology Results Conclusions Future Work 2

3 Reasons for Utilizing Tunnels Connect land masses Maintenance issues -Channel Tunnel, English Channel -Holland & Lincoln Tunnels, New York Bypass impeding geologic formations -Wolf Creek Pass, Colorado 3

4 Reasons for Utilizing Tunnels Stability issues Environmental concerns F(t) is the external source of excitation -Devil s Slide Tunnel, California Increase the flow of traffic -Whittier Tunnel, Alaska -Central Artery, Boston, Massachusetts 4

5 Background 50% of the world s population live in urban areas - 70% of that population live in earthquake prone areas Initially, tunnels were designed with no regard to seismic effects Recent enhanced awareness of seismic hazards for underground structures Damping is the energy loss mechanism Damping force is proportional to the velocity 5

6 Earthquake Effects on Tunnels Ground Shaking Body Waves Surface Waves Ground Failure Liquefaction Faulting Tectonic Uplift & Subsidence 6

7 NATM New Australian Tunneling Method (NATM) F(t) is the external source of excitation After tunneling, shotcrete is applied to surface Damping is the energy loss mechanism Surrounding rock or soil becomes integrated into the support structure Damping force is proportional to the velocity Adopted by many countries as primary method of tunnel construction 7

8 Objective To determine which soils types prevalent in different regions, when used in conjunction with a NATM tunnel, perform better when subjected to excitation caused by an earthquake. 8

9 Methodology Identify the physical problem. Describe physical structure. Identify the source of of dynamic excitation. Determine expected outcomes Define the model Define necessary inputs. Find a model of of the physical problem using inputs Find the solution of of the numerical model. Solve the problem to to obtain response. Review results. 9

10 Criteria for city selection Size Earthquake History Possibility of Tunnel Use Variation in Soil Types 10

11 World Earthquakes ( ) Avezzano, Italy Tangshan, China San Francisco, California Tokyo, Japan Mexico City, Mexico Chimbote, Peru Agadir, Morocco Shallowest Depth of Earthquake Deepest

12 Global Soil Regions

13 Location soil data Location Soil Order Soil Type Agadir, Morocco Alfisols Low Plasticity Clay Avezzano, Italy Chimbote, Peru Los Angeles, California Mexico City, Mexico Tangshan, China Tokyo, Japan Ultisols Entisols Mollisols Andisols Inceptisols Oxisols Low Plasticity Silt Gravel-Sand Mixture Organic Medium Plasticity Silt Sandy Gravel High Plasticity Clay 13

14 Physical Structure Tunnel geometry single circle, 22 m (diameter), buried 67m 14

15 Method of Analysis Finite Element Method VisualFEA Used to model and solve complex 2-D and 3-D engineering problems. Converts data into a visual representation of output. Can give data at specific points in the structure. 15

16 Finite Element Method Tunnel Parameters 2-D plane strain model Fixed vertical ends Dynamic input placed at bottom boundary Damper placed at bottom boundary Rayleigh damping=0.05 Data taken from point between surfaces above tunnel point of interest 16

17 Soil data Soil Type Internal Mass Elastic Poisson's Friction Cohesion Density Modulus Ratio Angle (Pa) (kg/m^3) (Pa) (deg.) Gravel Uniform E Sandy w/ few fines E Sandy w/ silt or clay E Mixture of gravel and E sand Sand Uniform, fine E Uniform, coarse E Uniform, well-graded E Silt Low plasticity E Medium to high E plasticity Clay Low plasticity E Medium plasticity E High plasticity E Organic E Rock Granite E E+07 17

18 Source of dynamic excitation Acceleration record 1995 Kobe, Japan Acceleration input applied to a flexible base. 18

19 Results: Comparison Uniform Gravel Medium to High Plasticity Silt Disp.= cm Disp.= cm 19

20 Results Location Agadir, Morocco Soil Type Low Plasticity Clay Maximum Displacement (cm) Avezzano, Italy Low Plasticity Silt Chimbote, Peru Los Angeles, California Gravel-Sand Mixture Organic Mexico City, Mexico Medium Plasticity Silt Tangshan, China Sandy Gravel w/ Silt Tokyo, Japan High Plasticity Clay

21 Conclusions The soils that contain between ten and fifty percent fine particles performed better under excitation than the soils with smaller amounts (<10%) of fine particles. Soils with the greatest amounts of fines (>50%) performed unfavorably as compared to the other soils. Finite element programs possess great tools for the exploration of complex problems and are, also, fine educational tools. 21

22 Possible Future Work 3-D analysis. Incorporation of other rock types and water table. Increase in layers to better represent ground layers. 22

23 References Kirzhner, F. and Rosenhouse, G., Numerical analysis of tunnel dynamic response to earth motions. Tunneling and Underground Space Technology, Volume 15, Issue 3, Merritt, J. L., Monsees, J. E., Hendron, A. J., Seismic design of underground structures: Proc of the 1985 Rapid Excavation and Tunneling Conference, New York. International Journal of Rock Mechanics and Mining Science & Geomechanics Abstracts, Volume 23, Issue 6, Intuition Software, VisualFEA-Visual Finite Element Analysis. Chonbuk, South Korea: Intuition Software atlas.geo.cornell.edu/education pghbridges.com/termstun.htm

24 Acknowledgements FAMU Undergraduate Program National Science Foundation REUJAT Program University of Tokyo Makola M. Abdullah, Ph. D. Terri R. Norton, M.S.C.E. 24

25 Thousands occur every year but are not sensed by humans.. The strong motion earthquakes are of more interest to engineers Thank You! 25