GEOSYNTHETIC-STABILIZED VEGETATED EARTH SURFACES FOR ENVIRONMENTAL SUSTAINABILITY IN CIVIL ENGINEERING JIE HAN PH.D.

Transcription

1 GEOSYNTHETIC-STABILIZED VEGETATED EARTH SURFACES FOR ENVIRONMENTAL SUSTAINABILITY IN CIVIL ENGINEERING JIE HAN PH.D., PE, PROFESSOR JUN GUO, RESEARCH ASSISTANT THE UNIVERSITY OF KANSAS, USA

2 OUTLINE OF PRESENTATION Introduction Problems Solutions Research at KU Concluding Remarks 2

3 GEOSYNTHETICS Manufactured polymer materials used for geotechnical applications Geotextile Geogrid Geocell Geomembrane Geonet Geosynthetic clay liner Geofibers Geofoam Geomat Geocomposite 3

4 THREE COMMONLY USED GEOSYNTHETICS Geotextile (GT) Geogrid (GG) Geocell (GC) 4

5 INSTALLATION OF GEOCELL 5

6 6

7 MAIN FUNCTIONS OF GEOSYNTHETICS Separation Filtration Water flow GT Drainage Reinforcement Barrier Tension GT GT, GG, and GC Erosion protection 7

8 TYPICAL PROBLEMS FOR SLOPES AND UNPAVED SHOULDERS Problems for slope surfaces Surficial slope instability Erosion Problems for unpaved shoulders Rutting Erosion 8

9 STABILITY OF NATURAL SLOPE Dry m:1 m:1 Seepage water FS tan tan 1.0 FS tan tan For typical soil, = 30 o 2(H):1(V) slope (27 o ) Stable 4(H):1(V) slope (14 o ) 9

10 SURFICIAL SLOPE FAILURE Shallow failure surface up to 1.2m (4ft) Failure mechanisms Poor compaction Low overburden stress Loss of cohesion Saturation Seepage force 10

11 SLOPE EROSION Loss of soil mass Failure mechanism Loss of vegetation cover Soil washed out by water 11

12 UNPAVED SHOULDER Rutting = accumulated permanent deformation due to traffic loading Road edge drop-offs due to wind/water erosion FHWA, USA, 2011 and

13 BIO-STABILIZATION 2ca FS 0. 5 H sin 2 tan tan c a Example: c a = 50 psf, H = 2 ft, = 120 pcf, = 30 o FS = 1.0 = 40 o (1:1 slope, no-seepage condition) = 27 o (2:1 slope, seepage condition) 13

14 EXAMPLES OF GEOSYNTHETIC-STABILIZED VEGETATED EARTH SURFACES Erosion mat Wrapped-around geogrid Wrapped-around geogrid Welded-wire basket Vegetation Vegetation Vegetation (a) Slope facing protected by erosion mat (b) Slope facing stabilized by wrapped-around geogrid (c) Slope or wall facing stabilized by welded-wire basket and wrapped-around geogrid Geocell Vegetation Pavement Vegetation Geocell Ditch (d) Slope facing stabilized by geocell (e) Unpaved shoulders stabilized by geocell 14

15 EROSION CONTROL Erosion Mat or Blanket: Enhance seed germination and erosion resistance UV protected Village at Westlake - Austin, TX 15

16 GEOGRID-WRAPPED SLOPE SURFACE 16

17 GEOGRID-WRAPPED WALL FACE inclination Stair-stepped shape with vegetation Welded-wire baskets R & B Chambers MSW Landfill Banks County, GA 17

18 GEOCELL-REINFORCED SLOPE FACE 18

19 SURFICIAL SLOPE STABILITY Saturated z H Primary reinforcement β Secondary reinforcement FS c' H 2 2 Hz cos tan ' T cos sin sin tan ' sat w sat Hz cos sin g T g = summation of geosynthetic resisting force (controlled by pullout or rupture) Collin (2006) 19

20 Presto VEGETATED GREEN SHOULDER Reduce PM10 Reduce truck turbulent kinetic energy (i.e. dust control) Erosion control Reduce wind/water erosion thus minimizing drop-off Green shoulder requires fines and moisture, which makes the shoulder weak for traffic loading. Geosynthetic reinforcement is expected to make shoulder stronger. 20

21 PARKING LOT WITH OR WITHOUT VEGETATION Gravel parking lot Vegetated parking lot 21

22 GREEN SHOULDER RESEARCH AT KU Material used in this study Well-graded aggregate base high strength but poor vegetation Native Top Soil (lean clay with organic content) low strength but good vegetation Soil Mixture sufficient strength and good vegetation Mixture 1: 50% aggregate & 50% top Soil (by dry weight) Mixture 2: 65% aggregate & 35% top Soil Triaxial geogrid and geocell 22

23 1.5 m by 1.5 m sections 1.6% slope for subgrade 4.2% slope for top surface TEST SECTIONS Geotextile wrapped aggregate for side drainage 23

24 TEST SECTIONS 24

25 TEST SECTIONS 25

26 PRIMARY GRASS TYPES Oregon State University 2009 USDA 1950 Tall Fescue (2.3 g/section) Perennial Ryegrass (2.3 g/section) 26

27 TEMPERATURE NOAA, USA 27

28 Precipitation (mm) PRECIPITATION Precipitation 35 Date Elapsed Date NOAA, USA 28

29 All Test Sections 29

30 BLADE LENGTH The length of longest green leaf on a sprout 8 random samples per section 30

31 GRASS DENSITY Number of sprouts in a 0.6 m by 0.6 m square frame The frame was placed on each section at random location 31

32 Blade Length (mm) Blade Length (mm) Blade Length (mm) Blade Length (mm) MEASURED BLADE LENGTH Day Elapsed Top soil Geocell 0C 8/2/ /10/2013 2/18/2014 Date 0R Day Elapsed Top soil/65-35 mix Geogrid 2C 8/2/ /10/2013 2/18/2014 Date 2R Day Elapsed Top soil/50-50 mix Geogrid 8/2/2013 9/21/201311/10/201312/30/20132/18/2014 4/9/2014 Date 4C 4R Day Elapsed Top soil/50-50 mix Geocell 6C 8/2/ /10/2013 2/18/2014 Date 6R 32

33 Number of Sprout in Selected Area Number of Sprout in Selected Area Number of Sprout in Selected Area Number of Sprout in Selected Area GRASS DENSITY Day Elapsed Day Elapsed Top soil Geocell mix Geogrid 50 0C 0R 50 3C 3R 0 8/2/2013 9/21/ /10/ /30/2013 2/18/2014 4/9/2014 Date Day Elapsed /2/2013 9/21/ /10/ /30/2013 2/18/2014 4/9/2014 Date Day Elapsed Top soil/50-50 mix Geogrid Aggregate/50-50 mix Geocell C 6R 0 8/2/2013 9/21/ /10/ /30/2013 2/18/2014 4/9/2014 Date 50 7C 7R 0 8/2/2013 9/21/ /10/ /30/2013 2/18/2014 4/9/2014 Date 33

34 Number of Sprout in Selected Area GRASS DENSITY Grass Density Day Elapsed Top soil/65-35 mix control mix control 0 8/2/2013 9/21/ /10/ /30/2013 2/18/2014 4/9/2014 Date 0C 0R 1C 1R 2C 2R 3C 3R 4C 4R 5C 5R 6C 6R 7C 7R 34

35 CONCLUDING REMARKS Geosynthetic erosion mats or geocells with vegetation minimize soil erosion. Geosynthetic reinforcement enhances surficial slope stability. Geosynthetic reinforcement does not affect vegetation growth. The surface soil does not have significant effect on the leaf blade length, but does affect the vegetation density. Geosynthetic reinforcement increases load capacities of unpaved roads Geosynthetic reinforcement is expected to provide a sustainable solution for vegetated slopes and green shoulders. 35

36 Thank you 36