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
OUTLINE OF PRESENTATION Introduction Problems Solutions Research at KU Concluding Remarks 2
GEOSYNTHETICS Manufactured polymer materials used for geotechnical applications Geotextile Geogrid Geocell Geomembrane Geonet Geosynthetic clay liner Geofibers Geofoam Geomat Geocomposite 3
THREE COMMONLY USED GEOSYNTHETICS Geotextile (GT) Geogrid (GG) Geocell (GC) 4
INSTALLATION OF GEOCELL 5
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MAIN FUNCTIONS OF GEOSYNTHETICS Separation Filtration Water flow GT Drainage Reinforcement Barrier Tension GT GT, GG, and GC Erosion protection 7
TYPICAL PROBLEMS FOR SLOPES AND UNPAVED SHOULDERS Problems for slope surfaces Surficial slope instability Erosion Problems for unpaved shoulders Rutting Erosion 8
STABILITY OF NATURAL SLOPE Dry m:1 m:1 Seepage water FS tan tan 1.0 FS tan 0. 5 1. 0 tan For typical soil, = 30 o 2(H):1(V) slope (27 o ) Stable 4(H):1(V) slope (14 o ) 9
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
SLOPE EROSION Loss of soil mass Failure mechanism Loss of vegetation cover Soil washed out by water 11
UNPAVED SHOULDER Rutting = accumulated permanent deformation due to traffic loading Road edge drop-offs due to wind/water erosion FHWA, USA, 2011 and 2013 12
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
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
EROSION CONTROL Erosion Mat or Blanket: Enhance seed germination and erosion resistance UV protected Village at Westlake - Austin, TX 15
GEOGRID-WRAPPED SLOPE SURFACE 16
GEOGRID-WRAPPED WALL FACE 35-70 inclination Stair-stepped shape with vegetation Welded-wire baskets R & B Chambers MSW Landfill Banks County, GA 17
GEOCELL-REINFORCED SLOPE FACE 18
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
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
PARKING LOT WITH OR WITHOUT VEGETATION Gravel parking lot Vegetated parking lot 21
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
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
TEST SECTIONS 24
TEST SECTIONS 25
PRIMARY GRASS TYPES Oregon State University 2009 USDA 1950 Tall Fescue (2.3 g/section) Perennial Ryegrass (2.3 g/section) 26
TEMPERATURE NOAA, USA 27
Precipitation (mm) PRECIPITATION Precipitation 35 Date Elapsed 1 21 41 61 81 101 121 141 161 181 201 221 241 261 281 30 25 20 15 10 5 0 Date NOAA, USA 28
All Test Sections 29
BLADE LENGTH The length of longest green leaf on a sprout 8 random samples per section 30
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
Blade Length (mm) Blade Length (mm) Blade Length (mm) Blade Length (mm) MEASURED BLADE LENGTH 180 160 140 120 100 80 60 40 20 0 Day Elapsed 0 100 200 Top soil Geocell 0C 8/2/2013 11/10/2013 2/18/2014 Date 0R 180 160 140 120 100 80 60 40 20 0 Day Elapsed 0 100 200 Top soil/65-35 mix Geogrid 2C 8/2/2013 11/10/2013 2/18/2014 Date 2R Day Elapsed 0 50 100 150 200 250 180 160 140 120 100 80 60 40 20 0 Top soil/50-50 mix Geogrid 8/2/2013 9/21/201311/10/201312/30/20132/18/2014 4/9/2014 Date 4C 4R 180 160 140 120 100 80 60 40 20 0 Day Elapsed 0 100 200 Top soil/50-50 mix Geocell 6C 8/2/2013 11/10/2013 2/18/2014 Date 6R 32
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 0 50 100 150 200 250 Day Elapsed 0 50 100 150 200 250 200 150 100 Top soil Geocell 200 150 100 65-35 mix Geogrid 50 0C 0R 50 3C 3R 0 8/2/2013 9/21/2013 11/10/2013 12/30/2013 2/18/2014 4/9/2014 Date Day Elapsed 0 50 100 150 200 250 0 8/2/2013 9/21/2013 11/10/2013 12/30/2013 2/18/2014 4/9/2014 Date Day Elapsed 0 50 100 150 200 250 200 150 Top soil/50-50 mix Geogrid 200 150 Aggregate/50-50 mix Geocell 100 100 50 6C 6R 0 8/2/2013 9/21/2013 11/10/2013 12/30/2013 2/18/2014 4/9/2014 Date 50 7C 7R 0 8/2/2013 9/21/2013 11/10/2013 12/30/2013 2/18/2014 4/9/2014 Date 33
Number of Sprout in Selected Area GRASS DENSITY Grass Density Day Elapsed 0 50 100 150 200 250 200 150 Top soil/65-35 mix control 100 50 65-35 mix control 0 8/2/2013 9/21/2013 11/10/2013 12/30/2013 2/18/2014 4/9/2014 Date 0C 0R 1C 1R 2C 2R 3C 3R 4C 4R 5C 5R 6C 6R 7C 7R 34
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
Thank you 36