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Geogrid Estimating Charts

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These pre-engineered tables provide an accurate estimate for geogrid reinforcement. To use the tables, follow these simple steps:
  1. Verify that the site condition of your retaining wall matches the table being used.
  2. Verify that the soil conditions at your site match the description given
  3. Choose the wall height needed for your site and read across to find the number of grid layers, embedment length and grid locations.
  4. Verify that excessive water runoff, or a high water table, is not present.
Design Parameters

Factors of Safety           Assumed Weights
Sliding = 1,5 Earth Backfill = 120 lbs/ft3(19 Kn/m3)
Overturning = 2,0 Filled Weight of AB = 131 lbs/ft3(20,5 Kn/m3)
Grid Pullout = 1,5 Allan Block = 21,1 Kn/m3
Grid Rupture = 1,5
General           Soils
Proper drainage provided. Cohesion = 0
Grid meets ASTM D-4595. Bearing Capacity 36° ≥ 191,520kPa
Bearing Capacity 32° ≥167,580kPa
Bearing Capacity 27° ≥119,700kPa
Grid
Long Term Allowable Design Strength (LTADS) ≥ 700 lbs/ft. (10,200 N/m) i.e., Fortrac 20/4-20, Miragrid 2XT, Strata 200, Raugrid 2/3-35, Synteen SF20, Tensar UX1000.



These charts should be used for estimating grid quantities for projects which match the site and soil descriptions provided, and only for projects which use grid strengths of 700 lbs/ft. (10,200 N/m) or higher. No provision or analysis for global stability or seismic activity.



Case A


Case B


Case C
Geogrid Chart
AB Classic 12° and
AB Three 87°
Soil Types:
Coarse to medium sand,
clean sand and gravel,
little or no fines

φ = 36°
Soil Types:
Uniform to well graded sands,
silty sands -

φ = 32°
Soil Types:
Sand-Silt-Clay mix,
Clayey sands

φ = 27°
Conditions Above Wall Wall Height
m
Buried Block
cm
# of grid
layers
Grid
length
m
# of grid
layers
Grid
length
m
# of grid
layers
Grid
length
m
Case A
Level Slope
Above Wall
0,9 8 0 - 0 - 2 1
1,2 15 3 1,1 3 1,1 3 1,1
1,5 15 4 1,3 4 1,3 4 1,3
1,8 15 5 1,6 5 1,6 5 1,6
2,1 18 6 1,7 6 1,7 6 1,7
2,4 20 7 2 7 2 7 2
2,7 23 7 2,2 7 2,2 7 2,2
3,0 25 8 2,3 8 2,3 8 2,3
Case B
Surcharge*
4.7 kPa

Top grid layer
must extend
an extra 0,9 m
0.9 15 2 1 2 1 2 1
1,2 15 3 1,1 3 1,1 3 1,1
1,5 15 4 1,3 4 1,3 4 1,3
1,8 15 5 1,6 5 1,6 5 1,6
2,1 18 6 1,7 6 1,7 6 1,7
2,4 20 7 2 7 2 7 2
2,7 23 7 2,2 7 2,2 7 2,2
3,0 25 8 2,3 8 2,3 9** 2,3
Case C
Slope 3H:1V above
the wall
0,9 8 0 - 0 - 2 1
1,2 15 3 1,1 3 1,1 3 1,1
1,5 15 4 1,3 4 1,3 4 1,3
1,8 15 5 1,6 5 1,6 5 1,6
2,1 18 6 1,7 6 1,7 6 1,7
2,4 20 7 2 7 2 8** 2
2,7 23 7 2,2 7 2,2 8** 2,3
3,0 25 8 2,3 9** 2,3 10** 2,6
Note: All walls which require geogrid reinforcement shall have a minimum of 6 in. (150 mm) of buried block.

*The Surcharge loading category above assumes a solid surface such as concrete, asphalt or pavers having a suitable supporting subgrade.
** 1 course spacing for first 3 layers of grid.
***1 course spacing for first 4 layers of grid.


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