Chapter 15 Hardscapes 419 Copyright Goodheart-Willcox Co., Inc. Geotextiles Some applications require a geotextile between the subsoil and a base or aggregate layer. Geotextiles are water-permeable synthetic fabrics used as weed barriers, separations between materials, such as soil and stone, or to reinforce a material. In this case, the soil and aggregate are kept separate but water may still permeate the fabric. Overlapping seams and allowing extra material to extend up the sides of the excavated area ensures the geotextile will serve its purpose. See Figure 15-28. STEM Connection Calculating Slope The following steps may be used to determine the slope between two points. Use feet and tenths as the units of measurement. 1. Use a survey instrument or a carpenter’s level resting on a 2×4 to measure the vertical difference (v) between the two points. 2. Measure the horizontal distance (h) between the two points. 3. Calculate the slope percentage using the formula Calculating slope between two points: Calculate slope between points A and B v = 2′ h = 16′ 2/16 = 0.125 × 100 = 12.5% slope Calculate the vertical change necessary to obtain a desired slope between two points: Calculate a 1% downslope between points A and B h = 16 % slope = –1% elevation A = 200.0 B = 199 16 × –0.01 = –0.16 elevation change for point B 200 – 0.16 = 199.84 elevation desired at point B Calculate an upslope between two points: Calculate a 4% upslope between points A and B h = 16 % slope = 4% elevation A = 200 B = 200 16 × 0.04 = 0.64 elevation change for point B 200 + 0.64 = 200.64 elevation desired at point B v × 100 = slope percentage. h Measure horizontal distance Vertical distance h v Point A 2 × 4 Point B Level Measure horizontal distance h Point A elevation 200 199.84 Point B 199 Measure horizontal distance h Point A elevation 200 200.64 Point B Evannovostro/Shutterstock.com Figure 15-28. A water permeable fabric separates subsoil and aggregate materials to prevent the aggregate from settling into the subsoil. HelloRF Zcool/Shutterstock.com