Patti Stouter has published another earthbag technical report. It is a summary of the state of testing to date, and also covers some of the codes related to earthbag. The following information is quoted from this report.
According to the new international earthen building standards, if earthbag walls with some reinforcing have shear strength equal to or greater than reinforced adobe they can be designed for building structures even in the most risky seismic regions. Since shear strength is related to friction between courses, soil filled poly bags were tested by a simple tilt table method to discover the approximate coefficient of static friction between the bags with barbed wire. Additional tests used barbed wire and metal pins, or pins alone. The force needed to pull barbed wire out axially from between bags was also tested.
– Results from more than 20 tilt tests indicated that full, moderately firm bags have coefficients of static friction between 1.5 and 1.9, up to 3 times higher than those needed to create an unreinforced geo-cell wall.
– Higher coefficients of friction (up to 2.7) resulted from providing small metal pins with 2 points. Length of barb did not appear to affect the coefficient of friction.
– Results from two axial tension tests indicated that barbed wire does not pull out until the barbs bend. Although static friction was overcome at 60- 80 pounds force, 120 pounds was required to remove the wire completely from between two partially cured bags.
– Instead of tearing the bags, all of the embedded barbs appeared to have bent.
– Barbed wire contributes to both the friction (related to shear strength) and the tensile strength of earthbag walls.