Ret. Wall Geotextile reinforement re: Das ex. problem

[cgrisier]

Hi all,

I have a question regarding Example Problem 8.5 in Das' Principles of Foundation Engineering (5th ed.)

In solving for Sv (vertical spacing of the geotextile reinforcement), the author calculates the required spacing at various depths as follows:

D=8 ft, Sv=33.6 in

D=12 ft, Sv=22 in

D=16 ft, Sv=16.8 in

However in his recommendations directly following the solutions are stated as:

D=0 to 8 ft, Sv=20 in

D>8 ft, Sv= 16 in

I do not see the correlation between the solved values and the suggested values considering at D=8 ft, the solved value was 33.6 in versus the 16 in recommended value.

Appreciate any insight someone might have on this.

 

[alwaysbored]

The values for Sv (vertical spacing) are grouped into two areas in the solution. Depths from 0 to 8 feet and depths from 8 to 16 ft for the 16 ft wall. Calcs were made at 8 ft, 12 ft, and 16 ft, results give needed Sv of 33.6 in, 22 in, and 16.8 in, respectively.

Estimates were made such that too much/too little spacing would not be shown for 0 to 8 ft and 8 to 16 ft (stability/cost savings). Clearly a spacing of 20 inches (closer than what is needed at 12 ft) will be sufficient for 0 to 8 ft (noting that spacings decrease with depth). In the same sense, spacing of 16 inches is the requirement at full depth of 16 ft (and would be fine above).

You could use, say 24 inches (0 to 8 ft) and 16 inches (8 to 16 ft) and still be satisfactory. You could divide the wall into say 4 sections (even distribution) if you would like and then give needed Sv for each of the four sections.

The goal is to be conservative (but not overly so) and to make the wall constructable.