Thanks everybody for the replies. I guess a more direct question would be what formula does everybody use to calculate the grouted soil anchors capacity? I have numerous references, and each one does it slightly different. I have the PTI manual, the FHWA Circular #4 and the California Shoring and Trenching manual. Do you typically take into account the weight of the soil over the anchor similar to helical anchors..or do you get your miniumum of 15' of cover and then just base it on bond strength of the soil/grout interface? Again any help would be greatly appreciated. Thanks in advance.
Grouted anchors are not designed like helical anchors. If you maintain the minimum cover over the anchor bond length, you can use the grout/soil bond strengths.
PEinc...thanks for the info. Do you take the minimum cover to the center of the bond length so you have an average cover over the bond length or to the begining of the bond length so that your whole anchor has at least the minimum cover. Thanks again for all your help.
Also one more question...do you use the 15' for a minimum cover as recommended by PTI in their Rock and Soil Anchor manual or do you use a different value. Thanks again.
I usually try to maintain about 12 to 15 feet of overburden above the beginning of the bond length. This usually is not a problem because most tieback anchors are installed at about 6 to 9 feet below the top of the sheeting wall. Then, at an angle of 15 to 45 degrees below horizontal, you will usually have enough cover. The important thing to conside is the grouting pressure if the anchor is shallow. You don't want to heave the ground surface. If you don't heave the ground and if the anchors test OK, then you must have enough cover.
The British Standard BS 8081-1989 "Soil and Rock Anchors" is an excellent reference. Your query on cover is explained and the standard has a good bibliography.
Good Luck
