Friction Factor TAN ?

[jagti]

What should be the Typical Friction Factor Value Modular Block wall resting over Granular Thickened Pad apparently Geo technical Engineer is asking me to use 0.35 which i think is overly conservative. My allowable friction angle for Engineered Thickened Granular Base is 36 Deg friction angle for Retained clear stone is 38 degrees Shouldn't i be using 0.67 X 36 deg=24 deg tan24:- 0.45.
If i use 0.35 Friction factor my Block Gravity wall fails in Base Sliding
He is kind of referring to Can Foundation Engineering Manual Table 24-4 page 382. Under Formed or pre-cast concrete coloum.

I want to convince him Modular Dry Cast Segmental Block falls under Mass Concrete or Masonry category in that table which relies on free draining material as backfill & base.

Help required in suggestions I am right in my approach.

 

[RFreund]

I would say neither. For modular walls we typically use NCMA's segmental wall design manual, which takes the lowest value of:

For conventional (no reinforcing grid)
1. The block sliding across the granular base:
Weight * tan(phi for granular base say 40deg) * u
where u is a reduction coeficient for the smooth block surface typically equal to 0.7.

2. The sliding of the foundation soil:
Weight * tan(foundation soil say 28deg)

For grid with reinforcing grid:
1. The granular pad sliding
Weight * tan(leveling pad say 40deg)

2. The sliding of the foundation soil:
Weight * tan(foundation soil say 28deg)

3. The sliding of the reinforced soil:
Weight * tan(reinforced soil say 34deg)

Foundation controls = 0.53



EIT

 

[jagti]

Thanks Rfreund,

What if the Engineered Granular Pad friction angle is 36 deg so would that mean the Friction factor would be Tan32 X 0.7 = 0.5 or 0.67X Tan36=0.49 or 0.5 X Tan 36=0.36.

i.e which is the appropriate value to use for Delta/ Masonry reduction factor

 

[RFreund]

If it were a gravity wall with no geogrid than I would use :

Tan(36)*0.7 for the block and pad
The u being a masonry reduction factor

I can reference the NCMA section on Monday if you'd like.

EIT