By Bob and George Koerner
In light of the number of mechanically stabilized earth (MSE) wall failures with geosynthetic reinforcement—our database is currently at 144 of which 34 have excessively deformed and 110 have partially collapsed—we began a field inspectors certification program in January of this year. We feel that a qualified field inspector can possibly improve the situation by providing at least two vital services:
- giving feedback to the design engineer about questionable plan and specification details—e.g., existence of site water, lack of back drainage design, etc.
- control of the contractor during wall construction for items or practices which are improper or unsatisfactory—e.g., poor soil backfill, lack of compaction control, etc.
This new certification program parallels our existing one on geosynthetic quality assurance and quality control in that a successful candidate must have six months of appropriate field experience, be recommended by an immediate supervisor, and pass a multiple-choice examination. Details are on our website. As examples of the examination, see the following:
Q1. The acronym “MSE” refers to layers of reinforcement in the:
A. surcharge fill
B. facing system
C. retained soil zone
D. reinforced soil zone
Q2. How are “walls and berms” distinguished from “slopes”?
A. by the angle of the surcharge slope
B. by the angle of the facing
C. by the type of facing
D. by the type of soil backfill being used
Q3. The most common types of MSE wall or berm facing are:
A. masonry block and precast panel concrete
B. masonry block and welded wire
C. cast-in-place concrete and precast panel concrete
D. welded wire and timber faced
Q4. The most common type of geosynthetic reinforcement for MSE structures is:
Q5. The leveling course for a low or moderately high MSE structure is usually:
A. reinforced concrete footing
B. precast concrete slabs
C. layer of coarse aggregate
D. layer of fine grained silt or clay
Q6. Concern over the stability of drainage pipes and other utilities in the reinforced soil zone is heightened when using:
A. well-compacted granular soil
B. well-compacted fine grained soil
C. poorly compacted granular soil
D. poorly compacted fine grained soil
Q7. A typical compaction specification for compacted soil in the reinforced soil zone is:
A. 95% standard Proctor
B. 95% modified Proctor
C. 50% standard Proctor
D. 50% modified Proctor
We currently have 30 MSE wall, berm, and slope certified inspectors in the program and the interest level is strong. It appears as though the landfill berm area is the most interested in the program due to the criticality and longevity of such structures and the owner/regulatory community’s acceptance is appreciated.
Federal, state, and other public transportation agencies have been informed of the program’s existence as well. Perhaps the area most in need of the program is that of private owners and developers, which is where the vast majority of failures have occurred. This area is very broad ranging, from major shopping centers to individual homeowners. We are indeed reaching out to as many related companies, trade organizations, building societies, etc., as possible but help and contacts from readers of Geosynthetics magazine are always appreciated. Thank you in this regard.