LAWN RANGER INC

Site Review of 5-2-11,  Prepared by Bill Martin, PE, Vice President of Chandler Materials, Tulsa for Jim Butcher residence at 4262 E 78th St, Tulsa, 918-269-7708 : 5-4-11 This is my second visit to this backyard retaining wall project. The first visit was at the request of the homeowner last fall, after an upper terrace wall failed for the second time. At that time, I met the contractor, Rick Mcilwain of Lawn Ranger for the first time. We have not provided Versa-Lok units to this contractor before or since this project was installed, to the knowledge of our office staff. Lawn Ranger built this job to about 50% completion with no technical knowledge of the product, according to Rick Mclwain. He believed that a wall did not need geogrid until above the 4 foot elevation, rather than from the base to near the top of a tall wall. He had asked for none of our tech notes or our installation DVD. He did not ask for any help in design in advance, which is always available. He did not get a building permit from the City of Tulsa, required for walls more than 4 feet high. The contractor was finished in October of 2010. The reason for his tall walls to fail was evident during my first visit. The homeowner has many photos of construction to refer to for forensic analysis. This wall had no geogrid. It was taken down and rebuilt with geogrid after my visit, however with no proof that it was done correctly. The soil above and behind this wall has sunk about 6 inches plus, which indicates the soil behind was not compacted in 6/1 lifts with a vibrating plate from the bottom to the top. If the soil was improperly compacted, it would have been at best about 85% proctor density, rather than 95% required, which would indicate the shrinkage of the soil we are viewing. Fortunately, the homeowner has taken many photos during construction, so a forensic analysis is easier. The homeowner has no construction experience in this type of installation, so his photo efforts allow others to evaluate. Geogrid installation shows no effort to properly use filter fabric between the soil and the drain rock behind the wall. As a result, the type of imported backfill chosen has infiltrated the drain rock, leaving no drain capabilities behind the wall. The wall batter is supposed to be 7 degrees. Measurements taken along the tall upper wall shows 2 degrees to 4 degrees. This does not imply failure is approaching, but does imply the wall is moving to take the slack out of the geogrid, which was not stretched and pinned before placement of backfill with a vibrating plate. A vibrating plate was used in the backfill in the grid zone. Whether or not it was used in 6/1 lifts to reach 95% plus standard proctor density is unknown. Soil settlement is obvious in each location behind the walls and at the steps. That fact points to improper compaction.-  Steps/Landing/Ramp condition - - Installation photos show that un-compacted soil backfill was used at steps. Large volumes of un-compacted fill means there should be voids of several inches underneath the step installations. The voids should increase with time as the soil slowly settles. Rains will wash this soil away without the use of filter fabric and drain rock. This leakage of soil is visible in the step areas. All fill below steps should have been crusher run placed in 6" lifts with the vibrating plate. Improper cap adhesive is causing caps to loosen around step areas. The problem is aggravated by settlement of the entire soil mass. The contractor placed 1 to 2 inches of asphalt in the new ramp area. That is not adequate, and problems are now visible. Four inches of asphalt is considered satisfactory in the paving industry. At one location on the East side of the new retaining wall, large voids are appearing where the very thin asphalt is eroding away, and wall failure could occur due to improper use of extremely sandy, silty soil as a base. This soil is likely to have ongoing erosion due to asphalt voids. Summary: Without proper compaction and the separation of soil from drain rock with filter fabric, the system is undergoing failure. The steps and landing are currently completely failed, requiring disassembly with reconstruction with a crusher run foundation (no soil of this type allowed). Filter fabric and drainage behind the walls must be used also. The wall stability is questionable, and they should be considered marginal for years to come. Geogrid was definitely used in some areas, but not likely in others. This is not a signed, sealed engineering document for use in litigation. Instead, it is information derived from 23 years of continual experience with retaining wall construction. The owner's photos should be considered as excellent forensic evidence. The outstanding wall designer in our region who appears as a court witness is Scott A. Miller, P E, of N. Little Rock, Ar., at 501-374-3546. He is a Geotechnical Engineer whose entire career revolves around structural analysis of tall walls.   Bill Martin, P E,  918-855-9485 cell Chandler Materials Company, Tulsa