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M9816BGE • • Caving soil materials were encountered in our test borings. It may be necessary to case the pier holes with temporary casing to prevent caving during pier construction. If drilled piers are considered as a viable foundation system for the proposed structure the owner should be aware of potential difficulties that may occur during the drilling of the pier holes. Drilling pier holes in soil materials that tend to cave may not be possible with the drill rigs locally available to Che area. Drilled pier foundations may require special considerations during the design and scheduling of construction. Difficult drilling conditions were encountered with our drill rig during our field study. We anticipate that pier drilling equipment available in the area may have difficulty drilling the formational material. It may be necessary to obtain specialty drilling equip- ment, possibly not available in western Colorado, to advance the drilled pier holes. we are available to discuss this with you. The contact between the weathered formational material and the unweathered formational material may be gradual and difficult to identify. The minimum penetration of the drilled pier into she unweathered formational material as discussed above is important for the long term performance of the pier foundation. We should be contacted to observe the pier drilling operation to verify the construction techniques used, the material encountered during the drilling operation and condition of the bottom of the drilled pier hole prior to placement of pier concrete. ~• The structural engineer should be consulted to provide structural design recommendations for the drilled piers and grade beam founda- tion system. 5.2 Spread Footings In our analysis it was necessary to assume that the material encountered in the test borings extended throughout the building site and to a depth below the maximum depth of the influence of the foundations. We should be contacted to observe the soils exposed in the foundation excavations prior to placement of foundations to verify the assumptions made during our analysis. We anticipate that the surface of the formational material may undulate which may result in a portion of the footings supported on the overlying soils and a portion of the foundation members sup- ported on the formational material. If this happens the founda- tions will perform differently between the areas supported on formational material and the areas supported on the non-formational 10 ~iambert ana ~,aoociateo CONWI.T,NO O[OT[ONNiC~I EMO~N[[q AND ~~TQOL f[[TIMO