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M98169GE • • We recommend that each structure be supported entirely on only one foundation type. Combining foundation types will result in differential and unpredictable foundation performance between the varying foundation types. All of the design parameters presented below are based on techniques performed by an experienced contractor, high quality craftsmanship, care during construction and poet construction cognizance of the potential soil volume change hazard, with appropriate post construction maintenance. The spread footing recommendations include recommended design and construction tech- niques to reduce the influence of volume changes of soil materials supporting the foundation but should not be interpreted as solu- tions for completely mitigating the potential for movement from volume changes of soil material supporting footings. 5.1 Drilled Piers Drilled piers or caissons that are drilled into the unweathered formational material may be used to support the proposed structure. The piers should be drilled into the formational material a dis- tance equal to at least t~•~o (2) pier diameters, or ten (10) Eeet, whichever is deeper. The piers should be designed as end bearing piers using a formational material bearing capacity of 30,000 pounds per square foot and a aide friction of 3,000 pounds per square foot for the portion of the pier in the unweathered formati- onal material. The drilled piers should be designed with a minimum dead load of 2,000 pounds per square foot. There are differing theories on the use of aide shear as part of the load carrying assessment of drilled pier foundation systems. One theory is that mobilization of the drilled pier is required to generate the aide shear soil strength values. This mobilization would require the movement of the bottom of the pier which may not be a desirable characteristic. Another theory is that the support materials will develop static frictional forces in contact with the materials along the surface of the pier. It is our opinion that sufficient movement of the piers to mobi- lize skin friction for bearing support may result in undesirable performance of the pier in the form of settlement. We suggest consideration to the amount of settlement tolerable to the struc- ture be included in your assessment if akin friction is used in your design as part of the bearing support of the drilled pier. When using skin friction for bearing support or resisting uplift we suggest that you discount the upper portion of the pier 8 ~iambert ana ~,ooociateo CONWI.TiNO OLOT[CNNN:~I INO,MlL113 •NO IMil~El TESTING