Kenneth D. Walsh

Evaluation of Changes to Soil Suction Resulting from Residential Development

When new development occurs in arid regions, the boundary conditions and in particular the amount of water applied to the soil is usually changed. This change in the boundary condition at the surface can induce a change in the soil suction profile. In the case where the soils underlying structures exhibit volume change in response to a change in soil suction, a change in the soil suction can in turn induce volume change in the soil. As a consequence, the degree (amount by which the suction changes) and extent (depth over which a change occurs) of soil suction change are of interest to designers developing recommendations for many aspects of new construction, including grading, floor and foundation support, and landscaping. A series of suction measurements are reported for samples recovered from over 30 sites in the Denver metropolitan area where single-family residential structures have been in-place between 7 and 62 years. Samples were obtained to depths of approximately 12 meters. A companion set of results are presented for sites at which no development has yet occurred. In general, comparison of these results suggests that residential development affects the underlying soil suction profile in complex ways. In several cases, no effect can be observed. In most, suction decreased in the upper 3 to 7 meters, and in a few cases deeper wetting was suggested. The depth of suction decrease did not correlate to the age of the structure. However, operating characteristics, in particular landscaping choices and watering policies, have a significant influence over the degree and extent of suction changes.

State of the Practice for Design of Groups of Laterally Loaded Drilled Shafts

Many state departments of transportation (DOTs) are beginning to use a larger percentage of drilled shafts for their deep foundations. Therefore, a clear understanding of current design methodology and specifications is important. The three most common design methods in use today are the group reduction factor, the p-multiplier method, and the modulus of subgrade reaction multiplier. A brief discussion of each method is presented. Telephone interviews were conducted with state DOTs to determine their current design procedure for groups of laterally loaded drilled shafts. Responses were obtained from all 50 states. Additional interviews were conducted with several well-known researchers in the field of deep foundations to determine what procedure they recommend. From these interviews it was clear that there is no uniformity in design methods or even in interpretation of the AASHTO recommendations for laterally loaded drilled shaft groups. The different interpretations of the AASHTO recommendations may be due to wording used in the AASHTO specifications, namely, the “ratio of lateral resistance of shaft in group to single shaft.” It is somewhat unclear as to whether this wording refers to the single-pile capacity or to the soil resistance. To understand the intended method of application of these factors, a historical search of the literature was conducted. It is clear that the source cited in the AASHTO specifications recommended using the reduction factors to reduce the modulus of subgrade reaction.

Meeting the computer competency expectations of the construction industry

A Microcomputer Applications in Construction course was developed to provide computer literacy for undergraduate construction students. The course topics and the results of construction industry computer literacy expectations research are presented. A critical issue was the question of the extent to which multimedia application development should be included in the course. It is recommended that there be continuous monitoring of computer courses and adaptation to change.