Development of load and resistance factor design method for shallow foundations

In shallow foundation design, the key improvement offered by Load and Resistance Factor Design (LRFD) over the traditional Allowable Stress Design (ASD) is the ability to provide a more consistent level of reliability. For LRFD to gain acceptance in geotechnical engineering, a framework for the objective assessment of resistance factors is needed. Such a framework is proposed in this thesis. In order for LRFD to fulfill its promise for designs with more consistent reliability, the methods used to execute a design must be consistent with the methods assumed in the development of the LRFD factors. A methodology for the estimation of soil parameters for use in design equations is proposed that should allow for more consistent uncertainty in design inputs. The cone penetration test (CPT) is used to illustrate a method to estimate soil parameters in a statistically consistent manner. Resistance factors for ultimate bearing capacity are computed using reliability analysis for shallow footings both in sand and in clay and are presented for use with both ASCE-7 load factors and AASHTO (1998) load factors. Also, a method to adjust resistance factors to account for code-specified load factors is presented