Who Designed the Ill-Fated St. Francis Dam?

Abstract

INTRODUCTION

BASE-TO-HEIGHT RATIO

Figure 1. Left pane shows the original maximum section through the St Francis Dam, made in July 1923. Middle pane shows the as-built drawing released by BWWS after the failure, showing a flared toe, up to 175 ft wide at elevation 1625. The right pane ...

Figure 2. Daily record of reservoir elevations between March 1, 1926 and March 13, 1928. Note the reservoir was not filled to capacity until March 2, 1928, 10 days before the failure (Committee Report for the State, 1928).

PAUCITY OF FOUNDATION EXPLORATION

FOUNDATION EXCAVATIONS AND KEYWAYS

ALLOWANCE FOR UPLIFT RELIEF

Figure 3. Plan of the dam dated November 1924, with the locations of the 10 test holes that were converted to uplift relief wells, split into rows of three shallow and seven deeper holes (LADWP).

GROUTING OF TRANSVERSE SHRINKAGE CRACKS

Figure 5. Stepped downstream face of the St. Francis Dam, as viewed looking upstream. Four prominent shrinkage cracks developed, shown in the lower diagram. These were caulked with oakum on the downstream face and grouted in early 1928 (author’s colle...

Figure 6. Upturned base of block #7, from the crest of the dam’s left abutment. The open fissure is transverse shrinkage crack #4, shown in the lower half of Figure 1 (Mayberry et al., 1928).

Figure 7. Plugging of the dam’s contraction joints on the downstream face could have had disastrous consequences by creating full reservoir pressure against the interior faces of the main dam, especially if the grouting behind the face was anything le...

Figure 8. Example of the “stress diagrams” described by Edgar Bayley, taken from Masonry Dam Design, 2nd Edition by Morrison & Brodie (1916). This shows a maximum compressive stress of 20 tons per square foot (tsf) along the ‘Line of Pressure-Reservoi...

CONCLUSIONS

REFERENCES