GEOTECHNICAL LESSONS FROM FAILURES
All structures that are founded on earth rely on our ability to design safe and economic foundations. Because of the natural vagaries of soils, failures do occur. Some failures have been catastrophic and have caused severe damage to lives and property; others have been insidious. Failures occur because of inadequate site and soil investigations; unforeseen soil and water conditions; natural hazards; poor engineering analysis, design, construction, and quality control; damaging postconstruction activities; and usage outside the design conditions.
When failures are investigated thoroughly, we obtain lessons and information that will guide us to prevent similar types of failure in the future. Some types of failure caused by natural hazards (earthquakes, hurricanes, etc.) are diffi cult to prevent, and our efforts must be directed toward solutions that mitigate damages to lives and properties.
One of the earliest failures that was investigated and contributed to our knowledge of soil behavior is the failure of the Transcona Grain Elevator in 1913 ). Within 24 hours after loading the grain elevator at a rate of about 1 m of grain height per day, the bin house began to tilt and settle. Fortunately, the structural damage was minimal and the bin house was later restored. No borings were done to identify the soils and to obtain information on their strength. Rather, an open pit about 4 m deep was made for the foundations and a plate was loaded to determine the bearing strength of the soil.
The information gathered from the Transcona Grain Elevator failure and the subsequent detailed soil investigation was used (Peck and Bryant, 1953; Skempton, 1951) to verify the theoretical soil bearing strength. Peck and Bryant found that the applied pressure from loads imposed by the bin house and the grains was nearly equal to the calculated maximum pressure that the soil could withstand, thereby lending support to the theory for calculating the bearing strength of soft clay soils. We also learn from this failure the importance of soil investigations, soils tests, and the effects of rate of loading.
The Transcona Grain Elevator was designed at a time when soil mechanics was not yet born. One eyewitness (White, 1953) wrote: “Soil Mechanics as a special science had hardly begun at that time. If as much had been known then as is now about the shear strength and behavior of soils, adequate borings would have been taken and tests made and these troubles would have been avoided. We owe more to the development of this science than is generally recognized.”
MARVELS OF CIVIL ENGINEERING—THE HIDDEN TRUTH:
The work that geotechnical engineers do is often invisible once construction is completed. For example, four marvelous structures—the Willis Tower (formerly called the Sears Tower, the Empire State Building , the Taj Mahal , and the Hoover Dam (Figure —grace us with their engineering and architectural beauty. However, if the foundations, which are invisible, on which these structures stand were not satisfactorily designed, then these structures would not exist. A satisfactory foundation design requires the proper application of soil mechanics principles, accumulated experience, and good judgment.
The stability and life of any structure—a building, an airport, a road, dams, levees, natural slopes power plants—depend on the stability, strength, and deformation of soils. If the soil fails, structures founded on or within it will fail or be impaired, regardless of how well these structures are designed. Thus, successful civil engineering projects are heavily dependent on geotechnical engineering.