ENGINEERING GEOLOGIC FAILURES AND COST OVERRUNS: EXAMPLES FROM MISSISSIPPI

The general surface geology of construction sites in Mississippi can be found on the 1969 state geologic map at a scale of 1:500,000, and, for many areas, on county and 7.5-minute quadrangle geologic maps at scales of 1:126,720 and 1:24,000, respectively. One measure of the value of these maps is in the added cost to engineering projects where they are not considered. Some recent examples in Mississippi include the following:

1. The supplemental cost of rock removal on the Highway 76 Bypass at Pontotoc, Mississippi, in 2003 was $1.2 million, where rock in the upper Ripley Formation was accurately mapped on the Pontotoc County geologic map.

2. Smectitic clay from weathered Glendon Limestone added such a large cost to the property bought for the new Brandon High School that there was an FBI investigation in 2004 and charges of a $5 million overpayment for the land.

3. Overly steep slopes in Miocene smectitic clays and overlying loess on Highway 61 at Cannonsburg, Mississippi, in 2004 caused a large slump and the destruction of the Keating house.

4. Overly steep slopes in the Porters Creek Clay and Yazoo Clay have caused highway and road failures across northeastern and central Mississippi. The Yazoo Clay outcrop belt across central Mississippi can be mapped by the rip-rap-supported structures along Interstate 20.

5. A leaking lake in Tishomingo State Park was built on karst limestone.