Abstract
Construction and maintenance of roadways and irrigation canals in southeastern San Joaquin (Central) Valley of California has entailed passing through large sections of the Porterville soil series, an expansive clay soil.
The geologic development of this expansive soil, as shown in outcrops along Highway 180 near Minkler, Fresno County, appears to have been dependent upon two coincident factors of general importance: 1) volcanic eruptions of ash (with approximately andesitic composition) resulting in lahars with some size sorting due to re-deposition; and 2) groundwater with excess Ca++ ions due to percolation through basic or ultra-basic plutonic rocks.
Widespread valley areas may have potential construction problems which are largely due to the erosion and redeposition of the expansive clay of Porterville and Mt. Olive soils. A new method is presented, derived from previous studies of expansive soil, for the measurement of the soil expansion pressure and its correlation with soil moisture and density, with small expansion volume. Methods of controlling volumetric changes in such soils are discussed.
The nature of the dominant clay mineral, montmorillonite, and the identification of the other soil minerals is presented, using X-ray diffraction, infra-red spectra, and differential thermal analytical methods.
