The k sub 0 stepped blade measures lateral pressures in situ in clay, silt, and sand soils. Pressures are measured after penetrationof the soil by progressively thicker steps of a thin blade, and data points identified as representing consoldating behavior of the soil are extrapolated to obtain a hypothetical pressure on a zero-thickness blade. Pressures are measured with teflon-covered pneumatic pressure cells designed to give 1-1 calibrations and ease of field repair. A new back-pressured readout system gives data reproducible to the nearest gauge dial increment, 1 psi (7 kpa). Most applications involve defining the soil stress history by measuring and plotting lateral stress versus depth. In nonexpansive soils the amount of prior surcharge may be estimated and the consolidation state established. Lateral stresses were used to delineate influences from compaction, expansive clays, adjacent shallow foundation loading, and interactions with pile and with retaining walls. For example, the lateral pressure on an existing wall was measured to test for pressures from expansive clay, relevant to the existing factor of safety. Passive pressures may indicate expansive clays or may warn of imminent bearing capacity failure per a cited example. Tests cannot be performed in stony soils, owing to difficulty in pushing the blade and the risk of damaging the pressure cells, nor can lateral stresses be measured invery soft clays where pressures from insertion of the blade exceed the limit pressure, which is probably attributable to the development of excess pore water pressure. This paper appears in transportation research record no. 1278, Dynamic testing of aggregates and soils and lateral stress measurements 1990.
Abstract