On the atypical strength anisotropy of weakly cemented sandstones

An atypical strength anisotropy manifesting itself in a monotone decrease in strength with decreasing angle between the maximum compressive stresses and the bedding plane was found in several series of independent tests of Cenomanian sandstone samples on a true triaxial loading facility. In the case of anisotropy of this type, an equal component stress field in the rock mass can cause breakouts on well walls in two opposite directions. Such breakouts were observed in direct physical modeling in samples with holes under the action of equal component compression. In an analysis of logging measurements, such breakouts in wells are usually interpreted as caused by the presence of an unequal component stress field in the rock mass. The presented data indicate the possibility of other interpretations.