Oedometric and shearing response of naturally cemented sands of southern New Mexico

This research aims to characterize the mechanical behavior of naturally cemented carbonate sands typically found in arid and semiarid regions of southern United States. The cementation in these deposits is due to the deposition of calcium carbonate carried downward by percolating water under unsaturated flow conditions at shallow depths. The available references describing the distinctive features, fabric and mechanical behavior of these soils are limited due in part to the difficulty in obtaining good-quality undisturbed samples. In this project, the block sampling technique was used to preserve the sand structure and minimize the degree of disturbance. The experimental program included the determination of standard index properties, pH, calcium carbonate content, scanning electron micrograph (SEM) images, direct shear tests, and oedometric tests. Testing conditions included undisturbed specimens, moist and saturated, and reconstituted specimens.;The results indicate that the shear strength of these sands decreases as the moisture content increases. The peak shear strength of saturated specimens dropped to almost half of that of specimens with very low moisture content under the same loading conditions. Saturated undisturbed specimens did not dilate during shearing. For a given normal stress, specimens with low moisture contents (up to 9%) reached greater peak shear stresses than specimens with higher moisture contents. The lowest values of peak shear strength were obtained on saturated specimens. The reduction of shear strength with moisture was more significant in cemented sands that had some degree of plasticity compared with the non-plastic cemented sands. The contribution from cementation on the shear strength and compressibility of these natural sands was determined by testing undisturbed specimens and reconstituted specimens of the sand matrix. Oedometric tests results indicate the hydrocollapse potential of these soils. The mechanical behavior of and carbonate cemented sands is influenced by moisture content, amount and type of fines, initial void ratio of the sand matrix, occurrence of carbonate nodules and their strength, and degree and nature of the soil cementation.