Moisture-induced tensile strength and cohesion in sand

Direct tension and low-stress level direct shear apparatuses and experimental procedures were developed to determine strength properties for moist sand. An extensive experimental program on quartz sand was carried out to examine the variation in tensile strength and cohesion as a function of moisture (water) content, relative density, presence of fines, and level of precompression (overconsolidation). Based on the experimental data, a simple theory and analysis technique was developed.; Results of the direct tension experiments provided the following important findings. Tensile strength increases with increasing moisture content, fines, and precompression level, and this trend is more noticeable with increasing relative densities. However, the influences of relative density and fines on the tensile strength very much depend on the moisture content. These effects are reduced at low water content levels (w < 0.5%). The precompression effects also depend on the moisture content as well as the duration of the precompression time. Tensile strength keeps increasing below the water contents of 15% (S = 0.6), and after this point the strength decreases. The theoretical tensile strength model predicts well the experimental data at low water content levels (w < 4%), but as the moisture content increases, the discrepancy between the measured and predicted data is detected. Simple engineering models that can predict tensile strength are developed.; Results of the direct shear experiments which were conducted to study the relationship between apparent cohesion and tensile strength also presented the following important facts. The apparent cohesion in the range of 0.21 kPa due to interlocking between particles is observed in dry sand at low normal stress levels (σ_n < 1 kPa). The additional apparent cohesion component due to capillary forces is also observed in moist specimens with water contents of 0.5% and 1.0%. The apparent cohesion and angle of internal friction of moist specimens are higher than those of dry specimens, and these increase with increasing water content. The relationship between the tensile strength and apparent cohesion at low moisture contents and stress levels was proposed.