The study aims to investigate the effects of three different construction and demolition materials (CDMs), including crushed waste asphalt (CWA), crushed waste bricks (CWB), and crushed waste concrete (CWC), on some geotechnical properties of low plastic clayey soil, particularly, the undrained shear strength (Su) and the hydraulic conductivity (k). A set of experimental tests were performed on clayey soil and on clayey soil-CDM mixtures at mixing ratios of 5%, 10%, 15%, and 20% by dry weight. The results show that the soil plasticity decreases as the CDMs increase. Quantitatively, it is found a maximum of 12%, 6%, and 6% decrease in the liquid limits (LL) and a maximum of 9%, 4%, and 6% decrease in the plasticity limit (PI) of the mixtures with 20% of CWA, CWB, and CWC, respectively. The results of the Su estimated empirically from the fall cone tests show that the Su decreases as the CDMs increase. The Su reduces by approximately 10% and 2% of the mixtures with 20% CWA and CWB, respectively. But the Su is not affected by the CWC additive for water content lower than approximately 35%. The k value increases as the CDMs increase. The results show that the reported k value increases by 75%, 79%, and 247% of the mixtures with 20% of CWA, CWB, and CWC, respectively. Additionally, the k values obtained from the consolidation test confirm the findings of the effect of the CDMs on the coefficient of hydraulic conductivity.
In-flight cone penetration tests (CPTs) have been conducted extensively to characterize centrifuge models of dry and saturated soils, but only a limited number of studies have focused on unsaturated soils. This paper presents centrifuge modeling of CPTs conducted on unsaturated clayey sand models prepared at various hydraulic conditions including as-compacted, wetting (rainfall) and drying (evaporation). The objectives of this study were to evaluate effects of stress level induced by centrifuge acceleration and to investigate the impact of hydraulic processes on the cone tip resistance (qc). Results shows that variations of qc with depth obtained from different centrifugal acceleration are in very good agreement and similarity of qc and water content distribution in centrifuge models is validated. In addition, it was found that matric suction has greater impact on the qc than total vertical stress. The CPTs performed on clayey sand show that the cone tip resistance increases as the degree of saturation decreases under different hydraulic conditions. A correlation between the cone tip resistance and degree of saturation is applicable to both wetting and drying processes. The CPT results and in-flight water content measurements provide a good indication of strength and stiffness change in unsaturated soil subject to changes in hydraulic conditions.
A commercial heat dissipation sensor was modified and tested for use in centrifuge modeling applications. This sensor can be used to directly measure water content that is used to estimate matric suction in soil. Advantages of the modified sensor include significant reduction in size and capability of measuring water content in a short period of time. The measured water content can be used to evaluate the corresponding soil matric suction. A series of experimental tests were conducted to establish the testing protocol to achieve the optimal RT for the modified sensor. A relationship between soil water content and temperature change measured from the heat dissipation sensor was generated for different soil types. The corresponding matric suction at a given water content was evaluated with soil water characteristic curves. Results were validated with results measured from a conventional tensiometer for static (no flow) and transient flow conditions. Good agreement was found, and the modified sensor provided similar results to those obtained with the tensiometer. The sensor was successfully implemented and tested in a geotechnical centrifuge under different g-levels. This study provides an alternative method for measuring water content that can be used in centrifuge modeling as well as other laboratory testing applications.
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