Search

A generalized water retention curve (WRC) model in a wide suction range considering the initial void ratio is presented in this paper. Both capillary and adsorbed water in soil pores are considered. Based on the experimental results that the adsorbed water content w a is not dependent on the initial void ratio, a new degree of saturation equation of adsorbed water is established. Meanwhile, a new degree of saturation equation of capillary water at various initial void ratios is proposed with a void ratio-related expression of the air entry value. Compared to Lu's model, only one parameter b is introduced in the established model, which can be easily calibrated using WRCs under two initial void ratios. The measured WRC results of 5 soils are used to verify the proposed model in comparison with the other 3 widely used WRC models. The soil used in the model validation covers a wide range of soil types from sandy soil to clay soil, including clayey silty sand, sandy clay till, clayey silt, expansive soil and lateritic soil. The proposed model is well verified for its ability to describe soil water retention characteristics in a wide suction range at various initial void ratios. [ABSTRACT FROM AUTHOR]

This paper presents the influence of temperature on the residual strength by analyzing shearing tests carried out in a temperature- and velocity-controlled ring shear apparatus. Temperature was applied in steps of cooling and heating ranging between 6 °C and 50 °C at a constant shearing velocity of 0.442 mm/min. Additional tests include the evaluation of the strength at 0.890 mm/min before and after the imposed temperature change. Six basic soil types characterized by different mineralogy, grain size and plasticity, as well as, mixture soils having different proportions of sand and clay, are evaluated and the results are interpreted in terms of their properties. The experimental results reveal that the temperature effect becomes relevant when fine particles and plasticity increase being negligible in the case of the sandy soil. Shear strength reacts immediately to temperature changes and a new residual strength establishes soon. The temperature effect is symmetric. An increase in temperature leads to a decrease in strength, and an equal and opposite trend is observed when temperature decreases. The magnitude of the strength variation is significant in clayey soils. For the case of high plasticity soils, the residual friction angle variation observed during cooling and heating (±50 °C) is around 2°. The strain rate effect evaluated in a smaller number of tests indicated a strain rate strengthening in all the materials tested except for the case of the sandy soil, which also was not reactive to temperature changes. The experiments are calibrated with a velocity, state, and temperature-dependent friction model. • Influence of temperature on residual shear strength have been characterized. • Heating leads to decrease in friction and cooling leads to an increase for high shearing rates. • Relevance of residual friction change with respect of temperature correlates with the soil plasticity. • No effect of temperature was measured for the clean sand tested. • The friction constitutive model developed by Chester (1994) can reproduce the tests performed. [ABSTRACT FROM AUTHOR]

Natural and man-made slope failure has been a phenomenon that has caused many deaths, destruction, and environmental damage. The use of bioengineering technique (grasses) has been widely approached for slope remediation work. However, slope failure still occurs even though it has been protected by a few grasses. Many previous findings have reported on root pull out and root tensile strength for different plant species. However, the type of soil was not taken into account. Therefore, this research was carried out to investigate the function of root mechanical properties in different types of soil. The dry and wet sieve analysis tests were performed to know the classification of the soil. In addition to that, the soil mineralogy test was also conducted to support the soil classification. Root tensile strength tests were carried out on well-grown and poorly-grown Bermuda grass toward sandy and clay soil in dry and wet conditions. The dry condition is considered the condition of Bermuda grass in hot weather, while the wet condition is the condition after the raining season. Bermuda grass was chosen since this type of grass is widely applied for slope stabilization. The site locations were chosen in Temerloh, Maran which consist of clay soil. The other locations chosen were Karak, Gambang, Kuantan, Dengkil, Batang Kali, Ulu Yam, Kuala Pilah, Gombak and Sabak Bernam consist of sandy soil. The results show that the single root of Bermuda grass has higher tensile strength in sandy soil with range values from 0.47 to 185 Mpa compared to clay soil with range values from 0.12 to 159.10 Mpa. In conclusion, the results indicate that soil is one of the factors that influence the growth of bioengineering techniques for slope reinforcement. • A bioengineering method is being used as an alternative for slope stabilization. • The soil stability will increase with time as the root grows. • The pull out force was much affected by tensile strength. • In term of tensile strength, the value decreases with increasing root diameter. • Roots have a great impact on tensile and pull out strength. [ABSTRACT FROM AUTHOR]

Rodent population dynamics and survival in semi-arid areas of Tanzania were investigated in fallow land and maize fields (land use) and two soil types (sandy loam and black clay). Capture-Mark-Release (CMR) methods with four 60 m × 60 m trapping grids, (two in maize and two in fallow mosaic fields) were used. Mastomys natalensis comprised >94% of the total captures, and the remaining six percent comprised 11 other small mammals species. The number of M. natalensis was higher in sandy loam (7.82) than in black clay (2.89) soils and higher in fallow land (40.25) than in maize fields (26.49). Highest rodent abundance was observed during the dry season (from June to August) of each year, while the lowest abundance was recorded during the wet seasons (February to April) in both habitats. A significantly different proportion of reproductively active female M. natalensis was observed in sandy loam than in black clay soils. It was observed that female M. natalensis are found to breed almost throughout the year. Survival of M. natalensis differed between dry and wet seasons and was lower in clay soils during the wet season compared to sandy soils. However, there were no significant effects with respect to interactions between soil type and land use, soil type and month, land use and month and soil type, land use and month. Management strategies should therefore, be aimed at emphasizing the importance of targeting March-May in order to interrupt reproduction and young rearing. • We found that Mastomys natalensis was the dominant rodent pest in the study area. • Highest abundance of M. natalensis was observed during the dry season and lowest in the wet season. • More reproductively active females were observed in sandy loam than in black clay soils. • Survival of M. natalensis was higher during the wet than during the dry season. • Survival of M. natalensis was higher in sandy soils than in clay soils. [ABSTRACT FROM AUTHOR]