Ventilation properties of blocky stones embankments

摘要

Blocky stones are used at slopes and in embankments as one of the measures to decrease the temperature of the embankment due to natural air convection in the construction of the Qinghai-Tibet Railway. The temperature field of a blocky stones embankment is affected directly by the size, porosity and ventilation properties of the blocky stones. Experimental results show that porosity increases with increasing block size ranges from about 42.3% for 0.04 m sized stones to 47% for 0.25 m sized blocks, moreover, the minimum porosity is that of mixed blocky stones. Experiments in a wind tunnel reveal that the wind pressure gradient in blocky stones has a nonlinear behaviour with the wind velocity, directly proportional to the square of the wind velocity. Our results also show that the resistance coefficient decreases with increasing stone size, and for mixed blocky stones the coefficient is the medium. Considering the prevailing wind velocities ( ≥3 m s~(-1)) on the Qinghai-Tibet plateau the airflow velocity through the blocky stones embankment of Qinghai-Tibet Railway is discussed in the paper. Our experiments and calculated results confirm that blocky stones layers have good ventilation ability. Thus it can be concluded that under the prevailing wind velocities of ≥ 3 m s~(-1) the forced air convection inside the blocky stones layer has a strong influence on the temperature field within and below the embankment and should be taken into account when calculating the temperature field.