【摘要】 采用块石路堤、护坡有利于冻土地区路基的稳定性 .基于气温波动条件下块石内部的温度波动幅度按指数规律衰减 ,介绍了块石的热扩散系数和导热系数测量方法 .实验中 ,采用封闭的块石试样筒 ,通过顶板温度波动的控制来模拟气温的周期性变化 ,整个试样筒用绝热性能良好的海棉包扎 ,使其侧向、底板绝热 .对粒径为 6～ 8cm ,4～ 6cm ,2～ 4cm的 3种块石试样进行了具体测量 ,由曲线拟合所得的结果具有较好的一致性 .分析显示粒径较小的块石其热扩散系数和导热系数也较小更多还原

【Abstract】 The ballast embankment and revetment is one of the main measures of construction that is helpful to the heat stability of a roadbed in cold region. Usually, the embankment and revetment ballast is a porous media. Determining the thermal diffusivity and conductivity is necessary in engineering practice for the ballast. Because the grain size of the ballast rock is larger, direct determination of thermal diffusivity and conductivity is very difficult. A determination of thermal diffusivity and conductivity on the ballast was introduced for the temperature amplitude exponentially decaying with depth of the ballast during air temperature cyclic fluctuations on its surface. A plexiglass cylinder with an inside diameter of 15 cm and a height of 59 cm was used in experiment. A dry compressed soil layer with a depth of about 4 cm was laid on the underlayer of the cylinder; ballast with a given grain size was compacted via vibration. There is spare space, approximately 5 cm high, at the upper part of the cylinder to set the top plate, which can control periodic fluctuations of temperature. By cyclic change of temperature of the top plate, cyclic fluctuations of air temperature may be simulated. The whole sample cylinder was wrapped up by a layer of 10 cm thick sponge to have good insulated characteristic, so as to be lateral and bottom insulated. The sample cylinder of the ballast rock on the tight test system was used in experiment. The sample cylinder was placed in the insulated cabinet of freezing thawing test apparatus. The tank temperature was constant and about equal to the mean value of the cyclic fluctuating temperature in top plate. Twenty two thermistors, which have been calibrated exactly, were located at the lateral along the sample height to measure the temperature change with time in the porous ballast, to determine the exponential decay of the temperature amplitudes with depth. Thus the thermal diffusivity and conductivity of the ballast sample can be obtained by regression analysis. A programmable electronic adjuster and a cooling unit in conjunction with a band heater regulate the temperature of the cooling liquid in the top plate, in order to make the periodic fluctuation of the top plate temperature according to a pre determined change. All measurements are fed automatically into a data acquisition system, which is connected to a computer. Specially, the temperature- fluctuation cycle of the top plate is 12 hours. Data were saved into the computer automatically every 10 minutes. The tested ballast specimens of embankment and revetment have three various particle sizes, i.e., 6～8 cm, 4～6 cm and 2～4 cm. Their porosities are 44.7%, 45.9% and 47.0%, respectively. There are six runs of test with various cycle numbers of the cyclic fluctuations of the top plate, ranging from 6 to 20 cycles. Under different temperature fluctuation condition with the temperature amplitudes of approximately 11.4 ℃, 19.8 ℃, 20.0 ℃ and 19.9 ℃, and with the mean temperatures of approximately 0.0 ℃, 0.0 ℃, -0.2 ℃ and -0.5 ℃, respectively, the thermal diffusivity and conductivity of the ballast with the grain size of 6～8 cm, are obtained. Curve fitting shows fairly consistency, i.e., approximately 0.00137 m 2·h -1 and 0.448 W·(m·K) -1 . For the porous ballast samples with grain sizes of 6～8 cm, 4～6 cm and 2～4 cm, the analysis indicates that the thermal diffusivity and conductivity of the ballast decreases with reducing the grain sizes. Therefore, the cylindrical porous ballast specimen on the tight test system can be used to determine fairly the thermal diffusivity and conductivity under a cyclic fluctuating temperature of the top plate更多还原