蒸发蒸腾作用对新型土工织物排水效率影响的试验研究

Experimental study on the effect of evaporation and transpiration action on a new geotextiles’drainage efficiency

相比于传统土工织物,新型土工织物是一种因编织了亲水尼龙织物而在非饱和环境下具有较高排水效率的新型材料,其排水效率受铺设方式、降雨、温度、相对湿度等因素影响。目前关于铺设方式、降雨对其排水效率的影响已有一定研究,但有关蒸发、蒸腾作用对排水效率的影响还缺乏系统研究。鉴于此,基于已开展的砂土自由排水和新型土工织物水平铺设(排水端延伸至空气中)下的排水试验,首先通过在砂土中设置一层不同铺设方式下的新型土工织物(排水端未延伸至空气中,无蒸发),开展排水对比试验;随后,在砂土中设置一层新型土工织物,开展排水端延伸至空气中(蒸发),排水端穿过植草土壤(蒸腾)下的排水对比试验,探究新型土工织物在蒸发、蒸腾作用下砂土湿润锋、砂土含水率(体积、质量)的变化规律。结果表明:在砂土中铺设一层新型土工织物后,虽增加了排水路径,但新型土工织物排水端未延伸至空气中,不能进行蒸发作用,加之铺设的新型土工织物上无湿度差,不能产生吸力差,水分迁移仅受重力影响,其排水效率接近砂土自由排水,反之,水分迁移将受重力和吸力双重作用,更多的水分被排出;新型土工织物蒸发作用下的排水效率是无蒸发作用下的1.25倍,蒸发作用对排水效率的影响大于铺设方式;蒸发作用相当于天然“水泵”,新型土工织物相当于排水“管道”,若排水时间足够长,新型土工织物能持续降低砂土中水分;为发挥新型土工织物最佳排水效率,须将新型土工织物排水端延伸至空气中进行蒸发作用;用于排水的材料若在非饱和环境下排水效率低,不仅不能排水,反而阻滞水分迁移,抬升地下水位,产生不利的影响;植物蒸腾和土壤蒸发作用能提高新型土工织物排水效率,但影响小于蒸发作用。研究成果可为新型土工织物的排水设计、施工提供参考。

Compared with conventional geotextiles,the new geotextile is a geomaterial woven with a hydrophilic nylon fabric that has a high drainage performance in an unsaturated environment;however,the drainage efficiency is affected by the installation method,precipitation,temperature,relative humidity,etc.Currently,certain studies have been conducted on the influence of installation method and precipitation on drainage efficiency;however,there is a lack of systematic research on the influence of evaporation and transpiration on drainage efficiency.In view of this limitation,based on the drainage test results of sand-free drainage and the new geotextile horizontal laying(drainage end extends to the air)and by setting a layer of new geotextile in the sand,the comparative drainage tests were first carried out under different laying methods(drainage end did not expose to air,so non evaporation).Second,by setting a layer of new geotextile in the sand,the comparative drainage tests were carried out between the drainage end exposed to the air(evaporation)and the drainage end passed through the grass-vegetated soil(transpiration)to explore the influence of evaporation and transpiration on the wetting front and the moisture content(volumetric and gravimetric).The results show that after installing a layer of new geotextile in the sand,although the drainage path was increased,the drainage end of the new geotextile was not exposed to air and then no evaporation occurred.In addition,there was no humidity difference on the new geotextile,and no suction difference was generated;therefore,the moisture movement was affected only by gravity,and its drainage efficiency was close to that of sand free drainage.Conversely,when the moisture movement was affected by the dual action of gravity and suction,more water would be drained out.The dewatering efficiency of the new geotextiles under the condition of evaporation was 1.25 times higher than that of the nonevaporation,and the evaporation exerted a much greater effect on dewatering than that of the installation method.Evaporation is equivalent to the natural“water pump”,and the new geotextile acts as a drainage pipe.If the dewatering time is long enough,water could be consistently reduced by this new geotextile.The drainage end of the new geotextile should be extended into the air for evaporation to maximize drainage efficiency.If the dewatering geomaterial has a low drainage performance in the unsaturated environment,it would not only fail to drain but also block water migration,leading to siltation and a rise in the water table,which would have a negative impact.Transpiration and soil evaporation increased the dewatering efficiency of the new geotextile.However,the effect was less than that of evaporation.The research results could provide a reference for the design and construction of this new geotextile.