路面结构新型排水系统性能及影响参数分析

路面结构中存在水分将会影响道路基层与路基土体的性能,造成土体弹性模量降低、承载能力减弱。随着时间的推移和路面车辆荷载的作用,路面结构将出现不同程度的破坏,例如开裂、车辙、坑洼、不均匀沉降等,因此需排除路面结构中存在的水分。传统的路面排水措施主要有：（1）路面侧边沟排水;（2）碎石排水基层排水;（3）采用土工织物进行排水。然而传统的排水措施仅限于在土体饱和条件下排除水分,在实际环境中道路基层与路基常常处于非饱和状态下,从而提出要在非饱和条件下排水的新技术。基于非饱和渗流理论,提出采用复合土工合成排水材料的新型路面排水系统,该系统由三部分组成,从上而下依次为水力传导层、毛细防渗层和隔离层。开展了新型路面排水系统模型试验、数值模拟以及参数分析,来研究降雨入渗条件下新型路面排水系统性能及影响参数。室内模型试验采用自制模型箱,通过控制自来水管水流速来模拟降雨,配合埋藏在土层中张力计和含水量监测仪,实时监测基层与路基中基质吸力和含水率;数值模拟建立与室内模型相同大小的数值模型,在相同降雨边界条件下监测基层与路基中基质吸力和含水率的变化规律;参数分析采用控制变量的方法,分别分析了Van Genuchte参数“a”、土工织物饱和渗透系数k_s、土工织物厚度k_t对水力传导层排水能力的影响。研究结果表明：新型路面排水系统可将入渗水快速有效排除,基层材料在试验过程始终处于非饱和状态,并在降雨停止后第10min基层的基质吸力开始回升;新型路面排水系统能够防止水下渗至路基, 降雨过程中路基土的吸力始终保持在初始吸力值;采用新型路面排水系统时,基层体积含水率在降雨过程中不断上升但未达到饱和体积含水率,路基体积含水率则保持不变;土工织物参数“a”值与饱和渗透系数对毛细屏障作用的影响较显著,随着“a”值和饱和渗透系数的增大,土工织物与土体接触面形成的毛细屏障越弱、排水越快,但当“a”值过大则无法发挥阻挡水流渗入路基的作用,结合数值结果以及其他文献研究建议“a”值取10kPa左右,饱和渗透系数取0.01~0.1m/s范围;而土工织物厚度改变对毛细屏障作用并不显著,结合实际制造工艺建议土工织物厚度取10~15mm为宜。

Analysis of Performance and Influence Parameters of New Pavement Drainage System

The existence of moisture in pavement structure will affect the performance of road base and subgrade soil, resulting in the decrease of elastic modulus and bearing capacity of soil. With the passage of time and the action of vehicle load on the pavement, the pavement structure will appear different degrees of damage, such as cracking, ruts, potholes, uneven settlement, etc., so it is necessary to remove the moisture in the pavement structure. The traditional road drainage measures are as follows :(1) road side ditch drainage;(2) gravel drainage base drainage;(3) use geotextiles for drainage. However, the traditional drainage measures are only limited to the removal of water under saturated soil conditions, and the road base and roadbed are often in unsaturated conditions in the actual environment, so a new drainage technology under unsaturated conditions is proposed. Based on the theory of unsaturated seepage, a new type of pavement drainage system based on composite geosynthetic drainage material is proposed. The model test, numerical simulation and parameter analysis of the new pavement drainage system were carried out to study the performance and influence parameters of the new pavement drainage system under rainfall infiltration conditions. In the laboratory model test, the self-made model box was used to simulate rainfall by controlling the water flow velocity of the tap pipe. In combination with the buried tension meter and moisture content monitor, the matric suction and moisture content in the base and roadbed were monitored in real time. A numerical model with the same size as the indoor model was established to monitor the variation of matric suction and moisture content in the base and subgrade under the same rainfall boundary conditions. The influence of the Van Genuchten parameter "a" value, geotextile saturation permeability coefficient k_sand geotextile thickness k_ton the drainage capacity of hydraulic conductivity layer was analyzed by using control variable method. The results showed that the new pavement drainage system could remove the infiltration water quickly and effectively, and the base material was always in the unsaturated state during the test process, and the matric suction began to pick up at 10min after the rain stopped. The new pavement drainage system can prevent water from seeping into the subgrade, and the suction of subgrade soil remains at the initial suction value during rainfall. When the new pavement drainage system is adopted, the volumetric moisture content of the base increases continuously during the rainfall but does not reach the saturated volumetric moisture content, while the volumetric moisture content of the subgrade remains unchanged. Geotextiles parameter "a" value and the saturated permeability coefficient has obvious effects on capillary barrier, with "a" value and the saturated permeability coefficient increases, geotextiles, the less contact with the soil formation of the capillary barrier, the faster the drainage, but when the "a" value is too large will not play a role of blocking water seeping into the roadbed, combining with the numerical results and other literature research suggested that "a" value take about 10 kPa, saturated permeability coefficient is 0.01 ~ 0.1 m/s scope; However, the thickness change of geotextile has no significant effect on the capillary barrier, so it is suggested that the thickness of geotextile should be 10~15mm based on the actual manufacturing process.