土基模量对水泥混凝土路面轮载疲劳开裂损伤的影响

基于有限元软件KENSLABS, 构建了水泥混凝土路面轮载损伤计算模型, 引入地基季节调整系数与零养护疲劳准则, 分析了土基模量整体削弱对路面疲劳开裂指数的影响, 探讨了当量轴载系数与多轴通过一次的计算次数对土基模量的依赖性, 研究了不同土基模量下板厚、水泥混凝土抗弯拉强度、单轴轴重、单轴每日重复作用次数等核心路面设计参数与路面开裂指数的关系。研究结果表明: 水泥混凝土路面疲劳开裂指数随着地基季节调整系数的减小而增大, 增大速度随地基季节调整系数的减小而加快, 当地基季节调整系数从1.0减小为0.8和从0.4减小为0.2时, 在单轴、双轴和三轴荷载作用下, 路面开裂指数分别增大了2.8、2.9、1.5倍和49.8、269.0、1 351.4倍; 当量轴载系数与多轴通过一次的重复计算次数受到板厚与土基模量的影响, 在土基模量为60 MPa, 板厚为15cm或35cm时, 单轴荷载比双轴荷载更易产生损伤, 双轴荷载比三轴荷载更易产生损伤, 在土基模量为20MPa, 板厚为15cm时也是如此, 但在土基模量为20MPa, 板厚为35cm时, 结论则与前相反; 水泥混凝土路面疲劳开裂指数随着面板厚度、水泥混凝土抗弯拉强度、单轴轴重、单轴每日重复作用次数而改变的幅度与土基模量直接相关, 当土基模量为20、60 MPa时, 面板厚度从21cm增加到25cm, 疲劳开裂指数分别减小1.18×10、1.18×10^-2, 当混凝土抗弯拉强度从4.0 MPa增大到4.4 MPa, 疲劳开裂指数分别减小1.28、2.20×10^-3, 当单轴轴重从80kN增大到160kN时, 疲劳开裂指数分别增大5.48、7.36×10^-3, 当单轴荷载每日重复作用次数从50增加到90时, 疲劳开裂指数分别增大2.05×10 -1、5.07×10^-4; 增设厚度为15cm的水泥稳定基层后, 设定工况下的路面疲劳开裂设计寿命增加3.42年; 在提高土基模量的同时, 宜优先考虑适当增加板厚, 严禁超载, 设置水泥稳定基层等措施, 可以控制水泥混凝土路面受轮载作用的疲劳开裂破坏。

Influence of subgrade modulus on fatigue cracking damage of cement concrete pavement under traffic load

Based on finite element software KENSLABS, the damage calculation model of cement concrete pavement under traffic load was established.Based on the foundation seasonal adjustment factor and the zero-maintenance fatigue criterion, the influence of overall decrease of subgrade modulus on the fatigue cracking index of pavement was analyzed, the dependence of equivalent axle load factor and number of repetitions for one passage of multiple axles on subgrade modulus was discussed, and the relationships between the cracking index of pavement and the core parameters of pavement design including slab thickness, modulus of rupture of cement concrete, uniaxial load weight, repeated times of uniaxial load in one day were studied.Analysis result indicates that when the seasonal adjustment factor of foundation decreases from 1.0 to 0.8 and from 0.4 to 0.2, the growth rates of cracking index of pavement are 2.8, 2.9, 1.5 and 49.8, 269.0, 1351.4 under the uniaxial load, biaxial load, triaxial load, respectively, so the fatigue cracking index of cement concrete pavement increases with the decrease of seasonal adjustment factor of foundation, and the smaller the seasonal adjustment factor of foundation is, the faster the increase of the fatigue cracking index is.When the subgrade modulus is 60 MPa and the thickness of slab are 15 cm or 35 cm, the uniaxial load is more destructive than the biaxial load, and the biaxial load is more destructive than the triaxial load.The same is true for 15 cm slab with a subgrade modulus of 20 MPa.But for 15 cm slab with a subgrade modulus value of 60 MPa, the order is reverse.So the equivalent axle load factor and the number of repetitions for one passage of multiple axles are affected by slab thickness and subgrade modulus.When the subgrade modui are 20 MPa and 60 MPa and the thickness of slab increases from 21 cm to 25 cm, the fatigue cracking indexes decrease by 1.18×10 and 1.18×10-2, respectively.When the modulus of rupture of cement concrete increases from 4.0 MPa to 4.4 MPa, the fatigue cracking indexes decrease by 1.28 and 2.20×10-3, respectively.When the uniaxial weight increases from 80 kN to 160 kN, the fatigue cracking indexes increases by 5.48 and 7.36×10-3, respectively.When the repeated times of uniaxial load in one day increases from 50 to 90, the fatigue cracking indexes increase by 2.05×10 -1 and 5.07×10-4, respectively.So when the fatigue cracking index of cement concrete pavement varies with slab thickness, modulus of rupture of cement concrete, uniaxial weight, repeated times of uniaxial load in one day, there is a direct relationship between its ranges and subgrade modulus.When 15 cm cement stabilized base is added, the fatigue cracking design life of pavement increases by 3.42 years under designing working condition.At the same time improving subgrade modulus, some measures including appropriately adding slab thickness, strictly forbidding overloading, setting cement stabilized base should be taken into account preferentially to control the fatigue cracking damage of cement concrete pavement under traffic load.