影响路面设计因素

有几个因素影响路面设计，最重要的是车轮负载。由于路面设计采取移动荷载，缓慢移动的负荷和静态负荷可以是有害的路面。

Temperature also influences pavement design especially the frost action which is very important in cold countries.

There are many factors that affect pavement design which can be classified into four categories as

1. 交通和装载，
2. Structural models,
3. 材料表征，
4. 环境

他们将在本章详细讨论。

1.交通和加载

Traffic is the most important factor in the pavement design. The key factors include contact pressure, wheel load, axle configuration, moving loads, load, and load repetitions.

接触压力：

The tyre pressure is an important factor, as it determines the contact area and the contact pressure between the wheel and the pavement surface. Even though the shape of the contact area is elliptical, for sake of simplicity in analysis, a circular area is often considered.

Wheel Load:

下一个重要的因素是决定路面的深度轮负荷要求，以确保路基土是没有失败。轮配置影响路面内的应力分布和偏转。许多商用车具有双后轮，确保了接触压力的限度内。通常的做法是将双轮转换成等效的单轮负荷，以使分析更简单。

车桥配置：

The load carrying capacity of the commercial vehicle is further enhanced by the introduction of multiple axles.

Moving Loads:

到路面的损伤是高得多，如果车辆正以爬行速度移动。许多研究表明，当速度为2公里/小时增加到24公里/小时时，应力和偏转减少了40％。

荷载重复：

The influence of traffic on pavement not only depends on the magnitude of the wheel load, but also on the frequency of the load applications. Each load application causes some deformation and the total deformation is the summation of all these. Although the pavement deformation due to single axle load is very small, the cumulative effect of number of load repetition is significant. Therefore, modern design is based on total number of standard axle load (usually 80 kN single axle).

2.Structural Models

The structural models are various analysis approaches to determine the pavement responses (stresses, strains, and deflections) at various locations in a pavement due to the application of wheel load. The most common structural models are layered elastic model and visco-elastic models.

Layered Elastic Model:

A layered elastic model can compute stresses, strains, and deflections at any point in a pavement structure resulting from the application of a surface load. Layered elastic models assume that each pavement structural layer is homogeneous, isotropic, and linearly elastic. In other words, the material properties are same at every point in a given layer and the layer will rebound to its original form once the load is removed. The layered elastic approach works with relatively simple mathematical models that relate stress, strain, and deformation with wheel loading and material properties like modulus of elasticity and poissons ratio.

3.材料表征

The following material properties are important for both flexible and rigid pavements.

When pavements are considered as linear elastic, the elastic moduli and poisson ratio of subgrade and each component layer must be specified.

If the elastic modulus of a material varies with the time of loading, then the resilient modulus, which is elastic modulus under repeated loads, must be selected in accordance with a load duration corresponding to the vehicle speed.

当材料被认为是非线性弹性，必须提供与弹性模量的应力的状态下的本构方程。

然而，许多这些材料特性的粘弹性模型，这是非常复杂的，在开发阶段使用。这本书涵盖需要的唯一的弹性和泊松比模量层状弹性模型。

4.环境al Factors

环境al factors affect the performance of the pavement materials and cause various damages. Environmental factors that affect pavement are of two types, temperature and precipitation and they are discussed below:

Temperature:

温度对沥青路面的效果是从该混凝土路面的不同。温度影响沥青层的弹性模量，而其诱导卷曲混凝土板的。在刚性路面，由于顶部和板坯的底部的温度差，温度应力或摩擦应力的发展。

While in flexible pavement, dynamic modulus of asphaltic concrete varies with temperature. Frost heave causes differential settlements and pavement roughness. Most detrimental effect of frost penetration occurs during the spring break up period when the ice melts and subgrade is a saturated condition.

Precipitation:

雨雪降水影响地表水渗透量为路基和地下水位的深度。排水不畅可能带来的缺乏剪切强度，抽，失去支持，等等。

Author

汤姆·V马修博士（IIT孟买）