The subgrade layer often represents the weakest component of a pavement system, and can significantly affect pavement response and performance under loading. Adequate characterization of subgrade properties is critical to the design and construction of long-lasting, economical pavement systems. The Mechanistic-Empirical (M-E) pavement design protocol implemented through AASHTOWare Pavement ME Design requires resilient modulus of the subgrade soil as one of the primary input parameters. However, performing repeated load triaxial tests to establish the resilient modulus properties of soils is a cumbersome task, and is rarely undertaken by state transportation agencies on a regular basis. The Idaho Transportation Department (ITD) has recently invested significant amount of time and resources to facilitate state-wide implementation of M-E pavement design practices. This study was recently undertaken to characterize typical subgrade soils in Idaho. Extensive laboratory characterization of the soils was carried out including repeated load triaxial testing for determining the resilient modulus values. Several different pavement sections were analyzed by using currently used default values and laboratory-established soil properties as subgrade layer inputs during M-E design. Default soil modulus values that are currently used, were found to be significantly higher than laboratory-established values, and therefore, resulted in the design of pavement sections that would fail considerably early into their service lives. The effect of moisture content on subgrade soil properties was also studied, and the importance of restricting soil moisture contents to the dry side of optimum was highlighted.

路基层通常代表路面系统中最薄弱的部分，并可能显着影响荷载作用下的路面响应和性能。路基特性的充分表征对于持久，经济的路面系统的设计和施工至关重要。通过AASHTOWare路面ME设计实现的机械-经验（ME）路面设计协议要求路基土的弹性模量作为主要输入参数之一。但是，进行重复的载荷三轴试验以建立土壤的弹性模量特性是一项繁琐的任务，并且很少由州运输机构定期进行。爱达荷州运输部（ITD）最近投入了大量时间和资源，以促进全州ME路面设计实践的实施。最近进行了这项研究，以表征爱达荷州的典型路基土壤。对土壤进行了广泛的实验室表征，包括重复载荷三轴试验以确定弹性模量值。在ME设计过程中，通过使用当前使用的默认值和实验室确定的土壤特性作为路基层输入，分析了几个不同的路面截面。发现当前使用的默认土壤模量值明显高于实验室确定的值，因此导致了路面部分的设计，而这些部分在其使用寿命中会相当早地失效。