Intermediate stiffness culverts behave in a manner between that of rigid structures, where the structural stiffness dominates, and flexible culverts where the soil properties are most important. Analysis and design of intermediate stiffness culverts requires a thorough understanding of soil-structure interaction. In addition the use of recycled concrete aggregate (RCA) as a backfill material to culverts is not well studied. Here the behaviour of two fully instrumented full scale intermediate stiffness culverts, one of which was backfilled with RCA, was examined by means of a series of large scale laboratory tests, detailed in situ testing and by a series of numerical models. It was found that the RCA behaves as a competent engineering material in a manner very similar to the natural sand and gravel tested. Both materials dilate strongly on loading and exhibit strong non-linearity of stiffness. The Hardening Soil Model (HSM) constitutive relationships were found to be well suited to these materials. A combination of in situ geophysics and some measurements and modelling of locally instrumented large scale laboratory testing was required to give the necessary input parameters. Monitoring of the 6 m high arch culvert showed the structure distorted in a linear elastic manner with distortions less than 20 mm, strains induced in the structural concrete less than 700 microstrain and earth pressures close to theoretical in situ (K₀) earth pressures. No measureable movement was observed in the 300 mm thick, 3 m high box culvert. The numerical models successfully captured the behaviour of both culverts. The work demonstrates that potential savings could be made in the development of intermediate stiffness culverts, particularly in the required thickness of the soil cover and the size of the backfill zone but possibly also in the size of the structural elements.

中等刚度涵洞的行为介于刚性结构（结构刚度占主导地位）和柔性涵洞（其中土壤特性最重要）之间。中等刚度涵洞的分析和设计需要对土壤-结构相互作用有透彻的了解。此外，使用再生混凝土骨料 (RCA) 作为涵洞的回填材料还没有得到很好的研究。在这里，通过一系列大型实验室测试、详细的现场测试和一系列数值模型，对两个全仪表全尺寸中等刚度涵洞的行为进行了检查，其中一个用 RCA 回填。发现 RCA 以与测试的天然沙子和砾石非常相似的方式充当合格的工程材料。两种材料在加载时都会强烈膨胀，并表现出很强的非线性刚度。发现硬化土壤模型 (HSM) 本构关系非常适合这些材料。需要结合原位地球物理学和一些本地仪器化大规模实验室测试的测量和建模来提供必要的输入参数。对 6 m 高拱涵的监测表明，结构以线弹性方式变形，变形小于 20 mm，结构混凝土中引起的应变小于 700 微应变，土压力接近理论原位 (K 需要将原位地球物理学与一些测量和本地仪器化大规模实验室测试的建模相结合，以提供必要的输入参数。对 6 m 高拱涵的监测表明，结构以线弹性方式变形，变形小于 20 mm，结构混凝土中引起的应变小于 700 微应变，土压力接近理论原位 (K 需要结合原位地球物理学和一些本地仪器化大规模实验室测试的测量和建模来提供必要的输入参数。对 6 m 高拱涵的监测表明，结构以线弹性方式变形，变形小于 20 mm，结构混凝土中引起的应变小于 700 微应变，土压力接近理论原位 (K₀ ) 土压力。在 300 mm 厚、3 m 高的箱形涵洞中没有观察到可测量的移动。数值模型成功地捕捉到了两个涵洞的行为。这项工作表明，在开发中等刚度涵洞方面可以节省潜在的成本，特别是在所需的土壤覆盖层厚度和回填区的尺寸方面，但也可能在结构元件的尺寸方面。