The need for large and ultra-large sanitary sewers is growing as community populations and conveyance flow requirements increase.  Many expert studies have estimated that the sanitary sewer market will grow at a 6% compound annual growth rate (CAGR) in the coming years.  With this growth, alternative materials, such as thermoplastics, are being designed more frequently due to the corrosive sanitary sewer environment.   When discussing designing large diameter sanitary, it should first be noted that there are differences between small diameter collections systems (4" – 15") versus the large diameter world of interceptors and trunk lines (36" – 120").  Typically, the larger diameters tend to have far less directional changes and lateral connections.  Also, interceptors tend to have deeper heights-of-cover in gravity flow applications.  Many interceptors are designed to flow 50% to 70% full, with minimal slope, deep covers, and within groundwater (requiring dewatering installation).  It is also not unusual for new interceptors/trunks to be miles of pipe using several diameters.

研究热塑管规范时 工程师或愿考虑以下关注领域:水力学、水密性、深层覆盖物和连接物。我们将详细研究前二

液压学

多数机构坚持曼宁的n值0.012,这一微值基于数十年混凝土管道设计,并应当指出,有热塑性材料提供粗度系数达0.009多工程师同意这一点并将其作为安全因子使用,但仍使用0.012值模型使用。更重要的是,几乎所有热塑胶都用实验室条件下相同的液压流测试测试。重要的是工程师知道并非所有热塑胶安装并装入环压缩后都用同样的液压充电。非强制聚丙烯等粘合弹性可能引起内部墙因环短和薄内墙而卷起。内部墙卷起可提高安装曼宁的n值从0.012升至0.017或更高,向上下降40%。HDPE有几件厚内墙和钢加固HDPE高模钢用于结构性能

水密性

保持水密接头和连接对防止I&I(输入/渗透)非常重要Most of the thermoplastic manufacturers advertise watertight bells and spigots meeting the requirements of ASTM D3212.  Some have welded connections that eliminate the bell and spigot all together.  When looking at specifications, one might again consider the difference in thermoplastics from the standpoint of modulus of elasticity.  For decades, PVC materials have been a leader in the thermoplastic sanitary world due to the relative material strength versus a deep and wet environment.  Weaker plastics such as non-reinforced HDPE or polypropylene have been used less due to the issues with long-term creep.  PVC modulus is four times (4x) that of HDPE, for example, and therefore does not creep under loading.  This is important for watertight connections that might have a reinforced bell but not a reinforced spigot.  Once installed, the pipe might pass an internalized pressure test that pushes the gasket outward into the reinforced bell, but during the design life of a gravity flow system, the spigot may creep causing leaks in the long-term.  Some thermoplastics, such as steel reinforced polyethylene (SRPE), use reinforced bells and spigots to prevent this long term phenomenon from occurring.