This document is the 101 Trench Installation (N-12 per AASHTO) Detail. Pipe detail, charts and notes provide descriptions and measurements.

The detail shows the minimum cover to rigid pavement, final backfill, minimum cover to flexible pavement, initial backfill, springline, haunch, bedding, suitable foundation and minimum trench width. Recommended minimum cover based on vehicle loading condition chart is included.

A chart with values for recommended minimum trench widths based on pipe diameter is shown. A 2nd chart for maximum recommended cover is based on vehicle loading conditions uses pipe diameter determined by Class I compacted/dumped, Class II and Class III measurements.

Note 1 states that all pipe systems shall be installed in accordance with ASTM D2321. Note 2 says that measures should be taken to prevent migration of native fines into backfill material. Note 3 explains that the foundation is based on where the trench bottom is unstable. Per the engineer, the trench bottom may be stabilized using a geotextile material. Note 4 is about bedding and suitable material, minimum bedding thickness shall be 4” for 4”-24” or 6” for 30”-60”. Note 5 clarifies that the initial backfill should be of suitable material in the pipe zone extending to the crown of pipe. Note 6 states that minimum cover for non-traffic applications is 12” from the top of pipe to ground surface. Additional cover may be required to prevent flotation. For traffic applications, minimum cover is 12” up to 48” diameter pipe and 24” of cover for 60” diameter pipe, measured from top of pipe to bottom of flexible pavement or to top of rigid pavement. For traffic applications with less than 4 feet of cover, embedment of the pipe shall be using only a Class I or Class II backfill.