Native soil Parameters

The table below has been copied from USBR and indicates native trench wall material properties. The link is give in the previous blog.

Material Type 1: Based on SPT, Cone Penetrometer Test (CPT), or in-place field density tests, the trench wall material has an E′n ≥ 2500. Minimum clearance between the pipe and the trench is all that is required.

Material Type 2: Based on SPT, CPT, or in-place field density tests, the trench wall material has an E′n ≥ 500 < 2500. The trench width will vary depending on the deflection requirements and the ratio of the stiffness between the embedment material and the trench wall material.

Material Type 3: When the trench walls are extremely soft (E′n < 500) and provide minimal pipe support.

When Material Type 3 soil conditions are identified prior to construction, design methods can be used to avoid a five pipe diameter wide trench. These methods are:
1. Specify only rigid pipe on an improved foundation.
 2. Increase the pipe stiffness factor (EI/r3 ) by increasing the wall thickness or increasing the thickness of mortar coatings, or both. Note: The haunch area still requires compaction.
3. Encase the pipe in reinforced concrete.
4. Completely remove Material Type 3 and replace with a suitable compacted material to a calculated trench width that will prevent excessive deflection.

E'n values can also be taken from the following:

Embedment Material Parameters

 we have copied below the table 5 from USBRs publication ' Methiod of Prediction of Flexible Pipe  Deflection' with the following link

https://www.usbr.gov/tsc/techreferences/mands/mands-pdfs/m-25report(pipedeflection)_rev08-05-15.pdf

Each E′ value in tables 5 and 6 is a typical value (i.e., for each category of soil type and classification, about one-half of the measured deflections were higher, and about one-half were lower, than the deflection predicted using the E′ value shown. To reduce the possibility that the actual deflection will exceed the predicted value, a design factor, Fd, is used.

Time-Lag Factor, Tf The time-lag factor, Tf, is used to calculate the increase in deflection of a flexible pipe with time. A flexible pipe continues to deflect over time for two reasons: Method for Prediction of Flexible Pipe Deflection  1. Increase in the soil load on the pipe. 2. Consolidation of the soil at the sides of the pipe. Table 5 gives values of Tf for use in the Reclamation Equation. The values are the ratio of long-term deflection to the initial deflection. The initial deflection is the deflection on the day the backfill was completed. For calculating initial deflections, a Tf value of 1.0 should be used