Disturbing bedding of existing RCP

[oengineer]

I am working on a project were we are having to provide a foundation for a proposed manhole which has an existing RCP going through it (see image):

My concern is the width of the bedding for the existing RCP. With the foundations encroaching upon the foundation bedding, what is the acceptable bedding width to be maintained for the existing RCP?

The foundation will still need to be able to support the manhole above it. Assume a 48" dia Wall C (wall thickness 5.75") existing RCP.

The following image is from the Design Data 9 - Standard Installations and Bedding Factors for the Indirect Design Method:

Comments/suggestion are appreciated.

 

[oengineer]

Is the "D[sub]o[/sub]/3" sufficient for the existing RCP bedding width or does a greater width need to be maintained?

 

[GC_Hopi]

To clarify, what is preventing you from temporary supporting the pipe and installing the manhole in a standard fashion? This is a typical method for the manhole over an existing pipe.

 

[oengineer]

I have been told that the pipe is old/delicate and that they would prefer to leave the existing pipe in place while building a foundation for the manhole.

 

[GC_Hopi]

The standard detail above is for leaving the existing pipe in place. The practice is to let the pipe span the excavation (provide temporary support as needed) and place the base slab under the existing pipe then install the doghouse section of the manhole. IMHO if the level of concern over the pipe integrity is so high that you can not temporarily support it then it probably means the pipe should be replaced.