Deep Trunk Sewer Excavation Methods

if i understand the question, you need to shore up the walls to prevent the sides from caving in. the method will depend on soil conditions and personal saftey. will you have men in the ditch for example. i doubt if you need sheet piling. i've seen concrete forms used to shore up the walls. of course you will need heavy bracing running from wall to wall. it would be best to hire an engineer. he can tell you the correct procedure and the engineer will assume the liablity

Open cut requires Shoring, you can not have one without the other. Sloping the trench open cut method is not practical at that depth.

Some context would be helpfull

Hooooookay, so you want to place a sewer trunk line 10m deep, of unspecified material, of unspecified length, at an unspecified location, of an unspecified capacity, in unspecified soil conditions, etc.

Well, first of all, 10m is almost 33 feet deep, which is a serious trench...

Driving sheet piling that deep can be a rather challenging, depending on the nature of the subsurface material, and that's if the material isn't very sandy, and seasonal groundwater levels don't affect the excavation.

Let's just simplistically say that such a vertical-walled trench would be required to be 1m wide. Then, the trench would require the removal of 10m-deep x 1m-wide x 1 m-thick amount of earth, which would be 10m3 to be removed for each linear meter of trench. That adds up fast.

For comparisons' sake, let's similarly say that the soil is such that it requires side-slopes of 1-to-1. Then the excavation would look like an inverted trapeziod sitting on a 1m side, be 10m high, and 21m wide at it's top. This would be 110 m3 per linear meter of trench. That adds up eleven times as fast as the vertical wall trench discussed above...

This collectively suggests that you follow the advice of ccoop610 in regards to "drilling or jacking or directional drilling", or even out-right tunneling.

However, sheet piling and open-trenching will probably have to be done to some extent as well.

Sewer lines have to start from somewhere with a connection to an existing sewer line, or other structure. This will probably require an area to be boxed-out to full-depth, with sheet piles, at least, in order to start said trunk line. Such a box-out area would probally have be big enough to hold the drilling machinery and crew to work 10m below surface grade.

Also, sewer lines might well have to have manholes and/or pumping stations every 50 to 400 meters along it's full length. These would also probably require similar boxed-out areas.

While this sort of work is not (rocket-surgery), it still has characteristic intrinsic complexities of it's own that should be fully taken into consideration.

At some point in such an effort, I would hope that a thorough geotechnical engineers' report, among others, would clarify some of the choices to carefully considered.

A design-build contract with bid-item alternatives for 2,3, or more methods, or combinations of methods, is strongly suggested. Fully qualified experience and capability is well worth paying for, if you get a minimum of three bids, for starters.

Let the engineers do the engineering, and the bidding process do the budgeting...