Cities across the US have adopted strategies for protecting tree roots close to or within the CRZ (critical root zone) during construction. The gold standard for trenching is the use of an aerating tool such as an Air Spade, which effectively penetrates and dislodges most types of soil, but is harmless to non-porous objects such as plant roots, buried pipes, or cables.
The Air Spade produces a stream of supersonic air moving at Mach 2, that first locates the roots and then works in conjunction with the backhoe to excavate carefully around tree roots. According to Chuck and Danny Lippi, ISA Board Certified Master Arborists, the process does not take much additional time once the backhoe operator understands the importance of preserving the tree roots.
For more information on preserving tree roots during trenching, and to see photos of projects where this method has been used, click here.