(A) Supplemental information pertinent to minimum requirements governing tunneling, jacking, or augering (boring) beneath paved county roads, as outlined under G.C.R.C. Sanitary Sewer and Water Main Installation within the Limits of County Highways, Item 5.10.
(1) General comments.
(a) On roads having open roadside ditches, the leading edge of all work pits for tunneling, jacking, and augering must be not closer to the pavement edge than shoulder point or 10 feet, whichever distance is greater. On curb and gutter sections, the front wall of all pits must be at least 5 feet away from back of curb.
(b) The sheeting of pits along any road will be required if unstable soil conditions exist and undermining of the pavement appears imminent. Because of their similarity with respect to effect on highways, augering (boring) and jacking methods are treated without distinction hereinafter. In general, those requirements applying to one method likewise is applicable to the other.
(2) Tunneling requirements.
(a) Tunnels for carrier pipe shall be lined (encased) with a smooth-walled pipe consisting of reinforced concrete pipe meeting minimum ASTM designated C-76 specifications or a steel casing of at least ½ inch wall thickness.
(b) Excavation shall be conducted from inside of the liner pipe at a maximum of 18 inches ahead of the leading pipe edge in firm clay soil. If unstable soil conditions are encountered, no excavation shall be allowed ahead of the leading pipe forward edge.
(c) Excavation shall be not more than 1 inch greater than the inside diameter of the liner pipe.
(d) Pressure concrete grouting is required to fill all voids around the circumference of the liner casing. The bulkheading of the space between the casing and carrier pipe will be required for a minimum of 12 inches measured toward the road centerline from the end of the casing pipe at each end.
(e) A minimum of 2 hydraulic jacks of sufficient power shall be used to apply pushing force for the casing or carrier pipe.
(3) Augering or jacking requirements on section line roads.
(a) Augering and jacking of paved roads established by time and use as section line roads (roads situated on or near section, quarter section, or eighth section line) require the use of a steel casing liner pipe having a minimum wall thickness of 1/4 inch.
(b) When the minimum 1/4-inch casing pipe is used, the void between casing pipe and carrier pipe must be filled by pressure grouting. If a 3/8 inch or thicker wall thickness casing is used, grouting throughout the space between casing and carrier will not be required; however, bulkheading at each end will be required.
(c) The leading (advance) end of the pipe must always precede the excavating operation (augering head or other excavation in advance of pipe will not be permitted).
(4) Augering or jacking requirements on paved residential streets.
(a) All installations of less than 2.5 inches outside pipe diameter must be made by a compactor type machine or similar method without removing existing soil, if soil conditions permit.
(b) For installations of pipe between 2.5 inches and 8 inches outside diameter, open boring (augering without casing pipe) will be permitted, provided the following conditions are met:
1. The ground at the site of installation must be firm clay. If sandy or other unstable conditions exist, crossings must be made according to subsection (A)(3) herein, except grouting will only be required to bulkhead ends between casing and carrier pipe regardless of wall thickness of casing;
2. The auger head must not be more than 1 inch larger than the outside diameter of the barrel of the pipe being installed;
3. Soil conditions for open boring must be determined as suitable for open boring method. This method may be terminated as an approved road crossing at the discretion of the DPW Engineer based on apparent soil conditions at time excavation next to roadway is made; and
4. Open boring will not be permitted for the installation of bell tile or similar types of pipe with enlarged diameters in excess of the barrel diameter unless approved under supplemental permit requirement.
(B) Further details pursuant to the crossing of county roads by means of tunnels, augering, or jacking may be obtained at 211 West Oakley Street, Flint, Michigan 48503.