(A) Rigid pipe may be broadly defined as that which does not depend on side support from trench backfill for its structural integrity (e.g., iron, steel, or concrete pipe). Rigid pipe shall be bedded with granular pipe bedding up to the horizontal centerline of the pipe. Backfill from the horizontal centerline to a level of one foot above the top of the pipe (initial backfill) shall be either of granular backfill or excavated earthen materials.
(B) Flexible pipe may be broadly defined as that which does depend on side support from trench backfill for its structural integrity (e.g., solid wall ABS, PE, PVC pipe, ABS composite pipe, or corrugated metal pipe). All flexible pipe shall be backfilled with granular pipe bedding to a level one foot above the top of the pipe (initial backfill). Clay pipe is included in this “flexible pipe” category so graded sand will be used for granular pipe bedding and granular backfill in pipe trenches when installing clay pipe.
(C) Initial backfill materials (up to a height of 12 inches above the pipe) shall be free from rocks and frozen material and shall be carefully deposited in uniform layers not exceeding six inches thick, loose measure. The filling of the trench shall be carried on simultaneously on both sides of the pipe in such a manner that damage to the pipe or injurious side pressures do not occur. The material in each layer shall be firmly compacted by ramming or tamping, to the same requirements set forth for bedding. Do not use compaction equipment directly over the pipe until sufficient backfill has been placed to ensure that such equipment will not damage or disturb the pipe.
(D) Methods for backfilling above the pipe bedding are outlined as follows.
(1) Method I. This method applies to pipes installed under yards and unimproved areas. In this method, the trench shall be backfilled with originally excavated materials in a manner which will not dislodge or damage the pipe or cause bridging action in the trench. The material shall be deposited in uniform layers not exceeding 12 inches thick, loose measure. Each layer shall be compacted by ramming or tamping or, if directed by the developer’s engineer, shall be inundated or deposited with water. If water jetting is used, it shall be considered incidental to piping installation and no additional compensation will be allowed. The top of the trench shall be left neatly rounded to allow for settlement. The top four inches shall be topsoil. Any rocks or clods greater than two inches in diameter shall be removed from the topsoil as it is spread.
(2) Method II. This method applies to all pipes installed in all alleys or parking areas which do not have permanent surfaces or oil and chip surfaces. In this method, the trench from the top of the granular pipe bedding to eight inches below the ground surface shall be backfilled with granular backfill. Then eight inches of temporary aggregate surface course, Type B, gradation CA 6 or CA 9, as specified in the Standard Specifications for Road and Bridge Construction, IDOT, shall be applied so that the finished surface of the aggregate is at the new elevation or matches the existing surface elevation. The temporary materials shall be removed as necessary during the final roadway construction.
(3) Method III. This method applies to all pipes installed beneath existing utilities or structures. In this case, the trench from the top of the granular pipe bedding to at least six inches above the existing utility or structure shall be backfilled with granular backfill. The granular material shall be deposited in uniform layers not exceeding six inches thick, loose measure, and each layer shall be compacted by ramming or tamping. The trench from six inches above the existing utility or structure to the surface shall then be backfilled in accordance with another applicable method; I; II; IV; V; or VI.
(4) Method IV. This method applies to all pipes installed in any area where the existing or new surface is portland cement concrete. In this case, the trench from the top of the granular pipe bedding to the bottom of the existing or proposed surface shall be backfilled with granular backfill.
(5) Method V. This method applies to all pipes installed beneath oil and chip driveways or streets or bituminous concrete surfaces and all other driveways or streets not covered by Method II. In this case, the trench from the top of the granular pipe bedding to 12 inches below the surface shall be backfilled with granular backfill. The top 12 inches of the trench shall be temporary aggregate surface course, Type B, CA 6 or CA 9 gradation. The temporary materials shall be removed as necessary during the final roadway construction.
(6) Method VI. This method applies to all pipes installed in cultivated fields. The backfill shall be placed as in Method I except that no excavated material shall be allowed within the upper zone originally occupied by topsoil. After the backfill reaches the approximate lower limit of the original topsoil zone, the stockpiled topsoil shall be spread in such a manner that natural settlement will not result in a depression along the sewer route. All rocks and boulders greater than two inches in diameter shall be removed from the topsoil as it is spread.
(7) Method VII. This method applies to all pipes constructed in earthen berms. From the top of the pipe bedding to 12 inches below the proposed finish grade, the trench shall be backfilled with Class A compacted select excavation materials in eight-inch layers. The top 12 inches shall be filled with topsoil.
(E) In lieu of the granular pipe backfill required by the division (D) above, Controlled Low-Strength Material (CLSM) may be used, if authorized by the developer’s engineer and the village’s Maintenance Superintendent. The CLSM shall conform to Mix 1 of the IDOT Special Provisions for CLSM, latest edition.
(F) (1) Material conforming to this specification for granular backfill shall be placed and compacted in those locations shown on the drawings. Granular backfill shall be used to fill the trench and shall be compacted by mechanical methods unless such compaction is waived by the developer’s engineer.
(2) Granular backfill for rigid pipe shall be coarse aggregate gradation CA 6, CA 9, or CA 13 as specified in the Standard Specifications for Road and Bridge Construction, IDOT. Granular backfill for flexible pipe shall be fine aggregate gradation FA 5 or FA 6 as specified in the Standard Specifications for Road and Bridge Construction, IDOT.
(3) Materials for granular backfill shall consist of washed sand, stone sand, crushed stone, pit run, or crushed gravel. Granular backfill shall be reasonably free from an excess of soft and unsound particles and other objectionable matter. Granular materials from local deposits, graded to the limits specified above, and authorized by the developer’s engineer, may be used for granular backfill. At the time of use, the granular backfill shall be free of frozen lumps and foreign materials that may have become mixed with it during handling.
(G) (1) Where water jetting is called for, all trench backfill shall be compacted by jetting and water-soaking in the manner described below. The trench compaction shall be started at the point of lowest elevation of the trench and work up along the trench. Jetting and water-soaking shall not begin until the trench has been backfilled to within six inches of the finished surface.
(2) The holes through which water is injected into the backfill shall be centered over the trench backfill and at longitudinal intervals of not more than six feet. Additional holes shall be provided if deemed necessary by the developer’s engineer to secure adequate settlement. All holes shall be jetted and shall be carried to a point one foot above the top of the pipe. Drilling the holes by means of augers or other mechanical means will not be permitted. Care shall be taken in jetting so to prevent direct contact with, or other disturbances of the pipe. No more than 100 linear feet of completed pipeline shall remain unjetted at any one time.
(3) The water shall be injected at a pressure and rate just sufficient to sink the holes at a moderate rate. After a hole has been jetted to the required depth, the water shall continue to be injected until it begins to overflow the surface. The subdivider shall bore test holes at such locations as the developer’s engineer may designate in order to determine the effectiveness of the water soaking. A soil auger shall be used for boring test holes. As soon as the jetting and water soaking has been completed, all holes shall be filled with soil and compacted. Surface depressions resulting from backfill subsidence caused by jetting and water soaking shall be filled and recompacted by tamping or rolling to the satisfaction of the developer’s engineer.
(4) Water shall be furnished at the subdivider’s expense. The subdivider shall use water only at those times designated by the village, and its use shall conform to municipal ordinances, rules, or regulations.
(H) Where there is a deficiency of suitable backfill material due to a rejection of part or all of the excavated material as unsatisfactory for backfill purposes, the contractor shall furnish satisfactory backfill material wasted from trench excavation in other locations or from other sources.
(Ord. 97-7, passed 7-1-1997, § 5.16)