CHAPTER  1100.  Pipe Installation and Embedment.

 

 1101. General. This chapter discusses the installation of pipe in trenches, the use of casings, the selection and installation of appurtenances, and the use of thrust blocking.

 

 1102. Installation in Trenches.

(1)        With all pipe products, proper installation procedures are essential to successful pipe performance.  Although recommended installation procedures for pipes do no vary substantially, understanding of significant differences is important.

 

(2)        The following installation recommendations, where properly implemented, should ensure trouble‑free, long‑term performance in buried piping systems designed for most applications. See figure 11-1.

 

 1103.  Embedment Materials. Embedment materials listed here include a number of processed materials plus the soil types defined according to the Unified Soil Classification System (USCS) in ASTM D2487, Standard Method for Classification of Soils for Engineering Purposes.  (See Table 64 for description of soil classification).  These materials are grouped into five broad categories according to their suitability for this application:

 

(1)        Class I ‑‑ Angular, 1/4 to 1 1/2 inches (6 to 40 mm) graded stone, including such as coral, slag, cinders, crushed shells and crushed stone. Note - The size range and resulting high voids ratio of Class I material make it suitable for use to dewater trenches during pipe installation. This permeable characteristic dictates that its use be limited to locations where pipe support will not be lost by migration of other embedment materials into the Class I material.  When such migration is possible, the material's minimum size range should be reduced to finer than 1/4 inch (6 mm) and the gradation properly designed to limit the size of the voids.

 

(2)        Class II ‑‑ Coarse sands and gravels with maximum particle size of 1 1/2 inch (40 mm), including variously graded sands and gravels containing small percentages of fines, generally granular and non-cohesive, either wet or dry.  Soil Types GW, GP, SW and SP are included in this class. Note - Sands and gravels which are clean or borderline between clean and with fines should be included.  Coarse‑grained soils with less than 12% but more than 5% fines are neglected in ASTM D2487 and the USCS and should be included.  The gradation of Class II material influences its density and pipe support strength when loosely placed.  The gradation of Class II material influences its density and pipe support strength when loosely placed.  The gradation of Class II material may be critical to the pipe support and stability of the foundation and embedment if the material is imported and is not native to the trench excavation.  A gradation other than well graded, such as uniformly graded or gap graded, may permit loss of support by migration into void spaces of a finer grained natural material from the trench wall and bottom.

 

(3)        Class III ‑‑ Fine sand and clayey (clay filled) gravels, including fine sands, sand‑clay mixtures and gravel‑clay mixtures.  Soil Types SM, GC, SM, and SC are included in this class.

 

(4)        Class IV ‑‑ Silt, silty clays and clays, including inorganic clays and silts of not to high plasticity and liquid limits. Soil Types MH, ML, CH, and CL are included in this class.

            Note‑‑ Caution should be used in the design and selection of the degree and method of compaction for Class IV soils because of the difficulty in properly controlling the moisture content under field conditions.  Some Class IV soils with medium to high plasticity and with liquid limits greater than 50% (CH, MH, CH‑MH) exhibit reduced strength when wet and should only be used for bedding, haunching and initial backfill in arid locations where the pipe embedment will not be saturated by ground water, rainfall and/or exfiltration from the pipeline system.  Class IV soils with low to medium plasticity and with liquid limits lower than 50% (CL, ML, CL‑ML) also require careful consideration in design and installation to control moisture content but need not be restricted in use to arid locations.

 

(5)        Class V ‑‑ This class includes the organic soils OL, OH, and PT as well as soils containing frozen earth, debris, rocks larger than 1 1/2 inch (40 mm) in diameter, and other foreign materials. These materials are not recommended for bedding, haunching or initial backfill.


 

TABLE 11‑1

 

 DESCRIPTION OF EMBEDMENT MATERIAL CLASSIFICATIONS

 

SOIL CLASS

SOIL TYPE

DESCRIPTION MATERIAL CLASSIFICATION

Class I Soils *

---

Manufactured angular, granular material, 3/4 to 1 1/2 inches (6 to 40 mm) size, including materials having regional significance such as crushed stone, or rock, broken coral, crushed slag, cinders, or crushed shells.

 

 

 

Class II Soil **

GW

Well‑graded gravels and gravel‑sand mixtures, little or no fines.  50% or more retained on No. 4 sieve.   More than 95% retained on No. 200 sieve.  Clean..

 

 

 

 

GP

Poorly graded gravels and gravel‑sand mixtures, little or no fines.  50% or more retained on No. 4 sieve.  More than 95% retained on No. 200 sieve. Clean

 

 

 

 

SW

Well‑graded sands and gravely sands, little or no fines.  More than 50% passes No. 4 sieve.  More than 95% retained on No. 200 sieve.  Clean.

 

 

 

 

SP

Poorly graded sands and gravelly sand, little or no fines.  More than 50% passes No. 4 sieve.  More than 95% retained on No. 200 sieve.  Clean.

 

 

 

Class III Soil ***

GM

Silty gravels, gravel‑sand‑silt mixtures.  50% or more retained on No. 200 sieve.

 

 

 

 

GC

Clayey gravels, gravel‑sand‑clay mixtures.  50% or more retained on No. 4 sieve.  More than 50% retained on No. 200 sieve.

 

 

 

 

SM

Silty sands, sand‑silt mixtures.  More than 50% passes No. 4 sieve.  More than 50% retained on No. 200 sieve.

 

 

 

 

SC

Clayey sands, sand‑clay mixtures.  More than 50% passes No. 4 sieve.  More than 50% retained on No. 200 sieve.


 

 

 

 

Class IV Soils

ML

Inorganic silts, very fine sands, rock flour, silty or clayey fine sands.  Liquid limit 50% or less. Soils 50% or more passes No. 200 sieve.

 

 

 

 

CL

Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays.  Liquid limit 50% or less. 50% or more passes No. 200 sieve.

 

 

 

 

MH

Inorganic silts, micaceous or diatomaceous fine sands or silts, elastic silts.  Liquid limit greater than 50%.  50% or more passes No. 200 sieve.

 

 

 

 

CH

Inorganic clays of high plasticity, fat clays. Liquid limit greater than 50%.  50% or more passes No. 200 sieve.

 

 

 

Class V Soils

OL

Organic silts and organic silty clays of low plasticity.  Liquid limit 50% or less.  50% or less.  50% or more passes No. 200 sieve.

 

 

 

 

OH

Organic clays of medium to high plasticity.  Liquid limit 50% or less.  50% or more passes No. 200 sieve.

 

 

 

 

PT

Peat, muck and other highly organic soils.

*          Soils defined as Class I materials are not defined in ASTM D2487.

**        In accordance with ASTM D2487, less than 5% pass No. 200 sieve.  

***      In accordance with ASTM D2487, more than 12% pass No. 200 sieve.  Soils with 5% to 12% pass No. 200 sieve fall in borderline classification, e.g. GP‑GC.

 

 

 


TABLE 11‑3

 

APPROXIMATE GUIDE FOR ESTIMATED RANGE OF DEGREE OF COMPACTION VERSUS EMBEDMENT CLASS AND METHOD OF PLACEMENT AS PERCENT OF STANDARD PROCTOR DENSITY OR RELATIVE DENSITY *   FOR GRANULAR MATERIALS IN PARENTHESIS **

 

 

CLASS OF EMBEDMENT

I

II

III

IV

 

 

 

 

 

 

 

MATERIAL DESCRIPTION

Manufactured Granular Materials

Sands and Gravel Soils‑ Clean

Mixed‑ Grain Soils

Fine Grain Soils

 

Optimum moisture content range limit % of dry weight

 

9‑12

9‑18

6‑30

 

 

 

 

 

 

 

Soil Consolidation Method

% of Proctor (or Relative) Density Range

 

 

 

 

 

 

 

 

 

Compact by power tamper or rammer

95‑100

(75‑100)

95‑100

(80‑100)

95‑100

90‑100

 

 

 

 

 

 

 

Densify by vibrators

80‑95

80‑95

80‑95

75‑90

 

 

(60‑75)

(60‑80)

 

 

 

 

 

 

 

 

 

Consolidate by saturation

80‑95

80‑95

 

 

 

 

(60‑75)

(60‑80)

 

 

 

 

 

 

 

 

 

Hand placing

60‑80

 

 

 

 

 

(40‑60)

 

 

 

 

 

 

 

 

 

 

Hand tamping

 

60‑80

60‑80

60‑75

 

 

 

(50‑60)           

 

 

 

 

 

 

 

 

 

Dumping

60‑80

60‑80

60‑80

60‑75

 

 

(40‑60)

(50‑60)

 

 

 

 

 

 

 

 

 

*          Relative density is noted in parentheses.

**        This table serves as an approximate guide defining average Proctor densities attained through various methods of soil consolidation in different classes of soil. The table is intended to provide guidance and is not recommended for design use.  Actual design values should be developed by the engineer for specific soils at specific moisture contents.

 


 

 1104.  Installation of Pipe.

(1)        A groove shall be excavated in the bottom of the trench to receive the bottom quadrant of the pipe. Before preparing the groove, the trench bottom shall be excavated or filled and compacted to an elevation sufficiently above the grade of the pipe so that, when completed, the pipe will be true to line and grade.  Bell holes shall be excavated so only the barrel of the pipe receives bearing from the trench bottom. Large rocks (over six inches) near the surface shall be removed and the hole refilled with approved backfill.

 

            (2)        Sewer and drain pipe shall be laid upgrade.  All pipe installation shall proceed with joints closely and accurately fitted.  Gaskets shall be fitted properly in place and care shall be taken in joining the pipe units to avoid twisting of gaskets.  Joints shall be clean and dry and a joint lubricant as recommended by the pipe supplier, shall be applied uniformly to the mating joint surfaces to facilitate easy positive joint closures.

 

            (3)        In addition to the above requirements, all pipe installation shall comply to the specified requirements of the pipe manufacturer.

 

 1105. Gravel for Drain Pipe.

            (1)        Sufficient sieve analysis of soil around proposed under-drains shall be made at the expense the subdivider to enable the city engineer to determine the proper gradation for the gravel envelopes ground drain pipes.

 

            (2)        Aggregate shall be carefully placed so as to avoid serration of grain size and mixing with the site soil.  Aggregate shall not have a free fall to exceed five feet where placed to prevent segregation of aggregate.

 

 1106. Requirements for Line and Grade. All sewer pipe shall be installed accurately to the defined line and grade within the following limits.  Variance from established line and grade shall not be greater than one thirty‑second of an inch per inch of pipe diameter and not to exceed one‑half inch, provided that such variation does not result in a level or reverse sloping invert; provided also, that variation in the invert elevation between adjoining ends of pipe, due to nonconcentricity of joining surface and pipe interior surfaces, does not exceed one sixty‑fourth inch per inch of pipe diameter, or one‑half inch maximum.

 

 1107. Tests. 

            (1)        Tests for displacement shall be conducted on the installed storm drain system.  The displacement test conducted by the Engineer shall consist of the following: a light will be flashed between manholes or, if the manholes have not as yet been constructed, between the location of the manholes, by means of a flashlight or by reflecting sunlight with a mirror.  If the illuminated interior of the pipe shows broken, mis-aligned or displaced pipe, or other defects, the defects designated by the Engineer shall be remedied by the contractor.

 

            (2)        All water pipes shall be installed at a minimum of five feet below finish grade to top of pipe.

 

 1108. Haunching. The most important factor affecting pipe performance and deflection is the haunching material and its density.  Material should be placed and consolidated under the pipe haunch to provide adequate side support to the pipe while avoiding both vertical and lateral displacement of the pipe from proper alignment.  Where coarse materials with voids have been used for bedding, the same coarse material should also be used for haunching and consideration should be given to using wide trench construction.  Haunching is placed up to the pipe springline.

 

 1109. Initial Backfill. Initial backfill is that portion of the pipe embedment beginning at the springline of the pipe and some distance over the top of the pipe.

 

            Initial Backfill shall be free of large stones, frozen lumps or any material or substance that would be detrimental to the performance or the life of the pipe.

 

 1110. Placement of Initial Backfill. Placement of initial backfill shall be done in such a manner as not to damage or displace the location of the pipe nor cause any detrimental conditions to exist within the trench or pipe laying area.

 

 1111. Compaction of Initial Backfill. Compacting equipment used in consolidating initial backfill shall be limited to hand operated mechanical and vibratory devices with weight limits of 250 lbs. These units when operated by qualified construction personnel shall be capable of rendering 95% of AASHTO T‑180 compacting effort.

 

 1112. Initial Backfill ‑ Special Conditions. In trench water conditions initial backfill shall be placed only after the trench has been de‑watered and inspection of the pipe and haunching material has been performed by the Project Engineer and the City Engineer.

 

            Variable gradation of the initial backfill should be considered in these areas and shall be approved by the City Engineer prior to placement.