**Minnesota Construction Specification 46---Tile Drains**

**1. SCOPE**

The work shall consist of furnishing and installing drain tile and
necessary fittings and appurtenances.

**2. MATERIALS**

Unless otherwise specified, the drain tile and fittings shall conform to
the requirements of Material Specification 543 or Material Specification
544, whichever is applicable.

**3. EXCAVATION**

Unless otherwise specified, excavation for and subsequent installation
of each tile line shall begin at the outlet end and progress upstream.

The trench or excavation for the tile shall be constructed to the depths
and cross sections shown on the drawings. The trench width may be
increased above the top of the tile, at the option of the contractor.

Trench shields, shoring and bracing, or other methods, necessary to
safeguard the workmen and work, and to prevent damage to the existing
improvements, shall be furnished, placed, and subsequently removed by
the contractor.

**4. PREPARING THE TILE BED**

In stable soils the tile shall be firmly and uniformly bedded throughout
its entire length to the specified depth and in the specified manner.

If the bottom of the trench does not provide a sufficiently stable or
firm foundation for the drain tile, cradles for the tile (constructed of
timber or fabricated lumber of a cleat-and-rail type construction), a
sand-gravel mix or other approved materials shall be used to stabilize
the bottom of the trench.

Drain tile shall not be laid on rock foundation. In the event that
boulders, rocks or ledge rock or cemented materials that prevent
satisfactory bedding are encountered at the required grade, the trench
shall be excavated to a depth of at least 6 inches below grade and
backfilled to grade with a sand-gravel mixture or other approved
material. The bedding material shall be compacted and shaped to grade.

**5. LAYING TILE AND JOINT COVERING**

Gaps between tile ordinarily shall be from 1/8 inch to 1/4 inch in clay,
clay loam, and cohesive soil. Tile is laid without gaps in sandy soils
and on lines to convey water with no intention of providing drainage.

Where tile is laid with the width of opening exceeding the limits stated
above in non-cohesive silts, and in fine and medium sands, the joint
shall be covered with a permanent type material such as coal tar pitch
treated roofing paper, fiber glass sheet or mat, or plastic sheeting.

For tile installations on a curve alignment, the outside tile gap shall
be covered with tile bats (broken tile) or covered as described above
when the gap exceeds the recommended gap for the type of soil
encountered. To maintain the gap within the allowable range, the inside
pipe lip may be chipped and fitted to secure the required joint opening.

The ends and inside surfaces of all tile shall be kept clean during
laying. All earth or other extraneous material in the tile shall be
removed before laying the next tile. At the end of each day\'s work and
when laying has been temporarily suspended, the inlet end shall be
blocked so that earth or other extraneous materials will not enter the
tile. The upper end of each tile line shall be blocked with permanent
type materials on completion of the line.

**6. CONNECTIONS**

Lateral connections will be made with manufactured junctions comparable
in strength with the specified tile unless otherwise specified.

Where existing tile lines not shown on the drawings are crossed, they
shall be bridged across the new trench or they shall be connected into
the new tile lines, as directed by the engineer.

**7. BLINDING OR FILTER MATERIAL**

As soon as the tiles are placed satisfactorily, they shall be blinded by
covering with friable soil material to a minimum depth of 6 inches.
Material used for blinding shall not be frozen and, unless otherwise
specified in section 9 of this specification, shall contain no rocks or
stones that when dropped may cause tile damage. Sandy and other
noncohesive soil shall not be used for blinding unless the joints are
covered. All tile placed during any day shall be blinded at the
completion of the work activities that day.

Blinding the joints is not required if the tile is backfilled with a
sand and gravel filter as shown in Figures 4-6b and 4-6c below, or
covered with a filter fabric.

![](media/image1.png){width="4.7in" height="3.623611111111111in"}

Figure 4-6b. Tubing Encased in Sand and Gravel Envelope Designed as a
Filter

Figure 4-6c. Tubing Encased in Sand and Gravel Envelope Designed as a
Filter with an Impermeable sheet such as Plastic

**8. BACKFILLING**

The backfilling of the trench shall be completed as rapidly as
consistent with the soil conditions.

Automatic backfilling machines may be used only when approved by the
engineer. Backfill shall extend above the ground surface and be well
rounded over the trench.

Unless otherwise specified, where drain tile are laid under roads,
through terraces, and at other designated locations shown on the
drawings, the backfill shall be placed in successive layers of not more
than 6 inches, and each layer shall be tamped before the next layer is
placed. The density of the compacted backfill shall not be less than the
density of the surrounding adjacent earth material unless otherwise
specified in section 9 of this specification.

**9. CONSTRUCTION DETAILS**