Town of Exeter – Standard Construction Details (Manholes, Sewers, Trenches, Roadways)

What are the intended performance criteria for a Typical Manhole (Standard Detail #4)?

The complete precast manhole assembly must provide adequate space, strength, and leak-proof service for more than 25 years, withstand 8 tons (H-20 loading), and have an allowable leakage of less than 1 gallon day per foot of vertical height for the life of the structure.

What are the material and component requirements for a Typical Manhole (Standard Detail #4)?

Manhole barrels and cone sections must be precast and reinforced. All precast sections (barrels, cones, bases) must meet ASTM C478. A flexible joint is required within $48$ inches of the structure, and manhole steps are not permitted.

Describe the invert and shelf construction for a Typical Manhole (Standard Detail #4).

The invert and shelf construction for a manhole must be brick-paved and sized to the sewer pipe. Inverts are laid on long-radius curves tangent to pipe center-lines, and the shelf elevation should equal the highest pipe crown, with its slope draining to the channel.

What are the specifications for the frame and cover of a Typical Manhole (Standard Detail #4)?

The main characteristics for a manhole frame and cover include being heavy-duty, having a clear opening of 30 inches, and cover lettering with 3 inch-high characters stating "SEWER" or "DRAIN."

What are the bedding material requirements for a Typical Manhole (Standard Detail #4)?

For a Typical Manhole, the bedding material (ASTM C33 gradation) should be gravel or crushed stone free of clay, loam, or organics.

What are the specifications for drop support concrete in a Typical Manhole (Standard Detail #4)?

Drop support concrete for manholes must be Class A, 3000 psi, with cement at 6.0 bags per square yd, water at 5.75 gal per bag , and a maximum aggregate size of 1 inch.

What is unique about shallow manholes (less than 6 ft depth) in Standard Detail #4?

For shallow manholes (less than 6 ft depth), a reinforced concrete slab cover with an eccentric opening rated for H-20 loading should be used.

What is the minimum pipe size for a Typical House Sewer (Standard Detail #5)?

The minimum house service diameter for a Typical House Sewer (Standard Detail #5) is 4 inches.

List approved pipe and joint materials for a Typical House Sewer (Standard Detail #5).

Approved pipe and joint materials for house sewers include PVC (ASTM D2729) and Cast-iron pipe (ANSI A21 series: A21.1, 4, 6, 8, 10; joints with ANSI A21.11 gaskets). Ductile iron (ANSI A21.50, A21.51) can also be used with joints per cast-iron specifications.

What are the joint requirements for a Typical House Sewer (Standard Detail #5)?

Joints for house sewers must depend on neoprene or elastomeric gaskets for a watertight seal, and transitions between dissimilar pipes require manufactured adapters.

How should tee/wye connections be made in a Typical House Sewer (Standard Detail #5), and what practices are prohibited?

For tee/wye connections in house sewers, factory tee/wye fittings should be used. If not present, saddles with bolts, clamps, or epoxy (per manufacturer instructions) are permitted. Prohibited methods include hammer taps, stuffing cloth, mortar smears, or other crude improvisations.

Outline the installation practices for a Typical House Sewer (Standard Detail #5).

Installation practices for house sewers require handling, placing, and jointing per manufacturer guides. Bedding needs 4 inches of crushed stone/gravel (ASTM C33) below the pipe, and backfill must be carefully tamped to 12 inches above the pipe crown.

What are the accepted methods for leakage testing a Typical House Sewer (Standard Detail #5)?

Leakage testing for house sewers (prior to backfill) can be done via three options:

• Option A: Observation-tee, inflatable plug, fill to $5$ ft head.
• Option B: Hose pipe & trench, simulate wet trench; inspect through clean-out.
• Option C: Fluorescent dye in wet trench; inspect next downstream manhole.
  Any observed leak requires removal and relaying of the pipe.

What types of connections are considered illegal for a Typical House Sewer (Standard Detail #5)?

Illegal connections to a house sewer include roof leaders, footing drains, sump pumps, rain water, and ground water.

Describe the requirements for water service proximity and bedding for a Typical House Sewer (Standard Detail #5).

For water service proximity to a house sewer, a separate trench is preferred. If shared, the water line must be above and offset per drawing. Bedding gradation for house sewers is the same as the manhole specification (ASTM C33-67), and stabilization (if ordered) uses stone 1.5 inches – 0.5 inches.

What location records are required for a Typical House Sewer (Standard Detail #5)?

For location records of a house sewer, tee/wye coordinates must be filed in municipal records, along with a ferrous "chimney" locator rod.

What happens if unsuitable sub-grade is excavated in a Typical Trench Section (Standard Detail #6)?

If unsuitable sub-grade is ordered excavated in a Typical Trench Section (Standard Detail #6), it must be refilled with bedding material.

Describe the bedding material requirements for a Typical Trench Section (Standard Detail #6).

Bedding material for a Typical Trench Section (Standard Detail #6) is screened gravel/crushed stone (ASTM C33 #67) with identical gradation limits as manholes. If engineer-ordered stabilization is required, stone measuring 1.5 inches – 0.5 inches is used.

What are the specifications for the sand blanket in a Typical Trench Section (Standard Detail #6)?

A sand blanket in a trench section should consist of clean sand with 90-100% passing a 0.5 inch sieve and less than 15% passing a #200 sieve. It may be omitted for cast-iron, ductile-iron, or reinforced-concrete pipe if no stone larger than 2 inches contacts the pipe.

What constitutes suitable backfill for roadways and cross-country areas in a Typical Trench Section (Standard Detail #6)?

Suitable backfill for roadways in a Typical Trench Section (Standard Detail #6) includes native excavation, excluding debris, pavement, organics, topsoil, wet/soft muck, peat, clay, and unsuitable ledge. For cross-country, the same exclusions apply, though the engineer may allow organic soils if stability and access are assured.

What standard applies to the base course in a Typical Trench Section (Standard Detail #6)?

If ordered, the base course in a Typical Trench Section (Standard Detail #6) must meet Division 300 of NHDOT Standard Specs.

What are the cut-off requirements for wood sheeting in a Typical Trench Section (Standard Detail #6)?

For wood sheeting in a trench section, if sheet piles extend below the pipe mid-diameter, they should be cut off at least 1 ft above the crown. If permanent sheeting is ordered, it should be cut at least 3 ft below finish grade, yet at least 1 ft above the pipe.

How is the maximum trench width ($W$) determined in a Typical Trench Section (Standard Detail #6)?

The maximum trench width (measured 12 inches above the crown) for pipes less than or equal to 15 inch diameter is 36 inches. For pipes greater than 15 inch diameter, 24 inches + outside diameter. This width controls the pay width for ledge and ordered over-excavation.

Describe the mounding requirement for cross-country backfill in a Typical Trench Section (Standard Detail #6).

Cross-country backfill in a trench section should be mounded 6 inches above the original grade.

What are the water–sewer separation rules (NHDES) for a Typical Trench Section (Standard Detail #6)?

NHDES requires a 10 ft horizontal separation between water and sewer lines. If the water line is at least 18 inches above and at least 3 ft lateral from the sewer, it is acceptable. Otherwise, the sewer must be installed in ductile-iron for 10 ft on either side of the crossing, or lines must be relocated to achieve separation.

What information does the Allowable Leakage – Water Mains table (Detail #7) provide and how is it used?

The Allowable Leakage – Water Mains table provides maximum permissible leakage in gallons per hour per 1000 ft for combined pipe diameters 3–54 inches at test pressures 100–450 psi (approximately 7–31 bar). To convert to Liters per hour, multiply by 3.785 . If a pipeline has mixed diameters, the total allowable leakage is the sum for each segment size.

According to Detail #7, what is the maximum permissible leakage for a 10 inch water main at 200 psi test pressure?

For a 10 inch diameter water main at 200 psi test pressure, the maximum permissible leakage is 1.06 gallons 1000 ft

Describe the cross-section elements of a Typical Curbed Roadway (Standard Detail #8 – Sheet A).

A Typical Curbed Roadway (Standard Detail #8 – Sheet A) includes elements such as Cape Cod or granite curb, 3 inches of Type "B" base pavement + 1 inch of Type "E" top pavement for the roadway, and 1.5 inches Type "B" base + 1 inch Type "E" top for sidewalks. The asphalt pavement depth is 4 inches, with a minimum 12 inch gravel base and a 6 inch crushed gravel layer. It has a longitudinal slope of 1/4 inch ft (approx 2%), with minimum shoulder/sidewalk widths showing a curb offset of 5 ft for typical and 6 ft for Cape Cod curbs.

What are the general geometry and design notes for Typical Curbed Roadway alternatives (Standard Detail #8 – Sheet B)?

Standard Detail #8 (Sheet B) shows numerous roadway/sidewalk/guard-rail configurations with slopes varying from 1.6% to 16%. Typical utility strips are 5 ft wide, guard-rail faces align with the curb, and slopes outside rails can be 6:1, 4:1, 3:1, or 2:1. Design notes include providing a minimum 10 ft panel for snow storage adjacent to the curb on multilane sections, a minimum 4 ft grass strip ahead of all sidewalks, and flexible dimensions to suit field conditions. Normal curb reveal is 7 inches for barrier curb at sidewalks, tapering from 0 to 7 inches in 8 ft, and urban islands have a slope curb tapering from 0 to 6 inches in 8 ft.

Outline the sequence for a Typical Concrete Pavement Patch (Standard Detail #9).

The sequence for a Typical Concrete Pavement Patch (Standard Detail #9) involves:

1. Saw-cutting straight edges around the excavation and removing damaged pavement after backfill & compaction.

2. Placing a 3000 psi concrete slab (thickness per design) with reinforcement.

3. After concrete sets, installing a 3 inch base course of Type "B" bituminous concrete.

4. Upon Highway Superintendent inspection, placing a 1 inch wearing course of Type "A."

5. Applying asphalt emulsion sealant around the perimeter, overlapping onto the base course, and broadcasting light sand to absorb excess.
   The Highway Superintendent may modify this procedure.

What are the common gradation limits (ASTM C33) used for manholes, sewers, and trenches?

The Common Gradation Table (ASTM C33) specifies the following percent passing limits for materials used in Manholes, Sewers, and Trenches:

• 100% through 1 inch screen

• 90–100% through 3/4 inch screen

• 20–55% through 3/8 inch screen

• 0–10% through #4 sieve

• 0–5% through #8 sieve.

What are the practical, ethical, and safety implications of these standard construction details?

Key practical, ethical, and safety implications of these standard details include:

• Long-term watertight integrity to minimize groundwater infiltration/exfiltration, protecting public health and reducing treatment costs.
• Strict prohibition of makeshift connections (hammer taps, cloth stuffing) to uphold workmanship quality and prevent environmental contamination.
• Mandated records (tee/wye location with ferrous marker) to ensure future maintenance and avoid utility conflicts.
• Water–sewer separation rules to safeguard potable water from cross-contamination.
• Testing protocols (hydrostatic head, dye) demonstrating a commitment to verify performance before concealment, reflecting an ethical duty of care.

How do these standard details connect to broader engineering and design principles?

These standard details connect to broader principles by:

• Following AWWA/ASTM/ANSI standards, illustrating the hierarchy from federal/state codes to town details.
• Using H-20 loading, which aligns with AASHTO highway bridge design loads.
• Employing bedding and backfill gradations that echo soil mechanics principles (granular support, drainage, avoidance of migration/fines).
• Featuring a leakage table that embodies continuity equation and hydraulic gradient concepts, showing allowable exfiltration proportional to pressure and circumference.