The Weak Links in the Wastewater Collection System: Manholes and Access Devices. Antonio V Almeida, PE CMOM 2014 Austin Texas August 19, 2014

Transcription

1 The Weak Links in the Wastewater Collection System: Manholes and Access Devices Antonio V Almeida, PE CMOM 2014 Austin Texas August 19, 2014

2 Agenda Manhole Design The Manhole Paradigm past, present & future Leakage Location Corrosion Structural Access Chambers Questions

3 The Manhole Design Technical Guidance? 100 years old 1914 (747) (50) pages VoL II (548) pages ASCE MOP #60 WEF # FD , 1935, 1962, 1982, 2007 (415) (9) Pages ASCE manual of practice # (74) pages

4 Wastewater Manhole Design: WEF Manual of Practice No. FD-5, ASCE MOP No.60 (415pages, Provide convenient 9 pages to manholes) access to the sewer for observation and maintenance The operations. functional design objective sewer. of wastewater collection manholes, structure. is fourfold: Cause a minimum of interference with hydraulics of the Be strong enough to support applied loads. Be a durable and generally watertight Provide convenient access to the sewer for observation and maintenance operations. Cause a minimum of interference with hydraulics of the sewer. (2 pages) Be a durable and generally watertight structure. Be strong enough to support applied loads.

5 Wastewater Manhole Design Paradigm Manhole Paradigm Shift Do you perceive that this manhole is watertight? How? Do you know when this manhole may not be watertight? Do we know the amount that this manhole leaks? Is location an issue? Does it matter?

6 Wastewater Manhole Regulatory Location Requirement (TCEQ) Chapter (j) Manholes and Related Structures Requires that a manhole must not be located In the low path of a water course, or In an area where ponding of surface water is probable.

7 Wastewater Manhole Regulatory Location Requirement (TCEQ) Chapter (j) Manholes and Related Structures New Proposed Regulatory Wording A manhole must not be located in a stream bed or where inundation may occur.

8 Wastewater Manhole Paradigm

9 Wastewater Manhole Paradigm

10 Wastewater Manhole Paradigm

11 Wastewater Manhole Design Manhole subjected to ground water above invert (A manhole must not be located in a stream bed or where inundation may occur)

12 Wastewater Manhole Leak Resistant Design Pipe connections Material Science Wall and joints Corbel Area Cover & Frame Frame seals Grade Rings Base Types

13 Wastewater Manhole Design Leak prevention- Materials Traditional (Difficult to achieve leak prevention goal) Brick Block Concrete precast or cast in place Newer Materials (Improve leak prevention goal) Fiberglass Reinforced Plastic (FRP) High Density Polyethylene (HDPE) Polymer concrete PVC

14 Wastewater Manhole Material Paradigm

15 Wastewater Manhole Paradigm Affiliated with the Cretex Companies, Inc., Cretex Specialty Products Gasketed Pipes Non-Gasketed Pipes Arch Pipe Elliptical Pipe Manhole adjusting rings Box Culvert, Single Cell Manholes, Sanitary Manholes Internal mechanical chimney seals External manhole chimney seals Applied manhole chimney seals Manhole adjusting rings Internal manhole barrel joint seals Internal pipe joint seals External joint wrap

16 Wastewater Manhole Design Newer Materials Lack of Industry Acceptance Buoyancy fears Perceived structural weakness Concrete ASTM C 478 HDPE ASTM F1759

17 Wastewater Manhole Design Newer Materials Lack of Industry Acceptance Inexperience issues & Change is Difficult Backfill and compaction requirements Layup procedures (FRP) Connection flexibility Fusion welding (HDPE) Grade adjustments

18 Wastewater Manhole Paradigm The Future of Manhole Material

19 Wastewater Manhole Design Leak Prevention Frame, and Cover Frame and cover originally not intended to be water tight New frame and covers offer machined surfaces with gasket seals that require bolts

20 Wastewater Manhole Design Leak Prevention Frame and Grade Ring Seals Frame and grade rings seals Challenge to meet leak prevention goal Not intended to be water tight Normally not easy to detect Many products in the market place

21 Wastewater Manhole Design Leak Prevention Frame Seal and Grade Rings The three functions of the frame seal and grade rings interface are. Difficult to achieve long term Support applied loads Absorb vibration & temperature movement Provide leak prevention

22 Wastewater Manhole Design Leak Prevention Frame Seal and Grade Rings

23 Wastewater Manhole Design Leak prevention-pipe-wall connections ASTM C923: 10 psig watertight sealing at 7 o axial deflection. 13psig watertight sealing in straight alignment

24 Wastewater Manhole Paradigm Leak prevention - Pipe-Wall Connections

25 Wastewater Manhole Design Leak Prevention-Wall Joints ASTM C 478 Steel reinforcement not required in the joint Joints are designed for axial compression Therefore testing for shear or load not required

26 Wastewater Manhole Design Manhole Types Cylindrical manholes barrel bottom Manhole Types Tangential manholes tee up

27 Wastewater Manhole Design Manhole Type Cylindrical Barrel bottom

28 Wastewater Manhole Design Manhole Type Tangential Tee up

29 Wastewater Manhole Regulatory Leakage Requirement (TCEQ) Chapter Testing Requirements for Manholes Requires that a new manhole must pass a leakage test Hydrostatic Test Allowable leakage of gallons per foot diameter per foot of manhole depth per hour Vacuum Test - common use A 2.0 minute long test holding a vacuum of 9.0 inches of mercury

30 Wastewater Manhole Regulatory Leakage Requirement (TCEQ) Chapter (j) Manholes and Related Structures New proposed regulatory wording for vacuum testing manholes Section (c) - If a manhole fails a vacuum test, grout must be applied to the exterior of the excavated manhole and the manhole must be retested in accordance with the requirements of this section.

31 Wastewater Manhole Design Venting Venting occurred at manhole covers with holes Venting will occur regardless Lack of design understanding in venting sewer gas Inhabited areas Need access for maintenance Reduce odor nuisance

32 Wastewater Manhole Design Corrosion

33 Wastewater Manhole Design Corrosion Resistance Coating and Liners Surface Preparation Cementations products Micro silica Alumina calcium Admixtures Thermoplastic Liners Polyethylene PVC Polypropylene Material selection Thermoset liners Cured in place Panel Inserts Lay up systems Polymers Epoxies Urethanes Urea's Composite Systems Application limitations Testing and inspection Performance expectations not realized

34 Wastewater Manhole Design Coating and liner failures

35 Wastewater Manhole Design Corrosion

36 Wastewater Manhole Paradigm Corrosion

37 Wastewater Manhole Regulatory Access Issues (TCEQ) Chapter (l) Manholes and Related Structures - (1A) manhole covers A manhole where personnel entry is anticipated requires At least a 30-inch diameter clear opening.

38 Wastewater Access Access Paradigm Issues A new paradigm in the making Current User response to this regulatory access issue Require all new manholes to be at least a 30-inch diameter clear opening or Continued with standard manhole lids in the system and restrict personnel entry.

39 Wastewater Access Access Paradigm Issues Paradigm Shift Questions? What is the benefit of providing personnel entry in manholes? Especially to pipe system that do not allow personnel access?

40 Wastewater Manhole Paradigm Wastewater Access Chambers In 1990, the introduction of the Wastewater Access Chamber (WAC) in Dallas, Texas,

41 Wastewater Manhole Design Wastewater Access Chambers

42 Wastewater Manhole Design Wastewater Access Chambers OSHA-confined space entry requirements TCEQ now 30- inch manhole covers April 1986 Dallas Correct use Improve access for cleaning and maintenance Less cost

43 Wastewater Manhole Paradigm Paradigm Shift-Need For Change Giant step to the perfect manhole/access chamber FRP HDPE polymer concrete Use of Portland cement based manholes with protective coatings internal and external seals rubber gasket joints flexible pipe connectors Continuous repairs to prevent extraneous inflow to manholes corrosion Change Change is the law of life and those that look to the past or present are certain to miss the future by JFK

44 Wastewater Manhole Paradigm Questions