Trenchless Technology

SEP 2018

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76 T R E N C H L E S S T EC H N O LO GY S E P T E M B E R 2018 N A S S C O R E P O R T : M A N H O L E R E H A B I L I T A T I O N C O M M I T T E E TRENCHLESS SEWER rehabilita- tion techniques offer many methods to correct deicient sanitary sewers. Generally, rehabilitation is divided into the piping system and manhole structures. Defects in manholes are typically classiied into two groups – structural failures or operation and maintenance (O&M) issues. Structural problems include such things as miss- ing bricks, exposed wire mesh, and bench /invert problems. O&M issues occur when foreign objects such as roots, debris, deposits, iniltration, inlow and encrustations are present. With so many issues to ix , coupled with an ever-expanding variety of products to ix them, it can get con- fusing. So, in an attempt to clarify, the products and procedures for manhole rehabilitation have been categorized below into four main groups. Cementitious Lining The irst and most commonly used system is cementitious lining. Ce- mentitious material is typically spray applied, spin cast or hand troweled to achieve a consistent lining thickness. Portland cement-based products are either used alone or with admixtures to aid in corrosion resistance. Calcium Aluminate and Geopolymer use simi- lar application techniques and provide enhanced performance. Cementitious lining is generally considered to be the least dificult to apply and can also be one of the least expensive. However, some applications may have a shorter life expectancy than other options. Polymers Polymers are applied using the same techniques as cementitious but typi- cally require a much drier, cleaner sur- face to ensure proper adhesion to the substrate. They are used for corrosion protection and to eliminate infiltration. Polymers are extremely fast setting and can be applied in thin coats, high build thick coats, and as a multi-layer com- posite systems. Polymers are more ex- pensive than cementitious but tend to last longer and provide excellent protec- tion against hydrogen sulfide and other types of chemical corrosion. Inserts Inserts and other options include fiberglass, precast and poured in place concrete which can all provide a full structure restoration to a severely de- teriorated manhole. Inserts are basi- cally freestanding barrel sections that are installed inside a manhole a‹er the existing casting and cone sections are removed. The manhole invert, cone and casting are then rebuilt or replaced, and all connections are made waterproof. Inserts can be made from fiberglass, polymer concrete or a variety of plastics. Poured-in-place concrete is achieved by making a form two to three inches in- side of the deteriorated manhole wall and placing concrete in this form. This newly formed concrete manhole is of- ten combined with a coating. CIPM Cured-in-place manhole (CIPM) lin- ers are fabric/felt liners saturated with a thermosetting resin and provide sig- niicant structural rehabilitation in addition to I/I removal and corrosion protection. The liners are custom fabri- cated, typically saturated onsite, placed in the structure, expanded against all surfaces, and cured under pressure. There are four types of resin systems available for use in a CIPM: polyester, vinyl ester, silicate, and epoxy. Each of the four solutions have positive attributes, and the selec- tion should be speciic to the unique characteristic of the manhole to be rehabilitated. Regardless of which so - lution is selected, the preparation of the manhole structure wall prior to rehabilitation is one of the most im- portant requirements. If lining /coating failure occurs, it can usually be traced back to improper sur- face preparation. Surface preparation is more of a concern with the cementi- tious and polymer products but still important for inserts and CIPM. Adher- ing to the manufacturer 's requirements along with quality cra‹manship is vital to the success of manhole rehabilita- tion. Proper specifications along with trained and knowledgeable inspection sta" will help ensure an acceptable finished product. Various testing pro- cedures such as visual, thickness, adhe- sion, material, holiday (spark), vacuum, and/or dye testing are recommended. Additionally, the interior of a man- hole structure must be resistant to varying levels of erosion, iniltra- tion, hydrogen sulide corrosion, and other corrosive chemicals. Not every sanitary sewer system is the same and not every manhole is subjected to the same type and intensity of deteriora- tion. It depends on the location and depth of the manhole within the sys- tem compared to the sewage strength, volume and velocity of low, how stag- nant or agitated the sewage is, prox- imity to water bodies, groundwater levels, etc. The products also provide varying levels of structural strength, surface strength, and lexibility. These variables are what have helped to pro- duce the assortment of manhole reha- bilitation products available today. Resources are available through the American Society of Civil Engineers Utility Engineering and Surveying Institute (UESI) (MOP 92) and the Na- tional Association of Sewer Service Companies (NASSCO) to provide more information about manhole rehabili- tation products and procedures and how best to select the most appropri- ate technology for a speciic job. This article was provided by Tad Powell, a member of NASSCO's Manhole Rehabilitation Committee. M a n h o l e R e h a b i l i tat i o n P r o d u c t s : H o w D o Yo u K n o w W h i c h O n e t o C h o o s e ? B y T a d P o w e l l

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