Manholes, Vaults and Structures in Casper, Wyoming

A single manhole section can weigh a couple of tons. A precast vault for a pump or a meter can weigh far more. Setting them takes a crane, a clear swing radius and a base that will not settle under the load. The structure goes in once, and everything attached to it, the pipe, the cable, the paving, depends on it being in the right place at the right elevation.

Underground structures are the access points of a buried system. Sewer manholes let crews clean and inspect lines. Storm structures collect surface water. Electrical vaults and handholes give cable a place to turn and splice. Valve vaults and meter pits give water crews a way to shut down a main. When they are right, nobody thinks about them. When they are wrong, they leak, heave, sink or get driven over by a plow.

We set structures with the crane and the grade rod, and we treat the base, the joints and the rim as three separate jobs, because each one fails differently.

Types of structures we build

Precast concrete manholes are the standard for sewer and storm. They come in barrel sections, a cone or flat top and a base, and the pieces stack with gasketed or mastic joints. We set a compacted aggregate base, place the base section to line and grade, stack the barrels, set the cone and finish with adjusting rings and a frame. Pipe connections are cored or cast in, sealed with flexible boots and finished with a smooth invert.

Larger or irregular structures are cast in place. A junction box with several pipes at odd angles, a deep vault that does not match a standard precast, or a structure that has to tie to existing concrete will use formwork and a poured wall. Electrical vaults, telecom handholes and valve pits are usually precast. Our electrical duct banks terminate in these structures, so we set the vault first and aim the conduit at the knockouts.

Specifications, loads and plan approval

Structures are designed for the loads they will see. A manhole in a roadway carries traffic, and its frame and cover are rated for it. A vault in a plant yard may carry forklifts and heavy equipment. The submittal process matters: precast shop drawings, pipe openings, frames and covers go to the engineer before we order. Commercial permits in Casper often call for engineered building and site plan drawings, and the structure details are part of that set.

Casper's climatic criteria list severe weathering, a 3,000 air freezing index and a 3 foot frost line to top of footing. For structures that means air-entrained concrete, sealed joints, and a detailing plan that keeps frost movement from pulling a ring apart. We follow the submitted details, and we ask for clarification when the details do not match field conditions, such as a pipe that arrives at a different elevation than shown.

Base, joints and rim

The base is the foundation. We excavate to firm soil, remove soft spots, place and compact aggregate to the specified thickness and check the elevation before the crane lifts. A base that settles tilts the entire structure, and pipes that enter at a tilt will open at their joints. A poured base is an option when soil is weak or groundwater is high.

Joints are the next risk. We clean each joint surface, seat the gasket or mastic evenly and check that the sections are plumb. After stacking, we test the structure by vacuum or water. Leaks in a new manhole become infiltration for the life of the sewer, and groundwater does not stop pushing. Last is the rim. We set it with adjusting rings to match the surface grade and use non-shrink grout where required. Setting the rim to final pavement grade, not to the dirt around it, is how we avoid the bump that every plow driver hates.

Groundwater, uplift and confined spaces

Where groundwater is high, a hollow structure wants to float. Buoyancy can push a manhole up out of the ground, especially after backfill when the trench is full of water. Cures include anti-flotation collars, thicker base slabs, dewatering until the structure is loaded and backfilling in stages. Casper sits on the North Platte River, and ground near the river holds water. The 2014 Poplar Street and CY Avenue rebuild included sewer and water line work, and street corridors like it carry many structures that have to be set and protected through the work.

Confined space rules apply once a structure is open. Inspectors and crews who enter a manhole follow entry procedures: atmosphere testing, ventilation, a standby person and retrieval gear. We seal pipe openings and keep covers on at the end of each shift. A manhole left open overnight is a hazard to pedestrians and animals.

Structures and the rest of the underground

Structures tie together the pipe work we do. They mark the turns and the changes in grade of a sanitary sewer and they set the elevations that the surface restoration has to match. For public owners, such as municipal and public works departments, the as-built record of every structure is part of what they accept.

A government and municipal facility may include its own vaults, metering and valve structures on site, and those need to match the utility's standards as well as the building's. Where a structure sits in a driving lane, we coordinate the pour of any collar or apron with the paving crew.

Where we set structures

We work across Casper and Natrona County, and we travel along the interstate toward Douglas when the project warrants it. Precast delivery distance affects price and schedule, and large structures need escorted or permitted loads on some roads. We schedule deliveries so the crane and the crew are ready when the truck arrives. In the town of Evansville and the surrounding area, we coordinate with each town's public works staff for inspection and acceptance.

Bring us the structure schedule

Send the structure table, the profile sheets and the soils report. We will tell you which structures need special bases, which need dewatering and what the crane plan looks like.

Questions Owners Ask

Why do manholes settle or heave?

Settlement usually comes from a poor base or poorly compacted backfill. Heave comes from frost grabbing the sides of the structure, or from groundwater uplift. A good compacted base, tight joints and backfill that drains reduce both. Rim adjustment after the first freeze cycle is common practice for owners with rough roads.

When is a cast-in-place structure better than precast?

Cast-in-place makes sense for odd shapes, many pipe entries at unusual angles, very large chambers and ties to existing concrete. Precast is faster and easier to inspect for quality. We recommend precast whenever it fits and cast-in-place only when the geometry demands it.

How do you test a new manhole?

Most specifications require a vacuum test or a water exfiltration test. We seal the openings, apply the vacuum or fill the structure and watch the gauge for a fixed time. If it fails, we find and fix the leak, usually at a joint or a pipe boot, and test again.

Can you adjust existing manholes to a new pavement grade?

Yes. We remove the frame, add or remove adjusting rings, reset the frame with non-shrink grout and restore the pavement around it. This is common on overlay and rebuild projects, and we coordinate with the paving crew so the rim lands flush after final lift.

How long does it take to set a manhole?

A standard structure in a prepared hole can be set in an hour or two once the crane is on site. The base prep, pipe connections, testing and backfill take the rest of the day. Large vaults need more time, and deep ones need shoring and a longer lift plan.

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