Road Subgrade Preparation in Casper, Wyoming

Detours via Ash Street are part of the plan for a two-year, $12.8 million reconstruction of Poplar Street (WYO 220) between CY Avenue and Collins Drive, with a contract completion date of September 30, 2028. The detour exists because the road has to be dug up, rebuilt and repaved, and the subgrade under it is the first thing that has to be right. Pavement is a thin skin over a platform of soil, and the platform does most of the work.

Road subgrade preparation is the sequence of work that brings the native soil to a uniform, stable, compacted condition at the elevation the pavement section requires. We excavate to subgrade, remove soft or organic material, scarify and recompact the top layer, stabilize where the engineer calls for it and proof-roll the result.

The work goes on in public view. Traffic keeps moving next to it, residents ask questions and the schedule is tied to a completion date. We plan for those pressures from the start.

Roads under reconstruction in the Casper area

The Poplar Street corridor shows the shape of local road work. An earlier WYDOT contract for Poplar Street between Collins Street and the North Platte River bridge covered $12.79 million with new road surface and storm and sanitary sewer and utility upgrades, and a follow-on contract continues the work to the west. Utilities are replaced before the road is rebuilt, so subgrade work follows trenching and backfill. Our notes on the Poplar Street corridor discuss how this plays out on the ground.

North of town, WYO 254 and the interstate exits serve logistics and industrial land that is still being developed. Private streets and truck courts there need subgrades as strong as the public roads they connect to, since the trucks that use them are the same. Streets for a municipal facility follow the public standard even when the owner is a single department, and the inspection record is kept in the same way.

Reading a reconstruction schedule is a skill. Contract dates are written around the seasons, and a job that starts in spring has one clear summer of subgrade work before cold weather forces the crew to stop. Owners who bid late in the year should expect the subgrade to be the activity that slips, and they should ask the contractor how much of it can safely be completed before the ground freezes.

Working inside a detour and a completion date

Road work runs on contract dates, often with liquidated damages. The subgrade is a critical-path activity: base, paving and striping cannot start until it is accepted. We build float into the schedule for weather and testing, and we phase the work in lengths that match the traffic control plan.

In a corridor with a detour, the staging matters. Open lanes, driveway access, and emergency vehicle routes all constrain the order of work. We hold daily coordination calls with the inspector and the traffic control crew and publish the next day's work area. When a section is ready, we say so and move to the next one, rather than leaving a long stretch half done.

From cut to accepted subgrade

We begin with removal of the existing pavement and base, which links to demolition and site prep, then excavate to the design subgrade elevation. We proof-roll the exposed surface and mark every soft or yielding area. Those areas are undercut, replaced with approved material and recompacted.

After that, the entire subgrade is scarified to a specified depth, moisture conditioned and compacted to density. If the engineer specifies stabilization, we use geogrid, cement or lime, as described under lime and cement soil treatment. Utility trenches that cross the road are checked for compaction, because a trench that settles shows up as a dip in the new pavement. Once the subgrade is accepted, the work rolls straight into asphalt paving base preparation.

Uniformity is the goal

A subgrade can be strong and still fail if it varies. A road with firm clay for fifty feet, then a soft pocket, then firm clay again will crack at the transitions. Our process aims for uniform support: we blend soils where needed, dry or wet them to the same moisture and compact with the same roller pattern throughout.

We use stringlines or machine control for grade and take elevations at close intervals before the base is placed. A subgrade that is a quarter inch high or low is not a problem, but one that is an inch off wastes base material or leaves it too thin. The final proof-roll catches any area where support is lacking, and the inspector witnesses it.

Standards, testing and acceptance

Public road projects follow the owner's specifications and testing frequencies. The owner may be the state, the city or the county, and each has its own pay items and acceptance rules. We read the spec book before we price, and we keep the testing agency informed of the working schedule so they can staff for it.

Casper lists a three-foot frost line and severe weathering in its climatic criteria. For roads, that raises the frost-susceptibility of the subgrade and the importance of drainage. Water trapped in the subgrade freezes and heaves the pavement, so we make sure side ditches, underdrains and cross-slopes work before the surface goes down.

Public and private buyers

Most road work comes from municipal and public works agencies, but developers and utility companies also need subgrades. A utility company restoring a street after a main replacement needs a subgrade that matches the road around it. We handle restoration with the same standards as a new road.

Traffic, trucks and tired drivers

Road work puts crews beside moving vehicles. Barriers, signs, lighting and flaggers are laid out before the first machine moves. Workers on foot wear high-visibility clothing, and equipment operators have spotters near traffic.

Haul trucks entering and leaving the work zone are a particular hazard, especially when the road is narrowed and the shoulder is soft, so we use a defined entrance and a flagger. At night, lighting and reflective gear matter even more. We review the traffic plan with the crew every morning and stop work when a barrier is missing or a lane has changed without notice.

Send the typical sections and the soils data

We will return a subgrade plan with the removal and stabilization options, the testing frequency and a schedule that fits the paving date.

Questions Owners Ask

What counts as a failed proof-roll?

Visible pumping, rutting or deflection under a loaded truck. The inspector marks the area and we undercut or stabilize it. After repair, the area is proof-rolled again and must pass before base goes on.

Can subgrade work continue in cold weather?

Only while the ground is not frozen. Frozen soil cannot be compacted and thaws into a soft layer. We stop and wait, or switch to non-earthwork tasks. In some cases, flowable fill or imported material is allowed by the owner.

How do you handle utility trenches in the road?

We check backfill compaction before the subgrade is accepted and repair any soft zones. Many owners require flowable fill in street cuts to avoid settlement. We coordinate with the utility crews to finish their work first.

How long does subgrade take per block?

It depends on the length, width and condition, but one block is typically a few working days when conditions are good. Rain, soft spots and testing can double.

What if the subgrade fails after we place base?

The base is removed in the failed area and the subgrade is repaired. That is expensive, which is why we do not place base until the subgrade has passed and the inspector has approved it.

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