The way to keep a St. Louis building pad on schedule through a wet fall or winter is to plan for wet clay before it happens: control water on the site, proof-roll early, have an approved fix for soft areas ready, and keep frost out of finished subgrade. Projects that wait until the pad fails a proof roll to decide what to do usually lose the most time.
Most of the St. Louis and St. Charles County area sits on clay soils that hold water, lose strength when wet and take a long time to dry in cool weather. From late fall through early spring, there are fewer drying days, and freezing and thawing make things worse. Here is how GCs, developers and engineers can keep pads moving.
Why do St. Louis clays cause so many schedule problems?
Fine-grained clays can only be compacted within a fairly narrow moisture range. When they are too wet, they rut and pump under equipment, density tests fail and proof rolls show deflection. In summer, you can disc and aerate wet soil and let the sun and wind do the work. In November or February, a site can sit wet for days or weeks after a single rain.
How do you keep water off the pad in the first place?
The cheapest wet-weather fix is keeping water from soaking in. Good practice on any pad going into the off-season includes:
- Sealing the pad surface with a smooth drum roller at the end of each day so rain runs off
- Grading the pad and surrounding areas with positive slope to ditches or sediment basins
- Building temporary swales and keeping inlets and basins working
- Limiting traffic on finished subgrade, especially when it is wet
- Opening only the areas that can be finished before the next rain
These steps also help with SWPPP compliance, since water that runs off a sealed pad into working controls carries less sediment.
When should you proof-roll?
Proof-rolling with a loaded truck or heavy roller, witnessed by the testing agency, shows where the subgrade deflects or pumps. On a fall or winter schedule, proof-roll as early as you can, before fill placement and again before the pad is turned over. Finding soft areas while there is still time to fix them keeps the GC's footing and slab crews from waiting.
Should you stabilize or undercut soft subgrade?
Once soft areas are found, there are usually two options the geotech will consider: treat the soil in place with lime or cement, or undercut it and replace it with imported material. The right answer depends on soil type, area, depth, haul distance and the price of import and disposal.
We cover that decision in detail in our lime vs. cement vs. undercut guide. For the schedule, the key points are:
- Get the geotech's approved approach and a mix design before the wet season, not after the first failed proof roll
- Price both options on the same quantities so the decision is fast when it comes up
- Know that undercut in wet weather means more truck traffic on soft haul roads, which can create new soft areas
- Check temperature limits in the spec; chemical stabilization has weather restrictions
How do you handle frost and freezing weather?
Frozen soil cannot be compacted properly, and fill should not be placed on frozen subgrade or with frozen material in it. Specs generally prohibit both. When a cold snap is coming:
- Finish and seal lifts before the freeze rather than leaving loose material exposed
- Strip any frozen material before placing the next lift
- Protect finished subgrade under footings and slabs with insulated blankets or cover where the GC needs it
- Re-test areas that froze and thawed before accepting them for concrete
Footing depths below frost are set by the local building code and structural drawings, but the earthwork contractor's job is to make sure frost doesn't get into finished bearing soils before concrete goes down.
What helps most on a winter schedule?
In our experience, the best winter outcomes come from having equipment and crews available to work hard when good days show up. Kuesel owns more than 300 pieces of equipment and self-performs grading and lime and cement stabilization, so we can move quickly when a weather window opens or when a soft area needs treatment.
Wet soil and winter earthwork FAQ
Can you keep grading in the rain?
Usually not on clay subgrade. Working wet clay often makes it worse. Sealing the surface and waiting, or switching to stabilization, is usually faster in the end.
Is lime or cement modification the same as stabilization?
Not always. Modification makes soil workable during construction; stabilization targets a design strength. The plans should say which one is intended.
Request a bid on your building pad
If your pad is scheduled for the wet season, send us your civil plans and geotech report through our bid invite and we'll price both stabilization and undercut options. Kuesel responds within one business day. Call (636) 978-3478, Monday through Friday, 7am to 4pm.