In Winston-Salem, pavement performance often comes down to what’s underneath. The Piedmont Triad’s residual silts and micaceous saprolite can look firm in dry weather and turn to jelly after a wet winter. We see this pattern repeat across Forsyth County — from the heavy truck routes off I-40 Business to the residential streets near Hanes Park. A flexible pavement design that works in the Coastal Plain won’t survive three seasons here without proper subgrade treatment. Our approach starts with the soil itself: sampling, lab characterization, and layer optimization. We tie that data to the actual traffic spectrum — not just generic ESALs — and build a pavement section that drains well and resists fatigue cracking. For subgrade evaluation we often pair CBR testing with a test pit campaign to verify the extent of weathered rock, and when moisture sensitivity is a concern we run Atterberg limits to quantify the plasticity of the local silt.
A Winston-Salem pavement section designed without accounting for micaceous saprolite typically loses 30% of its service life.
Scope of work
Area-specific notes
Pavement risk in Winston-Salem varies block by block. Over near Bowman Gray Stadium, the soils are mostly Cecil sandy clay loam — well-drained and predictable. But move south toward the Salem Creek floodplain and you encounter alluvial silts with high seasonal moisture fluctuation. The difference in subgrade support between these two areas can be a factor of two. The biggest failure mode we see in the city isn’t structural collapse; it’s fatigue cracking from repeated deflection at the asphalt base, accelerated by poor drainage. In commercial lots off Stratford Road, we’ve documented alligator cracking within five years where no edge drain was installed. Another local risk is differential heave on expansive clays in the northern part of the county — nothing dramatic like Texas black cotton soil, but enough to create longitudinal cracking along the wheel paths. Our designs address this through a combination of moisture-conditioned subgrade, geotextile separation, and, in extreme cases, stabilization with lime or cement grouting.
Standards used
AASHTO Guide for Design of Pavement Structures, 1993, NCDOT Standard Specifications for Roads and Structures, ASTM D1883 – CBR of Laboratory-Compacted Soils, ASTM D4318 – Atterberg Limits, ASTM D1557 – Modified Proctor
Linked services
Subgrade Investigation
Test pits, dynamic cone penetrometer (DCP), and Shelby tube sampling to map subgrade variability across the project footprint.
Laboratory Characterization
CBR (soaked and unsoaked), resilient modulus, Proctor, and Atterberg tests on representative soil samples.
Pavement Structural Design
Layer thickness and material specification using AASHTO 93 calibrated with local MR values and NCDOT traffic factors.
Drainage & Stabilization Plan
Design of edge drains, permeable base layers, and chemical stabilization protocols for subgrade improvement.
Typical parameters
Quick answers
What is the typical flexible pavement section for a Winston-Salem commercial parking lot?
For a lot with moderate auto and occasional truck traffic on a CBR 6 subgrade, a common section is 3 inches of S9.5C asphalt over 8 inches of aggregate base course (ABC). Where truck volumes are higher, we increase to 4.5 inches of asphalt with a 10-inch base.
How do Piedmont residual soils affect pavement performance?
These soils contain partially weathered mica and feldspar that break down further under moisture and load cycles. Their drained strength can be acceptable, but the undrained condition after heavy rain leads to rutting and fatigue cracking if the pavement section is under-designed for drainage.
Does NCDOT require a specific CBR value for subdivision streets in Forsyth County?
NCDOT typically requires a minimum soaked CBR of 6% at the top of the subgrade for local subdivision streets. If the natural soil tests below 6%, the subgrade must be stabilized or undercut and replaced with select material to a depth that achieves the required bearing.
What is the cost range for a flexible pavement design package in Winston-Salem?
A complete flexible pavement design — including field investigation, lab testing, and the final stamped report — typically falls between US$1,700 and US$5,550, depending on the number of borings or test pits and the extent of lab work required.
How long does a flexible pavement design project take from field work to final report?
Field investigation usually takes one to two days. Lab testing runs seven to ten days for standard CBR and Proctor, longer if resilient modulus is required. The draft report follows within one week of receiving lab results, so a typical timeline is three to four weeks.