In Long Beach, we often see pavement sections that fail early not because of traffic loading, but because the subgrade was never properly characterized. The city sits on a complex mix of Holocene alluvium, estuarine deposits, and artificial fill over the Wilmington anticline—conditions that make textbook pavement design unreliable. A flexible pavement is only as good as the support beneath it, and in the Port area or along the Los Cerritos Channel, that support can vary dramatically within a few hundred feet. Our approach ties CBR testing directly to the structural design of asphalt concrete, base, and subbase layers, using material properties measured on-site rather than assumed from regional maps. We also integrate in-situ density verification during construction to confirm that compaction meets the target values specified in the design report.
Coastal subgrade in Long Beach can lose 40% of its stiffness between the dry season and a wet winter—designing for the worst case avoids resurfacing every three years.
Local geotechnical context
The IBC and the Caltrans Highway Design Manual set minimum pavement structural requirements, but in Long Beach the real risk is ignoring the interaction between seasonal groundwater and fine-grained subgrade. The water table rises within three to six feet of the surface in much of the coastal plain, and when a pavement section lacks a positive drainage layer, pore pressure builds under traffic pulses and the base course pumps fines into the subbase. We see this failure mode repeatedly in industrial subdivisions east of the 710 freeway. Our flexible pavement design explicitly includes a drainage analysis: we specify the gradation envelope for the base, set the minimum permeability, and detail edge drains or daylighted sections. For streets that cross former marsh deposits—common west of Pacific Avenue—we also evaluate the liquefaction susceptibility of the subgrade using the liquefaction assessment framework, because post-seismic settlement can destroy a pavement profile in seconds.
Relevant standards
AASHTO Guide for Design of Pavement Structures (1993, supplemented by MEPDG methodology), ASTM D1883 (CBR of laboratory-compacted soils), ASTM D1557 (modified Proctor compaction), Caltrans Standard Specifications – Section 39 (asphalt concrete), IBC Chapter 18 (soils and foundations, subgrade preparation), ASTM D2487 (Unified Soil Classification for subgrade description)
Common questions
What does flexible pavement design cost for a typical Long Beach parking lot or access road?
For a commercial parking lot or short access road in Long Beach, the engineering package—subgrade investigation, CBR testing, pavement design report, and construction QA—generally runs between US$1,880 and US$5,870, depending on the number of borings and the traffic analysis required. A street segment with heavy truck loading will be at the upper end because of the additional lab work and MEPDG-level modeling.
How do you account for the high water table when designing flexible pavement in Long Beach?
We measure the depth to groundwater during the geotechnical investigation and include a drainage layer in the pavement section when the seasonal high water table is within 4 feet of the subbase. The base course gradation is specified to remain free-draining, and we often add edge drains or daylight the section to prevent pore pressure buildup under repeated loading.
Which design method do you use—AASHTO 1993 or MEPDG?
We use both, depending on the project. For most commercial and light-industrial pavements, the AASHTO 1993 method with Long Beach-specific subgrade inputs is efficient and accepted by local agencies. For heavy-duty pavements—port terminals, truck yards, or major arterials—we apply MEPDG (Mechanistic-Empirical Pavement Design Guide) to calibrate distress models against the actual climate and traffic spectrum.
Can you design a flexible pavement over soft Bay mud or old fill?
Yes, but it requires stabilization. We have designed flexible pavements over Bay mud by over-excavating the top 2–3 feet and replacing it with engineered fill, or by using geogrid reinforcement and a thicker aggregate base. The key is to raise the composite modulus of the subgrade-stabilization system above the threshold that triggers deep rutting.
How long does the design and testing process take before we can pave?
A typical schedule is two to three weeks from authorization to draft report: one week for field sampling and CBR testing, one week for lab work, and a few days for the structural analysis and report. We coordinate with the contractor’s schedule so that the design is ready before the grading phase ends.
