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Subgrade Evaluation
The careful investigation and recommendations for subgrade is an important aspect for the design of flexible and rigid pavements, building floor slabs, and large mat foundations. Previous site development can be an indication that random materials that include debris and high variability of soil density are present. Visual observation of existing pavement performance and a review of pavement maintenance records is also a method of identifying locations of poor subgrade.
Highly plastic soils, organic materials, very soft or saturated soils, soils with high shrink-swell potential, expansive slag, and low subgrade strength (California Bearing Ratio or resilient modulus) are examples of materials that must be identified to provide proper subgrade design. Developing a suitable subsurface exploration and laboratory testing program is essential to evaluating and recommending the proper subgrade design parameters and treatment methods.
The use of subgrade undercuts and backfilling with properly compacted soil or aggregate is a typical method of providing treatments to improve subgrade performance. Depending on the conditions (very soft or saturated soils), it is possible that the subgrade material can be aerated and re-compacted to the recommended density. The use of chemical stabilization (lime or cement) is also an alternative that reduces or replaces the amount of subgrade undercutting. Geosynthetic materials can also be used to improve the strength of the pavement section to allow for less subgrade treatment.
Highly plastic soils, organic materials, very soft or saturated soils, soils with high shrink-swell potential, expansive slag, and low subgrade strength (California Bearing Ratio or resilient modulus) are examples of materials that must be identified to provide proper subgrade design. Developing a suitable subsurface exploration and laboratory testing program is essential to evaluating and recommending the proper subgrade design parameters and treatment methods.
The use of subgrade undercuts and backfilling with properly compacted soil or aggregate is a typical method of providing treatments to improve subgrade performance. Depending on the conditions (very soft or saturated soils), it is possible that the subgrade material can be aerated and re-compacted to the recommended density. The use of chemical stabilization (lime or cement) is also an alternative that reduces or replaces the amount of subgrade undercutting. Geosynthetic materials can also be used to improve the strength of the pavement section to allow for less subgrade treatment.