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Soil Modulus After Ground Improvement Print

Evaluation of ground improvement is accomplished using a variety of methods, from simple elevation surveys to document the amount of compression caused, to geotechnical in-situ and laboratory testing, to geophysical testing. The most common types of geotechnical testing used to evaluate the modulus of the soil after ground improvement are penetration tests such as the Standard Penetration Test (SPT) or the Static Cone Penetration Test (CPT). Engineers occasionally ignore two significant factors when evaluating these test results: (1) continued increase of CPT or SPT values over time, and (2) an increased correlation between modulus and penetration resistance for overconsolidated soils, as compared to normally consolidated soils.

During performance of ground improvement, ground surface settlements of one to three feet are not uncommon at many sites. Calculated settlements under foundation loads are generally much less than the observed settlement. If the post-improvement geotechnical testing indicates little improvement has occurred, the geotechnical engineer is faced with the following question. “Was my observation that the soils have been prestrained incorrect or are the correlations between compressibility and the geotechnical testing parameter wrong?” Since the site settlement (i.e., prestraining) is an easily verifiable phenomenon, the answer is obvious. The next step is to determine how best to reconcile the known site settlement with the geotechnical testing.

This article is designed to provide readers with a better understanding of how to interpret geotechnical test results in improved ground.

The full document can be downloaded in PDF format below.

Soil Modulus After Ground Improvement