A Geophysical Approach to Construction Quality Assurance Testing of Compacted Soil Using Electrical Conductivity Measurements

摘要

Construction quality assurance (CQA) testing is typically performed in compacted fine-grained soils to measure in situ values of dry density {pi) and water content (w). The nuclear gauge is the most common method. However, electrical conductivity (σ) measurement is an attractive alternative. Previous researchers have developed relationships between σ and volumetric water content (θ), but the effect of compaction effort has not been investigated. Other researchers have related σ to degree of saturation (S), and the relationship is independent of compaction effort. However, specimens compacted at the same S can possess different values for θ, so σ cannot correlate equally well to both parameters. Therefore, a laboratory study was performed to assess the effects of compaction effort, S, and θ on σ in specimens of fine-grained soil. By measuring σ over a range of w and compaction effort, it was observed that σ correlates well with θ independent of compaction effort, while the correlation between σ and S is dependent upon compaction effort. It was also observed that θ is a reasonable indicator of whether or not a soil specimen is wet or dry of wopt, a common CQA acceptance criterion. Therefore, a new CQA method based on θ is proposed. Since θ can be predicted based on the measurement of σ, field geophysical measurement of σ may be used to quickly determine whether or not soil has been compacted in accordance with specifications.