Estimation of the detection distances of CPT resistance

• Published in: Engineering geology Vol. 313; p. 106953
• Main Authors: Xiao, Liang, Lu, Liang, Wang, Zongjian, He, Bing, Arai, Katsuhiko
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2023
• Subjects: Cavity expansion theory; CPT resistance; Detection distance; Engineering geology; Transparent soil; Engineering geology; Cavity expansion theory; Transparent soil; Detection distance; CPT resistance
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2022.106953

Cone penetration test (CPT), a common method for engineering geological exploration, is often used for empirical delineation of soil stratigraphy, but its accuracy mainly depends on the engineers' judgment of the detection distances of CPT resistance in the multi-layer soil. The detection distances, the distance from the cone tip to the soil interface when the resistance trend changes, were studied in this work. Firstly, a theoretical solution of cone resistance was proposed, based on cavity expansion theory and the geometry of the probe. The solution divided the disturbed soil around the probe into three regions, considering the strain-softening characteristics of soil. And an innovative assumption that the soil under the cone expands cylindrically with variable radius, was justified by the oval profile of soil particles in a series of transparent soil tests. Both theoretical results and test results illustrated that the detection distances of CPT resistance depended on the soil properties and the thickness of the interlayer. Compared with numerical results and literature data, the detection distances in the strong soil were greater than those in the weak soil of the two-layer soil, and the distances reduced as the strength difference of adjacent soil decreased. Besides, the thin-layer effect was investigated within the maximum thickness which was smaller in strong interlayer soil. When the maximum thickness was exceeded, the determination method for detection distances in two-layer soil could be applicable. The results contribute to the application of CPT in geologic investigation. •An analytical solution of CPT resistance is proposed for geologic investigation.•The disturbed soils are assumed to be cylindrical cavity with variable radius.•The transparent soil tests are used for investigation of penetration mechanisms.•The detection distances are dependent on relative properties between soil layers.•The minimum thickness of interlayer is obtained by DEM simulation.