Calibración de la resistencia al corte no drenada obtenida a partir de ensayos CPTu y DMT en un suelo fino característico de Concepción, Región del Biobío.
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Date
2025
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Universidad de Concepción
Abstract
La caracterización de suelos finos y cohesivos tradicionalmente requieren programas de ensayos que incluyen pruebas de laboratorio para determinar la resistencia al corte no drenada Su, preponderantemente ensayo Triaxiales no drenado UU y CIU. Sin embargo, gracias a la incorporación de nuevos métodos de prospección, es posible determinar la resistencia al corte no drenado a partir de ensayos practicados directamente insitu. Para mejorar la precisión de estas expresiones, la literatura especializada recomienda realizar calibraciones para una mejor caracterización mecánica de depositos de suelo fino caracteristicos de una zona en particular.
Este estudio tuvo como objetivo calibrar el parámetro Nkt del ensayo CPTu y el factor de modificación Δ para el ensayo DMT, utilizando como referencia los resultados de ensayos triaxiales UU en un limo característico del subsuelo de Concepción. El limo estudiado corresponde a depositaciones aluviales y coluvio de suelos residuales de la Formación Cosmito y se clasifica como limo de baja compresibilidad (ML) con un índice de plasticidad medio de 7.
Al comparar los resultados de tres ensayos triaxiales realizados a diferentes cotas con los ensayos in situ, se encontró que, para el ensayo CPTu, la variabilidad media fue de -9,32±0,35% utilizando un valor de Nkt igual a 14. Con base en estos resultados, se determinó un factor Nkt de 12,7, lo que reduce la variabilidad media a -0,05±0,36% para la estimación de la resistencia al corte no drenada en suelos finos de la zona evaluada.
En cuanto al ensayo DMT, se obtuvo una variabilidad media de -8,15±1,25% en comparación con los resultados de laboratorio. Se determinó un factor de modificación Δ igual a 1,089, que ajusta la variabilidad media a -0,02±1,37%.
Los resultados de este estudio contribuyen a mejorar la confiabilidad de los métodos in situ evaluados, permitiendo una estimación más precisa de la resistencia al corte no drenada en suelos cohesivos presentes en la zona evaluada. Sin embargo, dada la baja cantidad de ensayos que se disponen, no se puede asegurar que estos sean validos para toda la zona de Concepción. Por lo tanto, se recomienda continuar con programas de ensayos destinados a la calibracion de estos métodos de prospección insitu, como el CPTu y/o DMT.
The characterization of fine and cohesive soils traditionally requires testing programs that include laboratory tests to determine the undrained shear strength Su, predominantly using undrained triaxial tests (UU and CIU). However, with the incorporation of new prospecting methods, undrained shear strength can now be determined based on in-situ tests. To improve the accuracy of these estimates, specialized literature recommends performing calibrations for better mechanical characterization of fine soil deposits typical of a specific region. The objective of this study was to calibrate the Nkt parameter for the CPTu test and the incorporation of a factor Δ for the DMT test, using the results of undrained triaxial UU tests as a reference, on a silt typical of the subsurface of Concepción. The studied silt corresponds to alluvial and colluvial deposits of residual soils from the Cosmito Formation and is classified as low-compressibility silt (ML) with a plasticity index of 7. When comparing the results of three triaxial tests conducted at different depths with in situ tests, it was found that, for the CPTu test, the average variability was -9.32±0.35% using an Nkt value of 14. Based on these results, an Nkt factor of 12.7 was determined, which reduced the average variability to -0.05±0.36% for the estimation of undrained shear strength in fine soils from the evaluated area. Regarding the DMT test, an average variability of -8.15±1.25% was obtained in comparison with laboratory results. A correction factor Δ equal to 1.089 was determined, which adjusted the average variability to -0.02±1.37%. The results of this study contributed to improving the reliability of the evaluated in situ methods, allowing for a more accurate estimation of undrained shear strength in the cohesive soils present in the studied area. However, due to the limited number of available tests, it could not be confirmed that these findings are valid for the entire Concepción area. Therefore, it was recommended to continue testing programs aimed at the calibration of these in situ exploration methods, such as CPTu and/or DMT.
The characterization of fine and cohesive soils traditionally requires testing programs that include laboratory tests to determine the undrained shear strength Su, predominantly using undrained triaxial tests (UU and CIU). However, with the incorporation of new prospecting methods, undrained shear strength can now be determined based on in-situ tests. To improve the accuracy of these estimates, specialized literature recommends performing calibrations for better mechanical characterization of fine soil deposits typical of a specific region. The objective of this study was to calibrate the Nkt parameter for the CPTu test and the incorporation of a factor Δ for the DMT test, using the results of undrained triaxial UU tests as a reference, on a silt typical of the subsurface of Concepción. The studied silt corresponds to alluvial and colluvial deposits of residual soils from the Cosmito Formation and is classified as low-compressibility silt (ML) with a plasticity index of 7. When comparing the results of three triaxial tests conducted at different depths with in situ tests, it was found that, for the CPTu test, the average variability was -9.32±0.35% using an Nkt value of 14. Based on these results, an Nkt factor of 12.7 was determined, which reduced the average variability to -0.05±0.36% for the estimation of undrained shear strength in fine soils from the evaluated area. Regarding the DMT test, an average variability of -8.15±1.25% was obtained in comparison with laboratory results. A correction factor Δ equal to 1.089 was determined, which adjusted the average variability to -0.02±1.37%. The results of this study contributed to improving the reliability of the evaluated in situ methods, allowing for a more accurate estimation of undrained shear strength in the cohesive soils present in the studied area. However, due to the limited number of available tests, it could not be confirmed that these findings are valid for the entire Concepción area. Therefore, it was recommended to continue testing programs aimed at the calibration of these in situ exploration methods, such as CPTu and/or DMT.
Description
Tesis presentada para optar al título de Ingeniero/a Civil.
Keywords
Suelos Chile Octava Región, Suelos, Calibración Normas