EVALUATION OF BEARING CAPACITY OF PILES FROM CONE PENETRATION TEST DATA

This study presents an evaluation of the performance of eight cone penetration test (CPT) methods in predicting the ultimate load carrying capacity of square precast prestressed concrete (PPC) piles driven into Louisiana soils. A search in the DOTD files was conducted to identify pile load test reports with cone penetration soundings adjacent to test piles. Sixty piles were identified, collected, and analyzed. The measured ultimate load carrying capacity for each pile was interpreted from the pile load test using Butler-Hoy method, which is the primary method used by DOTD. The following methods were used to predict the load carrying capacity of the collected piles using the CPT data: Schmertmann, Bustamante and Gianeselli (LCPC/LCP), de Ruiter and Beringen, Tumay and Fakhroo, Price and Wardle, Philipponnat, Aoki and De Alencar, and the penpile method. The ultimate load carrying capacity for each pile was also predicted using the static "-method, which is used by DOTD for pile design and analysis.

Prediction of pile capacity was performed on sixty piles, however, the statistical analyses and evaluation of the prediction methods were conducted based on the results of thirty five friction piles plunged (failed) during the pile load tests. End-bearing piles and piles that did not fail during the load tests were excluded from the statistical analyses.

An evaluation scheme was executed to evaluate the CPT methods based on their ability to predict the measured ultimate pile capacity. Four different criteria were selected to evaluate the ratio of the predicted to measured pile capacities. These criteria are: the best-fit line, the arithmetic mean and standard deviation, the cumulative probability, and the Log Normal distribution. Each criterion was used to rank the prediction methods based on its performance. The final rank of each method was obtained by averaging the ranks of the method from the four criteria. Based on this evaluation, the de Ruiter and Beringen and Bustamante and Gianeselli (LCPC/LCP) methods showed the best performance in predicting the load carrying capacity of square precast prestressed concrete (PPC) piles driven into Louisiana soils. The worst prediction method was the penpile, which is very conservative (underpredicted pile capacities).

Dynamic Cone Penetration Test (DCPT) for Subgrade Assessment

In-situ penetration tests have been widely used in geotechnical and foundation engineering for site investigation in support of analysis and design. The standard penetration test (SPT) and the cone penetration test (CPT) are two typical in-situ penetration tests. The dynamic cone penetration test shows features of both the CPT and the SPT. The DCPT is similar to the SPT in test. It is performed by dropping a hammer from a certain fall height and measuring a penetration depth per blow for each tested depth. The shape of the dynamic cone is similar to that of the penetrometer used in the CPT. In road construction, there is a need to assess the adequacy of the subgrade to behave satisfactorily beneath a pavement. A recently completed Joint Transportation Research Program project showed that the DCPT can be used to evaluate the mechanical properties of compacted subgrade soils. In the present implementation project, the application of the DCPT is further investigated.

Present practice in determining the adequacy of a compacted subgrade is to determine the dry density and water content by the sand-cone method or with a nuclear gauge. However, the use of the resilient modulus (Mr) has become mandatory for pavement design. To find the Mr, a time consuming testing procedure is required which demands significant effort. Therefore a faster and easier alternative for compaction control in road construction practice is desired. To this end, the present project aimed to take a first step in the generation of data to create appropriate correlations among subgrade parameters and DCPT results.

The present research project consists of field testing, laboratory testing, and analysis of the results. The field testing includes the DCPT and nuclear gauge tests. In the planning stage, several road construction sites were selected for the field testing. For the selected road construction sites, both the DCPT and nuclear tests were performed at the same location, allowing a comparison between DCPT and nuclear test results. Soil samples for the selected project sites were also obtained for the laboratory testing program.

Groundwater Modeling by the Finite Element Method

SOIL_FOUNDATION_STRUCTURE_INTERACTION

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