Estimating soil fines contents from CPT data

In order to verify soil property correlations between Standard Penetration Test (SPT) and Cone Penetration Test (CPT) results, a specially designed field investigation and laboratory testing program was implemented. The field exploratory investigation program included grouped SPT and CPT explorations at selected locations. Each test group included two hollow-stem auger borings utilizing a standard penetration sampler and a modified California sampler, respectively, and a seismic CPT sounding. These SPT borings and CPT sounding were placed at the vertices of a triangle around which a circle with a diameter approximately 3m (10 feet) could be circumscribed. This paper presents the results of the comparison between laboratory measured fines contents and the calculated fines contents based on CPT data interpretation. From this information, a new empirical relationship is proposed. A comparison with published data from various papers and reports indicates that this proposed new relationship appears to provide a more reasonable estimation of fines contents of soils. 2 FIELD INVESTIGATIONS In order to compare the measured data with those estimated based on CPT interpretations, a specially designed field investigation program was set up and performed on a selected site (Site A). This site is located near the southern edge of the San Bernardino Valley, a portion of the Peninsular Ranges Geomorphic Province, and on a relatively youthful geomorphic surface associated with alluvial fans emanating from the Loma Linda Hills to the south and within the San Timoteo Wash. The native surficial materials at the site consist of very young sandy alluvial valley deposits of late Holocene age (Morton 1978; Morton and Miller, 2006). The soil conditions underlying this site were explored by means of three groups of exploratory borings and CPT soundings. Each group included two exploratory borings (one boring using a standard SPT sampler and the other boring using a modified California (MC) sampler) and one CPT sounding. In order to compare the results, soil borings and CPT sounding were placed close enough together so that soils at approximately the same depth could reasonably be assumed to be identical. On the other hand, they were placed far enough apart so as not to affect the penetration resistance results. It was finally determined to place soil borings and CPT sounding on vertices of an approximately equilateral triangle forming a circumcircle approximately 3m (10 feet) in diameter. A total of three groups of such borings and soundings were placed in an approximately equilateral triangular layout so as to cover the entire site with an area approximately 330 meters square. The MC sampler related results are not related to the topic of this paper and will be reported in other papers. 2.1 Exploratory Borings and Sampling The soil borings were drilled with hollow-stem auger, per ASTM D6151, using a truck-mounted CME 75 drill rig equipped for soil sampling. The diameter of SPT borehole was of 20.3 cm (8 inches). The inside diameter of the auger was 15.2 cm (6 inches). The standard SPT sampler was 5 cm (2 inches) in outer diameter and 3.5 cm (1-3/8 inches) in inner diameter. Samplers were driven at intervals of 76.0 cm (2.5 feet) with an automatic hammer that drops a 63.5 kilograms (140-pound) weight 76.0 cm (30 inches) for each blow. Blowcounts were recorded. Bulk samples obtained from standard SPT sampler were utilized for fines contents and/or Atterberg limits testing.