SPECIAL ISSUE : FEATURE ARTICLE Has Standard Penetration Testing Reached the Retirement Age? When ordering building and construction materials, the characteristics of the required material can be specified very accurately. For steel, the product of a man- made process and produced under well- defined and well-controlled conditions, the material parameters (e.g., yield strength and Young’s modulus) vary ever so slightly. These parameters are less constant for timber, yet, even for this natural product, engineers can use reliable and repeatable values to describe its behavior. Concrete falls somewhere in between steel and timber, but engineers have addressed this by defining quality classes, using characteristic values (e.g., 95% of the samples wi l l be higher than the characteristic value). In short, when these building materials arrive on site, there are, or at least should be, no surprises when it come to their characteristics. This is in huge contrast to soil. First, this material is not ordered; it has to be accepted as is on the given construction site. To determine the engineering properties and characteristics, the geotechnical engineer can test the soil with one or more soil testing methods, which fall into two groups: 1. Laboratory testing, where soil samples are taken and analyzed in a laboratory, just like the other construction materials. However, at the moment a sample is taken, the conditions of the sample change, influencing the test results. Note, this is why ASTM no longer uses the term “undisturbed soil samples,” as it is truly misleading. 2. In-situ testing, where the soil is tested in its original conditions, down in the ground. Common Practice: The Use of SPT Around the world, the in-situ standard penetration test (SPT) is undoubtedly the most commonly used in-si tu soi l investigation test. This method was initially developed for pile driving evaluation. Standard penetration testing involves driving a simple split tube sampler, representing a driven pile, to obtain penetration resistance, which is expressed in the number of blows per certain AUTHORS Marcel Bielefeld, Allnamics, and Gerald Verbeek, Allnamics USA DEEP FOUNDATIONS • MAY/JUNE 2019 • 97 Crawler-type drill rig used for performing soil borings and SPTs penetration depth or the so-called N-value, and to retrieve a representative soil sample. Results from the SPT are then used in various engineering applications, such as the determination of granular soil settlement, estimation of liquefaction potential, and the bearing capacity of piles. C N E A & R V U E S R S I A F I Y C T A I T L I A O U N Q
