Soil classification through dynamic soil signatures
The demand for a cost effective site investigation method has resulted in the introduction of various advanced in-situ testing techniques. These techniques utilise modern electronics instrumentation to monitor various soil parameters during site investigation. The data is then processed using high speed, low cost digital computers which allow an accurate and rapid assessment of the conditions of the foundation soil under a proposed construction site. In this thesis, a site investigation tool that drives a coring tube into the ground under a combination of vibration and impact is considered. This machine, called a vibro-impact corer, is fully instrumented to provide penetrometer-type information and a core sample for further inspection in the laboratory. The self-adjusting mechanism inherent in this machine delivers the minimum level of energy required to overcome soil resistance which thereby allows continuous penetration of the coring tube. This mechanism is also results in minimal induced disturbance during the coring process. This thesis investigates use of the vibro-impact corer as a soil classification tool. It involves the design of data analysis software to perform the soil classification procedure. Due to the nature of the system, the resistance monitored through the annular load cell fitted at the tip of the coring tube consists of the dynamic end resistance waveform and the peak magnitude of these waveforms over a sampling period. The vibro-impact soil classification system is based on the distinct self-adjusting mechanism of the machine. The self-adjustment mechanism imparts a different level of impact and vibration as soil conditions change which produces distinct dynamic soil resistance waveforms. In addition, the penetration rate and the magnitude of the soil resistance encountered also varies according to the material being penetrated. These two features are used to form the basis of the soil classification system in this software. The software also includes options for empirical correlation of the results obtained from the vibro-impact penetrometer with the CPT and SPT tests to allow comparison. The vibro-impact soil classification software is designed to be user-friendly. It reads the data files from a Biodata Transient Capture System for the classification process. The output devices such as plotter and printer are used to produce hardcopy records for various data. All the options are menu driven. A two degree freedom simulation of the operational responses of the vibro-impact machine is also included in this thesis. The main objective of this simulation is to study the soil response during vibro-impact mode of driving. This allows a comparison of the simulation soil responses to the model test results to provide an understanding of the soil behaviour under a combination of both vibratory and impact loadings. This thesis presents the results of several laboratory model and full scale vibro-impact penetrometer tests. It concentrates on the main subject of soil classification during the discussions although in some occasions the operational mechanism of the machine is mentioned. The results justify the approaches adopted for the soil classification system using a vibro-impact machine.