Ground Vibrations Induced by Impact Pile Driving

The importance of vibration problems induced by pile driving is addressed and guidelines for establishing limiting vibration levels with respect to buildings with different foundation conditions are presented. Basic concepts of pile dynamics and stress-wave measurements, which were developed for the determination of driving resistance and bearing capacity of impact-driven piles, provide important information about ground vibration induced by pile penetration. Dynamic hammer properties and geometry as well as the driving process are important for ground vibration emission from the pile. It is shown that the energy-based, empirical approach, which is still widely used by practicing engineers, is too crude for reliable analysis of ground vibrations and can even be misleading. The main limitations of the energy approach are the assumption that driving energy governs ground vibrations, the omission of geotechnical conditions and soil resistance, and the uncertainty with regard to input values. Three types of ground waves are considered when analyzing pile driving: spherical waves emitted from the pile toe, cylindrical waves propagating laterally from the pile shaft, and surface waves, which are generated by wave refraction at the ground surface at a critical distance from the pile. These three wave types depend on the velocity-dependent soil resistance at the pile-soil interface. The most important factor for analyzing ground vibrations is the impedance of each system component, i.e., the pile hammer, the pile, and the soil along the shaft and at the pile toe. Guidance based on geotechnical conditions is given as to the selection of appropriate impedance values for different soil types. A theoretical concept is presented, based on a simplified model that considers the strain-softening effect on wave velocity in the soil, making it possible to calculate the attenuation of spherical and surface waves and of cylindrical waves generated at the pile toe and the pile shaft, respectively. The concept is applied to define k-values, which have been used in empirically developed models and correlated to type of wave and soil properties. An important aspect of the proposed prediction model is the introduction of vibration transmission efficacy, a factor which limits the amount of vibration force that can be transmitted along the pile-soil interface (toe and shaft). Results from detailed vibration measurements are compared to values calculated from the proposed model. The agreement is very good and suggests that the new model captures the important aspects of ground vibration during penetration of the pile into different soil layers. Finally, based on the presented model, factors influencing the emission of ground vibrations during impact pile driving are discussed

Effective stress analysis and set-up for shaft capacity of piles in clay

ABSTRACT A case history of repeated dynamic and static loading tests in Alberta on two pipe piles during dissipation of driving-induced pore pressures is presented together with three reanalyzed published case histories involving similar records. The four case histories demonstrate that, for each case, the same effective-stress proportionality coefficients, beta-coefficients, fit the capacities at different degrees of dissipation of excess pore pressures. For two of the test sites, the beta-coefficients back-calculated from the tests differed considerable from the values determined from the soil plasticity relation, while for two, the agreement is good. For one case, the backcalculated shaft resistance agreed well with the values of vane shear strength, while a less good agreement was found for the other tests. Neither case showed good agreement was found for methods combining undrained shear strength and effective overburden stress. Capacity calculations for two cases employing methods based on CPT soundings gave excellent agreement with one test and a poor agreement with the other. The increase of capacity due to aging after dissipation of excess pore pressures did not agree with cited recommendation for calculations of aging effect

Nitric oxide-an endogenous inhibitor of gastric acid secretion in isolated human gastric glands

BACKGROUND: Endothelial nitric oxide synthase (eNOS) has previously been detected in the glandular part of the human gastric mucosa. Furthermore, nitric oxide (NO) has been shown to influence gastric secretion in various animal models. The present study was conducted to investigate the influence of exogenously and endogenously derived NO on histamine- and cAMP-stimulated gastric acid secretion in isolated human oxyntic glands. METHODS: Oxyntic glands were isolated from human gastric biopsies and were subsequently pre-treated with NO donors and nitric oxide synthase inhibitors and then exposed to histamine or dibutyryl-cAMP (db-cAMP). The secretory response of the glands was determined as accumulation of [(14)C]aminopyrine. RESULTS: The histamine- or db-cAMP-induced acid secretion was attenuated by L-arginine, a known source of endogenous NO, and also by the NO-donors sodium nitroprusside (SNP) and S-nitroso-N-acetyl-penicillamine (SNAP). Pre-treatment with either of the NOS inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME) or N(G)-nitro-L-arginine (L-NNA) enhanced the secretory response. CONCLUSION: Our results show that NO inhibits gastric acid secretion in isolated human gastric glands, and that there is endogenous formation of NO within the glandular epithelium in the vicinity of the parietal cells

Antiviral therapies against Ebola and other emerging viral diseases using existing medicines that block virus entry

Emerging viral diseases pose a threat to the global population as intervention strategies are mainly limited to basic containment due to the lack of efficacious and approved vaccines and antiviral drugs. The former was the only available intervention when the current unprecedented Ebolavirus (EBOV) outbreak in West Africa began. Prior to this, the development of EBOV vaccines and anti-viral therapies required time and resources that were not available. Therefore, focus has turned to re-purposing of existing, licenced medicines that may limit the morbidity and mortality rates of EBOV and could be used immediately. Here we test three such medicines and measure their ability to inhibit pseudotype viruses (PVs) of two EBOV species, Marburg virus (MARV) and avian influenza H5 (FLU-H5). We confirm the ability of chloroquine (CQ) to inhibit viral entry in a pH specific manner. The commonly used proton pump inhibitors, Omeprazole and Esomeprazole were also able to inhibit entry of all PVs tested but at higher drug concentrations than may be achieved in vivo. We propose CQ as a priority candidate to consider for treatment of EBOV

Artificial neural network (ANN) approach for modelling of pile settlement of open-ended steel piles subjected to compression load

This study was devoted to examine pile bearing capacity and to provide a reliable model to simulate pile load-settlement behaviour using a new artificial neural network (ANN) method. To achieve the planned aim, experimental pile load test were carried out on model open-ended steel piles, with pile aspect ratios of 12, 17, and 25. An optimised second-order Levenberg-Marquardt (LM) training algorithm has been used in this process. The piles were driven in three sand densities; dense, medium, and loose. A statistical analysis test was conducted to explore the relative importance and the statistical contribution (Beta and Sig) values of the independent variables on the model output. Pile effective length, pile flexural rigidity, applied load, sand-pile friction angle and pile aspect ratio have been identified to be the most effective parameters on model output. To demonstrate the effectiveness of the proposed algorithm, a graphical comparison was performed between the implemented algorithm and the most conventional pile capacity design approaches. The proficiency metric indicators demonstrated an outstanding agreement between the measured and predicted pile-load settlement, thus yielding a correlation coefficient (R) and root mean square error (RMSE) of 0.99, 0.043 respectively, with a relatively insignificant mean square error level (MSE) of 0.0019. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group