No abstract

Down-the-hole hammer (DTH) drilling is an air hammer drilling technique designed for drilling through bedrock and features a typical drill string length of 200 m or shorter due to its technical specifications. During DTH drilling of granite-like hard rocks, the impacts of the piston-bit-rock system cause the drill string to generate severe vibration and noise pollution. In addition, the rapid wear of the button bit and drill string significantly decreases the drilling efficiency. Based on a distributed parameter drill string model of a DTH, this paper studies the phenomenon of the drill string’s axial forced vibration with a periodic impacting force under DTH drilling in an innovative manner. With the focus of study on the DTH button bit, the transient impact force on the button bit during the drilling of the piston-bit-rock system is determined, and the impact force is converted to a periodic excitation force function using polynomial fitting. Then, the periodic impulse is transformed into a harmonic series using Fourier transforms, and finally, the drill string vibration response under the harmonic excitation force series is determined. The results reveal that a periodic impulse can mainly be determined by the nature of the DTH drill string and rock and the impact frequency during drilling. Further evidence demonstrates that at least one frequency component of the impulse harmonic series will be equal to the modal frequencies of the drill string insofar as the condition [Formula: see text] is met; the coupling of the short drill string with the DTH may cause resonance at a specific hole depth, whose resonance regions are adjacent to but not continuous with the extension of the drill string. This work should serve as an important theoretical guide for designers in the dynamic design, modification, and use of a DTH drilling system.

The undisturbed sampling of the overburden soil is attracting increased attention due to the rapid increases in the construction of large-scale domestic foundations and environmental protection engineering. To date, systematic theoretical research on sonic drilling technology has rarely been published. In the present paper, the vibration response induced by sonic harmonic excitation is studied by modeling the flexible drill string of a sonic drill; its dynamic theory and design methodology have been developed, which reveal effects of the excitation frequency, the structural parameters on vibration response of the drill string. The study of sonic drill string vibration is beneficial for improving the drilling efficiency and reducing the damage.

Based on the general finite element software ABAQUS, the FE model of 30-story SRC frame-RC core wall hybrid structure is established and the simulation analysis is conducted to the evolution of storey damage under cyclic loading, then the law of storey damage evolution affected by component damage is revealed. The analysis results show that the storey damage evolution is affected more by the damage of SRC column and RC shear wall than by the SRC beam's, when the single component has similar damage; and also is affected greatly by the damage of RC shear wall, when the two different types of components have similar damage. Based on the results of numerical simulation, the mathematical relations between the component damage and the storey damage are established, which would provide theoretical support to the hybrid structure damage model under earthquake excitation.

The weld of T-joint segments is the weakest link during the excavation of a metro crossing passage tunnel with the shield method. The stress on the weld is one of the key factors and should be given special attention. This paper aims to monitor the stress and strain of the weld of the T-joint segments during the construction process of the metro crossing passage tunnel of Ningbo Metro Line 3, the world first metro crossing passage tunnel by the shield method. A finite element model of the metro crossing passage tunnel is established. The CAE (Computer Aided Engineering) simulation is conducted by the sub-model approach. The calibration analysis between test data and CAE results for the strain of the weld under several key cases is performed. Based on this, the vary regulation of the stress and strain of the weld seam at various positions of the steel tube sheet under critical working conditions is obtained. Consequently, an authentic, reliable and advanced simulation process is established, and the weld strength of the T-joint segments of such kind constructions can be well assessed and predicted.