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The ice-breaking process of the double-layer charge at a depth of 150 cm underwater is simulated by LS-DYNA. This paper analyzes the load type, shock wave pressure characteristics and propagation behavior of the double-layer charge during underwater explosion. By analyzing the impact of the shock wave pressure in the water under different charge intervals and time intervals on the shock wave pressure of the double charge, it is concluded that the peak pressure of the double charge explosion shock wave is jointly determined by the double charge. In this range, the second peak pressure value of the drug is greater than the pressure value of the first peak of the drug, and the attenuation is slow; the delay time of the upper charge has little effect on the peak pressure value of the shock wave in the water; the delay time is higher than that of the lower charge Initiation, at the same position, the total pressure peak of the shock wave formed by the delay of the upper charge is larger.

Foam as a soil conditioning agent has been extensively employed in earth pressure balanced (EPB) tunnel boring machines (TBM) to change the mechanical and hydraulic properties of soils for effective excavation. Foam stability is a critical parameter that influences the performance of foam and foam-conditioned soils. This paper examines foam stability under pressure through a novel foam generation – pressure chamber – foam capture testing system. A comprehensive suite of foam experiments was performed to examine the physical phenomenon of foam degradation and time-dependent foam properties under pressure. Testing results suggest that foam liquid loss is not an effective indicator for characterizing foam stability, while foam volume loss is a more appropriate measure of foam stability. Results also reveal that foam liquid drainage is significantly retarded at higher chamber pressure because foam bubbles are smaller and more uniform. Bubble size was not appreciably different in dry and wet foams.

Proper soil conditioning is critical for effective earth pressure balanced tunnel boring machine (EPBM) operation. Foam as a soil conditioner has been extensively used in EPBM tunneling to modify the excavated soil properties. A critical characteristic of foam-conditioned soil is stability, i.e., the ability to maintain the engineering properties throughout the residency time (30–90 min) in the mixing chamber. A comprehensive suite of experiments on foam-conditioned soil was conducted at both microscale and macroscale to investigate the fundamentals of foam-soil interaction and engineering properties of foam-conditioned soil. A foam-soil capture device and an optical microscope were used to capture bubble-grain images at a microscale under pressure. A pressurized testing chamber (PTC) was used to examine the stability of the mechanical properties of foam-conditioned soil. The compressibility, vane shear strength, pore pressure, and effective stress of foam-conditioned soil with elapsed time were obtained from the PTC test. The bubble-grain image analysis results reveal that foam is more stable when mixed with soil than by itself, indicating that soil particles help stabilize foam bubbles. Soil particles create a barrier to bubble coalescence and coarsening. The PTC test results show that the engineering properties of foam-conditioned soil remained constant over the 60-minute test duration. The results suggest that the accumulated “air bubble” at the top of the mixing chamber during EPBM tunneling is not due to the de-stabilization of foam bubbles when mixed with soil.

Precast, prestressed hollow-core (PHC) slabs are widely used in floor and roof decks because of their economic benefits. Because no shear reinforcement can be provided because of fabrication restraints, designers have to opt for deeper profile or filling PHC slab cores with concrete when the load demand exceeds the limited concrete shear capacity of PHC slabs. This research project is exploring an innovative technique for strengthening the web-shear capacity of PHC slabs by bonding external fiber-reinforced polymer (FRP) sheets along the internal perimeter of the slab voids. Experimental testing and numerical simulation on full-scale single web, I-shaped beam specimens cut out longitudinally from full-width hollow-core slabs have been performed during the first phase of this research to investigate the feasibility and effectiveness of this new technique. The influence of several design parameters, including the length and the width of the strengthened zone, the thickness of applied FRP sheets, and...

Prismatic members subjected to internal axial loads exist widely in engineering applications. Because the effects of internal loads and end loads on stability are quite different, the traditional effective length method is not applicable. Engineers require an efficient and convenient method for solving the stability problem of such members. A two-bar model is proposed to illustrate the concept that the effect of compressive axial loads on the stability of sway-inhibited columns can be understood as a negative lateral stiffness. After obtaining the expression of negative lateral stiffness, a relationship between end loads and internal loads can be established so that the internal loads can be considered equivalent to end loads. Then, the column subjected to internal loads can be analyzed as a normal column (without internal axial loads), and the critical buckling load can be obtained easily with the Euler formula. Eigenvalue buckling analyses were performed to examine the proposed method, and the c...

Foam generation in porous media and foam flow through pipes have been studied extensively to date as uncoupled processes. The coupled dynamics of foam generation and pipe flow, however, are comparatively understudied, despite their importance to industrial applications. We consider an experimental system that generates foam by flowing air and surfactant solution through a bead pack, after which the foam flows through a pipe to a downstream pressure chamber. We systematically vary the foam flow rate, bead diameter, bead pack length, pipe length, and chamber pressure. We measure the corresponding impact on flow pressures, densities, velocities, composition, and textures throughout the system, including direct measurements of bubble diameter distributions. We show that with the proper non-dimensionalization, the generator and pipe flows collapse to surprisingly simple friction-factor relationships. We also show that the mean foam bubble diameter exiting the bead pack decreases with increasing flow rate, up to a minimum value set by the pore length-scale K , where K is the bead pack permeability. We also explore the impact of foam texture and composition on the effective foam viscosities within the pipe. Finally, we show that foam properties evolve within the pipe, such that the pipe and bead pack play equally important roles in determining outlet foam properties.