Law governing variations in water-pressure transmission rate in confined aquifers

The water pressure in aquifers is transmitted as energy, with a transmission rate much higher than the migration rate of water particles. The water-pressure transmission rate holds great significance for the safe construction and disaster forecast and prediction of underground engineering under high-pressure water aquifers and bodies. Focusing on the confined aquifers bearing no cohesive soil, this study explored the law governing the changes in the water-pressure transmission rate through theoretical analysis, numerical simulations, field experiments, and laboratory physical model tests. Key findings are as follows: (1) The transmission of water-pressure changes in the aquifers exhibited noticeable hysteresis. The transmission rate was not infinitely high or close to the speed of sound, being subjected to gradual decay with increasing transmission distance. For the radial transmission of the water pressure, there was a quadratic function relationship between the lag time t and the distance r. (2) A higher stable-boundary hydraulic head corresponded to a higher transmission rate under the same water pressure in the confined aquifers, and a greater permeability coefficient was associated with a higher water-pressure transmission rate. (3) Under a certain permeability coefficient, the fitting coefficient C between the lag time and distance of the water-pressure transmission decreased exponentially with an increase in the stable-boundary hydraulic head. (4) Field tests show that when the stable-boundary hydraulic head differed slightly, the average water-pressure transmission rate roughly remained the same in the case of a long transmission distance. (5) As indicated by laboratory tests, with an increase in the transmission distance, the transient pulse water pressure exhibited significant variations in waveforms, a gradual decrease in the peak pressure, prolonged wavelength of pulse pressure waves, and a decrease in the transmission rate of the peak pressure. The transmission rate of the transient pulse water pressure decreased exponentially with an increase in the transmission distance, indicating rapid energy decay with an increase in the transmission distance. (6) For the transient pulse pressure, a higher value corresponded to a higher transmission rate of the initial stage; however, the decay amplitude of its transmission rate increased with an increase in the transmission distance. The results of this study can serve as an important theoretical and practical guide for understanding the influencing mechanisms of the law governing the variations in water-pressure transmission rate and their application in the prediction, prevention, and treatment of water inrush disasters in underground engineering.