Design and application of a pore water pressure loading device for long-term hydration reactions
[Objective]As underground space development progresses into deeper parts of the Earth,the geological conditions of rock formations become more complex.The change in the mechanical properties of rocks under pore water pressure has become a key focus in rock mechanics,particularly in deep underground projects such as resource extraction and tunnel construction.Pore water pressure testing is an important method for analyzing the effects of pore water pressure on rocks.However,traditional pore water pressure loading devices encounter challenges,especially in maintaining stability during long-term loading,leading to pressure fluctuations and decreases.Power outages can also result in pressure drops,which affects the accuracy and reliability of the experimental results.These issues have prevented indoor simulations from accurately replicating real deep rock water environments.Therefore,this study designed and developed a pore water pressure loading device that can simulate various water environments and ensure long-term rock hydration reactions.This development is crucial for understanding the mechanical changes in deep rocks under pore water pressure and ensuring the long-term safety and stability of underground projects.[Methods]The proposed pore water pressure loading device is designed to meet the requirements of long-term hydration reactions.The device consists of a symmetric structure,including the main body,inlet and outlet pipelines,and control valves.The structure is simple,reliable,and easy to operate.The pore water pressure loading process can be completed by rotating the control rods.Once the water pressure reaches the required level,the shut-off valves are adjusted to maintain the desired pressure for the test.Minor pressure deviations during long-term loading can be corrected by manually adjusting the control rods in real time,thus ensuring stable pore water pressure and accurately simulating rock water conditions.The device was used in conjunction with Sichuan University's Deep High-Stress High-Permeability Environment Simulation System to treat rock samples for 60 days,during which pore water pressure changes were recorded.After treatment,Brazilian splitting tests were conducted using an MTS815 testing machine to determine the Mode I fracture toughness of the different samples.[Results]During the 60-day loading process,the pore water pressure slightly decreased on Days 16,42,and 58 with a reduction of approximately 0.5 MPa,indicating that the device maintained stable pore water pressure with minimal fluctuations,meeting the experimental requirements.The results also showed differences in fracture toughness among the three marble samples.Specifically,samples simulating deep rock water conditions(Sample A)and those soaked in a NaOH solution(pH=9,Sample B)showed a reduction of 10.1%and 7.6%,respectively,compared with those under natural conditions(Sample C).This finding indicates that rock fracture toughness decreases,to some extent,under water saturation,particularly in deep water environments where pore water pressure promotes crack propagation,further reducing fracture toughness.[Conclusions]The pore water pressure loading device developed in this study achieves long-term,stable,and high-precision pore water pressure loading,meeting the experimental needs for sustained pressure applications.The device can simulate different water environments by adjusting the water solution in the internal tank,creating ideal conditions for analyzing rock hydration reactions in various underground environments.The mechanical adjustment of the device,without the need for power,makes it simple to operate and compatible with conventional rock mechanics testing equipment,such as triaxial rock testing machines.The development and use of this device will facilitate further experimental studies on the effects of pore water pressure on rock mechanical properties under more complex conditions.
rock mechanicspore water pressurelong-term loading devicehydration reaction
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