Ground hydraulic fracturing plays a crucial role in controlling the far-field hard roof,making it imperative to identify the most suitable target stratum for effective control.Physical experiments are conducted based ...Ground hydraulic fracturing plays a crucial role in controlling the far-field hard roof,making it imperative to identify the most suitable target stratum for effective control.Physical experiments are conducted based on engineering properties to simulate the gradual collapse of the roof during longwall top coal caving(LTCC).A numerical model is established using the material point method(MPM)and the strain-softening damage constitutive model according to the structure of the physical model.Numerical simulations are conducted to analyze the LTCC process under different hard roofs for ground hydraulic fracturing.The results show that ground hydraulic fracturing releases the energy and stress of the target stratum,resulting in a substantial lag in the fracturing of the overburden before collapse occurs in the hydraulic fracturing stratum.Ground hydraulic fracturing of a low hard roof reduces the lag effect of hydraulic fractures,dissipates the energy consumed by the fracture of the hard roof,and reduces the abutment stress.Therefore,it is advisable to prioritize the selection of the lower hard roof as the target stratum.展开更多
A new hydraulic cementitious binder was developed by mainly utilizing industrial byproducts phosphogypsum（PG）and ground granulated blast furnace slag（GGBFS）with small addition of ordinary portland cement（OPC）.Th...A new hydraulic cementitious binder was developed by mainly utilizing industrial byproducts phosphogypsum（PG）and ground granulated blast furnace slag（GGBFS）with small addition of ordinary portland cement（OPC）.The hydration process and microstructure were studied by X-ray diffraction（XRD） and scanning electronic microscopy（SEM）.OPC hydrated first at early age to form primarily C-S-H gel,ettringite and calcium hydroxide（CH）.GGBFS activated by CH and sulfate ions hydrated continuously at later age,producing more and more hydration products,C-S-H gel and ettringite.Thus the paste developed a denser microstructure and its strength increased.The 28 d compressive strength of the mixture of 50%PG,46% GGBFS and 4%OPC exceeded 45 MPa.The setting time was faster and 3 d and 7 d strength were higher when the proportion of OPC increased.But the 28 d strength decreased when OPC exceeded 4%due to large amount of ettringite formed at late hydration age which damaged the microstructure.展开更多
基金the National Natural Science Foundation of China(No.51974042)National Key Research and Development Program of China(No.2023YFC3009005).
文摘Ground hydraulic fracturing plays a crucial role in controlling the far-field hard roof,making it imperative to identify the most suitable target stratum for effective control.Physical experiments are conducted based on engineering properties to simulate the gradual collapse of the roof during longwall top coal caving(LTCC).A numerical model is established using the material point method(MPM)and the strain-softening damage constitutive model according to the structure of the physical model.Numerical simulations are conducted to analyze the LTCC process under different hard roofs for ground hydraulic fracturing.The results show that ground hydraulic fracturing releases the energy and stress of the target stratum,resulting in a substantial lag in the fracturing of the overburden before collapse occurs in the hydraulic fracturing stratum.Ground hydraulic fracturing of a low hard roof reduces the lag effect of hydraulic fractures,dissipates the energy consumed by the fracture of the hard roof,and reduces the abutment stress.Therefore,it is advisable to prioritize the selection of the lower hard roof as the target stratum.
文摘A new hydraulic cementitious binder was developed by mainly utilizing industrial byproducts phosphogypsum（PG）and ground granulated blast furnace slag（GGBFS）with small addition of ordinary portland cement（OPC）.The hydration process and microstructure were studied by X-ray diffraction（XRD） and scanning electronic microscopy（SEM）.OPC hydrated first at early age to form primarily C-S-H gel,ettringite and calcium hydroxide（CH）.GGBFS activated by CH and sulfate ions hydrated continuously at later age,producing more and more hydration products,C-S-H gel and ettringite.Thus the paste developed a denser microstructure and its strength increased.The 28 d compressive strength of the mixture of 50%PG,46% GGBFS and 4%OPC exceeded 45 MPa.The setting time was faster and 3 d and 7 d strength were higher when the proportion of OPC increased.But the 28 d strength decreased when OPC exceeded 4%due to large amount of ettringite formed at late hydration age which damaged the microstructure.
