A Modeling Method for Predicting the Strength of Cemented Paste Backfill Based on a Combination of Aggregate Gradation Optimization and LSTM

Cemented paste backill(CPB)is a susta inable mining technology that is widely used in mines and helps to improve the mine environment.To investigate the relationship between aggregate grading and different affecting factors and the uniaxial compressive strength(UCS)of the cemented paste backill(CPB),Talbol gradation theory and neural networks is used to evaluate aggregate gradation to determine the optimum aggregate ratio.The mixed aggregate ratio with the least amount of cement(waste stone content river sand content=7:3)is obtained by using Talbol grading theory and pile compactness function and combined with experiments.In addition,the response surface method is used to design strength speaific ratio experiments.The UCS prediction model which ues the ISTM and considers the aggregates gradation have high accuracy.The root mean square error(RMSE)of the prediction results is 0.0914,the coefficient of determination(R^(2))is 0.9973 and the variance account for(VAF)is 99.73.Compared with back propagation neural network(BP-ANN),extreme lea ming machine(ELM)and madal basis function neural network(RBF ANN),LSTM can efectively characterize the nonlinear relationship between UCS and individual affecting factors and predict UCS with high accuracy.The sensitivity analysis of different affecting factors on UCS shows that all 4 factors have significant effect on UCS and sensitivity is in the following ranking:cement content(0.9264)>slurry concentration(0.9179)>aggregate gradation(waste rodk content)(0.9031)>curing time(09031).

Synthesis of bulk lanthanum polyphosphate and other rare earth phosphates through hydrothermal hot-pressing

Bulk samples of lanthanum polyphosphate were synthesized through a hydrothermal hot-pressing(HHP)process.In this process,pressing temperature,pressure and volume of water were varied in order to improve the density and strength of the resulting materials.The strength of the bulk samples was estimated through drilling and ultrasonic treatments.In order to improve the strength of the materials,the use of microwave irradiation was examined.Lanthanum polyphosphate formed porous bulk samples with a filling factor of approximately 70%,which was calculated from real and theoretical densities.With respect to machinable strength,a drilled hole greater than 7.0 mm in diameter was obtained on some bulk samples,and the diameter of the samples was 14 mm.The HHP process is a useful method for obtaining bulk samples of lanthanum polyphosphate.Bulk lanthanum polyphosphate containing water crumbled easily to a powder form upon ultrasonication.However,these bulk samples retained their shape upon ultrasonication,despite containing water,after exposure to microwave irradiation,and also experienced minimal weight loss.Furthermore,to study the effect of microwave heating,bulk lanthanum orthophosphate,yttrium orthophosphate and polyphosphate were also examined.