Prediction of Backfill Strength Based on Support Vector Regression Improved by Grey Wolf Optimization

In order to predict backfill strength rapidly with high accuracy and provide a new technical support for digitization and intelligentization of mine,a support vector regression(SVR)model improved by grey wolf optimization(GWO),GWO-SVR model,is established.First,GWO is used to optimize penalty term and kernel function parameter in SVR model with high accuracy based on the experimental data of uniaxial compressive strength of filling body.Subsequently,a prediction model which uses the best two parameters of best c and best g is established with the slurry density,cement dosage,ratio of artificial aggregate to tailings,and curing time taken as input factors,and uniaxial compressive strength of backfill as the output factor.The root mean square error of this GWO-SVR model in predicting backfill strength is 0.143 and the coefficient of determination is 0.983,which means that the predictive effect of this model is accurate and reliable.Compared with the original SVR model without the optimization of GWO and particle swam optimization(PSO)-SVR model,the performance of GWO-SVR model is greatly promoted.The establishment of GWO-SVR model provides a new tool for predicting backfill strength scientifically.

Correlative Mechanism of Hydraulic-mechanical Property in Cemented Paste Backfill

Hydraulic characteristic is a good indication of binder hydration, which determines the strength development of cemented paste backfill（CPB）. Therefore, the hydraulic characteristic should be communicated with the mechanical property to provide an advanced knowledge that can help mine workers make a rational strategy and reduce the mining cycle. An experimental program was performed to obtain the hydraulic（monitored by suction and volumetric water content） and mechanical properties（unconfined compressive strength（UCS） test） of CPB at the 28 days curing age. According to the monitoring and testing results, the relationships between the hydration reaction rate and volumetric water content（VWC）, suction and VWC, suction and UCS were established. The hydration degree showed a liner rise as the VWC decreased. Curves of the VWC and UCS were featured with a nonlinear reduction and nonlinear growth（both are exponential functions） as the suction rising, respectively. These established relationships validated the strong correlative mechanism of hydraulic and mechanics behavior for CPB. Also, the results of the present research indicated that the hydraulic characteristics and mechanical property were strongly coupled. These correlations and couplings will be of great importance to understand the hardening process of CPB and bring to a safe CPB field operation.

Stability analysis of shallow tunnels subjected to eccentric loads by a boundary element method

This paper presents the results of the shear strength（frictional strength） of cemented paste backfillcemented paste backfill（CPB-CPB） and cemented paste backfillerock wall（CPB-rock） interfaces. The frictional behaviors of these interfaces were assessed for the short-term curing times（3 d and 7 d） using a direct shear apparatus RDS-200 from GCTS（Geotechnical Consulting ＆ Testing Systems）. The shear（friction） tests were performed at three different constant normal stress levels on flat and smooth interfaces. These tests aimed at understanding the mobilized shear strength at the CPB-rock and CPB-CPB interfaces during and/or after open stope filling（no exposed face）. The applied normal stress levels were varied in a range corresponding to the usually measured in-situ horizontal pressures（longitudinal or transverse） developed within paste-filled stopes（uniaxial compressive strength, s c 150 k Pa）. Results show that the mobilized shear strength is higher at the CPB-CPB interface than that at the CPB-rock interface. Also, the perfect elastoplastic behaviors observed for the CPB-rock interfaces were not observed for the CPB-CPB interfaces with low cement content which exhibits a strain-hardening behavior. These results are useful to estimate or validate numerical model for pressures determination in cemented backfill stope at short term. The tests were performed on real backfill and granite. The results may help understanding the mechanical behavior of the cemented paste backfill in general and, in particular, analyzing the shear strength at backfillebackfill and backfill-rock interfaces.