To optimize the distance between the bells in pile design,this paper reports a series of small scale tests on the uplift capacity of double belled piles embedded in dry dense sand considering different bell space rati...To optimize the distance between the bells in pile design,this paper reports a series of small scale tests on the uplift capacity of double belled piles embedded in dry dense sand considering different bell space ratios.Finite element modelling is also performed to evaluate the range of soil failure around the piles during pile uplift displacement.Test results show that when bell space ratio is 6 or 8,the uplift capacity reaches the peak value.The upper bell bears more load than the lower one for the piles with bell space ratio less than 6,while the lower bell bears more load than the upper one for the piles with bell space ratio larger than 8.展开更多
Based on the field destructive test of six rock-socketed piles with shallow overburden,three prediction models are used to quantitatively analyze and predict the intact load−displacement curve.The predicted values of ...Based on the field destructive test of six rock-socketed piles with shallow overburden,three prediction models are used to quantitatively analyze and predict the intact load−displacement curve.The predicted values of ultimate uplift capacity were further determined by four methods(displacement controlling method(DCM),reduction coefficient method(RCM),maximum curvature method(MCM),and critical stiffness method(CSM))and compared with the measured value.Through the analysis of the relationship between the change rate of pullout stiffness and displacement,a method used to determine the ultimate uplift capacity via non-intact load−displacement curve was proposed.The results show that the predicted value determined by DCM is more conservative,while the predicted value determined by MCM is larger than the measured value.This suggests that RCM and CSM in engineering applications can be preferentially applied.Moreover,the development law of the change rate of pullout stiffness with displacement agrees well with the attenuation form of power function.The theoretical predicted results of ultimate uplift capacity based on the change rate of pullout stiffness will not be affected by the integrity of the curve.The method is simple and applicable for the piles that are not loaded to failure state,and thus provides new insights into ultimate uplift capacity determination of test piles.展开更多
This paper proposes an empirical formula to estimate the shear strength of hydraulic expansion rockbolts.The field experimental results were obtained from eleven pullout tests to evaluate the results computed by the p...This paper proposes an empirical formula to estimate the shear strength of hydraulic expansion rockbolts.The field experimental results were obtained from eleven pullout tests to evaluate the results computed by the proposed formula.It was found that shear resistance of hydraulic expansion rockbolts significantly depends on the uniaxial compressive strength and elastic modulus of rock,with high correlation coefficients of 0.7651 and0.8587,respectively.The developed formula enables estimation of the maximum pullout load in an analytical process without pullout tests in the field.Conversely,due to the poor interlocking at the initial pullout load,the measured displacements were higher than the estimated ones.To reduce the interlocking effects between bolt and rock,we recommend preloading of 29.4 kN.Preload allows reducing the distance between the measured and estimated displacement and making two load-displacement curves practically identical with marginal differences of 1.1 to 1.5 mm at the maximum pullout load.展开更多
The mixed model of improved exponential and power function and unequal interval gray GM(1,1)model have poor accuracy in predicting the maximum pull-out load of anchor bolts.An optimal combination model was derived usi...The mixed model of improved exponential and power function and unequal interval gray GM(1,1)model have poor accuracy in predicting the maximum pull-out load of anchor bolts.An optimal combination model was derived using the optimally weighted combination theory and the minimum sum of logarithmic squared errors as the objective function.Two typical anchor bolt pull-out engineering cases were selected to compare the performance of the proposed model with those of existing ones.Results showed that the optimal combination model was suitable not only for the slow P-s curve but also for the steep P-s curve.Its accuracy and stable reliability,as well as its prediction capability classification,were better than those of the other prediction models.Therefore,the optimal combination model is an effective processing method for predicting the maximum pull-out load of anchor bolts according to measured data.展开更多
基金Project(51778346) supported by the National Natural Science Foundation of ChinaProject(2019GSF111007) supported by the Key Research and Development Project of Shandong Province of China+1 种基金Project(ZR201808040034) supported by the Natural Science Foundation of Shandong Province of ChinaProject(2015RCJJ010) supported by the Talent Introduction Research Start-up Fund Project of Shandong University of Science and Technology,China。
文摘To optimize the distance between the bells in pile design,this paper reports a series of small scale tests on the uplift capacity of double belled piles embedded in dry dense sand considering different bell space ratios.Finite element modelling is also performed to evaluate the range of soil failure around the piles during pile uplift displacement.Test results show that when bell space ratio is 6 or 8,the uplift capacity reaches the peak value.The upper bell bears more load than the lower one for the piles with bell space ratio less than 6,while the lower bell bears more load than the upper one for the piles with bell space ratio larger than 8.
基金Project(2016YFC0802203)supported by the National Key R&D Program of ChinaProject(2013G001-A-2)supported by the Science and Technology Research and Development Program of China Railway CorporationProject(SKLGDUEK2011)supported by the State Key Laboratory for GeoMechanics and Deep Underground Engineering,China University of Mining&Technology。
文摘Based on the field destructive test of six rock-socketed piles with shallow overburden,three prediction models are used to quantitatively analyze and predict the intact load−displacement curve.The predicted values of ultimate uplift capacity were further determined by four methods(displacement controlling method(DCM),reduction coefficient method(RCM),maximum curvature method(MCM),and critical stiffness method(CSM))and compared with the measured value.Through the analysis of the relationship between the change rate of pullout stiffness and displacement,a method used to determine the ultimate uplift capacity via non-intact load−displacement curve was proposed.The results show that the predicted value determined by DCM is more conservative,while the predicted value determined by MCM is larger than the measured value.This suggests that RCM and CSM in engineering applications can be preferentially applied.Moreover,the development law of the change rate of pullout stiffness with displacement agrees well with the attenuation form of power function.The theoretical predicted results of ultimate uplift capacity based on the change rate of pullout stiffness will not be affected by the integrity of the curve.The method is simple and applicable for the piles that are not loaded to failure state,and thus provides new insights into ultimate uplift capacity determination of test piles.
基金supported by 2016 Hongik University Research Fund and the Convergence R&D program of MSIP/NST[Convergence Research-14-2-ETRI,Development of Internet of Things(IoT)-based Urban Underground Utility Monitoring and Management System]
文摘This paper proposes an empirical formula to estimate the shear strength of hydraulic expansion rockbolts.The field experimental results were obtained from eleven pullout tests to evaluate the results computed by the proposed formula.It was found that shear resistance of hydraulic expansion rockbolts significantly depends on the uniaxial compressive strength and elastic modulus of rock,with high correlation coefficients of 0.7651 and0.8587,respectively.The developed formula enables estimation of the maximum pullout load in an analytical process without pullout tests in the field.Conversely,due to the poor interlocking at the initial pullout load,the measured displacements were higher than the estimated ones.To reduce the interlocking effects between bolt and rock,we recommend preloading of 29.4 kN.Preload allows reducing the distance between the measured and estimated displacement and making two load-displacement curves practically identical with marginal differences of 1.1 to 1.5 mm at the maximum pullout load.
基金The National Natural Science Foundation of China(No.51778485).
文摘The mixed model of improved exponential and power function and unequal interval gray GM(1,1)model have poor accuracy in predicting the maximum pull-out load of anchor bolts.An optimal combination model was derived using the optimally weighted combination theory and the minimum sum of logarithmic squared errors as the objective function.Two typical anchor bolt pull-out engineering cases were selected to compare the performance of the proposed model with those of existing ones.Results showed that the optimal combination model was suitable not only for the slow P-s curve but also for the steep P-s curve.Its accuracy and stable reliability,as well as its prediction capability classification,were better than those of the other prediction models.Therefore,the optimal combination model is an effective processing method for predicting the maximum pull-out load of anchor bolts according to measured data.
