The control of slurry pressure aiming to be consistent with the external water and earth pressure during shield tunnelling has great significance for face stability,especially in urban areas or underwater where the su...The control of slurry pressure aiming to be consistent with the external water and earth pressure during shield tunnelling has great significance for face stability,especially in urban areas or underwater where the surrounding environment is very sensitive to the fluctuation of slurry pressure.In this study,an optimal control method for slurry pressure during shield tunnelling is developed,which is composed of an identifier and a controller.The established identifier based on the random forest(RF)can describe the complex non-linear relationship between slurry pressure and its influencing factors.The proposed controller based on particle swarm optimization(PSO)can optimize the key factor to precisely control the slurry pressure at the normal state of advancement.A data set from Tsinghua Yuan Tunnel in China was used to train the RF model and several performance measures like R2,RMSE,etc.,were employed to evaluate.Then,the hybrid RF-PSO control method is adopted to optimize the control of slurry pressure.The good agreement between optimized slurry pressure and expected values demonstrates a high identifying and control precision.展开更多
This research develops a knowledge model for Software Process Improvement (SPI) project based on knowledge creation theory and its twenty-four measurement items, and proposes two hypothesizes about the interaction of ...This research develops a knowledge model for Software Process Improvement (SPI) project based on knowledge creation theory and its twenty-four measurement items, and proposes two hypothesizes about the interaction of explicit knowledge and tacit knowledge in SPI. Eleven factors are extracted through statistical analysis. Three knowledge-creation practices for capturing tacit knowledge contribute greatly to SPI, which are communication among members, crossover collaboration in practical work and pair programming. Two knowledge-creation practices for capturing explicit knowledge have significant positive impact on SPI, which are integrating project document and on-the-job training. Ultimately, suggestions for improvement are put forward, that is, encouraging communication among staff and integrating documents in real time, and future research is also illustrated.展开更多
Many empirical and analytical methods have been proposed to predict fracturing pressure in cohesive soils.Most of them take into account three to four specific influencing factors and rely on the assumption of a failu...Many empirical and analytical methods have been proposed to predict fracturing pressure in cohesive soils.Most of them take into account three to four specific influencing factors and rely on the assumption of a failure mode.In this study,a novel data-mining approach based on the XGBoost algorithm is investigated for predicting fracture initiation in cohesive soils.This has the advantage of handling multiple influencing factors simultaneously,without pre-determining a failure mode.A dataset of 416 samples consisting of 14 distinct features was herein collected from past studies,and used for developing a regressor and a classifier model for fracturing pressure prediction and failure mode classification respectively.The results show that the intrinsic characteristics of the soil govern the failure mode while the fracturing pressure is more sensitive to the stress state.The XGBoost-based model was also tested against conventional approaches,as well as a similar machine learning algorithm namely random forest model.Additionally,several large-scale triaxial fracturing tests and an in-situ case study were carried out to further verify the generalization ability and applicability of the proposed data mining approach,and the results indicate a superior performance of the XGBoost model.展开更多
This study aims to investigate hydrofracturing in double-layered soil through theoretical and experimental analysis,as multilayered soils where the difference in mechanical properties exists are generally encountered ...This study aims to investigate hydrofracturing in double-layered soil through theoretical and experimental analysis,as multilayered soils where the difference in mechanical properties exists are generally encountered in practical engineering.First,an analytical solution for fracturing pressure in two different concentric regions of soil was presented based on the cavity expansion theory.Then,several triaxial hydraulic fracturing tests were carried out to validate the analytical solution.The comparison between the experimental and analytical results indicates the remarkable accuracy of the derived formula,and the following conclusions were also obtained.First,there is a linear relationship between the fracturing pressure and confining pressure in concentric double-layered cohesive soil.Second,when the internal-layer soil is softer than the external-layer soil,the presence of internal soil on the fracturing pressure approximately brings the weakening effect,and the greater strength distinction between the two layers,the greater the weakening effect.Third,when the internal-layer soil is harder than the external-layer soil,the existence of the internal-layer soil has a strengthening effect on the fracturing pressure regardless of the proportion of internal-layer soil.Moreover,the influence of strength distinction between the two layers on the fracturing pressure is significant when the proportion of internal-layer soil is less than half,while it’s limited when the proportion is more than half.The proposed solution is potentially useful for geotechnical problems involving aspects of cohesive soil layering in a composite formation.展开更多
A bio-inspired approach for efficient conversion of cellulose to formic acid （FA） was developed in an aqueous alkaline medium. Metalloporphyrins mimicking cytochrome P450 exhibit efficiently and selectively catalyti...A bio-inspired approach for efficient conversion of cellulose to formic acid （FA） was developed in an aqueous alkaline medium. Metalloporphyrins mimicking cytochrome P450 exhibit efficiently and selectively catalytic per- formance in catalytic conversion of cellulose. High yield of FA about 63.7% was obtained by using sulfonated iron（IlI） porphyrin as the catalyst and O2 as the oxidant. Iron（III）-peroxo species, TSPPFemOO , was involved to cleave the C--C bonds of gluconic acid to FA in this catalytic system. This approach used relatively high concen- tration of cellulose and ppm concentration of catalyst. This work may provide a bio-inspired route to efficient con- version of cellulose to FA.展开更多
基金This work was supported by the Fundamental Research Funds for the Central Universities(2020YJS141)the Key Project of High-speed Rail Joint Fund of National Natural Science Foundation of China under Grant No.U1834208.
文摘The control of slurry pressure aiming to be consistent with the external water and earth pressure during shield tunnelling has great significance for face stability,especially in urban areas or underwater where the surrounding environment is very sensitive to the fluctuation of slurry pressure.In this study,an optimal control method for slurry pressure during shield tunnelling is developed,which is composed of an identifier and a controller.The established identifier based on the random forest(RF)can describe the complex non-linear relationship between slurry pressure and its influencing factors.The proposed controller based on particle swarm optimization(PSO)can optimize the key factor to precisely control the slurry pressure at the normal state of advancement.A data set from Tsinghua Yuan Tunnel in China was used to train the RF model and several performance measures like R2,RMSE,etc.,were employed to evaluate.Then,the hybrid RF-PSO control method is adopted to optimize the control of slurry pressure.The good agreement between optimized slurry pressure and expected values demonstrates a high identifying and control precision.
文摘This research develops a knowledge model for Software Process Improvement (SPI) project based on knowledge creation theory and its twenty-four measurement items, and proposes two hypothesizes about the interaction of explicit knowledge and tacit knowledge in SPI. Eleven factors are extracted through statistical analysis. Three knowledge-creation practices for capturing tacit knowledge contribute greatly to SPI, which are communication among members, crossover collaboration in practical work and pair programming. Two knowledge-creation practices for capturing explicit knowledge have significant positive impact on SPI, which are integrating project document and on-the-job training. Ultimately, suggestions for improvement are put forward, that is, encouraging communication among staff and integrating documents in real time, and future research is also illustrated.
基金supported by the National Natural Science Foundation of China(Grant No.52008021).
文摘Many empirical and analytical methods have been proposed to predict fracturing pressure in cohesive soils.Most of them take into account three to four specific influencing factors and rely on the assumption of a failure mode.In this study,a novel data-mining approach based on the XGBoost algorithm is investigated for predicting fracture initiation in cohesive soils.This has the advantage of handling multiple influencing factors simultaneously,without pre-determining a failure mode.A dataset of 416 samples consisting of 14 distinct features was herein collected from past studies,and used for developing a regressor and a classifier model for fracturing pressure prediction and failure mode classification respectively.The results show that the intrinsic characteristics of the soil govern the failure mode while the fracturing pressure is more sensitive to the stress state.The XGBoost-based model was also tested against conventional approaches,as well as a similar machine learning algorithm namely random forest model.Additionally,several large-scale triaxial fracturing tests and an in-situ case study were carried out to further verify the generalization ability and applicability of the proposed data mining approach,and the results indicate a superior performance of the XGBoost model.
基金This study was supported by the Key Project of High-speed Rail Joint Fund of National Natural Science Foundation of China(Grant No.U1834208)the Fundamental Research Funds for the Central Universities(2020YJS141)。
文摘This study aims to investigate hydrofracturing in double-layered soil through theoretical and experimental analysis,as multilayered soils where the difference in mechanical properties exists are generally encountered in practical engineering.First,an analytical solution for fracturing pressure in two different concentric regions of soil was presented based on the cavity expansion theory.Then,several triaxial hydraulic fracturing tests were carried out to validate the analytical solution.The comparison between the experimental and analytical results indicates the remarkable accuracy of the derived formula,and the following conclusions were also obtained.First,there is a linear relationship between the fracturing pressure and confining pressure in concentric double-layered cohesive soil.Second,when the internal-layer soil is softer than the external-layer soil,the presence of internal soil on the fracturing pressure approximately brings the weakening effect,and the greater strength distinction between the two layers,the greater the weakening effect.Third,when the internal-layer soil is harder than the external-layer soil,the existence of the internal-layer soil has a strengthening effect on the fracturing pressure regardless of the proportion of internal-layer soil.Moreover,the influence of strength distinction between the two layers on the fracturing pressure is significant when the proportion of internal-layer soil is less than half,while it’s limited when the proportion is more than half.The proposed solution is potentially useful for geotechnical problems involving aspects of cohesive soil layering in a composite formation.
基金This work was financially supported by the National Natural Science Foundation of China （Nos. 21372068, 21572049）, the Science and Technology Program of Hunan Province, China （No. 2014GK3115） and the Science and Technology Program of Changsha, China （No. K1508004-11）.
文摘A bio-inspired approach for efficient conversion of cellulose to formic acid （FA） was developed in an aqueous alkaline medium. Metalloporphyrins mimicking cytochrome P450 exhibit efficiently and selectively catalytic per- formance in catalytic conversion of cellulose. High yield of FA about 63.7% was obtained by using sulfonated iron（IlI） porphyrin as the catalyst and O2 as the oxidant. Iron（III）-peroxo species, TSPPFemOO , was involved to cleave the C--C bonds of gluconic acid to FA in this catalytic system. This approach used relatively high concen- tration of cellulose and ppm concentration of catalyst. This work may provide a bio-inspired route to efficient con- version of cellulose to FA.
