Propagation and sealing efficiency of chemical grouting in a two-dimensional fracture network with flowing water

In this study, an orthogonal array experiment is conducted by using a transparent fracture network replica. Image processing and theoretical analysis are performed to investigate the model sealing efficiency(SE), factors influencing SE, and the effect of flowing water on propagation. The results show that grout propagation can be classified into three patterns in the fracture network: sealing off, partial sealing,and major erosion. The factors controlling the SE in a descending order of the amount of influence are the initial water flow speed, fracture aperture, grout take, and gel time. An optimal value for the combination of the gel time and grout take(artificial factors) can result in a good SE. The grouting and seepage pressures are measured, and the results reveal that their variations can indicate the SE to some extent. The SE is good when the seepage pressure at each point increases overall;the frequent fluctuations in the seepage pressure indicate a moderately poor SE, and an overall decline in the seepage pressure indicates a major erosion type. The deflection effect of grouting shows an approximately elliptical propagation with the long axis expanding along the wider fracture opening, demonstrating further application in grouting design.

DynamicMechanical and Chemorheology Analysis for the Blended Epoxy System with Polyurethane Modified Resin

As the important matrix material,epoxy resin has been widely used in the composites for various fields.On account of the poor toughness of epoxy resin limiting their suitability for advanced applications,considerable interests have been conducted to modify the epoxy resin to meet the engineering requirements.In this study,the bio-based polyurethane(PU)modified resin was adopted to modify the pure bisphenol-A epoxy by blending method with various proportions.Aiming to illuminate the curing behavior,mechanical and thermal properties,the blended epoxy systems were characterized by viscosity-time analysis,dynamic mechanical analysis(DMA)at different frequencies and temperatures,mechanical tensile test,thermogravimetric analysis(TGA)and Fourier transform infrared(FT-IR)spectroscopy.The results indicated that the introduction of PU modified epoxy was found to significantly inhibit the viscosity growth rates especially when the content of PU modified epoxy resin is higher than 60%.Notwithstanding the dynamic modulus and T_(g)reduced with the increment of PU modified epoxy,remarkable increment on the elongation at break was found and the flexibility was greatly promoted with the introduction of PU modified epoxy.The proportion of PU modified epoxy in the blends should be put balance considerations to obtain optimal mechanical properties.TGA results and FTIR spectrum demonstrated that the addition of PU modified epoxy did not change the thermal decomposition mechanism and chemical reaction mechanism,but the addition of PU modified epoxy inhibits the curing reaction of epoxy resin by measured and calculated the damping temperature domain
T from 35.7℃ to 48.9℃.

四洞交叠盾构隧道近距离下穿既有桥梁桩基施工控制技术研究

在密集的城市建筑环境中,在城市地下交通的大规模兴建过程中不可避免地会出现各类近接施工工程。依托一实际工程,针对四洞交叠盾构隧道近距离下穿既有桥梁桩基施工控制技术开展实践研究,总结提出了“两阶段法理论预测+主动控制与被动保护”的近接施工微扰动控制技术体系。该技术体系的核心内容包括:1)通过引入附加地层损失率,建立多线隧道近接施工时桩基变形的理论计算方法,实现近接施工对邻近建(构)筑物影响的工前预测。2)建立隧道-地层-桩基多元耦合模型,分析四线交叠盾构隧道施工全过程力学行为。3)结合工程实践经验,分别从主动控制和被动保护两方面提出依托工程的控制措施。在依托工程开挖完成过程中,邻近桥梁桩基变形得到有效控制,表明所提出的近接施工微扰动控制技术是合理可行的。

A Pull-Out Test Study on the Working State of Fully Grouted Bolts

The present study examines the working conditions of fully grouted bolts used for the construction and expansion of high slopes.On the basis of a pull out destructive test,the work load and the ultimate load are obtained on site,and the Flac3d numerical simulation method is employed to determine the axial force distribution and the effective anchor length.The test results show that(1)the Q-S(load-displacement)curve of the bolt displays a certain degree of deformation coupled with the creep of the surrounding rock;(2)the working load of the bolt is closely related to the sliding deformation trend of the slope,while the ultimate load depends on the design parameters of the bolt and the lithology of the slope;(3)the distribution of bolt axial force is characterized by a single peak along the bolt length and the effective anchorage length of the bolt is 3 m;(4)after 20 years,the bolt’s ultimate load has a maximum loss of 31.94%.

Short-term prediction of on-street parking occupancy using multivariate variable based on deep learning

Short-term prediction of on-street parking occupancy is essential to the ITS system,which can guide drivers in finding vacant parking spaces.And the spatial dependencies and exogenous dependencies need to be considered simultaneously,which makes short-term prediction of on-street parking occupancy challenging.Therefore,this paper proposes a deep learning model for predicting block-level parking occupancy.First,the importance of multiple points of interest(POI)in different buffers is sorted by Boruta,used for feature selection.The results show that different types of POI data should consider different buffer radii.Then based on the real on-street parking data,long short-term memory(LSTM)that can address the time dependencies is applied to predict the parking occupancy.The results demonstrate that LSTM considering POI data after Boruta selection(LSTM(+BORUTA))outperforms other baseline methods,including LSTM,with an average testing MAPE of 11.78%.The selection process of POI data helps LSTM reduce training time and slightly improve the prediction performance,which indicates that complex correlations among the same type of POI data in different buffer zones will also affect the prediction accuracy of LSTM.When there are more restaurants on both sides of the street,the prediction performance of LSTM(+BORUTA)is significantly better than that of LSTM.

Experimental study of aerodynamic interference effects on aerostatic coefficients of twin deck bridges

The aerodynamic interference effects on aero-static coefficients of twin deck bridges with large span were investigated in detail by means of wind tunnel test.The distances between the twin decks and wind attack angles were changed during the wind tunnel test to study the effects on aerodynamic interferences of aerostatic coefficients of twin decks.The research results have shown that the drag coefficients of the leeward deck are much smaller than that of a single leeward deck.The drag coefficients of a windward deck decrease slightly com-pared with that of a single deck.The lift and torque coefficients of windward and leeward decks are also affected slightly by the aerodynamic interference of twin decks.And the aerodynamic interference effects on lift and torque coefficients of twin decks can be neglected.