单压法标准湿度发生器的设计及不确定度评定

标准湿度发生器在湿度量传的过程中起到重要的作用。我们设计开发的标准湿度发生器采用单压法原理,使用某单位自主研制的压缩空气干燥器、分流法湿度发生器产生的气源,通过温度、压力、饱和器系统的合理设计,能够发生(-70℃^+20℃)露点范围的湿气气源,量值范围宽,准确度高。经过冷镜式精密露点仪的验证,结果表明装置满足我国湿度一级标准的技术指标。按照不确定度评定方法评定了装置的不确定度。

单桩竖向抗压静载法在某栋宿舍楼中的运用

文章结合实际工程通过单桩竖向抗压静载试验的方法,得出Q-S曲线,对桩在设计阶段的承载能力进行测定,为优化设计提供了可靠参数,从而节约了相当可观的投资。

单桩竖向抗压静载法在工程建设中的应用

随着现代社会对于建筑工程质量要求的不断提高,建筑工程技术也在实践应用中得到不断深入与创新。单桩竖向抗压静载法作为我国在建筑施工中的承重测量法,不管是在测量建筑抗压静载极限承载力还是在保证施工中主体架构的结构稳固都具有重要作用。本文通过对静载法在建筑实验中的注意事项进行阐述的基础上,探究其在建筑工程中的具体应用。

旋翼翼型高速风洞试验壁压法修正研究

基于已有的单参数线化壁压信息法,在做相应简化改动后应用于旋翼翼型高速试验数据修正,着力解决工程上遇到的旋翼翼型高速风洞试验结果不理想的问题。文中采用该方法对FL-21风洞得到的OA309旋翼翼型试验数据进行了修正。结果表明,修正后的旋翼翼型气动特性曲线与国外已有结果吻合较好。该方法能有效满足旋翼翼型高速风洞试验修正的需要。

单片下压法矫治122例完全型房室间隔缺损

目的 总结单片下压法矫治完全型房室间隔缺损（CAVSD）外科治疗的经验.方法 2007年3月至2013年4月,122例CAVSD患儿接受治疗.男64例,女58例;年龄1个月～13岁,其中＜6个月47例（38.5％）,＞6个月75例（61.5％）;体质量3.0～50.0 kg.Rastelli分型：A型83例,B型12例,C型27例.房室瓣反流轻度18例,中度32例,中重度72例.肺动脉高压重度92例,中度22例,轻度8例.采用单片下压法一期手术矫治,同期修补合并畸形.同时对三尖瓣成形术进行改良.术中均经食管超声心动图检查.结果 术后均入重症监护室,患儿中心静脉压7～ 12 cmH2O（1 cmH2O=0.098 kPa）,呼吸机辅助9～ 240 h,监护室停留1～ 27天.全组术后死亡3例（2.46％）,其中＜6个月者1例,1例3个月患儿死于肺动脉高压危象,1例二尖瓣重度反流、死于低心排血量综合征,1例死于右心功能衰竭、脑部并发症和严重感染.复查超声心动图示室间隔缺损残余分流（直径＞2 mm）3例,二尖瓣反流中重度9例,中度27例,轻度或无反流86例.术后随访随访3～ 75个月,平均33个月.随访期间心电图示：Ⅰ度房室传导阻滞24例,完全性右束支阻滞28例,无Ⅲ度房室传导阻滞.术后早期再次手术2例,1例为瓣膜缝线撕脱;1例为二尖瓣中心性反流,不能脱离呼吸机,再次行二尖瓣双孔成形术.5例因重度反流再次手术,其中1例术后5年再次手术,术后心力衰竭死亡.结论 单片下压法简化了CAVSD手术方案,体外循环时间明显缩短,手术并发症减少,更适用于婴幼儿特别是小婴儿.

ANALYSIS OF NONLINEAR PIEZOELECTRIC CIRCULAR SHALLOW SPHERICAL SHELLS BY DIFFERENTIAL QUADRATURE ELEMENT METHOD

The static behavior of piezoelectric circular spherical shallow shells under both electrical and mechanical loads is studied by using the differential quadrature element method (DQEM). Geometrical nonlinearity effect is considered. Detailed formulations and procedures are given for the first time. Several examples are analyzed and accurate results are obtained by the DQEM. Based on the results in this paper, one may conclude that the DQEM is a useful tool for obtaining solutions of structural elements. It can be seen that the shell shape may be theore tically controlled and snap through may occur when the applied voltage reaches a critical value even without mechanical load for certain geometric configurations.

Effects of confining pressure on deformation failure behavior of jointed rock

For a deeper understanding of the deformation failure behavior of jointed rock, numerical compression simulations are carried out on a rock specimen containing non-persistent joints under confining pressure with the bondedparticle model. The microscopic parameters which can reflect the macroscopic mechanical properties and failure behavior of artificial jointed specimens are firstly calibrated. Then, the influence of joint inclination and confining pressure on stress-strain curves, crack patterns, and contact force distributions of jointed rock are investigated. The simulation results show that both the compressive strength and elastic modulus of the specimens increase with increasing confining pressure, and these two mechanical parameters decrease first and then increase with the increase of joints inclination. The sensitivity of strength and elastic modulus to confining pressure is not the same in different joints inclinations, which has the least impact on specimens with α=90°. Under low confining pressure, the failure modes are controlled by the joint inclination. As the confining pressure increased, the initiation and propagation of tensile crack are gradually inhibited, and the failure mode is transferred from tensile failure to shear-compression failure. Finally, the reinforcement effect of prestressed bolt support on engineering fractured rock mass is discussed.

Utilizing partial least square and support vector machine for TBM penetration rate prediction in hard rock conditions

Rate of penetration(ROP) of a tunnel boring machine(TBM) in a rock environment is generally a key parameter for the successful accomplishment of a tunneling project. The objectives of this work are to compare the accuracy of prediction models employing partial least squares(PLS) regression and support vector machine(SVM) regression technique for modeling the penetration rate of TBM. To develop the proposed models, the database that is composed of intact rock properties including uniaxial compressive strength(UCS), Brazilian tensile strength(BTS), and peak slope index(PSI), and also rock mass properties including distance between planes of weakness(DPW) and the alpha angle(α) are input as dependent variables and the measured ROP is chosen as an independent variable. Two hundred sets of data are collected from Queens Water Tunnel and Karaj-Tehran water transfer tunnel TBM project. The accuracy of the prediction models is measured by the coefficient of determination(R2) and root mean squares error(RMSE) between predicted and observed yield employing 10-fold cross-validation schemes. The R2 and RMSE of prediction are 0.8183 and 0.1807 for SVMR method, and 0.9999 and 0.0011 for PLS method, respectively. Comparison between the values of statistical parameters reveals the superiority of the PLSR model over SVMR one.

科学的检测手段在发现和指导处理桩基础工程质量隐患中的作用

在地质情况较复杂石灰岩地区进行桩基础施工,保证质量很重要。全面准确了解桩基础的质量情况,离不开科学的检测方法。

Simulation of rock deformation and mechanical characteristics using clump parallel-bond models

To properly simulate hard rock with a high ratio of the uniaxial compressive strength to tensile strength(UCS/TS) and realistic strength-failure envelope,the rock deformation and mechanical characteristics were discussed in detail when the particle simulation method with the clump parallel-bond model(CPBM) was used to conduct a series of numerical experiments at the specimen scale.Meanwhile,the effects of the loading procedure and crack density on the mechanical behavior of a specimen,which was modeled by the particle simulation method with the CPBM,were investigated.The related numerical results have demonstrated that:1) The uniaxial compressive strength(UCS),tensile strength(TS) and elastic modulus are overestimated when the conventional loading procedure is used in the particle simulation method with the CPBM; 2) The elastic modulus,strength and UCS/TS decrease,while Poisson ratio increases with the increase of the crack density in the particle simulation method with the CPBM; 3) The particle simulation method with the CPBM can be used to reproduce a high value of UCS/TS(>10),as well as a high friction angle and reasonable cohesion strength; 4) As the confining pressure increases,both the peak strength of the simulated specimen and the number of microscopic cracks increase,but the ratio of tensile cracks number to shear cracks number decreases in the particle simulation method with the CPBM; 5) Compared with the conventional parallel-bond model,the CPBM can be used to reproduce more accurate results for simulating the rock deformation and mechanical characteristics.

Discrete element simulation of mechanical characteristic of conditioned sands in earth pressure balance shield tunneling

The discrete element method (DEM) was used to simulate the flow characteristic and strength characteristic of the conditioned sands in the earth pressure balance (EPB) tunneling. In the laboratory the conditioned sands were reproduced and the slump test and the direct shear test of the conditioned sands were implemented. A DEM equivalent model that can simulate the macro mechanical characteristic of the conditioned sands was proposed,and the corresponding numerical models of the slump test and the shear test were established. By selecting proper DEM model parameters,the errors of the slump values between the simulation results and the test results are in the range of 10.3%-14.3%,and the error of the curves between the shear displacement and the shear stress calculated with the DEM simulation is 4.68%-16.5% compared with that of the laboratory direct shear test. This illustrates that the proposed DEM equivalent model can approximately simulate the mechanical characteristics of the conditioned sands,which provides the basis for further simulation of the interaction between the conditioned soil and the chamber pressure system of the EPB machine.

Treatment of bauxite residue dust pollution by improving structural stability via application of synthetic and natural polymers

The residue drying area(RDA)is the major source of fugitive red sand(RS)dust emissions in the bauxite mining industry and causes serious environmental and safety detriments.Polymer stabilizer(PS)is one of the promising non-traditional stabilizers to mitigate such issues.This research investigated the unconfined compressive strength(UCS)of RS using synthetic polymer stabilizer(SPS)and natural polymer stabilizer(NPS),and to determine the optimum application concentration and mixing ratio of the PAM and Guar gum mixture.Results illustrated that PAM apparently outperform Guar gum in stabilizing sand particles.The mixture of PAM and Guar gum is more effective than individual use.The optimum polymer concentration and the mixing ratio are 0.94 wt.%and 0.6(PAM:total(PAM+Guar gum)),respectively.A rigorous regression model was developed to predict the UCS value based on application concentration and mixing ratio for the purpose of cost and time efficiency.

Rock burst prediction based on genetic algorithms and extreme learning machine

Rock burst is a kind of geological disaster in rock excavation of high stress areas.To evaluate intensity of rock burst,the maximum shear stress,uniaxial compressive strength,uniaxial tensile strength and rock elastic energy index were selected as input factors,and burst pit depth as output factor.The rock burst prediction model was proposed according to the genetic algorithms and extreme learning machine.The effect of structural surface was taken into consideration.Based on the engineering examples of tunnels,the observed and collected data were divided into the training set,validation set and prediction set.The training set and validation set were used to train and optimize the model.Parameter optimization results are presented.The hidden layer node was450,and the fitness of the predictions was 0.0197 under the optimal combination of the input weight and offset vector.Then,the optimized model is tested with the prediction set.Results show that the proposed model is effective.The maximum relative error is4.71%,and the average relative error is 3.20%,which proves that the model has practical value in the relative engineering.

Prediction of blast boulders in open pit mines via multiple regression and artificial neural networks

The most important objective of blasting in open pit mines is rock fragmentation.Prediction of produced boulders(oversized crushed rocks) is a key parameter in designing blast patterns.In this study,the amount of boulder produced in blasting operations of Golegohar iron ore open pit mine,Iran was predicted via multiple regression method and artificial neural networks.Results of 33 blasts in the mine were collected for modeling.Input variables were:joints spacing,density and uniaxial compressive strength of the intact rock,burden,spacing,stemming,bench height to burden ratio,and specific charge.The dependent variable was ratio of boulder volume to pattern volume.Both techniques were successful in predicting the ratio.In this study,the multiple regression method was superior with coefficient of determination and root mean squared error values of 0.89 and 0.19,respectively.

Correlations between direct and indirect strength test methods

The difficulties associated with performing direct compression strength tests on rocks lead to the development of indirect test methods for the rock strength assessment. Indirect test methods are simple, more economical, less time-consuming, and easily adaptable to the field. The main aim of this study was to derive correlations between direct and indirect test methods for basalt and rhyolite rock types from Carlin trend deposits in Nevada. In the destructive methods, point load index, block punch index, and splitting tensile strength tests are performed. In the non-destructive methods, Schmidt hammer and ultrasonic pulse velocity tests are performed. Correlations between the direct and indirect compression strength tests are developed using linear and nonlinear regression analysis methods. The results show that the splitting tensile strength has the best correlation with the uniaxial compression strength.Furthermore, the Poisson's ratio has no correlation with any of the direct and indirect test results.