Gongcheng Kexue Yu Jishu/Advanced Engineering Science

In mountain rivers with coarse sediments, the ratio of water depth to sediment diameter (h/d) is relatively small especially under the condition of shallow water depth. Therefore, the vertical velocity distribution along the river cannot be described accurately with traditional logarithmic or logarithmic-wake law. In this paper, flume experiments were carried out with two kinds of sediments (glass beads d=1.4 cm and pinpong d=4 cm) to test the influence of coarse sediment on vertical velocity distribution under different h/d. In the presence of coarse sediment bed, one of the problems encountered is how to determine the reference level y0. For practical purpose, the present study assumes that y0 does not varies with h/d, namely, y0=0.2d. The measured data were first converted to dimensionless and then compared to theoretical results calculated by logarithmic-wake law. In addition, the coefficient B and another wake coefficient Π in in logarithmic compensation formula were calibrated to fit for the measured data. The results indicate that when the value of h/d is small, the coefficient B decreases with the increase of h/d while the wake coefficient Π presents an opposite trend, when the value of h/d becomes larger, both B and Π tend to a constant. Finally, a modified logarithmic-wake law is derived to describe the velocity distribution in mountain river flows with small h/d. The modified model agrees well with the experimental data conducted in the present laboratory flume. Furthermore, it also has a good adaptability to riverbed with coarse sediments.

In order to perfect the salt expansion theory of coarse-grained saline soil and explore the influencing factors and mechanism of the salt−frost heaving force, 96 groups of coarse-grained sulphate saline soil samples are prepared artificially then indoor model tests have been carried out by self-designed test device. Test results showed that the sensitive range of temperature on the salt−frost heaving force is −0.2℃～−1.0℃. The salt content had no influence on the rules that the salt−frost heaving force increasing with temperature and determines the maximum salt−frost heaving force together with water content. For samples with same void ratio, the increasing water content led to an increased amount of the salinity which resulted in the maximum salt−frost heaving force. When the salt content kept constant, however,the increase of water content caused the decrease of maximum salt−frost heaving force. The maximum salt−frost heaving force achieved the maximum and minimum values ​​when the void ratio was 0.58 and 0.55, respectively, which was related to the crystallization position of salt in the soil frame. Furthermore, based on the test results, a mathematical expression of frost heaving limit depth of coarse-grained sulphate saline soil is given by the hierarchical synthesis method, which is expected to provide guidance for the quantitative evaluation and design of salt− frost heaving deformation of coarse-grained sulphate saline soil.which was related to the crystallization position of salt in the soil frame. Furthermore, based on the test results, a mathematical expression of frost heaving limit depth of coarse-grained sulphate saline soil is given by the hierarchical synthesis method, which is expected to provide guidance for the quantitative evaluation and design of salt−frost heaving deformation of coarse-grained sulphate saline soil.which was related to the crystallization position of salt in the soil frame. Furthermore, based on the test results, a mathematical expression of frost heaving limit depth of coarse-grained sulphate saline soil is given by the hierarchical synthesis method, which is expected to provide guidance for the quantitative evaluation and design of salt−frost heaving deformation of coarse-grained sulphate saline soil.

As an important space carrier to participate in global competition, the Guangdong-Hong Kong-Macao Greater Bay area is facing the pressure from the energy demand and environment protection. Developing geothermal resources is an effective way to solve the problem. In this paper, the possibility of geothermal development in Greater Bay area was reasoned, based on the analysis of regional geotectonic, stratigraphic lithology and geothermal field. Considering deep ground temperature, rock thermal physical parameters and terrestrial heat flow, geothermal water resource and hot dry rock resource were quantitatively assessed through raster units. Further, high potential geothermal zones were distinguished. Results show that:1) the intersected fault structures and widely distributed granite in the Greater Bay area provide a favorable geological environment for the storage and formation of geothermal resource, which is verified by the measured terrestrial heat flow; 2) the computing results indicates that temperature would be over 70 at depth of over 1.3 km and 168.81~233.61 at depth of 5 km, showing a high potential of geothermal resource; 3) The estimate geothermal resources in the Greater Bay area amount to 5.83×1017 kJ within the depth of 5 km. It is equivalent to the thermal value of standard coal of 5.94×109 t and can reduce the emission of CO2 by 4.04×109 t, when recovery rate is set at 30%. 4) The area of high potential geothermal resources is mainly distributed along the northeast deep fault, i.e. in Foshan, Zhongshan, Jiangmen, Shenzhen and Hong Kong, where the unit geothermal resource potential is equivalent to standard coal of 5.19×105 t per square kilometer, and should be taken as key area for geothermal prospecting and exploitation.

There are few in-situ creep test data of tunnel anchor for suspension bridge. To obtain the creep deformation law of tunnel anchor of Xingkang Bridge on Yakang Expressway and enrich creep test data of tunnel anchor of super-large suspension bridge, creep tests of 1∶10 in-situ shrinkage model of the Ya’an side slope tunnel anchor of Xingkang Bridge were carried out, based on the specific geological conditions in the Ya’an side slope tunnel anchorage area of Xingkang Bridge and the similar theory of elastic mechanics. According to the creep characteristics of the model anchor and surrounding rock mass under 1.0P, 3.5P and 7.0P loads, the whole creep process of the model anchor, surrounding rock and interfacial dislocation were analyzed. The results show that under 1.0P, 3.5P and 7.0P loads, the maximum creep deformation of anchor body was 0.62 mm, 0.97 mm and 1.58 mm, the maximum creep deformation of surrounding rock was 0.49 mm, 0.85 mm and 1.38 mm, and the maximum creep deformation of anchor body and surrounding rock was 0.15 mm, 0.64 mm and 1.43 mm, respectively. On the basis of in-situ scale tests, the three-dimensional viscoelastic-plastic numerical analysis of the interaction between anchorage and surrounding rock mass was carried out by using FLAC3D finite element software. The comparison between the field measured values and numerical analysis results shows that the measured creep deformation and calculation results of the anchorage and surrounding rock of the Ya’an side bank slope tunnel of Xingkang Bridge have the similar evolution trends and range of amounts. The creep of tunnel anchorage and surrounding rock mass of Xingkang Bridge on Yakang Expressway belong to stable creep stage under various loads. The long-term stability of suspension bridge was not affected by the creep of anchorage and surrounding rock mass. The test results provide a basis for the reliability evaluation of the tunnel anchorage system of Xingkang Bridge, and also provide a reference for similar engineering designs.

Volumetric error (VE) is determined by machine tool geometric error elements (GEE). Most of VE models in recent studies have a common issue that some GEE are missing in models explicit mathematical expressions, which directly affects machine tool VE prediction accuracy. Therefore, a methodology for complete modeling machine tool VE was proposed. Multi-body system theorem and homogeneous coordinate transformations were borrowed as analysis approaches. On the basis that initial positions and original errors eigen matrix were fully considered, VE model was guaranteed to have total machine tool GEE. Furthermore, aiming at the residual error limitation in traditional NC code VE compensation technique, NC code coordinates optimization design problem was described to replace the former reversal accumulation process. Genetic algorithm (GA) was then utilized to solve the proposed optimization problem so that VE compensation residual error was eliminated. A horizontal machining center was selected as study object, on which both numerical and experimental analyses were performed to verify the proposed modeling methodology and compensation technique. The results indicated that complete VE model comprises total 21 GEE of machining center and that VE prediction was fairly accurate. It was also showed that NC code optimized compensation technique presented in this paper may promote machining center volumetric position precision (VPP). The maximum growth of VPP, compared to uncompensated value, was 90.92%. Research results can be regarded as theorem and engineering supports for investigations on numerical manufacturing equipment precision problems.