Pressure from surrounding rock of three shallow tunnels with large section and small spacing

With the increasing traffic demand, the closely built three or more tunnels with large section play a significant role in the tunnel construction. However, the interaction among tunnels has important influences on the security and economy of tunnel engineering, and the calculation of pressure from the surrounding rock during the excavation is one of the problems that need to be solved urgently. Based on the practical engineering of three tunnels, the load model of three tunnels was proposed in consideration of the interaction and excavation sequence between tunnels. In comparison with the load model of single tunnel, the construction mechanical characteristics of the three tunnels were analyzed. The results show that the rock pressure of three tunnels calculated by the current tunnel design code is not reliable, and the interaction force increases with the spacing between tunnels.

We Live on a Small Space Comet: The Third Extraordinary Motion of Earth towards the North Pole and Its Various Effects

The idea of research started with a crazy imaginary theory in the field of astrogeography, saying: We often taught ourselves and then convinced the students that the planet Earth moves despite not feeling the vibrations of traffic, and we listed successive scientific confirmations to indicate the rotation of the planet in a regular movement around its axis once every 24 hours, and it is running in another second movement around the sun once every 365¼ days, so are they only two movements, no more?! Is it possible for him to run at a regular speed in an additional direction?

Model test to investigate failure mechanism and loading characteristics of shallow-bias tunnels with small clear distance

Based on the similarity theory,a tunnel excavation simulation testing system under typical unsymmetrical loading conditions was established.Using this system,the failure mechanism of surrounding rock of shallow-bias tunnels with small clear distance was analyzed along with the load characteristics.The results show that:1) The failure process of surrounding rock of shallow-bias tunnels with small clear distance consists of structural and stratum deformation induced by tunnel excavation; Microfracture surfaces are formed in the tunnel surrounding rock and extend deep into the rock mass in a larger density; Tensile cracking occurs in shallow position on the deep-buried side,with shear slip in deep rock mass.In the meantime,rapid deformation and slip take place on the shallow-buried side until the surrounding rocks totally collapse.The production and development of micro-fracture surfaces in the tunnel surrounding rock and tensile cracking in the shallow position on the deep-buried side represent the key stages of failure.2) The final failure mode is featured by an inverted conical fracture with tunnel arch as its top and the slope at tunnel entrance slope as its bottom.The range of failure on the deep-buried side is significantly larger than that on the shallow-buried side.Such difference becomes more prominent with the increasing bias angle.What distinguishes it from the "linear fracture surface" model is that the model proposed has a larger fracture angle on the two sides.Moreover,the bottom of the fracture is located at the springing line of tunnel arch.3) The total vertical load increases with bias angle.Compared with the existing methods,the unsymmetrical loading effect in measurement is more prominent.At last,countermeasures are proposed according to the analysis results: during engineering process,1) The surrounding rock mass on the deep-buried side should be reinforced apart from the tunnel surrounding rock for shallow-buried tunnels with small clear distance; moreover,the scope of consolidation should go beyond the midline of tunnel(along the direction of the top of slope) by 4 excavation spans of single tunnel.2) It is necessary to modify the load value of shallow-bias tunnels with small clear distance.

Compressive sensing for small moving space object detection in astronomical images

It is known that detecting small moving objects in as- tronomical image sequences is a significant research problem in space surveillance. The new theory, compressive sensing, pro- vides a very easy and computationally cheap coding scheme for onboard astronomical remote sensing. An algorithm for small moving space object detection and localization is proposed. The algorithm determines the measurements of objects by comparing the difference between the measurements of the current image and the measurements of the background scene. In contrast to reconstruct the whole image, only a foreground image is recon- structed, which will lead to an effective computational performance, and a high level of localization accuracy is achieved. Experiments and analysis are provided to show the performance of the pro- posed approach on detection and localization.

Theoretical understandings, key technologies and practices of tight conglomerate oilfield efficient development: A case study of the Mahu oilfield, Junggar Basin, NW China

A series of theoretical explorations and field tests have been carried out to efficiently develop the Mahu tight conglomerate oilfield in the Junggar Basin.Concepts of steered-by-edge fracturing and proactive fracturing interference were proposed.A series of innovative technologies were developed and implemented including optimization of 3-D staggered well pattern,proactive control and utilization of spatial stress field,and synergetic integration of multiple elements.Different from shale,the unique rock fabric and strong heterogeneities of tight conglomerate formation are favorable factors for forming complex fractures,small space well pattern can proactively control and make use of interwell interference to increase the complexity of fracture network,and the"optimum-size and distribution"hydraulic fracturing can be achieved through synergetic optimization.During pilot phase of this field,both depletion with hydraulically fractured vertical wells and volume fracturing in horizontal wells were tested after water injection through vertical wells,then the multi-stage fracturing with horizontal well was taken as the primary development technology.A series of engineering methods were tested,and key development parameters were evaluated such as well spacing,lateral length,fractures spacing,fracturing size,and fracturing operation process.According to geoengineering approach,the 100 m/150 m tridimensional tight-spacing staggered development method was established with systematic integration of big well clusters,multiple stacked pay zones,small well spacing,long lateral length,fine perforation clustering,zipper fracturing and factory operation.According to half-year production performance,100 m/150 m small spacing wells outperformed 500 m/400 m/300 m spacing wells.Its average estimated ultimate recovery(EUR)of wells was identical with those best wells from large-spacing area.Compared with the overall performance of Mahu oilfield,the drainage efficiency and estimated recovery factor of this pilot were significantly boosted with improved economics.

Research on Modified Shifting Balance Genetic Algorithms

The increasing overlap of core and colony populations during the anaphase of evolution may limit the performance of shifting balance genetic algorithms. To decrease such overlapping,so as to increase the local search capability of the core population,the sub-space method was used to generate uniformly distributed initial colony populations over the decision variable space. The core population was also dynamically divided,making simultaneous searching in several local spaces possible. The algorithm proposed in this paper was compared to the original one by searching for the optimum of a complicated multi-modal function. The results indicate that the solutions obtained by the modified algorithm are better than those of the original algorithm.

Spatial Governance of Old Community in Pingguoyuan Street of Shijingshan District

The community is the basic development unit and governance unit of a city,and it is a direct tool to improve the happiness and sense of acquisition of residents.In the context of high-quality urban development,how to improve the community environment,enhance the quality of community life,and satisfy residents’ yearning for a better life has attracted more and more attention from all walks of life.The study selected Pingguoyuan Street in Shijingshan District as the research object.Based on the optimization and transformation of community micro-space,meeting the needs of residents is taken as the core,and a comprehensive survey of the street’s historical buildings,public spaces,characteristic resources and community supporting facilities,etc.is conducted,and the current issues are concluded and summarized.Moreover,spatial optimization suggestions are proposed in areas such as functional implantation,image regeneration,and historical inheritance.

Influence of mechanical damage generated by small space debris on electrostatic discharge

Recent studies have indicated that hypervelocity impacts by meteoroids and space debris can induce spacecraft anomalies. However, the basic physical process through which space debris impacts cause anomalies is not entirely clear. Currently, impact-generated plasma is thought to be the primary cause of electrical spacecraft anomalies, while the effects of impact-generated mechanical damage have rarely been researched. This paper presents new evidence showing that impact-generated mechanical damage strongly influences electrostatic discharge. Hypervelocity impact experiments were conducted in a plasma drag particle accelerator, using particles with diameters of 200–500 ?m and velocities of 2–7 km/s. The impact-generated mechanical damage on a specimen surface was measured by a stereoscopic microscope and 3D Profilometer and it indicated that microscopic irregularities around the impact crater could be responsible for local electric field enhancement. Furthermore, the influence of impact-generated mechanical damage on electrostatic discharge was simulated in an inverted potential gradient situation. The experimental results show that the electrostatic discharge voltage threshold was significantly reduced after the specimen was impacted by particles.