基于单齿侵入理论的牙轮钻头钻速方程

考虑井底水平地应力、钻井流体压力及地层孔隙压力,基于单齿侵入理论推导单齿侵入井底岩石的侵深公式,建立纯滚动锥形齿、楔形齿和滚动、剪切复合运动锥形齿等牙轮钻头的钻速方程.通过实验分析刃尖角、井底液柱压力对单齿侵入深度的影响,以及转速、轴向载荷对微钻头、牙轮钻头机械钻速的影响.结果表明:随着牙齿刃尖角的增大,锥形齿和楔形齿的侵深呈指数递减趋势;随着井底液柱压力的增大,牙齿侵入深度呈指数递减趋势,其中锥形齿降低速率大.在软到中硬地层中,牙齿侵入深度大,冲击侵入、回转剪切复合破岩方式的破岩效率高;在硬度地层中,牙齿侵入深度小,纯滚动冲击侵入破岩效率高.为分析实钻时牙轮钻头的机械钻速提供计算方法.     

Reliability analysis of retractable drill bit with air reverse circulation used for drilling while casing

Casing-while-drilling(CWD) with down the hole(DTH) hammer drilling technology has been widely used in unconsolidated formations,due to its advantages in protecting the borehole wall,excellent rock cuttings capacity,and fast penetration rate in hard rock.As an important component of the CWD system,the structure of the retractable drill bit needs not only to ensure to form stronger reverse circulation,but also to be expandable or retractable as needed,otherwise the drill bit cannot be lift and put...     

Fracture analysis for torsion problems of a gravity platform column with cracks under wind load

Ocean platforms are subjected to a variety of environment loads, such as those from winds, waves, currents, etc. In this study, the torsion problems of a gravity platform column with cracks under wind load were investigated. The column was assumed to be a composite cylinder. Therefore the torsion fracture problem of a composite cylinder was considered, and new boundary integral equations for the Saint-Venant torsion problem of a composite cylinder with curvilinear cracks were derived. The problem was reduced to solving the boundary integral equations on every boundary. By using the new boundary element method, the torsion problem of the gravity platform column with a straight crack under various wind loads was calculated. The obtained results were compared with those obtained for a torsion problem of the same column without cracks to prove the applicability of the present method. The comparison showed that the detrimental effect of cracks in a column should be considered in marine engineering.     

单轴压缩条件下不同含水率黑云母二长花岗岩破坏特征与机制

花岗岩在不同含水率条件下的变形破坏特征和机制对此类工程岩体稳定性评价具有重要的意义。开展不同含水率黑云母二长花岗岩单轴压缩试验,分析破坏特征和应力-应变曲线特征,开展断口扫描电镜试验,分析微观形貌特征,研究破坏机制。试验结果表明:黑云母二长花岗岩具有明显的应变软化特征;随含水率增大,曲线上微裂隙压密阶段长度逐渐增加,稳定破裂阶段及非稳定破裂阶段长度均逐渐缩短,但所占比例增大,曲线上峰前阶段涨落交替现象加剧;饱和时单轴抗压强度和弹性模量相比干燥时分别降低了40.68%,20.3%;变形破坏过程可大致分为以下5个阶段:平静期、裂纹萌生期、裂纹扩展伴随颗粒弹射期、片状碎片剥落伴随颗粒弹射期及崩落式破坏期;随含水率增大,花岗岩破坏时的剧烈程度、发出的声响及脆性程度均逐渐降低;花岗岩破坏机制为拉-剪复合破坏,低含水率时以压致拉张破坏为主,随含水率增大呈现拉张破坏减少而剪切破坏增多的趋势,饱和时以剪破坏为主。研究结果可为黑云二长花岗岩与水之间的耦合模型构建提供理论支撑,对水-岩耦合环境下工程岩体稳定性分析具有重要科学意义。      

Ground subsidence mechanism of a filling mine with a steeply inclined ore body

Long-term field monitoring finds that serious surface subsidence can still occur even if the high strength cemented fill method is adopted. Combining the results of numerical simulations with global position system(GPS) monitoring, we took a typical filling mining mine with a steeply inclined ore body as an example, and explored its ground subsidence mechanism. The results show that the ground subsidence caused by the mining of steep ore body is characterized by two settlement centers and a sign...     

Landscape changes and their ecological effects of Miaodao Archipelago with human disturbances and under natural conditions in the past 30 years

The modern landscape patterns of islands usually show obvious spatial heterogeneity and complex ecological effects due to the vulnerability of ecosystems with natural characteristics under increasing human activities. In this work, we studied the variation in landscape pattern of the Miaodao Archipelago in Bohai Sea, North China, from 1990 to 2019, and an evaluation index system was established to explore the impacts of natural conditions and human disturbances on the ecological effects in the pressure-state-response(PSR) framework. Empirical analysis was conducted on the natural conditions, human disturbances, and ecological effects. The results show that forest was the main component of the landscape pattern in the archipelago. Both of the areas offorest and construction land were increasing, and the areas of cropland and grassland were declining. Other landscape types changed slightly, and the landscape fragmentation was increasing. The natural condition exhibited positive effects while human disturbance showed negative effects on the local ecology. Human disturbances come mainly from shoreline use while the natural conditions were mainly from the elevation change. The ecological effects were resulted mainly from the net primary productivity and water yield.     

Large deformation and failure mechanism analyses of Tangba high slope with a high-intensity and complex excavation process

The Tangba high slope is mainly composed of coarse soils and supplies core wall materials for the construction of the Changheba dam. Since the filling intensity of the Changheba dam is high, the Tangba high slope suffers from a high-intensity excavation process, and reinforcement measures are usually not implemented immediately. Moreover, the distribution of useful materials is uneven and insufficient, and the mixing of different soil materials is necessary; thus, multiple simultaneous excavations and secondary excavation are inevitable. In the construction period from 2012 to 2016, large deformations occurred in this area, and one of the largest monitored horizontal deformations whose direction points to the opposite side of the valley even reached more than 8000 mm. According to field investigation, site monitoring and theoretical analysis, the large deformation in the Tangba high slope can be divided into two phases. In the first phase, the excavation construction breaks the original stress equilibrium state; in the second phase, the precipitation infiltration accelerates the deformation. Thus, the excavation construction and precipitation infiltration are the two major factors promoting the deformation, and the high-intensity and complex excavation process is the fundamental cause. Notably, rate of slope deformation significantly accelerated in rainy seasons due to precipitation infiltration; the rate also accelerated in early 2016 due to the high-intensity, complex excavation process. Comprehensively considering the above factors, timely and effective reinforcement measures are essential.     

低物源供给模式下沟谷—坡折体系控砂机制——以车排子凸起东翼白垩系呼图壁组为例

为明确车排子凸起东翼白垩系呼图壁组砂体分布的控制因素,在古地貌恢复基础上,综合利用测井、录井及三维地震资料,以沉积学和层序地层学理论为指导,探讨低物源供给模式下沟谷—坡折体系对砂体分布的控制作用。结果表明:在低物源供给模式下,研究区发育扇三角洲及滨浅湖滩坝两种成因砂体。扇三角洲砂体规模局限,主要充填于低位域时期形成的古沟谷;滨浅湖厚层坝砂在平面上的展布与坡折带的走向趋于一致,在垂向上主要发育于湖侵域及高位域早期。该成果对物源供给不足地区坡折带的储层预测具有指导意义。