Geochemical characteristics of Sr isotopes in the LS33 drill core from the Qiongdongnan Basin, South China Sea, and their response to the uplift of the Tibetan Plateau

Making full use of modern analytical and testing techniques to explore and establish new indexes or methods for extracting paleoseawater geochemical information from sediments will help to reconstruct the sedimentary paleoenvironment in different research areas.The connection between the subsidence of the South China Sea basin and the uplift of the Tibetan Plateau has been a scientific concern in recent decades.To explore the information on the sedimentary paleoenvironment,provenance changes and uplift of Tibetan Plateau contained in core sediments(debris),we selected core samples from Well LS33 in the Qiongdongnan Basin,South China Sea,and analyzed the contents of typical elements(Al,Th,and rare earth elements)that can indicate changes in provenance and the Sr isotopic compositions,which can reveal the geochemical characteristics of the paleoseawater depending on the type of material(authigenic carbonate and terrigenous detritus).The results show the following:(1)during the late Miocene,the Red River transported a large amount of detrital sediments from the ancient continental block(South China)to the Qiongdongnan Basin.(2)The authigenic carbonates accurately record changes in the 87Sr/86Sr ratios in the South China Sea since the Oligocene.These ratios reflect the semi-closed marginal sea environment of the South China Sea(relative to the ocean)and the sedimentary paleoenvironment evolution process of the deep-water area of the Qiongdongnan Basin from continental to transitional and then to bathyal.(3)Since the Neogene,the variations in the 87Sr/86Sr ratio in the authigenic carbonates have been consistent with the variations in the uplift rate of the Tibetan Plateau and the sediment accumulation rate in the Qiongdongnan Basin.These consistent changes indicate the complex geological process of the change in the rock weathering intensity and terrigenous Sr flux caused by changes in the uplift rate of the Tibetan Plateau,which influence the Sr isotope composition of seawater.

Fluid-solid coupling model for studying wellbore instability in drilling of gas hydrate bearing sediments

As the oil or gas exploration and development activities in deep and ultra- deep waters become more and more, encountering gas hydrate bearing sediments （HBS） is almost inevitable. The variation in temperature and pressure can destabilize gas hydrate in nearby formation around the borehole, which may reduce the strength of the formation and result in wellbore instability. A non-isothermal, transient, two-phase, and fluid-solid coupling mathematical model is proposed to simulate the complex stability performance of a wellbore drilled in HBS. In the model, the phase transition of hydrate dissociation, the heat exchange between drilling fluid and formation, the change of mechanical and petrophysical properties, the gas-water two-phase seepage, and its interaction with rock deformation are considered. A finite element simulator is developed, and the impact of drilling mud on wellbore instability in HBS is simulated. Results indicate that the re- duction in pressure and the increase in temperature of the drilling fluid can accelerate hydrate decomposition and lead to mechanical properties getting worse tremendously. The cohesion decreases by 25% when the hydrate totally dissociates in HBS. This easily causes the wellbore instability accordingly. In the first two hours after the formation is drilled, the regions of hydrate dissociation and wellbore instability extend quickly. Then, with the soaking time of drilling fluid increasing, the regions enlarge little. Choosing the low temperature drilling fluid and increasing the drilling mud pressure appropriately can benefit the wellbore stability of HBS. The established model turns out to be an efficient tool in numerical studies of the hydrate dissociation behavior and wellbore stability of HBS.

THE SEEPAGE CHARACTERISTICS OF HETEROGENEOUS BODY WITH DIFFERENT SPREADING SOLUTION MODES AND ITS APPLICATIONS

As the dump was a typically heterogeneous body, the seepage was different with varied spreading solution modes. The phenomenon of lamination that occured in the site was simulated using three layers in an indoor experiment, and the seepage effect comparison experiment of the inside spreading solution model and the top spreading solution model have been carried out. In the inside spreading solution mode, the phreatic planar flew without infiltration and the parallel layer motion model was used to calculate the seepage coefficient and equivalent seepage coefficient of each state respectively. In the top spreading solution model, the phreatic planar flew with an even infiltration on the surface, and the vertical layer motion model was adopted to calculate the above coefficient. The results showed that the seepage coefficient of the inside model was larger than the top model in the heterogeneous body, The ratio of them was between 1.42 and 3.07. On the basis of these results, the following new technologies were discussed： installing a few small diameter mechanical pore sand piles with every lamination in the using dump; drilling some holes one-off in the unused dump. These two methods could changed the top spreading solution into the inside model, thus the seepage in the dump was improved.

Discovery of lacustrine shale deposits in the Yanshan Orogenic Belt,China: Implications for hydrocarbon exploration

The mechanism of formation of lacustrine deposits within stable orogenic belts and their potential for shale oil and gas exploration are frontier themes of challenge in the fields of sedimentology and petroleum exploration. Orogenic belts witness strong tectonic activities and normally cannot host stable lacustrine basins and deep shale formations. Therefore, basins in orogenic belts are considered to have no potential to form shale hydrocarbon reservoirs. Here we investigate the Luanping Basin located in the Yanshan orogenic belt where previous studies regarded rivers and fan deltas as the major main Mesozoic deposits. Based on detailed field exploration and scientific drilling, we report the finding of a large number of lacustrine shale continental deep-water deposits in the Mesozoic strata. Our finding of the occurrence of active shale oil and gas also in this basin also subvert the previous perceptions.We report SHRIMP zircon U-Pb age that define the bottom boundary of the target interval as 127.6 ± 1.7 Ma belonging to the early Cretaceous strata. Tectonics and climate are considered to be the main factors that controlled the deep-water sedimentation during this period. The drill cores revealed evidence of shale gas and the TOC of shale is 0.33%–3.60%, with an average value of 1.39% and Ro is 0.84%–1.21%, with an average value of 1.002%. The brittleness index of shale is between 52.7% and 100%. After vertical well fracturing, the daily gas production is more than 1000 m^(3). Our findings show that the basin has considerable potential for shale oil and gas. The geological resources of the shale gas in the Xiguayuan Fm. are estimated as 1110.12 × 10^(8) m^(3), with shale oil geological resources of 3340.152 × 10^(4) t. Our findings indicate that the Yanshan orogenic belt has potential exploration prospect. This work not only redefines the Luanping Basin as a rift deep-water Mesozoic Lake Basin, but also rules out the previous notion that the basin is dominated by shallow water sediments. The discovery of shale oil and gas also provides an important reference for subsequent petroleum exploration and development in this basin. Our study shows that shale oil and gas reservoirs can be found in the lacustrine basins of orogenic belts which were strongly influenced by volcanism. These results have significant implications for the sedimentology and oil exploration in the Qinling and Xingmeng Orogenic Belts of China, as well as those in other terranes of the world including the New England Orogenic Belt in Australia.

FGC-15D large-diameter DTH air hammer drilling system and its application in offshore rock-socketed pile hole drilling

In the past two decades, numerous large-diameter rock-socketed piles were constructed in China to support foundations of skyscrapers, great bridges or to retain soil in potential geological hazard areas. However, drilling large-diameter rock-socketed pile holes with conventional drilling method such as rotary drilling or cable tool drilling is time-consuming and the cost is usually very high. In order to drill large-diameter rocksocketed pile holes faster at relatively low cost, the FGC15A large-diameter DTH air hammer drilling system was developed in 1987 and was given the second-clasa award by Ministry of Geology and Mineral Resources in 1991. Since it was innovated the drilling system has been used in more than twenty important and tough pro- jects on land, and wonderful results were acquired. At the same time the large-diameter DTH air hammer drilling system was improved continuously. The FGC15D is the latest version of the technique.

Calculation method of composite foundation sedimentation of grouting pile with cover plate under embankment load

Grouting pile is a new soft soil foundation treatment method with characteristics such as no vibration, no noise, no soil compaction, light construction machines and quick construction velocity and so on. At present, study on reinforcement mechanism and design calculation method of composite foundation of grouting pile is initially started without design specifications, so it is usually required to draw on design specifications of stump pile when designing composite foundation of grouting pile while grouting pile has its characteristics and difference although reinforcement mechanisms and construction processes of two types of piles are similar. Sedimentation formula of composite foundation of grouting pile with cover plate is educed and a suitable deformation mode is proposed by aiming to deformation characteristics of composite foundation of grouting pile with cover plate under embankment load on basis of relevant sedimentation theories of composite foundation by combination of characteristics of composite foundation of grouting pile. The sedimentation calculation formula of grouting pile with cover plate under embankment load is educed according to balance relation of force and displacement coordination conditions by elastic theory and sedimentation calculation model established is validated by sedimentation monitoring documents of one expressway in China.

Leak-Off Mechanism and Pressure Prediction for Shallow Sediments in Deepwater Drilling

Deepwater sediments are prone to loss circulation in drilling due to a low overburden gradient. How to predict the magnitude of leak-off pressure more accurately is an important issue in the protection of drilling safety and the reduction of drilling cost in deep water. Starting from the mechanical properties of a shallow formation and based on the basic theory of rock-soil mechanics, the stress distribution around a borehole was analyzed. It was found that the rock or soil on a borehole is in the plastic yield state before the effective tensile stress is generated, and the effective tangential and vertical stresses increase as the drilling fluid density increases; thus, tensile failure will not occur on the borehole wall. Based on the results of stress calculation, two mechanisms and leak-off pressure prediction models for shallow sediments in deepwater drilling were put forward, and the calculated values of these models were compared with the measured value of shallow leak-off pressure in actual drilling. The results show that the MHPS(minimum horizontal principle stress) model and the FIF(fracturing in formation) model can predict the lower and upper limits of leak-off pressure. The PLC(permeable lost circulation) model can comprehensively analyze the factors influencing permeable leakage and provide a theoretical basis for leak-off prevention and plugging in deepwater drilling.

EXPERIMENTAL STUDY ON TIME EFFECT OF WET DRILLING PILE

Time effect of wet drilling pile is investigated through the static load experiment on pile No. 22 of Guanhe Bridge. Post-grouting under pile tip is adopted in the project. To study the bearing performance of the pile, the self-balanced method is used and two load cells are assembled in the pile body. The experiments are carried out before and after post-grouting. The upper part of the pile is not influenced by post-grouting under the pile tip. Experimental results of the upper part of the pile show that the bearing capacity and the rigidity of wet drilling pile increase with time passing on. Analysis results show the time effect of wet drilling pile is influenced by many factors, such as alteration of stress field around pile, characteristics of soil around pile, variety of mud cake, and property of residue under pile tip.

Effect of sediment on vertical dynamic impedance of rock-socketed pile with large diameter

Based on the fictitious soil pile model, the effect of sediment on the vertical dynamic impedance of rock-socketed pile with large diameter was theoretically studied by means of Laplace transform technique and impedance function transfer method. Firstly, the sediment under rock-socketed pile was assumed to be fictitious soil pile with the same sectional area. The Rayleigh-Love rode model was used to simulate the rock-socketed pile and the fictitious soil pile with the consideration of the lateral inertial effect of large-diameter pile. The layered surrounding soils and bedrock were modeled by the plane strain model. Then, by virtue of the initial conditions and boundary conditions of the soil pile system, the analytical solution of the vertical dynamic impedance at the head of rock-socketed pile was derived for the arbitrary excitation acting on the pile head. Lastly, based on the presented analytical solution, the effect of sediment properties, bedrock property and lateral inertial effect on the vertical dynamic impedance at rock-socketed pile head were investigated in detail. It is shown that the sediment properties have significant effect on the vertical dynamic impedance at the rock-socketed pile head. The ability of soil-pile system to resist dynamic vertical deformation is weakened with the increase of sediment thickness, but amplified with the increase of shear wave velocity of sediment. The ability of soil pile system to resist dynamic vertical deformation is amplified with the bedrock property improving, but the ability of soil-pile system to resist vertical vibration is weakened with the improvement of bedrock property.

Research on Horizontal Vibration of Heavy-Weight Drill Pipes in Directional Drilling

The mode of load and deformation of directional drilling string and the expression of trigonometric series of deflection equation are established by means of elastic deformation energy and of the vertical and horizontal bending. A calculation formula for natural frequency of horizontal resonance and rotational speed is derived based on the calculation method by Ritz, with which analysis is made for the cause and affecting factors of the excessive abrasion of heavy-weight drill pipe in high-angle holes so as to provide reference and basis for rational selection of drilling parameters and drilling tools in the future high-angle directional drilling.

Assessment of Underwater Anthropogenic Noise Associated with Construction Activities in Bechers Bay, Santa Rosa Island, California

Acoustic monitoring and mitigation of underwater construction noise was conducted during marine pier demolition and reconstruction activities near Santa Rosa Island, California. Activities spanned two construction seasons and used both auger and pneumatic percussion drilling methods for pile placement. Pile drilling activities during construction resulted in sound pressure levels (SPL) ranging from 121.0 to 184.5 dB re 1 μPa. No significant difference was found for calculated source SPLs between the Season 1 and Season 2 methods of pile drilling (KW = 2.28, p = 0.15). Additionally, no significant difference was found for calculated source SPLs during active drilling between the Season 1 and Season 2 methods of pile drilling (KW = 3.39, p = 0.07). The average calculated source SPL documented during this study was lower than the NOAA Fisheries mandated safety zone threshold (160.0 dB re 1 μPa [rms]) for harassment to marine mammals. This is the first known report of SPL data collected in concert with marine pile drilling via the auger drilling technique. The results from this study can be used to improve information for and assist with the development of regulatory policies and techniques regarding sound level thresholds and mitigation monitoring.

On measures to improveeffectiveness of pump suc-tionreverse circulation drillin,

ＯＮＭＥＡＳＵＲＥＳＴＯＩＭＰＲＯＶＥＥＦＦＥＣＴＩＶＥＮＥＳＳＯＦＰＵＭＰＳＵＣＴＩＯＮＲＥＶＥＲＳＥＣＩＲＣＵＬＡＴＩＯＮＤＲＩＬＬＩＮＧＷｕＧｕａｎｇｌｉｎＣｈｅｎｇｄｕＩｎｓｔｉｔｕｔｅｏｆＴｅｃｈｎｏｌｏｇｙ，Ｃｈｅｎｇｄｕ６１００５９，Ｃ...

Nonlinear analysis of pile load-settlement behavior in layered soil

A simplified approach is presented to analyze the single pile settlement in multilayered soil. First, a fictitious soil-pile model is employed to consider the effect of layered soil beneath pile toe on pile settlement behavior. Two approximation methods are proposed to simplify the nonlinear load transfer function and simulate the nonlinear compression of fictitious soil-pile, respectively. On this basis, an efficient program is developed. The procedures for determining the main parameters of mathematical model are discussed. Comparisons with two well-documented field experimental pile loading tests are conducted to verify the rationality of the present method. Further studies are also made to evaluate the practicability of the proposed approach when a soft substratum exists, and the results suggest that the proposed method can provide a constructive means for assessing the settlement of a single pile for use in engineering design.

Pore Water Pressure Arising during Pile Drilling in Sand

The pile working load depends on the imperfections which may be taken place in pile-soil system, during pile construction, among many other factors. This subject attracted the researcher＇s attention world wide in the last decades. Types of imperfections either geotechnical or structural are documented in literature and well explained. Nevertheless, the influence of these imperfections in pile load calculations is still ambiguous. The work presented herein is devoted to study soil disturbance during construction of piles using continuous flight auger, CFA. The study of soil disturbance due to drilling needs some evidence. The source of this evidence is field observations collected from four different construction sites, which are documented in this paper. The study concluded that the disturbed zone of soil by CFA has a conical shape and extending laterally to a distance equivalent to ten times of the pile diameter around the auger at the cutting bits and has an inclined surface of4：1 （vertical ： horizontal）. Furthermore excess pore water pressure was induced in soil in the vicinity of pile drilling. Due to this excess pore water pressure, 3.5% to 6.5% of piles constructed by CFA showed percolation of water from the top of the piles through fresh concrete. Also, subsidence of fresh concrete in pile hole was recorded in few of the constructed piles. Pile loading tests showed that the percolation of water and/or subsidence of fresh concrete have not appreciable influence on the load-displacement characteristics of the piles. Moreover, percolation of water at pile heads.

Analysis on Pore-Forming Pouring Pile Construction Technology of House Building Project

Compared with the in-place pile, the pore-forming pouring pile is more simple and convenient, with a wider range of construction. In the actual construction process, it is able to pass through complex bottom layer and water layer underground without very high requirements in equipment. The actual bearing capacity of single pile is very strong, so that it can be better to adapt to the actual needs of different scales or the different geological conditions in building. And it has been promoted and used greatly in building construction work [1]. This paper introduces the concept of the pore-forming pouring pile technology, analyzes the pore-forming construction technology and the pile construction technology, then talks about prevention problems of the pore-forming pouring pile construction in House Building Project, at last draws a conclusion that the pore-forming pouring pile technology is the most basic construction technology and is the most effective and convenient way of construction.

水流作用下桩基局部水沙动力特征数值模拟

基于VOF方法追踪水气界面,利用不可压缩流体连续方程和运动方程对流体进行描述,通过嵌套网格技术建立三维数值水槽,湍流采用RNG k–ε模型,泥沙运动基于Van Rijn方法。基于验证后的数值水槽模型,开展水流作用下高桩承台结构局部水动力和冲刷规律研究,讨论不同来流条件下桩基桩周流场分布、泥沙输运和床面局部冲刷特征。结果表明,桩基冲刷特征受冲刷时间、流速、水位、水流攻角等来流条件的影响,同时也受桩间距的影响。当流速较小时,高桩承台桩基各桩之间相互作用较小,泥沙冲淤形态彼此独立,与单桩冲刷特征相似。流速较大时,前桩对后桩出现较为明显的遮蔽作用,前桩水流涡旋影响后桩,后桩周围流速明显降低,此时泥沙冲刷坑彼此相连构成群桩整体冲刷坑,且在最后排桩桩间形成条状冲刷坑,冲刷深度最大。

考虑桩底沉渣时沉降后浇带提前封闭时间计算方法:以秦望广场综合体工程为例

为了合理确定沉降后浇带提前封闭时间,开展了考虑桩底沉渣效应时沉降后浇带封闭时机研究工作。首先基于模型试验结果和秦望广场综合体工程的原位试桩试验结果,提出了考虑桩底沉渣效应的单桩沉降模型。基于该单桩沉降模型,根据施工过程中的常见工况组合,考虑了浮荷载对单桩刚度的改变,计算得到后浇带最早可封闭时间,并分析了沉渣厚度对后浇带可封闭时间的影响。模拟结果表明:当沉渣厚度符合设计要求时,恒载、活载、浮载组合工况引起的后浇带两侧差异沉降最大,但随着沉渣厚度的增大,恒载、活载组合工况逐渐转变为控制工况;当沉渣厚度较小时,所有工况下的差异沉降均呈线性发展,此时可以通过前期沉降观测值对后期变形进行预测;当沉渣厚度较大时,后浇带可封闭时间显著延后,甚至无法提前封闭。

钻孔灌注桩在基坑维护施工中的质量控制措施

结合实际案例,按照钻孔灌注桩施工工艺流程顺序,从钻孔前、钻孔中、成孔、钢筋笼吊装及混凝土浇筑等环节,对钻孔灌注桩在深基坑维护施工中的质量控制措施进行简要分析,如钻孔前应建立合理的质量控制流程等;钻孔过程中要做好护筒埋设、设备就位与安装、成孔等环节的质量控制;钢筋笼吊装要做好钢筋笼起吊点计算等工作;混凝土浇筑应避免堵孔、断桩等质量缺陷。

圆形抗滑桩-拱形挡土板支挡性能与参数分析

为规避当前施工方法的不足,发展安全、高效和可靠的施工方法。依托东北地区某高速铁路路堑边坡工程,采用适于机械钻孔的圆形抗滑桩代替现行矩形抗滑桩,预制拱形挡土板,本文提出一种新型拱形板-桩墙支挡体系;并构建有限元模型,分析桩长、桩径、桩间距以及拱形挡土板矢跨比对新型拱形板-桩墙支挡体系支护性能的影响;揭示不同参数下桩顶水平位移与桩身内力的变化规律。研究结果表明:桩长与桩身弯矩和剪力大小呈正相关关系,与桩顶水平位移呈负相关关系。桩长超过14 m时,其对桩顶水平位移、桩身弯矩和剪力的影响效应明显减弱;随着桩间距增大,桩顶水平位移增大但变化幅度逐渐减小。拱形挡土板矢跨比增大时,桩顶水平位移、桩身弯矩和剪力均减小。影响拱形板-桩墙体系支挡性能的因素依次为桩间距、桩长、桩径和矢跨比。研究结果为圆形抗滑桩-拱形挡土板支挡体系在实际工程中的应用提供新思路。

深水钻井井口吸力桩稳定性计算和校核方法

深水松软土质下,传统喷射法安装的表层导管在钻井阶段存在下沉和倾斜的风险。为了提升深水钻井水下井口的稳定性,提出了井口吸力桩表层建井的方法,开展了吸力桩下入深度和稳定性分析。基于桩基承载理论和广义Winkler地基梁模型,建立了井口吸力桩稳定性理论模型,并通过有限元方法和有限差分法研究了井口吸力桩稳定性特征及影响因素。以南中国海某井工程参数为依据,对井口吸力桩稳定性开展理论计算,与有限元计算结果进行对比,竖向极限承载力误差为4.23%,最大水平位移误差为6.0%,最大弯矩误差为2.96%,印证了计算结果的准确性。在钻井工况极限载荷作用下,相比于传统表层导管,井口吸力桩竖向承载力提升了43.91%,水平位移减少了63.21%,抗弯安全系数是前者的24.5倍。分别对井口吸力桩施加不同水平位移和弯矩,结果表明水平载荷对横向稳定性影响较为显著。井口吸力桩具有很高的竖向承载力和横向承载力,显著提高了水下井口的稳定性,研究结果为其在深水松软土质中表层建井提供了理论依据。