Tunnelling and Hydrogeological Issues: A Short Review of the Current State of the Art

Since the 1960s, there has been an increasing interest in the understanding of the hydraulic flow inside a hard rock mass, since water inflow into deep tunnels constitute a hazard, in addition to being an important factor in controlling the advancement of excavation. The characterisation of fluid flow through hard rock masses is still one of the most challenging problems faced by geologists and engineers. A rock mass is characterised by networks of discrete and ubiquitous discontinuities that strongly affect its hydraulic properties, but detailed knowledge of the discontinuity properties allows for the evaluation of the hydraulic flow in the rock mass affected by the excavation of a tunnel. A geostructural field survey is fundamental in order to correctly define the discontinuity types, settings and networks. Numerous approaches have been proposed to estimate the water inflow based on empirical relations supported by field experience and case studies, as well as analytical solutions. Often, however, these approaches are not easily applicable in standard practice and in complex scenarios. The most appropriate approach to characterising the hydraulic flow of the rock mass and to predicting in the most effective way the expected water inflow during the excavation of a tunnel is based on a detailed geological model and geostructural analysis as described in this paper.     

确定摩擦桩承载力的一种动测法

本文在分析单桩的承载能力取决于桩身条件、桩周岩土介质的力学参数和受载的作用时间的基础上,探讨了单桩的动力和静力的承载机制。提出一种考虑桩周岩土介质动、静力学强度指标和加载速率的动测法,用它来确定摩擦桩的极限承载力。动测与静压试桩对比和工程应用表明,该法简便有效。     

A Dynamic Measurement of Bearing Capacity for Frictional Piles

Based on the fact that the bearing capacity of pile depends of the condition of pile body, mechanical parameters of the media around it, and loading period, the mechanism of dynamic and static bearing capacity for the single-pile is studied. Considering loading rate and difference between dynamic and static mechanical strengths of rock and soil media, a dynamic measurement is proposed to determine critical bearing capacity of frictional piles, which has been proved to be simple and effective with engineering applications and comparison between dynamic and static tests.     

Changes in Properties of Clay Surrounding Cast in situ Piles

Often pile load carrying capacity is derived from friction between pile and the surrounding soil. This magnitude of friction mobilised, in the main, depends on pile material, properties of the soil and method of construction. In terms of construction, piles may be either pre-formed or cast in situ. Cast in situ piles are formed by boring a hole and filling it with concrete. It is envisaged that water and both calcium and hydroxyl ions migrate from the fresh concrete to the surrounding soil and have an impact on soil properties. An experimental study was undertaken to examine the extent of soil (Oxford clay) around the pile was affected by fresh concrete. Time related study included load tests on model piles. The investigation showed that there was about 4% increase in the moisture content of the surrounding soil soon after fresh concrete was placed and with time this dissipated. It showed that there was an increase in both hydroxyl and calcium ions in the vicinity of the pile. These also affected the adhesion factor, which increased with time to a limiting value. Time related tests showed that there was a small increase in pile load capacity with time.     

The Influence of Rate of Loading on the Behaviour of Continuous-Flight-Auger Bored Piles in Soft Clay

A total of 27 piles were installed at the Engineering and Physical Science Research Council soft clay test site at Bothkennar, Scotland using the continuous-flight-auger boring technique. Twelve of the piles of different lengths and diameters were tested in axial compression, using the others as reaction piles. Various testing programmes were employed to investigate relationships between axial load, movement and rate of movement. Strain measurements were facilitated by installing exten"someters in the piles, thus enabling the distributions of load and shaft resistance down each pile to be evaluated. Shaft resistances were found to be approximately constant even though the clay is known to increase in strength with depth. Peak shaft resistances were found to be dependent on rate of movement while ultimate shaft resistances were dependent only on magnitude of movement.     

树根桩在地基托换加固中的应用

以已建建筑软土地基为实例，介绍在建筑物出现不均匀沉降时，用树根桩对地基进行加固的处理技术，其加固效果好，且施工噪声小，方便灵活，不改变原建筑物的静力平衡。     

PHC管桩动测及桩身倾斜缺陷对竖立承载力的影响

结合工程实践介绍低应变动测法检测发现PHC管桩的缺陷波形特征,并结合静载荷试验情况分析缺陷对竖向承载力的影响。     

Depth of Fixity of Piles in Clay Under Dynamic Lateral Load

Dynamic experiments were carried out on instrumented model aluminium single piles embedded in clay of different consistencies to study its bending behaviour under lateral loads. Piles with different length to diameter ratios were used. Dynamic lateral load of different magnitudes ranging from 7 to 30 N at wide range of frequencies from 2 to 50 Hz were applied. The load transferred to the pile, pile head displacement and the strain variation along the pile length were measured using a dedicated data acquisition system. Static lateral load tests were also performed to investigate the magnification of dynamic response of piles in clay. It is found that the maximum bending moment due to dynamic load is magnified by about 1.5–4 times in comparison to the static load for short piles but about 9 times for long piles. Depth of fixity and effective pile length is also largely amplified under dynamic loads, thus indicating that a pile which behaves as a flexible pile under static load, may not exhibit flexible behaviour under dynamic load.     

黏土矿物古气候意义研究的现状与展望

系统地分析了利用海洋沉积物、古土壤、湖盆沉积物中黏土矿物进行古气候环境研究的现状、存在问题和发展趋势。海洋沉积物的物源范围广,影响因素复杂,其中的碎屑黏土矿物所指示的古气候参数只能用于解释母源区的气候变化,而只有自生黏土矿物才能指示沉积区的气候;古土壤形成于特定的地质背景条件下,尤其是发育于火山物质母岩之上的风化自生黏土矿物,可以准确地指示该区的古气候条件;湖盆沉积物的物源范围小,沉积物中的黏土矿物可以更有效地运用于古气候环境的分析。对于沉积物中黏土矿物来源的分析,可以借助晶体中cv空位和tv空位的精细结构特征进行判断;在风化改造的红土剖面研究中,因强烈的化学风化、淋滤和迁移,黏土矿物方法具有独特的优势。风化过程中形成的一些亚种或过渡性黏土矿物,以及同生沉积过程中形成的黏土矿物,对气候环境的变化更加敏感,应加强这方面的研究。此外,在造山带的气候环境演化研究中,自生黏土矿物稳定同位素可以更可靠地指示气候环境的变化。     

Hydrofracture: State Of The Art In South Africa

During the past five years, the Department of Water Affairs and Forestry of South Africa have hydrofractured a large number of low yielding boreholes in different geological and geohydrological regimes. In the Swartwater study area (10 holes), the results indicate that boreholes that were scientifically sited in order to intersect geological features such as faults or contacts are the most likely to be sucessfully stimulated. In the case of random site selection, the sucess rate was extremely low. By using the newly developed hydrofracture unit and carefully selecting the holes to be stimulated, a low-yielding water borehole can be sucessfully converted into a production hole for between 35 and 45% of the cost of drilling another borehole.     

老黏土地基承载力的确定

对比分析了各种确定地基承载力的方法,阐述了理论公式计算确定老黏土地基承载力的重要性.结合武昌地区的工程实例,用各种方法计算确定了老黏土的地基承载力值.研究表明,原位测试方法得到的承载力值偏低,而理论公式计算较合理.为了提高老黏土地基承载力的可信度和精度,在岩土工程勘察中除采用原位测试方法外,有必要结合理论公式计算来获取老黏土地基承载力值.     

郑州某大厦试验桩承载力初探

通过某工程的实测数据,运用最小二乘法原理,采用试算法对桩侧阻力进行分析。     

Clay smear: Review of mechanisms and applications

Clay smear is a collection of fault processes and resulting fault structures that form when normal faults deform layered sedimentary sections. These elusive structures have attracted deep interest from researchers interested in subsurface fluid flow, particularly in the oil and gas industry. In the four decades since the association between clay-smear structures and oil and gas accumulations was introduced, there has been extensive research into the fault processes that create clay smear and the resulting effects of that clay smear on fluid flow. We undertake a critical review of the literature associated with outcrop studies, laboratory and numerical modeling, and subsurface field studies of clay smear and propose a comprehensive summary that encompasses all of these elements. Important fault processes that contribute to clay smear are defined in the context of the ratio of rock strength and in situ effective stresses, the geometric evolution of fault systems, and the composition of the faulted section. We find that although there has been progress in all avenues pursued, progress has been uneven, and the processes that disrupt clay smears are mostly overlooked. We highlight those research areas that we think will yield the greatest benefit and suggest that taking these emerging results within a more process-based framework presented here will lead to a new generation of clay smear models.     

Timing, Displacement and Growth Pattern of the Altyn Tagh Fault: A Review

The Altyn Tagh Fault (ATF) is the longest, lithospheric scale and strike-slip fault in East Asia. In the last three decades, multidisciplinary studies focusing on the timing, displacement of strike-slip and growth mechanics of the ATF have made great progresses. Most studies revealed that the ATF is a sinistral strike-slip and thrust fault, which underwent multiple episodes of activation. The fault is oriented NEE with a length of 1600 km, but the direction, timing of activity and magnitude of its extension eastward are still unclear. The AFT was predominately active during the Mesozoic and Cenozoic, in relation to the Mesozoic collision of the Cimmerian continent (Qiangtang and Lhasa block) and Cenozoic collision of India with Asia. The AFT strike-slipped with a left-lateral displacement of ca. 400 km during the Cenozoic and the displacement were bigger in the western segment and stronger in the early stage of fault activation. The slip-rates in the Quaternary were bigger in the middle segment than in the western and eastern segment. We roughly estimated the Mesozoic displacement as ca. 150-300 km. The latest paleomagnetic data showed that the clockwise vertical-axis rotation did not take place in the huge basins (the Tarim and Qaidam) at both side of ATF during the Cenozoic, but the rotation happened in the small basins along the ATF. This rotation may play an important role on accommodating the tectonic deformation and displacement of the ATF. Even if we have achieved consensus for many issues related to the ATF, some issues still need to be study deeply; such as: (a) the temporal and spatial coupling relationship between the collision of Cimmerian continent with Asia and the history of AFT in the Mesozoic and (b) the tectonic deformation history which records by the sediments of the basins within and at both side of AFT and was constrained by a high-resolution and accurate chronology such as magnetostratigraphy and paleomagnetic data.     

海洋天然气水合物成藏系统研究进展

在系统总结海洋天然气水合物形成的物质来源及成因机理、物理化学响应、形成环境及成藏模式、分布规律和资源评价进展的基础上,提出了我国开展天然气水合物成藏机理研究的方向和科学问题。2007年4—6月通过钻探获得了测井、原位测量、沉积物岩心及其顶空气、孔隙水、微生物、水合物等样品和资料。南海北部陆坡神狐海域是研究天然气水合物成藏机理和分布规律的理想区域。采用重点分析天然气水合物成藏的物质基础、形成环境、成藏过程、响应机理和成藏系统等研究思路,针对天然气水合物成藏系统中气—水—沉积物—水合物体系的相互作用机理、天然气水合物成藏过程中的物理化学响应机理、天然气水合物成藏要素的耦合控矿机理等3个关键科学问题,开展天然气水合物成藏物源、地质与温压场等成藏条件、成藏演化热动力学机理、成藏响应机理和天然气水合物成藏系统等5个方面研究。     

桩底注浆对钻孔灌注桩竖向承载性能的影响

依据某工程中采用桩底注浆和没有注浆的2根试桩的单桩竖向抗压静荷载试验结果,通过对基桩的竖向极限承载力性状、桩身轴力传递特性以及桩侧阻力发挥特性和桩端阻力发挥特性的综合分析研究,揭示了桩底注浆对基桩承载性状的影响情况。     

A New SPT-Based Method for Estimating Axial Capacity of Driven Piles in Glacial Deposits

Geotechnical and Geological Engineering - This paper proposes a new design method for the axial capacity of driven piles in glacial deposits with the standard penetration test (SPT) based on a...     

A State-of-the-Art Review of Stone/Sand-Column Reinforced Clay Systems

This paper presents a state-of-the-art review of published research papers and reports that focus on the modeling, testing, and analysis of soft clays that are reinforced with sand/stone columns in relation to bearing capacity and settlement considerations. The review is presented in chronological order to shed light on the development of this field of research in the last 40+ years. The objective of the study is to assemble published results from field, laboratory, and numerical investigations of sand/stone columns in clay in one resource to provide future researchers and designers with easy access to information and data. The majority of the reviewed papers include an experimental component that is based on field or laboratory scale tests (1-g, triaxial, or centrifuge) conducted on clay specimens reinforced with partially or fully penetrating, encased or ordinary, stone or sand columns that were installed as single columns or as column groups. Some papers included numerical experiments that were based on finite element models, while others presented analytical solutions for modeling the response of the composite system. A compilation of the important findings from physical, numerical, and analytical models in addition to a summary table that facilitates access to information from various research efforts are presented in the paper.     

Strontium Isotope Stratigraphy: Principles and State of the Art

The methodical basis, development, and current state of a new method of chronostratigraphic studies, i.e., strontium isotope stratigraphy (SIS), are considered. This method makes it possible to date and correlate geographically distant sedimentary sequences without involving the biostratigraphic and isotope geochronological data. SIS is based on secular variations in ⁸⁷Sr/⁸⁶Sr in the paleocean, resulting from the redistribution of the roles of two global strontium flows formed in the mantle and continental reservoirs of the Earth. Isotopic homogeneity of Sr in the paleoceans and in the linked seas leads to the fact that the ⁸⁷Sr/⁸⁶Sr ratio in the sea basins is individual for each geological time point and is inherited in marine chemogenic sediments under deposition of dissolved Sr as an isomorphic impurity. Low-Mg calcite and also fragments of fossilized paleontological remains buried in situ are the best minerals that are capable of retaining the Sr isotopic signature of the sedimentation environment. SIS is carried out with geochemical diagnostics of secondary alteration of the studied material and selective dissolution of the samples to produce a carbonate material that adequately reflects isotopic signature of the sedimentary basin. Interregional correlations of the Proterozoic and Cenozoic sea sediments and their relation to the SIS-based stratigraphic scale are given as an example.     

试论水泥喷射搅拌桩的单桩承载力测试

水泥喷射搅拌桩（以下简称粉喷桩）是软土地基加固的一种方法。按规范，一般测试复合地基承载力作为加固效果的评判标准。粉喷桩是复合地基的基础，很多设计单位和建设单位要求对单桩进行承载力检测，验证桩的设计参数，检查施工质量。由于粉喷桩承载力能否测试，如何取值等，没有规范依据，给检测工作带来困难。本文就此问题谈一点看法。