Currently, there are six cities constructing their metro systems in China, among which, the Nanjing metro project is characterized by its complicated and unfavorable geological conditions, such as varied topography, rugged bedrocks, many faults passing through, rapid variation in lithology and geotechnical properties, soft ground, high groundwater table and multiple groundwater types. Therefore, the geological and geotechnical investigations play a vital role in the project. This paper describes and discusses the investigations taken in the project. From a seismological point of view, the project is in a relatively stable tectonic setting, the major regional active faults are a little far. Among many faults found in the city area, the NWW Dinghuaimen-Gulou fault and the NNW Nanjing-Hushu fault merit attention to their influences on the foundation stability. High groundwater table and multiple groundwater types feature the hydrogeological conditions. The paper describes the hydrogeological characteristics and parameters on the basis of groundwater type division. The inflow prevention of abundant pore water in ancient riverbed, fault water in Gulou and karst water in Xiaohongshan are diffcult. Along the metro axis, the local morphology can be divided into five sections: three sections of tectonic denudated lowrise hills and two sections of ancient channel alluvial plains. As many as 50 of Quaternary soil formations have been encountered. They are too many for architects to conceive and establish the engineering geological model. Therefore, generalization and division of engineering geological strata groups is necessary. The Quaternary deposits at the Metro site were divided according to their origin and relevant age into four engineering geological strata groups and subdivided on the basis of their composition, physical state and geotechnical properties into distinct subgroups. Data from this study indicate that the division is feasible and the subgroup II2 (CS) and III2 (CS), which are soft cohesive soils of Holocene and late Pleistocene respectively, represent the most sensitive and weak geotechnical unit, and the Holocene sandy soils subgroup II4 (SL) is of the most potential danger of liquefaction. None of the current rock mass classification systems has been found to originate from and be adequate for the shallow metro tunnel. The CGIMC, Vp and BQ systems have been combined in this study. The study indicates that the combination of multiple systems, qualitative and quantitative, is helpful to ensure the reliability of rock masses evaluation. To overcome the deficiency of the rock mass intactness index Kv and the BQ system in the national standard, their determination methods were modified. The paper describes in details the modified Kv and BQ procedure taking account of the characteristics of the rock masses at the metro site. The rock masses are categorized into very poor, poor and fair quality. The poor conditions of the rock masses are largely due to intensive weathering and dense fracturing. Along the metro axis, eight geotechinal zones were divided according to their identical characters of topographical, engineering geological and hydrogeological conditions and construction methods. The paper highlights the different geotechnical problems and challenges that will be encountered in different geotechnical zones.

Rock-gas outbursts, including sandstone-gas outbursts, become more and more serious with increasing depth of engineering and more difficult geological environments and their prediction and prevention are one of the major challenges to the rock mechanics and rock engineering community. Comparatively speaking, sandstone-gas outbursts have not been well studied and are less documented than coal-gas outbursts. So the exchange of information, especially in the field of the prediction and prevention of sandstone-gas outbursts, is important. This paper outlines an outburst in which over 2000 tonnes of oil-bearing sandstone were ejected with 900,000m3 of gas in the air shaft of Haishiwan Colliery; this is the largest sandstone-gas outburst in China to date. The theoretical and technical investigation relating to the prediction and prevention of such sandstone-gas outbursts, taking the Haishiwan Colliery project as the background, are described in the paper. A comprehensive prediction method employing a suite of macro-and micro-indices gained from test drilling and laboratory testing on rock cores is proposed in the paper. It is found that the combination and comparison of the results of field observations, measurements and laboratory tests are helpful to ensure the reliability of outburst prediction. The principle and scheme of preventive drilling and discharging, including the pattern and number of releasing boreholes and the safety distance for drilling, were studied. It is revealed that discharging of gas can also release rock mass strain energy, which should be taken into consideration in the determination of the number of releasing boreholes. For the purpose of releasing, the Tubular Destressed and Depressurized Protective Zone (TDDPZ) pattern proposed in the paper is more efficient and economical than the currently applied fan-shaped pattern of releasing boreholes. The accuracy of prediction and the efficiency of the preventive measures were verified by successful excavation through the oil-and gas-bearing sandstone units in Haishiwan Colliery.

声波测试是工程岩体质量评价的最主要手段之一。将岩体与岩块的纵波波速比的平方定义为岩体的完整性系数，不仅为国内外学者广泛认同，而且是现行规范的定义。这是源于如下认识：原位岩体的纵波波速小于其中岩块的波速；岩体越破碎，小得越多。然而，通过润扬大桥声波测试发现，用通常手段得到的大部分岩体的测井波速反而大于岩样波速。对该桥基岩40余个钻孔数百个岩样进行了多种手段的对比研究和综合分析，探讨了测试结果的可靠性及产生原因，进而提出了岩芯卸荷扰动和卸荷敏感岩体的概念和相应的工程对策。

由于风化会对岩石强度、刚度和耐久性产生重大影响，故在岩石工程勘察设计中需对其进行重点研究。风化是润扬大桥花岗岩类基岩岩体质量和桥基选址与设计的控制因素之一。系统的地质分析和多种测试结果表明，桥区风化壳厚度的变化很大，岩性以及地壳升降、断裂切割、卸荷作用、江水下切与入渗等地质作用是控制花岗岩风化作用及其风化岩分布的主要因素；桥区花岗岩易风化、卸荷敏感，处于化学风化的早期阶段；细密的蚀变裂隙对岩石强度起着控制作用。在此基础上讨论了风化带来的主要岩土工程问题以及桥型方案、基础选址与设计、地基参数取值以及风化因素控制等方面的工程对策。

工程地质岩组的划分是岩体质量评价的基础。当大型工程揭露土层很多时，进行土体工程地质层组的划分亦是十分必要的。它可以更为清晰的反映场地地质结构的变化规律，便于地质模型的概化和参数研究，有助于抓住主要工程地质问题进行评价，便于设计师的理解和应用。以南京地铁南北线一期工程为例，探讨了土体工程地质岩组的划分问题。通过以层组为基础的参数离散性统计、工程地质模型与工程地质问题的分析可以看出该层组划分方案的合理性与工程意义。