中-新生代软岩一般裂隙不发育，但孔隙多且胶结强度低，易扰动性显著，其岩块试验成果折减后进行岩体力学参数取值，普遍造成软弱地基力学指标远低于实际值，是目前工程界面临的一大困惑。通过对一批工程实测案例分析表明，中-新生代软弱岩体有别于多裂隙性岩体，岩块与原位试验结果相比具有反尺寸效应：现场岩体载荷试验的比例界限值、极限强度值分别大于Rc值的1.62～20倍、2.4～50倍，桩侧摩阻力试验参数值与现行有关规范Rc值折减法取值有明显提高，极软岩原位试验的变形模量大于岩块的试验值，实测岩体完整性指数Kv普遍大于1。采用基本质量评价的BQ法，该类岩体级别的划分主要由Rc值主导，实测Kv值不直接参与基本质量指标计算，它从物理意义上主要反映了软弱岩石坚硬程度低而易扰动的特性。软弱岩体的“原位性”即保持其天然结构和状态是保持软岩基本力学性质的关键，因此，原位岩体力学试验是研究其变形特性、地基承载力（桩端阻力）和桩侧极限摩阻力的必要选择，应在大量工程实例应用及成熟经验的基础上达到试验方法的标准化。

The fissure of soft rock of Mesozoic era and Cenozoic era isn’t developmental normally. But there exist many pores in this rock and the cementation intensity of this rock is very low. Easy disturbance is notable. Mechanics parameters are valued after rebating test result of rock block. It makes mechanics index of weak foundation to be greatly lower than actual value. This is a bemusement in the field of engineering at present. The research result from several engineering illustrations shows that soft rock mass of Mesozoic era and Cenozoic era is different from the rock mass with many fissures. At the same time，the rock block possesses anti-size effect compared with test result in situ：The proportional limit value of rock mass of load test in situ is normally more than 1.62-20 times Rc. The ultimate intensity value of rock mass of load test in situ is more than 2.4-50 times Rc. The test parameter value of lateral frictional resistance of pile is obviously increased. Rc value is also increased obviously by reduction method in current code. The modulus of deformation of badly soft rock in situ is more than the test value of rock block. Actually measured Kv is more than 1 generally. Grading rock mass is classified by Rc according to BQ method. Base quality index isn’t calculated directly by measured Kv.Kv reflects mainly low hardness and disturbing characteristic of soft rock in view of physics meaning. The performance of soft rock in situ（namely keeping its crude structure）and state are the key that soft rock keeps mechanics property. So，the mechanics test of rock mass in situ is the obligatory choice to study deformation property，bearing capacity of foundation（end bearing of pile），and lateral ultimate friction resistance of pile. More test methods are boosted to reach standardization on the basis of ripe experience and a lot of engineering examples.