Soft rock masses represent a significant percentage of rock material on the earth’s crust. The engineering properties of these rocks are related to their composition, geological history, and degree of weathering. Mudrocks (claystone, mudstone, argillite), marl, shale, sandstone, and conglomerates with weak cementing material are the most common example of these rocks which can be subjected to a wide variation of their engineering properties. Generally, they can be grouped in a broad sense, as geological materials with very low intact rock properties, namely, high deformability and low strength that span the range between soils and hard rocks. This paper is organized to suggest a classification for these rocks, dealing with the main geological and engineering aspects and features that characterize these materials. The two indices of soft rock number (SRN) and soft rock activity (SRA) have been introduced in this classification. The SRN is obtained based on the geomechanical properties of soft rocks, and it is within a range from 0 to 100 (0 for very weak rocks and 100 for strong ones). On the other hand, the SRA index, which indicates how rocks respond to disturbance, is calculated using an empirical graph. This index can have values from 0 to 1. If the index is closer to 0, the rock mass will be less sensitive to disturbance. Based on the two indices, the weakest group of soft rocks, which is called swelling soft rocks, has SRNs less than 20 and SRAs higher than 0.8. Excavation of these rocks can be accompanied by various types of failures. Moreover, in high-strength soft rocks, SRNs and SRAs have values higher than 80 and lower than 0.25, respectively. These rocks have good geomechanical properties and the lowest sensitivity to disturbance, so excavation them results in the fewest failures.

软岩体占地壳中岩石材料的很大一部分。这些岩石的工程性质与其组成，地质历史和风化程度有关。这些岩石中最常见的例子是泥浆岩（粘土岩，泥岩，泥锌矿），泥灰岩，页岩，砂岩和砾岩，这些岩浆具有较弱的固结材料，它们是最常见的例子，它们的工程特性可能会发生很大的变化。通常，它们可以广义地归类为具有非常低的完整岩石特性的地质材料，即具有高变形性和低强度的地质材料，其跨越土壤和硬岩石之间的范围。本文旨在为这些岩石提供分类建议，涉及地质和工程学的主要方面以及表征这些材料的特征。在此分类中引入了软岩数（SRN）和软岩活度（SRA）的两个指标。SRN是根据软岩的地质力学特性获得的，其范围为0到100（对于非常弱的岩石为0，对于强烈的岩石为100）。另一方面，使用经验图来计算SRA指数，该指数指示岩石如何响应扰动。该索引的值可以从0到1。如果该索引更接近于0，则岩体对扰动的敏感性将降低。根据这两个指标，最软弱的一组软岩（称为膨胀软岩）的SRN小于20，SRA大于0.8。这些岩石的开挖可能伴有各种类型的破坏。此外，在高强度软岩中，SRN和SRA的值分别大于80和小于0.25。