两种典型碳酸盐岩红土风化剖面的物理化学特征

通过对贵州遵义和平坝两种典型碳酸盐岩风化剖面的系统采样,在室内进行了岩土工程上常用的13项物理指标的测试和12项常量化学元素的全分析,在此基础上论述了它们在风化剖面上的分布及变化特征.指出土层孔隙率(孔隙比)由表层土到深处由高到低的变化,导致岩(土)层透水率逐渐降低和含水量的增加,是土层物理性质及相关力学性质变化的主因;表层土以粘土粒组为主,到靠近基岩附近变为以粉土粒组为主,说明后期红土化作用可使土粒变细;靠近岩石界面土层的粒径与组成石灰岩和白云岩矿物颗粒大小相当,这可能是地下水溶蚀-交代矿物颗粒继承发育的结果;通过分析界面各层(基岩-溶滤层-杂色粘土层)化学成分的变化可以看出,由岩石到土层可溶性组分(CaO、MgO)大量的被水溶蚀带走,成土元素(SiO2、Al2O3、Fe2O3等)呈突跃式增加,而且两类岩石溶蚀成土的初期阶段(由岩石到溶滤层)可溶元素被溶蚀及成土元素的积累有很大的差别.

PHYSICAL AND CHEMICAL PROPERTIES OF TWO TYPICAL WEATHERED PROFILES OF CARBONATE ROCKS

Through systematic sampling from two typical weathered profiles of carbonate rock at Zunyi and Pingba in Guizhou province and experiments of the specimens with 13 tests on physical indices and 12 tests on chemical total analysis of macro-elements which are in common use in geo-engineering field, the distribution and variable characteristics of these indices and elements in the profiles are discussed. The porosity of soil layers decreases with the increase of the buried depth,which results in the increase of moisture content and the gradual decrease of permeability of the rock (soil) layers, the latter being the major reason of the variety of physical and mechanical properties of the soil layers. The clay fraction takes dominant place on the top layer of the soil, while the silt fraction is dominant near the bottom layer of the soil. This phenomenon shows that the later laterization can make the soil grain becoming finer. The grain size of the soil layers near the interface of the bedrock is almost equivalent to the size of the mineral grains that constitute the limestone and dolomite, which may be the result of the continuous development of the erosion-replacement mineral grains made by groundwater. Through the analysis of variable chemical composition of all interfaces (bedrock to leached layer to versicolor clay layer), it can be seen that most of the dissoluble components (CaO, MgO) has been dissolved and run away with water, the soil-forming elements (SiO_2, Al_2O_3, Fe_2O_3 etc.) increase abruptly, and the erosion of the dissoluble elements and the accumulation of soil-forming elements of the two type of rocks differ remarkably in the primary stage of rock's erosion and pedogenesis.