Nén ONE-chiều Trong các chương trước, sự biến dạng của đất đã được tách thành nén tinh khiết và cắt tinh khiết. Tinh khiết nén là một sự thay đổi của khối lượng trong trường hợp không có bất kỳ thay đổi hình dạng, trong khi cắt tinh khiết là một sự thay đổi hình dạng, khối lượng không đổi. Lý tưởng nhất là kiểm tra trong phòng thí nghiệm nên có hình dạng không đổi hoặc loại khối lượng không đổi, nhưng đó không phải đơn giản như vậy. | Chapter 14 ONE-DIMENSIONAL COMPRESSION In the previous chapters the deformation of soils has been separated into pure compression and pure shear. Pure compression is a change of volume in the absence of any change of shape whereas pure shear is a change of shape at constant volume. Ideally laboratory tests should be of constant shape or constant volume type but that is not so simple. An ideal compression test would require isotropic loading of a sample that should be free to deform in all directions. Although tests on spherical samples are indeed possible it is more common to perform a compression test in which no horizontal deformation is allowed by enclosing the sample in a rigid steel ring and then deform the sample in vertical direction. In such a test the deformation consists mainly of a change of volume although some change of shape also occurs. The main mode of deformation is compression however. Confined compression test In the confined compression test or oedometer test a cylindrical soil sample is enclosed in a very stiff steel ring and loaded through a porous plate Figure Confined compression test. strain will be equal to that strain at the top see Figure . The equipment is usually placed in a somewhat larger container filled with water. Pore water may be drained from the sample through porous stones at the bottom and the top of the sample. The load is usually applied by a dead weight pressing on the top of the sample. This load can be increased in steps by adding weights. The ring usually has a sharp edge at its top which enables to cut the sample from a larger soil body. In this case there can be no horizontal deformations by the confining ring xx yy 0. This means that the only non-zero strain is a vertical strain. The volume vol zz. For convenience this strain will be denoted as . The load of the sample is a vertical stress ơzz which will be denoted as Ơ Ơ ơzz . 84 Arnold Verruijt Soil Mechanics 14. ONE-DIMENSIONAL .
