Showing papers in "Geotechnique in 1952"

The Sensitivity of Clays

Abstract: Synopsis The sensitivity of clays is defined as the ratio of their undisturbed and remoulded strengths, and varies from about 1·O for heavily over-consolidated clays to values of over 100 for the so-called extrasensitive or “quick” clays. As a result of experimental work it is shown that thixotropy can account for low or medium sensitivity but not for high sensitivity. Both laboratory and field evidence, however, show that a reduction in the salt concentration in the pore water, caused by leaching clays of marine or estuarine origin, can result in high sensitivities. Moreover, of the small number of clays so far investigated, those which have not been leached are found to exhibit only low or medium sensitivities of the order of magnitude explicable in terms of thixotropy. But it is, nevertheless, not suggested that leaching is the sole cause of high sensitivity and other possibilities are briefly discussed. Reasons are given, supported by experimental work, for the insensitivity of heavily overconsolidate...

The Effect Measured of the Rubber Membrane on the Triaxial Compression Strength of Clay Samples

Abstract: Synopsis In the undrained triaxial compression test the rubber membranes enclosing the specimens give rise to an apparent increase in strength. This article presents the results of tests to determine the magnitide of this effect together with an approximate theoretical treatment. Triaxial tests on remoulded London clay, employing rubber membranes of three different thicknesses, when compared with unconfined compression tests at the same moisture content show that the strength contributed by the rubber membrane is:— independent of specimen strength proportional to the stiffness of the membrane independent of cell pressure. In compression tests, with the specimen enclosed in a rubber membrane but with no lateral pressure, the effect is smaller than in the normal triaxial test. Filter paper drains, used to accelerate consolidation, add further to the compression strength and consequently a larger correction must be applied to the measured strength. A method for estimating the rubber correction from a simple ...

The Computation of Permeability from Simple Soil Tests

Abstract: Synopsis Estimates of permeability of the ground are frequently required by civil engineering work involving the seepage of water. Several published formulae relating the permeability of beds of granular material to their geometrical properties are quoted. In order to assess the value of these formulae in calculating permeability, a comparison is made between measured and calculated values of permeability for a wide range of sands. Hazen's formula is quite useful because of its simplicity but the result may be inaccurate to the extent of ±2. Kozeny's formula is the best of those quoted, and if an estimate of the “angularity” of the grains is made, permeabilities of sand can be computed to an accuracy of about ±20 per cent. An empirical formula is given which is equally accurate and more simple to use. Computations of permeability by the methods described can be made only on clean sands. Pour les travaux de genie civil relatifs a des infiltrations d'eau, il est souvent něcessaire de faire 1'evaluation de l...

Stresses in Rock About Cavities

Abstract: Synopsis The article contains a discussion of the influenceof the shape of cavities, such as tunnels or spheroidal chambers, on the state of stress in the surrounding rock. The mathematical methods which have been used for computing the stresses are given in an appendix. The results of the computations show that the stresses in the rock surrounding spheroidal cavities are lower than those in the rock about tunnels with the same cross-section, located at the same depth. As the ratio between the height and the diameter of a spheroidal cavity decreases, the stresses in the rock adjacent to the equator increase, but the height and width of the zone of stress concentration decreases. If the rock located within this zone is not strong enough to sustain the stresses, it flows or it is crushed, but the local failure has little influence on the state of stress in the rock above the roof of the cavity. The most important error involved in the determination of the stresses is due to the uncertainties involved in the...

The Movement and Distribution of Water in Soils

Abstract: Synopsis Moisture plays a particularly important role in the soil mechanics of shallow foundations, because of the comparatively large seasonal changes occurring in the moisture condition of the soil close to the earth's surface. In particular, methods of estimating the changes which occur in the moisture condition when soil is paved are required in the design of roads and airfields. This article discusses the fundamental factors which give rise to moisture movements in soil and, on the basis of this discussion, methods are outlined for estimating the moisture distribution with depth beneath impervious pavements under equilibrium conditions. Differences in the soil moisture suction (or reduced pressure at which water is retained in the soil structure) provide the “potential” causing water to move within a soil mass. The movements which occur can only be expressed in terms of moisture content if the relationship between soil moisture suction and moisture content for the soil is known. The nature of this re...

Investigations Concerning a Deep Cofferdam in the Thames Estuary Clay at Shellhaven

Abstract: Synoposis During the construction of a deep cofferdam in the Thames Estuary clay at Shellhaven, the opportunity was taken of measuring the loads transmitted from the sheet-piling walls to the walings, and the loads in the struts. A detailed investigation was also made of the soil properties by means of insitu vane tests and by laboratory tests on undisturbed samples, some taken from a borehole and others taken during the excavation of a shaft immediately adjacent to the cofferdam. In Parts I and II of the article the soil properties and load observations are recorded. In Part III the results are interpreted by means of earth pressure calculations, and it is concluded that the observed loads in the bracing of the cofferdam can be accounted for in terms of deflexions of the sheet piling prior to placing the struts in position, and without the need for assuming any redistribution of earth pressure. Au tours de la construction d'un coffrage a grande profondeur dans l'argile de l'estuaire de la Tamise a Shellh...

A General Plasticity Theory for Clay

Abstract: Synopsis For fully saturated clay with internal friction and cohesion the equations of a general plasticity theory have been developed, assuming a linear increase of the undrained shear strength with the depth, as well as a sinusoidal variation of this strength with the inclination of the failure plane. In this general case the “ Rankine ” solution has been investigated and applied to the earthpressure problem. The result confirms the correctness of the usual procedure, which consists of adding or subtracting twice the shear strength, provided that this shear strength is taken as half the compression strength at the depth in question and for shear along the failure plane in question. The inclination of the failure planes is, however, 45° ± ½ φe instead of 45°. In the special case of homogeneous, isotropical clay (with internal friction) a “ Prandtl ” type solution has been investigated and applied to the foundation pressure problem. Also in this case the result confirms the correctness of the usual formul...

Foundations for Ringsend Power Station, Dublin

Abstract: Synopsis This article describes the “Benoto” system for sinking 3-foot-3-inch-diameter steel cylinders through water-bearing gravel and silt to bedrock at a depth of approximately 140 feet below ground surface level. Sinking of a cylinder is effected under its own weight by grabbing-out the contained material while, at the same time, the cylinder is continually rotated backwards and forwards about its vertical axis through an angle of 8 degrees. When a cylinder is sunk to sound rock, it is filled with concrete thus forming a pile which is to carry a load of approximately 450 tons, including its own weight, together with frictionally applied load from settlement of the surrounding ground. The specialized plant used in sinking is a “Benoto” grab and a “Benoto” tubing machine. The grab is a 35-inch-diameter, single rope type, weighing 1,984 lb. and operated by a crane made for the purpose. The tubing machine consists of a double acting hydraulic jack operated by a hydraulic pump. The jack oscillates a 21-foo...