Soils strength

Over a large range of increasing soil strength Mask Farquhar (1988) observed a decrease in A of 3.7 x 10 and a doubling of W. The decrease in A was also accompanied by a reduction in the value of p measured by gas-exchange. 

Masle, J. Farquhar, G.D. (1988). Effects of soil strength on the relation of water use efficiency and growth to carbon isotope discrimination in wheat seedlings. Plant Physiology, 6,147-55. 

Masle, J. Passioura, J.B. (1987). Effects of soil strength on the growth of wheat seedlings. Australian Journal of Plant Physiology, 141, 643-56. 

Taylor, H.M. Ratliff, L.F. (1969). Root elongation rates of cotton and peanuts as a function of soil strength and soil water content. Soil Science, 108, 113-19. 

Protection against physical stress Respon.se to high soil strength through inodilication of interface through lubrication and amelioration of rhizosphere soil... 

Soil strength Water-holding capacity Field capacity/wilting point Hydraulic conductivity Fertility... 

Stress-strain relationships for soil are difficult to model due to their complexity. In normal practice, response of soil consists of analyzing compression and shear stresses produced by the structure, applied as static loads. Change in soil strength with deformation is usually disregarded. Clay soils will exhibit some elastic response and are capable of absorbing blast-energy however, there may be insufficient test data to define this response quantitatively. Soil has a very low tensile capacity thus the stress-strain relationship is radically different in the tension region than in compression. 

The postmining land-use objective must be selected with the characteristics of the topsoil in mind. Chemical soil properties are more easily amended than physical properties such as texture. Thus, when adequate topsoil is not available, the substitute material must be selected with special attention to texture, coarse-fragment content, and mineral content. Bulk density and soil strength must be considered during soil handling. Methods and equipment used for redistribution of topsoil must be selected to minimize compaction, which can inhibit root penetration and movement of air and water. 

Increases soil strength and decreases permeability wide application... 

Gerard, C.J., Sexton, P, Shaw, G., 1982. Physical factors influencing soil strength and root growth. Agron. J. 74, 875-879. 

The CPT was originally known as the Dutch CPT. The test is a versatile sounding method that can be used to determine the stratigraphic identification, soil strength, deformation, and dynamic properties of sediments. In recent years, this has been expanded to include chemical data and hydraulic properties of the subsurface strata. The current cone penetrometer has its beginnings in the early 1930s in the Netherlands. Cone penetrometers... 

A number of techniques have been developed to convert the total penetration force to sediment shear strength. They t5qjically involve splitting up the force into various components which correspond to different elements of an assumed mode of soil failure. A soil penetration model based on Newton s second law has been presented by True (1975). If the penetrometer motion is known, then the soil strength can be determined. 

The propagation of water waves over a permeable seabed exerts a time varying pressure at the sediment/water interface. The time varying pressure will cause cyclic variations in pore pressure and stresses within the bed. The effective stress varies in response to wave loading. Since soil strength is directly related to effective stress, any change in the effective stress state within the bed will affect bed strength and stability. Many coastal structures such as pipelines, platforms, anchors, and breakwaters that interact with the seabed will be affected by both cyclic effective stresses and the erosion potential of the bottom sediments. 

Alpha method The alpha procedure was derived by Drewry, Weidler, and Hwong (1977) from the same data set used for the original lambda correlation. For pile-capacity calculations the procedure utilizes a multiplier a on the undrained shear strength (Su) of the clay. The API code has traditionally recommended a value of 1.0 for Gulf of Mexico-type clays or a value that varies with strength for other types of clays. The API (2000) code varies the a value with the ratio of undrained soil strength to effective soil overburden ( / = S /a ) is as given in Equation 10.21 ... 

Determination of SRD There are two primary methods available to determine SRD. These methods are (1) CPT method (de Ruiter and Beringen, 1979), and (2) utilization of soil strength data from soil investigations (Toolan and Fox, 1977). 

In the second method, soil strength data from soil investigations are used to compute the SRD. In this procedure, remolded friction values are used directly in sands and clays, while for pile tip resistances the undisturbed values are used (Toolan and Fox, 1977). 

The screw-in, auger, or helical anchor uses one or more single-turn helical plates attached to a rigid shaft to screw itself into the soil. This anchor system was developed for use on land to anchor guy wires for towers and poles. It has had limited use on the seabed to anchor pipelines and cables. Anchor penetration is dependent upon reaction force and torque from the drive unit in addition to soil strength. 

For short-term or undrained loading analysis (( ) = 0) the factor N is zero and the factor N c is selected from Figure 10.43 for the anticipated relative embedment depth D/B and soil cohesion (a distance B above the anchor) in the soft rupture zone. The soil cohesion can be measured in place with a field vane or cone penetrometer or determined from laboratory tests on core samples such as the unconfined compression or triaxial CU test. If soil strength data are not available, the strength profile can be estimated using d CTot = 0.30, where the vertical effective stress (o J is estimated using a buoyant unit weight of 4 kN/m. ... 

Depth Soil Strength Bottom Pressure General Comments... 

Triaxial tests are normally carried out on nominal 100 mm or 38 mm diameter samples with height to diameter ratio 2 1. If the height to diameter ratio is reduced to 1 1 the end platens should be lubricated Undrained tests measure undrained strength s . Drained tests, or undrained tests with measurement of pore pressure, evaluate the Mohr Coulomb parameters c and 4> Since soil strength depends on strain it is necessary to state whether the strength corresponds to the peak state, the critical state or the residual (Atkinson 1993)... 

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