Foundation soil resistance

In order to understand this phenomenon, it has to be remembered that the soil shear strength can be represented by  

When the interstitial water pressure grows with a constant total pressure in the same location, the soil shear strength decreases. 

Moreover, tests and experience show that in rather loose sands, when the load increases the sand 

The various study and evaluation means of this phenomenon can be summarized in various levels of importance, but they are not exclusive to one another  

As indicated, for first approximation evaluations, the assessment of the susceptibility to liquefaction can be omitted when the saturated soil is located more than 20 m below the surface. Moreover, as the liquefaction is a threshold phenomenon, the analysis can be omitted when, for a sufficiently long return time, the vibratory ground motion at the surface has a peak acceleration lower than 0.15g. 

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Owing to shear stresses induced in the foundation soils by the vertical eccentric foxm-dation load, the magnitude of horizontal load that the foundation soils can sustain may decrease witii an increase in vertical load. This fact must be recognized when computing and evaluating sliding resistance by the simplified procedures described below. 

Rausche, E, Mosses, F. Goble, G. 1972. Soil resistance predictions from pile dynamics. ASCE Journal of the Soil Mechanics and Foundation Division. 98. SM9. 

Verification of the soil strength should not, however, neglect the foundation soil bearing capacity for higher loads caused by an earthquake, the resistance of slopes, soil support walls or of other works of interest for safety, also considering potentially induced indirect effects, such as flood waves in streams due to the failure of dams (Hansen, 1970 Meyerhof, 1951 Janbu, 1957 Morgenstern and Price, 1965 Sarma, 1975, 1981 Espinoza, Bourdeau and Muhunthan, 1994). 

In order to define the dynamic characteristics of the foundation soils, in relation to the choice of an elastic site-compatible spectrum, it is advisable to evaluate the profile of the shear wave velocity. This profile should be determined on-site by down-hole geophysical tests. As an alternative, it can be defined with the aid of empirical correlations with the site penetration resistance (SPT, CPT) or with other geotechnical properties. For a more complete definition of the dynamical characteristics, it might be necessary to define shear wave velocity values compatible with the deformations induced in the ground by the passage of seismic waves. 

The limit bearing capacity of the foundation soil, glim, can be calculated by the empirical formulation proposed by various authors, such as Hansen (1970) and Meyerhof (1951), who correlate gum with the soil resistance characteristics and with the dimensions of the foundation structure. 

The overall characteristics which make a structure particularly resistant to an earthquake are its symmetry in the distribution of masses and rigidities, its compactness, possibly its low height, the good connection between horizontal and vertical elements, the connection between isolated foundation elements, the uniformity and competency of the foundation soil, the provisions against impact between adjacent structures, and the absence of negative effects of non-structural elements (filling walls, etc.) (CasteUani et al., 2000 Livolant et al., 1979). 

Reinforcement in a slope contributes to stability in two ways. Firstly, the reinforcement directly improves the shear resistance of the soil to resist the shear loading caused by the steep face. Secondly, the reinforced zone acts to hold the unreinforced soil mass of the interior in equilibrium without overstressing the underlying foundation soils. 

The wall of the pipe has a thickness of 6 mm. The soil resistance is equal to 3000 Q cm. Because of a construction error, the pipe is in contact with the reinforcement of a building s concrete foundation, thus forming a galvanic cell. The corrosion potential of the metal reinforcement is equal to /Scor.ii = +0-6 V. How long will it take the corrosion to pierce a hole in the pipe ... 

In pile foundations the mechanical parameters for the springs are frequently obtained from experimental results (leading to P-y curves for lateral and N-z curves for axial loading) as well as from very simplified models. A commonly used P-y curve is the lateral soil resistance versus deflection relationship proposed by the American Petroleum Institute (API) ... 

Some of the common design measures to mitigate these failures include the following remove or improve problematic foundation soils by ground treatment and adequately compact the dam fills, use wide core zones of plastic soils that are resistant to erosion, use well-graded wide filter zones upstream of the core, construct chimney drains downstream of the core to lessen soil saturation and reduce downstream seepage, and use dam crest and downstream slope details to provide protection of the dam in the event of an overtopping. 

Kinematic interaction is the deviation of the soil response from the free-held motion due to the resistance of the stiffer foundation to conform to the distortions of the soil imposed by the traveling seismic waves. It is commonly expressed in terms of frequency-dependent transfer functions relating the disturbed motion at the interface foundation/soil to the free-held motion. 

Foundations are always constructed of reinforced concrete. Blast resistant buildings can be supported on pited or soil supported mats. Spread footings arc used with a grade beam system to minimize relative displacements between individual footings,... 

Preliminary design of the foundation will include evaluating overturning, bearing pressures and lateral load resistance. The foundation must be able to resist the applied blast loads with a degree of safety to account for uncertainties in prediction of soil properties. Foundation failure can cause serious collapse hazards, thus it is prudent to maintain a conservative design. Also, should an incident occur, it is many times desirable to be able to remove the building structure and rebuild on the same foundation. 

Since a conservative approach is used, it is quite common practice to design the foundation using static loads. Typically, this involves applying the resistance of the roof and walls as uniform static loads and computing reactions. Support reactions from frame analyses arc also checked to ensure that local foundation failures don t occur. Dynamic analysts of foundations can be accomplished if appropriate soil properties are provided. 

Scientific and engineering investigations into the properties and behavior of particulate solids date back to the early work of Coulomb, who in 1776 developed a theory on soil pressure and resistance, thus laying sound foundations for important engineering... 

Brick and mortar materials should only be used alone where the fact that gas and liquid can penetrate, though slowly, through them is not important, but where their considerable compressive strength (load bearing ability), combined with their resistance to chemical attack can be useful. Examples of these types of structures are self-supporting chimney liners (some of them 800+feet tall), foundations set in acid contaminated soil, and supports for chemical equipment subject to splash or spill. 

Regardless of its source, oil released into the subsurface soil moves along the path of least resistance and downwards, under the influence of gravity, as shown in Figure 31. Oil often migrates towards excavated areas such as pipeline trenches, filled-in areas around building foundations, utility corridors, and roadbeds. Such areas are often filled with material that is more permeable or less compacted than the material removed during the excavation. 

It was shown by equation (11-1) that the total soil loading, to be considered in the design of tower foundations, is the sum of Si, the dead load, and S2, the load caused by the overturning or wind moment. There is no overturning moment on guyed towers however, the wind pressure does have an important effect on the foundation, as the soil is required to resist the vertical component of the pull on the guy wires. 

Reinforcement to Resist Uplift Stresses. The wind moment creates a positive soil load on one side of the centerline, and a negative load on the opposite side. In other words, the action of the wind tends to lift the foundation on the negative side. This upward force, or uplift effect, is resisted by the weight of the concrete base itself, and by the weight of the earth fill on top of the base. It, therefore, becomes necessary to reinforce the top of the base to resist the resulting negative bending moment. 

In special cases, values d > 1.0 and d > 1.0 may still be used, provided that the foundation installation procedure and other critical aspects allow for the mobilization of resisting shear stresses in the soil above the foundation level. In such cases the following expressions for d, valid for d upper limit of this contribution ... 

Seed, H.B. 1966. A method for earthquake resistant design of earth dams. Journal of the Soil Mechanics and Foundations Division, ASCE, 92, No. SM-1, pp. 13-41. 

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