# Shallow And Deep Foundation Pdf

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- Shallow and Deep Foundations under Fault Rupture Or Strong Seismic Shaking
- DESIGN OF SHALLOW AND DEEP FOUNDATIONS FOR EARTHQUAKES
- Foundation (engineering)
- Shallow Foundation and Deep Foundation

*In engineering, a foundation is the element of a structure which connects it to the ground, and transfers loads from the structure to the ground. Foundations are generally considered either shallow or deep.*

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## Shallow and Deep Foundations under Fault Rupture Or Strong Seismic Shaking

One such example of foundation failure involving toppling of apartment blocks due to liquefaction during the Niigata Earthquake is presented in Figure 1. Earthquake effects on shallow and deep foundations are accounted for by designing them structurally to provide necessary strength and ensure serviceability. Strength considerations essentially involves ensuring that the foundation loads remain well below that dictated by the allowable bearing capacity under seismic conditions and serviceability is ensured by designing the substructure for the estimated permanent ground deformation.

Simple procedures for estimating bearing capacity and permanent ground deformation under earthquake conditions are presented in this note. Figure 1. Tilted apartment buildings 2. Any further increase in the amplitude of ground motion will lead to the failure of soil layer without any further increase in resistance. It needs to be emphasized that the response discussed here can be reached irrespective of earthquake-related pore water pressure increase or liquefaction.

Roy 2 Figure 2. Subsurface state of stress Liquefaction is triggered when earthquake-related increase of pore water pressure causes a remarkable reduction of effective stress.

The notion of liquefaction used here is thus not identical to the classical viewpoint that defines liquefaction as the state of zero effective stress.

Saturated loose to medium dense sands and soft and sensitive clays of low plasticity are susceptible to liquefaction. The procedures for estimating the ultimate bearing capacities under earthquake loads at non-liquefied and liquefied sites are discussed below.

A simple approach to account for these effects is to reduce the static bearing capacity factors using Figure 3. In Figure 3 subscripts E and S signify earthquake and static conditions. The ratio of seismic to static bearing capacity factors depend on the acceleration ratio, v h k k 1 , where k h and k v are the horizontal and vertical seismic coefficients within the failure zone. The seismic coefficients are often assumed according to max 5. Alternatively, the average acceleration over the zone affected by shear failure can be estimated from a free-field site-response calculation using, e.

The usual value of the factor of safety for estimating the allowable seismic bearing capacity for shallow footings is 2. If the thickness of non-liquefiable layer below the bottom of footing is thin, shallow foundations supported within the layer may punch through. Roy 3 Figure 3. Ratio of seismic to static bearing capacity factors from Richards et al. The foundation designer must ensure adequate factor of safety against such possibilities as indicated below.

Punching The ultimate resistance for a strip footing against punching can be estimated using: 1 2 u ult s T q 1 where T is the thickness of non-liquefiable crust below the footing base and s u1 is the undrained shear strength of the non-liquefiable crust.

For footings of limited length, multiplier 2 on the right hand side of Equation 1 should be replaced with the perimeter of the footing footprint.

A factor of safety of safety of 2 should be provided in this regard. Bearing Capacity The bearing capacity problem related to liquefaction is essentially an undrained problem.

The problem is conveniently treated using the static bearing capacity factor, N c , for layered soils shown on Figure 4, in which Layer 1 represents the non-liquefiable crust and Layer 2 represents liquefied soil. Since liquefaction of Layer 2 is likely to cause a significant reduction in the amplitude of ground motion at surface, the static value of N c may be used to estimate the ultimate bearing capacity even under earthquake condition. However, if triggering of liquefaction fails to damp out the ground motion at surface, N cE should be estimated using the chart on the right side of Figure 4.

The undrained strength for non-liquefiable crust can be estimated from a field Vane Shear Test or the CPT if the layer is comprised of fine-grained soils.

For the liquefiable layer, the post-liquefaction undrained shear strength can be estimated using Equations 4 and 5 Olson and Stark, Roy 4 value of the factor of safety for estimating the allowable bearing capacity for shallow footings in a site underlain by liquefiable soils is 2. Figure 4. However, footings tend to undergo continually increasing permanent vertical deformation settlement with the progress of earthquake-related cyclic moment and shear loading.

Consequently, permanent displacements may become the critical consideration in structural design for earthquake loads instead of bearing capacity. For sites not affected by liquefaction, Richards et al. A similar simple framework is not available for multi directional earthquake ground motion. At liquefiable sites vertical settlement is usually estimated using the correlations presented in Figure 5.

In this figure symbols D r , N 1 and q c1 expressed in MPa have been used to denote relative density, stress normalized SPT blow count and stress normalized cone tip resistance, respectively. Factor of safety against liquefaction is estimated following the procedures outlines in Youd et al. Figure 5 has been prepared accounting for this difference.

The total permanent ground settlement related to liquefaction is obtained by multiplying the thicknesses of soil layers by the appropriate of the volumetric strain read out from Figure 5 and summing up the results for all individual layers within the soil column underlying a site. Roy 5 Figure 5. Volumetric strain due to liquefaction after Ishihara and Yoshimine, Differential settlements rather than total settlements usually govern structural design.

Several case histories involving failure of piles can nevertheless be found in the literature, two of which are shown on Figure 6. Most earthquake-related failure of pile foundations is due to permanent ground displacement e. Roy 6 4. The interaction between the pile and the surrounding soil is approximated by idealizing the soil resistance to relative movement between pile and soil by the so-called p y, t z, and the Q z, springs, representing horizontal translation, vertical translation of the pile shaft and vertical translation of the pile tip, respectively.

Symbols p, t and Q have been used here to represent the horizontal force, vertical force along pile shaft and the vertical force at the pile tip, respectively, while y and z represent vertical and horizontal displacements, respectively. A widely used empirical procedure for constructing these nonlinear springs for cyclic loading conditions like earthquakes can be found in API RP2A American Petroleum Institute A simplified, quasi-static analytical includes the following steps: a estimation of the free field deformation without considering the existence of the piles , b applying these deformations across the p y, t z, and the Q z, springs to the piles, c recalculating the deformations, d applying the recalculated deformations across the p y, t z, and the Q z, springs to the piles and e iterating through steps c and d until the input deformation field becomes compatible with the pile deformation within an acceptable range of tolerance.

A very simple method of pile design for earthquake-related permanent ground deformation used by the Japanese Road Association JRA involves consideration of a distributed load along the pile shaft as shown on Figure 7 along with other structural loads.

Figure 7. Lateral load for pile design for earthquake-related permanent ground deformation Concerns have been raised over recent years regarding the adequacy of this design procedure because it neglects the possibility of bucking resulting from the remarkable reduction of lateral restraint within the liquefied layer Bhattacharya et al.

However, to take proper account of liquefaction-related loss of lateral restraint development of an elaborate numerical model based on finite element or finite difference becomes necessary.

It should be noted that several case histories describing earthquake-related failures of structures due to loss of lateral restraint for piles in cohesive deposits can also be found in the literature.

Although finite difference computer codes have been developed to account for this possibility Matlock and Foo , a simple empirical procedure for estimating gap formation as a function of soil strength and number of cycles of earthquake load is not yet available.

Roy 7 4. A suite of earthquake accelerograms are used in these analyses. Sourcing information and a brief description of the capabilities of these packages can be found at www. The grade beams are typically designed to carry one tenth of the maximum column load. Mat foundation is often considered a viable foundation option under earthquake loading conditions especially in areas underlain by liquefiable deposits.

Uneven permanent ground deformations in such situations are bridged relatively easily by an appropriately designed mat foundation. Pile foundations also perform well under earthquake loads and are therefore commonly used in seismically active areas.

Pile caps are also often interconnected with grade beams and structurally designed floor slab. SUMMARY Structural design of foundations involves satisfying two requirements: a a factor of safety of 2 or more is available against bearing capacity failure under seismic loading and b the permanent ground deformation can be accommodated by the foundation system and superstructure. Some of the simple empirical procedures available to account for these issues for common foundation types have been discussed in this note.

Common strategies adopted by geotechnical engineers in foundation design have also been briefly discussed. Recommended practice for planning, desigining and constructing fixed offshore platforms Working stress design. Bhattacharya S. An alternative mechanism for pile failure in liquefiable deposits during earthquakes. Gotechnique, 54 3 : Gajan, S. Centrifuge modeling of load-deformation behavior of rocking shallow foundations.

Soil Dynamics and Earthquake Engineering, 25, Ishihara, K. Evaluation of settlements in sand deposits following liquefaction during earthquakes. Soils and Foundations. Matlock, H. Axial analysis of piles using a hysteretic and degrading soil model. Roy 8 Newmark, N. Effects of earthquakes on dams and embankments. Gotechnique, 15, Olson, S. Yield strength ratio and liquefaction analysis of slopes and embankments.

Journal of Geotechnical and Geoenvironmental Engineering. Richards, R. Seismic bearing capacity and settlements of foundations. Journal of Geotechnical Engineering. Yuminamochi, F. Air photographs of the Niigata City immediately after the earthquake of Japanese Geotechnical Society.

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## DESIGN OF SHALLOW AND DEEP FOUNDATIONS FOR EARTHQUAKES

Those which transfer the loads to subsoil at a point near to the ground floor of the building such as strips and raft. A shallow foundation is a type of foundation which transfers building loads to the earth very near the surface, rather than to a subsurface layer or a range of depths as does a deep foundation. Shallow foundations include spread footing foundations, raft foundation known as mat-slab foundations, slab-on-grade foundations, strip foundations, buoyancy foundations, pad foundations, rubble trench foundations, and earth bag foundations. These foundation is according to BS : Shallow foundations are taken to be those where the depth below finished ground level is less than 3 m and include strip, pad and raft foundations. Shallow foundations where the depth breadth ratio is high may need to be designed as deep foundations. Shallow foundations are those foundations that have a depth-of-embedment-to-width ratio of approximately less than four.

One such example of foundation failure involving toppling of apartment blocks due to liquefaction during the Niigata Earthquake is presented in Figure 1. Earthquake effects on shallow and deep foundations are accounted for by designing them structurally to provide necessary strength and ensure serviceability. Strength considerations essentially involves ensuring that the foundation loads remain well below that dictated by the allowable bearing capacity under seismic conditions and serviceability is ensured by designing the substructure for the estimated permanent ground deformation. Simple procedures for estimating bearing capacity and permanent ground deformation under earthquake conditions are presented in this note. Figure 1.

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## Foundation (engineering)

Foundation is one of the most important parts of the structure. It transfers the total loads from the structure to the soil and provides stability to the structure. Foundation can be primarily classified into two parts, such as Shallow Foundation and Deep Foundation. They are basically classified depending on the depth at which the foundation is provided. Shallow foundation and deep foundation have several differences.

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*A shallow foundation is a type of building foundation that transfers building loads to the earth very near to the surface, rather than to a subsurface layer or a range of depths as does a deep foundation. Shallow foundations include spread footing foundations, mat-slab foundations, slab-on-grade foundations, pad foundations, rubble trench foundations and earthbag foundations. A spread footing foundation, which is common in residential buildings, has a wider bottom portion than the load-bearing foundation walls it supports.*

### Shallow Foundation and Deep Foundation

Earthquake Geotechnical Engineering pp Cite as. Two topics of interest in soil—foundation—structure interaction are presented: the first refers to the consequences on shallow and deep foundations and their superstructures from a seismic fault rupture emerging directly underneath them; the second topic addresses the seismic response of tall structures resting on shallow foundations that experience uplifting and inducing large inelastic deformations in the soil. The numerical and analytical methodologies developed for each topic have been calibrated with centrifuge experiments. The outlined parametric results provide valuable insight to the respective soil—foundation interplay, and could explain qualitatively the observed behaviour in a number of case histories from recent earthquakes. Unable to display preview. Download preview PDF.

Discounts are ending soon; Register Now and Save. Learn More. Introduction Shallow and deep foundations signify the relative depth of the soil on which buildings are founded.

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PDF | Many aspects of foundation design and construction in tropical soils are the same as those in sedimented soils, about which many text books have | Find.

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