Engineering Properties of Natural Soil

Table of Contents

What is the variability of Soil?

What is the sensitivity of soil? 

Coarse-grained Soil

Normally Consolidated Soil 

Over-consolidated Soil

Residual Deposit Soil

Organic Deposit Soil

Normalizing Vs for field assessments

Soil–structure interaction for seismic assessment and design of bridges

What is the variability of Soil?

Soils change throughout time in fields and between farms. Uneven litter decay, soil moisture content, vegetation composition, topographic position, land use pattern, and soil management technique can all contribute to soil spatial variability. In different peat lands, these factors may have a distinct impact on chemical and biological processes.

What is the sensitivity of soil? 

The sensitivity of soil is defined as the ratio of the unconfined compression strength of clay in the natural or undisturbed condition to that in the remoulded state, without any change in water content.

The strength of soil can be higher in its unbroken state than in its remoulded state. This category includes a lot of cohesive soils. Soil sensitivity is the ratio of shear strength in the uninterrupted condition to that in the entirely remoulded state, and it describes this behaviour.

A decrease in intensity is frequently noticed when the strength of an unmoved piece of clay is assessed and then determined again after reshaping to the same dry density at the same water content. This is a serious occurrence that has the potential to cause harm and is measured with the formula below.

St = Su (undisturbed) / Su (remoulded)                 

Coarse-grained Soil

Individual grains that pass through a No. 200 (0.075 mm) sieve are described as coarse-grained soils. The smallest grains may usually be seen with the naked eye, though a hand-held magnifying glass may be required to see the tiniest grains. Gravel and sand are soils with a coarse grain.

Normally Consolidated Soil 

This situation is described as normally consolidated when the first vertical effective stress is approximately equivalent to the pre-consolidation stress.

That is why, even if the soil is typically consolidated, the values acquired are rarely similar. To prevent misclassifying soil, we'll assume it's generally consolidated if the initial vertical effective stress and pre-consolidation stress are around 20% of one other.

Over-consolidated Soil

Over-consolidation is a relative phrase that compares the stress acting on the soil in its current state to the soil's greatest stress level. If the current stress is less than that previously applied, the soil is already over-consolidated, and vice versa.

Residual Deposit Soil

A residual deposit is one that has formed due to the alteration of an existing rock that has lost a considerable portion of its contents due to dissolution and has thus become enriched in specific minerals or other elements. Bauxite, for example, is an aluminium ore generated through the modification of several types of rock containing aluminium elements.

Organic Deposit Soil

When temperature or pressure is lowered, heavy hydrocarbons precipitate, causing damage. These deposits are frequently found in tubing, gravel packs, and perforations, as well as inside the formation. The use of cold treatment fluids encourages the growth of organic deposits. Aromatic organic solvents like toluene or xylene resolubilize organic deposits like paraffin or asphaltenes.

Normalizing Vs for field assessments

The observed Vs of deeper layers would be expected to be greater than those of shallow layers even when the site has homogeneous density, as the mean effective stress increases with increasing depth in natural soil deposits.

The effect of confinement (or overburden stress) must be taken into account when assessing the density of a material based on in situ Vs. Vs normalisation with depth or overburden pressure has long been acknowledged in various investigations, particularly those for SPT (Standard Penetration Test) and CPT.

When the in situ vertical stress is 100 kPa (Pa), the normalisation was meant to provide a benchmark value for the shear wave velocity at a specific depth, typically the depth equivalent to an overburden pressure equal to an atmospheric pressure of 100 kPa (PA).

Because Vs takes null values if the mean effective stress is zero, this aspect presents significant challenges if surface conditions are to be considered This limitation necessitated the adoption of an alternate normalising strategy that incorporates the midway condition of a specific seismic stratigraphic layer, as indicated.

A layer's midpoint pressure becomes the standard for normalisation, therefore Vsn = Vs at that midpoint becomes the benchmark velocity for normalisation.

Soil–structure interaction for seismic assessment and design of bridges

Nonlinear behaviour in supporting soil deposits rises with the increasing magnitude of the earthquake, allowing for more adaptability and dampening at the soil-to-foundation interface. Modern FE codes integrate a wide range of advanced soil constitutive laws.

It is still a difficult computational task to simulate the simultaneous development of inelastic mechanisms in the soil, foundation, and structure. This is because of both the material and epistemic uncertainty. To better understand how earthquakes interact with soil, foundation stiffness, and soil-foundation interfacial friction are all being studied.

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What is soil stabilization and its principles

A hysteretic continuum of nonlinear weight and Poisson's ratio, g = 18kN/m3, is supposed to be under the foundation of the building. At the surface, the soil's low-strain shear modulus is zero, whereas, at 10 m below the surface, it is 213 MPa. Seed and Idriss (1970) advocated for sand the fluctuations in shear moduli and damping ratios with shear strain.

At a depth of ten metres, the soft soil layer sits on top of a hard one. Using the PILE-3D finite element mesh (Wu and Finn, 1997; Finn et al., 2019), the soil deposit was split into 10 sublayers of varied thicknesses. The soil-pile interaction effects are stronger toward the surface, hence the sublayer thicknesses are thinner there.

Most design guides use the mean shear wave velocity Vs to a depth of 30 m (Vs;30) and the accompanying site classes to quantify the influence of the site on seismic design. Because of this, in most earthquake code standards, the top 30 metres of ground are used to characterise a site class. This single parameter, Vs;30, determines the site's classification. Vs;30 (in m/s units) can be calculated for a profile with n soil or rock layers by

In the ith layer, the shear wave velocity Vsi is proportional to the height of the ith layer, which ranges from 0 to 30 metres. The characteristic period of soil Tc, defined as the transition period between the constant acceleration and constant velocity segment of the elastic spectrum, is another attribute that distinguishes the various soil types by category.

It's possible that soil's unpredictable and nonlinear behaviour could result in insufficient reliability. The variety of soil qualities can have a major impact on bridge behaviour at the ultimate and serviceability limit states, which is why they must be taken into account.

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