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Senior Civil Engineering major.

Input regarding Pore Water Pressure

The buoyancy effects of water have a large impact on certain soil properties such as the effective stress present at any point in a soil medium. Consider an arbitrary point five meters below the ground surface. In dry soil, particles at this point experience a total overhead stress equal to the depth underground (5 meters), multiplied by the specific weight of the soil. However, when the local water table height is within said five meters, the total stress felt five meters below surface is decreased by the product of the height of the water table in to the five meter area, and the specific weight of water, 9.81 kN/m^2. This parameter is called the effective stress of the soil, basically equal to the difference in a soil’s total stress and pore water pressure. The Pore water pressure is essential in differentiating a soil’s total stress from its effective stress. A correct representation of stress in soil is necessary for accurate field calculations in a variety of engineering trades.

JK Mitchell of the University of California, Berkeley reports that pore water pressure develops as a result of four scientific phenomena: Water elevation difference, hydrostatic water pressure, osmotic pressure, and absorption pressure. It is a fundamental notion in fluid mechanics that water flows from higher elevation to lower elevation. This elevation difference causes a velocity head, or with water flow, as exemplified in the Bernoulli’s energy equation. Hydrostatic water pressure exists for any water body, as the water particles exert force in all directions due to applied pressures along with self-weight. A congregation of water is unlikely to be homogeneous in terms of ion concentration. This variance also causes a force in water particles as they attract by the molecular laws of attractions. The last factor affecting the development of pore water pressure is the absorption pressure of water and surrounding soil particles.

At any point above the water table, in the vadose zone, the effective stress is approximately equal to the total stress, as proven by Terzaghi’s principle. Realistically, the effective stress is greater than the total stress, as the pore water pressure in these partially saturated soils is actually negative. This is primarily due to the surface tension of pore water in voids throughout the vadose zone causing a suction effect on surrounding particles. This capillary action is the “upward movement of water through the vadose zone” (Coduto, 266). Capillary effects in soil are more complex than in free water due to the randomly connected void space and particle interference through which to flow; regardless, the height of this zone of capillary rise, where negative pore water pressure is generally peaks, can be closely approximated by a simple equation. The height of capillary rise is inversely proportional to the diameter of void space in contact with water. Therefore, the smaller the void space, the higher water will rise due to tension forces. Sandy soils consist of more coarse material with more room for voids, and therefore tends to have a much shallower capillary zone than do more cohesive soils, such as clays and silts.

Input regarding the Infinity Tower

The Infinity Tower is a skyscraper set to be finished by 2013. It’s said to contain 79 floors in total. It is the first building in Dubai to offer it’s residents a full 360 degree view of the illustrious city, sea, and marina. When finished it will be the tallest twisting building in the world. As of July 30th 2012, the Infinity Tower reaches it’s 90% completion milestone mark. 73 floors have been fully built and the tower is estimated to stand at a height of 330 meters. The group designing this giant skyscraper is the Company Cayan, becoming one of the biggest real estate developers in the world. Cayan, however, hired the SOM (Skidmore Owings & Merrill) architectural group, the same group who built the Burj Dubai, in Dubai. They were also the same architectural group who helped build the Trump Tower in Chicago, Illinois. The floors of this monstrous skyscraper include residential living condos, spas, among a few other technical things such as a mechanical floor for all these mechanic in the building. The Infinity Tower will have house financing options available for those residents who may want to lease out their weekend or holiday condo. Infinity will also develop a contract with Palma for real estate market options. Those residents who look to make Infinity Tower a permanent home could do so by contacting Palma Real Estate directly. Special designs by SOM architectural group keep the building looking as modern as ever. The rooms won’t be affected by direct sunlight due to titanium metal panels on cast-in-place concrete columns aided with repetitive staggered screen panels to stop penetrating sunlight from disturbing the residents of the unit. As for convenience, the Infinity Tower spared no expense at making sure their residents are taken care of. With premium wooden floors, marble counter-tops, and leading name brand kitchen fixtures, Infinity Tower is one of the most luxurious condominiums in the world. Infinity also includes a 5-story parking garage behind the giant skyscraper, complete with 24-hour security surveillance. Equipped on the seventh floor are several pools, with floors just above the seventh floor containing conference rooms, cigar lounges, nursery’s, tennis courts, and fully equipped outdoor park

Several modes of failure for earth slopes include falls, topples, slides, and flows. In slopes with coarse grained soil or rocks, falls typically occur as the rapid descent of rocks and other loose slope material. A slope topples when a large column of soil tilts over its vertical axis at failure. Typical slope stability analysis considers sliding failures, categorized mainly as rotational slides or translational slides. As implied by the name, rotational slides fail along a generally curved surface, while translational slides fail along a more planar surface. A slope failing as a flow would resemble a fluid flowing downhill. Analysis: Geotechnical engineers consider two types of slopes when analyzing stability, finite and infinite slopes. Most slopes are analyzed in the 20th and 21st century using principles pertaining to the limit equilibrium concept. This method analyzes a finite or infinite slope as if it were about to fail along its sliding failure surface. Equilibrium stresses are calculated along the failure plane, and compared to the soils shear strength as determined by Terzaghi’s shear strength equation. Stability is ultimately decided by a factor of safety equal to the ratio of shear strength to the equilibrium stresses along the failure surface. A factor of safety greater than one generally implies a stable slope, failure of which should not occur assuming the slope is undisturbed. A factor of safety of 1.5 is acceptably safe in practice.

The analysis of an infinite slope is made possible by several engineering assumptions: The failure surface is planar and infinitely long, it is parallel to the above ground slope, and the soil composing the medium in question is homogenous and isotropic, meaning the same throughout. The assumption of an isotropic soil medium includes that the groundwater table, if present, is parallel to the failure surface, and thus the ground surface above. Swedish Slip Circle Method of Analysis The Swedish Slip Circle method is used in slope analysis under the assumption that the friction angle of the soil is equal to zero. This simplifies the factor of safety calculation in the way it affects the soil’s shear strength parameter. Terzaghi concludes that shear strength is equal to the soil cohesion value added to the product of the effective stress and the tangent of the soils friction angle. When friction angle is considered to be zero, the effective stress term goes to zero, thus equating the shear strength to the cohesion parameter of the given soil. The Swedish slip circle method assumes literally a circular failure plane, and analyzes stress and strength parameters using circular geometry and statics. The moment caused by the internal driving forces of a slope is compared to the moment cause by forces resisting slope failure. If resisting forces are greater than driving forces, the slope is assumed stable. Ordinary Method of Slices The method of slices is another analysis method for determination of slope stability. The Swedish slip circle method only accounts for soil with a friction angle equal to zero; therefore, the method of slices is needed for soils having a friction angle greater than zero. The ordinary method of slices, commonly referred to as OMS, neglects the equal and opposite forces on any given soil slice. This allows for a simple static equilibrium calculation, considering only soil weight, along with shear and normal stresses along the failure plane. Modified Bishop’s Method of Analysis The Modified Bishop’s method for analyzing slope stability is slightly different than the ordinary method of slices in its assumptions regarding side forces on each slice considered. Instead of assuming equal and opposite side forces, the Modified Bishop’s Method considers these forces equal to zero. Such an assumption improves accuracy in factor of safety calculations. Spencer’s Method Spencer’s Method of analysis requires a computer program capable of cyclic algorithms, but makes slope stability analysis easier. It is not as accurate as the Modified Bishop’s method, but is acceptably accurate in engineering practices.

Deep Foundations

There are three ways to place piles for a deep foundation. They can be driven, drilled, or installed by use of an auger. Driven piles are extended to their necessary depths with the application of external energy in the same way a nail is hammered. There are four typical hammers used to drive such piles: drop hammers, diesel hammers, hydraulic hammers, and air hammers. Drop hammers simply drop a heavy weight onto the pile to drive it, while diesel hammers use a single cylinder diesel engine to force piles through the Earth. Similarly, hydraulic and air hammers supply energy to piles through hydraulic and air forces, as air and water are both incompressible fluids. Energy imparted from a hammer head varies with type of hammer chosen, and can be as high as a million foot pounds for large scale diesel hammers, a very common hammer head used in practice. Piles are made of a variety of material including steel, timber, and concrete. Drilled piles are created by first drilling a hole to the appropriate depth, and filling it with concrete. Drilled piles can typically carry more load than drilled piles, simply due to a larger diameter pile. The auger method of pile installation is similar to drilled pile installation, but concrete is pumped into the hole as the auger is being removed.

Soil compaction is the removal of air, while consolidation is the removal of water from a soil medium.