Soil mechanics Assignment

Soil mechanics Assignment Words: 2362

Steps for optimizing identification process Poor Human construction fills , specify placement conditions (water content ,density ,depth of layers etc) Select appropriate equipment roller, vibrato compaction, tamping. Method of compactor patterns of tamping Set up adequate control procedures. Types of compaction shallow surface compaction Deep surface compaction Shallow surface compaction Achieved by static pressure and or dynamic pressure caused by impact or vibration.

Rollers used Static Rollers Impact or vibratory Equipments Smooth steel rollers and pneumatic tired rollers Tamper, rammers and plate compacters Sheepfold rollers vibrating rollers Grid rollers Impact rollers Deep compaction Techniques: Identification of deep soil is achieved by the following techniques. Prepossession: Pre loaded by means of a surcharge on the surface in an array of boreholes, causing a ground to consolidate, Explosion: Explosives are detonated on the surface in an array of boreholes causing a loose soil structure to collapse.

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Heavy tamping: A large mass is dropped in to the ground surface, causing compaction and possibly long term consolidation. Vibration: Identification is achieved by a vibratory probe or piles. Compaction grouting 21. 1 Vibrato-Ground Improvement The use of vibratory techniques to improve soils at depth has been practiced for more than 70 years. Originally introduced in Europe, these techniques are nowadays used worldwide for a range of applications.

Improvement is accomplished by means of purpose-built vibrators that generate radial vibrations, forcing the soil particles into a tighter configuration or directly reinforcing weak soils, thus creating a soil matrix with greater density and increased mechanical properties (shear strength, stiffness, and bearing capacity) Vibrato-Compaction and Vibrato-Replacement (stone column) construction are the primary methods of ground improvement. Selection of the appropriate technique is a function to the subsurface conditions and the objective of the improvement program.

Vibrato-Compaction is effective in improving the relative density to natural granular soils or Fill materials with suitable gradations and limited fines contents. This technique can permit spread footing or other shallow foundation construction, reduce settlement under individual or large real loads (tanks and other storage facilities), and mitigate liquefaction potential. Vibrato- Replacement (Stone Column) installation increases the range of treatable soils to include cohesive, mixed and layered soils that typically cannot be improved by vibration alone.

Stone columns can be used to support foundation systems for a wide range of structures from multi-story buildings to bridges to large storage tanks. The stone column technique is also frequently used to treat foundation soils and permit rapid construction of large MS retaining walls and highway embankment fills for transportation infrastructure projects, to stabilize peak soils in waterfront areas to permit new marine construction, and to improve the debility of existing slopes under static and dynamic loads.

In seismically active areas, stone columns installed to mitigate liquefaction potential are beneficial in increasing in situ density and shear strength, aiding the dissipation of excess pore water pressure, and reducing predicted post-liquefaction settlements and lateral spreading (Kong, et al 2001). 2. 1. 1. 1 Vibrato-Compaction Vibrato compaction is a ground improvement technique that identifies clean, connectionless granular soils by means of a downhill vibrator (Feeling & Oklahoma, 2000).

The vibrator is typically suspended from a crane and lowered vertically not the soil under its own weight. Penetration is usually aided by water jets integrated into the vibrator assembly. After reaching the bottom of the treatment zone, the soils are identified in lifts as the probe is extracted. During vibrato compaction, clean sand backfill is typically added at the ground surface to compensate for the reduction in soil volume resulting from the identification process.

The vibratory energy reduces the inter-granular forces between the soil particles, allowing them to move into a denser configuration, typically achieving a relative density of 70 to 85 percent. The treated soils have increased density, ruction angle and stiffness. Compaction is achieved above and below the water table. The improved soil characteristics depend on the soil type and gradation, spacing of the penetration points and the time spent performing the compaction. Generally, the vibrato compaction penetration spacing is between 6 feet and 14 feet, With centers arranged On a triangular Or square pattern.

Compaction takes place without setting up internal stresses in the soil, thus ensuring permanent identification (Creatures & Leonie – 2008). The use Of clean sand backfill during vibrato compaction allows the original site elevation to be maintained. However, n sites where the planned final grade is below the existing grade, lowering Of the site elevation may be desirable. In these instances, the ground surface is allowed to subside during the compaction effort (Mosey & Kirsch, 2004).

Vibrato compaction permits the use of economical spread footings with design bearing pressures generally of 5 SF up to 10 SF. Settlement and seismic liquefaction potentials are reduced. The required treatment depth is typically in the range of 15 to 50 feet, but vibrato compaction has been performed to depths as great as 120 feet. Examples of previously performed applications include increasing rearing capacity, decreasing settlement and mitigating liquefaction for planned structures, embankments, railways and roadways.

Vibrato compaction rigs can be fully instrumented with an on-board computer to monitor parameters during vibrato compaction, Monitoring these parameters allows the operator to correct any deviations in real-time during the construction process to keep the vibrato compaction within project specifications. Data from the Data Acquisition (DADS) system such as amperage and lift rate are recorded and displayed in real-time alongside specified target values on an in-cab monitor (Burke, 2007).

During the Vibrato-Compaction process: ; Sand and gravel particles are rearranged into a more dense state (higher relative density DRY ) ; A significant increase is achieved in the horizontal to vertical effective stress ratio ; Soil hydraulic conductivity (permeability) is significantly reduced ; Angle Of internal friction is increased ; Settlement of the compacted soil mass (2 to 15%) is achieved ; Soil deformation modulo are increased The Vibrato-Compaction process results in: ; Increased bearing capacity, permitting shallow foundation construction ; Settlement reduction under static and dynamic loading Near-elimination of differential settlement for large foundations ; Liquefaction mitigation ; Prevention of lateral spreading ; Reduction in soil permeability 2. 1 . I . 2 Vibrato-Replacement (stone columns) This is a ground improvement technique to improve the load bearing capacity and reduce the settlement Of the soil (Miranda et al 2011). On many occasions, it is noted that the local soil is, by nature, unable to bear the proposed structure, so the use Of ground improvement techniques may be necessary. Use Of stone columns is one such technique. The stone column consists of crushed coarse aggregates of various sizes. The ratio in which the stones of different sizes will be mixed is decided by design criteria.

The aforementioned crushed aggregates in the definite proportion are to be placed into the soil at regular intervals throughout the area of the land where the soil bearing capacity is to be improved. This is done either by using the dry or the wet top feed vibrators which are forced into the ground, The aggregates are then allowed to take the place of the displaced soil which exerts a pressure on the surrounding soil, hence helping to improve the soil’s load-bearing capacity, The vibrating probe breaks own the pores of the surrounding soil, thereby identifying the soil. The crushed aggregates or the gravel that is poured in takes the place of the soil and keeps up the pressure on the soil that was created by the vibrating probe.

These columns are made across the area to be built on in a grid pattern at regular intervals, During the Vibrato-Replacement process: relative density DRY ) ; Mixed or fine-grained soils are radically displaced outwards and reinforced ; A significant increase is achieved in the horizontal to vertical effective stress ratio in the area surrounding each column ; Angle of internal friction is increased Limited settlement Of the compacted soil mass is achieved ; Soil deformation The Vibrato-Replacement process results in: ; Increased bearing capacity, permitting shallow foundation construction or reduction of foundation sizes ; Transfer of vertical loads to reinforced or more competent soils at depth ; Increased composite shear strength for improved stability ; Significant increases in effective lateral stresses ; Settlement reduction under static and dynamic loading ; prevention of lateral spreading (Kirsch & Bell, 2012) SELECTING THE MOST APPROPRIATE CONSTRUCTION METHOD The Top Feed Method should be used where: Water for flushing is available ; The working platform allows flushing avatar to flow towards settling ponds ; The soil type does not lead to problems handling the soil particles in the process water ; Space is available for a 5000 fat or suitably-sized sedimentation pond ; The installation crew has sufficient experience in the more demanding installation methodology The Bottom Feed Method should be used where: ; Water for flushing is not available ; Washout of soil to the surface must be prevented due to potential soil contamination and/or difficulties in removing the washout ; Space is a limiting factor Very controlled column diameters are required ; The soil type does not allow for water flushing (i. E. Peat, very soft soils) Advantages to the Bottom Feed Method ; Stone flow is mechanically controlled and automatically recorded ; Stone can be accurately delivered to precise depth levels ; Spoil return to the surface is minimal, resulting in lower stone consumption ; Mud handling is eliminated ; Surface loss of aggregate is reduced 2. 1. 13 VIBRATO CONCRETE COLUMNS Vibrato concrete columns is a ground improvement technique that transfers loads through weak strata to a firm underlying stratum, using high modulus concrete alumnus. A bottom-feed down-hole vibratory probe is advanced through the weak strata to the underlying firm Stratum. Granular bearing soils are identified by the vibrator.

Concrete is then pumped through the bottom feed termite tube. The vibrator is raised and lowered several times Within the bearing depth to construct an expanded base. The vibrator is then raised to the surface as concrete fills the void created by the vibrator during extraction. Typically, the vibrator also repatriates the top of the column to construct an enlarged head which is subsequently overlain by a groggier reinforced soil relieving platform. The technique has been used to increase allowable bearing pressure and decrease settlement for planned structures, embankments and tanks, and increase global stability for embankments (Generate, 2004).

VIBRATO Vibrato Piers is a ground improvement technique that constructs short, stiff aggregate piers to reinforce fine grained soils, The pier location is initially prevailed for soils in which the hole will remain open. In soils that cave or collapse, a bottom feed vibrator can be employed, The downhill vibrator is lowered vertically to the designed tip of the pier typically with a standard crane. Aggregate (new crushed stone or recycled concrete) is then introduced into the hole and is compacted in lifts by repeated penetrations with the vibrator. The vibratory energy from the vibrator identifies the aggregate and any surrounding granular soil. The high modulus pier reinforces the treatment zone.

The technique has been used to increase bearing capacity and decrease settlement for planned structures, embankments, tanks and towers (Reedy et al, 2008). 2. 1. 1. 4 DYNAMIC COMPACTION Dynamic compaction is a ground improvement technique that identifies soils and fills by using a drop weight. The drop weight, typically hardened steel plates, is lifted by a crane and repeatedly dropped on the ground surface. The drop locations are typically located on a grid pattern, the spacing of which is determined by the subsurface conditions and foundation loading and geometry. Treated granular soils and fills have increased density, friction angle and stiffness. The technique has been used to increase bearing capacity, and decrease settlement and liquefaction potential for planned structures.

In shallow karts geologies, it has been used to collapse voids prior to construction, thereby reducing sinkhole potential. Dynamic compaction has also been used to compact landfills prior to construction of a parking lots, roadways, and embankments (Federal Highway Administration,2004). 2. 1. 1. 5 Fibrillation The Fibrillation technique is used for compacting granular soil only. The vibration is a cylindrical tube containing water jets at top and bottom and equipped with a rotating eccentric weight, which develops a horizontal vibratory motion. The vibration is sunk into the soil using the lower jets and is then raised in successive small increments, during which the surrounding material is compacted by the vibration process.

The enlarged hole around the vibration is backfilled With suitable granular material. This method is very effective for increasing the density off sand deposit for depths up to 30 m. Probe spacing of compaction holes should be on a grid pattern Of about 2 m to produce relative densities greater than 70 percent over the entire area. If the sand is coarse. The spacing may be somewhat larger. In soft cohesive soil and organic soils the Fibrillation technique has been used with gravel as the backfill material. The resulting identified stone column effectively reinforces softer soils and acts as a rearing pile for foundations (Ian smith, 2013). 2. 1. INJECTION SYSTEM FOR EXPANSIVE SOIL Injection stabilization is a ground environment technique that reduces the heave of in situ expansive clays, using the pressure injection fluids. Purpose- built injection units drive injection pipes beneath existing structures or planned building pads. An aqueous solution of water, lime slurry, or potassium chloride is injected into the soil, The process results in reduced shrink/suavely potential, The technique has been used to treat below planned and existing railways, roadways and buildings (Robinson & Thatches, 2004). . 13 RIGID INCLUSIONS ( CONTROLLED STEEPNESS COLUMNS) Rigid inclusions is a ground improvement technique that transfers loads through weak strata to a firm underlying stratum using high modulus, controlled stiffness columns.

A bottom-feed mandrel with a top-mounted vibrator is advanced through the weak strata to the underlying firm stratum. Granular bearing soils are identified by displacement. Concrete is then pumped through the mandrel, which opens as it is raised. The mandrel may be raised and lowered several times within the bearing depth to construct an expanded base if required by the design. The mandrel is then extracted while a positive concrete head is maintained. The concrete fills the void created by the mandrel during extraction, and terminates in an upper strong stratum or is subsequently overlain by an engineered relieving platform, The improved performance results from the reinforcement to the compressible strata with the high modulus columns.

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