WET Process BORED PILING METHOD
In wet process bored piling, bentonite or other sort of suitable drilling slurry is used as drilling fluid to help the borehole in the course of building. A steel temporary casing is generally used to case the leading weak soil put through heavy building loads. Drilling and reinforcement cage installation and concrete putting are successively executed under drilling slurry. The concret is poured with tremie pipes, displacing the slurry well above the cutoff level. The temporary casing is then extracted right away immediately after concreting.
CHARACTERISTICS OF CONCRETE AND CONCRETE MIX
Concrete mix for bored piles is developed according to concrete pouring process and mechanical properties required. Concrete for wet process piles needs to become specially mixed having cohesiveness with good workability (high slump/excellent fluidity) which can be not prone to segregation and retain it workability as far as you possibly can throughout the tremie placing operation for that full pour. Addition to those characteristics, compaction below selfweight, potential to deal with harsh atmosphere, potential to deal with leaching, and appropriate strength are crucial.
Workability
Excellent fluidity is crucial how the concrete has got the capacity to circulate readily via the tremie pipe, circulation laterally by means of a reinforcement cage as well as a high lateral pressure up against the sides of borehole. High workability is very best achieved with rounded all-natural aggregates and all-natural sand inside the mix.
Self Compaction
Compaction under self-weight is crucial as vibration of concrete is impractical, except close to the surface. How much compaction achieved is dependent upon the density ratio (the number of density actually achieved to the density from the identical concrete completely compacted). The advised compacting aspect for that necessary workability of tremie concrete is 0.95 to 0.96 (Xanthakos 1994). Fresh concrete is usually placed by way of tremie pipes and displaces the slurry by gravity action only. In certain instances, insufficient self-compaction inside the concrete will lead to defects, like reversed "hanging up", and "whirls" within the completed pile. If the initial shear from the concrete is extremely high, the flow is likely to restrain, leading to bentonite kept in locations not reached through the concrete (Xanthakos 1994).
Resistance to Segregation
The concrete mix ought to be cohesive and resistant against segregation, as improperly developed mixes will segregate for the duration of placement, resulting in inferior concrete containing honeycombs and permeable zones within the pile shaft. Concrete that bleeds or disintegrates under the pressures of their own weight can also block the tremie pipe or accept bentonite.
Controlled Setting
The concrete should retain it fluidity thorough the depth of borehole in the course of full placement with the concrete in the borehole and attain an appropriate strength inside a reasonable time after placement. Retarders are used to prevent premature stiffening of some cements in order to delay stiffening below tough putting circumstances. The setting time should be checked against the time necessary to full the position. The retarders ought to be used under competent technical advice and after adequate testing.
Resistance to Aggressive conditions
The concrete must have high density and low permeability to face up to the attainable (chemical and physical) attack of your aggressive sub-subsurface condition. In some instances there is certainly an underground flow of water that could lead to a weakening with the concrete right after it's placed, along with a properly designed mix really should be resistant against such flow. Nevertheless, if the rate of ground water flow is substantial, a lasting casing will be essential.
Good Mechanical Performance
The mechanical properties of hardened concrete may be happy generally in most situations. Even so, suitable tensile strength for the concrete with out reinforcement in piles and degree of bending and axial tension should be deemed in some situations.
Reese and O'Neil (1988) emphasis how the design with the concrete mix should be offered appropriate focus as well as the style in the mix depends strongly around the certain job, along with the cement will be selected to be constant with all the style requirement. They observed that bleeding isn't a problem for concrete mixes that are effectively developed. The trial mix approach is generally used inside the laboratory. It truly is necessary to follow-up to see the materials and proportions used through the batch plant are those of which might be recommended. Inspection in the batch plant ought to consist of checking the character, quantity and temperature of the components of the mix, the aggregates, cement, water, admixtures and from the completed mix for conformance using the specifications. For testing in the job web site, the business of the job has to be in a way that time required to execute tests in the job web site is kept to a minimum. Excessive job-site testing can lead to dangerous effects. No delay in pouring really should take place on account of field test.
Adding water for the concrete with very low slump on site to increase the workability can have detrimental effect of decreasing the strength, compactability and impermeability of the concrete. The results of adding water could be a substantial change in the characteristics of mix and also the possibility of segregation as the pour is produced. Segregation of concrete during pouring may also lead to boost in permeability of concrete, especially in the leading area of piles on account of upward migration water within the concrete mix. Adding of water to the concrete on website need to 't be allowed unless specified.
WET Process BORED PILING METHOD
In wet process bored piling, bentonite or other sort of suitable drilling slurry is used as drilling fluid to help the borehole in the course of building. A steel temporary casing is generally used to case the leading weak soil put through heavy building loads. Drilling and reinforcement cage installation and concrete putting are successively executed under drilling slurry. The concret is poured with tremie pipes, displacing the slurry well above the cutoff level. The temporary casing is then extracted right away immediately after concreting.
CHARACTERISTICS OF CONCRETE AND CONCRETE MIX
Concrete mix for bored piles is developed according to concrete pouring process and mechanical properties required. Concrete for wet process piles needs to become specially mixed having cohesiveness with good workability (high slump/excellent fluidity) which can be not prone to segregation and retain it workability as far as you possibly can throughout the tremie placing operation for that full pour. Addition to those characteristics, compaction below selfweight, potential to deal with harsh atmosphere, potential to deal with leaching, and appropriate strength are crucial.
Workability
Excellent fluidity is crucial how the concrete has got the capacity to circulate readily via the tremie pipe, circulation laterally by means of a reinforcement cage as well as a high lateral pressure up against the sides of borehole. High workability is very best achieved with rounded all-natural aggregates and all-natural sand inside the mix.
Self Compaction
Compaction under self-weight is crucial as vibration of concrete is impractical, except close to the surface. How much compaction achieved is dependent upon the density ratio (the number of density actually achieved to the density from the identical concrete completely compacted). The advised compacting aspect for that necessary workability of tremie concrete is 0.95 to 0.96 (Xanthakos 1994). Fresh concrete is usually placed by way of tremie pipes and displaces the slurry by gravity action only. In certain instances, insufficient self-compaction inside the concrete will lead to defects, like reversed "hanging up", and "whirls" within the completed pile. If the initial shear from the concrete is extremely high, the flow is likely to restrain, leading to bentonite kept in locations not reached through the concrete (Xanthakos 1994).
Resistance to Segregation
The concrete mix ought to be cohesive and resistant against segregation, as improperly developed mixes will segregate for the duration of placement, resulting in inferior concrete containing honeycombs and permeable zones within the pile shaft. Concrete that bleeds or disintegrates under the pressures of their own weight can also block the tremie pipe or accept bentonite.
Controlled Setting
The concrete should retain it fluidity thorough the depth of borehole in the course of full placement with the concrete in the borehole and attain an appropriate strength inside a reasonable time after placement. Retarders are used to prevent premature stiffening of some cements in order to delay stiffening below tough putting circumstances. The setting time should be checked against the time necessary to full the position. The retarders ought to be used under competent technical advice and after adequate testing.
Resistance to Aggressive conditions
The concrete must have high density and low permeability to face up to the attainable (chemical and physical) attack of your aggressive sub-subsurface condition. In some instances there is certainly an underground flow of water that could lead to a weakening with the concrete right after it's placed, along with a properly designed mix really should be resistant against such flow. Nevertheless, if the rate of ground water flow is substantial, a lasting casing will be essential.
Good Mechanical Performance
The mechanical properties of hardened concrete may be happy generally in most situations. Even so, suitable tensile strength for the concrete with out reinforcement in piles and degree of bending and axial tension should be deemed in some situations.
Reese and O'Neil (1988) emphasis how the design with the concrete mix should be offered appropriate focus as well as the style in the mix depends strongly around the certain job, along with the cement will be selected to be constant with all the style requirement. They observed that bleeding isn't a problem for concrete mixes that are effectively developed. The trial mix approach is generally used inside the laboratory. It truly is necessary to follow-up to see the materials and proportions used through the batch plant are those of which might be recommended. Inspection in the batch plant ought to consist of checking the character, quantity and temperature of the components of the mix, the aggregates, cement, water, admixtures and from the completed mix for conformance using the specifications. For testing in the job web site, the business of the job has to be in a way that time required to execute tests in the job web site is kept to a minimum. Excessive job-site testing can lead to dangerous effects. No delay in pouring really should take place on account of field test.
Adding water for the concrete with very low slump on site to increase the workability can have detrimental effect of decreasing the strength, compactability and impermeability of the concrete. The results of adding water could be a substantial change in the characteristics of mix and also the possibility of segregation as the pour is produced. Segregation of concrete during pouring may also lead to boost in permeability of concrete, especially in the leading area of piles on account of upward migration water within the concrete mix. Adding of water to the concrete on website need to 't be allowed unless specified.
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