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Design and construction of pile static

Author: ChenLongFei From: www.yourpaper.net Posted: 2010-07-08 04:03:24 Read:
Abstract: in this paper, the advantages of static piling, design and construction of static pressure pile are discussed, and puts forward some problems existed in the static pressure pile.
Keywords: static pile; blow count of standard penetration test; pile spacing; the final pressure
In recent years, with the popularization and use of precast pile, a new static pressure precast pile (referred to as the static pressure pile) with no noise, no vibration, high bearing capacity of single pile and easy to control, simple construction, high efficiency has been widely applied.In the basis of design or construction specification, static pressure pile into piles, however, provisions on the static pressure pile technology mostly programmatic, no more in-depth discussion, operability is poor, especially for building foundation construction and acceptance standard of Guangdong Province "(DBJ15-201-91).", and no mention of static pile construction technology of this standard, apparently has lagged far behind.In the engineering practice in recent years, the static pressure pile is a new pile type, both in design and construction there are many problems worth discussion.
1, the engineering geological conditions of static pressure pile
Precast pile is a pile of a pile, geological conditions of great influence, especially the ability of static pressure pile penetration of each layer of the soil.In the engineering geological investigation report, usually provides each layer soil N63.5 blow count, the blow count of standard penetration test, static pressure pile penetration ability of each soil layer can control N63.5 numerical analysis and the maximum static pressure pile machine to do the general judgment.The massive project practice proof, the static pressure pile is especially suitable for general clay, silt, sand, silt or silty soil, but for the thin interbed of underground soft layer is thick or hard (such as compact sand, gravel sand gravel layer of weathered, etc.) do not apply to the geological.In the project, often encounter the static pressure pile can penetrate sand problem, the master to the rules are as follows: the static pressure pile can be through the dense sand in the following, for dense sand, when the small thickness (usually less than 1 meters), can also through.In addition, the greatest pressure pile construction machinery on the static pressure pile through the sand layer also has the very big relations, static pressure pile is less than the maximum of 2400KN pile pressing machine, its capabilities through sand layer is relatively limited, the thicker sand, now more commonly used is the guide hole penetration method, through the guide hole then, the static pressure pile the pressure of pile, the pile pressing through the 5-6M in the dense to dense sand, such as our city has built Jin Li Garden, a layer of 5-6M thick sand under 5-6M deep soil layer, is to use the maximum static pressure pile machine for 3200KN of the prefabricated pressure wear this sand, and my city is now the new library project, is also a guide hole penetration method, using static pressure pile machine for 4000KM construction, compact sand through 7M.Therefore, the use of prefabricated pile must take full account of the engineering geological conditions of the site and pile machine models.
2, the pile into the depth control
bearing stratum
As friction pile and end-bearing pile precast pile, pile into the support layer depth shall meet the relevant requirements, to ensure the pile design capacity.
Over the years both at home and abroad on the carrying capacity of pile a lot of research, and also raised a lot of failure mode.It is worth mentioning that, when it comes to the failure mode of pile Maillet Hof proposed: Pile in the pile bottom soil especially above 6-10D and pile bottom 2-4D (D is the diameter of the pile) range, when the pile failure, shear surface of soil through this part of the soil.So the nature of this part of soil are very important to the bearing capacity of pile, a lot of practice, this section on the pile bottom soil layer to the pile embedded in actual plays a role, a great impact on the side friction of pile, and the pile bottom soil will directly affect the pile end bearing capacity, so the design selection of bearing layer when, should pay attention to consider bearing layer are transition layer is dense or hard.If the precast pile is directly to the hard soil layer through the soft soil, because of the soft soil of pile side friction resistance (i.e. embedded force) is very small, so we must deepen pile into the support layer depth.To ensure the bearing capacity of the pile can meet the design requirements.
3, the pile spacing to determine the
Precast pile is the pile, either driven or pressed, it will need the original soil out of the way, in order to pile into, so, the original soil except the part is compressed, a considerable part of (especially water saturated soil) cannot be compressed, this part will be to geological conditions of weak direction of extrusion and even cause to rise, in this case, the pile may first press will be pressed piles the impact has been lifted, resulting in the formation of "end-suspended pile".So from the standard design prescribed number of pile soil compaction pile, pile distance minimum Center shall be not less than 3.5d.More should be 4.0d and through saturated soft soil.Therefore the design chosen pile type, pile length should be determined first, and then the superstructure load passed down with pile, the pile of cloth to avoid too dense brings difficulties for the construction of pile foundation, and even lead to quality problems.
4, the final pressure of static pressure pile (Q) achieved
The final pressure of static pressure pile, stopping pressure standard is not only the static pressure pile construction, but also the resistance of pile end pressure.It is mainly composed of dynamic friction of pile end of the punching shear resistance and pile side soil composition, but not equal to the static pressure of the ultimate bearing capacity, according to the experience, it and the bearing capacity of static pressure pile (RK) is a proportional relation, as follows:
(1), for the friction pile, general with pile elevation control as the main standard, Q= (1-1.3) RK.
(2), for end bearing pile Q= (2.5-3) RK.
(3) Q= pile length less than 20M friction and end bearing (2-2.5) RK.By friction and low value, high value to end bearing.
(4) the pile length greater than 20M: Q= (1.5-2) RK.By friction and low value, high value to end bearing.At present, due to the national and local have not worked on the static pressure pile end pressure of the settlement control standard, different pile length, different pile and pile end soil conditions of static pressure pile control standards, so in determining the final pressure value, it is necessary to combine the construction experience, and not the final pressure value bigger is better.The high ratio of length to diameter of pile, if the final pressure value is too high, because the soil around the pile is not yet to consolidation, the lateral soil force is small, the pile top pressure is too large for the quality of pile body and pile joints are lose everything and gain nothing, there is no need to.The local approach is often invited survey, design, supervision, quality supervision departments, through field test piles to determine the specific final pressure standard and settlement control standard.
Pile splicing process of
5, the static pressure pile
Indicates that the technical code for building pile foundations: "connection method of pile welding method, flange connection and sulfur mortar anchor three".
Now, our country specific requirements and practices are not the same, such as the Shanghai either pile driving or static pressure pile, pile joints are used welding method.In some places, the vast majority of static pressure pile using sulfur mortar joints.But for the seismic fortification intensity is high, the pile length is relatively large, generally more than 2 joints, joint construction quality of sulfur mortar is reliable, there has been a lot of differences of opinion.From the construction site pile splicing technology, joint method, using sulfur mortar construction of fast, easy operation, but on the joint more long pile, from the point of view of seismic fortification, joint quality is an important part of.In view of this situation, unified regulation in our city by welding joint.

6, the construction quality problems of static pressure pile
Construction quality problems of static pressure pile, some in the construction process can be shown, some in the excavation of pile testing and platform to show.Exhibit in the construction process are: the pile (head) cracking or breaking, the deviation of pile, pile sinking depth is not enough.Completed later demonstrated mainly has: the pile top deviation exceeds the standard requirements, the defects of pile or joint loosening, static load or small strain test unqualified, these problems are caused in the construction process.Therefore the construction must be done the following several aspects:
(1) measurement line must be accurate, to ensure the pile position not offset.
(2) the weight number of pile machine should ensure enough, to ensure the pile end reaches the design requirements to meet the bearing layer.
(3) the strength of the pile should be checked before use, appearance found unqualified (bending, uneven, serious chipping, cracks) pile, resolutely not; the appearance quality of the qualified pile, still need to rebound checks.
(4) pile should ensure the verticality piles and pile joint welding quality, to ensure the full welding and 8 minutes of intermittent cooling before the beginning of piling operations, upper and lower pile must be the center, ensure that the pile not due to eccentric compression and bending problem of piles.
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