Why dare not calculate the pressure of pile foundation
Publish: 2021-05-01 02:06:55
1. The actual length of the pile body is the effective length of the vertical bearing capacity of the foundation pile. The parameters of ultimate side resistance and ultimate end resistance used in calculating the bearing capacity of single pile by empirical parameter method are obtained from the statistics without considering the self weight of pile body, that is, the influence of self weight of pile body has been included. When the ultimate bearing capacity of single pile is determined by single pile static load test method, the dead weight of pile body is also not taken as the load. Therefore, no matter what method is used to determine the ultimate bearing capacity of single pile, the dead weight of pile body should not be used to calculate the load. But for uplift pile, because the self weight of pile is a part of bearing capacity, its vertical uplift bearing capacity should be included in the self weight of pile
for pile foundations such as bridges and offshore platforms, most of them belong to high cap pile foundations, and the length of the pile body exposed to the ground varies greatly, so the self weight of the pile body should be calculated when determining its bearing capacity.
for pile foundations such as bridges and offshore platforms, most of them belong to high cap pile foundations, and the length of the pile body exposed to the ground varies greatly, so the self weight of the pile body should be calculated when determining its bearing capacity.
2. On the one hand, there are significant differences in concept, property, numerical value and effect between the pile pressing force and ultimate bearing capacity of jacked pile. The pile driving force is the static pressure exerted by the pile to penetrate into the soil ring the pile driving process, which mainly overcomes the pile driving resistance composed of pile end resistance and pile peripheral friction when the pile is punching and shearing the soil downward.
3. There are many factors that affect the horizontal bearing capacity of single pile, mainly including the section stiffness, material strength, soil conditions on the side of the pile, the depth of the pile into the soil and the constraint on the top of the pile. Pile foundation generally bears vertical load, horizontal load and moment. Therefore, in addition to the vertical bearing capacity, the horizontal load bearing capacity must be considered in the design< (1) the larger the diameter of the pile, the higher the material strength of the pile (such as high-strength concrete or steel), and the higher the bending rigidity of the pile, the stronger its ability to resist horizontal load. For the pile with poor bending resistance, its horizontal bearing capacity is controlled by the strength of the pile body. For example, for the cast-in-place pile with low reinforcement ratio, the pile body usually cracks first and then breaks; For the piles with good flexural performance, such as precast reinforced concrete piles and steel piles, although the pile body is not broken under the horizontal load, when the soil beside the pile rises significantly or the horizontal displacement of the pile top greatly exceeds the allowable value of the superstructure, the pile should also be considered to have reached the limit state of the horizontal bearing capacity
(2) the better the soil condition on the pile side, the greater the horizontal resistance or the horizontal resistance coefficient on the foundation, the higher the horizontal bearing capacity of the pile, especially the bearing capacity of the topsoil on the pile side (within the range of 3-4 times of the pile diameter) greatly affects the horizontal bearing capacity of the pile. Therefore, when the topsoil is poor, it is generally necessary to adopt the scheme of improving and strengthening the topsoil such as backfilling gravel Panshi, which can greatly improve the horizontal bearing capacity of the pile 3 The horizontal resistance coefficient decreases exponentially with the increase of horizontal displacement of pile. Therefore, the better the constraint on the horizontal displacement of the pile top, the greater the horizontal resistance of the soil beside the pile. The actual working state of the connection between the pile top and the pile cap is between the rigid joint and the hinged joint. This is because the length of the pile top embedded in the pile cap is short (5 ~ 10cm), the concrete of the pile cap is poured twice, and the main reinforcement of the pile top is anchored into the pile cap for 30dg. Under the action of small horizontal force, the concrete around the pile top appears plastic deformation, forming the incomplete embedded state of transferring shear force and partial bending moment, It can not only rece the displacement of the pile top (relative to the free condition of the pile top), but also rece the restraint bending moment of the pile top (relative to the fully embedded condition), and redistribute the bending moment of the pile
(4) with the increase of the depth of the pile, the soil on the side of the pile will get enough embedment to minimize the ground displacement. When the depth of the pile into the soil is small, the embedment effect of the soil on the side of the pile is insufficient, the ground displacement is likely to be too large to be allowed by the upper structure, and at the same time, there is a considerable moment and displacement at the bottom of the pile, which requires the soil at the bottom of the pile to have sufficient embedment capacity. However, when the penetration depth of the pile reaches a certain value (the depth of the unbounded steel is 4.0/a), increasing the penetration depth of the pile will not affect the horizontal bearing capacity of the pile. Therefore, it is advisable to increase the depth of the pile into the soil to improve the horizontal bearing capacity of the pile. Due to the interaction between piles, or the action of dynamic load and cyclic load, the horizontal resistance coefficient of the foundation will also be reced, and the horizontal bearing capacity of the pile will be reced. In addition, the horizontal bearing capacity of piles can be greatly improved by setting tie beams (or ground beams), using caps with greater stiffness, setting inclined piles and ensuring the stiffness of pile joints.
(2) the better the soil condition on the pile side, the greater the horizontal resistance or the horizontal resistance coefficient on the foundation, the higher the horizontal bearing capacity of the pile, especially the bearing capacity of the topsoil on the pile side (within the range of 3-4 times of the pile diameter) greatly affects the horizontal bearing capacity of the pile. Therefore, when the topsoil is poor, it is generally necessary to adopt the scheme of improving and strengthening the topsoil such as backfilling gravel Panshi, which can greatly improve the horizontal bearing capacity of the pile 3 The horizontal resistance coefficient decreases exponentially with the increase of horizontal displacement of pile. Therefore, the better the constraint on the horizontal displacement of the pile top, the greater the horizontal resistance of the soil beside the pile. The actual working state of the connection between the pile top and the pile cap is between the rigid joint and the hinged joint. This is because the length of the pile top embedded in the pile cap is short (5 ~ 10cm), the concrete of the pile cap is poured twice, and the main reinforcement of the pile top is anchored into the pile cap for 30dg. Under the action of small horizontal force, the concrete around the pile top appears plastic deformation, forming the incomplete embedded state of transferring shear force and partial bending moment, It can not only rece the displacement of the pile top (relative to the free condition of the pile top), but also rece the restraint bending moment of the pile top (relative to the fully embedded condition), and redistribute the bending moment of the pile
(4) with the increase of the depth of the pile, the soil on the side of the pile will get enough embedment to minimize the ground displacement. When the depth of the pile into the soil is small, the embedment effect of the soil on the side of the pile is insufficient, the ground displacement is likely to be too large to be allowed by the upper structure, and at the same time, there is a considerable moment and displacement at the bottom of the pile, which requires the soil at the bottom of the pile to have sufficient embedment capacity. However, when the penetration depth of the pile reaches a certain value (the depth of the unbounded steel is 4.0/a), increasing the penetration depth of the pile will not affect the horizontal bearing capacity of the pile. Therefore, it is advisable to increase the depth of the pile into the soil to improve the horizontal bearing capacity of the pile. Due to the interaction between piles, or the action of dynamic load and cyclic load, the horizontal resistance coefficient of the foundation will also be reced, and the horizontal bearing capacity of the pile will be reced. In addition, the horizontal bearing capacity of piles can be greatly improved by setting tie beams (or ground beams), using caps with greater stiffness, setting inclined piles and ensuring the stiffness of pile joints.
4.
1、 The effect is different
1. Pile pressing: the soil is compacted to reinforce the foundation
Pile foundation detection: a method used to detect the vertical compressive bearing capacity of foundation piles 2. Different construction methods 1. Pile pressing: precast reinforced concrete pile and prestressed concrete pile. The precast pile is driven (pressed) into the soil by the impact energy of the pile hammer. The construction methods of sinking pile mainly include: hammer driving, vibration driving, water jetting, static pressing and drilling embedded pile Pile foundation detection: the main methods of pile foundation detection include static load test, core drilling method, low strain method, high strain method, acoustic transmission method, etc Pile pressing: as an important temporary structure of driven pile construction, driven pile guiding device should first ensure that the construction accuracy and efficiency of driven pile meet the requirements of design and construction, and also have the characteristics of simple structure, convenient disassembly and assembly, safe and reliable, economical and applicable. There is no clear specification for its structural design, and there are few systematic research results on its structural form2. Pile foundation detection: in pile foundation detection, each detection means needs to be used together. Only by making use of their own characteristics and advantages and flexibly using various methods according to the actual situation, can we make a comprehensive and accurate evaluation of pile foundation
5. 2 times only meet the bearing capacity calculated according to the design report. Due to the inertia of the design, the bearing capacity of the pile can be improved by providing the value conservatively and testing the pile truthfully, so as to shorten the pile length or rece the number of piles and save some money for the boss of Party a. That would be great. Moreover, 106 code also requires the actual limit value of the test pile.
6. The design pile length is the length from the top to the bottom of the pile as shown in the drawing. Because the length is still in design, or in theory, it has not been verified in practice. It is the design pile length. The effective pile length is the length from the bottom of the pile to the top of the pile when the pile pressing force in the drawing design is reached. For example, if the design is 20 meters, the actual 18 meters will meet the requirements. Then the design pile length is 20 meters, and the effective pile length is 18 meters. No matter how you match the pile, if the pile is more than 18 meters, the effective pile length is only 18 meters. The length of pile delivery refers to the distance from the natural horizon to the pile top elevation. It is to send the pile down from the natural horizon. Generally, the hammer is not more than 6 meters, and the static press is not more than 8 meters. Now you should know whether the truncated pile length should be calculated into the actual pile length?
7. Jacked pile is a kind of soil compaction pile. When the soil around the pile is squeezed out, a large local compressive stress will be proced, which seriously affects the process and quality of the subsequent pressed pile (the unilateral compressive stress will also force the subsequent pressed pile to deviate). Under normal conditions, it should wait until the local compressive stress of the hard foundation soil disappears naturally, and the pile should not be pressed continuously.
8. The load and bearing capacity of jacked pile are different
A: the load and bearing capacity of jacked pile are different. Answer questions first and discuss later
I'm also thinking about your question:
1. For example, the pressure gauge on the static pressure pile machine calculates 100kN. After the rest period, the friction increases as the soil shrinks. In principle, the bearing capacity test should exceed 100kN, so I answer you: "the load and bearing capacity of jacked pile are different."
2. Can static pressure pile not be tested for bearing capacity? Because it is 1000KN calculated by the pressure gauge on the jacked pile machine, if the design characteristic value is 500kN, the bearing capacity test must be greater than 1000KN. I think I pressed this pile with 1000KN, its characteristic value is 500kN, and the bearing capacity test must be greater than 1000KN. I'm thinking that the bearing capacity test of jacked pile can be omitted
3. I started to make a comparison. I asked them to hand over the inspection lot and test report of pile pressing to our department. I was disappointed after several years of work! If the static pressure converted from the inspection lot is large, the pile test report is small, and if the static pressure converted from the inspection lot is small, the pile test report is large. There is no correspondence. None of them is right
4. Analyze the reasons: I think the inspection lot data of pile pressing is false! It's a fake company. It's wholesale by the documenter. It has no credibility! Testing unit level, flat, I see although qualified, but not qualified in the actual nonsense! I think the state and government departments should pay attention to it.
A: the load and bearing capacity of jacked pile are different. Answer questions first and discuss later
I'm also thinking about your question:
1. For example, the pressure gauge on the static pressure pile machine calculates 100kN. After the rest period, the friction increases as the soil shrinks. In principle, the bearing capacity test should exceed 100kN, so I answer you: "the load and bearing capacity of jacked pile are different."
2. Can static pressure pile not be tested for bearing capacity? Because it is 1000KN calculated by the pressure gauge on the jacked pile machine, if the design characteristic value is 500kN, the bearing capacity test must be greater than 1000KN. I think I pressed this pile with 1000KN, its characteristic value is 500kN, and the bearing capacity test must be greater than 1000KN. I'm thinking that the bearing capacity test of jacked pile can be omitted
3. I started to make a comparison. I asked them to hand over the inspection lot and test report of pile pressing to our department. I was disappointed after several years of work! If the static pressure converted from the inspection lot is large, the pile test report is small, and if the static pressure converted from the inspection lot is small, the pile test report is large. There is no correspondence. None of them is right
4. Analyze the reasons: I think the inspection lot data of pile pressing is false! It's a fake company. It's wholesale by the documenter. It has no credibility! Testing unit level, flat, I see although qualified, but not qualified in the actual nonsense! I think the state and government departments should pay attention to it.
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