CN108625410B - Method for testing pile side frictional resistance - Google Patents
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Abstract
The invention discloses a method for testing pile side frictional resistance, which comprises the following steps: step one, manufacturing a load box; placing a load box; step three, pouring concrete; step four, pile top loading; step five, data acquisition; step six, calculating the side frictional resistance of the pile; step seven, measuring a single soil layer; step eight, calculating the side frictional resistance of the single soil layer; the invention has the beneficial effects that: compared with the traditional measuring method, the method has more obvious rationality and superiority. The method can really realize the simplification of the test method, the reduction of the test working strength, the expansion of the detection range and the improvement of the detection efficiency, the test result is more in line with the reality, and the accuracy and the objectivity of the test result can be better ensured.
Description
Technical Field
The invention relates to a method for testing frictional resistance, in particular to a method for testing pile side frictional resistance.
Background
At present, pile foundations are a foundation form which is widely applied. The piles and the soil are in contact at the side wall and the end part, and the complexity of stress of the piles and the soil is determined due to the variability of the soil layer and the interaction of the piles and the soil. The bearing capacity of the pile comprises two parts of side friction resistance and end bearing capacity, wherein the side friction resistance is a large variable quantity. In the current relevant specifications, according to the influence degree of main factors such as the characteristics of pile-soil materials, the characteristics of pile-soil interfaces, the pile construction process and the like on the pile side frictional resistance, after conclusion, the limit value has a relatively fixed value range under the condition that the soil layer and the pile type are fixed, indirect value taking can be carried out according to the total bearing capacity, but the value difference among different specifications is large. In the engineering practice, it is found that the side frictional resistance also changes greatly along with different specific engineering conditions such as end supporting conditions, pile stress direction, property close to soil layer, depth of soil layer and the like. The conditions of complex soil layers encountered in the pile foundation construction process are more and more, and the soil property categories listed in the specifications do not meet the requirements of actual engineering. Therefore, in order to ensure the engineering quality and reasonably evaluate the bearing capacity of the pile foundation, the key problem is how to directly and accurately determine the side frictional resistance of the pile.
At present, a direct test method for determining the side frictional resistance of a pile mainly comprises the steps of embedding steel bar meters in different soil layer sections, reading measured strain data, calculating through various complex stress-strain relationships and sizes of pile bodies to obtain the axial force of the pile bodies on the sections of the soil layers, wherein the difference value between the axial force and the stress-strain relationship is the side frictional resistance of the pile body of the soil layer, and the sum of the side frictional resistances of all the layers is the total side frictional resistance of the pile. The method firstly needs to consider the influence of different environments on the steel bars; secondly, the stress-strain relationship between the pile body concrete and the steel bar is very complex and difficult to describe accurately. This results in the method often using some empirical parameters in the calculation, which may reduce the accuracy and reliability. Meanwhile, the strain gauge has high requirements on the pasting process and position, the survival rate of the strain gauge is excessively depended on, different steel bars need to be calibrated in advance, the construction process is complex, and the cost is high.
Disclosure of Invention
The invention aims to provide a method for testing pile side frictional resistance, which aims to solve various problems in the existing method for testing pile side frictional resistance.
The invention provides a method for testing pile side frictional resistance, which comprises the following steps:
step one, manufacturing a load box:
manufacturing two circular discs with the diameter smaller than the diameter of the pile to be measured by using a steel plate, wherein the circular discs are respectively used as an upper bearing disc and a lower bearing disc, and then fixing a plurality of anchor cable meters on the lower bearing disc, wherein one anchor cable meter is positioned at the central position of the lower bearing disc, and the other anchor cable meters are uniformly distributed on a concentric circle close to the outer side of the lower bearing disc; a hanging ring is welded at the center of the upper bearing plate and used for hoisting; finally, the upper bearing disc and the lower bearing disc are connected through six tooth bars, each tooth bar is matched with a nut, and light protective covers are arranged at two ends of the upper bearing disc and the lower bearing disc so as to ensure that the anchor cable meter is not influenced by external conditions in the construction process;
step two, placing a load box:
after the pile hole is determined to be qualified, leveling the pile bottom by using concrete, placing the load box into the pile bottom by using a crane through a lifting ring after the concrete leveling layer is solidified, and checking and ensuring that the load box is in a horizontal position; after the load box is installed, placing the reinforcement cage into the pile body; binding the data wire of the anchor cable meter and the pile body steel bar together, and leading out from the pile top;
step three, pouring concrete:
after the first step and the second step are determined to be completed, pouring of pile body concrete is carried out;
step four, pile top loading:
after the concrete maintenance of the pile body reaches the related technical requirements, loading the pile top by adopting a slow-speed load maintaining method according to the standard, and determining a test method and termination conditions according to the existing standard;
step five, data acquisition:
respectively acquiring pile top load Q, displacement s and pressure Q borne by each anchor cable meter in the loading processiQ has the unit kN, QiThe unit of (a) is kN, i is 1-n, and n is the number counted by the actual anchor cable;
step six, calculating the side frictional resistance of the pile: the pile side frictional resistance Q is calculated according to the following formulasu：
Step seven, single soil layer measurement:
when the friction force Q is needed to the side of a pile in a single soil layerSu sheetDuring testing, the pile can be stopped when being poured to the lower interface of the soil layer, the pile is used as a leveling layer in the second step, and then the second step and the third step are repeated; stopping pouring when the concrete in the third step is poured to the upper interface of the soil layer, and repeating the second step, the third step, the fourth step and the fifth step after leveling;
step eight, calculating the side frictional resistance of the single soil layer:
and seventhly, the difference value between the sum of the readings of the load boxes in the lower interface and the sum of the readings of the load boxes in the upper interface is the side frictional resistance of the soil layer, and the calculation formula is as follows:
In the method, the number of the detected piles can be determined according to actual requirements. The pile body concrete pouring, pile top loading and data acquisition in the method are all the prior art provided by the existing relevant specifications and methods, so the specific steps are not repeated.
The invention has the beneficial effects that:
1. the invention provides a method for testing the side frictional resistance of a pile, which is to install a load box at the bottom of the pile and directly measure the resistance Q of the pile end by using an anchor cable meter in the load boxbuAnd the dead weight G of the pile body, and then calculating the difference between the pile top load and the reading of the load box, so as to directly obtain the side frictional resistance of the pile body. The steel bars, the concrete and the like do not need to be calibrated before testing, and complex detection processes such as strain gauge sticking and the like are avoided. The method has more remarkable rationality and superiority compared with the traditional measuring method in terms of definition, principle, test precision, reliability, operability and the like.
2. The method provided by the invention is suitable for various complex strata and soil properties, and can avoid the problem that the value range of the pile side frictional resistance cannot be determined due to the incomplete soil properties contained in the specification. And the influence of different specific engineering conditions such as the property of an adjacent soil layer, the depth of the soil layer and the like on the calculation result of the frictional resistance of the side of the pile does not need to be considered. The method can really realize the simplification of the test method, the reduction of the test working strength, the expansion of the detection range and the improvement of the detection efficiency, the test result is more in line with the reality, and the accuracy and the objectivity of the test result can be better ensured.
Drawings
Fig. 1 is a schematic structural view of the load box of the present invention.
Fig. 2 is a schematic top view of the lower bearing plate of the load box of the present invention.
1. An upper bearing disc 2, a lower bearing disc 3, an anchor cable meter 4, a lifting ring 5 and a tooth bar
7. Light protection casing 8, concrete screed-coat 9, steel reinforcement cage 10, pile body 11, data line.
Detailed Description
Please refer to fig. 1 and fig. 2:
the invention provides a method for testing pile side frictional resistance, which comprises the following steps:
step one, manufacturing a load box:
manufacturing two circular discs with the diameter smaller than the diameter of the pile to be measured by using a steel plate, wherein the circular discs are respectively used as an upper bearing disc 1 and a lower bearing disc 2, and then fixing a plurality of anchor cable meters 3 on the lower bearing disc 2, wherein one anchor cable meter 3 is positioned at the center of the lower bearing disc 2, and the other anchor cable meters 3 are uniformly distributed on a concentric circle close to the outer side of the lower bearing disc 2; a lifting ring 4 is welded at the center of the upper pressure bearing disc 1 for lifting; finally, the upper pressure bearing disc 1 and the lower pressure bearing disc 2 are connected through six tooth bars 5, each tooth bar 5 is provided with a nut, and light protective covers 7 are arranged at two ends of the upper pressure bearing disc 1 and the lower pressure bearing disc 2 so as to ensure that the anchor cable meter 3 is not influenced by external conditions in the construction process, and in the manufacturing process of a load box, the flatness of the upper pressure bearing disc 1 and the lower pressure bearing disc 2 is ensured so as to ensure that the anchor cable meter 3 can be uniformly stressed;
step two, placing a load box:
after the pile hole is determined to be qualified, leveling the pile bottom by using concrete, placing the load box into the pile bottom by using a crane through a lifting ring 4 after the concrete leveling layer 8 is solidified, and checking and ensuring that the load box is in a horizontal position; after the load box is installed, the reinforcement cage 9 is placed into the pile body 10; binding the data wire 11 of the anchor cable meter 3 with the steel bar of the pile body 10 together, and leading out from the pile top;
step three, pouring concrete:
after the first step and the second step are determined to be completed, pouring concrete of the pile body 10 is carried out;
step four, pile top loading:
after the concrete maintenance of the pile body 10 meets the relevant technical requirements, the pile top loading is carried out by adopting a slow-speed load maintaining method according to the standard, and a test method and termination conditions are determined according to the existing standard;
step five, data acquisition:
respectively acquiring pile top load Q, displacement s and pressure Q borne by each anchor cable meter 3 in the loading processiQ has the unit kN, QiThe unit of (a) is kN, i is 1-n, and n is the number of the actual anchor cable meters 3;
step six, calculating the side frictional resistance of the pile: the pile side frictional resistance Q is calculated according to the following formulasu：
Step seven, single soil layer measurement:
when the friction force Q is needed to the side of a pile in a single soil layerSu sheetDuring testing, the pile can be stopped when being poured to the lower interface of the soil layer, the pile is used as a leveling layer in the second step, and then the second step and the third step are repeated; stopping pouring when the concrete in the third step is poured to the upper interface of the soil layer, and repeating the second step, the third step, the fourth step and the fifth step after leveling;
step eight, calculating the side frictional resistance of the single soil layer:
and seventhly, the difference value between the sum of the readings of the load boxes in the lower interface and the sum of the readings of the load boxes in the upper interface is the side frictional resistance of the soil layer, and the calculation formula is as follows:
In the method, the number of the detected piles can be determined according to actual requirements. The pile body concrete pouring, pile top loading and data acquisition in the method are all the prior art provided by the existing relevant specifications and methods, so the specific steps are not repeated.
The following illustrates a specific procedure of the evaluation method:
(1) overview of the engineering
The ground layer of a railway passing through the stratum is mainly brownish red pozzolanic silt, and the stratum revealed by rotary drilling is divided into a volcanic accumulation layer, silt, fine gravel and the like which flood the accumulation layer. The existing railway bridge and culvert foundation and foundation design specifications in China have no value range suggestion value with the pile side frictional resistance of volcanic ash clay and silty soil. And the railway bridge pile foundation mostly adopts friction piles. The diameter of the test pile is 1000mm, and the pile length is 30m, 45m and 50m respectively.
(2) Load box fabrication
The upper and lower bearing discs of the load box are both 25mm thick steel plates, and the diameter is 900 mm; six anchor cable meters 3 are shared, wherein the center of each anchor cable meter is 1, and 5 anchor cable meters are uniformly distributed on a circle which is concentric with the pressure bearing disc and has the diameter of 600 mm; the upper and lower bearing discs are connected by 6 tooth bars 5 which are concentric with the bearing disc and are uniformly distributed on a circle with the diameter of 700 mm; the center of the upper bearing disc 1 is provided with a hanging ring 4, and a light protective cover 7 is arranged around the load box.
(3) Detection process
When the concrete of the pile body 10 is poured to a specified position, the pouring of the concrete is stopped. After the concrete is initially set, the load box is transferred into the pile by a crane, and after the load box is installed, the load box is checked to be in a horizontal position. After the load box is installed, the reinforcement cage 9 is placed into the pile body 10. And binding the data line 11 of the load box with the steel bar of the pile body, and leading out from the pile top. And pouring concrete to the pile top, maintaining to the designed strength, and then loading by adopting a slow-speed load maintaining method, wherein the graded load is 1/20 of the maximum loading capacity or the estimated limit bearing capacity, and the first stage is 2 times of the graded load. And collecting related data strictly according to the standard requirement in the loading process.
(4) The result of the detection
And after the detection is finished, calculating the pile side frictional resistance according to the detection data result. The detection data and calculation results are shown in table 1 below.
TABLE 1 test data and calculation results
Claims (1)
1. A method for testing the side frictional resistance of a pile is characterized by comprising the following steps: the method comprises the following steps:
step one, manufacturing a load box:
manufacturing two circular discs with the diameter smaller than the diameter of the pile to be measured by using a steel plate, wherein the circular discs are respectively used as an upper bearing disc and a lower bearing disc, and then fixing a plurality of anchor cable meters on the lower bearing disc, wherein one anchor cable meter is positioned at the central position of the lower bearing disc, and the other anchor cable meters are uniformly distributed on a concentric circle close to the outer side of the lower bearing disc; a hanging ring is welded at the center of the upper bearing plate and used for hoisting; finally, the upper bearing disc and the lower bearing disc are connected through six tooth bars, each tooth bar is matched with a nut, and light protective covers are arranged at two ends of the upper bearing disc and the lower bearing disc so as to ensure that the anchor cable meter is not influenced by external conditions in the construction process;
step two, placing a load box:
after the pile hole is determined to be qualified, leveling the pile bottom by using concrete, placing the load box into the pile bottom by using a crane through a lifting ring after the concrete leveling layer is solidified, and checking and ensuring that the load box is in a horizontal position; after the load box is installed, placing the reinforcement cage into the pile body; binding the data wire of the anchor cable meter and the pile body steel bar together, and leading out from the pile top;
step three, pouring concrete:
after the first step and the second step are determined to be completed, pouring of pile body concrete is carried out;
step four, pile top loading:
after the concrete maintenance of the pile body reaches the related technical requirements, loading the pile top by adopting a slow-speed load maintaining method according to the standard, and determining a test method and termination conditions according to the existing standard;
step five, data acquisition:
respectively acquiring pile top load Q, displacement s and pressure Q borne by each anchor cable meter in the loading processiQ has the unit kN, QiThe unit of (a) is kN, i is 1-n, and n is the number counted by the actual anchor cable;
step six, calculating the side frictional resistance of the pile: the pile side frictional resistance Q is calculated according to the following formulasu：
Step seven, single soil layer measurement:
when the friction force Q is needed to the side of a pile in a single soil layerSu sheetDuring testing, the pile can be stopped when being poured to the lower interface of the soil layer, the pile is used as a leveling layer in the second step, and then the second step and the third step are repeated; stopping pouring when the concrete in the third step is poured to the upper interface of the soil layer, and repeating the second step, the third step, the fourth step and the fifth step after leveling;
step eight, calculating the side frictional resistance of the single soil layer:
and seventhly, the difference value between the sum of the readings of the load boxes in the lower interface and the sum of the readings of the load boxes in the upper interface is the side frictional resistance of the soil layer, and the calculation formula is as follows:
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| CN109932116B (en) * | 2019-02-25 | 2020-12-11 | 河海大学 | Side friction resistance and end bearing force testing system and measuring method |
| CN109826249B (en) * | 2019-03-07 | 2023-08-22 | 中铁大桥（南京）桥隧诊治有限公司 | Pile foundation side friction resistance measuring device and measuring method |
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