CN115059126A - Device and method for pit-type static load test of existing building pile foundation - Google Patents
Device and method for pit-type static load test of existing building pile foundation Download PDFInfo
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- CN115059126A CN115059126A CN202210911934.5A CN202210911934A CN115059126A CN 115059126 A CN115059126 A CN 115059126A CN 202210911934 A CN202210911934 A CN 202210911934A CN 115059126 A CN115059126 A CN 115059126A
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D33/00—Testing foundations or foundation structures
Abstract
The invention discloses a device and a method for a pit-type static load test of pile foundations of an existing building, which can realize a bearing capacity static load test of the pile foundations at the bottom of a bearing platform or a raft plate of the existing building without breaking and dismantling the existing building; during testing, subtracting a vertical displacement value at the upper part of a bearing platform or a raft from a relative displacement value of the pile top and the bearing platform or the raft structure under the action of each level of load to obtain a vertical displacement actual value of the test pile under the action of each level of load, and corresponding the displacement actual values under each level of load one by one to determine a bearing capacity test limit value of the test pile; and finally, finally determining the bearing capacity characteristic value of the test pile according to the static load test Q-S curve. The potential safety hazard is eliminated to the utmost extent, engineering and test safety is ensured, the problems of high detection difficulty, high manufacturing cost and high risk caused by detection through pile top counter weight in the traditional detection method are avoided, and the method has good use effect and popularization value.
Description
Technical Field
The invention relates to a device and a method for a pit-type static load test of a pile foundation of an existing building.
Background
The static load test of the pile foundation is a technology for detecting the bearing capacity of the pile foundation in engineering, and is the most accurate and reliable test method in the aspect of determining the ultimate bearing capacity of a single pile. Whether a certain dynamic load test method is mature or not is judged according to the comparison error of static load test results. Therefore, the single pile static load test is listed as the first place in each foundation design and treatment specification.
At present, three methods for the field load test of the pile foundation are provided, namely: the pile loading method, the anchor pile method and the self-balancing method are all pile foundation test methods of new construction, and a certain working surface is required to be arranged around a pile body so as to facilitate hoisting of test instruments, a load distribution beam and a load box. The static load test of the bearing capacity of the engineering pile under the existing building is difficult to realize by adopting a conventional test method, and if the bearing capacity of the engineering pile under the existing building needs to be detected, the upper structure of the existing building needs to be broken and disassembled, so that the original structure is damaged, and the safety of the structure is even influenced.
Disclosure of Invention
In view of the above problems, the present invention provides a device and a method for a pit-type static load test of an existing building pile foundation, which aims to perform a bearing capacity static load test on an existing building bearing platform or a raft bottom pile foundation without breaking the existing building, and the existing building can still be used normally during construction. The test device and the method provide counter force by utilizing the self weight of the existing building, abandon the traditional stacking method for erecting a large-area loading platform and stacking, eliminate potential safety hazards to the maximum extent, ensure the safety of engineering structures and tests, and save cost and working time.
In order to achieve the technical purpose and achieve the technical effect, the invention is realized by the following technical scheme:
the utility model provides a device for existing building pile foundation pit type static test, includes static test system, still includes jack, oil pump pressure system and sets up the experimental stake in cushion cap or raft board below, coaxial pile cap, pile top pressure-bearing steel sheet, jack and the top pressure-bearing steel sheet of being provided with in order between experimental stake and cushion cap or the raft board, the top of cushion cap or raft board is provided with the vertical displacement test equipment who is used for monitoring the vertical displacement of existing building vertical structure, be provided with electron displacement sensor between experimental pile top and cushion cap or the raft board, electron displacement sensor and oil pump pressure system link to each other with static test system respectively, oil pump pressure system links to each other with the jack and static test system passes through oil pump pressure system control jack action.
Preferably, the top of the test pile is provided with a pile cap, the pile cap is provided with an electronic displacement sensor support, the upper end of the electronic displacement sensor is fixed at the bottom of the bearing platform or the raft, and the lower end of the electronic displacement sensor is in contact with the electronic displacement sensor support.
Preferably, the number of the electronic displacement sensors is two, and the two electronic displacement sensors are symmetrically arranged on two sides of the jack.
Preferably, the pile cap is made of a steel hoop and a cementing material.
Preferably, the jack is connected with an oil pump pressure system through an oil return pipe at the top and an oil inlet pipe at the bottom.
The method for the pile foundation pit type static load test of the existing building is adopted for the test, and the concrete steps of the method comprise:
step 1, determining a test pile needing static load test and measuring and positioning the test pile on site;
step 4, chiseling and leveling the pile head of the test pile, and manufacturing a pile cap at the pile head of the test pile by adopting a steel hoop and a cementing material;
step 5, chiseling and leveling the bottom of the bearing platform or the raft plate, leveling by adopting repair mortar and maintaining to the designed strength;
step 6, installing a pile top pressure-bearing steel plate, and ensuring that the center of the pile top pressure-bearing steel plate is positioned on the central axis of the test pile;
step 7, mounting a jack, and placing the jack in the center of the pile top pressure-bearing steel plate;
step 8, mounting a top pressure-bearing steel plate, so that the center of the top pressure-bearing steel plate is positioned on the axis of the jack;
step 9, symmetrically installing two electronic displacement sensors on two sides of the jack, wherein the upper ends of the electronic displacement sensors are fixed at the bottom of a bearing platform or a raft, and the lower ends of the electronic displacement sensors are in contact with the electronic displacement sensor support;
step 15, during testing, according to the maximum test load value of the test pile, loading step by step in a plurality of stages according to design requirements until a loading termination condition is met, wherein after the loading of the previous stage is finished and the settlement is stable, the loading of the next stage can be carried out;
and step 16, data acquisition and arrangement.
Preferably, in step 15, the step-by-step loading is performed in 10 stages according to design requirements, and when the settling volume per hour is less than 0.1mm within two continuous hours, the settling is considered to be stable, and then the next stage of loading is performed.
Preferably, after each level of loading settlement is stable, reading and recording real-time data of the static load testing system and the vertical displacement testing equipment of each level of load at the same moment to obtain a vertical displacement actual value of the test pile under the action of each level of load; and drawing a curve graph of the load and the displacement of the test pile according to the data obtained by the test.
Preferably, the single-pile vertical ultimate bearing capacity is divided by the safety factor 2 to obtain a single-pile vertical bearing capacity characteristic value (R) a ) When the extreme difference meeting the limit value of the bearing capacity of the pile foundation of the statistical test pile does not exceed 30% of the average value, the average value is taken as the vertical limit bearing capacity of the single pile; when the range exceeds 30% of the average value, determining the vertical ultimate bearing capacity of the single pile by increasing the number of the test piles and analyzing the reason of overlarge range and combining the concrete conditions of the engineering; to pairAnd taking the minimum value of the limit value of the bearing capacity of the pile foundation as the vertical limit bearing capacity of the single pile.
And (3) making a load-settlement (Q-s) curve and other curves required by auxiliary analysis, wherein the limit value of the bearing capacity of the pile foundation is determined by the following method:
a) when the steep descending section is obvious, taking the load value corresponding to the starting point of the steep descending section as the limit value of the bearing capacity of the pile foundation;
b) when the settlement ratio of the nth level load to the (n + 1) th level load is more than or equal to 2 and is not stable for 24 hours, taking the previous level load value as the limit value of the bearing capacity of the pile foundation;
c) when the Q-s curve is in slow deformation, the load value corresponding to the total settlement s of the pile top which is 40mm is taken as the limit value of the bearing capacity of the pile foundation, and when the length of the pile is more than 40m, the elastic compression of the pile body is preferably considered;
d) when the judgment is difficult according to the method, the comprehensive judgment can be combined with other auxiliary analysis methods. The limit value of the bearing capacity of the pile foundation is selected according to specific conditions by a person with special requirements on the settlement of the pile foundation.
The invention has the beneficial effects that:
the method is characterized in that the bearing capacity of the pile foundation of the existing building is tested, the dead weight of the existing building is used as a balance weight, a static load test is carried out at the bottom of a bearing platform or a raft, the dead weight of the existing building is fully utilized to provide counter force, a transmission method that a large-area loading platform is erected and piled manually and mechanically in a cooperation mode is abandoned, potential safety hazards are eliminated to the maximum extent, engineering and test safety is ensured, and the problem that the bearing capacity of the pile foundation under the existing building cannot be detected due to site limitation in the traditional static load test is solved.
Secondly, because the space in the pit is narrow, the vertical displacement value of the pile foundation under the static load effect is difficult to accurately measure in the pit, so the invention directly measures the relative displacement value of the pile top and the bottom structure of the bearing platform or the raft under the load effect of each level and the vertical displacement value of the top of the bearing platform or the raft in the foundation pit, subtracts the vertical displacement value of the top from the relative displacement value of the bottom to be equal to the actual vertical displacement value of the pile under the load effect of each level, corresponds the actual displacement values under each level of load one to one, and finally determines the bearing capacity test limit value of the pile. The invention does not need to break and dismantle the original foundation structure, avoids the problems of high detection difficulty, high manufacturing cost and high danger caused by detection through the pile top counterweight in the traditional detection method, and has good use effect and popularization value.
Thirdly, the invention makes full use of the existing building to provide counter force, saves the material cost of the load platform erection, the pile loading, the buttress and the like, saves the cost of the transportation, the hoisting, the buttress foundation treatment and the like, can still be normally used during the construction period, saves the working hours, and is economic and reliable.
Drawings
FIG. 1 is a schematic structural diagram of an apparatus for a pit-type static load test of a pile foundation of an existing building;
the reference numerals of the drawings have the following meanings:
1: an operation tunnel; 2: the vertical structure of the existing building; 3: a cap or raft; 4: a top pressure-bearing steel plate; 5: an electronic displacement sensor; 6: a jack; 7: pile top pressure-bearing steel plate; 8: pile caps; 9: an electronic displacement sensor support; 10: testing piles; 11: engineering piles; 12: vertical displacement test equipment; 13: a static load test system; 14: an oil pump pressure system.
Detailed Description
The present invention will be better understood and implemented by those skilled in the art by the following detailed description of the technical solution of the present invention with reference to the accompanying drawings and specific examples, which are not intended to limit the present invention.
The invention relates to a device for a pit type static load test of a pile foundation of an existing building, belongs to the technical field of pile foundation detection, and can be widely applied to tests of bearing capacity of various types of pile foundations of the existing building. The device includes static test system 13, still includes jack 6, oil pump pressure system 14 and sets up at cushion cap or raft 3 below test stake 10, coaxial pile cap 8, pile cap pressure-bearing steel sheet 7, jack 6 and top pressure-bearing steel sheet 4 of being provided with in order between test stake 10 and cushion cap or raft 3.
Preferably, the pile head of the test pile 10 is made of a steel hoop and a cementing material to form a pile cap 8, and an electronic displacement sensor 5 is installed between the pile cap 8 and the bearing platform or raft 3, namely the electronic displacement sensor 5 is arranged between the top of the test pile 10 and the bearing platform or raft 3.
Preferably, be provided with electron displacement sensor support 9 on the pile cap 8, the upper end of electron displacement sensor 5 is fixed in the bottom of cushion cap or raft 3, electron displacement sensor 5 lower extreme contacts with electron displacement sensor support 9. In fig. 1, the number of the electronic displacement sensors 5 is two, and the two electronic displacement sensors 5 are symmetrically arranged on two sides of the jack 6.
The top of cushion cap or raft 3 is provided with the vertical displacement test equipment 12 that is used for monitoring the vertical displacement of existing building vertical structure 2, electronic displacement sensor 5 and oil pump pressure system 14 link to each other with static load test system 13 respectively, oil pump pressure system 14 links to each other with jack 6, and two oil pipe, general are relied on in the connection of both, jack 6 is connected with oil pump pressure system 14 through the oil pipe that advances of the oil pipe and bottom that returns at top. The static load test system 13 controls the jack 6 to act through an oil pump pressure system 14.
The invention can realize the bearing capacity static load test of the pile foundation at the bottom of the bearing platform or the raft of the existing building without breaking the existing building, during the test, the vertical displacement value at the upper part of the bearing platform or the raft is subtracted from the relative displacement value of the pile top and the bearing platform or the raft structure under the action of each level of load to obtain the actual vertical displacement value of the test pile under the action of each level of load, the actual displacement values under each level of load are in one-to-one correspondence to determine the bearing capacity test limit value of the test pile, and finally, the bearing capacity characteristic value of the test pile is finally determined according to the Q-S curve of the static load test. Specifically, the method for the pit-type static load test of the pile foundation of the existing building comprises the following specific steps:
1. determining a test pile 10 to be subjected to static load test and measuring and positioning the test pile on site;
2. cleaning the soil around the bottom of a bearing platform or a raft 3, a test pile 10 and an engineering pile 11 by using the operation underground tunnel 1 and adopting a manual hole digging method, wherein the excavated space meets the static load test requirement;
3. cutting off the top of the test pile 10, wherein the cutting height meets the height requirement required by the installation of the jack 6;
4. the pile head of the test pile 10 is trimmed and leveled, and a pile cap 8 is made at the pile head of the test pile 10 by adopting a steel hoop and a cementing material;
5. picking and chiseling the bottom of a bearing platform or a raft 3 at the top of the test pile 10 to be smooth, leveling by adopting repair mortar and maintaining to the designed strength;
6. installing a pile top pressure-bearing steel plate 7, and ensuring that the center of the pile top pressure-bearing steel plate 7 is positioned on the central axis of the test pile 10;
7. installing a jack 6, and ensuring that the jack 6 is placed in the right center of the pile top pressure-bearing steel plate 7;
8. installing a top pressure-bearing steel plate 4, and ensuring that the center of the top pressure-bearing steel plate 4 is positioned on the axis of the jack 6;
9. two electronic displacement sensors 5 are symmetrically arranged on two sides of a jack 6, wherein the upper ends of the electronic displacement sensors 5 are fixed at the bottom of a bearing platform or a raft 3, and the lower ends of the electronic displacement sensors 5 are in contact with an electronic displacement sensor support 9;
10. connecting a jack 6 with an oil pump pressure system 14 by two oil pipes, wherein the top of the jack 6 is provided with an oil return pipe, the bottom of the jack 6 is provided with an oil inlet pipe, and the oil return pipe at the top of the jack 6 and the oil inlet pipe at the bottom of the jack are respectively connected with the oil pump pressure system 14;
11. connecting the two electronic displacement sensors 5 to a static load test system 13;
12. connecting the oil pump pressure system 14 to the static load test system 13;
13. mounting a vertical displacement test device 12 at the top of the bearing platform or raft 3, and during testing, monitoring the vertical displacement of the vertical structure 2 of the existing building by using the vertical displacement test device 12, and then determining the vertical displacement value of the bearing platform or raft 3;
14. zeroing initial values of an oil pump pressure system 14, a static load test system 13 and vertical displacement test equipment 12 at the top of a bearing platform or raft plate 3;
15. during the test, according to the maximum test load value of the test pile 10, loading step by step in a plurality of steps according to the design requirement until the condition of stopping loading is met, wherein, after the loading of the previous step is finished and the settlement is stable, the loading of the next step can be carried out. For example, the maximum test load value of the test pile 10 is 3400kN, during the test, the test pile is loaded step by step in ten steps according to the design requirements, and after the previous step is loaded and the settlement is stable, the next step can be loaded. Among these, the stable standard: in two continuous hours, if the sedimentation amount per hour is less than 0.1mm, the sedimentation tends to be stable, and the next-stage loading can be carried out;
16. data acquisition and arrangement: after each level of loading settlement is stable, reading and recording real-time data of the static load testing system 13 and the vertical displacement testing equipment 12 of each level of load at the same moment, obtaining a vertical displacement actual value of the test pile 10 under the action of each level of load, and drawing a load-displacement curve chart of the test pile 10 according to the data obtained by the test;
17. the unloading stage number can be half of the loading stage number, the unloading stage number is carried out in an equivalent manner, the rebound quantity is read and recorded every time when the unloading stage number is unloaded at an interval of 0.5h, and the total rebound quantity is read and recorded at an interval of 3h after all loads are unloaded. After each stage of unloading is stable, reading and recording real-time data of the static load testing system 13 and the vertical displacement testing equipment 12 of each stage of load at the same moment, obtaining an actual vertical displacement value of the test pile 10 unloaded at each stage, and drawing a load-displacement curve chart of the test pile 10 according to the data obtained by the test.
18. The conditions for terminating the loading during the test may be:
a) when a load-settlement (Q-s) curve has a steep settlement section capable of judging the ultimate bearing capacity, and the total settlement of the pile top exceeds 40 mm;
b) when the ratio of the settling volume of the nth level load to the settling volume of the (n + 1) th level load is more than or equal to 2, the stability is not achieved after 24 hours;
c) when the Q-s curve of the non-socketed pile with the height of more than 25m is in slow deformation, the total settlement of the pile top is more than 60-80 mm;
d) under special conditions, the total settlement of the pile top can be loaded to be more than 100mm according to specific requirements.
19. Dividing the vertical ultimate bearing capacity of the single pile by the safety factor 2 to obtain the characteristic value (R) of the vertical bearing capacity of the single pile a ) When the extreme difference of the limit value meeting the bearing capacity of the pile foundation does not exceed 30 percent of the average value, the average value of the experimental piles is taken as the vertical direction of a single pileUltimate bearing capacity; when the range exceeds 30% of the average value, determining the vertical ultimate bearing capacity of the single pile by increasing the number of the test piles and analyzing the reason of overlarge range and combining the specific conditions of the engineering; and taking the minimum value of the limit value of the bearing capacity of the pile foundation as the vertical limit bearing capacity of the single pile for the lower pile platform with 3 piles and less than 3 piles.
And (3) making a load-settlement (Q-s) curve and other curves required by auxiliary analysis, and determining a limit value of the bearing capacity of the pile foundation by the following method:
a) when the steep descending section is obvious, taking the load value corresponding to the starting point of the steep descending section as the limit value of the bearing capacity of the pile foundation;
b) when the settlement ratio of the nth level load to the (n + 1) th level load is more than or equal to 2 and is not stable for 24 hours, taking the previous level load value as the limit value of the bearing capacity of the pile foundation;
c) when the Q-s curve is in slow deformation, the load value corresponding to the total settlement s of the pile top which is 40mm is taken as the limit value of the bearing capacity of the pile foundation, and when the length of the pile is more than 40m, the elastic compression of the pile body is preferably considered;
d) when the judgment is difficult according to the method, the comprehensive judgment can be combined with other auxiliary analysis methods. The limit value of the bearing capacity of the pile foundation is selected according to specific conditions by a person with special requirements on the settlement of the pile foundation.
The technology has been successfully applied in a plurality of projects, obtains good implementation effect and achieves the purpose of the vertical bearing capacity static load test of the existing building pile foundation.
The invention has the beneficial effects that:
the method is characterized in that the bearing capacity of the pile foundation of the existing building is tested, the dead weight of the existing building is used as a balance weight, a static load test is carried out at the bottom of a bearing platform or a raft, the dead weight of the existing building is fully utilized to provide counter force, a transmission method that a large-area loading platform is erected and piled manually and mechanically in a cooperation mode is abandoned, potential safety hazards are eliminated to the maximum extent, engineering and test safety is ensured, and the problem that the bearing capacity of the pile foundation under the existing building cannot be detected due to site limitation in the traditional static load test is solved.
Secondly, because the space in the pit is narrow, the vertical displacement value of the pile foundation under the static load effect is difficult to accurately measure in the pit, so the invention directly measures the relative displacement value of the pile top and the bottom structure of the bearing platform or the raft under the load effect of each level and the vertical displacement value of the top of the bearing platform or the raft in the foundation pit, subtracts the vertical displacement value of the top from the relative displacement value of the bottom to be equal to the actual vertical displacement value of the pile under the load effect of each level, corresponds the actual displacement values under each level of load one to one, and finally determines the bearing capacity test limit value of the pile. The invention does not need to break and dismantle the original foundation structure, avoids the problems of high detection difficulty, high manufacturing cost and high danger caused by detection through the pile top counterweight in the traditional detection method, and has good use effect and popularization value.
Thirdly, the invention makes full use of the existing building to provide counterforce, saves the material cost of load platform erection, pile loading, buttress and the like, saves the cost of carrying, hoisting, buttress foundation treatment and the like, can still be normally used during construction, saves working hours, and is economic and reliable.
The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (10)
1. The device for the pit type static load test of the pile foundation of the existing building comprises a static load test system (13) and is characterized by further comprising a jack (6), an oil pump pressure system (14) and test piles (10) arranged below a bearing platform or a raft plate (3), wherein a pile cap (8), a pile top bearing steel plate (7), the jack (6) and a top bearing steel plate (4) are sequentially and coaxially arranged between the test piles (10) and the bearing platform or the raft plate (3), vertical displacement test equipment (12) used for monitoring the vertical displacement of the vertical structure (2) of the existing building is arranged at the top of the bearing platform or the raft plate (3), an electronic displacement sensor (5) is arranged between the top of the test piles (10) and the bearing platform or the raft plate (3), the electronic displacement sensor (5) and the oil pump pressure system (14) are respectively connected with the static load test system (13), the oil pump pressure system (14) is connected with the jack (6), and the static load test system (13) controls the jack (6) to act through the oil pump pressure system (14).
2. The device for the pile foundation pit type static load test of the existing building according to claim 1, wherein a pile cap (8) is arranged at the top of the test pile (10), an electronic displacement sensor support (9) is arranged on the pile cap (8), the upper end of the electronic displacement sensor (5) is fixed at the bottom of a bearing platform or a raft (3), and the lower end of the electronic displacement sensor (5) is in contact with the electronic displacement sensor support (9).
3. The device for the pit-type static load test of the pile foundation of the existing building is characterized in that the number of the electronic displacement sensors (5) is two, and the two electronic displacement sensors (5) are symmetrically arranged on two sides of the jack (6).
4. Device for pot-type static load testing of existing building pile foundations according to claim 1, characterized in that the pile cap (8) is made of steel hoop and cementitious material.
5. Device for foundation pit type static load test of existing buildings according to claim 1 characterized in that the jack (6) is connected to the oil pump pressure system (14) through oil return pipe at the top and oil inlet pipe at the bottom.
6. A method for the pile foundation pit type static load test of the existing building, which is characterized in that the device for the pile foundation pit type static load test of the existing building, which is disclosed by the claims 1-5, is used for testing, and the specific steps comprise:
step 1, determining a test pile (10) to be subjected to static load test and measuring and positioning the test pile on site;
step 2, cleaning the soil around the bottom of the bearing platform or raft (3), the test pile (10) and the engineering pile (11) by adopting a manual hole digging method, wherein the excavated space meets the static load test requirement;
step 3, cutting off the top of the test pile (10), wherein the cutting-off height meets the height requirement required by the installation of the jack (6);
step 4, picking and chiseling the pile head of the test pile (10) to be flat, and manufacturing a pile cap (8) at the pile head of the test pile (10) by adopting a steel hoop and a cementing material;
step 5, chiseling and leveling the bottom of the bearing platform or raft plate (3), leveling by adopting repair mortar and maintaining to the designed strength;
step 6, installing a pile top pressure-bearing steel plate (7) and ensuring that the center of the pile top pressure-bearing steel plate (7) is positioned on the central axis of the test pile (10);
step 7, mounting the jack (6) to enable the jack (6) to be placed in the center of the pile top pressure-bearing steel plate (7);
step 8, mounting the top pressure-bearing steel plate (4) to enable the center of the top pressure-bearing steel plate (4) to be located on the axis of the jack (6);
step 9, symmetrically installing two electronic displacement sensors (5) on two sides of a jack (6), wherein the upper ends of the electronic displacement sensors (5) are fixed at the bottom of a cushion cap or a raft (3), and the lower ends of the electronic displacement sensors (5) are in contact with an electronic displacement sensor support (9);
step 10, respectively connecting an oil return pipe at the top and an oil inlet pipe at the bottom of the jack (6) with an oil pump pressure system (14);
step 11, respectively connecting the two electronic displacement sensors (5) to a static load test system (13);
step 12, connecting an oil pump pressure system (14) to a static load test system (13);
step 13, mounting vertical displacement testing equipment (12) at the top of the cushion cap or raft (3);
14, zeroing initial values of a pressure system (14) of the oil pump, a static load testing system (13) and vertical displacement testing equipment (12) at the top of a bearing platform or raft plate (3);
step 15, during testing, according to the maximum test load value of the test pile (10), loading step by step in a plurality of steps according to design requirements until a load termination condition is met, wherein after the loading of the previous step is finished and the settlement is stable, the loading of the next step can be carried out;
and step 16, data acquisition and arrangement.
7. The method for the pit-type static load test of the pile foundation of the existing building as claimed in claim 6, wherein in step 15, the step-by-step loading is carried out in 10 steps according to the design requirement, and when the settling amount per hour is less than 0.1mm within two consecutive hours, the settling is considered to be stable, and the next step of loading is carried out.
8. The method for the pit type static load test of the pile foundation of the existing building according to claim 6, characterized in that after each stage of loading settlement is stable, real-time data of a static load test system (13) and a vertical displacement test device (12) of each stage of loading at the same moment are read and recorded to obtain an actual vertical displacement value of the test pile (10) under the action of each stage of loading; and drawing a curve chart of the load and the displacement of the test pile (10) according to the data obtained by the test.
9. Method for the pit-type static load test of the pile foundation of the existing building according to claim 8, characterized in that the single-pile vertical ultimate bearing capacity divided by the safety factor 2 is the single-pile vertical bearing capacity characteristic value (R) a ) When the extreme difference meeting the limit value of the bearing capacity of the pile foundation of the statistical test pile does not exceed 30% of the average value, the average value is taken as the vertical limit bearing capacity of the single pile; when the range exceeds 30% of the average value, determining the vertical ultimate bearing capacity of the single pile by increasing the number of the test piles and analyzing the reason of overlarge range and combining the specific conditions of the engineering; and taking the minimum value of the limit value of the bearing capacity of the pile foundation as the vertical limit bearing capacity of the single pile for the lower pile platform with 3 piles and less than 3 piles.
10. And (3) making a load-settlement (Q-s) curve and other curves required by auxiliary analysis, wherein the limit value of the bearing capacity of the pile foundation is determined by the following method:
a) when the steep descending section is obvious, taking the load value corresponding to the starting point of the steep descending section as the limit value of the bearing capacity of the pile foundation;
b) when the settlement ratio of the nth level load to the (n + 1) th level load is more than or equal to 2 and is not stable for 24 hours, taking the previous level load value as the limit value of the bearing capacity of the pile foundation;
c) when the Q-s curve is in slow deformation, the load value corresponding to the total settlement s of the pile top which is 40mm is taken as the limit value of the bearing capacity of the pile foundation, and when the length of the pile is more than 40m, the elastic compression of the pile body is preferably considered;
d) when the judgment is difficult according to the method, the comprehensive judgment can be combined with other auxiliary analysis methods;
the limit value of the bearing capacity of the pile foundation is selected according to specific conditions by a person with special requirements on the settlement of the pile foundation.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115928818A (en) * | 2023-03-14 | 2023-04-07 | 沧州路桥工程有限责任公司 | Static load test device for pile foundation detection |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115928818A (en) * | 2023-03-14 | 2023-04-07 | 沧州路桥工程有限责任公司 | Static load test device for pile foundation detection |
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