CN115233752B - Reverse self-balancing pile testing method based on pile body double-load box - Google Patents
Reverse self-balancing pile testing method based on pile body double-load box Download PDFInfo
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- 238000012360 testing method Methods 0.000 title claims abstract description 24
- 238000006073 displacement reaction Methods 0.000 claims abstract description 74
- 238000011068 loading method Methods 0.000 claims abstract description 58
- 238000006243 chemical reaction Methods 0.000 claims abstract description 21
- 238000012544 monitoring process Methods 0.000 claims abstract description 18
- 238000004873 anchoring Methods 0.000 claims abstract description 15
- 238000007789 sealing Methods 0.000 claims description 26
- 238000000034 method Methods 0.000 claims description 15
- 238000010998 test method Methods 0.000 claims description 15
- 239000002689 soil Substances 0.000 claims description 11
- 230000009471 action Effects 0.000 claims description 8
- 229910000831 Steel Inorganic materials 0.000 claims description 3
- 230000006835 compression Effects 0.000 claims description 3
- 238000007906 compression Methods 0.000 claims description 3
- 239000010959 steel Substances 0.000 claims description 3
- 238000012937 correction Methods 0.000 claims description 2
- 239000010720 hydraulic oil Substances 0.000 description 4
- 238000013461 design Methods 0.000 description 3
- 238000009434 installation Methods 0.000 description 3
- 230000003068 static effect Effects 0.000 description 3
- 230000008859 change Effects 0.000 description 2
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- 230000004048 modification Effects 0.000 description 1
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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
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D27/00—Foundations as substructures
- E02D27/10—Deep foundations
- E02D27/12—Pile foundations
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
- E02D5/22—Piles
- E02D5/52—Piles composed of separable parts, e.g. telescopic tubes ; Piles composed of segments
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
- E02D5/74—Means for anchoring structural elements or bulkheads
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D2600/00—Miscellaneous
- E02D2600/10—Miscellaneous comprising sensor means
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D2600/00—Miscellaneous
- E02D2600/30—Miscellaneous comprising anchoring details
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- General Life Sciences & Earth Sciences (AREA)
- Mining & Mineral Resources (AREA)
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Abstract
The invention discloses a reverse self-balancing pile testing method based on a pile body double-load box, which comprises the steps of determining an upper balance point and a lower balance point, and dividing piles into an upper pile section, a middle pile section and a lower pile section; a load box is respectively arranged at the top of the pile at the upper section and between the piles at the adjacent sections, and is sequentially marked as a first load box, a second load box and a third load box; the load boxes comprise jacks and pressure sensors; the reaction anchoring system is arranged at the top of the upper pile section and comprises a reaction end plate and an anchor cable for anchoring and connecting the reaction end plate with the middle pile section; arranging a displacement monitoring system for respectively monitoring the displacement of the upper section pile, the middle section pile and the lower section pile; sequentially loading a third load box, a second load box and a first load box, and obtaining the positive limit bearing capacity of each section of pile according to the load displacement curve of each loading; and adding to obtain the total ultimate bearing capacity of the pile foundation. The pile foundation loading method avoids the problem that the balance points of pile body loading and pile top loading are not coincident in the prior art, and the obtained pile foundation bearing capacity is more in line with the actual situation.
Description
Technical Field
The invention belongs to the field of civil engineering, relates to a reverse self-balancing pile testing method technology, and in particular relates to a reverse self-balancing pile testing method based on a pile body double-load box.
Background
At present, static load tests are considered to be the most accurate and reliable test method for foundation pile bearing capacity detection at home and abroad. According to different counterforce systems in engineering, static load tests are mainly divided into a pile loading method, an anchor pile method and a self-balancing method. The pile-up method is the most reliable method for detecting the bearing capacity of foundation piles. The counter force of the static load test is provided by the heavy object, but the construction site condition is limited, and high installation and transportation cost is required; the anchor pile method is mainly used for testing the bearing capacity of the large-diameter cast-in-place pile by taking the anchor piles as a counterforce system, and four or more anchor piles are often needed, so that the test cost is increased; the self-balancing method does not need a loading platform and an anchor pile counter-force system, has extremely high technical requirements on construction technicians, and because whether a test can be successful or not, the test load born by the pile body is only half of the design load limit bearing capacity, and the uncertainty of the value from negative frictional resistance to positive frictional resistance of the test pile under the limit bearing capacity cannot be measured. Therefore, we propose a reverse self-balancing pile test method, which adds a pile top loading device on the basis of the self-balancing pile test method.
The reverse self-balancing pile has the advantages that a loading platform and an anchor pile counterforce system are not needed, and the technical problem that the negative frictional resistance of the pile at the upper section of the self-balancing pile needs to be converted into the positive frictional resistance is solved.
However, the reverse self-balancing pile test method has the problem that the upper pile section is easy to pull up when the pile top is loaded, because the pile body loading and the pile top loading have different requirements on the position of the balance point, the pile body loading is suitable for calculating the position of the balance point, and the pile top loading is suitable for calculating the position of the balance point. Meanwhile, due to inaccurate geological survey data, errors in the installation position of a load box and the like, the upper pile section and the lower pile section loaded on the pile body cannot reach the limit at the same time, and therefore the obtained test result is smaller than the actual test result.
As shown in FIG. 1, two sets of loading devices, namely pile body loading and pile top loading, are arranged in the reverse self-balancing pile testing method. The change of the loading sequence can cause the change of the pile body side friction resistance distribution and the neutral point position, and when the pile body is loaded, the pile body is made to be
Q fd2 + ＝A p q r ，Q fu - For the upper pile to bear vertical downward negative friction force, Q fd1 + For the lower pile to bear vertical upward positive friction force, Q fd2 + To the lower pile in the vertical directionEnd resistance on the upper part, in order to reach equilibrium, the requirement of Q is satisfied fu _ +G u ＝Q fd1 + +Q fd2 + The position of the load box is lower, and the counterforce of the pile end of the lower section pile can be exerted more completely, so that the position of the suitable load box is lower; when pile top is loaded, Q fu + For the upper pile to receive vertical upward positive friction force, Q fd _ Subjecting the lower pile to vertical downward negative frictional resistance, wherein Q fd1 + +Q fd2 + >Q fd _ Therefore, the balance point can not meet the pile top loading when meeting the pile body loading; there is also an urgent need for a technique that can eliminate this drawback so that the ultimate bearing capacity of the pile foundation obtained is closer to the true ultimate bearing capacity in an effort to facilitate the application of the reverse self-balancing pile test method in foundation pile engineering.
Disclosure of Invention
Aiming at the problem that the positions of the balance points needed by pile body loading and pile top loading are inconsistent in the reverse self-balancing pile test method, the invention provides a reverse self-balancing pile test method based on a pile body double-load box.
In order to solve the technical problems, the invention adopts the following technical scheme:
the reverse self-balancing pile testing method based on the pile body double-load box is characterized by comprising the following steps of:
step 1, determining an upper balance point and a lower balance point through calculation or judgment according to geological data experience, dividing the pile into an upper section pile, a middle section pile and a lower section pile, wherein the two balance points are respectively positioned between two adjacent sections of piles;
And 7, calculating the vertical compression-resistant total ultimate bearing capacity of the pile, wherein the calculation formula is as follows:
Q pressing And G is the total dead weight of the pile.
Compared with the prior art, the invention has the following effects:
according to the invention, the problem that the positions of balance points needed by pile body loading and pile top loading are inconsistent in the traditional reverse self-balancing pile testing method is solved by selecting two balance points to set two pile body jacks, the pile foundation ultimate bearing capacity is obtained by three loading sections, and then the total pile foundation ultimate bearing capacity is calculated, so that the problem that the balance points of pile body loading and pile top loading are not coincident in the original technical scheme is avoided, the obtained pile foundation bearing capacity is more in line with the true ultimate bearing capacity of a pile foundation, and a more accurate design basis is provided for an engineering pile.
Drawings
FIG. 1 is a diagram showing stress of a reverse self-balancing method in the prior art.
Fig. 2 is a schematic structural diagram of a reverse self-balancing pile testing device based on a pile body double-load box in an embodiment of the invention.
Fig. 3 is a schematic view of pile stress when a third load box is loaded in an embodiment of the present invention.
Fig. 4 is a schematic view of pile stress when the second load box is loaded in the embodiment of the invention.
Fig. 5 is a schematic view of pile stress when the first load box is loaded in an embodiment of the present invention.
1-a counterforce end plate; 2-percentage table; 3-a hydraulic oil station; 4-a data acquisition system; 5-upper section piles; 6-anchor cables; 7-a displacement rod; 8-an upper section pile bottom sealing end plate; 9-a middle pile top end sealing plate; 10-steel axle bolts; 11-middle section piles; 12-a middle pile bottom sealing end plate; 13-a third load box; 14-a pile top sealing end plate at the lower section; 15-lower section piles; 16-jack; 17-a pressure sensor; 18-upper pile top end sealing plate, 19-second load box and 20-first load box.
Detailed Description
Embodiments of the present invention are described in further detail below with reference to the accompanying drawings and examples. The following examples are illustrative of the invention but are not intended to limit the scope of the invention.
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
The invention is further described below with reference to the drawings and specific examples, which are not intended to be limiting.
As shown in fig. 2, the invention provides a reverse self-balancing pile testing device based on a pile body double-load box, which comprises a pile, a counter-force anchoring system, a loading system and a displacement monitoring system; the pile comprises an upper section pile 5, a middle section pile 11 and a lower section pile 15, wherein the top of the upper section pile 5, the bottom of the upper section pile 5, the top of the middle section pile 11, the bottom of the middle section pile 11 and the top of the lower section pile 15 are provided with end sealing plates;
the loading system comprises three load boxes and a hydraulic oil station 3, wherein each load box comprises a jack 16 and a pressure sensor 17 which are arranged in a superposition manner, and the pressure sensor 17 is generally arranged at the free telescopic end of the jack 16 and is used for measuring the actual loading force of the jack 16; the jacks 16 of the three load boxes are connected with the hydraulic oil station 3 through an oil way control system, the hydraulic oil station 3 controls the loading and unloading of each jack 16, and how to control the jacks has no influence on solving the technical problem of the invention; the second load box 19 is arranged between the upper pile 5 and the middle pile 11, in particular between the middle pile top end sealing plate 9 and the upper pile bottom end sealing plate 8; the third load box is arranged between the middle pile 11 and the lower pile 15, and is specifically arranged between the lower pile top sealing end plate 14 and the middle pile bottom sealing end plate 12.
The reaction anchoring system comprises a reaction end plate 1 and a plurality of anchor cables 6, wherein the reaction end plate 1 is arranged at the top of the pile, the reaction end plate 1 is arranged at the top of the first load box, the tops of the anchor cables 6 are fixedly connected with the reaction end plate 1, and the lower end of the reaction end plate freely passes through the upper section pile 5 and is then fixed on the middle section pile top sealing end plate 9; and through holes for the anchor cable 6 to freely pass through are formed in the upper pile top end sealing plate 18 and the upper pile bottom end sealing plate 8.
As a preferred embodiment, the anchor cables 6 are uniformly distributed around the first load box, so as to prevent unbalanced load in the loading process.
As a preferred embodiment, the lower end of the anchor cable 6 is fixed at the bottom of the middle pile top sealing end plate 9 through a steel shaft bolt 10, so that the fixing is simple and convenient, and the anchoring requirement can be met.
It should be noted that the pile in the invention can be a model pile in a model test or an engineering pile, and the invention is only used for illustrating a principle method, so that the installation sequence of the load box and the displacement monitoring system can be selected according to the requirement, and the invention is not limited to a specific form.
The displacement monitoring system comprises a data acquisition system 4, four displacement rods 7 and a dial indicator 2 which is arranged at the top of the corresponding displacement rods 7 and used for measuring the displacement of the displacement rods 7, wherein the first displacement rod freely passes through the upper-section pile 5 and is then fixed on an upper-section pile bottom sealing end plate 8 and used for measuring the pile bottom displacement of the upper-section pile 5; the second displacement rod freely passes through the upper section pile 5 and then is fixed on the middle section pile top sealing end plate 9, and is used for measuring pile top displacement of the middle section pile 11; the third displacement rod freely passes through the upper section pile 5 and the middle section pile 11 and is then fixed on the middle section pile bottom sealing end plate 12, and is used for measuring the pile bottom displacement of the middle section pile 11; the fourth displacement rod freely passes through the upper section pile 5 and the middle section pile 11 and then is fixed on the lower section pile top sealing end plate 14 for measuring pile top displacement of the lower section pile 15.
The four dial indicators 2 are hung on an external member or are fixed by an independent bracket, the four displacement rods 7 move up and down along with the respective fixed end sealing plates in the loading process, and the up and down moving distance of each displacement rod 7 can be read through the dial indicators 2, namely the displacement of the corresponding section pile.
As shown in fig. 3 to 4, the present invention provides a reverse self-balancing pile testing method based on the reverse self-balancing pile testing device, which comprises the following steps:
step 1, determining an upper balance point and a lower balance point through calculation or judgment according to geological data experience, dividing the pile into three sections, namely an upper section pile 5, a middle section pile 11 and a lower section pile 15, wherein the two balance points are respectively positioned between two adjacent sections of piles;
And 7, calculating the vertical compression-resistant total ultimate bearing capacity of the pile, wherein the calculation formula is as follows:
Q pressing And G is the total dead weight of the pile.
As a preferred embodiment, in step 1, two equilibrium point determination methods are as follows:
step 1.1, firstly, primarily dividing the pile into an upper-section pile and a lower-section pile, and determining a first balance point through a balance point calculation formula, wherein the calculation formula is as follows:
in the above-mentioned method, the step of,
in the above description, i represents the number of layers of soil layers around the pile, lambda i The weighting correction coefficient of the soil layer around the upper pile is represented, cohesive soil and silt are taken out to be 0.8, and sand is taken out to be 0.7; u represents the circumference of the pile body, l i Representing the corresponding sectional length of the soil layer around the pile, q ik Representation and l i The standard value of the frictional resistance between the pile side and the soil layer corresponding to the length is represented by G, ap represents the pile end sectional area, qr represents the allowable bearing capacity of the soil at the pile end, and the left summation formula
Pile side resistance summation representing upper pile, right summation formula->
Representing the pile side drag summation of the lower pile.
Step 1.2, after the first balance point is obtained by calculating the length of the upper pile, selecting a point in the middle of the preliminary lower pile according to an empirical value as a second balance point (for example, the second balance point is selected from one third to two thirds of the length of the preliminary lower pile, the specific position of the balance point is not particularly important, and the calculation inaccuracy of the first balance point is sufficiently corrected as long as the second balance point is set), and dividing the preliminary lower pile into two sections, thereby obtaining the upper pile, the middle pile and the lower pile.
It should be noted that the first balance point calculating method can refer to the highway bridge foundation and the basic design specification (JTG D63-2007).
As a preferred embodiment, the central axes of the jacks and the pressure sensors in the three load boxes are coincident with the central axis of the pile.
As a preferred embodiment, the pressure sensor is a cylindrical pressure sensor with anti-unbalanced load capability.
In step 5 to step 7, the jack 16 in the load box is loaded in a staged loading mode, and each stage of loading is 1/10-1/15 of the estimated limit load.
As a preferred embodiment, in step 5 to step 7,
the displacement of each hour is not more than 0.1mm and appears twice continuously, and the relative stability is considered to be achieved, and the load of the next stage is added; when one of the download conditions occurs, the loading can be terminated;
(1) The limit loading value has been reached;
(2) Under the action of a certain level of load, the displacement of the pile is 5 times of the displacement of the pile under the action of a previous level of load;
(3) Under the action of a certain level of load, the displacement of the pile is 2 times larger than that under the action of a previous level of load, and the pile is not relatively stable after 24 hours;
(4) The accumulated pulling-up amount exceeds 100mm.
The above embodiments are only for illustrating the present invention, and are not limiting of the present invention. While the invention has been described in detail with reference to the embodiments, those skilled in the art will appreciate that various combinations, modifications, and substitutions can be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (9)
1. The reverse self-balancing pile testing method based on the pile body double-load box is characterized by comprising the following steps of:
step 1, determining an upper balance point and a lower balance point through calculation or judgment according to geological data experience, dividing the pile into an upper section pile, a middle section pile and a lower section pile, wherein the two balance points are respectively positioned between two adjacent sections of piles;
step 2, arranging a load box between the upper section pile and the middle section pile at the top of the upper section pile, and arranging a load box between the middle section pile and the lower section pile respectively, wherein the load boxes are sequentially marked as a first load box, a second load box and a third load box, and each load box comprises a jack and a pressure sensor which are overlapped or a jack with the pressure sensor;
step 3, arranging a reaction anchoring system at the top of the upper pile, wherein the reaction anchoring system comprises a reaction end plate arranged at the top of the first load box and an anchor cable for anchoring and connecting the reaction end plate with the middle pile, and the anchor cable freely passes through the upper pile;
step 4, arranging a displacement monitoring system to monitor the displacement of the upper section pile, the middle section pile and the lower section pile respectively;
step 5, loading the pile body, loading a jack in a third load box, forcing the middle-section pile and the lower-section pile to move oppositely, drawing a load displacement curve graph of the middle-section pile and the lower-section pile according to the displacement of the middle-section pile and the lower-section pile obtained by a displacement monitoring system and the force obtained by a pressure sensor in the third load box, and obtaining the negative limit bearing capacity Q of the middle-section pile according to the curve trend um - And the positive limit bearing capacity Q of the lower section pile ud + ；
Step 6, loading the pile body, loading a jack in the second load box, forcing the upper section pile and the middle section pile to move oppositely, and obtaining according to a displacement monitoring systemThe displacement of the upper pile and the middle pile and the force obtained by the pressure sensor in the second load box are drawn, the load displacement curve graph of the upper pile and the middle pile is drawn, and the negative limit bearing capacity Q of the upper pile is obtained through curve trend uu - And the positive limit bearing capacity Q of the middle pile um + ；
Step 7, loading the pile top, loading a jack in the first load box, forcing the upper section pile and the middle section pile to generate opposite displacement, drawing a load displacement curve graph of the upper section pile and the middle section pile according to the displacement of the upper section pile and the middle section pile obtained by the displacement monitoring system and the force obtained by the pressure sensor in the first load box, and obtaining the positive limit bearing capacity Q of the upper section pile according to the curve trend uu + And the negative limit bearing capacity Q of the middle pile um - ；
And 7, calculating the vertical compression-resistant total ultimate bearing capacity of the pile, wherein the calculation formula is as follows:
Q pressing And G is the total dead weight of the pile.
2. The reverse self-balancing pile test method according to claim 1, wherein: in step 1, the two equilibrium point determination methods are as follows:
step 1.1, firstly, primarily dividing the pile into an upper-section pile and a lower-section pile, and determining a first balance point through a balance point calculation formula, wherein the calculation formula is as follows:
in the above description, i represents the number of layers of soil layers around the pile, lambda i The weight correction coefficient of the soil layer around the pile of the upper section pile is represented, u represents the circumference of the pile body, and l i Representing the corresponding sectional length of the soil layer around the pile, q ik Representation and l i Standard value of frictional resistance corresponding to pile side and soil layer, G table aboveThe dead weight of the upper section pile is shown, ap represents the sectional area of the pile end, qr represents the allowable bearing capacity of soil at the pile end, and the left summation formula
Pile side resistance summation representing upper pile, right summation formula->
Representing pile side resistance summation of the lower section pile;
and 1.2, after a first balance point is obtained by calculating the length of the upper pile, selecting a point in the middle of the preliminary lower pile according to an empirical value as a second balance point, and dividing the preliminary lower pile into two sections so as to obtain an upper pile, a middle pile and a lower pile.
3. The reverse self-balancing pile test method according to claim 1, wherein: sealing plates are arranged at the top of the lower section pile, the bottom of the middle section pile, the top of the middle section pile, the bottom of the upper section pile and the top of the upper section pile; and the lower end of the anchor cable of the counter-force anchoring system freely penetrates through the anchor cable sleeve and is then fixed on the end sealing plate at the top of the middle-section pile.
4. A reverse self-balancing pile test method according to claim 3, wherein: the displacement monitoring system comprises four displacement rods and a dial indicator arranged at the tops of the corresponding displacement rods and used for measuring displacement rod movement displacement, the first displacement rod freely penetrates through the upper section pile and then is fixed on the upper section pile bottom end sealing plate, the second displacement rod freely penetrates through the upper section pile and then is fixed on the middle section pile top end sealing plate, the third displacement rod freely penetrates through the upper section pile and the middle section pile and then is fixed on the middle section pile bottom end sealing plate, and the fourth displacement rod freely penetrates through the upper section pile and the middle section pile and then is fixed on the lower section pile top end sealing plate.
5. A reverse self-balancing pile test method according to claim 3, wherein: the lower end of the anchor cable is fixed on the end sealing plate at the top of the middle pile through a steel shaft bolt.
6. The reverse self-balancing pile test method according to claim 1, wherein: the central axes of the jacks and the pressure sensors in the three load boxes are coincident with the central axis of the pile.
7. The reverse self-balancing pile test method according to claim 6, wherein: the pressure sensor is a cylindrical pressure sensor with unbalanced load resistance.
8. The reverse self-balancing pile test method according to claim 1, wherein: in the step 5 to the step 7, the jack in the load box is loaded in a grading loading mode, and each grade of loading is 1/10-1/15 of the estimated limit load.
9. The reverse self-balancing pile test method according to claim 1, wherein: in the steps 5 to 7 of the present invention,
the displacement of each hour is not more than 0.1mm and appears twice continuously, and the relative stability is considered to be achieved, and the load of the next stage is added; when one of the download conditions occurs, the loading can be terminated;
(1) The limit loading value has been reached;
(2) Under the action of a certain level of load, the displacement of the pile is 5 times of the displacement of the pile under the action of a previous level of load;
(3) Under the action of a certain level of load, the displacement of the pile is 2 times larger than that under the action of a previous level of load, and the pile is not relatively stable after 24 hours;
(4) The accumulated pulling-up amount exceeds 100mm.
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| CN110453733B (en) * | 2019-09-18 | 2023-12-29 | 国网安徽省电力有限公司建设分公司 | Pile foundation bearing capacity self-balancing test device and test method in model test |
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| CN215947940U (en) * | 2021-03-16 | 2022-03-04 | 广西岩土新技术有限公司 | Double-load-box self-balancing test pile loading device |
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