CN113529815B - On-site test method for testing negative frictional resistance neutral points of PHC pipe piles in soft soil areas - Google Patents
On-site test method for testing negative frictional resistance neutral points of PHC pipe piles in soft soil areas Download PDFInfo
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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
- E02D5/58—Prestressed concrete piles
Abstract
The invention discloses a field test method for testing negative friction neutral points of PHC pipe piles in a soft soil area, which comprises the following steps: 1) stratigraphic layering: drilling by a drilling machine in a spiral drilling mode to obtain stratum layering information of soil around the pile; 2) burying layered settlement equipment: the inclined pipe is horizontally placed on the ground, the inclined pipe is sequentially clamped into the settling rings from the bottom, stratum information obtained by the number and the positions of the settling rings is determined, and the settling plate is fixed on the pile head; 4) stacking: stacking and loading a region enclosed by the pile head and the inclined tube, wherein a stacking and loading soil body is cohesive soil, and rolling by using a rolling machine while stacking and loading until the stacking and loading height is reached; 5) and (3) settlement data acquisition: connecting a layered settlement probe and a layered settlement data acquisition instrument with two ends of a measuring line respectively, vertically lowering the layered settlement probe into an inclined tube, and repeatedly testing layered settlement data; 6) and (6) calculating and analyzing. The method is easy to implement and simple and convenient to operate, and can effectively solve the problem of distortion of the negative friction resistance neutral point of the PHC tubular pile obtained by indoor tests at present.
Description
Technical Field
The invention belongs to the technical field of pile foundation engineering in geotechnical engineering, and particularly relates to a field test method for testing negative frictional resistance neutral points of a PHC pipe pile in a soft soil area, which is suitable for a test for determining the negative frictional resistance neutral points of the pile.
Background
In recent years, more and more high-rise buildings are built, shallow foundations cannot meet the requirements of structures on foundation strength, deformation and the like, and pile foundations are widely applied due to the advantages of good integrity, high rigidity, small settlement, capability of bearing larger horizontal load and vertical load and the like. PHC tubular pile, namely prestressed high-strength concrete tubular pile. The hollow cylindrical concrete prefabricated member is prepared by adopting a pre-tensioned prestressing centrifugal forming process and steam curing at about 180 ℃ under 10 atmospheric pressures (about 1.0 Mpa), the standard section length is 10m, the diameter is 400-800 mm, and the strength grade of concrete is not less than C80. In soft soil areas, particularly in under-consolidated soft soil areas, negative frictional resistance may be adversely affected around the body of the PHC pile. The reason for the generation of the negative frictional resistance is that the upper load is transmitted to the foundation through the PHC tubular pile body, the vertical load is born by the frictional resistance of the pile side soil and the resistance of the pile end soil, and when the settlement of the pile periphery soil which is larger than that of the foundation pile is generated under the actions of self-weight consolidation, ground load and the like, the pile is subjected to pull-down load, namely negative frictional resistance. Obviously, negative frictional resistance is unfavorable for the stake, can make the effective bearing capacity of foundation pile reduce, makes the basis produce uneven settlement, can make the pile body destroy when serious, is the huge hidden danger of pile foundation engineering.
The neutral point is the characteristic point of the change of the relative displacement of the pile body and the soil around the pile, the positive and negative friction force, the stress strain and the axial pressure along the pile body, and is an important parameter for determining the negative friction force of the pile foundation. To analyze the negative frictional resistance generated by the pile, the center point location must first be determined. Currently, the determination of the neutral point is often determined by an empirical formula, for example, technical specification of building pile foundation (JGJ94-2008) shows an empirical determination method of the neutral point depth Ln of different bearing layers, and for silt, the neutral point is located at 0.5-0.6 times the pile length. However, because the neutral point has many influence factors, such as soil layer properties, pile type, etc., the neutral point is determined by an empirical formula, which may cause an erroneous result and adversely affect the pile foundation engineering. Although some scholars adopt a theoretical method and a numerical simulation method to analyze the position of the neutral point, the problems that the stress state and the construction working condition of a complex soil body of an actual project cannot be truly simulated and the project practice cannot be known by the theory still exist. In order to solve the problem, some scholars also invent a negative friction neutral point test method or a calculation method (for example, patent 201610139233.9), however, most of the methods are indoor model groove tests, and the actual soil layer properties on site cannot be truly reflected, if the negative friction neutral point tests under different combination conditions are required to simulate the influence factors of different pile diameters, pile distances and the like, a large number of model tests are required, the operation range is wide, the workload is high, the working efficiency is reduced, and the test cost is increased. On the other hand, the method for determining the negative friction neutral point of the pile is obviously based on field tests, although some invention patents (such as invention patents 201410005769.2 and 202011180544.2) adopt field test methods, the settlement of the pile is mostly determined by carrying out inverse calculation on the stress of a pile body, the calculated neutral point is not actually measured and has certain errors, and the methods are generally too complicated, and the layered settlement in the soil is not easy to measure.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a field test method for testing the negative friction neutral point of the PHC pipe pile in the soft soil area, is easy to implement and simple and convenient to operate, and can effectively solve the problem of distortion of the negative friction neutral point of the PHC pipe pile obtained by indoor test or theoretical calculation at present.
In order to achieve the purpose, the invention adopts the following technical measures:
a field test method for testing a PHC pipe pile negative friction neutral point in a soft soil area comprises the following steps:
(1) stratigraphic layering: and (3) extending the diagonal line of the square pile head outwards to obtain the position of the layered settlement of the soil around the tested pile, and drilling by using a drilling machine in a spiral drilling manner to obtain the stratum layered information of the soil around the pile.
(2) Burying layered settlement equipment: the method comprises the following steps of (1) horizontally placing a first inclinometer pipe on the ground, sequentially clamping settlement rings from the bottom, determining the number and the positions of the settlement rings according to stratum information obtained in the step (1), clamping each set of settlement rings in the same method, clamping the settlement rings into preset positions along clamping grooves of the first inclinometer pipe, clamping a baffle above the first settlement rings, winding three steel claws connected to the first settlement rings for one circle by using water soluble ropes, cleaning holes by using a drilling machine in a spiral drilling mode again, vertically placing the first inclinometer pipe into the drilled holes, filling the drilled holes with fine sand (common), and vertically connecting a second inclinometer pipe upwards by using an inclinometer pipe joint for the first inclinometer pipe.
(3) Embedding a pile head settlement plate (common): the surface of the pile head is shoveled by a shovel, the settlement plate is placed on the surface of the pile head, the settlement plate is aligned with the center of the pile head, four expansion screws are driven into four corners of the settlement plate, the settlement plate is fixed on the pile head, and a first steel pipe is connected above the center of the settlement plate through welding.
(4) Stacking: pile head and first deviational survey pipe enclose into the region and pile and carry, pile and carry the soil body for the stickness soil, pile and carry the limit and roll with the bucker, pile and carry and adopt the heap year mode step by step, first layer heap soil is piled and is carried the back of accomplishing, connects first joint and connect the second steel pipe above first steel pipe, carries out the heap of second layer heap soil again, connects the second joint and connect the third steel pipe above the second steel pipe simultaneously. Until the height s (the height s is meter, s is P/N, P is the stacking load in kPa, N is the gravity of cohesive soil in kN/m)3) And finishing the stacking.
(5) And (3) settlement data acquisition: and during stacking, after each level of stacking is finished, testing the settlement of the PHC tubular pile by using an RTS100 type total station. The method comprises the steps of respectively connecting a C70 layered settlement probe and a CFC-40 layered settlement data acquisition instrument with two ends of a measuring line, vertically placing the layered settlement probe into a first inclination measuring pipe and a second inclination measuring pipe, taking an orifice as an elevation, making the layered settlement data acquisition instrument emit 'Du' sound when the layered settlement probe is intersected with a settlement ring, recording an indicated value on the measuring line, repeatedly testing the layered settlement data for 2-4 times, and averaging the indicated value recorded each time to obtain a layered settlement test result of soil around the pile. After the loading is finished, when the settlement delta h of the pile head is formedp(delta h) for settlement with soil around pilesWhen the standard of sedimentation stability is reached, the test is finished.
(6) Calculating and analyzing: settlement delta h of pile headpThe calculation formula is as follows:
⊿hp＝hp measurement-hp is a
In the form of (delta h)pIs the pile head settlement value; h isp measurementThe absolute value of the settlement of the pile head in the process of stacking and after stacking is shown; h isp is aFor piling or loading front pile headsAbsolute value of sedimentation.
Settlement delta h of soil around pilesThe calculation formula is as follows:
⊿hs＝hs measurement-hs preliminary
In the form of (delta h)sThe settlement value of the soil around the pile; h is a total ofs measurementTesting the settlement absolute value of the soil around the pile by using a layered settlement data acquisition instrument in the process of stacking and after the stacking; h iss preliminaryThe absolute value of the settlement of the soil around the pile is obtained by testing with a layered settlement data acquisition instrument before stacking.
Respectively drawing (delta h)p、⊿hsThe development of sedimentation over time t. Comparing delta h of each layer of soilsAnd (delta h)pFinding out delta hs>⊿hpAnd (delta h)s<⊿hpCorresponding soil depth h1And h2The calculation formula of the neutral point h of the negative frictional resistance of the PHC tubular pile is as follows:
h＝h1+(h2-h1)/2
in the formula, h is the depth of a neutral point; h is a total of1Is (delta) hs>⊿hpThe depth of the time; h is2Is (delta) hs<⊿hpThe corresponding depth.
And finally, obtaining h, namely the PHC tubular pile negative friction neutral point obtained by the field test method for testing the PHC tubular pile negative friction neutral point in the soft soil area.
In the field test method for testing the negative friction neutral point of the PHC tubular pile in the soft soil area, the diameter of the drilled hole in the step (1) is 100mm, and the depth of the drilled hole is equal to the pile length of the PHC tubular pile.
Further, the diameter of the first inclinometer pipe in the step (2) is 72mm, and the length of the first inclinometer pipe is equal to the pile length of the PHC pipe pile.
Further, in the step (2), the number of the sedimentation rings is equal to 2 multiplied by the number of the soil layers +1, and the clamping positions of the sedimentation rings are the boundary point of each layer of the stratum and the thickness position of 1/2 layers of each layer of the stratum.
Further, the sedimentation plate in the step (3) is made of steel and has the size of 0.5m multiplied by 5 mm.
Further, the height of each layer of mound in the step (4) is 0.5m, and the side length of the cross section of each layer of mound is equal to the pile distance which is formed by enclosing an area by the pile head and the first inclinometer pipe and expanding one time.
Further, the settlement stability standard in the step (5) is delta hp<0.01 m/day and delta hs<0.01 m/day
Preferably, the diagonal outward extension distance of the square pile head 1 in the step (1) is 0.2 times of the pile diameter.
Preferably, the data acquisition frequency during the stacking in the step (5) is 1 time/2 days after the stacking of each layer of soil is completed.
The technical scheme principle of the field test method for testing the negative frictional resistance neutral point of the PHC pipe pile in the soft soil area is as follows: the pile loading is utilized to simulate the actual working condition load, the depth equal to the settlement value of the pile head and the pile surrounding soil at different depths is found by monitoring the pile loading process and the settlement value of the pile head and the pile surrounding soil after the pile loading, and thus the negative friction resistance neutral point of the PHC tubular pile (prestressed high-strength concrete tubular pile) is obtained.
The technical measures of the six steps are that the key step (2) and the key step (3) mainly solve the technical problem that the negative friction resistance neutral point of the PHC tubular pile in the soft soil area is difficult to test, the test method principle is that the neutral point position is determined based on the depth with the equal settlement value of the pile head and the surrounding soil of the pile, and the principle is clear and accurate. In addition, the key step (6) solves the technical difficulty of inaccurate measurement of negative friction neutral points of PHC tubular piles in soft soil areas, and the neutral points obtained according to the technical scheme of the invention are determined values, which have higher accuracy than the neutral point range values based on technical Specifications for building pile foundations (JGJ94-2008) commonly used in the engineering field. Compared with the existing method for determining the negative frictional resistance neutral point of the PHC tubular pile, the technical progress of the invention is as follows: compared with a numerical analysis method, the technical scheme of the invention has the advantages of simple test method and clear principle, can truly simulate the negative friction neutral point of the PHC tubular pile in a real field under the actual working condition, and has stronger engineering applicability; compared with a standard experience method, the standard experience method can only obtain a range value, the technical scheme of the invention can obtain a fixed value, and the accuracy of the test result is higher; compared with an indoor model test method, the technical scheme of the invention can avoid the defect that the similarity ratio of the indoor model test is difficult to determine according to a field test, and the obtained result can be directly used for the design and construction of the pile foundation. Through a plurality of (5-10) tests, the test result is real and reliable, and the range value of the depth of the neutral point calculated based on the technical specification of the building pile foundation (JGJ94-2008) can be improved to an accurate determination value (for example, in a comparative test 2, the range values of the neutral point obtained by a standard method are 10-12 m and 12.5-15 m, and the results obtained by using the technical scheme of the invention are 10.05m and 14.25 m); the testing precision is higher, the precision (the highest precision is 1.0m) of the neutral point obtained by the standard method can be improved to 1.0cm, and the testing precision is improved by 100 times.
Compared with the prior art, the invention has the following advantages and effects:
the principle is clear, and the data accuracy is high. The technical scheme principle is based on the concept of the negative friction neutral point, and because the calculation method of the negative friction neutral point according to the building pile foundation technical specification (JGJ94-2008) obtains a group of range values, the method can obtain the accurate negative friction neutral point and has higher accuracy.
② the cost is low. All the test equipment and materials are common laboratory instruments and consumables, and can be recycled, so that the test cost is reduced.
And thirdly, the operation is simple. Large instruments are not constructed on the site, the instruments are convenient to assemble, the test method is simple and easy to implement, operation of professional technicians is not needed, and manpower and material resources are reduced.
And fourthly, the original PHC tubular pile is not adversely affected. The technical scheme of the invention does not damage the PHC pipe pile, and the hole sealing is also carried out on the test of the soil around the pile, thereby not generating adverse effect on the existing pile foundation.
And the test result is simple to analyze, and the working efficiency is improved. The testing result can be obtained by the tester only by hand without complex calculation, so that the working efficiency of the tester is improved.
And sixthly, the test data has wide application range. The test can obtain the negative friction resistance neutral point, can also obtain the settlement value of the pile foundation and the soil between the piles under the action of load, and the result can be used for evaluating the deformation rule of the foundation, thereby enlarging the application range of the test.
Drawings
FIG. 1 is an operation flow chart of a field test method for testing negative frictional resistance neutral points of PHC pipe piles in a soft soil area;
FIG. 2 is a schematic diagram showing the relative positions of a settlement plate of a pile head and a layered settlement test point of soil around the pile;
FIG. 3 is a schematic diagram of formation layering and settlement ring burying;
FIG. 4 is a schematic diagram of the field test method for testing the negative frictional resistance neutral point of the PHC pipe pile in the soft soil area, wherein the settlement ring in the step (2) is clamped into the first inclinometer pipe;
FIG. 5 is a schematic diagram of embedding of a pile head settlement plate in the step (3) in the field test method for testing the negative frictional resistance neutral point of the PHC pipe pile in the soft soil area;
FIG. 6 is a schematic diagram of the stacking load in step (4) in the field test method for testing the negative frictional resistance neutral points of the PHC pipe pile in the soft soil area;
fig. 7 is a schematic diagram of the test results of example 1 of a field test method for testing negative frictional resistance neutral points of PHC tubular piles in soft soil areas (a time-dependent development curve of pile head settlement);
fig. 8 is a test result diagram of the example 1 of the field test method for testing the negative frictional resistance neutral point of the PHC pipe pile in the soft soil area (the settlement of the soil around the pile at different depths along the time development curve);
fig. 9 is a schematic diagram of the test result of example 2 of the field test method for testing the negative frictional resistance neutral point of the PHC tubular pile in the soft soil area (the settling curve of the pile head along with time);
fig. 10 is a test result diagram of the example 2 of the field test method for testing the negative frictional resistance neutral point of the PHC pipe pile in the soft soil area (the sedimentation of the soil around the pile at different depths along the time development curve);
FIG. 11 is a schematic diagram showing the comparison of the test results of example 1 and the comparative test of a field test method for testing negative frictional resistance neutral points of PHC tubular piles in a soft soil area;
fig. 12 is a schematic diagram illustrating a principle of error generation of a comparative test result of a field test method for testing a negative frictional resistance neutral point of a PHC pipe pile in a soft soil area.
Wherein: 1-pile head, 2-settlement plate, 3 a-first layer of mound, 3 b-second layer of mound, 3C-third layer of mound, 4 a-first steel pipe, 4 b-second steel pipe, 4C-third steel pipe, 5 a-first inclinometer, 5 b-second inclinometer, 6-PHC pipe pile, 7 a-first soil layer, 7 b-second soil layer, 7 a-third soil layer, 8 a-first settlement ring, 8 b-second settlement ring, 8C-third settlement ring, 8 d-fourth settlement ring, 8 e-fifth settlement ring, 8 f-sixth settlement ring, 8 g-seventh settlement ring, 9 a-first joint, 9 b-second joint, 10 a-first expansion screw, 10 b-second expansion screw, 10C-third expansion screw, 10 d-fourth expansion screw, 11-100 type expansion instrument, 12-measuring line, 13-70-total station type settlement probe, and CFC-14-layered settlement probe, 15-pull-down load, 16-soil layer settlement contour line, 17-baffle, 18 a-first steel claw, 18 b-second steel claw, 18 c-third steel claw, 19-water soluble rope and 20-inclinometer pipe joint.
All of the above additional components are commercially available.
Detailed Description
In order to make the objects, contents and advantages of the present invention clearer, a field test method for testing negative friction neutral points of PHC tubular piles in soft soil areas according to embodiments of the present invention is further described in detail with reference to the accompanying drawings.
Example 1:
the test site of example 1 is an under-consolidated soft soil stratum, the soil layers are from top to bottom, the first layer is soft soil, and the layer thickness is about 10 m; the second layer of soil is clay, and the thickness of the layer is about 4 m; the third layer of soil is silty clay with a thickness of about 6 m. The PHC tubular pile has the pile diameter of about 0.5m, the pile spacing of about 3.0m, square arrangement, pile heads of about 1.5m, about 0.35m and about C30 concrete cast-in-place, and the basic pile length of about 20 m. The heaped soil body adopted in the test is compacted cohesive soil, the heaped loading height of the compacted soil is about 5m, the heaped loading is carried in grades, the total number is 10, and each grade is about 0.5 m.
As shown in fig. 1, a field test method for testing negative frictional resistance neutral points of PHC pipe piles in soft soil areas comprises the following steps:
(1) stratigraphic layering A: as shown in fig. 2, the diagonal line of the square pile head 1 extends outwards by 0.2 times of the pile diameter, namely the extension is about 10cm, the position of the layered settlement of the soil around the pile is tested, a hole is drilled by an XY-1A type drilling machine produced by China Yuejie corporation in a spiral drilling mode, the diameter of the drilled hole is about 100mm, the depth of the drilled hole is about 25m of the pile length of the PHC tubular pile 6, and the depth of the drilled soil sample is recorded, so that the stratum layered information of the soil around the pile is obtained.
As shown in fig. 3, the soil layers around the pile are subjected to stratum stratification, from top to bottom, the first soil layer 7a is soft soil with a layer thickness of about 10m, the second soil layer 7b is clay with a layer thickness of about 4m, and the third soil layer 7c is silty clay with a layer thickness of about 6 m.
(2) Burying of layered settlement equipment B: the first inclinometer pipe 5a with the diameter of about 72mm and the length equal to about 20m of the pile length of the PHC tubular pile 6 is horizontally placed on the ground, a plurality of groups of settlement rings are sequentially clamped into the bottom of the first inclinometer pipe 5a, the number and the positions of the settlement rings are determined according to the stratum information obtained in the step (1), specifically, the number of the settlement rings is equal to 2 multiplied by the number of soil layers +1, the clamping positions of the settlement rings are the boundary point of each layer of stratum and the 1/2 layer thickness position of each layer of stratum, as shown in FIG. 3, the number of the settlement rings of the embodiment 1 is 7, and the positions of the first settlement ring 8a to the seventh settlement ring 8g are respectively located at about 20m, about 17m, about 14m, about 12m, about 10m, about 5m and about 0m underground.
The manner of each settling ring is the same, and taking the step of clamping the first settling ring 8a as an example, as shown in fig. 4, the first settling ring 8a is clamped into a predetermined position (underground 20m) along the clamping groove of the first inclinometer pipe 5a, the baffle 17 is clamped above the first settling ring 8a, and the first steel claw 18a, the second steel claw 18b and the third steel claw 18c connected to the first settling ring 8a are wound by one turn with the water soluble rope 19. The rest of the second to seventh settling rings 8b to 8g are sequentially clamped according to the method and the preset positions. And (3) cleaning the hole by using a drilling machine in a spiral drilling mode again, vertically putting the first inclinometer pipe 5a into the drilled hole with the diameter of about 100mm, filling the drilled hole with fine sand, and vertically connecting the first inclinometer pipe 5a with the second inclinometer pipe 5b upwards by using an inclinometer pipe joint 20.
(3) Embedding a pile head settlement plate C: as shown in fig. 5, the surface of the pile head 1 is shoveled by a shovel, a steel settlement plate 2 having a size of about 0.5m × about 5mm is placed on the surface of the pile head 1, the settlement plate 2 is aligned with the center of the pile head 1, first expansion screws 10a, second expansion screws 10b, third expansion screws 10c, and fourth expansion screws 10d are driven into four corners of the settlement plate 2, the settlement plate 2 is fixed to the pile head 1, and the first steel pipe 4a is connected to the upper center of the settlement plate 2 by welding.
(4) And (4) stacking and loading D: as shown in fig. 6, pile head 1 and first inclinometer 5a are enclosed to form an area for piling, the piled soil is cohesive soil, rolling is carried out while piling, the piling adopts a step-by-step piling mode, the height of the first layer of piled soil 3a is about 0.5m, and the side length of the cross section is equal to the pile distance which is doubled by enclosing the area between pile head 1 and first inclinometer 5a and extending outwards.
After the first layer of the mound 3a is completely stacked, a first joint 9a is connected above the first steel pipe 4a and connected with a second steel pipe 4b, then the second layer of the mound 3b is stacked, and simultaneously, a second joint 9b is connected above the second steel pipe 4c and connected with a third steel pipe 4 c. And finishing the stacking until the height of the stacked load is about 4.0 m.
(5) And (4) settlement data acquisition E: during the stacking, after each level of stacking is completed, the settlement of the PHC tubular pile 6, i.e., the settlement test result of the pile head, is tested by using an RTS100 type total station 11 manufactured by suzhou yiguan instruments ltd.
The two ends of a measuring line 12 are respectively connected with a C70 type layered settlement probe 13 produced by Wuhan-based deep prospecting instrument research institute and a CFC-40 type layered settlement data acquisition instrument 14 produced by Wuhan-based deep prospecting instrument research institute, the layered settlement probe 13 is vertically placed in a first inclined measuring pipe 5a and a second inclined measuring pipe 5b, an orifice is used as elevation, when the layered settlement probe 13 is intersected with a settlement ring, the layered settlement data acquisition instrument 14 sends out 'Du' sound, an indicated value on the measuring line 12, namely the depth value of the actual settlement ring is recorded, the layered settlement data is repeatedly tested for 2 times or 3 times, and the average value of the depth value recorded each time is taken as the layered settlement test result of soil around the pile.
After the pile loading is finished, acquiring the settlement value of the pile head after the pile loading and the layered settlement value of soil around the pile according to the acquisition frequency of 1 time/2 days, and when the settlement of the pile head is (delta h)p(delta h) for settlement with soil around pilesWhen the average value is less than 0.01 m/day, the test is finished.
(6) Calculation and analysis F: settlement delta h of pile headpThe calculation formula is as follows:
⊿hp＝hp measurement-hp is a
In the form of (delta h)pIs the settlement value of the pile head; h isp measurementThe settlement absolute value is obtained by testing by using a total station 11 in the process of stacking and after stacking; h isp is aThe absolute value of the settlement obtained by the test of the total station 11 before the stacking is obtained.
Settlement delta h of soil around pilesThe calculation formula is as follows:
⊿hs＝hs measurement-hs is as
In the formula (delta h)sThe settlement value of the soil around the pile; h iss measurementThe absolute value of the settlement of the soil around the pile is obtained by testing with a layered settlement data collector 14 in the process of stacking and after stacking; h iss preliminaryThe absolute value of the settlement of the soil around the pile is obtained by testing with the layered settlement data acquisition instrument 14 before the pile is loaded.
Respectively drawing delta hp、⊿hsThe development of sedimentation over time t. Comparing delta h of each layer of soilsAnd (delta h)pFinding out delta hs>⊿hpAnd (delta h)s<⊿hpCorresponding soil depth h1And h2Calculating the neutral point h of the negative friction resistance of the PHC tubular pile according to the following formula:
h＝h1+(h2-h1)/2
in the formula, h is the depth of a neutral point; h is1Is (delta) hs>⊿hpThe depth of the time; h is2Is (delta) hs<⊿hpThe corresponding depth.
And finally, obtaining h, namely the PHC tubular pile negative friction neutral point obtained by the field test method for testing the PHC tubular pile negative friction neutral point in the soft soil area.
For example 1, according to the field test method for testing the negative friction neutral point of the PHC tubular pile in the soft soil area, a settlement time-dependent development curve (fig. 7) of the pile head and settlement time-dependent development curves (fig. 8) of soil around the pile at different depths are obtained, and the obtained negative friction neutral point of the PHC tubular pile is about 10.05m below the pile head.
Example 2:
in order to better test the general applicability of the field test method for testing the negative friction neutral point of the PHC tubular pile in the soft soil area, a soft soil stratum different from that in the embodiment 1 is selected, the test field in the embodiment 2 is a lake-phase soft soil stratum, the soil layers are respectively from top to bottom, the first layer is silt soft soil, and the layer thickness is about 12 m; the second layer of soil is silt, and the thickness of the layer is about 9 m; the third layer of soil is clay with the thickness of about 4 m. In addition, different from the pile diameter, the pile spacing and the pile length of the PHC pipe pile in example 1, the pile diameter of the PHC pipe pile in example 2 is about 0.6m, the pile spacing is about 4.0m, the basic pile length is about 25m, the PHC pipe pile is arranged in a triangular mode, the pile head of about 1.5m, about 0.35m is arranged on the pile top, and the pile head is cast in situ by using C30 concrete. The heaped soil body adopted in the test is compacted cohesive soil, the heaped loading height of the compacted soil is about 5m, the heaped loading is carried in grades, the total number is 10, and each grade is about 0.5 m.
As shown in fig. 1, a field test method for testing negative frictional resistance neutral points of PHC pipe piles in soft soil areas comprises the following steps:
(1) stratigraphic layering A: as shown in fig. 2, the diagonal line of the square pile head 1 extends outwards by 0.2 times of the pile diameter, namely the extension is about 12cm, the position of the layered settlement of the soil around the pile is tested, a hole is drilled by an XY-1A type drilling machine produced by China Yuejie corporation in a spiral drilling mode, the diameter of the drilled hole is about 100mm, the depth of the drilled hole is about 25m of the pile length of the PHC tubular pile 6, and the depth of the drilled soil sample is recorded, so that the stratum layered information of the soil around the pile is obtained.
As shown in fig. 3, the soil layers around the pile are subjected to stratum stratification, from top to bottom, the first soil layer 7a is silt soft soil with a layer thickness of about 12m, the second soil layer 7b is silt soil with a layer thickness of about 9m, the third soil layer 7c is clay with a layer thickness of about 4 m.
(2) Burying of layered settlement equipment B: the first inclinometer 5a with the diameter of 72mm and the length equal to the pile length 25m of the PHC tubular pile 6 is horizontally placed on the ground, multiple sets of settlement rings are sequentially clamped into the bottom of the first inclinometer 5a, the number and the positions of the settlement rings are determined according to the stratum information obtained in the step (1), specifically, the number of the settlement rings is equal to 2 × the number of soil layers +1, the clamping positions of the settlement rings are the boundary point of each layer of stratum and the 1/2 layer thickness position of each layer of stratum, as shown in fig. 3, the number of the settlement rings in embodiment 1 is 7, and the positions of the first settlement ring 8a to the seventh settlement ring 8g are respectively located at the positions of about 25m, about 23.5m, about 21m, about 16.5m, about 12m, about 6m and about 0m underground.
The manner of each settling ring is the same, and taking the step of clamping the first settling ring 8a as an example, as shown in fig. 4, the first settling ring 8a is clamped into a predetermined position (underground 20m) along the clamping groove of the first inclinometer pipe 5a, the baffle 17 is clamped above the first settling ring 8a, and the first steel claw 18a, the second steel claw 18b and the third steel claw 18c connected to the first settling ring 8a are wound by one turn with the water soluble rope 19. The rest of the second to seventh settling rings 8b to 8g are sequentially clamped according to the method and the preset positions. And (3) cleaning the hole by using a drilling machine in a spiral drilling mode again, vertically putting the first inclinometer pipe 5a into the drilled hole with the diameter of 100mm, filling the drilled hole with fine sand, and vertically connecting the first inclinometer pipe 5a with the second inclinometer pipe 5b upwards by using an inclinometer pipe joint 20.
(3) Embedding a pile head settlement plate C: as shown in fig. 5, the surface of the pile head 1 is shoveled by a shovel, a steel settlement plate 2 having a size of about 0.5m × about 5mm is placed on the surface of the pile head 1, the settlement plate 2 is aligned with the center of the pile head 1, first expansion screws 10a, second expansion screws 10b, third expansion screws 10c, and fourth expansion screws 10d are driven into four corners of the settlement plate 2, the settlement plate 2 is fixed to the pile head 1, and the first steel pipe 4a is connected to the upper center of the settlement plate 2 by welding.
(4) And (4) stacking and loading D: as shown in fig. 6, pile head 1 and first inclinometer 5a enclose into an area for piling, the piled soil is cohesive soil, rolling is carried out while piling, the piling adopts a step-by-step piling mode, the height of the first layer of piled soil 3a is 0.5m, and the side length of the cross section is the pile distance which is doubled by the area enclosed by pile head 1 and first inclinometer 5 a.
After the first layer of mound 3a is stacked, a first joint 9a is connected above the first steel pipe 4a and connected with a second steel pipe 4b, then the second layer of mound 3b is stacked, and simultaneously, a second joint 9b is connected above the second steel pipe 4c and connected with a third steel pipe 4 c. And finishing the stacking until the height of the stack reaches 4.0 m.
(5) And (4) settlement data acquisition E: during the stacking, after each level of stacking is completed, the settlement of the PHC tubular pile 6, i.e., the settlement test result of the pile head, is tested by using an RTS100 type total station 11 manufactured by suzhou yiguan instruments ltd.
The two ends of a measuring line 12 are respectively connected with a C70 type layered settlement probe 13 produced by the Wuhan base deep prospecting instrument research institute and a CFC-40 type layered settlement data acquisition instrument 14 produced by the Wuhan base deep prospecting instrument research institute, the layered settlement probe 13 is vertically placed in a first inclined measuring tube 5a and a second inclined measuring tube 5b, an orifice is taken as elevation, when the layered settlement probe 13 intersects with a settlement ring, the layered settlement data acquisition instrument 14 sends out 'beep' sound, an indicated value on the measuring line 12, namely the depth value of the actual settlement ring is recorded, the layered settlement data is repeatedly tested for 2 times or 4 times, and the average value recorded each time is taken as the layered settlement test result of the depth value of soil around the pile.
After the pile loading is finished, acquiring the settlement value of the pile head after the pile loading and the layered settlement value of soil around the pile according to the acquisition frequency of 1 time/2 days, and when the settlement of the pile head is (delta h)p(delta h) for settlement with soil around pilesWhen the average value is less than 0.01 m/day, the test is finished.
(6) Calculation and analysis F:
settlement delta h of pile headpThe calculation formula is as follows:
⊿hp＝hp measurement-hp is a
In the form of (delta h)pIs the settlement value of the pile head; h is a total ofp measurementThe settlement absolute value obtained by the test of the total station 11 in the process of stacking and after stacking；hp is aThe absolute value of the settlement obtained by the test of the total station 11 before the stacking is obtained.
Settlement delta h of soil around pilesThe calculation formula is as follows:
⊿hs＝hs measurement-hs preliminary
In the form of (delta h)sThe settlement value of the soil around the pile; h iss measurementThe absolute value of the settlement of the soil around the pile is obtained by testing with a layered settlement data collector 14 in the process of stacking and after stacking; h iss preliminaryThe absolute value of the settlement of the soil around the pile is obtained by testing the layered settlement data collector 14 before the pile is loaded.
Respectively drawing delta hp、⊿hsThe development of sedimentation over time t. Comparing delta h of each layer of soilsAnd (delta h)pFinding out delta hs>⊿hpAnd (delta h)s<⊿hpCorresponding soil depth h1And h2Calculating the neutral point h of the negative friction resistance of the PHC tubular pile according to the following formula:
h＝h1+(h2-h1)/2
in the formula, h is the depth of a neutral point; h is1Is (delta) hs>⊿hpThe depth of the time; h is2Is (delta) hs<⊿hpThe corresponding depth.
And finally, obtaining h, namely the PHC tubular pile negative friction neutral point obtained by the field test method for testing the PHC tubular pile negative friction neutral point in the soft soil area.
For example 2, according to the field test method for testing the negative friction neutral point of the PHC tubular pile in the soft soil area, a settlement time-dependent development curve (fig. 9) of the pile head and settlement time-dependent development curves (fig. 10) of the soil around the pile at different depths are obtained, and the obtained negative friction neutral point of the PHC tubular pile is about 14.25m below the pile head.
Comparative experiment 1:
in the field test method for testing the negative friction neutral point of the PHC pipe pile in the soft soil area, the selection of the position for testing the layered settlement of the soil around the pile in the stratigraphic layering in the step (1) has great influence on the settlement value of the soil around the pile, and indirectly influences the test precision. Therefore, comparative test 1 uses the same test ground layer and the same properties of the PHC pile and pile type of example 1, but uses different layered settlement positions of the soil around the pile, and for this position, example 1 extends outward 0.2 times the pile diameter for the diagonal line of square pile head 1, and comparative test 1 extends outward 0.3 times, 0.5 times, and 1.0 times the pile diameter for the diagonal line of square pile head 1. The experimental procedure and procedure for comparative experiment 1 were exactly the same as in example 1.
The neutral points of the negative friction resistance of the PHC tubular pile obtained by the comparative test 1 at different positions are respectively positioned at the positions 9.61m, 9.32m and 9.15m below the pile head. The results of comparative test 1 and example 1 are shown in FIG. 12.
Comparative experiment 2:
in order to compare the technical scheme of the invention with the advantages and disadvantages of a method for taking the negative friction neutral point of the PHC tubular pile commonly adopted in the prior art according to technical specification of building pile foundation (JGJ94-2008), a comparative test 2 adopts the same test stratum and the same properties of the PHC tubular pile and the pile type as those of example 1 and example 2, and adopts a formula calculation method, according to the method for taking the negative friction neutral point according to technical specification of building pile foundation (JGJ94-2008), "the supporting layer is cohesive soil and silt, and the depth of the neutral point is 0.5-0.6 times of the lower limit depth of the peripile settlement deformation soil layer", the neutral points of the negative friction resistance of the PHC tubular pile of the comparative test 2 are respectively located 10-12 m below the pile head (the same test conditions as those of example 1) and 12.5-15 m (the same test conditions as those of example 2).
Comparing example 1 with comparative test 1, it can be found that the selection of the position of the layered settlement of the soil around the pile has a large influence on the settlement value of the soil around the pile, and the farther the distance from the center of the pile, the smaller the center point of the negative friction resistance of the PHC pipe pile obtained by the test, and the mechanism is shown in fig. 12, that the pull-down load 15 caused by the negative friction resistance drives the PHC pipe pile 6 to sink and further drives the soil around the pile to sink, and the farther the soil layer settlement isoline 16 is located above the neutral point from the soil around the pile, i.e. the farther the test position of the layered settlement of the soil around the pile is located, the smaller the center point of the negative friction resistance of the PHC pipe pile obtained by the test is located, so as to ensure the accuracy of the test result, the test position of the layered settlement of the soil around the pile should be as close to the PHC pipe pile 6 as possible, but considering the influence of the size of the pile head 1 and the diameter of the first inclinometer 5a, the test position of the layered settlement of the soil around the pile proposed in example 1 is optimally selected as the diagonal extension of the square pile head 1 outward by 0.2 times.
According to the foregoing, the central points of negative friction resistance of the PHC tubular pile obtained in embodiments 1 and 2 are located 10.05m and 14.25m below the pile head, and the results obtained by the method for taking the value of the neutral point of negative friction resistance based on technical specification of building pile foundation (JGJ94-2008) of comparative test 2 are 10m to 12m and 12.5m to 15m, which indicates that the results obtained by using the technical scheme of the present invention meet the results required by the current technical specification.
The above embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention, and any simple modifications, changes and equivalent structural changes of the above embodiments according to the principles of the present invention still fall within the protection scope of the technical solution of the present invention.
Claims (6)
1. A field test method for testing a PHC pipe pile negative friction neutral point in a soft soil area comprises the following steps:
(1) stratigraphic layering: extending the diagonal line of the square pile head by 0.2 times of the pile diameter outwards to obtain the position of the layered settlement of the soil around the tested pile, and drilling by a drilling machine in a spiral drilling mode to obtain the stratum layered information of the soil around the pile;
(2) burying layered settlement equipment: horizontally placing the first inclinometer pipe on the ground, sequentially clamping the first inclinometer pipe into the settling rings from the bottom, determining the number and the positions of the settling rings according to the stratum information obtained in the step (1), clamping each set of settling rings in the same method, clamping the settling rings into a preset position along the clamping grooves of the first inclinometer pipe, clamping a baffle above the first settling rings, winding three steel claws connected to the first settling rings for one circle by using water-soluble ropes, cleaning holes by using a drilling machine in a spiral drilling manner again, vertically placing the first inclinometer pipe into the drilled holes, filling the drilled holes with fine sand, and vertically connecting the first inclinometer pipe with an inclinometer pipe joint upwards to form a second inclinometer pipe;
(3) embedding a pile head settlement plate: leveling the surface of a pile head by using a shovel, placing a settlement plate on the surface of the pile head, aligning the settlement plate with the center of the pile head, driving four expansion screws into four corners of the settlement plate, fixing the settlement plate on the pile head, and connecting a first steel pipe above the center of the settlement plate by welding;
(4) stacking: stacking and loading a region defined by a pile head and a first inclinometer pipe, wherein a stacking and loading soil body is cohesive soil, rolling by a rolling machine while stacking and loading, stacking and loading are carried out in a step-by-step stacking mode, after the first layer of stacking and loading is finished, a first joint is connected above a first steel pipe and connected with a second steel pipe, then stacking and loading of a second layer of stacking is carried out, meanwhile, a second joint is connected above the second steel pipe and connected with a third steel pipe until the stacking and loading reaches a height s, and the stacking and loading are finished;
(5) and (3) settlement data acquisition: during pile loading, after each level of pile soil is loaded, testing the settlement of the PHC tubular pile by using an RTS100 type total station, respectively connecting a C70 type layered settlement probe and a CFC-40 type layered settlement data acquisition instrument with two ends of a measuring line, vertically descending the layered settlement probe into a first inclinometer pipe and a second inclinometer pipe, taking an orifice as elevation, recording an indicated value on the measuring line by using the sound emitted by the layered settlement data acquisition instrument when the layered settlement probe is intersected with a settlement ring, repeatedly testing the layered settlement data for 2-4 times, averaging the indicated value recorded each time as a layered settlement test result of the pile soil, and after the pile loading is finished, settling h of the pile headp(delta h) for settlement with soil around pilesThe sedimentation stability standard is achieved, and the test is finished;
(6) calculating and analyzing: settlement delta h of pile headpThe calculation formula is as follows:
⊿hp= hp measurement-hp is a
In the form of (delta h)pIs the pile head settlement value; h isp measurementThe absolute value of the settlement of the pile head in the process of stacking and after stacking is shown; h isp is aIs the absolute value of the settlement of the pile head before piling and loading；
Settlement delta h of soil around pilesThe calculation formula is as follows:
⊿hs= hs measurement-hs preliminary
In the formula (delta h)sThe settlement value of the soil around the pile; h iss measurementThe settlement absolute value of the soil around the pile is obtained by utilizing a layered settlement data acquisition instrument to test in the process of stacking and after stacking; h iss preliminaryThe absolute value of the settlement of the soil around the pile is obtained by testing with a layered settlement data acquisition instrument before the pile is loaded;
respectively drawing delta hp、⊿hsComparing the delta h of each layer of soil with the settlement development curve of the time tsAnd (delta h)pFinding out delta hs>⊿hpAnd (delta h)s<⊿hpCorresponding soil depth h1And h2The calculation formula of the neutral point h of the negative frictional resistance of the PHC tubular pile is as follows:
h= h1+(h2-h1)/2
in the formula, h is the depth of a neutral point; h is1Is (delta) hs>⊿hpThe depth of the time; h is a total of2Is (delta) hs<⊿hpThe depth of the time;
and finally, obtaining h PHC pipe pile negative friction neutral points obtained by a field test method for testing the PHC pipe pile negative friction neutral points in the soft soil area.
2. The field test method for testing the negative frictional resistance neutral point of the PHC tubular pile in the soft soil area according to claim 1, which is characterized in that: the diameter of a hole drilled in the step (1) is 100mm, and the drilling depth is equal to the pile length of the PHC tubular pile.
3. The field test method for testing the negative frictional resistance neutral point of the PHC tubular pile in the soft soil area according to claim 1, which is characterized in that: the diameter of the first inclinometer pipe in the step (2) is 72mm, and the length of the first inclinometer pipe is equal to the pile length of the PHC pipe pile; in the step (2), the number of the sedimentation rings is equal to 2 multiplied by the number of the soil stratification layers plus 1, and the clamping positions of the sedimentation rings are the boundary point of each layer of stratum and the 1/2 layer thickness position of each layer of stratum.
4. The field test method for testing the negative frictional resistance neutral point of the PHC pipe pile in the soft soil area according to claim 1, which is characterized in that: the sedimentation plate in the step (3) is made of steel, and the size of the sedimentation plate is 0.5m multiplied by 5 mm.
5. The field test method for testing the negative frictional resistance neutral point of the PHC pipe pile in the soft soil area according to claim 1, which is characterized in that: in the step (4), the height of each layer of mound is 0.5m, and the side length of the cross section of each layer of mound is equal to the pile distance which is doubled by enclosing an area by the pile head and the first inclinometer pipe.
6. The field test method for testing the negative frictional resistance neutral point of the PHC tubular pile in the soft soil area according to claim 1, which is characterized in that: the settlement in the step (5) is delta hp<0.01 m/day and delta hs<0.01 m/day.
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