Pile construction method

Abstract

To provide a pile construction method for easily determining the maximum bearing capacity of each pile by a loading test using a pile construction machine and economically setting allowable bearing capacity to a long-term load on the basis of the actually found maximum bearing capacity in foundation pile construction of a small-scale building such as a detached house.SOLUTION: The method includes a process of pushing a pile (a) to a predetermined depth by a pile construction machine 1 on the basis of a ground investigation result, applying a load to a pile head by using the pile construction machine 1 as a reaction force, and determining the maximum bearing capacity of the pile (a) on the basis of the load and a settlement amount. Further, in principle, a step of setting the long-term allowable support force of the pile by using a predetermined safety factor of about 1.5 to 2.0 with respect to the maximum support force is performed for all or almost all piles to be constructed. According to the present invention, the actual maximum bearing capacity of each pile (a) is directly confirmed, and the pile can be designed with a safety factor smaller than a conventional one, so that the construction period can be shortened, the foundation can be designed with high accuracy, and the construction cost can be greatly reduced.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a method for determining the bearing capacity of piles and a construction method for confirming the bearing capacity of piles that are constructed primarily as foundation piles for small buildings such as detached houses. By conducting a static pile head load test on the piles to be constructed using a simple device, the bearing capacity of the piles can be determined easily and accurately, and the allowable bearing capacity of the piles against long-term loads can be set within the range of the pile's maximum bearing capacity without being bound by the legally binding safety factor of 3. [Background technology]

[0002] Static load tests on piles are conducted under loading conditions similar to those of actual buildings, so highly reliable data on the bearing capacity of piles can be obtained, such as being able to directly confirm the load-subsidence relationship of the piles and the maximum bearing capacity (ultimate bearing capacity) of the piles.

[0003] For this reason, the general rule is to check the bearing capacity of a pile by conducting a vertical load test on the pile at the site after it has been buried, and when designing piles to be installed as foundation piles in particular, it is desirable to conduct a static load test on all piles to be installed.

[0004] However, for the foundation piles of small buildings such as detached houses, prefabricated piles such as steel piles or reinforced concrete piles are mainly installed, and depending on the size of the building, around 30 to 50 prefabricated piles are generally installed. Therefore, if load tests are conducted on all the piles for one building, not only will the pile driving work be prolonged, but it will also be necessary to arrange various equipment for pile head load tests, such as loading devices and reaction devices for applying loads to the pile heads.

[0005] Furthermore, in the case of ordinary buildings such as apartment buildings, even when piles with a diameter of approximately 500 mm are installed, a load of several hundred tons is required. Therefore, the construction of reaction piles for load tests, the assembly of load test equipment, and the execution of load tests require a large amount of money and time, making them uneconomical and therefore not currently carried out.

[0006] Incidentally, as an alternative construction method to conducting vertical load tests on piles at each site, a method that is commonly used is to conduct a large number of pile load tests (clinical tests) on different ground to investigate the relationship between the N-value of the ground and the bearing capacity of the pile (the tip bearing capacity of the pile and the surface friction force of the pile), and then have the test results reviewed by a performance evaluation organization designated by the government, such as the Building Center of Japan, thereby constructing piles without conducting load tests at each site.

[0007] Furthermore, for example, Patent Document 1 discloses an invention for a method for confirming the bearing capacity of a pile, which can be carried out cost-effectively despite being a static load test, by conducting a vertical load test on the pile using a pile construction machine.

[0008] The invention disclosed in Patent Document 1 is a method in which, since it would take a long time to conduct a vertical load test on each and every pile, a vertical load test is carried out to the end on a representative pile to examine the load-subsidence characteristics of the pile, and then a load test is carried out partway on another pile to predict the load-subsidence relationship of this pile from the test data obtained up to that point.This method does not require various equipment for load tests, such as load-applying devices and reaction devices, and is said to be able to shorten the time required for load tests. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-069992 [Patent Document 2] Patent Publication No. 2021-031858 [Patent Document 3] Japanese Patent Application Publication No. 2020-101069 [Patent Document 4] Special Publication No. 63-44890 Summary of the Invention [Problem to be solved by the invention]

[0010] Construction based on official performance certification, such as an evaluation report, is extremely easy to use because it does not require any load tests at each site. However, the bearing capacity of the piles specified in the official certification had to be designed with a design safety factor of 3, which is set to take into account variations in the ground N-value and variations in the pile materials.

[0011] For this reason, even if the bearing capacity of a pile is, for example, 1000KN, the maximum long-term allowable bearing capacity of the pile is 1000 / 3 = 330KN, and since values ​​greater than this cannot be applied as the long-term allowable bearing capacity of the pile, extremely uneconomical designs were forced.

[0012] Furthermore, the invention of the method for confirming the bearing capacity of piles in Patent Document 1 uses a pile construction machine to carry out a vertical load test on a specific pile to the end, but loads are only applied partway through on other piles, and the load-settlement relationship is predicted from the data of the load test on the specific pile. In other words, the aim is to shorten the overall construction period for pile construction, including the load test, and to make construction more economical by shortening the time for the load test, but it does not provide a method for evaluating the safety factor of the bearing capacity of a pile.

[0013] The present invention has been made to solve the above problems, and aims to provide a pile construction method that, in principle, allows for pile head load tests to be conducted on all piles to be constructed, thereby making it possible to easily and accurately determine the bearing capacity of each pile, and that makes it possible to set the allowable bearing capacity of the pile against long-term loads within the range of the pile's maximum bearing capacity, without being bound by the legally binding safety factor of 3. [Means for solving the problem]

[0014] The pile construction method of the present invention is a pile construction method that checks the bearing capacity of piles that are mainly constructed as foundation piles for small buildings such as detached houses, and (1) The process of driving piles to the design depth using a pile construction machine based on a preliminary ground survey of the construction site. (2) After the pile is driven to the design depth, a load is applied to the pile head using the pile construction machine as a reaction force, and the maximum bearing capacity of the pile is determined based on the applied load. (3) A process of calculating the long-term allowable bearing capacity of the pile using a specified safety factor less than 3, which is required when no load test is conducted, for the maximum bearing capacity, and confirming that the pile has the specified design bearing capacity. (4) If it is determined in step (3) above that the pile does not have the specified design bearing capacity, the step of further pushing the pile in or redoing the construction of the pile. The method is characterized in that the steps (1) to (4) are repeated for a plurality of piles to be installed at the site.

[0015] In principle, steps (1) to (4) above should be performed on all or almost all piles to be installed. However, if the target ground is good, they may be performed on only some of the piles. Furthermore, the present invention can be implemented not only by a normal load test in which a static load is applied to the pile head, but also by a dynamic load test in which a weight is dropped onto the pile head and driven into the pile, or by a load test in which the load applied by a dynamic method such as embedding the pile using a vibrating vibrator is converted into a static load.

[0016] Here, the predetermined safety factor smaller than 3 required when no load test is conducted can be set, for example, in the range of 1.5 to 1 / 2.0, and the allowable bearing capacity for the long-term load acting on the pile based on this safety factor can be set in the range of 1 / 1.5 to 1 / 2.0 of the maximum bearing capacity of the pile determined in (2) above. This safety factor is also used to calculate the short-term allowable bearing capacity (allowable bearing capacity during an earthquake) when no load test is conducted, and can be said to be a value that does not cause any particular problems as a safety factor.

[0017] The present invention is not intended for large diameter piles that cannot be subjected to load tests, but for small piles and small diameter piles, and is particularly suitable for confirming the bearing capacity of piles installed as foundation piles for small buildings such as detached houses.

[0018] For example, if a pile with a diameter of about 100 mm is used instead of 500 mm, the tip bearing capacity of the pile is proportional to the square of the pile diameter, so if a pile with a diameter of 500 mm has a pile bearing capacity of 3000 KN, a pile with a diameter of 100 mm will have a pile bearing capacity of 3000 KN / (5 x 5) = 120 KN.

[0019] In contrast, even small pile driving machines weigh around 100-200KN, so a load test of around 120KN can be carried out with a conventional pile driving machine. This makes it possible to carry out load tests on all piles using the pile driving machine, and the results can be used to determine the bearing capacity of the piles. Also, if the weight of the pile driving machine alone is insufficient to provide the reaction force required to drive the piles in, the auger provided on the pile driving machine can be inserted into the ground to provide the reaction force.

[0020] The specific safety factor can be determined according to the ground conditions, for example, based on the results of numerous test constructions under different ground conditions and actual pile construction.

[0021] Regarding the determination of the maximum bearing capacity of the pre-construction pile in step (2) above, the amount of settlement due to the load applied to the head of the pre-construction pile using a pile construction machine as a reaction force can be measured, and the determination can be made based on the load-settlement curve that shows the relationship between the applied load and the amount of settlement of the pre-construction pile.

[0022] A common method for determining the maximum bearing capacity is to measure the amount of settlement of the pile due to the applied load when a load is applied to the head of the pile using a pile construction machine as a reaction force, to obtain a load-settlement curve that shows the relationship between the applied load and the amount of settlement, and to determine the maximum bearing capacity of the pile from the load-settlement curve.

[0023] However, the determination of the maximum bearing capacity of a pile is not limited to the case where the determination is based on the load-settlement curve, and the method of determining the maximum bearing capacity of a pile in the present invention is not particularly limited.

[0024] Other methods for determining maximum bearing capacity include using the maximum load in a load test as the maximum bearing capacity, or using the maximum bearing capacity when the settlement reaches 10% of the pile diameter.In addition to the method of determining it from the peak load on the load-settlement curve mentioned above, other methods that can be used include using the maximum value of the load applied by the construction machinery, or using the maximum bearing capacity when the settlement reaches 10% of the pile diameter.

[0025] When constructing buildings or condominiums, preliminary soil investigations at construction sites are usually carried out using standard penetration tests (SPT tests), while when constructing houses, screw weight penetration tests (SWS tests) are generally used. However, screw driver sounding tests (SDS tests) or standard penetration tests (SPT tests) may also be used ("SDS" is a registered trademark). [Effects of the Invention]

[0026] The present invention uses the same construction machine as the one used to construct the piles, and in principle, performs static pile head load tests on all piles to be constructed, which has the effect of accurately determining the bearing capacity of each pile and significantly shortening the construction period for pile construction, including the pile head load test.

[0027] Furthermore, since the present invention involves carrying out load tests, it is possible to set the allowable bearing capacity of the pile against long-term loads within a safety factor range of 1.5 to 2.0, i.e., within a range of 1 / 1.5 to 1 / 2.0, rather than 1 / 3 of the maximum bearing capacity (ultimate bearing capacity) of the pile when the safety factor is set to 3, thereby enabling the design of foundation piles to be carried out extremely economically. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a side view of a pile construction machine that constructs prefabricated piles. [Figure 2] FIG. 1 is a side view showing a method for performing a pile head load test on a precast pile using a pile construction machine. [Figure 3] FIG. 1 is a diagram showing a load-sinkage curve. DETAILED DESCRIPTION OF THE INVENTION

[0029] Figures 1-3 show an embodiment of the present invention. In the figure, the symbol A denotes a prefabricated pile used as a foundation pile for a small building such as a detached house. For the prefabricated pile A, steel piles or reinforced concrete piles with a diameter of about 100 to 250 mm are used.

[0030] Furthermore, reference numeral 1 denotes a pile construction machine (pile driver) that constructs prefabricated piles I, and the pile construction machine 1 is, for example, a push-type pile construction machine that pushes prefabricated piles I into the ground using a hydraulic jack or the like that the pile construction machine 1 is equipped with, and a medium-sized pile construction machine ranging in size from that of a building is used.

[0031] Symbol 2 is a load-loading device that applies load to the pile head of the prefabricated pile (i) using a jack or the like provided on the pile construction machine 1, and is also a load measuring device for measuring the load, which is usually mounted on the pile construction machine 1.

[0032] The symbol 3 denotes a pile head settlement measuring device for measuring the amount of settlement δ of the pile head of prefabricated pile I due to the load P applied to the pile head of prefabricated pile I, and is composed of, for example, a gauge 3a attached to the head of prefabricated pile I and graduated in the axial direction (vertical direction) of the prefabricated pile I, and an auto-level 3b installed to the side of it at a distance from the gauge 3a and reading the scale of the gauge 3a as the pile head settles.

[0033] In this configuration, a method for checking the bearing capacity of the precast pile A will now be described. (1) The prefabricated pile I to be constructed first is erected into the pre-set pile core and pushed to the designed depth by the hydraulic jack (not shown) equipped on the pile construction machine 1 (see Figure 1).

[0034] (2) Next, a predetermined load P is applied to the head of the prefabricated pile A that has been driven to the design depth by a hydraulic jack provided on the same pile construction machine 1. If the reaction force is insufficient with the weight of the pile construction machine 1 alone, the reaction force can be obtained by inserting an auger (not shown) provided on the pile construction machine 1 into the ground.

[0035] (3) Next, the amount of settlement δ of the precast pile I after a certain time has elapsed since the load P was applied is measured by the settlement measuring device 3. In this case, the amount of settlement δ of the pile head of the precast pile I can be measured in real time by reading the scale of the gauge 3a, which has descended as the precast pile I sinks, using the auto-level 3b.

[0036] Furthermore, the application of load P to the head of precast pile (i) and the measurement of the settlement δ of precast pile (i) due to the applied load P are carried out for each applied load P while increasing the applied load P in stages. When the head settlement δ of precast pile (i) due to the applied load P exceeds a specified amount (for example, 10% of the pile diameter of precast pile (i)), the applied load P at that depth is taken as the maximum bearing capacity (ultimate bearing capacity) of the precast pile (i). In addition, a load-settlement curve is calculated that shows the relationship between the load P applied to the head of precast pile (i) in parallel with the pushing of precast pile (i) and the head settlement δ due to the load P (see Figure 3).

[0037] In this way, all precast piles (i) are installed in order at each pile core, and a load-settlement curve showing the relationship between the applied load (P) and the pile head settlement (δ) is obtained for all precast piles (i).

[0038] (4) The maximum bearing capacity (ultimate bearing capacity) of each precast pile can be estimated from the load-settlement curve obtained.

[0039] In addition, the allowable bearing capacity of precast piles (I) against long-term loads can be set within a safety factor range of 1.5 to 2.0, rather than 1 / 3 of the maximum bearing capacity (ultimate bearing capacity) of the pile.

[0040] Figure 3 shows the pile head load-settlement curve obtained by the static load test of the present invention. In the figure, symbol a represents the maximum bearing capacity (ultimate bearing capacity) of precast pile A, which is the load P at the point when the settlement δ of precast pile A due to the load P exceeds the specified amount (10% of the pile diameter of precast pile A).

[0041] Furthermore, the symbol b is the long-term allowable bearing capacity of the precast pile A, and can be set in the range of 1 / 1.5 to 1 / 2.0, rather than 1 / 3 of the maximum bearing capacity (ultimate bearing capacity) of the pile.

[0042] It is desirable to carry out the steps (1) to (4) for all piles to be constructed, but in cases where the construction ground is good, it is possible to carry out the steps only for some of the piles. [Industrial Applicability]

[0043] In principle, the present invention allows for more accurate determination of the bearing capacity of foundation piles by conducting pile head load tests on all piles to be constructed, and also allows for extremely economical design of foundation piles by setting the allowable bearing capacity for long-term loads of the piles in the range of a safety factor of 1.5 to 2.0, i.e., 1 / 1.5 to 1 / 2.0, rather than 1 / 3 of the maximum bearing capacity (ultimate bearing capacity) of the pile when the safety factor is 3. [Explanation of symbols]

[0044] 1 Pile construction machinery 2 Loading device and load measuring device 3 Pile head settlement measuring device 3a gauge 3b Auto Level B. Prefabricated piles P Applied load δ Pile cap settlement

Claims

1. (1) The process of driving piles to the design depth using a pile construction machine based on a preliminary ground survey of the construction site. (2) After the pile is driven to the design depth, a load is applied to the pile head using the pile construction machine as a reaction force, and the maximum bearing capacity of the pile is determined based on the applied load. (3) A process of calculating the long-term allowable bearing capacity of the pile using a specified safety factor less than 3, which is required when no load test is conducted, for the maximum bearing capacity, and confirming that the pile has the specified design bearing capacity. (4) If it is determined in step (3) above that the pile does not have the specified design bearing capacity, the step of further pushing the pile in or redoing the construction of the pile. and repeating steps (1) to (4) for a plurality of piles to be constructed at the site.

2. 2. The pile construction method according to claim 1, wherein the predetermined safety factor is set in the range of 1.5 to 1 / 2.0, and the allowable bearing capacity for the long-term load acting on the pile is set in the range of 1 / 1.5 to 1 / 2.0 of the maximum bearing capacity of the pile.

3. 2. The pile construction method according to claim 1, wherein the maximum bearing capacity of the pile is determined by measuring the amount of subsidence caused by the load applied to the head of the pile using the pile construction machine as a reaction force, and based on a load-subsidence curve showing the relationship between the load and the amount of subsidence of the pile.

4. 4. The pile construction method according to claim 1, wherein steps (1) to (4) are repeated for all or almost all of the piles to be constructed.

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