An in-situ static testing method for the bearing capacity of pile foundations of existing buildings

Abstract

This invention proposes an in-situ static testing method for the bearing capacity of existing building pile foundations. Static tests measure the relationship between pile cap settlement and external load N1. Finite element analysis is then used to determine the superstructure reaction force N2 for varying pile cap settlements. Finally, the pile foundation bearing capacity is calculated based on the static test results, the superstructure reaction force N2, and the deadweight N3. This method avoids damage to the superstructure during testing while also accounting for the impact of the superstructure reaction force due to pile cap settlement on the pile foundation bearing capacity test results.

Description

Technical Field

[0001] The present invention relates to the technical field of building measurement, in particular to an in-situ static detection method for the bearing capacity of pile foundations of existing buildings. Background Art

[0002] Testing the bearing capacity of completed pile foundations to ensure they meet design requirements is a prerequisite for ensuring the safe operation of the entire structure. However, existing pile foundation testing and standards are designed for individual pile foundations in new buildings. For renovation and expansion projects of existing buildings, pile foundation bearing capacity testing cannot be performed without dismantling and damaging the superstructure. Summary of the Invention

[0003] In order to overcome the defect in the above-mentioned prior art that pile foundation bearing capacity cannot be tested without dismantling and damaging the superstructure, the present invention proposes an in-situ static testing method for the bearing capacity of pile foundations of existing buildings, which can safely and quickly test the bearing capacity of pile foundations without destroying the existing structure.

[0004] The present invention proposes an in-situ static testing method for the bearing capacity of pile foundations of existing buildings, comprising the following steps:

[0005] S1. Excavate and cover the soil around the foundation;

[0006] S2. Arrange settlement observation points on the cap; select deformation monitoring targets among the columns surrounding the cap and deploy deformation monitoring points on these targets; and arrange crack observation points on the superstructure. The superstructure includes the portion of the cap exposed above the ground and the building structure supported by the cap.

[0007] S3. Perform a cap load test and record the external load data N1, which is the maximum load that can be applied to the cap during the cap load test.

[0008] Preferably, in S2, a total station is set at the deformation monitoring point, and the deformation of the deformation monitoring point is measured by the total station midpoint method trigonometric height measurement; and during the measurement process, the column farthest from the loading area in the same building is used as the reference point.

[0009] Preferably, the external load data N1 is the smaller value of the following two items:

[0010] C. The maximum external load that can be applied during the pile cap load test, that is, the external load applied during the pile cap load test when the pile cap settlement reaches the set settlement value or the deformation of the deformation monitoring point reaches the set deformation value;

[0011] D. The external load applied by the pile load test when the maximum crack width at the crack observation point reaches the set limit.

[0012] Preferably, a crack observation point is provided at the beam end adjacent to the pedestal in the superstructure.

[0013] Preferably, after S3, the following steps are further included:

[0014] S4. Establish a finite element analysis model of the upper structure of the pedestal;

[0015] S5. Calculate the superstructure reaction force N2 caused by the pile cap settlement using the finite element model;

[0016] S6. Calculate the superstructure deadweight load N3, i.e., the deadweight of the superstructure;

[0017] S7. Calculate the pile bearing capacity of the cap as (N1-N2+N3) / (kn), where k is the safety factor and n is the number of piles under a single cap.

[0018] Preferably, k takes a value of 2.0.

[0019] The advantages of the present invention are:

[0020] (1) The present invention proposes an in-situ static testing method for the bearing capacity of pile foundations of existing buildings. The method measures the relationship between the settlement of the pile cap and the external load N1 through a static test. Then, the reaction force N2 of the superstructure at different settlements of the pile cap is obtained through finite element analysis. Finally, the pile foundation bearing capacity is calculated based on the static test results, the superstructure reaction force N2, and the deadweight N3. This avoids damage to the superstructure during the testing process and takes into account the influence of the reaction force generated by the superstructure due to the settlement of the pile cap on the pile foundation bearing capacity test results.

[0021] (2) When testing the bearing capacity of pile foundations in the reconstruction and expansion of existing buildings, ignoring the reaction force of the superstructure will lead to an overly high pile foundation bearing capacity test result. When the test results are directly used for pile foundation design calculations, the results are unsafe. The method for testing the bearing capacity of pile foundations of existing buildings proposed in the present invention uses a finite element model to derive the reaction force of the superstructure, which not only avoids damage to the superstructure but also takes into account the influence of the reaction force of the superstructure, making the test results safer and more reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is an implementation flow chart of the present invention. DETAILED DESCRIPTION

[0023] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0024] like Figure 1 As shown, the present embodiment proposes an in-situ static testing method for the bearing capacity of pile foundations of existing buildings, comprising the following steps:

[0025] S1. Excavate the soil around the cap to expose the cap and meet the space requirements for the cap load test;

[0026] During the specific implementation of this step, the foundation that needs to be excavated is determined based on engineering experience, combined with design parameters and geological conditions, and the structure is positioned properly to avoid damage to the pile foundation during excavation and affect the test results.

[0027] S2. Settle pedestal settlement observation points on the pedestal to observe the settlement of the pedestal after load application. Select deformation monitoring targets from the columns surrounding the pedestal based on testing requirements and set deformation monitoring points on the targets to observe their deformation. Settle crack observation points on the superstructure to observe the development of cracks in the superstructure. The superstructure includes the portion of the pedestal exposed above the ground and the building structure supported by the pedestal.

[0028] Based on engineering experience, deformation monitoring points are located in locations less susceptible to construction site impacts, and appropriate protective measures are in place. Deformation at these points is measured using total station midpoint trigonometric height measurement. Deformation calculations are based on the column farthest from the loading area within the same building as the reference point.

[0029] S3. Perform a cap load test and record the external load data N1, which is the maximum load that can be applied to the cap during the cap load test.

[0030] Specifically, in this step S3, the mass and quantity of the required counterweight blocks are first determined based on the indoor height and the bearing capacity of the pedestal, that is, the pedestal load to be loaded is determined based on the indoor height and the weight of the existing superstructure; during the pedestal loading test, a large-scale dial indicator is used to collect the pedestal settlement at the pedestal settlement observation point in real time.

[0031] The test ends when the pile load reaches the ultimate load or the settlement of the pedestal causes the cracks in the superstructure to develop to the point where it is not suitable to continue loading, that is, when the crack development at the crack observation point reaches the limit; the load loaded on the pedestal at this time is recorded, which is the external load data N1.

[0032] The ultimate load is the maximum external load that can be applied in the pile load test of the cap, that is, the external load applied in the pile load test of the cap when the settlement of the cap reaches the set settlement value or the deformation of the deformation monitoring point reaches the set deformation value;

[0033] The setting of crack observation points allows for real-time observation of crack development in the superstructure during loading, i.e., observation of the damage state of the superstructure to avoid damage to the superstructure caused by excessive external load during the test. Specifically, crack observation points can be set at the ends of the beams adjacent to the pier in the superstructure. The loading rate can be controlled based on the observed crack width. When the maximum crack width approaches the set limit, the loading rate is slowed. When the limit is reached, the test is stopped, i.e., the loading is stopped.

[0034] S4. Establish a finite element analysis model of the upper structure of the pedestal;

[0035] Specifically, appropriate finite element software such as ABAQUS, PKPM, and Midas can be used based on actual conditions. Modeling should be based on actual component dimensions, concrete strength, and reinforcement. When simplifying a complex structure, relevant theoretical support should be provided. Required material parameters vary between software programs, but should comply with relevant regulatory requirements. Finite element analysis models can be constructed using any existing method, which will not be detailed here.

[0036] S5. Calculate the superstructure reaction force N2 caused by the pile cap settlement using the finite element model;

[0037] Specifically, according to the pedestal settlement detected at the pedestal settlement observation point during the test, the finite element analysis model was adjusted according to the external load added during the test, and the pedestal settlement was added to the finite element analysis model to obtain the stress distribution and reaction force of the superstructure.

[0038] The superstructure reaction force refers to the reaction force generated by the superstructure due to the bearing of the foundation settlement.

[0039] S6. Calculate the superstructure deadweight load N3, i.e., the deadweight of the superstructure;

[0040] The deadweight load of the superstructure has a significant impact on the test results. Ignoring this load will result in a smaller bearing capacity of the pile foundation. Therefore, it is necessary to combine the actual load conditions of the superstructure and calculate the deadweight of the superstructure as the deadweight load N3 of the superstructure.

[0041] It is worth noting that after the finite element analysis model is established in S5, N2 and N3 are both calculated by the finite element analysis model. This is the existing technology and will not be described in detail here.

[0042] In addition, if the superstructure design data is complete, N3 can also be calculated.

[0043] S7. Calculate the bearing capacity of the pile foundation as (N1-N2+N3) / (kn), where k is the safety factor, which may be 2.0, and n is the number of piles under a single cap.

[0044] Of course, it will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, but also encompasses the same or similar structures that can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and it is intended that all variations that fall within the meaning and range of equivalents of the claims be encompassed within the present invention. Any reference signs in the claims should not be construed as limiting the claim to which they relate.

[0045] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0046] The technology, shape, and structure not described in detail in the present invention are all well-known technologies.

Claims

1. An in-situ static testing method for the bearing capacity of pile foundations of existing buildings, characterized in that: The following steps are involved: S1. Excavate and cover the soil around the foundation pile; S2. Arrange settlement observation points on the cap; select deformation monitoring targets among the columns surrounding the cap and deploy deformation monitoring points on these targets; and arrange crack observation points on the superstructure. The superstructure includes the portion of the cap exposed above the ground and the building structure supported by the cap. S3. Perform a cap load test and record the external load data N1, which is the maximum load that can be applied to the cap during the cap load test. S4. Establish a finite element analysis model of the upper structure of the pedestal; S5. Calculate the superstructure reaction force N2 caused by the pile cap settlement using the finite element model; S6. Calculate the superstructure deadweight load N3, i.e., the deadweight of the superstructure; S7. Calculate the pile bearing capacity of the cap as (N1-N2+N3) / (kn), where k is the safety factor and n is the number of piles under a single cap.

2. The in-situ static testing method for the bearing capacity of pile foundations of existing buildings according to claim 1, characterized in that: In S2, a total station is set up at the deformation monitoring point, and the deformation of the deformation monitoring point is measured by the total station midpoint method trigonometric height measurement; and during the measurement process, the column farthest from the loading area in the same building is used as the reference point.

3. The in-situ static testing method for the bearing capacity of pile foundations of existing buildings according to claim 1, characterized in that: The external load data N1 is the smaller value of the following two: A. The maximum external load that can be applied in the pile cap load test, that is, the external load applied in the pile cap load test when the pile cap settlement reaches the set settlement value or the deformation of the deformation monitoring point reaches the set deformation value; B. The external load applied by the cap load test when the maximum crack width at the crack observation point reaches the set limit.

4. The in-situ static testing method for the bearing capacity of pile foundations of existing buildings according to claim 1, characterized in that: A crack observation point is set at the beam end adjacent to the pedestal in the superstructure.

5. The in-situ static testing method for the bearing capacity of pile foundations of existing buildings according to any one of claims 1 to 4, characterized in that: The value of k is 2.0.

Images