A method for judging pile head damage in pile static load test

Abstract

The present invention discloses a method for judging pile head damage in a static load test of a pile foundation. The method comprises the following steps: installing the equipment required for the static load test; setting the total number of load application levels; calculating the target load control value for each load application level, and applying the load through an oil pump; calculating the average value of the pile displacement change and the average value of the pile pressure change recorded each time during the time of applying the current load level; and calculating the judgment value k. i and the oil pump loading rate, according to the judgment value k i The invention can distinguish and warn the oil pump power and pile damage, and can estimate the later loading time.

Description

Technical Field

[0001] The present invention belongs to the field of static load test in pile bearing capacity detection, and specifically relates to a method for judging pile head damage in pile static load test. The method is applicable to the prevention and control of the collapse of the test platform caused by pile head damage and the subsequent engineering accidents in single pile vertical compression, single pile vertical pull-out and single pile horizontal static load tests. Background Art

[0002] In the static load test of pile foundation, the pile head of the static load test often bears high vertical load (or horizontal load) and eccentric load. According to the requirements of the pile foundation inspection specification, whether it is a cast-in-place pile or a precast pile, the pile head needs to be processed to ensure the normal test. For precast piles, the pile head is generally processed by hoop head, concrete core filling, etc.; while cast-in-place piles are generally processed by pouring the pile head. On the basis of chiseling out the loose and broken layer of concrete in the original pile body, the concrete pile cap is re-cast, and the test is carried out after the pile cap reaches the strength.

[0003] In view of the treatment of pile heads, domestic researchers have applied for corresponding patents, such as patent application number CN201720510080.4 static load pile head protection device and static load test system; the utility model mainly provides a static load pile head protection device and a static load test system, the static load pile head protection device includes a clamping member and a reinforcing structure; the clamping member is first connected, sleeved on the outer wall of the pile head, and clamped, this device limits the axial deformation of the pile head by clamping the pile head, thereby preventing the pile head from bursting. Patent application number CN200920172114.9 detachable cast-in-place pile compression static load pile head protection device, the utility model invention is a detachable cast-in-place pile compression static load pile head protection device, the protection device consists of two semi-circular arc pipe clamps, bolts screw the two semi-circular arc pipe clamps together and fix them on the outer circumference of the pile head to protect the pile head from damage during the static load test.

[0004] Although the specifications require that the pile heads be treated and protected during static load tests, during on-site inspections, the treatment of the pile heads on site often results in problems such as inappropriate hoop head size, failure to strictly follow the specifications during the pouring of the concrete pile cap, and unqualified pouring quality. As a result, pile head damage is still common during static load test engineering inspections. Although some test piles are treated, the pile head top surface is often damaged due to unevenness, eccentric installation of the jack, and influence of groundwater level.

[0005] In the static load test, after the pile head is damaged, not only can the load no longer be applied, the static load test cannot be carried out, but quality accidents are very likely to occur, which will also cause conflicts between the construction and testing parties.

[0006] At present, static load tests are basically carried out automatically using static load testers, which can ensure the safety of on-site test personnel and equipment to a large extent, and can also increase test efficiency and ensure the accuracy of on-site test data. At present, static load testers control the application of pressure by limiting the length of time the oil pump rotates. However, there are differences in the oil pump output during the oil pump rotation time and the load-bearing capacity of the on-site test object. If the time is set too long, even if the pile head is damaged, the pile is damaged, or there is a problem with the oil pump on site, the instrument will still control the oil pump to continue to apply the load, resulting in an accident. If the loading time is set too short, it is very easy to trigger an alarm condition, affecting the efficiency of on-site detection. Therefore, it is very necessary to embed the judgment algorithm of pile head damage in static load tests and the supporting early warning function in the static load collector. Summary of the invention

[0007] The purpose of the present invention is to address the above-mentioned technical problems existing in the prior art and to provide a method for judging pile head damage in a static load test of a pile foundation. The method can be used for estimating and judging the time for applying a load in a static load test of a pile foundation and can be used for protecting against pile head damage and the application of an oil pump loading control load in a static load test, thereby ensuring the safety of a reaction force platform for a field test. By embedding the present invention in a static load tester, the safety of field tests and equipment can be ensured while increasing the efficiency of field tests.

[0008] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0009] A method for determining pile head damage in a pile foundation static load test comprises the following steps:

[0010] Step 1: Install the equipment required for the static load test according to the requirements of the pile static load test;

[0011] Step 2, controlling the front-end host to set the total load application level n according to the maximum test load value of the static load test;

[0012] Step 3, controlling the front-end host to calculate the target load value applied at each load level in the process from the initial load value to the maximum test load value;

[0013] Step 4: The front-end control host sends the target control load value corresponding to the current level of load application to the oil pump drive device, thereby controlling the rotation of the oil pump and applying the load through the oil pump;

[0014] Step 5: Calculate the oil pump loading rate V i ;

[0015]

[0016] in:

[0017] V iis the oil pump loading rate of the i-th level load;

[0018] Q i is the real-time load value after the i-th level load is applied;

[0019] Q i-1 is the real-time load value before the i-th level load is applied. When i=1, Q 0 is the initial load value;

[0020] T i is the time after the i-th level load is applied;

[0021] T i-1 is the time before the i-th level load is applied;

[0022] i is the load application level number; i∈{1~n}

[0023] n is the total number of load application stages;

[0024] Step 6: Obtain the oil pump loading rate V i After that, the oil pump loading rate V i The total load change ΔQ of the static load test of the next level of load is calculated, and the total loading time T of the next level of load is calculated. i+1 , T i+1 =ΔQ / V i ;

[0025] Step 7: Use the static load acquisition instrument to sequentially segment the time of the current level load application obtained by the front-end control host, and record the pile displacement and pile pressure multiple times, calculate the pile displacement change value and pile pressure change value recorded in each time segment during the time of the current level load application, and calculate the average value of the pile displacement change Δs recorded in each time segment during the time of the current level load application. j and the average value of pile pressure variation Δq j ; where j is the serial number of the current load level segment number record, j∈{1~m}, m is the total number of current load level time segments,

[0026] At the beginning of the current level of load application, the judgment value k is calculated j :

[0027]

[0028] in:

[0029] k j is the ratio of load to displacement in the jth time period of the current load level, in kN / mm;

[0030] Δq j is the growth value of the load in the jth time period of the current load;

[0031] Δq j-1 is the growth value of the load in the j-1th time period of the current load;

[0032] Δs j is the average growth value of the test displacement table in the jth time period of the current load;

[0033] Δs j-1 is the average growth value of the displacement table tested in the j-1th time period of the current load;

[0034] j is the serial number of the time segment number record of the current load level, and the calculation judgment value k j When , the value of j is greater than or equal to 2 and less than or equal to m;

[0035] Step 8: During the process of loading and supplementing, if V i When the value is equal to 0 or less than the V of the i-1st load level i-1 When the value is 1 / 3, the oil pump power warning is given and the static load test is stopped;

[0036] Step 9: Apply the next level of load as the current level of load, and return to step 4 until all levels of load application are completed. During the process of applying all levels of load, if the judgment value k j If the value ≤0 appears twice in succession, it is judged that the pile head, pile body or bearing layer around the pile is damaged, or the reinforcement of the pile body is broken, and a pile damage warning is issued and the static load test is stopped.

[0037] The calculation method for calculating the load time period as mentioned above is based on the following steps: if the maximum test load value is ≤2000kN, the value of m is 2. For every increase of 1000 kN in the maximum test load value over 2000kN, the value of m increases by 1.

[0038] In step 7 as described above, the pile displacement and pile pressure within the time when the current level of load is applied are recorded multiple times at the same time interval.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. The present invention can judge the vertical compression resistance, vertical pull-out resistance and horizontal test of a single pile in static load of foundation piles, and has wide applicability.

[0041] 2. During the static load test, the present invention can also estimate the later load time by calculating the oil pump loading rate, thereby realizing automatic judgment and automatic setting of the loading time, and thus preventing the maximum loading time from being too long or too short. While increasing the test efficiency of the on-site test, it also ensures the safety of the on-site test platform, oil pump, and jack to the greatest extent.

[0042] 3. The present invention embeds a control front-end host connected to the static load collector, and the pile head damage can be judged and responded to in the fastest time. It can also distinguish between the problems of no hydraulic oil in the oil pump, oil leakage in the oil pipe, insufficient reaction force on site and the pile head damage problem, refine the alarm content, reduce misjudgment, and affect the efficiency of on-site testing.

[0043] 4. The present invention is embedded in a control front-end host connected to a static load acquisition instrument, and the calculation is realized by judging the program in the control front-end host, thereby ensuring that the present invention does not affect the normal progress of the static load test when embedded in the control front-end host. DETAILED DESCRIPTION

[0044] In order to facilitate those skilled in the art to understand and implement the present invention, the present invention is further described in detail below with reference to examples. It should be understood that the implementation examples described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0045] Embodiment 1:

[0046] A method for determining pile head damage in a pile foundation static load test comprises the following steps:

[0047] Step 1: Install the equipment required for the static load test according to the requirements of the static load test, enter the information required for the static load test, such as the test load information, the jack rating equation, and the oil pump used, turn on the static load acquisition instrument, and conduct the static load test;

[0048] Step 2, controlling the front-end host to set the total load application level n according to the maximum test load value of the static load test;

[0049] Step 3, controlling the front-end host to calculate the target load value applied at each load level in the process from the initial load value to the maximum test load value;

[0050] Step 4: The front-end control host sends the target control load value corresponding to the current level of load application to the oil pump drive device, thereby controlling the rotation of the oil pump and applying the load through the oil pump;

[0051] Step 5: Calculate the oil pump loading rate V i ;

[0052]

[0053] in:

[0054] V i is the oil pump loading rate of the i-th level load, in kN / S;

[0055] Q i is the real-time load value after the i-th level load is applied;

[0056] Q i-1 is the real-time load value before the i-th level load is applied. When i=1, Q 0 is the initial load value;

[0057] T i is the time after the i-th level load is applied;

[0058] T i-1 is the time before the i-th level load is applied;

[0059] i is the load application level number; i∈{1~n}

[0060] n is the total number of load application stages;

[0061] Step 6: Obtain the oil pump loading rate V i After that, the oil pump loading rate V i The total load change ΔQ of the static load test of the next level of load is calculated, and the total loading time T of the next level of load is calculated. i+1 , T i+1 =ΔQ / V i ;

[0062] Step 7: Use the static load acquisition instrument to sequentially segment the time of the current level load application obtained by the front-end control host, and record the pile displacement and pile pressure multiple times, calculate the pile displacement change value and pile pressure change value recorded in each time segment during the time of the current level load application, and calculate the average value of the pile displacement change Δs recorded in each time segment during the time of the current level load application. j and the average value of pile pressure variation Δq j ; Where j is the serial number of the current load level segment number record, j∈{1~m}, m is the total number of current load level time segments;

[0063] At the beginning of the current level of load application, the judgment value k is calculated j :

[0064]

[0065] in:

[0066] k j is the ratio of load to displacement in the jth time period of the current load level, in kN / mm;

[0067] Δq j is the growth value of the load in the jth time period of the current load;

[0068] Δq j-1 is the growth value of the load in the j-1th time period of the current load;

[0069] Δs jis the average growth value of the test displacement table in the jth time period of the current load;

[0070] Δs j-1 is the average growth value of the displacement table tested in the j-1th time period of the current load;

[0071] j is the serial number of the time segment number record of the current load level, and the calculation judgment value k j When , the value of j is greater than or equal to 2 and less than or equal to m;

[0072] m is the total number of current load level sections; the value of m is taken as follows: if the maximum test load value is ≤2000kN, then the value of m is 2, and the value of m increases by 1 for every 2000kN increase in the maximum test load value on the basis of 2000kN; for example, when the maximum test load is 10000kN, the value of m is 6.

[0073] T i To T i+1 The time is divided into m segments, and the total length of the m time segments is T i+1 -T i , the length of the first m-1 time periods is (T i+1 -T i ) / m is rounded down.

[0074] Step 8: During the process of loading and supplementing, if V i When the value is equal to 0 or less than the V of the i-1st load level i-1 When the value is 1 / 3, the oil pump power warning is given and the static load test is stopped;

[0075] Step 9: Apply the next level of load as the current level of load, and return to step 4 until all levels of load application are completed. During the process of applying all levels of load, if the judgment value k j If the value ≤0 appears for two consecutive times, it is judged that the pile head, pile body or bearing layer around the pile is damaged, or the reinforcement of the pile body is broken, and a pile damage warning is issued and the static load test is stopped.

[0076] Embodiment 2:

[0077] Since 2020, after the judgment method described in Example 1 was embedded in the static load tester, early warnings of pile head damage and insufficient oil pump power appeared in multiple tests. While protecting the reaction force platform of the on-site static load test, the oil pump was also protected.

[0078] Table 1 is a measurement table of real-time load values ​​and pile displacements in this embodiment.

[0079]

[0080] As shown in the table above, after the load was increased from 2160kN to 2430kN, the pressure decreased and there were no test personnel on site.

[0081] At 12:24:04, the front-end control host of the static load tester RSM-JC5(A) automatically issued an alarm, stopped the static load test, and controlled the oil pump to automatically stop rotating. The front-end control host of the static load tester RSM-JC5(A) popped up a prompt "The on-site test object may be damaged. Please check the site before deciding whether to continue the test."

[0082] The treated pile head was inspected on site and found to be completely cracked. The oil pump was stopped in time to continue pressurizing, thus avoiding the accident at the test site.

[0083] Since the present invention is embedded in the front-end control host of the static load tester, it has issued warnings many times, avoiding the occurrence of on-site static load test accidents, while also ensuring the property safety of on-site test equipment to the greatest extent and avoiding accidents caused by pile head damage.

[0084] It should be noted that the specific embodiments described in the present invention are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the attached claims.

Claims

1. A method for determining pile head failure in a pile static load test. It is characterized in that The following steps are involved: Step 1: Install the equipment required for the static load test according to the requirements of the pile static load test; Step 2, controlling the front-end host to set the total load application level n according to the maximum test load value of the static load test; Step 3, controlling the front-end host to calculate the target load value applied at each load level in the process from the initial load value to the maximum test load value; Step 4: The front-end control host sends the target control load value corresponding to the current level of load application to the oil pump drive device, thereby controlling the rotation of the oil pump and applying the load through the oil pump; Step 5: Calculate the oil pump loading rate V i ; in: V i is the oil pump loading rate of the i-th level load; Q i is the real-time load value after the i-th level load is applied; Q i-1 is the real-time load value before the i-th level load is applied. When i=1, Q 0 is the initial load value; T i is the time after the i-th level load is applied; T i-1 is the time before the i-th level load is applied; i is the load application level number; i∈{1~n} n is the total number of load application stages; Step 6: Obtain the oil pump loading rate V i After that, the oil pump loading rate V i The total load change ΔQ of the static load test of the next level of load is used to calculate the total loading time T of the next level of load i+1 , T i+1 =ΔQ / V i ; Step 7: Use the static load acquisition instrument to sequentially segment the time of the current level load application obtained by the front-end control host, and record the pile displacement and pile pressure multiple times, calculate the pile displacement change value and pile pressure change value recorded in each time segment during the time of the current level load application, and calculate the average value of the pile displacement change Δs recorded in each time segment during the time of the current level load application. j and the average value of pile pressure variation Δq j ; where j is the serial number of the current load level segment number record, j∈{1~m}, m is the total number of current load level time segments, At the beginning of the current level of load application, the judgment value k is calculated j : in: k j is the ratio of load to displacement in the jth time period of the current load level, in kN / mm; Δq j is the growth value of the load in the jth time period of the current load; Δq j-1 is the growth value of the load in the j-1th time period of the current load; Δs j is the average growth value of the test displacement table in the jth time period of the current load; Δs j-1 is the average growth value of the displacement table tested in the j-1th time period of the current load; j is the serial number of the time segment number record of the current load level, and the calculation judgment value k j When , the value of j is greater than or equal to 2 and less than or equal to m; Step 8: During the process of loading and supplementing, if V i When the value is equal to 0 or less than the V of the i-1th level load i-1 When the value is 1 / 3, the oil pump power warning is given and the static load test is stopped; Step 9: Apply the next level of load as the current level of load, and return to step 4 until all levels of load application are completed. During the process of applying all levels of load, if the judgment value k j If the value ≤0 appears twice in succession, it is judged that the pile head, pile body or bearing layer around the pile is damaged, or the reinforcement of the pile body is broken, and a pile damage warning is issued and the static load test is stopped.

2. A method for determining pile head failure in a pile foundation static load test according to claim 1, It is characterized in that The calculation method for the load time period is based on the following steps: if the maximum test load value is ≤2000kN, the value of m is 2. For every increase of 1000kN in the maximum test load value over 2000kN, the value of m increases by 1.

3. According to the method for determining pile head damage in a pile foundation static load test according to claim 1, It is characterized in that In step 7, the pile displacement and pile pressure within the time when the current level of load is applied are recorded multiple times at the same time interval.

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