A method for calculating the correction value of dynamic penetration rod length considering multiple collisions

Abstract

The present invention discloses a method for calculating a correction value of a dynamic penetration rod length in the field of geotechnical engineering in-situ tests taking into account multiple collisions. First, the initial value of the acceleration of the soil body on the probe rod is calculated, and then the drop hammer speed, the probe rod speed, and the probe rod kinetic energy increment after the ith collision are calculated until the speed of the drop hammer after the collision is equal to the speed of the probe rod or the speed of the drop hammer is equal to 0, and the calculation is stopped; the sum of the kinetic energy increment of the probe rod after each collision and the sum of the kinetic energy of the drop hammer at the end are used as the effective hammer energy of the dynamic penetration test, and the effective hammer energy of the dynamic penetration test is used to correct the acceleration of the soil body on the probe rod, and the iterative method is used to correct the effective hammer energy of the dynamic penetration test, and the iterative method is used to calculate the rod length correction coefficient. The present invention takes into account the characteristics of non-completely elastic collisions between the drop hammer and the probe rod, multiple collisions between the drop hammer and the probe rod, and the resistance of the soil body to the probe rod, and can provide guidance for the calculation of the correction value of the rod length in the dynamic penetration test.

Description

Technical Field

[0001] The invention relates to the field of geotechnical engineering in-situ tests, and in particular to a method for calculating a correction value of a dynamic penetration rod length taking multiple collisions into consideration. Background Art

[0002] The cone dynamic penetration test is an in-situ test for geotechnical engineering that uses a certain amount of hammer kinetic energy to drive a cone probe of a certain specification into the soil. The change of soil layers is determined according to the impedance at the time of penetration. The soil layers are stratified, the physical and mechanical properties of the soil layers are estimated, and the density of the soil is identified. It is a simple and easy-to-use in-situ test for geotechnical engineering. It is widely used in the field of in-situ investigation and detection of geotechnical engineering.

[0003] The current specifications provide a rod length correction factor in the range of 0 to 20 m based on one-dimensional collision theory combined with engineering experience. However, it does not provide a calculation method for rod length correction factors for rods longer than 20 m. Existing research results mostly use acceleration sensors and strain gauges to measure hammer energy to correct rod length. This method has the disadvantages of high requirements for workers and expensive equipment. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for calculating the correction value of the length of a dynamic penetration rod taking into account multiple collisions, so as to solve the problem of lack of a correction coefficient for rods longer than 20m in the current specifications.

[0005] In order to achieve the above purpose, the embodiment of the present invention adopts the following technical solution:

[0006] A method for calculating a correction value of a dynamic penetration rod length considering multiple collisions comprises the following steps:

[0007] Step S1, using the following formula to calculate the initial value of the acceleration a of the soil on the probe:

[0008]

[0009] m=lm'+m"

[0010] Wherein, M is the mass of the falling hammer; h is the falling distance of the falling hammer; m is the mass of the probe rod; N is the number of hammer blows of the dynamic penetration test; l is the length of the probe rod, m' is the weight of the probe rod per linear meter, and m" is the total mass of the guide rod, hammer pad, and probe;

[0011] Step S2, calculate the ratio k of the gravitational acceleration g and the acceleration a of the soil on the probe:

[0012] Step S3, using the following formula to calculate the drop speed V after the first collision 1 and probe speed v 1 , the first collision probe kinetic energy increment ΔE 1 ;

[0013]

[0014]

[0015]

[0016] Wherein, e is the impact recovery coefficient of steel used in the dynamic penetration test;

[0017] Step S4, calculate the hammer drop velocity V before the second collision 2,0 , probe speed v 2,0 :

[0018]

[0019]

[0020] Where Δv n-1 =V n-1 -v n-1 , n = 2, then Δv 1 =V 1 -v 1 ;

[0021] Step S5, calculate the hammer drop velocity V after the second collision using the following formula: 2 and probe speed v 2 , the kinetic energy increment of the probe in the second collision ΔE 2 : Where n = 3,

[0022]

[0023]

[0024]

[0025] Step S6, update the n value in sequence, repeat the above steps S4 and S5, and obtain the hammer drop velocity V after the i-th collision i and probe speed v i , and the probe kinetic energy increment ΔE in the i-th collision i , until V i =v i or V i =0, recorded as the jth collision, and the calculation ends;

[0026] Step S7, using the following formula to calculate the kinetic energy of the falling weight in the final state:

[0027]

[0028] Among them, V 终止 Calculate the velocity of the falling weight at the end of the collision cycle;

[0029] Step S8, using the following formula to calculate the effective hammer energy of dynamic penetration:

[0030]

[0031] Step S9, calculating the acceleration a according to the following formula, and calculating the effective hammer energy E by an iterative method;

[0032]

[0033] Step S10, obtaining the measured hammer blow number N 1 , and the rod length l during the dynamic penetration test 1 , bring into steps S1 to S9 to calculate the measured hammer number N 1 Measured rod length l 1 Hammer energy E(l 1 ,N 1 ), and the measured hammer blow number N 1 , the standard rod length of the dynamic penetration is brought into steps S1 to S9 to calculate the measured hammer number N 1 Standard rod length standard Hammer energy E under the condition 2 =E(l standard ,N 1 );

[0034] Step S11, calculate the corrected hammer number N using the following formula: 2 :

[0035]

[0036] N 2 and standard rod length l standard Substitute the rod length calculated in steps S1 to S10 into the standard rod length l standard , the number of hammer blows is N 2 Hammer Energy E 2 '=E(l standard ,N 2 ), judge E 2 With E 2 'Whether the absolute value of the difference is less than the preset value:

[0037] Step S12, if E 2 With E 2 'If the absolute value of the difference is not less than the preset value, E 2 'Assign to E 2 , calculate N again 2 , and repeat step S11:

[0038] Step S13: If E 2 With E 2'If the absolute value of the difference is less than the preset value, the number of hammer blows obtained in the last cycle is taken as the number of hammer blows after the correction is completed N 2 , and calculate the rod length correction value α as follows:

[0039]

[0040] The preset value in step S11 is 0.00001J.

[0041] Wherein, in step S1, N is the number of hammer blows when the penetration is 10 cm.

[0042] Wherein, before step S3, the method further includes:

[0043] Obtain the impact restitution coefficient of steel used in dynamic penetration testing determined through field tests.

[0044] The method for calculating the effective hammer energy by an iterative method in step S9 includes:

[0045] The acceleration a calculated in step S9 is brought into step S2, and is calculated sequentially to step S9 to calculate a new acceleration a. The new acceleration a is then brought into step S2, and is calculated sequentially to step S9 to calculate an updated acceleration a. The calculation is repeated in this way until the difference between the acceleration a calculated twice is less than the preset difference, and the effective hammer energy calculated for the last time is used as the calculation result of the final effective hammer energy.

[0046] Among them, the preset difference is 0.001m / s 2 .

[0047] The embodiments of the present invention have the following beneficial effects:

[0048] The method for calculating the correction value of the dynamic penetration rod length considering multiple collisions provided by the embodiment of the present invention first calculates the initial value of the acceleration of the soil on the probe rod, and calculates the drop hammer speed, the probe rod speed, and the probe rod kinetic energy increment after the ith collision; the calculation is stopped until the speed of the drop hammer after the collision is equal to the speed of the probe rod or the speed of the drop hammer is equal to 0; the sum of the kinetic energy increment of the probe rod after each collision and the sum of the kinetic energy of the drop hammer at the end is taken as the effective hammer energy of the dynamic penetration test, the effective hammer energy of the dynamic penetration test is used to correct the acceleration of the soil on the probe rod, the iterative method is used to correct the effective hammer energy of the dynamic penetration test, and the iterative method is used to calculate the rod length correction coefficient. Compared with the existing dynamic penetration resistance calculation method, the present invention has the characteristics of considering the non-completely elastic collision between the drop hammer and the probe rod, the multiple collisions between the drop hammer and the probe rod, and the resistance of the soil to the probe rod, and can provide guidance for the calculation of the correction value of the dynamic penetration test rod length.

[0049] Of course, it is not necessary to achieve all of the advantages described above at the same time to implement any product or method of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0051] Figure 1 The present invention is a flowchart of a method for calculating a correction value of a dynamic sounding rod length taking into account multiple collisions according to an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the accompanying drawings can be arranged and designed in various different configurations. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can also be combined with each other.

[0053] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. In the description of the present invention, the terms "first", "second", "third", "fourth", etc. are only used to distinguish the description and cannot be understood as just or implying relative importance.

[0054] An embodiment of the present invention provides a method for calculating a correction value of a dynamic sounding rod length taking into account multiple collisions. The method comprises the following steps: first, calculating an initial value of the acceleration of the soil on the sounding rod, and calculating the drop hammer speed, the sounding rod speed, and the kinetic energy increment of the sounding rod after the first collision; calculating the drop hammer speed and the sounding rod speed before the second collision; calculating the drop hammer speed, the sounding rod speed, and the kinetic energy increment of the sounding rod after the second collision; calculating the drop hammer speed, the sounding rod speed, and the kinetic energy increment of the sounding rod after the third, fourth, fifth, ... collisions in sequence, until the drop hammer speed after the collision is equal to the sounding rod speed or the drop hammer speed is equal to 0, and then stopping the calculation; taking the sum of the kinetic energy increments of the sounding rod after each collision and the sum of the kinetic energy of the sounding rod at the end as the effective hammer energy of the dynamic sounding, using the effective hammer energy of the dynamic sounding to correct the acceleration of the soil on the sounding rod, using the iterative method to correct the effective hammer energy of the dynamic sounding, and using the iterative method to calculate the rod length correction coefficient. Compared with the existing dynamic penetration resistance calculation method, the present invention has the characteristics of considering the non-completely elastic collision between the drop hammer and the probe rod, multiple collisions between the drop hammer and the probe rod, and the resistance of the soil to the probe rod, and can provide guidance for the calculation of the correction value of the dynamic penetration test rod length.

[0055] like Figure 1As shown in, it is a flow chart of a method for calculating a correction value of a dynamic penetration rod length considering multiple collisions provided by an embodiment of the present invention, and the method comprises the following steps:

[0056] Step S1, calculating the initial value of the acceleration a of the soil on the probe;

[0057]

[0058] m=lm'+m" (2)

[0059] Wherein, M is the mass of the drop hammer; h is the drop distance of the drop hammer; m is the mass of the probe rod (including the guide rod, hammer pad and probe); N is the number of hammer blows of the dynamic penetration, where the number of hammer blows when the penetration is 10 cm is taken; l is the length of the probe rod, m' is the weight of the probe rod per linear meter, and m" is the total mass of the guide rod, hammer pad and probe.

[0060] Step S2, calculate the ratio k of the gravitational acceleration g and the acceleration a of the soil on the probe:

[0061] k=g / a (3)

[0062] Step S3, calculating the velocity V of the falling hammer after the first collision 1 and probe speed v 1 , the first collision probe kinetic energy increment ΔE 1 .

[0063]

[0064]

[0065]

[0066] Wherein, e is the collision recovery coefficient of the steel used in the dynamic penetration test, which can be determined through field tests before step S3.

[0067] Step S4, calculate the hammer drop velocity V before the second collision 2,0 , probe speed v 2,0 :

[0068]

[0069]

[0070] Where Δv n-1 =V n-1 -v n-1 , here we take n = 2, then Δv 1 =V 1 -v 1 .

[0071] Step S5, calculate the hammer drop velocity V after the second collision 2 and probe speed v 2 , the kinetic energy increment of the probe in the second collision ΔE 2 , where n = 3,

[0072]

[0073]

[0074]

[0075] Step S6, update the n value in sequence, repeat the above steps S4 and S5, and obtain the hammer drop velocity V after the i-th collision i and probe speed v i , and the probe kinetic energy increment ΔE in the i-th collision i , until V i =v i or V i = 0, the calculation ends. For example, take n = 3, repeat step S4, take n = 4, repeat step S5, and obtain the velocity V of the falling hammer after the third collision. 3 and probe speed v 3 , the probe kinetic energy increment ΔE in the third collision 3 Repeat steps S4 and S5 to calculate the 4th, 5th, 6th, ..., i-th collisions in turn, and calculate the increased kinetic energy of the probe using ΔE i Indicates that until V i =v i or V i =0, recorded as the jth collision, and the calculation ends.

[0076] Step S7, calculating the kinetic energy of the falling weight in the final state:

[0077]

[0078] Among them, V 终止 Calculates the velocity of the falling weight at the end of the collision cycle.

[0079] Step S8, calculating the effective hammer energy of dynamic penetration:

[0080]

[0081] Step S9, calculate the acceleration a, and calculate the effective hammer energy E by an iterative method:

[0082]

[0083] Since the initial value of the acceleration of the soil on the probe rod given in step S1 is an estimated value, in order to accurately solve it, it is necessary to calculate the acceleration a according to the above formula (14), and then calculate the effective hammer energy E by an iterative method. The specific method is: bring the acceleration a calculated in step 9 into step S2, and calculate it in sequence to step S9 to calculate a new acceleration a, then bring the new acceleration a into step S2, and calculate it in sequence to step S9 to calculate an updated acceleration a, and repeat the calculation in this way until the difference between the acceleration a calculated twice is less than the preset difference, and use the effective hammer energy calculated for the last time as the calculation result of the final effective hammer energy. The preset difference is 0.001m / s 2 .

[0084] Step S10, obtaining the measured hammer blow number N 1 , and the rod length l during the dynamic penetration test 1 , bring into steps S1 to S9 to calculate the measured hammer number N 1 Measured rod length l 1 Hammer energy E(l 1 ,N 1 ), and the measured hammer blow number N 1 , the standard rod length of the dynamic penetration is brought into steps S1 to S9 to calculate the measured hammer blow number N 1 Standard rod length standard Hammer energy E under the condition 2 =E(l standard ,N 1 );

[0085] Step S11, calculate the corrected hammer number N using the following formula: 2 :

[0086]

[0087] N 2 and standard rod length l standard Substitute the rod length calculated in steps S1 to S10 into the standard rod length l standard , the number of hammer blows is N 2 Hammer Energy E 2 '=E(l standard ,N 2 ), judge E 2 With E 2 'Is the absolute value of the difference less than 0.00001J:

[0088] Step S12, if E 2 With E 2 'If the absolute value of the difference is not less than 0.00001J, then E 2 'Assign to E 2 , calculate N again 2, and repeat step S11:

[0089] Step S13: If E 2 With E 2 If the absolute value of the difference is less than 0.00001J, the number of hammer blows obtained in the last cycle is taken as the number of hammer blows after the correction is completed. 2 , and calculate the rod length correction value α as follows:

[0090]

[0091] Among them, N 1 is the measured hammer blow number, N 2 The number of hammer blows after the correction is completed.

[0092] In the above calculation process, the derivation process of equations (4), (5) and (6) in step S3 is as follows:

[0093] The velocity of the falling hammer before the first collision can be calculated by the following formula:

[0094]

[0095] Among them, g is the acceleration due to gravity; h is the drop distance of the falling weight.

[0096] According to the conservation of impulse before and after the first collision, we can get equation (18):

[0097] MV 1,0 +mv 1,0 =MV 1 +mv 1 (18)

[0098] Where M is the mass of the falling weight; V 1,0 is the speed of the falling hammer before the first collision; g is the acceleration of gravity; h is the falling distance of the falling hammer; V 1 is the speed of the hammer after the first collision; m is the mass of the probe rod (including the guide rod, hammer pad and probe); v 1,0 is the velocity of the probe before the first collision, where v 1,0 =0;v 1 is the probe speed after the first collision.

[0099] According to the definition of collision restitution coefficient, we can get formula (19):

[0100]

[0101] From equations (17), (18), and (19), we can get the speed of the drop weight and the probe rod after the first collision, as shown in equations (20) and (21):

[0102]

[0103]

[0104] Combining the kinetic energy calculation method with formula (21), we can obtain the kinetic energy increment ΔE of the probe after the first collision: 1 .

[0105]

[0106] In step S5, the derivation process of equations (9), (10) and (11) is as follows:

[0107] It can be seen from formula (4) that the falling hammer still has a certain amount of kinetic energy after the first collision. After the first collision occurs, the speed of the probe rod is reduced due to the constraint of the soil layer. Due to the effect of gravity, the speed direction of the falling hammer after the first collision, whether it is upward or downward, will cause a second collision with the probe rod, and the energy of the falling hammer will be penetrated into the probe rod again. In order to more accurately calculate the hammer energy transmitted to the probe rod by the falling hammer, this patent considers the first collision and subsequent multiple collisions until the hammer energy is small enough to be ignored or the speed of the falling hammer and the probe rod is always the same and no collision occurs.

[0108] Here we calculate the n-1th collision. It is assumed that the speed of the probe before the n-1th collision is v n-1,0 The velocity of the falling weight is V n-1,0 .

[0109] According to the conservation of impulse before and after the n-1th collision:

[0110] MV n-1,0 +mv n-1,0 =MV n-1 +mv n-1 (twenty three)

[0111] According to the definition of the coefficient of restitution:

[0112]

[0113] From equations (23) and (24), the drop weight velocity and probe rod velocity after the n-1th collision can be calculated by equations (25) and (26).

[0114]

[0115]

[0116] Then, during the n-1th collision, the increment of the probe rod kinetic energy can be calculated by formula (27):

[0117]

[0118] In step S4, the derivation process of equations (7) and (8) is as follows:

[0119] Here, only the changes of the falling hammer velocity and the probe rod velocity during the collision process are calculated. In order to calculate the changes of the falling hammer velocity and the probe rod velocity between two collisions, the following analysis is performed:

[0120] From formula (26), it can be seen that after the n-1th collision, the probe rod obtains a large downward speed, but this speed will continue to decay due to the influence of soil resistance. Here, the resistance of the soil to the probe rod is assumed to be a constant, and the acceleration generated by the resistance is a. Then the speed of the probe rod during deceleration can be expressed by formula (28):

[0121] v=v n-1 -(ag)t (28)

[0122] It can be seen from formula (25) that after the n-1th collision, the velocity direction of the falling hammer may be upward, downward or 0. Here, the downward velocity is positive. The velocity of the falling hammer is less than the velocity of the probe rod, but under the influence of gravity, the velocity of the falling hammer continues to increase after the collision. Its movement process can be expressed by formula (29).

[0123] V=V n-1 +gt (29)

[0124] From equations (28) and (29), the time t between two collisions can be expressed by equation (30):

[0125]

[0126] Then the speed of the drop hammer and the probe rod before the nth collision can be expressed by equations (31) and (32) respectively:

[0127]

[0128]

[0129] To make the formula more concise, let

[0130] k=g / a (33)

[0131] Δv n-1 =V n-1 -v n-1 (34)

[0132] Then equations (31) and (32) can be expressed as equations (35) and (36):

[0133] V n,0 =V n-1 -2kΔv n-1 (35)

[0134] v n,0 =v n-1 +2(1-k)Δv n-1 (36)

[0135] Since the soil resistance is a process of continuous deceleration of the probe rod, when the speed is reduced to 0, the speed of the probe rod will no longer change. n,0 <0, take v n,0 =0, that is, when the following equation (37) holds, take v n,0 =0.

[0136]

[0137] When equation (37) holds true, the probe speed is v n It keeps decreasing to 0, which is a uniform deceleration process, and its acceleration is -(ag). Then the distance the probe rod descends from the nth collision to the n+1th collision can be expressed by formula (38):

[0138]

[0139] According to the conservation of mechanical energy of the falling weight, equation (39) exists:

[0140]

[0141] Substituting equation (38) into equation (39), we can obtain the velocity of the falling hammer before the n+1th collision, which is expressed by equation (40):

[0142]

[0143] From equations (35), (36), and (40), the velocity of the falling hammer before the nth collision can be obtained as shown in equation (41):

[0144]

[0145] The velocity of the probe rod before the nth collision is shown in formula (42):

[0146]

[0147] In step S11, the derivation process of formula (15) is as follows:

[0148] Assuming that the energy required for the same type of dynamic penetration to penetrate the soil layer is constant, the number of dynamic penetration hammer blows under different probe rod lengths and measured hammer blows has a conversion relationship as shown in equations (43) and (44):

[0149]

[0150]

[0151] Where α is the rod length correction factor, N 1 Measured hammer blow number, N 2 Corrected hammer blow number, l1 Measured rod length, l standard Standard rod length, E(l 1 ,N 1 ) The hammer energy calculated under the conditions of the measured rod length and hammer number, E(l standard ,N 2 ) Hammer energy calculated under the conditions of standard rod length and corrected number of hammer blows.

[0152] From equation (44), we can see that both sides of the equation contain unknown numbers N 2 , so it is necessary to use iterative calculation method to solve it.

[0153] In step S9, the derivation process of formula (14) is as follows:

[0154]

[0155] Among them, F is the resistance of the soil to the probe rod during the penetration process, and s is the penetration amount of the dynamic probe in one shot / m.

[0156] It can be seen from the above technical solutions that the method for calculating the correction value of the length of a dynamic sounding rod taking into account multiple collisions provided in an embodiment of the present invention, compared with the existing method for calculating the dynamic penetration resistance, has the characteristics of taking into account the non-completely elastic collision between the drop hammer and the probe rod, multiple collisions between the drop hammer and the probe rod, and the resistance of the soil to the probe rod, and can provide guidance for the calculation of the correction value of the length of the dynamic sounding test rod.

[0157] The above description is only a preferred embodiment of the present invention and an explanation of the technical principles used. It is not intended to limit the scope of the invention claimed for protection, but only represents the preferred embodiment of the present invention. Those skilled in the art should understand that the scope of the invention involved in the present invention is not limited to the technical solution formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention.

Claims

1. A method for calculating the correction value of the dynamic penetration rod length considering multiple collisions, characterized in that: The following steps are involved: Step S1, using the following formula to calculate the initial value of the acceleration a of the soil on the probe: m=lm'+m" Wherein, M is the mass of the falling hammer; h is the falling distance of the falling hammer; m is the mass of the probe rod; N is the number of hammer blows of the dynamic penetration test; l is the length of the probe rod, m' is the weight of the probe rod per linear meter, and m" is the total mass of the guide rod, hammer pad, and probe; Step S2, calculate the ratio k of the gravitational acceleration g and the acceleration a of the soil on the probe: Step S3, using the following formulas to calculate the drop hammer velocity V1 and the probe rod velocity v1 after the first collision, and the kinetic energy increment ΔE1 of the probe rod after the first collision; Wherein, e is the impact recovery coefficient of steel used in the dynamic penetration test; Step S4, calculate the hammer drop velocity V before the second collision 2,0 , probe speed v 2,0 : Where Δv n-1 =V n-1 -v n-1 , n = 2, then Δv1 = V1-v1; Step S5, using the following formula to calculate the drop hammer velocity V2 and the probe rod velocity v2 after the second collision, and the probe rod kinetic energy increment ΔE2 in the second collision: where n=3, Step S6, update the n value in sequence, repeat the above steps S4 and S5, and obtain the hammer drop velocity V after the i-th collision i and probe speed v i , and the probe kinetic energy increment ΔE in the i-th collision i , until V i =v i or V i =0, recorded as the jth collision, and the calculation ends; Step S7, using the following formula to calculate the kinetic energy of the falling weight in the final state: Among them, V 终止 Calculate the velocity of the falling weight at the end of the collision cycle; Step S8, using the following formula to calculate the effective hammer energy of dynamic penetration: Step S9, calculating the acceleration a according to the following formula, and calculating the effective hammer energy E by an iterative method; Step S10, obtain the measured hammer blow number N1 and the rod length l1 during the dynamic penetration test, and bring them into steps S1 to S9 to calculate the hammer energy E(l1,N1) under the conditions of the measured hammer blow number N1 and the measured rod length l1, and bring the measured hammer blow number N1 and the standard rod length l1 of the dynamic penetration test into steps S1 to S9 to calculate the measured hammer blow number N1 and the standard rod length l1 standard The hammer energy under the condition of E2=E(l standard ,N1); Step S11, calculate the corrected hammer blow number N2 using the following formula: N2 and the length of the standard rod l standard Substitute the rod length calculated in steps S1 to S10 into the standard rod length l standard When the number of hammer blows is N2, the hammer energy E2'=E(l standard ,N2), determine whether the absolute value of the difference between E2 and E2' is less than the preset value: Step S12: If the absolute value of the difference between E2 and E2' is not less than the preset value, assign E2' to E2, calculate N2 again, and repeat step S11: Step S13: If the absolute value of the difference between E2 and E2' is less than the preset value, the number of hammer blows obtained in the last cycle is taken as the number of hammer blows N2 after the correction is completed, and the rod length correction value α is calculated by the following formula:

2. A method for calculating the correction value of the dynamic penetration rod length considering multiple collisions according to claim 1, characterized in that: The preset value in step S11 is 0.00001J.

3. The method for calculating the correction value of the dynamic penetration rod length considering multiple collisions according to claim 1 is characterized in that: In the step S1, N is the number of hammer blows when the penetration is 10 cm.

4. The method for calculating the correction value of the dynamic penetration rod length considering multiple collisions according to claim 1 is characterized in that: The step S3 also includes: Obtain the impact recovery coefficient e of the steel used in the dynamic penetration test determined through field tests.

5. The method for calculating the correction value of the dynamic penetration rod length considering multiple collisions according to claim 1 is characterized in that: The method for calculating the effective hammer energy by an iterative method in step S9 includes: The acceleration a calculated in step S9 is brought into step S2, and is calculated sequentially to step S9 to calculate a new acceleration a. The new acceleration a is then brought into step S2, and is calculated sequentially to step S9 to calculate an updated acceleration a. The calculation is repeated in this way until the difference between the acceleration a calculated twice is less than the preset difference, and the effective hammer energy calculated for the last time is used as the calculation result of the final effective hammer energy.

6. A method for calculating the correction value of the dynamic penetration rod length considering multiple collisions according to claim 5, characterized in that: The preset difference is 0.001m / s 2 .

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