A method for calculating dynamic penetration resistance of dynamic penetration testing considering multiple collisions

Abstract

The present invention relates to a method for calculating the dynamic penetration resistance of dynamic penetration testing in the field of geotechnical engineering in-situ testing, which takes into account multiple collisions. The method comprises: calculating the initial value of the acceleration of the soil body on the probe rod, calculating the drop hammer speed, the probe rod speed, and the probe rod kinetic energy increment after the ith collision, 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 then stopping the calculation; taking the sum of the probe rod kinetic energy increment after each collision and the sum of the kinetic energy of the drop hammer at the end as the effective hammer energy of dynamic penetration testing, using the effective hammer energy of dynamic penetration testing to correct the acceleration of the soil body on the probe rod, using the iteration method to correct the effective hammer energy of dynamic penetration testing, and calculating the dynamic penetration resistance. Compared with the existing dynamic penetration resistance calculation method, 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 dynamic penetration testing.

Description

Technical Field

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

[0002] The cone dynamic penetration test is an in-situ test of geotechnical engineering that uses a certain hammer kinetic energy to drive a cone probe of a certain specification into the soil, and judges the change of soil layer according to the impedance size when driving, stratifies the soil layer, estimates the physical and mechanical properties of the soil layer, and identifies the density of the soil. It is simple and easy to use, and is widely used in the field of in-situ investigation and detection of geotechnical engineering. Using dynamic penetration resistance as a dynamic penetration index has the following significance: using dynamic penetration resistance per unit area as a measurement index has a clear mechanical dimension, which is convenient for comparison with other physical quantities; it is convenient for comparative analysis of the results of different penetration parameters (hammer energy, probe size).

[0003] The existing dynamic penetration resistance calculation method is mainly the Dutch formula, which assumes that the collision between the probe and the drop hammer is an absolutely inelastic collision (i.e., the coefficient of recovery of the collision is 0). However, the probe, hammer pad, and drop hammer commonly used in dynamic penetration tests are all made of steel, and their collision recovery coefficient is greater than 0. The physical model established based on the above assumptions is quite different from the actual cone dynamic penetration test process. However, when the collision between the drop hammer and the probe is calculated as a non-completely elastic collision, a secondary collision occurs under the action of gravity and soil resistance because the speeds of the drop hammer and the probe are not equal after the collision.

[0004] It can be seen that the current calculation method of dynamic penetration resistance is not accurate enough and this problem needs to be solved urgently. Summary of the invention

[0005] The embodiment of the present invention provides a method for calculating the dynamic penetration resistance of a dynamic probe taking into account multiple collisions, so as to solve the problems raised by the prior art.

[0006] In order to achieve the above purpose, the embodiment of the present invention adopts the following technical solution:

[0007] An embodiment of the present invention provides a method for calculating dynamic penetration resistance of dynamic penetration testing considering multiple collisions, comprising the following steps:

[0008] Step S1, using the following formula to calculate the initial value of the acceleration a of the soil on the probe:

[0009]

[0010] Among them, M is the mass of the falling hammer; g is the acceleration of gravity; h is the falling distance of the falling hammer; m is the mass of the probe rod; N is the number of hammer blows measured by dynamic penetration;

[0011] Step S2, calculating the ratio k of the gravitational acceleration g to the acceleration a of the soil on the probe rod;

[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 velocity V before the second collision using the following formula: 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, using the following formula to calculate the dynamic penetration resistance R:

[0034]

[0035] Where A is the cross-sectional area of ​​the probe.

[0036] Wherein, in step S1, N is the number of hammer blows when the penetration is 10 cm.

[0037] Wherein, before step S3, the method further includes:

[0038] Obtain the impact restitution coefficient of steel used in dynamic penetration testing determined through field tests.

[0039] The method for calculating the effective hammer energy by an iterative method in step S9 includes:

[0040] 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 a preset value, and the effective hammer energy calculated for the last time is used as the calculation result of the final effective hammer energy.

[0041] Among them, the preset value is 0.001m / s 2 .

[0042] The embodiments of the present invention have the following beneficial effects:

[0043] The method for calculating the dynamic penetration resistance of dynamic sounding considering multiple collisions provided in an embodiment of the present invention first calculates the initial value of the acceleration of the soil on the probe rod, calculates the drop hammer speed, the probe rod speed, and the probe rod kinetic energy increment after the first collision; calculates the drop hammer speed and the probe rod speed before the second collision; calculates the drop hammer speed, the probe rod speed, and the probe rod kinetic energy increment after the second collision; calculates the drop hammer speed, the probe rod speed, and the probe rod kinetic energy increment after the third, fourth, fifth, ... collisions in sequence, until the drop hammer speed after the collision is equal to the probe rod speed or the drop hammer speed is equal to 0, and stops calculating; takes the sum of the probe rod kinetic energy increments after each collision and the sum of the kinetic energy of the hammer at the end as the effective hammer energy of the dynamic sounding, uses the effective hammer energy of the dynamic sounding to correct the acceleration of the soil on the probe rod, uses the iterative method to correct the effective hammer energy of the dynamic sounding, and calculates the dynamic penetration resistance. 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 dynamic penetration tests.

[0044] 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

[0045] 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.

[0046] Figure 1 The present invention is a flowchart of a method for calculating dynamic penetration resistance of dynamic probing based on multiple collisions according to an embodiment of the present invention. DETAILED DESCRIPTION

[0047] 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.

[0048] 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.

[0049] An embodiment of the present invention provides a method for calculating the dynamic penetration resistance of dynamic sounding considering multiple collisions. The method first calculates the initial value of the acceleration of the soil on the probe rod, calculates the drop hammer speed, the probe rod speed, and the probe rod kinetic energy increment after the first collision; calculates the drop hammer speed and the probe rod speed before the second collision; calculates the drop hammer speed, the probe rod speed and the probe rod kinetic energy increment after the second collision; calculates the drop hammer speed, the probe rod speed and the probe rod kinetic energy increment after the third, fourth, fifth, ... collisions in sequence, until the drop hammer speed after the collision is equal to the probe rod speed or the drop hammer speed is equal to 0, and stops calculating; takes the sum of the probe rod kinetic energy increment after each collision and the sum of the kinetic energy of the probe rod at the end of the drop hammer as the effective hammer energy of the dynamic sounding, uses the effective hammer energy of the dynamic sounding to correct the acceleration of the soil on the probe rod, uses the iterative method to correct the effective hammer energy of the dynamic sounding, and calculates the dynamic penetration resistance. 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 more scientific and accurate guidance for dynamic penetration tests.

[0050] like Figure 1 FIG. 1 is a flow chart of a method for calculating dynamic penetration resistance of dynamic penetration testing considering multiple collisions according to an embodiment of the present invention, which includes the following steps:

[0051] Step S1, calculating the initial value of the acceleration a of the soil on the probe;

[0052]

[0053] Where M is the mass of the hammer; g is the acceleration of gravity; h is the distance of the hammer; m is the mass of the probe rod (including the guide rod, hammer pad and probe); N is the number of hammer blows measured by dynamic penetration, which is the number of hammer blows when the penetration is 10 cm. The acceleration a calculated in this step is the initial value.

[0054] Step S2, calculating the ratio of the gravitational acceleration g to the acceleration a of the soil on the probe;

[0055] k=g / a (2)

[0056] 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 .

[0057]

[0058]

[0059]

[0060] Wherein, e is the collision recovery coefficient of the steel used in the dynamic penetration test, and the collision recovery coefficient e of the steel used in the dynamic penetration test can be determined through field tests before step S3.

[0061] Step S4, calculate the hammer drop velocity V before the second collision 2,0 , probe speed v 2,0 :

[0062]

[0063]

[0064] Where Δv n-1 =V n-1 -v n-1 , here we take n = 2, then Δv 1 V 1 -v 1 .

[0065] 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 :

[0066]

[0067]

[0068]

[0069] In the above formula, n=3.

[0070] Step S6, update the n value in sequence to 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, end the calculation. 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 again, calculate the 4th, 5th, 6th, ..., i, ... nth 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.

[0071] Step S7, calculating the kinetic energy of the falling weight in the final state:

[0072]

[0073] Among them, V 终止 Calculates the velocity of the falling weight at the end of the collision cycle.

[0074] Step S8, calculating the effective hammer energy of dynamic penetration:

[0075]

[0076] Step S9, calculating the acceleration a, and calculating the effective hammer energy E by an iterative method;

[0077]

[0078] 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 (13), and then calculate the effective hammer energy E by an iterative method. The specific method is: bring the acceleration a calculated in step S9 into step S2, and calculate to step S9 in sequence to calculate a new acceleration a, then bring the new acceleration a into step S2, and calculate to step S9 in sequence to calculate an updated acceleration a, and repeat the calculation until the difference between the acceleration a calculated twice is less than the preset value, and use the effective hammer energy calculated for the last time as the calculation result of the final effective hammer energy. Among them, the preset value can be 0.001m / s 2 .

[0079] Step S10, calculating the dynamic penetration resistance R:

[0080]

[0081] Where A is the cross-sectional area of ​​the probe, and s is the penetration of the dynamic probe in one shot / m.

[0082] In the above calculation process, the derivation process of formula (3), formula (4) and formula (5) in step S3 is as follows:

[0083] The velocity of the falling hammer before the first collision can be calculated by the following formula:

[0084]

[0085] Among them, g is the acceleration due to gravity; h is the drop distance of the falling weight.

[0086] According to the conservation of impulse before and after the first collision, we can get equation (16):

[0087] MV 1,0 +mv1,0 =MV 1 +mv 1 (16)

[0088] Among them, 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 velocity of the falling hammer after the first collision; 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.

[0089] According to the definition of collision restitution coefficient, we can get formula (17):

[0090]

[0091] From equations (15), (16), and (17), we can get the speed of the drop weight and the probe rod after the first collision, as shown in equations (18) and (19):

[0092]

[0093]

[0094] Combining the kinetic energy calculation method with formula (19), we can get the kinetic energy increment ΔE of the probe after the first collision: 1 .

[0095]

[0096] In step S5, the derivation process of equations (8), (9) and (10) is as follows:

[0097] It can be seen from formula (18) that the drop 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 drop hammer after the first collision, whether it is upward or downward, will collide with the probe rod for the second time, and transfer the energy of the drop hammer to the probe rod again. In order to more accurately calculate the hammer energy transferred to the probe rod by the drop hammer, this patent considers the first collision and subsequent multiple collisions until the hammer impact energy is small enough to be ignored or the speed of the drop hammer and the probe rod is always the same and no collision occurs.

[0098] 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 .

[0099] According to the conservation of impulse before and after the n-1th collision:

[0100] MV n-1,0 +mvn-1,0 =MV n-1 +mv n-1 (twenty one)

[0101] According to the definition of the coefficient of restitution:

[0102]

[0103] From equations (21) and (22), the drop weight velocity and probe rod velocity after the n-1th collision can be calculated by equations (23) and (24).

[0104]

[0105]

[0106] Then, during the n-1th collision, the increment of the probe rod kinetic energy can be calculated by formula (25):

[0107]

[0108] In step S4, the derivation process of equations (6) and (7) is as follows:

[0109] In order to calculate the changes in the drop weight velocity and the probe rod velocity between two collisions, the following analysis is performed:

[0110] From formula (24), 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 (26):

[0111] v=v n-1 -(ag)t (26)

[0112] It can be seen from formula (23) 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 (27).

[0113] V=V n-1 +gt (27)

[0114] From equations (26) and (27), the time t between two collisions can be expressed by equation (28):

[0115]

[0116] Then the speed of the drop hammer and the probe rod before the nth collision can be expressed by equations (29) and (30) respectively:

[0117]

[0118]

[0119] To make the formula more concise, let

[0120] k=g / a (31)

[0121] Δv n-1 =V n-1 -v n-1 (32)

[0122] Then equations (29) and (30) can be expressed as equations (33) and (34):

[0123] V n,0 =V n-1 -2kΔv n-1 (33)

[0124] v n,0 =v n-1 +2(1-k)Δv n-1 (34)

[0125] Since the soil resistance is a process of continuous deceleration of the probe rod, when the speed is reduced to 0, the probe rod speed will no longer change. n,0 <0, take v n,0 =0, that is, when the following equation (35) holds, take v n,0 =0.

[0126]

[0127] When equation (35) 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 n-1th collision to the nth collision can be expressed by formula (36):

[0128]

[0129] According to the conservation of mechanical energy of the falling weight, equation (37) exists:

[0130]

[0131] Substituting equation (36) into equation (37), we can obtain the velocity of the falling hammer before the nth collision, which is expressed by equation (38):

[0132]

[0133] From equations (33), (34), and (38), the velocity of the falling hammer before the nth collision can be obtained as shown in equation (39):

[0134]

[0135] The velocity of the probe rod before the nth collision is shown in formula (40):

[0136]

[0137] In step S9, the derivation process of formula (13) is as follows:

[0138]

[0139] 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.

[0140] It can be seen from the above technical scheme that an embodiment of the present invention provides a method for calculating the dynamic penetration resistance of dynamic probing taking into account multiple collisions, which belongs to the field of in-situ tests in geotechnical engineering. The method includes the steps of: calculating the initial value of the acceleration of the soil on the probe rod, calculating the drop hammer speed, the probe rod speed, and the probe rod kinetic energy increment after the first collision; calculating the drop hammer speed and the probe rod speed before the second collision; calculating the drop hammer speed, the probe rod speed, and the probe rod kinetic energy increment after the second collision; calculating the drop hammer speed, the probe rod speed, and the probe rod kinetic energy increment after the third, fourth, fifth, ... collisions in turn, until the drop hammer speed after the collision is equal to the probe rod speed or the drop hammer speed is equal to 0, and then stopping the calculation; taking the sum of the probe rod kinetic energy increments after each collision and the sum of the kinetic energy of the hammer at the end as the effective hammer energy of the dynamic probing, using the effective hammer energy of the dynamic probing to correct the acceleration of the soil on the probe rod, using the iterative method to correct the effective hammer energy of the dynamic probing, and calculating the dynamic penetration resistance. 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 dynamic penetration tests.

[0141] 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 dynamic penetration resistance of dynamic penetration testing considering multiple collisions. It is 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: Among them, M is the mass of the falling hammer; g is the acceleration of gravity; h is the falling distance of the falling hammer; m is the mass of the probe rod; N is the number of hammer blows measured by dynamic penetration; Step S2, calculating the ratio k of the gravitational acceleration g to the acceleration a of the soil on the probe rod; Step S3, using the following formula to calculate the falling hammer velocity V after the first collision 1 and probe speed v 1 , the first collision probe kinetic energy increment ΔE 1 ; Wherein, e is the impact recovery coefficient of steel used in the dynamic penetration test; Step S4, calculate the hammer velocity V before the second collision using the following formula: 2,0 , probe speed v 2,0 : Where Δv n-1 =V n-1 -v n-1 , n = 2, then Δv 1 V 1 -v 1 ; Step S5, calculate the velocity V of the drop hammer after the second collision using the following formula 2 and the velocity v of the probe rod 2 , the kinetic energy increment ΔE of the probe rod in the second collision 2 , 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, using the following formula to calculate the dynamic penetration resistance R: Where A is the cross-sectional area of ​​the probe.

2. A method for calculating dynamic penetration resistance of dynamic penetration testing considering multiple collisions according to claim 1, It is characterized in that In the step S1, N is the number of hammer blows when the penetration is 10 cm.

3. A method for calculating dynamic penetration resistance of dynamic penetration testing considering multiple collisions according to claim 1, It is characterized in that The step S3 also includes: Obtain the impact restitution coefficient of steel used in dynamic penetration testing determined through field tests.

4. A method for calculating dynamic penetration resistance of dynamic penetration testing considering multiple collisions according to claim 1, It 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 a preset value, and the effective hammer energy calculated for the last time is used as the calculation result of the final effective hammer energy.

5. A method for calculating dynamic penetration resistance of dynamic penetration testing considering multiple collisions according to claim 4, It is characterized in that The preset value is 0.001m / s 2 .

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