Gravel pile composite foundation dynamic sounding hammering number correction method and application

Abstract

The invention discloses a gravel pile composite foundation dynamic penetration hammer count correction method and application, and the method comprises the steps: carrying out the statistics of the hammer count per 10cm obtained by each dynamic penetration according to 1m, and obtaining a preliminary statistical hammer count curve; a median method is adopted, statistics is carried out by taking a plurality of root piles as a statistical group, the median is obtained, and the median is taken as the representative value of the dynamic sounding hammering number of the detection area; deriving a rod length correction coefficient based on a Newton elastic collision theory and a Hailey piling formula; the method is applied to a scene when the depth of the gravel pile exceeds 20 meters. According to the method, aiming at the ultra-deep gravel pile (the depth exceeds 20 meters), a correction method for the depth exceeding 20 meters is not provided in the existing Geotechnical Engineering Reconnaissance Specification (GB50021-2001) 2009 edition; according to the method, the discreteness is reduced by adopting a median method aiming at the problem that the discreteness of a single-pile test result is large, so that the subsequent foundation reinforcement effect evaluation is difficult.

Description

TECHNICAL FIELD

[0001] The application belongs to a kind of gravel pile, sand pile and other granular pile dynamic sounding hammer correction method in soft soil foundation, which can also be applied to standard penetration correction, and specifically relates to a kind of gravel pile composite foundation dynamic sounding hammer correction method and application. BACKGROUND

[0002] As a common in-situ soil test method, dynamic sounding is often used to evaluate the in-situ foundation density and bearing capacity, and is also often used to evaluate the gravel pile forming state. The basic principle of dynamic sounding is that the potential energy of the falling hammer is converted into hammering energy after free falling, which drives the probe rod and probe to move and causes penetration damage to the soil. The energy conversion rate is affected by many factors such as mechanical equipment type, operation factors, probe length, soil type, etc., so the energy conversion rate has high variability, which brings difficulties to the evaluation based on the number of hammerings. According to the existing domestic specifications, it is generally believed that the probe rod has a significant impact on the hammering energy, the longer the rod length, the lower the energy transmission rate, and the higher the number of hammerings, so a coefficient less than 1.0 is needed, and the coefficient changes with the rod length.

[0003] At present, when the rod length is corrected, the 2009 version of "Geotechnical Engineering Investigation Specification" (GB50021-2001) is usually referred to for correction, however, this method only provides a correction method for the rod length within 20m and the number of hammerings within 50, and does not give any instructions for the super-deep gravel pile with a rod length exceeding 20m. Secondly, the correction coefficient of this method is mainly obtained by fitting in the test of semi-infinite body foundation, the strength of the cross plate increases linearly with the depth, according to the theory of granular pile, the strength of the granular pile is related to the constraint state of the surrounding soil, therefore, the greater the confining pressure of the surrounding soil, the higher the strength index of the soil, and the higher the strength of the gravel pile, and the corresponding number of hammerings should be greater.

[0004] The main problems of the current statistical and correction methods are: (1) the current correction is directly corrected based on the results of single gravel pile detection, since the number of hammerings of the gravel pile is affected by many factors during dynamic sounding, the number of hammerings has high discreteness, but according to the results of the foundation plate load test, the foundation bearing capacity is relatively stable, which indicates that the level of foundation bearing capacity is not completely linearly related to the number of single pile hammerings, which brings difficulties to the evaluation of foundation reinforcement effect; (2) from the trend of the corrected curve, after correction according to the appendix of the "Geotechnical Engineering Investigation Specification", the number of hammerings basically does not change with the depth or even shows a downward trend, which is contrary to the theory of granular pile and basic physics, indicating that the correction method according to the specification overestimates the change of the correction coefficient with the rod length; (3) no correction method is given for more than 20 meters. SUMMARY

[0005] In view of the defects or deficiencies of the prior art, the technical problem to be solved by the present application is a gravel pile composite foundation dynamic sounding hammer blow number correction method and application.

[0006] To solve the above technical problems, the present application realizes the following technical solutions:

[0007] The present application proposes a gravel pile composite foundation dynamic sounding hammer blow number correction method, which comprises:

[0008] The number of blows per 10 cm obtained by each dynamic sounding is counted per 1 m to obtain a preliminary statistical blow curve;

[0009] The median method is used to count a plurality of piles as a statistical group to obtain the median, and the median is used as the representative value of the dynamic sounding hammer blow number of the detection area;

[0010] The rod length correction coefficient is derived based on Newton's elastic collision theory and the Hiley pile driving formula.

[0011] Further optionally, in the above-mentioned median method, at least 6 piles are counted as a statistical group.

[0012] Further optionally, in the above-mentioned derivation of the rod length correction coefficient based on Newton's elastic collision theory and the Hiley pile driving formula, it comprises:

[0013]

[0014] Where m0 is the sounding rod mass when the rod length is equal to a certain fixed rod length; m L is the probe rod mass when the rod length is greater than the fixed length; k is the restitution coefficient when the hammer rod collides, M is the weight of the hammer, and the heavy sounding rod length correction coefficient is calculated according to the above formula.

[0015] Further optionally, a test statistical array is counted according to the above method, and the correction method is compared with the correction method of "Water Resources and Hydropower Engineering Geology Investigation Specification" GB50487-2008 and "Highway Engineering Geology Investigation Specification" JTJ064-98.

[0016] The present application also proposes an application of the gravel pile composite foundation dynamic sounding hammer blow number correction method, which is applied to the scene where the depth of the gravel pile exceeds 20 meters.

[0017] Compared with the prior art, the present application has the following technical effects:

[0018] The present application can be used for super deep gravel pile (depth more than 20 meters), and the existing in-force standard "Code for Investigation of Geotechnical Engineering" (GB50021-2001) 2009 edition does not provide correction method for depth more than 20 meters; the present application is based on Newton elastic collision theory and Healy pile driving formula to deduce the change of theoretical hammering number with rod length, and consider the influence of effective mass when the rod length is more than 20 meters, to obtain the theoretical envelope line of hammering number and rod length change rule; the present application is used for the problem that the test results of single pile are greatly discrete, which brings difficulties to subsequent foundation reinforcement effect evaluation, and the median method is used to reduce the discreteness. BRIEF DESCRIPTION OF DRAWINGS

[0019] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments made with reference to the accompanying drawings:

[0020] Figure 1 Flow chart of gravel pile composite foundation dynamic sounding hammering number correction method in an embodiment of the present application;

[0021] Figure 2 Schematic diagram of hammering number curve after average of original hammering number of test pile per meter in an embodiment of the present application;

[0022] Figure 3 Schematic diagram of dynamic sounding hammering number representative value of a statistical group in an embodiment of the present application;

[0023] Figure 4 Schematic diagram of rod length correction coefficient calculated by Healy formula method in an embodiment of the present application;

[0024] Figure 5 Comparison effect diagram of different correction methods in an embodiment of the present application. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0026] As shown in the drawings, Figure 1 In one of the embodiments of the present application, a gravel pile composite foundation dynamic sounding hammering number correction method comprises:

[0027] The hammering number per 10 cm obtained by each dynamic sounding is counted per 1 m to obtain a preliminary statistical hammering number curve;

[0028] The median method is used, a plurality of piles are taken as a statistical group for statistics, the median is obtained, and the median is taken as a representative value of the dynamic sounding hammer number of the detection area.

[0029] The rod length correction coefficient is derived based on Newtonian elastic collision theory and the Hiley pile driving formula.

[0030] The present application can be used for super-deep gravel piles (depth exceeding 20 meters), and the existing in-force specification “Geotechnical Engineering Investigation Specification” (GB50021-2001) 2009 edition does not provide a correction method for depths exceeding 20 meters. The present application derives the change of the theoretical hammer number with the rod length based on Newtonian elastic collision theory and the Hiley pile driving formula, and considers the influence of the effective mass when the rod length exceeds 20 meters or more, to obtain the theoretical envelope line of the change law of the hammer number and the rod length. The present application reduces the discreteness by using the median method for the discreteness of the single pile test results.

[0031] In the present embodiment, the number of hits per 10 cm obtained by each dynamic sounding is counted per 1 m, and a preliminary statistical hit number curve is obtained, which can be referred to as shown in Figure 2 .

[0032] In the present embodiment, in the above-mentioned statistics by using the median method and taking a plurality of piles as a statistical group, the median method is used to take at least 6 piles as a statistical group for statistics, and a statistical group takes the median as a representative value of the dynamic sounding hammer number of the detection area. A schematic diagram can be referred to as shown in Figure 3 . From Figure 3 , it can be seen that the median method is used as a representative value of a group, the median is within the 95% confidence interval, the discreteness of the data can be well reduced, compared with the average method, the median method is less affected by the extreme maximum value and the extreme minimum value, the data has better stability, the correlation of the overall trend is better, and the curve trend of the median has better correlation with the trend of the vane strength.

[0033] Specifically, to reduce the discreteness of the single pile data, the concept of “statistical group” is introduced, and the specific implementation logic is as follows:

[0034] Group sample size determination: divide the engineering detection area into statistical units, and each unit contains at least 6 gravel piles (verified by sensitivity analysis: when the number of piles is greater than or equal to 6, the coefficient of variation of the median can be reduced from 25% of the single pile to less than 8%, meeting the 95% confidence interval requirement);

[0035] Median calculation rule: the number of hits of 6 piles at the same depth (such as 5 m, 10 m, 20 m) is sorted from small to large, and the average value of the 3rd-4th hit number is taken as the “median hit number” of the depth;

[0036] Area representative curve generation: connecting the median number of blows at each depth, the representative curve of the dynamic sounding number of blows in the detection area is obtained (reference Figure 3 , The curve is compared with the single pile curve: the smoothness of the median curve is significantly improved, and the correlation coefficient R 2 of the cross-shear strength curve (τ / kPa) measured at the same period is 0.85, which is much higher than the average value of 0.62).

[0037] Compared with the traditional "average value method", the median method can effectively avoid the interference of extreme values (such as the sudden increase / decrease of the number of blows of a single pile due to the abnormal local gravel density), for example, in a certain project, the number of blows of a pile at a depth of 20m reaches 55 (extreme value), the average value method will make the representative value of this depth 18% higher, and the median method only deviates by 3%; The quantitative basis of "≥6 pile groups" is clear, solving the "arbitrariness of the number of piles in the group" problem of the traditional method, making the data processing more standardized.

[0038] Further, in the above derivation of the rod length correction coefficient α based on Newton's elastic collision theory and the Heyer pile formula in this embodiment, it includes:

[0039]

[0040] Wherein, m0 is the mass of the probe rod when the rod length is equal to a certain fixed length; m L is the mass of the probe rod when the rod length is greater than the fixed length; M is the mass of the weight (for heavy cone dynamic sounding test, M is 63.5kg), k is the restitution coefficient when the hammer hits the rod (according to engineering measurement, the value range is 0.6-0.8, the value of steel probe rod is 0.75, and the value of wooden probe rod is 0.65, the traditional specification does not specify the value basis of k), the heavy sounding rod length correction coefficient calculated according to the above formula can be seen in Figure 4 . The correction coefficient α of the depth interval of 20-50m is calculated according to the above formula, and the "blow number-rod length" theoretical envelope is obtained (reference Figure 4 , The curve shows that for every 5m increase in rod length, α decreases from 0.92 to 0.78, showing a linear decreasing trend, which is consistent with the effective mass growth rule).

[0041] This embodiment first introduces "effective mass" into the correction of super-deep rod length, solving the "20m above correction coefficient fault" problem of the traditional specification; the engineering value range of the restitution coefficient k is clear, so that the theoretical formula can be directly applied, rather than pure theoretical derivation.

[0042] Further, in this embodiment, a test statistical array is statistically processed according to the above method, and the correction method of "Code for Geotechnical Investigation of Water Resources and Hydropower Engineering" GB50487-2008 and "Code for Geotechnical Investigation of Highway Engineering" JTJ064-98 is compared, and the comparison chart can be seenFigure 5 The statistical method is the median method, and the correction is carried out by using the above-mentioned several different correction methods. Figure 5 It can be seen that the method based on theoretical derivation is close to the "Water Conservancy and Hydropower Specification" and "Highway Engineering Specification" by using the median method for statistics and using the above-mentioned several different correction methods for correction. After correction, the corrected blow counts can still reflect the trend of the blow counts changing with the soil strength and the confining pressure. The corrected blow counts of the "Geotechnical Engineering Specification" deviate from the laws of physics. In comparison with the theoretical method and the "Water Conservancy and Hydropower Specification" and "Highway Engineering Specification", the correction results of the three methods are almost the same within 20 meters. Within 20 meters to 30 meters, the overall trend of the theoretical derivation method has better correlation with the cross plate strength curve, and thus is more optimal.

[0043] The super deep scene advantage: in the depth range of 20-30m, the correlation (R 2 =0.88) of the blow counts corrected by the method and the cross plate strength curve is significantly higher than that of the water conservancy and hydropower specification (0.76) and the highway engineering specification (0.72), and can better reflect the physical correlation of "soil strength-confining pressure-blow count";

[0044] The specification compatibility: within 20m, the results are highly consistent with the existing specifications, and the traditional method can be directly replaced to reduce the learning cost of engineering personnel;

[0045] The physical law compliance: the "Geotechnical Engineering Specification" deviates from the physical law of "increasing of deep soil confining pressure leading to increasing of blow count" because the effective mass of the super deep rod length is not considered, and the corrected blow count appears "cliff-like drop" (from 35 to 22) after 25m. However, the corrected blow count of the method rises from 35 to 42 smoothly, which is in line with the engineering practice.

[0046] The embodiment also proposes the application of the gravel pile composite foundation dynamic sounding hammer blow count correction method, which is applied to the scene where the depth of the gravel pile exceeds 20 meters.

[0047] Specifically, the deep foundation pit support gravel pile: in the subway foundation pit support, the depth of the gravel pile is often 25-35m. The method can accurately evaluate the foundation bearing capacity of the support structure and avoid the deformation of the foundation pit caused by correction deviation; the deep soft foundation treatment of the highway: when the depth of the gravel pile in the soft soil layer exceeds 20m, the method can reduce the evaluation deviation of the foundation bearing capacity from 25% to within 8%, and guide the optimization of the cushion thickness; the gravel pile of the port wharf yard: affected by the sea tide, the water content of the deep soil of the wharf foundation is high. The median method of the method can effectively exclude the "abnormal blow count caused by local water accumulation", and improve the detection accuracy. In addition, the "rod length correction coefficient formula" of the method can be further popularized to the dynamic sounding correction of other granular material piles such as sand pile and cement soil pile, and has the universality of cross-pile type.

[0048] The present application can be used for ultra-deep stone piles (depth exceeding 20 meters), and the existing in-force standard "Geotechnical Engineering Investigation Standard" (GB50021-2001) 2009 edition does not provide a correction method for depths exceeding 20 meters; the present application is based on the Newtonian elastic collision theory and the Heyler pile driving formula to deduce the change of the theoretical hammering number with the length of the rod, and considers the influence of the effective mass when the length of the rod exceeds 20 meters or more, to obtain the theoretical envelope of the change law of the hammering number and the length of the rod; the present application uses the median method to reduce the discreteness of the single pile test results, to solve the problem that the discreteness of the single pile test results brings difficulties to the subsequent evaluation of the effect of foundation reinforcement. Therefore, the present application has good market application prospect.

[0049] In the description of the present application, unless explicitly specified and limited, the terms "connected", "connected", "fixed" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrated; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0050] In the present application, unless explicitly specified and limited, the first feature "on" or "under" the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the first feature "on", "above" and "above" the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "below" and "below" the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0051] In the description of the present embodiment, the terms "up", "down", "left", "right", and other orientations or positional relationships are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of description and simplification of operation, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" are only used to distinguish in the description, and have no special meaning.

[0052] The above embodiments are only used to illustrate the technical solutions of the present application and not to limit, and the present application is described in detail with reference to the preferred embodiments. Those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the present application, and all should be covered within the scope of the claims of the present application.

Claims

1. A method for correcting the number of blows in dynamic penetration testing of a composite foundation with crushed stone piles, characterized in that, include: The number of blows per 10cm obtained from each power penetration test was statistically analyzed over 1m to obtain a preliminary statistical blow count curve. The median method was used, and multiple piles were statistically grouped together to obtain the median. The median was then used as the representative value of the number of dynamic penetration hammer blows in this test area. The rod length correction coefficient is derived based on Newton's elastic collision theory and Hellley's piling formula.

2. The method for correcting the number of blows in dynamic penetration testing of composite foundation with crushed stone piles according to claim 1, characterized in that, The above-mentioned method of using the median method to statistically analyze multiple root stumps as a statistical group includes: using the median method to statistically analyze at least 6 root stumps as a statistical group.

3. The method for correcting the number of blows in dynamic penetration testing of composite foundation with crushed stone piles according to claim 1, characterized in that, The rod length correction coefficients derived above based on Newton's elastic collision theory and Heyley's piling formula include: Where m0 is the mass of the probe when the rod length is equal to a certain fixed rod length; m L is the probe mass when the rod length is greater than a fixed length; k is the recovery coefficient when the hammer rod collides; M is the mass of the heavy hammer; and the correction coefficient for the length of the heavy probe rod is calculated according to the above formula.

4. The method for correcting the number of blows in dynamic penetration testing of composite foundation with crushed stone piles according to claim 3, characterized in that, The above method was used to statistically analyze an experimental statistical array, and the results were compared with the correction methods in the "Code for Geological Investigation of Water Conservancy and Hydropower Engineering" GB50487-2008 and the "Code for Geological Investigation of Highway Engineering" JTJ064-98.

5. The application of the method for correcting the number of blows in dynamic penetration testing of composite foundations with crushed stone piles as described in any one of claims 1 to 4, characterized in that, It is applicable to scenarios where the depth of the crushed stone pile exceeds 20 meters.

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