Pile foundation percussion drilling geological layering method

Abstract

The present application relates to the field of pile foundation engineering impact drilling geological layering, in order to improve the accuracy of pile foundation impact drilling geological layering, a pile foundation impact drilling geological layering method is provided, comprising: step 1, collecting drilling original data; step 2, calculating drilling index mu i and relative drilling index lambda i based on the drilling original data: mu i = 60DeltaV i / (E i T i ), DeltaV i represents the impact drilling volume, E i represents the impact potential energy of the impact drill, T i represents the impact drilling time, DeltaV i = 1 / 4piD 2 DeltaH i , D represents the drilling diameter, DeltaH i represents the cumulative footage drilled in each drilling period, E i = Mgh i N i , M represents the weight of the impact drill hammer, h i represents the stroke, N i represents the number of impacts; n is the number of drilling periods counted; step 3, draw the drilling index-hole depth curve and the relative drilling index-hole depth curve; step 4, based on the curve drawn in step 3, impact drilling geological layering. The above steps improve the accuracy of pile foundation impact drilling geological layering.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of pile foundation engineering impact drilling geological layering, and particularly relates to a pile foundation impact drilling geological layering method. BACKGROUND

[0002] In the field of pile foundation engineering such as highway engineering, railway engineering and house building engineering, the pile foundation needs to meet the design requirements of bearing capacity, and the pile foundation bearing capacity is mainly provided by the rock-soil mass around the pile and at the pile end. Therefore, it is very important to find out the pile foundation geological conditions in the pile foundation design stage and the pile foundation construction stage. In the pile foundation design stage, the method of geological drilling is mainly used to find out the pile foundation geological conditions through the rock core revealed by drilling, and to carry out geological layering to provide correct geological data for pile foundation design. Influenced by factors such as engineering scale, site topographic conditions and exploration depth, the geological conditions of each pile may not be found out in the design stage. Therefore, in the pile foundation construction process, it is particularly important to make pile foundation construction geological records, combine with the previous exploration results, scientifically carry out pile foundation geological layering, and provide accurate geological data for dynamic design of pile foundation, so as to ensure that the pile foundation engineering is reasonable, safe and economical.

[0003] At present, the pile foundation construction hole-forming methods mainly include impact drilling, rotary drilling and manual hole digging. Among them, the hole-forming methods such as manual hole digging and rotary drilling can directly observe the pile surrounding geological conditions (such as the depth of the overburden layer, the weathering degree and the integrity of the bedrock, etc.) through the slag sample (rock core) or the hole wall, and the pile foundation geological layering is simple. However, for the impact drilling hole-forming method, since the hole is formed by using a heavy hammer to impact, the pile hole is in a mud environment during the impact drilling operation, and the geological conditions of the hole wall cannot be directly observed. Moreover, due to the mechanical crushing effect of the rock-soil mass, the returned slag sample is relatively difficult to reflect the geological conditions of the pile surrounding, and the geological conditions of the pile surrounding are mainly judged by experience such as the speed of footage and slag sample to carry out geological layering.

[0004] The above methods have the following main drawbacks and problems: ① Current percussion drilling geological stratification relies more on experience. It is relatively easy to judge when there are obvious differences in drilling properties between soil and rock masses, but it is difficult to judge when the differences in drilling properties are not significant. For example, the drilling speed of dense gravel and relatively soft bedrock may not differ much. In this case, it is relatively difficult to perform geological stratification without reliable preliminary geological exploration results; ② Judging the geological conditions of the pile foundation from the drilling time often has a large error, because during the drilling process, there may be situations such as stuck drill, deviation, grout leakage, and hole collapse. If the driller does not record the time spent on these abnormal situations, it will often cause a large error, or even an error, in the geological stratification of the pile foundation; ③ Relying on percussion drilling cuttings to judge the geological conditions of the pile foundation also has certain defects. For example, if the parent rock composition of the overburden layer and the underlying bedrock are the same type of rock, the cuttings returned by the percussion drill are often similar. In this case, it is difficult to accurately judge the geological conditions around the pile and perform geological stratification of the pile foundation. ④ At present, the geological stratification of pile foundation impact drilling relies more on one or several attributes of the drilling, without comprehensively considering factors such as soil and rock properties, hammer weight, stroke, number of impacts and pile hole size. It is more of an empirical qualitative judgment and has not established a quantitative judgment index that takes into account the comprehensive influence of various factors. Summary of the Invention

[0005] To improve the accuracy of geological stratification in pile foundation impact drilling, this application provides a method for geological stratification in pile foundation impact drilling.

[0006] The technical solution adopted by the present invention to solve the above problems is:

[0007] Geological stratification methods for pile foundation impact drilling include:

[0008] Step 1: Collection of raw borehole data;

[0009] Step 2: Calculate the drilling index μ based on the original borehole data. i and relative drilling index λ i :

[0010] μ i =60ΔV i / (E i T i ), ΔV i E represents the drilling volume of the impact drill. i T represents the impact potential energy of an impact drill. i Impact drilling time, ΔV i =1 / 4πD 2 ΔH i D represents the borehole diameter, ΔH i E represents the cumulative drilling footage within each drilling cycle. i =Mgh iN i , M represents the hammer weight of the impact drill, h i represents the stroke, N i represents the number of impacts;

[0011] n is the statistical number of drilling periods;

[0012] Step 3, draw the drilling index-hole depth curve and the relative drilling index-hole depth curve;

[0013] Step 4, impact drilling geological layering based on the curve drawn in step 3.

[0014] Specifically, the step 4 is specifically:

[0015] Cover layer division: the overall curve shows an increasing trend from top to bottom, and the μ and λ values are relatively discrete;

[0016] Strongly weathered bedrock division: the overall curve shows a straight line, and the μ and λ values change little;

[0017] Medium weathered bedrock division: the overall curve shows a vertical line, and the μ and λ values are basically unchanged or have a small change range.

[0018] In order to improve the layering accuracy, it also includes: step 5, correcting the impact drilling geological layering result of step 4 based on artificial exploration results and / or slag samples;

[0019] Step 6, using the corrected drilling geological layering to guide the dynamic design of the pile foundation.

[0020] The present application has the beneficial effects compared with the prior art: considering the impact drilling time, footage, hammer weight, stroke, impact number and pile hole size and other factors, a kind of impact drilling geological layering quantitative index (impact drilling drilling index μ, relative drilling index λ) and its calculation method are established, and the above quantitative index is used for geological layering, and slag sample, early geological exploration result is verified with each other, to a certain extent, the limitation that current pile impact drilling geological layering depends on experience qualitative judgment is solved, and the geological layering accuracy is improved. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is pile impact drilling geological layering method flow chart;

[0022] Figure 2 It is μ-h curve and division result schematic diagram of 1# pile;

[0023] Figure 3 It is λ-h curve and division result schematic diagram of 1# pile;

[0024] Figure 4 It is μ-h curve and division result schematic diagram of 2# pile;

[0025] Figure 5 Fig. 2 is a schematic diagram of a λ-h curve and division result of a 2# pile;

[0026] Figure 6 Fig. 3 is a schematic diagram of a μ-h curve and division result of a 3# pile;

[0027] Figure 7 Fig. 4 is a schematic diagram of a λ-h curve and division result of a 3# pile. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to examples. It should be understood that the specific examples described herein are only used to explain the present application and should not be used to limit the present application.

[0029] As shown in Figure 1 , the pile foundation impact drilling geological layering method comprises:

[0030] Step 1, collecting drilling original data;

[0031] Step 2, calculating drilling index μ i and relative drilling index λ i based on the drilling original data:

[0032] μ i = 60ΔV i / (E i T i ), ΔV i represents the impact drilling volume, E i represents the impact potential energy of the impact drill, T i represents the drilling time of the impact drill, ΔV i = 1 / 4πD 2 ΔH i , D represents the drilling diameter, ΔH i represents the cumulative footage drilled in each drilling period, E i = Mgh i N i , M represents the weight of the impact drill hammer, h i represents the stroke, and N i represents the number of impacts;

[0033] n is the number of drilling periods counted;

[0034] Step 3, drawing the drilling index-hole depth curve and the relative drilling index-hole depth curve;

[0035] Step 4, impact drilling geological stratification based on the curve drawn in step 3; in this embodiment, it is mainly to divide the overburden layer, strong weathering bedrock layer and medium weathering bedrock layer, specifically:

[0036] Overburden layer division: the curve generally shows an increasing trend from top to bottom, and the μ and λ values are relatively discrete;

[0037] Strong weathering bedrock division: the curve is generally a straight line, and the μ and λ values change little;

[0038] Medium weathering bedrock division: the curve is generally a vertical line, and the μ and λ values are basically unchanged or have a small change range;

[0039] Further, in order to improve the stratification accuracy, step 5, based on artificial exploration results and / or slag samples, the impact drilling geological stratification results of step 4 are corrected: the pile foundation geological preliminary stratification results (mainly the base-cover boundary, weathering boundary, etc.) of step 4 are compared with the previous exploration design data, slag samples, etc. For the previous design data with exploration, mainly compare and verify with exploration results, slag samples, etc. If the geological stratification is roughly the same, no correction is needed; if there is a difference, the geological stratification based on quantitative indicators and the previous design results geological stratification should be carefully reviewed to find out the reasons for the difference and make corrections. For the previous design data without exploration, the geological stratification is based on the adjacent drill hole speculation, mainly compared and verified with the slag sample, and the difference between the geological stratification results based on the quantitative indicators and the design speculated geological stratification is compared, and according to the specific difference, the original design geological stratification (base-cover boundary, weathering boundary, etc.) is adjusted to provide accurate geological data for dynamic design of pile foundation.

[0040] Step 6, use the corrected drilling geological stratification to guide the dynamic design of pile foundation.

[0041] Embodiment

[0042] 1. Project overview

[0043] A bridge project is located in the valley of the southwest mountainous area, which is a prestressed concrete box girder bridge. The design of the bridge foundation is a bored pile (rock-embedded pile), the length of the pile foundation is 30-35 m, the pile diameter D = 2.2 m, and the design requires that the pile foundation is embedded in the medium weathering rock mass with a depth of not less than 3D.

[0044] 2. Engineering geological conditions

[0045] According to the survey results, the overburden of the bridge site is Quaternary Holocene alluvial-proluvial (Q4 pl+al ) gravel soil, with relatively dense structure, and drilling reveals that the thickness is about 15-20 m; the underlying bedrock is a variable thickness interbedded metamorphic sandstone and silty sandstone of the Upper Triassic Zhuzi Group (T3zh), with strong weathering about 1-3 m thick, and below it is a medium weathering rock mass with hard rock quality.

[0046] 3. Pile construction conditions

[0047] The pile foundation was formed by percussion drilling, with a hammer weight of 5.0 t. Due to the limitations of topography and other conditions during the survey and design phase, geological drilling was not performed for some of the bridge piers, and the pile foundation geological conditions were mainly referenced from the results of adjacent drilling. Therefore, detailed percussion drilling data need to be collected during the construction phase to further understand the pile foundation geological conditions and provide accurate geological data for dynamic pile foundation design.

[0048] 4. Engineering application of percussion drilling geological stratification method based on quantitative indicators

[0049] (1) Pile design conditions

[0050] Three piles (Nos. 1#, 2#, and 3#) were selected for analysis, and the pile design conditions are shown in Table 1:

[0051] Table 1. Pile design conditions

[0052]

[0053] (2) Drilling data collection

[0054] The drilling conditions of the above three piles were accurately recorded, including pile number, pile diameter, opening elevation, drilling time, stroke, impact number, drilling depth, cumulative depth, drilling conditions, and geological conditions, etc., and slag samples were collected.

[0055] (3) Drilling data processing

[0056] The drilling data of the above three piles were sorted and counted, and the drilling index μ i and the relative drilling index λ i were calculated:

[0057] μ i = 60ΔV i / (E i T i ), ΔV i represents the percussion drilling volume, E i represents the percussion drilling potential energy, T i represents the percussion drilling time, ΔV i = 1 / 4πD 2 ΔH i , D represents the drilling diameter, ΔH i represents the cumulative drilling footage per drilling period, E i = Mgh i N i , M represents the percussion drill hammer weight, h i represents the stroke, and N i represents the number of impacts;

[0058] n is the number of drilling cycle statistics.

[0059] Draw the drilling index-hole depth curve (μ-h curve) and the relative drilling index-hole depth curve (λ-h curve).

[0060] (4) Geological stratification based on quantitative indicators

[0061] Using the drilling index-hole depth curve (μ-h curve) and the relative drilling index-hole depth curve (λ-h curve) drawn above, the three pile impact drillings are geologically stratified, and the overburden, strong weathered bedrock, and medium weathered bedrock are divided. Specifically:

[0062] ① Overall judgment

[0063] According to the μ-h curve and the λ-h curve, the overall judgment is made by analyzing the size of the drilling index (μ) and the relative drilling index (λ) and their variation with depth (h). The overburden is generally easier to drill than the bedrock, so the quantitative stratification indicators, drilling index (μ) and relative drilling index (λ), should be larger than those of the bedrock, and there will be a large difference between them. The μ-h curve and the λ-h curve of the overburden above the bedrock-overburden interface generally show an upward trend, and the μ-h curve and the λ-h curve of the bedrock below the bedrock-overburden interface are generally linear, basically unchanged or with very small changes.

[0064] ② Overburden division

[0065] The soil is a heterogeneous medium, and different soils have different drilling difficulties due to their material composition, particle size composition, compaction degree, and burial depth. The drilling index (μ) and the relative drilling index (λ) are relatively discrete and have a large variation range. For the same soil layer, as the burial depth increases and the lateral confining pressure increases, the μ and λ values decrease. The μ-h curve and the λ-h curve of the overburden generally show an upward trend, and the μ and λ values are relatively discrete. If this characteristic is met, the overburden can be preliminarily divided.

[0066] ③ Strong weathered bedrock division

[0067] The strong weathered bedrock has engineering geological properties generally between the soil layer and the medium weathered bedrock, so its drilling difficulty is between the two. The drilling index (μ) and the relative drilling index (λ) are smaller than those of the overburden and larger than those of the medium weathered rock mass. The μ and λ values generally decrease with increasing depth, but the change amplitude is smaller than that of the overburden. The μ-h curve and the λ-h curve of the strong weathered bedrock are generally linear, and the μ and λ values change little. If this characteristic is met, the strong weathered bedrock can be preliminarily divided.

[0068] ④ Medium weathered bedrock division

[0069] The moderately weathered bedrock generally has high strength and is relatively uniform, and is difficult to drill. The quantitative stratification indexes, drilling index (μ) and relative drilling index (λ), are smaller than those of strongly weathered rock mass and soil, and the μ and λ values have very small variation range and are basically unchanged or slightly changed with the increase of depth. The μ-h curve and λ-h curve of the moderately weathered bedrock are generally vertical lines, and the μ and λ values are basically unchanged or have very small variation range. In accordance with this feature, the moderately weathered bedrock can be preliminarily divided.

[0070] The μ-h curve, λ-h curve and stratification result of the 1# pile are shown in Figure 2 , Figure 3 The μ-h curve, λ-h curve and stratification result of the 2# pile are shown in Figure 4 , Figure 5 The μ-h curve, λ-h curve and stratification result of the 3# pile are shown in Figure 6 , Figure 7 .

[0071] The geological stratification of each pile is shown in the following table:

[0072] 1# pile geological stratification quantitative index statistics and geological stratification result table

[0073]

[0074] 2# pile geological stratification quantitative index statistics and geological stratification result table

[0075]

[0076] 3# pile geological stratification quantitative index statistics and geological stratification result table

[0077]

[0078] 1# pile geological stratification result:

[0079] 0-17.0 m, floating egg gravel soil; the μ-h curve and λ-h curve are generally large at the top and small at the bottom; the drilling index μ and the relative drilling index λ data are relatively discrete, decrease with the increase of depth, and have large variation range; the drilling index μ ranges from 0.026 to 0.100, with an average value of 0.057; the relative drilling index λ ranges from 0.038 to 0.144, with an average value of 0.082;

[0080] 17.0-18.0 m, strongly weathered sandstone; the μ-h curve and λ-h curve are generally inclined straight lines; the drilling index μ and the relative drilling index λ decrease with the increase of depth, and have small variation range; the drilling index μ ranges from 0.007 to 0.024, with an average value of 0.015; the relative drilling index λ ranges from 0.010 to 0.034, with an average value of 0.022;

[0081] 18.0~31.2m, weathered sandstone; μ-h curve, λ-h curve is roughly vertical line type; drilling index μ, relative drilling index λ changes very small, with depth increasing, basically remains unchanged; drilling index μ range 0.006~0.008, average value 0.007; relative drilling index λ range 0.009~0.011, average value 0.010.

[0082] 1# pile above geological stratification results and impact drilling slag sample are compared and verified, basically consistent, it shows that based on drilling index μ, relative drilling index λ geological stratification results are reliable. The pile has no drilling data in early stage, it is presumed that the overburden depth is about 20m, during construction, according to impact drilling results, the actual overburden is about 17m, the overburden depth presumed in design stage has certain difference with actual depth, the actual overburden depth is shallower than the design overburden depth; it is presumed that the strongly weathered bedrock thickness is 3.0m, the actual thickness is about 1m.

[0083] 2# pile geological stratification results:

[0084] 0~16.0m, floating pebble gravel soil; μ-h curve, λ-h curve is generally large down small type; drilling index μ, relative drilling index λ data are relatively discrete, with depth increasing and decrease, change amplitude is large; drilling index μ range 0.016~0.136, average value 0.079; relative drilling index λ range 0.024~0.201, average value 0.118;

[0085] 16.0~20.0m, strongly weathered sandstone; μ-h curve, λ-h curve is roughly inclined straight line type; drilling index μ, relative drilling index λ decreases with depth increasing, change amplitude is small; drilling index μ range 0.012~0.014, average value 0.013; relative drilling index λ range 0.018~0.021, average value 0.019;

[0086] 20.0~31.7m, moderately weathered sandstone; drilling index μ, relative drilling index λ changes very small, with depth increasing, slightly decreases; drilling index μ range 0.004~0.011, average value 0.008; relative drilling index λ range 0.006~0.016, average value 0.012.

[0087] 2# pile above geological stratification results and impact drilling slag sample and early stage drilling are compared and verified, basically consistent, it shows that based on drilling index μ, relative drilling index λ geological stratification results are reliable.

[0088] 3# pile geological stratification results:

[0089] 0~20.8m, gravelly soil; the μ-h curve and the λ-h curve are generally large-small type from top to bottom; the drilling index μ and the relative drilling index λ are discrete, and decrease with the increase of depth, with large variation range; the drilling index μ ranges from 0.015 to 0.136, with an average of 0.061; the relative drilling index λ ranges from 0.034 to 0.374, with an average of 0.167;

[0090] 20.8~24.6m, strongly weathered sand slate; the μ-h curve and the λ-h curve are generally straight line type; the drilling index μ and the relative drilling index λ decrease with the increase of depth, with small variation range; the drilling index μ ranges from 0.011 to 0.012, with an average of 0.011; the relative drilling index λ ranges from 0.023 to 0.026, with an average of 0.025;

[0091] 24.6~31.2m, moderately weathered sand slate; the μ-h curve and the λ-h curve are generally vertical line type; the drilling index μ and the relative drilling index λ change little, and slightly decrease with the increase of depth; the drilling index μ ranges from 0.002 to 0.008, with an average of 0.006; the relative drilling index λ ranges from 0.005 to 0.020, with an average of 0.015.

[0092] 3# pile above the geological stratification results and the impact of drilling slag sample are basically consistent, which shows that the geological stratification results based on the drilling index μ and the relative drilling index λ are reliable. The pile has no drilling data in the early stage, and it is speculated that the overburden depth is about 18m. According to the impact drilling results during construction, the actual overburden is about 21m, and there is a certain difference between the design stage and the actual depth.

[0093] The drilling index (μ) and the relative drilling index (λ) of different rock masses of the above three piles are counted, and the statistical results are shown in the following table:

[0094] Statistical results of drilling index (μ) and relative drilling index (λ) of different rock masses

[0095]

[0096] ①The overall law of drilling index (μ) and relative drilling index (λ) is gravelly soil > strongly weathered sand slate > moderately weathered sand slate, which shows that the drilling difficulty of different rock masses is different, and sand slate is more difficult to drill than gravelly soil, which is consistent with the actual situation;

[0097] ②The drilling index (μ) and the relative drilling index (λ) of gravelly soil have large variation range, which ranges from 0.015 to 0.136 and from 0.024 to 0.374 respectively, with an average of 0.064 and 0.121 respectively, which is preliminarily analyzed as the difference in composition, particle size and density of the overburden parent rock;

[0098] ③ Strongly weathered sandstone drilling index (μ), relative drilling index (λ) has certain change range, but the overall change is not big, the change range is 0.007~0.024, 0.010~0.034 respectively, the average is 0.013, 0.021 respectively;

[0099] ④ Medium weathered sandstone drilling index (μ), relative drilling index (λ) change range is small, the change range is 0.011~0.007, 0.020~0.012 respectively, the average is 0.007, 0.012 respectively, preliminary analysis is due to the small difference of bedrock lithology, weathering degree, hardness and completeness.

Claims

1. A method for geological stratification of a pile foundation impact drilling, characterized in that, Comprise: Step 1, collecting drilling original data; Step 2, Calculate drilling index μ based on drilling raw data i and relative drilling index λ i : μ i = 60 ΔV i / (E i T i ), ΔV i represents the volume drilled by the hammer drill, E i represents the impact potential energy of the hammer drill, T i represents the hammer drill drilling time, ΔV i = 1 / 4 πD 2 ΔH i , D represents the borehole diameter, ΔH i represents the cumulative footage drilled per drilling cycle, E i = Mgh i N i , M represents the hammer drill hammer weight, h i represents the stroke, N i represents the number of impacts; n is the number of drilling cycle statistics; Step 3, drawing drilling index-hole depth curve and relative drilling index-hole depth curve; Step 4, impact drilling geological stratification based on the curve drawn in step 3.

2. A piling impact drilling method according to claim 1, characterized in that, The step 4 is specifically: Cover layer division: the curve generally shows an increasing trend from top to bottom, and the values of mu and lambda are relatively discrete; Strongly weathered bedrock division: the curve generally shows a straight line, and the values of mu and lambda change little; Medium weathered bedrock division: the curve generally shows a vertical line, and the values of mu and lambda are basically unchanged or change within a small range.

3. Pile foundation impact drilling stratigraphic layering method according to claim 1 or 2, characterized in that, Also include: Step 5, correcting the impact drilling geological stratification results of step 4 based on artificial exploration results and / or slag samples; Step 6, using the corrected drilling geological stratification to guide dynamic design of pile foundation.

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