A method for pile foundation investigation optimization in granite boulder area

Abstract

The application discloses a method for pile foundation investigation optimization in granite boulder area, comprising the following steps: determining the feature geology drilling of the target building, dividing the boulder development degree according to the site condition such as site boulder rate or line boulder rate, researching the stress model of pile foundation bearing capacity with boulder diameter as the variable, drawing the load-depth relationship diagram, analyzing and calculating to obtain relevant data, and judging whether to carry out pile-by-pile exploration in the area according to the obtained data. The application aims at the spatial law of boulder development in granite area, provides a theoretical basis for investigation workload arrangement optimization, fills the specification and theoretical blank, reduces the economic cost for the project construction party, and has high popularization significance.

Description

Technical Field

[0001] This invention relates to the field of pile foundation investigation technology, specifically a method for optimizing pile foundation investigation in granite boulder areas. Background Technology

[0002] Granite is widely distributed in my country, and its weathered layers often contain a considerable number of isolated boulders. During pile driving, these hard boulders frequently hinder pile formation, preventing the piles from reaching the intended depth. Direct construction under such conditions can easily damage equipment, pose safety hazards to workers, and delay the project. Therefore, prior site investigation is crucial to ensure safety and efficiency. Typically, surveying and design units conduct pile foundation investigations in areas with isolated boulders and provide recommendations for pile-by-pile exploration to manage risks. This approach is relatively conservative. However, in certain special circumstances, continuing to use pile-by-pile exploration may be unnecessary and wasteful of resources and costs.

[0003] Therefore, a method for optimizing pile foundation investigation in granite boulder areas is needed to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a method for optimizing pile foundation investigation in granite boulder areas, in order to solve the problems mentioned in the background art.

[0005] To address the aforementioned technical problems, this invention provides the following technical solution: a method for optimizing pile foundation exploration in granite boulder areas. The method includes: firstly determining characteristic geological boreholes in the granite boulder area; classifying the degree of boulder development based on site conditions; conducting a pile foundation bearing capacity stress model study with boulder diameter as a variable; drawing a load-depth relationship diagram; analyzing and calculating relevant data; and using the obtained data to determine whether to conduct pile-by-pile exploration in the area, thus providing a theoretical basis for the layout of exploration workload.

[0006] Furthermore, the characteristic geological borehole is an exploration borehole used to characterize the representative stratigraphic distribution within a specific building area. There can be one characteristic geological borehole, or multiple boreholes when geological conditions are complex. Through the characteristic geological borehole, relevant data about the granite boulder area can be obtained, including: the thickness of the characteristic soil layer. Security Depth h s Danger depth h d Balance depth, site visibility rate, and optimization index;

[0007] Furthermore, the thickness of the characteristic soil layer The average thickness of each characteristic soil layer used to characterize the building features, representing the borehole's features;

[0008] The safety depth h s The pile length required to meet the bearing capacity requirements of the pile foundation after embedding a boulder to a certain depth in a characteristic geological borehole;

[0009] The danger depth h d The critical pile length required to meet the bearing capacity requirements of the pile foundation after the maximum depth of the boulder embedded in the characteristic geological borehole is reached.

[0010] The equilibrium depth is the pile length between the safe depth and the danger depth;

[0011] The site's isolated rock encounter rate is the proportion of isolated rocks revealed in all exploratory boreholes; that is:

[0012] Site boulder exposure rate = (Number of boreholes revealing boulders within the site area / Total number of boreholes within the site area) × 100%;

[0013] Based on the depth range of the boulder distribution, the proportion of boulders revealed at the depth of the exploration borehole is determined by the depth h of the boulder burial from the top of the pile. g Conforms to h g ≥h s When the boulders are exposed at shallow depths, this is called the safe boulder exposure rate; the proportion of boulders exposed at shallow depths of the borehole is [value missing] at a depth of h. g Conforms to h g ≤h d When the burial depth of the isolated rock is h, it is called the danger level of the isolated rock; g Conforms to h d ≤h g ≤h s The proportion of isolated rocks at a given time is called the equilibrium isolation rate.

[0014] The following relationships exist among the four:

[0015] Site visibility rate = Dangerous visibility rate + Balanced visibility rate + Safe visibility rate;

[0016] Optimization Index = 100% * (Dangerous Encounter Rate + Safe Encounter Rate) / Site Encounter Rate.

[0017] Furthermore, the classification of the development degree of isolated boulders is as follows: based on the rate of isolated boulders or linear isolated boulders revealed in all exploration boreholes, and combined with their potential impact on the actual project, the development degree of isolated boulders is classified into three levels, including: strongly developed isolated boulders, moderately developed isolated boulders, and weakly developed isolated boulders; classifying the development degree of isolated boulders can provide a basis for determining whether pile-by-pile exploration should be carried out in this area.

[0018] The line boulder rate is the vertical layer thickness of the boulder in the exploration hole divided by the thickness from the exposed bedrock surface (moderately weathered, slightly weathered) to the final hole depth, expressed as a percentage (%).

[0019] The site conditions for a site with well-developed isolated boulders, as defined by the isolation rate being greater than 30% or the linear isolation rate being greater than 20%, are as follows:

[0020] The site conditions for a moderately developed solitary rock formation are: a solitary rock appearance rate greater than 10% and less than 30%, or a linear solitary rock appearance rate greater than 5% and less than 20%.

[0021] The site conditions for a site classified as having weakly developed isolated boulders are defined as an isolated boulder visibility rate of less than 10% or a linear isolated boulder rate of less than 5%.

[0022] Furthermore, the pile foundation bearing capacity stress model with the diameter of the boulder as the variable is specifically as follows: the pile foundation bearing capacity consists of three parts, including: the characteristic value R of the total skin friction of the pile side overlying soil layer on the boulder. sa Characteristic value of side friction resistance R of isolated boulder in rock section ra and the characteristic value of total end resistance of the bearing layer R pa Calculate according to the following formula:

[0023]

[0024] R ra =u p C2f rs h r ;

[0025] R pa =C1f rp A p ;

[0026] The characteristic value R of the vertical bearing capacity of a single pile can be obtained according to the following formula. a :

[0027] R a =R sa +R ra +R pa ;

[0028] Where h is the total thickness of the overburden layer on the boulder, calculated from the top of the pile. r A is the depth at which the pile tip penetrates the boulder. p U is the cross-sectional area of ​​the pile tip, and u is the perimeter of the pile foundation cross-section of the pile side resistance section. p Where C1 and C2 are coefficients, representing the perimeter of the rock-embedded section of the pile, and are adopted according to Table 10.2.4 of the "Code for Design of Building Foundations" (DBJ 15-31-2016). rs f rp The natural moisture uniaxial compressive strength of rock samples from the pile side strata and pile tip strata are respectively. The characteristic value of the average side friction resistance within the thickness range of the overlying layer above the boulder is calculated using the following formula:

[0029]

[0030] Among them, h i q represents the thickness of the i-th soil layer; sia Let i be the characteristic value of the skin friction of the i-th soil layer;

[0031] The characteristic value R of the vertical bearing capacity of a single pile was calculated. a This allows us to determine whether the load on the top of the pile meets the bearing capacity requirements of the pile foundation.

[0032] Furthermore, in the pile foundation bearing capacity stress model with the diameter d of the boulder as the variable, when the pile tip is embedded in the boulder and the minimum critical thickness from the pile tip to the bottom of the boulder meets the punching shear bearing capacity requirement, the pile tip embedded in the boulder can be regarded as an enlarged spherical head, and the end resistance area A of the pile tip is... p The foundation can be considered as an enlarged foundation, with the pile tip value taken as the natural moisture compressive strength of the strongly weathered rock layer. Since the layer below the boulder is generally a fully weathered or strongly weathered layer with a large compression modulus, the overall settlement of the pile foundation is controllable, so the overall settlement of the pile foundation is not considered. The thickness of the complete and continuous boulder below the pile tip needs to meet the punching shear bearing capacity requirements. The single pile bearing capacity can still be calculated according to the rock-socketed pile formula. When the diameter of the boulder can meet the minimum critical thickness of the punching shear bearing capacity requirements, and the thickness from the pile tip to the bottom of the boulder is not less than 3D, it can be completely considered as a rock-socketed pile. In this case, after the stress at the pile bottom is diffused through the continuous boulder stress, the bearing capacity of the strongly weathered layer can meet the requirements of the bearing layer.

[0033] Furthermore, the determination of whether to conduct pile-by-pile exploration, providing a theoretical basis for the allocation of exploration workload, specifically includes:

[0034] In a characteristic geological borehole, for a boulder of a certain diameter d and a pile top load T, there exists a safe depth h, measured from the pile top. s When the pile length h ≥ h s At that time, regardless of the diameter of the boulder, there will always be h. s This meets the requirements for pile foundation bearing capacity, namely the characteristic value R of the vertical bearing capacity of a single pile. a ≥T; and there is also a dangerous depth h. d When the pile length h ≤ h d If an isolated rock is encountered above this depth, it should be traversed.

[0035] When the exploration borehole reveals the burial depth of the isolated rock h g Conforms to h d ≤h g ≤h s When the rate of isolated points is high, a site survey should be conducted on a pile-by-pile basis. If the rate of isolated points is low in the above depth range during the detailed survey stage, advanced geological drilling can be used to investigate during the construction stage.

[0036] Therefore, when the burial depth of the isolated rock revealed by the detailed exploration borehole is h...g Conforms to h g ≥h s At that time, the pile tip entered the boulder, and the pile length was h. s No need for pile-by-pile exploration;

[0037] Similarly, when the shallow part of the detailed exploration borehole reveals a boulder buried at a depth of h... g Conforms to h g ≤h d At this time, the pile tip should pass through the isolated rock and look downwards for the bearing layer. There is no need to conduct pile-by-pile exploration. The above analysis of the necessity of pile-by-pile exploration avoids the waste of construction resources.

[0038] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0039] This invention focuses on the study of weathered boulders. Addressing the spatial patterns of boulder development in granite areas, it proposes an optimization index concept. Based on project practice and corresponding boulder development levels, it concludes that under different boulder development levels, when the boulder burial depth meets certain conditions and the optimization index reaches a certain value, pile-by-pile exploration is unnecessary. This innovative approach provides guidance for the layout of pile foundation exploration work in granite boulder development areas, offering a theoretical basis for optimizing exploration work layout, filling relevant gaps in standards, and reducing economic costs for project management. Attached Figure Description

[0040] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0041] Figure 1 This is a schematic diagram illustrating the implementation process of a method for optimizing pile foundation investigation in granite boulder areas according to the present invention.

[0042] Figure 2 This is a load-depth relationship diagram in an embodiment of the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Please see Figures 1 to 2 The present invention provides a technical solution: a method for optimizing pile foundation investigation in granite boulder areas, comprising the following steps:

[0045] First, characteristic geological boreholes are drilled in the granite boulder area to further determine the diameter and depth range of the boulders within the site. These characteristic geological boreholes are exploratory boreholes used to characterize the distribution of representative strata within the specific building area. Through these characteristic geological boreholes, relevant data for the granite boulder area can be obtained, including: the thickness of characteristic soil layers. Security Depth h s Danger depth h d Balance depth, site visibility rate, and optimization index.

[0046] The development level of boulders is classified according to the site conditions. Based on the rate of boulders or linear boulders revealed in all exploration boreholes and their potential impact on the actual project, the development level of boulders is divided into three levels: strong development of boulders, moderate development of boulders, and weak development of boulders.

[0047] The line boulder rate is the vertical layer thickness of the boulder in the exploration hole divided by the thickness from the exposed bedrock surface (moderately weathered, slightly weathered) to the final hole depth, expressed as a percentage (%).

[0048] The site conditions for strong development of isolated boulders are an isolated boulder rate greater than 30% or a linear isolated boulder rate greater than 20%.

[0049] The site conditions for moderately developed boulders are a boulder visibility rate of greater than 10% and less than 30% or a linear boulder rate of greater than 5% and less than 20%.

[0050] Site conditions for weakly developed solitary boulders are a solitary boulder visibility rate of less than 10% or a linear solitary boulder rate of less than 5%.

[0051] A stress model for pile foundation bearing capacity was studied, with the diameter of the boulder as the variable. The pile foundation bearing capacity consists of three parts: the soil layer over the boulder, and the characteristic value of the total skin friction R between the pile and the pile. sa Characteristic value of side friction resistance R of isolated boulder in rock section ra and the characteristic value of total end resistance of the bearing layer R pa Calculate according to the following formula:

[0052]

[0053] R ra =u p C2f rs h r ;

[0054] R pa =C1f rp A p ;

[0055] The characteristic value R of the vertical bearing capacity of a single pile can be obtained according to the following formula. a :

[0056] Ra =R sa +R ra +R pa ;

[0057] Where h is the total thickness of the overburden layer on the boulder, calculated from the top of the pile. r A is the depth at which the pile tip penetrates the boulder. p U is the cross-sectional area of ​​the pile tip, and u is the perimeter of the pile foundation cross-section of the pile side resistance section. p Where C1 and C2 are coefficients, representing the perimeter of the rock-embedded section of the pile, and are adopted according to Table 10.2.4 of the "Code for Design of Building Foundations" (DBJ 15-31-2016). rs f rp The natural moisture uniaxial compressive strength of rock samples from the pile side strata and pile tip strata are respectively. The characteristic value of the average side friction resistance within the thickness range of the overlying layer above the boulder is calculated using the following formula:

[0058]

[0059] Among them, h i q represents the thickness of the i-th soil layer; sia Let be the characteristic value of the skin friction of the i-th soil layer.

[0060] Draw a load-depth diagram to determine the safe and dangerous depths. Based on the calculated boulder development level and optimization index, determine whether to conduct pile-by-pile exploration of the site, providing a theoretical basis for the layout of exploration work. Specifically, in representative geological boreholes, for boulders of a certain diameter d and a pile top load T, a safe depth h exists, calculated from the pile top. s When the pile length h ≥ h s At that time, regardless of the diameter of the boulder, there will always be h. s This meets the requirements for pile foundation bearing capacity, namely the characteristic value R of the vertical bearing capacity of a single pile. a ≥T; and there is also a dangerous depth h. d When the pile length h ≤ h d If an isolated rock is encountered above this depth, it should be traversed.

[0061] When the exploration borehole reveals the burial depth of the isolated rock h g Conforms to h d ≤h g ≤h s When the rate of isolated points is high, a site survey should be conducted on a pile-by-pile basis. If the rate of isolated points is low in the above depth range during the detailed survey stage, advanced geological drilling can be used to investigate during the construction stage.

[0062] Therefore, when the burial depth of the isolated rock revealed by the detailed exploration borehole is h... g Conforms to h g ≥hs At that time, the pile tip entered the boulder, and the pile length was h. s No need for pile-by-pile exploration;

[0063] When the shallow part of the detailed exploration borehole reveals the burial depth of the isolated rock h g Conforms to h g ≤h d At this time, the pile tip should penetrate the isolated rock and search downwards for the bearing layer; there is no need to conduct pile-by-pile exploration.

[0064] The above analysis of the necessity of pile-by-pile exploration avoids the waste of construction resources.

[0065] Example 1:

[0066] Firstly, the detailed exploration phase involved drilling at a certain density, providing a table summarizing the distribution of boulders, determining their occurrence rate, and gaining some understanding of the depth range of boulder distribution in the site. Based on the data, a basic understanding of the granite erosion baseline of this site was established. Through statistical analysis, the diameter, burial depth, and distribution regularity of the granite boulders were revealed; among which:

[0067] The rate of finding isolated boulders = (number of exploration boreholes revealing isolated boulders within the site area / total number of exploration boreholes within the site area) × 100%. The specific statistics for the diameter range of isolated boulders are as follows: Based on the list of known isolated boulder distributions, the maximum and minimum values ​​are taken, while appropriately widening the range based on experience. If a known isolated boulder diameter of 2.9m is found through detailed exploration, then the maximum diameter can be appropriately taken as 4m; if a known isolated boulder diameter of 0.8m is found through detailed exploration, which is less than the 1m requirement for embedding in bedrock, then the minimum diameter of this isolated boulder is taken as 1m.

[0068] The statistics on the burial depth range of boulders include: the burial depth of the site is less than h. d The number of isolated boulders, the site area, and the burial depth greater than h s The number of isolated boulders and the total number of isolated boulders developed in the site;

[0069] Based on the detailed exploration layout of longitudinal and transverse profiles, combined with topography and rock surface exposure, representative characteristic geological boreholes that can characterize the soil layer distribution of the building site were identified. Considering that the soil layer distribution at the location of a single building is not significantly different, these characteristic boreholes generally represent the soil layer distribution within the building area. However, there is some uncertainty regarding the depth and diameter of isolated boulders. Therefore, further statistical research was conducted on the diameter and depth range of isolated boulders within the site area. Based on the site conditions of isolated boulders, including the development of isolated boulders on the surface, the rate of isolated boulders seen in the exploration boreholes, or the rate of linear isolated boulders, and considering their potential impact on the actual project, the development of isolated boulders was classified according to Table 1.

[0070] Table 1 Grading of the Development Level of Isolated Rocks

[0071]

[0072] Based on the characteristic boreholes and the statistical analysis of boulder diameters (e.g., d = 2, 3, 4, 5 m), and considering the fixed embedment depth of the pile foundation into the boulder, the vertical axis represents the load or bearing capacity, and the horizontal axis represents the distance from the pile top to a certain depth into the boulder (i.e., the pile length). Plot the bearing capacity of the pile foundation as a function of the boulder embedment depth h for different boulder diameters. g The relationship curve of (pile length) variation is plotted, and the load curve is plotted in the same coordinate system, which is a straight line parallel to the horizontal axis.

[0073] When the diameter of the boulder varies within a certain range, the maximum and minimum boulder diameters (not less than the pile foundation diameter D) intersect the load line at points S and D, respectively. Figure 2 The load (kN) - depth (m) relationship graph (with the boulder diameter d as a variable, unit: m) is shown. The safe depth h is determined based on the above curve. s Danger depth h d Regardless of the diameter of the boulder, there is always a safe depth h. s When the pile length h ≥ h s At that time, regardless of the diameter of the boulder, there will always be h. s This meets the requirements for pile foundation bearing capacity, namely the characteristic value R of the vertical bearing capacity of a single pile. a ≥T, it is safe for the pile foundation to embed a boulder, and the diameter of the boulder is irrelevant to the safety of the pile foundation; regardless of the diameter of the boulder, there is always a safe depth h. d When the pile length h ≤ h d At this point, regardless of whether an isolated rock is encountered above this depth range, even if the diameter of the isolated rock is relatively large and the bearing capacity of the pile foundation fails to meet the load requirements of the pile foundation, it should still be passed through.

[0074] Therefore, according to statistics, the probability of encountering boulders below the safe depth is the safe encounter rate; the probability of encountering boulders above the danger depth is the danger encounter rate. When the majority of the boulders are distributed below the safe depth or above the danger depth, the pile foundation must pass through the boulders regardless, or the pile foundation is safe regardless. Based on the statistical law of the proportion of boulders mentioned above, the optimization index is calculated according to technical theory, specifically as follows:

[0075] 1) The rate of isolated rocks found in this building is the proportion of isolated rocks revealed in the boreholes within the scope of this building;

[0076] The rate of finding isolated rocks in this building = (number of exploration holes revealing isolated rocks within this building area / total number of exploration holes within this building area) × 100%;

[0077] 2) Based on the depth range of the boulder distribution, for the proportion of boulders exposed at the depth of the exploration borehole, the boulder burial depth h, calculated from the top of the pile, is... g Conforms to h g ≥h s When this occurs, it is called the safe orphanage rate;

[0078] Safe exposure rate of isolated boulders = (the depth of the isolated boulders exposed within this building area is greater than h) s (Number of exploration boreholes / Total number of exploration boreholes within this building area) × 100%;

[0079] 3) For the proportion of boulders exposed in the shallow part of the exploration borehole, the depth of the boulders (h) measured from the top of the pile is... g Conforms to h g ≤h d This is called the danger level or the rate at which an isolated case is detected.

[0080] Dangerous boulder exposure rate = (the depth of the exposed boulders within this building area is less than h) d (Number of exploration boreholes / Total number of exploration boreholes within this building area) * 100%;

[0081] 4) The burial depth of the isolated rock is h g Conforms to h d ≤h g ≤h s The proportion of isolated rocks at a given time is called the equilibrium isolation rate.

[0082] Balanced exposure rate of isolated rocks = (the number of isolated rocks exposed within this building area that meets h) d ≤h g ≤h s (Number of exploration boreholes / Total number of exploration boreholes within this building area) * 100%;

[0083] 5) Optimization Index = 100% * (Dangerous Oddity Detection Rate + Safe Oddity Detection Rate) / Oddity Detection Rate of This Building;

[0084] The following relationship exists: Building-wide isolation rate = Dangerous isolation rate + Balanced isolation rate + Safe isolation rate;

[0085] Based on the obtained safety depth h s Danger depth h d And optimization index, according to Table 2, provide suggestions on whether to carry out pile-by-pile exploration for the pile foundation of each building;

[0086] Table 2 Workload Arrangement Suggestions

[0087]

[0088] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0089] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for optimizing pile foundation investigation in granite boulder areas, characterized in that: The method includes first determining the characteristic geological boreholes in the granite boulder area, classifying the degree of boulder development according to the site conditions, conducting a pile foundation bearing capacity stress model study with boulder diameter as the variable, drawing a load-depth relationship diagram, analyzing and calculating relevant data, and using the obtained relevant data to determine whether to conduct pile-by-pile exploration in the area, providing a theoretical basis for the layout of exploration workload. The characteristic geological boreholes are exploration boreholes used to characterize the representative stratigraphic distribution within a specific building area. Through these characteristic geological boreholes, relevant data for the granite boulder area can be obtained, including: the thickness of the characteristic soil layer. Safety depth h s Danger depth h d Balance depth, site visibility rate, and optimization index; The characteristic soil layer thickness The average thickness of each characteristic soil layer used to characterize the building features, representing the borehole's features; The safety depth h s The pile length required to meet the bearing capacity requirements of the pile foundation after embedding a boulder to a certain depth in a characteristic geological borehole; The danger depth h d The critical pile length required to meet the bearing capacity requirements of the pile foundation after the maximum depth of the boulder embedded in the characteristic geological borehole is reached. The equilibrium depth is the pile length between the safe depth and the danger depth; The site's isolated rock rate represents the proportion of isolated rocks revealed in all exploratory boreholes. Based on the depth range of the boulder distribution, the proportion of boulders revealed at the depth of the exploration borehole is determined by the depth h of the boulder burial from the top of the pile. g Conforms to h g ≥h s When the boulders are exposed at shallow depths, this is called the safe boulder exposure rate; the proportion of boulders exposed at shallow depths of the borehole is [value missing] at a depth of h. g Conforms to h g ≤h d When the burial depth of the isolated rock is h, it is called the danger level of the isolated rock; g Conforms to h d ≤h g ≤h s The proportion of isolated rocks at a given time is called the equilibrium isolation rate. The following relationships exist among the four: Site visibility rate = Dangerous visibility rate + Balanced visibility rate + Safe visibility rate; Optimization Index = 100% * (Dangerous Encounter Rate + Safe Encounter Rate) / Site Encounter Rate The determination of whether to conduct pile-by-pile exploration, providing a theoretical basis for the allocation of exploration workload, specifically includes: In a characteristic geological borehole, for a boulder of a certain diameter d and a pile top load T, there exists a safe depth h, measured from the pile top. s When the pile length h ≥ h s At that time, regardless of the diameter of the boulder, there will always be h. s This meets the requirements for pile foundation bearing capacity, namely the characteristic value R of the vertical bearing capacity of a single pile. a ≥T; and there is also a dangerous depth h. d When the pile length h ≤ h d If you encounter an isolated rock within this depth range, you should proceed through it. When the exploration borehole reveals the burial depth of the isolated rock h g Conforms to h d ≤h g ≤h s When the rate of isolated points is high, a site survey should be conducted on a pile-by-pile basis. If the rate of isolated points is low in the above depth range during the detailed survey stage, advanced geological drilling can be used to investigate during the construction stage. Therefore, when the burial depth of the isolated rock revealed by the detailed exploration borehole is h... g Conforms to h g ≥h s At that time, the pile tip entered the boulder, and the pile length was h. s No need for pile-by-pile exploration; Similarly, when the shallow part of the detailed exploration borehole reveals a boulder buried at a depth of h... g Conforms to h g ≤h d At this time, the pile tip should pass through the isolated rock and look downwards for the bearing layer, without the need for pile-by-pile exploration.

2. The method for optimizing pile foundation investigation in granite boulder areas according to claim 1, characterized in that: The classification of the development level of boulders is as follows: based on the rate of boulders or the rate of boulders encountered in all exploration boreholes, the development level of boulders is divided into three levels, including: strong development of boulders, moderate development of boulders, and weak development of boulders. The line boulder rate is the thickness of the vertical layer of boulders in the exploration hole divided by the thickness from the exposed bedrock surface to the final hole depth, expressed as a percentage (%).

3. The method for optimizing pile foundation investigation in granite boulder areas according to claim 1, characterized in that: The pile foundation bearing capacity stress model with the diameter of the boulder as the variable is as follows: the pile foundation bearing capacity consists of three parts, including: the characteristic value R of the total skin friction of the pile side over the boulder, the soil layer covering the boulder, and the soil layer. sa Characteristic value of side friction resistance R of isolated boulder in rock section ra and the characteristic value of total end resistance of the bearing layer R pa Calculate according to the following formula: R sa =`q sa uh; R ra =u p C2f rs h r ; R pa =C1f rp A p ; The characteristic value R of the vertical bearing capacity of a single pile can be obtained according to the following formula. a : R a =R sa +R ra +R pa ; Where h is the total thickness of the overburden layer on the boulder, calculated from the top of the pile. r A is the depth at which the pile tip penetrates the boulder. p U is the cross-sectional area of ​​the pile tip, and u is the perimeter of the pile foundation cross-section of the pile side resistance section. p Where C1 and C2 are coefficients, and f is the perimeter of the rock-embedded section of the pile. rs f rp The natural moisture uniaxial compressive strength of rock samples from the pile side strata and pile tip strata are respectively. The characteristic value of the average side friction resistance within the thickness range of the overlying layer above the boulder is calculated using the following formula: ； Among them, h i q represents the thickness of the i-th soil layer; sia Let be the characteristic value of the skin friction of the i-th soil layer.

4. The method for optimizing pile foundation investigation in granite boulder areas according to claim 3, characterized in that: The pile foundation bearing capacity stress model with the diameter d of the boulder as the variable assumes that, after the pile tip is embedded in the boulder, the pile tip to the bottom of the boulder has a minimum critical thickness that meets the punching shear bearing capacity requirement. In this case, the pile tip embedded in the boulder can be considered as an enlarged spherical head, and the end resistance area A of the pile tip is... p It can be considered as an enlarged foundation, with the pile tip value taken as the natural moisture compressive strength of the strongly weathered rock layer; the thickness of the complete continuous boulder below the pile tip needs to meet the punching shear bearing capacity requirements, and the single pile bearing capacity calculation can still be performed according to the rock-socketed pile formula; when the diameter of the boulder can meet the minimum critical thickness of the punching shear bearing capacity requirements, and the thickness from the pile tip to the bottom of the boulder is not less than 3D, it can be completely considered as a rock-socketed pile. In this case, after the stress at the pile bottom is diffused through the continuous boulder stress, the bearing capacity of the strongly weathered layer can meet the requirements of the bearing layer.

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