A method for calculating the avoidance distance of active fault rock foundation

Abstract

A method for calculating the avoidance distance of rock foundations on active faults includes detecting the geological parameters of the main fault and deformation zone of a dip-slip fault, determining the effective foundation thickness, classifying the basic quality grade of the effective foundation rock mass, and calculating the avoidance distance. The present invention decomposes the avoidance factors of a building's seismic fortification on active faults and proposes the main factors affecting a building's seismic fortification: effective foundation thickness, basic quality grade classification of the effective foundation rock mass, effective foundation safe avoidance distance, and factors affecting the surface rupture length of the active fault. Related calculations are then performed to ultimately arrive at a precise method for calculating the avoidance distance of a building's rock foundation on a dip-slip active fault.

Description

Technical Field

[0001] The present invention relates to the field of engineering geophysical exploration technology, and in particular to a method for measuring the avoidance distance of an active fault rock foundation. Background Art

[0002] Earthquakes are sudden, destructive natural disasters that pose serious threats to human life and the safety of buildings. The Wenchuan earthquake and other historical earthquake damage examples show that most buildings built directly on or along active faults suffer severe damage. The closer to the seismic active fault, the more severe the damage to a building; buildings farther from an active fault experience less damage. In building seismic fortification, national standards clearly stipulate minimum avoidance distances for seismic faults, but not for active faults. Active faults are those that have been active since the Late Quaternary (approximately 100,000 years ago). The document "Discussion and Recommendations on Avoidance for Active Faults" suggests that for strike-slip faults, the minimum avoidance distance is 15 meters outside the main fault and deformation zone boundary. For dip-slip faults, including reverse faults and normal faults, the minimum avoidance distance for the footwall is 15 meters from the geological deformation zone boundary, while for the hanging wall, the minimum avoidance distance is 30 or 45 meters from the geological deformation zone boundary. The IBC code in Utah, USA, generally specifies a avoidance distance of 6 to 15 meters. These suggestions or recommendations for active fault avoidance distances all have the common characteristics of being simplistic, rough and artificial.

[0003] Although there are some related patents in the prior art that disclose the spatial distribution detection, activity direction and growth direction detection of active faults, such as:

[0004] Patent CN202010913484.4 discloses a hidden fault imaging method for urban active fault detection. This patent uses "hidden fault imaging" to detect the spatial distribution characteristics of the main fault structure and its relationship with regional strong earthquake activity.

[0005] Patent CN201310283822.0 discloses a method for interpreting the activity intensity and growth direction of active faults through artificial seismic analysis. By determining the growth trend and activity intensity of active faults and predicting their future changes, it is helpful to reduce geological disasters caused by active faults.

[0006] Patent CN202011126946.4 discloses an active fault fusion detection system that uses "deep radar detection" to determine the underground active fault conditions in the area to be detected.

[0007] However, the above patents do not disclose how to calculate the active fault avoidance distance. Summary of the Invention

[0008] The main purpose of the present invention is to propose a method for calculating the avoidance distance of an active fault rock foundation, aiming to solve the above technical problems.

[0009] To achieve the above object, the present invention proposes a method for calculating the avoidance distance of an active fault rock foundation, comprising the following steps:

[0010] Step S1: Detecting geological parameters of the main fault and deformation zones on both sides of the dip-slip fault, including: the nature of the main fault, whether it is a reverse fault or a normal fault; the location of the main fault and the boundary lines of the footwall and hanging wall of the deformation zone; the dip angle a of the fault; the average surface slope b in the direction of the hanging wall avoidance zone of the fault zone; and the surface rupture length L of the dynamic fault.

[0011] Step S2: Determine the effective foundation and its thickness, obtain the foundation bottom line and the foundation bottom line depth h1, in meters; calculate the effective foundation thickness h2 based on the basic value of the effective foundation thickness and the active fault surface rupture length L;

[0012] Step S3: Calculating the footwall side avoidance distance: Calculating the footwall side avoidance distance based on the basic avoidance distance value and the active fault surface rupture length L;

[0013] Step S4: Estimation of the hanging wall side avoidance distance: Estimate the hanging wall side avoidance distance based on the foundation base line depth h1, the effective foundation thickness h2, the fault dip angle a, and the average surface slope b in the direction of the hanging wall avoidance zone of the fault zone, and determine the estimated boundary line of the hanging wall side avoidance distance;

[0014] Step S5: classify the basic quality grade of the effective bedrock mass and calculate the number k of effective bedrock systems;

[0015] Step S6: Avoidance distance calculation: Calculate the effective foundation safety avoidance distance, and calculate the avoidance distance on the hanging wall side of the reverse fault or normal fault.

[0016] Preferably, in step S2, the effective foundation thickness h2 is calculated as follows:

[0017] h2=h0·c;

[0018] Where:

[0019] h2 is the effective foundation thickness, in m;

[0020] h0 is the basic value of effective foundation thickness, generally 10, in m.

[0021] c=1~1.25, when L<50km, c=1; when 50km≤L<250km, c=1.1; when L≥250km, c=1.25, L is the surface rupture length of the active fault.

[0022] Preferably, in step S3, the lower wall side avoidance distance is calculated as follows:

[0023] S下 =S0·c;

[0024] Where:

[0025] S 下 is the avoidance distance on the footwall side of the reverse fault or normal fault, in meters;

[0026] S0 is the basic value of the avoidance distance, generally set to 15, in meters;

[0027] c=1~1.25, when L<50km, c=1; when 50km≤L<250km, c=1.1; when L≥250km, c=1.25, L is the surface rupture length of the active fault.

[0028] Preferably, in step S4, the upper wall side avoidance distance estimation value is calculated as follows:

[0029] S=(h1+h2+S 下 / cos a)·(sin(π / 2-a)) / sin(ab)·cos b;

[0030] Where:

[0031] S is the estimated value of the upper wall side avoidance distance, in meters;

[0032] h1 is the depth of the foundation line;

[0033] h2 is the effective foundation thickness;

[0034] a is the dip angle of the fault, in radians;

[0035] b is the average surface slope in the direction of the fault hanging wall avoidance zone, unit radian.

[0036] Preferably, in step S5, the effective foundation range is enclosed by the foundation lower line, the side avoidance distance estimation line of the hanging wall, the effective foundation thickness lower line, and the side avoidance distance estimation line of the hanging wall, which is about 30 m away, to conduct exploration and geophysical testing, complete the basic quality grade classification of the rock mass, and obtain the effective bedrock system number k:

[0037] When the basic quality grade of the rock mass is Grade I or Grade II, k = 1;

[0038] When the basic quality grade of the rock mass is Grade III, k = 1.15;

[0039] When the basic quality grade of the rock mass is IV or V, k = 1.3.

[0040] Preferably, in step S6, the effective base safety avoidance distance is calculated as follows:

[0041] S a =k·S下 ;

[0042] Where:

[0043] S a is the effective base safety avoidance distance, in meters;

[0044] S 下 is the avoidance distance on the footwall side of the reverse fault or normal fault, in meters;

[0045] k is the number of effective bedrock systems.

[0046] Preferably, in step S6, the calculation method of the avoidance distance on the hanging wall side of the reverse fault or normal fault is:

[0047] S 上 =r·(h1+h2+S a / cos a)·(sin(π / 2-a)) / sin(ab)·cos b;

[0048] Where:

[0049] S 上 is the avoidance distance on the hanging wall side of the reverse fault or normal fault, in meters;

[0050] r is the fault coefficient, r = 1 for normal fault and r = 1.2 for reverse fault;

[0051] h1 is the depth of the foundation line;

[0052] h2 is the effective foundation thickness;

[0053] a is the dip angle of the fault, in radians;

[0054] b is the average surface slope in the direction of the fault hanging wall avoidance zone, unit radian.

[0055] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0056] This paper decomposes the avoidance factors of buildings on active faults during seismic fortification, identifying key factors influencing building seismic fortification: effective foundation and thickness, effective foundation rock mass quality classification, effective foundation safe avoidance distance, and factors influencing the length of active fault surface ruptures. Related calculations are then performed, ultimately yielding a precise method for calculating the avoidance distance of a building's rock foundation on active faults. In urban construction and various other building projects, where land is often scarce or avoidance is impossible, the avoidance distance for active faults cannot be the current approximate or basic approach; it requires scientific and detailed testing and calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0058] Figure 1 Schematic diagram of the avoidance distance calculation method for active fault rock foundation in the present invention. DETAILED DESCRIPTION

[0059] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0060] Combine Figure 1 As shown, a method for calculating the avoidance distance of an active fault rock foundation includes the following steps:

[0061] Step S1, according to the national standard "Active Fault Detection" (GB / T 36072-2018) and related technical documents, detect the geological parameters of the main fault of the dip-slip fault and the deformation zones on both sides, including: determining whether the main fault is a reverse fault or a normal fault, determining the position of the main fault and the boundary line of the footwall side of the deformation zone and the boundary line of the hanging wall side of the deformation zone, the dip angle a of the fault, the average surface slope b in the direction of the fault zone's hanging wall avoidance zone (positive for downward inclination and negative for upward inclination), and determining the surface rupture length L of the active fault.

[0062] Step S2: Determine the effective foundation and its thickness: Using the geological report and the building design report, obtain the foundation lower line and the foundation lower line depth h1, in meters; and calculate the effective foundation thickness h2 according to the following formula:

[0063] h2=h0·c;

[0064] Where:

[0065] h2 is the effective foundation thickness, in m;

[0066] h0 is the basic value of effective foundation thickness, generally 10, in m.

[0067] c=1~1.25, when L<50km, c=1; when 50km≤L<250km, c=1.1; when L≥250km, c=1.25, L is the surface rupture length of the active fault.

[0068] In this embodiment, the foundation bottom line depth h1 is the vertical distance from the surface line to the foundation bottom line; h2 is the thickness of the effective foundation in the vertical direction.

[0069] Step S3: Calculation of the footwall side avoidance distance of the reverse fault or normal fault: Calculate the footwall side avoidance distance based on the basic value of the avoidance distance and the surface rupture length L of the active fault. Specifically, the footwall side avoidance distance is calculated as follows:

[0070] S 下 =S0·c;

[0071] Where:

[0072] S 下 is the avoidance distance on the footwall side of the reverse fault or normal fault, in meters;

[0073] S0 is the basic value of the avoidance distance, generally set to 15, in meters;

[0074] c=1~1.25, when L<50km, c=1; when 50km≤L<250km, c=1.1; when L≥250km, c=1.25, L is the surface rupture length of the active fault.

[0075] In this embodiment, S 下 It is the horizontal avoidance distance from the intersection of the boundary line of the footwall of the deformation zone at the surface line.

[0076] Step S4: Calculate the estimated value of the hanging wall side avoidance distance: Based on the foundation base line depth h1, the effective foundation thickness h2, the fault dip angle a, and the average surface slope b in the direction of the fault zone hanging wall avoidance zone, the hanging wall side avoidance distance is estimated and the estimated boundary of the hanging wall side avoidance distance is determined. Specifically, the calculation method of the estimated value of the hanging wall side avoidance distance is:

[0077] S=(h1+h2+S 下 / cos a)·(sin(π / 2-a)) / sin(ab)·cos b;

[0078] Where:

[0079] S is the estimated value of the upper wall side avoidance distance, in meters;

[0080] h1 is the depth of the foundation line;

[0081] h2 is the effective foundation thickness;

[0082] a is the dip angle of the fault, in radians;

[0083] b is the average surface slope in the direction of the fault hanging wall avoidance zone, unit radian.

[0084] Step S5: Classify the effective foundation rock mass by its basic quality grade and calculate the effective foundation rock system number k. Specifically, the effective foundation range is defined by the foundation base line, the estimated sideline of the hanging wall side avoidance distance, the effective foundation thickness line, and the estimated sideline of the hanging wall side avoidance distance extending approximately 30 meters beyond it. Survey and geophysical testing are conducted in accordance with the "Geotechnical Engineering Investigation Code" and related technical documents to complete the classification of the basic rock mass quality grade and obtain the effective bedrock system number k. When the basic rock mass quality grade is Grade I or II, k = 1; when the basic rock mass quality grade is Grade III, k = 1.15; and when the basic rock mass quality grade is Grade IV or V, k = 1.3.

[0085] Step S6: Calculate the effective foundation safety avoidance distance and the hanging wall side avoidance distance of the reverse fault or normal fault. Specifically, the calculation method of the effective foundation safety avoidance distance is:

[0086] S a =k·S 下 ;

[0087] Where:

[0088] S a is the effective foundation safety avoidance distance, in meters; that is, the shortest vertical distance from the lower line of the effective foundation thickness to the boundary line of the upper plate side of the deformation zone.

[0089] S 下 is the avoidance distance on the footwall side of the reverse fault or normal fault, in meters;

[0090] k is the number of effective bedrock systems.

[0091] The calculation method for the hanging wall side avoidance distance of a reverse fault or normal fault is:

[0092] S 上 =r·(h1+h2+S a / cos a)·(sin(π / 2-a)) / sin(ab)·cos b;

[0093] Where:

[0094] S 上 is the avoidance distance on the hanging wall side of the reverse fault or normal fault, in meters;

[0095] r is the fault coefficient, r = 1 for normal fault and r = 1.2 for reverse fault;

[0096] h1 is the depth of the foundation line;

[0097] h2 is the effective foundation thickness;

[0098] a is the dip angle of the fault, in radians;

[0099] b is the average surface slope in the direction of the fault hanging wall avoidance zone, unit radian.

[0100] In this embodiment, S 上 It is the horizontal avoidance distance from the intersection of the upper plate side boundary line of the deformation zone at the surface line.

[0101] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformation made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A method for calculating the avoidance distance of an active fault rock foundation, characterized in that: include: Step S1: Detecting geological parameters of the main fault and deformation zones on both sides of the dip-slip fault, including: the nature of the main fault, whether it is a reverse fault or a normal fault; the location of the main fault and the boundary lines of the footwall and hanging wall of the deformation zone; the dip angle a of the fault; the average surface slope b in the direction of the hanging wall avoidance zone of the fault zone; and the surface rupture length L of the dynamic fault. Step S2: Determine the effective foundation and its thickness, obtain the foundation bottom line and the foundation bottom line depth h1, in meters; calculate the effective foundation thickness h2 based on the basic value of the effective foundation thickness and the active fault surface rupture length L; Step S3: Calculating the footwall side avoidance distance: Calculating the footwall side avoidance distance based on the basic avoidance distance value and the active fault surface rupture length L; Step S4: Estimation of the hanging wall side avoidance distance: Estimate the hanging wall side avoidance distance based on the foundation base line depth h1, the effective foundation thickness h2, the fault dip angle a, and the average surface slope b in the direction of the hanging wall avoidance zone of the fault zone, and determine the estimated boundary line of the hanging wall side avoidance distance; Step S5: classify the basic quality grade of the effective bedrock mass and calculate the number k of effective bedrock systems; Step S6: Avoidance distance calculation: Calculate the effective foundation safety avoidance distance and the hanging wall side avoidance distance of the reverse fault or normal fault; In step S2, the effective foundation thickness h2 is calculated as follows: h2=h0·c; Where: h2 is the effective foundation thickness, in m; h0 is the basic value of effective foundation thickness, generally 10, in m. c=1~1.25, when L<50km, c=1; when 50km≤L<250km, c=1.1; when L≥250km, c=1.25, L is the surface rupture length of the active fault; In step S3, the bottom wall side avoidance distance is calculated as follows: S 下 =S0·c; Where: S 下 is the avoidance distance on the footwall side of the reverse fault or normal fault, in meters; S0 is the basic value of the avoidance distance, generally set to 15, in meters; c=1~1.25, when L<50km, c=1; when 50km≤L<250km, c=1.1; when L≥250km, c=1.25, L is the surface rupture length of the active fault; In step S4, the upper wall side avoidance distance estimation value is calculated as follows: S=(h1+h2+S 下 / cos a)·(sin(π / 2-a)) / sin(ab)·cos b; Where: S is the estimated value of the upper wall side avoidance distance, in meters; h1 is the depth of the foundation line; h2 is the effective foundation thickness; a is the dip angle of the fault, in radians; b is the average surface slope in the direction of the fault hanging wall avoidance zone, unit radian; In step S5, the effective foundation range is enclosed by the foundation lower line, the side avoidance distance estimation line of the hanging wall, the effective foundation thickness lower line, and the side avoidance distance estimation line of the hanging wall, which is about 30m away. The survey and geophysical test are carried out to complete the basic quality grade classification of the rock mass and obtain the effective bedrock system number k: When the basic quality grade of the rock mass is Grade I or Grade II, k = 1; When the basic quality grade of the rock mass is Grade III, k = 1.15; When the basic quality grade of the rock mass is IV or V, k = 1.3; In step S6, the effective base safety avoidance distance is calculated as follows: S a =k·S 下 ; Where: S a is the effective base safety avoidance distance, in meters; S 下 is the avoidance distance on the footwall side of the reverse fault or normal fault, in meters; k is the number of effective bedrock systems; In step S6, the calculation method of the hanging wall side avoidance distance of the reverse fault or normal fault is: S 上 =r·(h1+h2+S a / cos a)·(sin(π / 2-a)) / sin(ab)·cos b; Where: S 上 is the avoidance distance on the hanging wall side of the reverse fault or normal fault, in meters; r is the fault coefficient, r = 1 for normal fault and r = 1.2 for reverse fault; h1 is the depth of the foundation line; h2 is the effective foundation thickness; a is the dip angle of the fault, in radians; b is the average surface slope in the direction of the fault hanging wall avoidance zone, unit radian.

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