CN108978651B - Optimization determination method for rock slope prestress anchor rod reinforcement parameters - Google Patents

Optimization determination method for rock slope prestress anchor rod reinforcement parameters Download PDF

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CN108978651B
CN108978651B CN201810770680.3A CN201810770680A CN108978651B CN 108978651 B CN108978651 B CN 108978651B CN 201810770680 A CN201810770680 A CN 201810770680A CN 108978651 B CN108978651 B CN 108978651B
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anchor rod
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贺可强
信校阳
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Qingdao University of Technology
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    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
    • E02D5/74—Means for anchoring structural elements or bulkheads
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D17/00—Excavations; Bordering of excavations; Making embankments
    • E02D17/20—Securing of slopes or inclines
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A10/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE at coastal zones; at river basins
    • Y02A10/23—Dune restoration or creation; Cliff stabilisation

Abstract

The invention relates to the field of slope stability evaluation and landslide reinforcement and prevention and control, and relates to an optimization determination method for rock slope pre-stressed anchor rod reinforcement parameters, which comprises the following steps: determining basic physical and mechanical parameters of a slope to be reinforced; determining the stability coefficient of the rock slope; determining a rock slope stability correction coefficient; fourthly, determining anchor rod layout and anchor rod reinforcing anti-sliding force values; fifthly, determining the optimal incident angle of the rock mass side slope prestressed anchor rod; determining a quantitative relation between the bonding strength of the rock anchor and the uniaxial compressive strength of the rock anchor; step seven, determining the optimal anchoring length of the prestressed anchor rod; and step eight, determining the optimal design total length of the prestressed anchor rod. The method has good economic benefit and practical value in the slope reinforcement project, can accurately measure the incidence angle and the anchoring length of the anchor rod, and is more economic, reasonable and safe when the method is used for designing the prestressed anchor rod.

Description

Optimization determination method for rock slope prestress anchor rod reinforcement parameters
Technical Field
The invention relates to the field of slope stability evaluation and landslide reinforcement and prevention, relates to an optimization determination method for rock slope pre-stressed anchor rod reinforcement parameters, and particularly relates to an optimization determination method for plane failure mode rock slope pre-stressed anchor rod reinforcement parameters.
Background
In recent years, the prestressed anchor rod has the characteristics of higher tensile strength, better reinforcing effect and low manufacturing cost, and is widely applied to the fields of slope reinforcement and landslide prevention and control. The prestressed anchor support belongs to active support, namely, the reinforcing and treating effect can be played without the displacement of a slope body. Because the support method applies prestress to the slope body of the side slope, the unstable slope body is compressed by the resilience of the steel bar after the anchoring, and the slope body is in a compressed state, the displacement of the slope body can be effectively reduced, and the reinforcement effect is better than that of the traditional treatment method. In addition, the prestressed anchor rod has the advantages of flexible arrangement, large reinforcing depth, capability of fully playing the strength and self-stability of rock-soil bodies, no damage to the integrity of the slope bodies in construction, high construction speed and the like. In the design of the prestressed anchor rod, the determination of the incident angle and the anchoring length of the prestressed anchor rod plays a crucial role in whether the supporting and reinforcing effect can be normally exerted, effectively reducing the manufacturing cost of the reinforcing engineering, shortening the construction period and the like, and is also a core technical problem of the prestressed anchor rod reinforcing engineering design. If the optimal incident angle and anchoring length can be obtained, the anchoring effect can be fully exerted, and the manufacturing cost and the construction period can be greatly saved.
Comprehensive analysis of a large number of engineering practices and technical economy shows that the incident angle and the anchoring length of the prestressed anchor rod are not only mechanical technical problems, but also economic benefits. The prestressed anchor rod is designed to achieve the purposes of minimizing the total length (including a free section, an anchoring section, a tensioning section and the like) of the prestressed anchor rod and minimizing the drilling workload on the premise of meeting the total anchoring force. At present, the determination of the incidence angle of prestress and the anchoring length of a bolt is estimated according to technical specifications of rock-soil anchoring and shotcrete supporting engineering (GB 50086-2015). The formula only considers the influence of the anchor rod and the parameters of the reinforcing body, and does not consider the influence of the potential slip surface inclination angle on the prestress value. In engineering practice, the incidence angle and anchoring length of the prestressed anchor often differ greatly from the regulations and recommendations of relevant specifications. For multiple rows of anchor rods, equal-length anchor rod construction is often adopted for construction convenience. However, for a slope with a plane sliding surface, the thickness of the sliding body at different elevations is different and is a variable rather than a constant, and therefore, the design method for the length of the equal anchor rod anchoring section is undoubtedly not an optimal reinforcement design scheme, because the required anchoring forces for the top, middle and toe parts of the slope are different, if the anchor rod anchoring length is designed uniformly according to the position where the required anchoring force is the largest, the waste is undoubtedly caused for the part with smaller required anchoring force, and meanwhile, the great waste is caused on the whole design length. Although the existing slope engineering also shortens the anchor rods at the top and the bottom of the slope qualitatively, the theory and design basis is lacked. The length of the anchor portion of the anchor is not constant, and therefore, the anchor reinforcing scheme is not optimal. The number and the length of anchor rods are increased too much to ensure the stability of the side slope, so that the reinforcement engineering cost, the construction period and the waste of manpower and material resources are caused.
Disclosure of Invention
Aiming at the defects, the invention provides an optimization determination method suitable for the reinforcement parameters of the prestressed anchor rod of the planar failure mode rock slope.
The technical scheme for solving the technical problems is as follows:
the method comprises the following steps: determination of basic physical and mechanical parameters of slope to be reinforced
Performing geotechnical engineering investigation and on-site in-situ test on the rocky slope according to the current geotechnical engineering investigation Specification (GB50021-2001) to obtain the standard value of the rock friction angle of the slope body of the slope
Figure GDA0003007353360000021
The weight gamma of the rock mass, the cohesive force c, the slope angle beta of the rock slope and the slope height H; drawing a profile of the slope by a surveying and mapping method. And simultaneously, taking a plurality of points on the slope body of the side slope, respectively measuring the uniaxial compressive strength value Rc and the rock anchor limit bonding strength value qr of the rock through a rock saturated uniaxial compressive strength test and an anchor rod limit pulling test, and drawing a qr and Rc relation curve.
Step two: determination of rock slope stability coefficient Fs
Equivalent internal friction angle psi of rock massdThe standard value of the internal friction angle of the rock block can be determined by the step one
Figure GDA0003007353360000022
Determining according to the rock mass fracture development degree multiplied by the reduction coefficient listed in the table 1; according to the technical specification of building slope engineering (GB50330-2002), the inclination angle of the plane damage potential sliding surface of the rock slope can be determined to be
Figure GDA0003007353360000031
TABLE 1 reduction coefficient of internal friction angle of slope rock mass
Figure GDA0003007353360000032
Determining the stability coefficient Fs of the plane sliding method by using a formula (1) as follows:
Figure GDA0003007353360000033
in the formula: Ψ d is an equivalent internal friction angle of the rock mass, and theta is an inclination angle of a plane damage potential slip plane of the slope of the rock mass.
Step three: rock slope stability correction coefficient delta FSIs determined
Defining a slope stability correction factor Δ FSThe difference between the slope safety coefficient K and the slope overall stability coefficient Fs is as follows:
ΔFS＝K-FS (2)
in the formula: Δ FSSlope stability correction factor
K-the slope safety factor, the value is as shown in Table 5.3.1 in the technical Specification for supporting foundation pits of buildings (JGJ120-2012), and is specifically shown in Table 2 below:
TABLE 2 Stable safety factor of slope
Figure GDA0003007353360000034
Step four: anchor rod layout and determination of anchor rod reinforcing anti-slip force value
1) Determination of side slope anchor rod laying interval
And determining the anchor rod layout condition according to the regulation of 10.3 in the current technical Specification for building slope engineering (GB 50030-2013). The anchor rods are arranged in a row and column manner; the horizontal distance between the anchor rods is not less than 1.5 m; the vertical spacing of the anchor rods is not less than 2.0 m. The width of the landslide body is set to be LbThe transverse distance between the prestressed anchor rods is b, wherein b is the edge of the first anchor rod at the two ends of the slip mass and is far away from the edge of the slip mass, and the number of the anchor rods in each row is as follows:
Figure GDA0003007353360000041
according to the technical Specification of construction slope engineering (GB50030-2013), the distance between the first row of anchor rods and the top of the slope is 1.5 m-2.0 m. If the vertical interval of stock is hm, the side slope height is H, and first row stock is apart from the top of the slope distance and is H1, then the stock row number is:
Figure GDA0003007353360000042
2) determination of the stability correction factor Δ Fsri assumed by a single anchor
Vertical strip division is carried out to the rock mass side slope body, and the effective effect scope of single stock is assumed and is got the sum of equalling divide of scope between this stock and the adjacent stock, so the gliding force that the stock bore the rock mass and produce is that the rock mass gravity of potential slip surface top in the effective effect scope produces, and then the proportion of the stability correction coefficient that each single stock bore can be divided according to the proportion of the rock mass gravity who undertakes:
Figure GDA0003007353360000043
gri-rock mass gravity borne by i anchor rods in the r-th row
3) Determining the required reinforcing anti-sliding force value of each anchor rod of the rock mass side slope:
ΔFri＝ΔFsri×Grisinθ (6)
in the formula: Δ Fri — the amount of reinforcement slip resistance applied by the i bolts in the r-th row.
Step five: determination of optimal incident angle of rock mass side slope prestressed anchor rod
Aiming at the plane failure type landslide, the inclination angles of the rock mass side slope fracture surfaces are the same, so the incidence angle alpha of the anchor rod driven into the rock mass is the same, and the reinforcement prestress value delta fri is determined according to the formula (8):
ΔFri＝Δfri sin(α+θ)tanΨd+Δfri cos(α+θ) (7)
Figure GDA0003007353360000044
derivation of α in the formula (8) formula (9)
Figure GDA0003007353360000045
In the formula: Ψ d-is an equivalent internal friction angle of the rock body;
theta-is the inclination angle of the rock slope fracture surface;
alpha-anchor angle.
Let equation (9) equal zero, and perform extremum analysis on equations (7) and (8) to obtain: Δ fri takes a maximum value when α ═ Ψ d- θ. According to the specification of item 4.6.5 in technical Specification of geotechnical anchoring and shotcrete support engineering (GB50086-2015), the reinforcement incident angle of the slope anchor rod is preferably kept from forming an angle of-10 degrees to +10 degrees with the horizontal plane, so that the optimal incident angle for the reinforcement of the slope anchor rod is determined as follows:
(1) when the Ψ d-theta is larger than or equal to 10 degrees, the optimal incidence angle for reinforcing the slope anchor rod is alpha' ═ Ψ d-theta;
(2) when Ψ d- θ is less than 10 °, the slope anchor reinforcement optimum incidence angle is α' 10 °.
Step six: determination of quantitative relation between rock anchor bonding strength and uniaxial compressive strength thereof
According to data analysis obtained by a large number of field tests, the relation curve of the rock anchor ultimate bonding strength and the rock uniaxial compressive strength conforms to an ln function curve, so that the function relation of the rock anchor bonding strength qr and the rock uniaxial compressive strength Rc can be assumed as follows:
qr＝alnRc+b(10)
in the formula, the values of a and b can be obtained by fitting the rock anchor ultimate bonding strength and rock uniaxial compressive strength of a plurality of different measuring points measured by the test method in the step one by using a least square method, and the calculation process is as follows: equation (10) is taken as a linear combination of two elementary functions (11) (12):
Figure GDA0003007353360000051
Figure GDA0003007353360000052
and (3) setting m as the number of test data, and knowing the calculation principle by a least square method:
Figure GDA0003007353360000053
Figure GDA0003007353360000054
Figure GDA0003007353360000061
Figure GDA0003007353360000062
Figure GDA0003007353360000063
substituting the calculation result of the formula into the formula (18) to calculate a and b:
Figure GDA0003007353360000064
step seven: determination of optimal anchoring length of prestressed anchor
Substituting the rock uniaxial compressive strength Rc determined by the rock saturated uniaxial compressive strength test in the first step into the formula (10) in the sixth step to obtain the rock anchor ultimate bonding strength qr, and determining the optimized anchoring body length delta lri of each anchor rod according to a calculation formula of the anchoring force of 4.6.10 in technical specification of rock-soil anchoring and shotcrete support engineering (GB 50086-2015):
Figure GDA0003007353360000065
in the formula: Δ lri-row r i anchors optimize anchor length (m);
d, the diameter (mm) of the anchor rod anchoring body;
qr-ultimate bond strength (MPa) between the surface of the anchor and the surrounding rock mass;
delta fri-reinforcement prestress value (kN) of i anchor rods in the r-th row;
k' -the bond resistance to plucking safety coefficient between the anchor and the surrounding rock mass, the values are taken according to Table 3;
n is the number of the steel bars or steel strands;
xi-coefficient of reducing the bonding strength of the interface, and is 0.70-0.85;
psi, coefficient of influence of anchoring length on bond strength, was taken as in table 4.
TABLE 3 bond resistance to plucking safety factor between anchor and surrounding rock mass
Figure GDA0003007353360000071
TABLE 4 influence coefficient psi of anchoring length on bond strength
Figure GDA0003007353360000072
Step eight: determination of optimal designed total length of prestressed anchor
1) Determining the distance from the slope of the rock mass slope at each anchor rod construction position to the intersection point of the anchor rod and the potential slip surface according to a formula (20) as the free section length delta Lri of the anchor rod, and deducing the principle:
Figure GDA0003007353360000073
2) the optimum overall design length of the bolt is determined according to equation (21):
lri＝ΔLri+Δlri (21)
in the formula: lri-total length of the design of the i anchor rods in the r-th row;
delta Li-length of free section of i anchor rods in the r-th row;
α' -optimum angle of incidence of the anchor;
beta-the slope angle of the rock mass side slope;
theta is the inclination angle of the plane damage potential slip plane of the rock slope;
hri is the slope height at the intersection of the ith row of i anchor rods and the slope surface of the rock body.
The principle is as follows: the principle of the invention for calculating the length of the anchoring free section of the prestressed anchor is as follows:
the slope height hi at the intersection of the ith anchor rod and the rock slope surface, the free section length delta Li of the ith anchor rod, the optimal incident angle alpha 'of the anchor rod, the dip angle theta of the rock slope surface damage potential slip surface and the included angle alpha' + theta of the anchor rod and the potential slip surface.
Figure GDA0003007353360000081
Figure GDA0003007353360000082
Figure GDA0003007353360000083
Figure GDA0003007353360000084
Anchoring free length delta Li of ith anchor rod:
Figure GDA0003007353360000085
compared with the prior art, the invention has the beneficial effects that: aiming at the defects of high reinforcement engineering cost, long construction period and the like caused by the traditional anchor rod reinforcement design method, on the basis of the analysis of the prestress anchor rod side slope reinforcement mechanism and the evaluation of the reinforcement stability, the optimal incident angle and the anchoring section length of the rock slope anchor rod with a plane potential slip surface are optimally designed, the optimal incident angle and the anchoring section length under the premise of ensuring the maximum potential of the prestress anchor rod can be found and determined, and the design and measurement method of the optimal incident angle and the anchoring section length of the prestress anchor rod is provided, so that the aims of saving the engineering cost and the construction period under the premise of ensuring the safety and the stability of the rock slope are fulfilled. By comparing the design length of the anchor rod determined by the correction software, the design method greatly reduces and optimizes the design length of the anchor rod, and has good economic benefit and practical value in slope reinforcement engineering. The method not only can accurately measure the incident angle and the anchoring length of the anchor rod, but also is more economical, reasonable and safe to design the prestressed anchor rod by applying the method.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a diagram illustrating the relationship between qr and Rc functions;
FIG. 3 illustrates the Gri calculation range according to the present invention;
fig. 4 is a schematic diagram of calculation of the distance from the slope surface to the potential slip surface of the anchor rod.
Detailed Description
The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.
To better illustrate the present invention, the feasibility of the method is now described in detail in conjunction with a specific engineering application to demonstrate the practical significance and value of the method.
The specific implementation and calculation process is as follows:
the method comprises the following steps: determination of basic physical and mechanical parameters of slope to be reinforced
According to the current geotechnical engineering investigation Specification (GB50021-2001) on a rock slope, through geotechnical engineering investigation and on-site in-situ test, the landslide is 35m high and 12m wide, the slope angle beta of the slope is 70 degrees, the cohesive force c is 5KPa, and the internal friction angle
Figure GDA0003007353360000091
Is 40 degrees and the severe gamma is 20kN/m3. The qr and Rc test values are shown in FIG. 2. Has no underground water function.
Step two: determination of rock slope stability coefficient Fs
Determining that the reduction coefficient of the internal friction angle of the slope rock mass is 0.87 according to the development degree of the rock mass fracture obtained by the investigation in the step one and referring to table 1, so that the reduction coefficient can be defined by the equivalent internal friction angle Ψ d of the rock mass: Ψ d — 40 ° × 0.87 — 34.8 °; according to the technical specification of building slope engineering (GB50330-2002), the inclination angle of the plane damage potential sliding surface of the rock slope can be determined to be
Figure GDA0003007353360000092
Determining the stability coefficient Fs of the plane sliding method by using a formula (1) as follows:
Figure GDA0003007353360000093
step three: rock slope stability correction coefficient delta FSIs determined
According to the existing technical code of building slope engineering (GB50030-2013), the safety grade of the slope is set as two levels, and the safety factor K of the slope can be determined to be 1.3.
Defining a slope stability correction factor Δ FSThe difference between the slope safety coefficient K and the slope overall stability coefficient Fs is as follows:
ΔFS＝K-FS＝1.3-0.49＝0.81
step four: anchor rod layout and determination of anchor rod reinforcing anti-slip force value
1) Determination of side slope anchor rod laying interval
The anchor rod row spacing is fixed as 5m, and the first row anchor rod is 5m away from the top of the slope. The number of rows of anchor rods is represented by formula
Figure GDA0003007353360000101
To obtain
To obtain
Figure GDA0003007353360000102
The transverse spacing of the anchor rods is set to be 3 m. The number of anchor rods in each row is represented by the formula
Figure GDA0003007353360000103
To obtain
Figure GDA0003007353360000104
2) Determination of stability correction coefficient delta F borne by single anchor rod and reinforcement anti-sliding force value required by each anchor rod of rock mass slope
Vertical strip division is carried out to the rock mass side slope body, and the effective effect scope of single stock is assumed and is taken the sum of dividing equally of scope between this stock and the adjacent stock, so the gliding force that the stock undertakes the rock mass and produce is that the rock mass gravity of potential slip surface top produces in the effective effect scope, then the proportion of the stability correction coefficient that each single stock undertakes can be divided according to the proportion of the rock mass gravity that undertakes, and the calculation is as follows:
Figure GDA0003007353360000105
step five: determination of optimal incident angle of rock mass side slope prestressed anchor rod
The slope fracture surface of the rock body slope has the same inclination angle due to the fact that the slope fracture surface is only directed at the plane failure type landslide, the incidence angle alpha of the anchor rod driven into the rock body is the same, and the reinforcement prestress value delta fri is determined according to the formula (8):
ΔFri＝Δfrisin(α+θ)tanΨd+Δfricos(α+θ) (7)
Figure GDA0003007353360000111
derivation of α in the formula (8) formula (9)
Figure GDA0003007353360000112
In the formula: Ψ d-is an equivalent internal friction angle of the rock body;
theta-is the inclination angle of the rock slope fracture surface;
alpha-anchor angle.
Let equation (9) equal zero, and perform extremum analysis on equations (7) and (8) to obtain: when α ═ ΨdΔ fri takes a maximum value at-30.2 °. According to the specification of item 4.6.5 in technical specification of geotechnical anchoring and shotcrete support engineering (GB50086-2015), the reinforcement incident angle of the slope anchor rod is preferably kept from forming an angle of-10 degrees to +10 degrees with the horizontal plane, so that the optimum incident angle for reinforcing the slope anchor rod is alpha' 10 degrees.
Substituting α' into equation (8) for 10 ° results in the following:
Figure GDA0003007353360000113
step six: determination of quantitative relation between rock anchor bonding strength and uniaxial compressive strength thereof
The test data totaled 19 groups, i.e. m is 19. Calculated by equations (13) to (17):
Figure GDA0003007353360000114
Figure GDA0003007353360000115
Figure GDA0003007353360000116
Figure GDA0003007353360000117
Figure GDA0003007353360000118
substituting the data into equation (18) yields:
a＝0.73，b＝-1.64。
therefore, the function relation of the rock anchor bonding strength qr and the rock uniaxial compressive strength Rc is as follows:
qr＝0.73lnRc-1.64
step seven: determination of optimal anchoring length of prestressed anchor
The parameters required by calculation are determined according to 4.6 in the current technical Specification for rock-soil anchoring and shotcrete support engineering (GB 50086-2011). The rod body is a twisted steel with the diameter of 16 mm. n is 1, K is 2.0; qr 1.3 Mpa; d is 50 mm; d is 16 mm; ψ is 1.0 and ξ is 0.82.
Figure GDA0003007353360000121
According to the technical specification of geotechnical anchoring and shotcrete support engineering (GB50086-2015) 4.6.10 item calculation formula (see formula 19), the calculation result is as follows:
1 2 3 4 5 6 7
Δlri(m) 2.20 2.32 2.54 2.36 2.20 1.80 1.37
step eight: determination of optimal designed total length of prestressed anchor
Determining the distance from the slope of the rock body slope at the construction position of each anchor rod to the intersection point of the anchor rod and the potential slip plane according to a formula (20) as the free section length delta Lri of the anchor rod, determining the optimal designed total length Lri of each anchor rod according to a formula (21), and calculating the following results:
Figure GDA0003007353360000122
the above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (4)

1. An optimization determination method for rock slope pre-stressed anchor rod reinforcement parameters is characterized by comprising the following steps:
determining basic physical and mechanical parameters of a slope to be reinforced: carrying out geotechnical engineering investigation and on-site in-situ test on the rocky slope according to the current geotechnical engineering investigation Specification (GB50021-2001) to obtain the standard value of the internal friction angle of the rock of the slope body of the side slope
Figure FDA0003007353350000011
The weight gamma of the rock mass, the cohesive force c, the slope angle beta of the rock slope and the slope height H; drawing a side slope section diagram by using a surveying and mapping method, simultaneously taking a plurality of points on a side slope body, and respectively measuring a rock uniaxial compressive strength value Rc and a rock anchor ultimate bonding strength value q by a rock saturated uniaxial compressive strength test and an anchor rod ultimate tensile testrAnd drawing qrRc relation curve;
step two, determining the stability coefficient F of the rock slopes: equivalent internal friction angle psi of rock massdFrom the standard value of the internal friction angle of the rock
Figure FDA0003007353350000012
Determining according to the rock mass crack development degree multiplied by the reduction coefficient of the internal friction angle of the slope rock mass; determining the inclination angle of the plane damage potential sliding surface of the rock mass side slope according to the technical specification of building side slope engineering (GB50330-2002)
Figure FDA0003007353350000013
Determination of rock slope stability coefficient F by plane sliding methodsComprises the following steps:
Figure FDA0003007353350000014
in the formula: ΨdThe equivalent internal friction angle of the rock mass is theta, and the inclination angle of the plane damage potential slip plane of the slope of the rock mass is theta;
step three, determining the rock slope stability correction coefficient delta Fs：
Slope stability correction coefficient Delta FsIs a slope safety coefficient K and a slope integral stability coefficient FsThe difference of (a) is:
△Fs＝K-Fs
in the formula: delta FsThe coefficient is a slope stability correction coefficient, K is a slope safety coefficient, and the value of K is shown in table 5.3.1 in the technical specification of building foundation pit support (JGJ 120-2012);
step four, determining anchor rod layout and anchor rod reinforcing anti-slip force value delta Fri：
1) Determining the arrangement distance of the side slope anchor rods: determining the arrangement condition of anchor rods according to the regulation of 10.3 in the current technical Specification for building slope engineering (GB50030-2013), wherein the anchor rods are arranged in a determinant manner; the horizontal distance between the anchor rods is not less than 1.5 m; the vertical spacing of the anchor rods is not less than 2.0m, and the width of the landslide body is LbThe transverse distance between the prestressed anchor rods is b, wherein b is the distance between the first anchor rod at the two ends of the slip mass and the edge of the slip mass, and the number n of the anchor rods in each rowHComprises the following steps:
Figure FDA0003007353350000021
according to the technical Specification of construction slope engineering (GB50030-2013), the distance between the first row of anchor rods and the top of the slope is 1.5-2.0 m, and the vertical distance between the anchor rods is hmThe height of the side slope is H, and the distance from the first row of anchor rods to the top of the slope is H1The number of rows of anchor rods nvComprises the following steps:
Figure FDA0003007353350000022
2) stability correction factor delta F borne by single anchor rodsriDetermination of (1):
vertical strip division is carried out to the rock mass side slope body, and the effective effect scope of single stock is assumed and is got the sum of equalling divide of scope between this stock and the adjacent stock, so the gliding force that the stock bore the rock mass and produce is that the rock mass gravity of potential slip surface top in the effective effect scope produces, and then the proportion of the stability correction coefficient that each single stock bore can be divided according to the proportion of the rock mass gravity who undertakes:
Figure FDA0003007353350000023
in the formula: griThe rock mass gravity borne by the i anchor rods in the r-th row is less than or equal to nv，i≤nH；
3) Determining the required reinforcing anti-sliding force value of each anchor rod of the rock mass side slope:
△Fri＝△Fsri×Grisinθ
in the formula: delta FriA reinforcing anti-slip value applied to the ith row of i anchor rods;
step five, determining the optimal incident angle alpha' of the rock slope prestressed anchor rod:
for plane failure type landslides, the slope fracture surfaces of the rock body side slopes have the same inclination angle, so that the incidence angle alpha of the anchor rod driven into the rock body is the same, and the reinforcing prestress value delta fri：
Figure FDA0003007353350000024
Deriving α in the above formula:
Figure FDA0003007353350000025
in the formula: ΨdThe equivalent internal friction angle of the rock mass; theta is the inclination angle of the rock slope fracture surface; alpha is the anchor rod incidence angle;
according to the specification of item 4.6.5 in technical Specification of geotechnical anchoring and shotcrete support engineering (GB50086-2015), the reinforcement incident angle of the slope anchor rod is preferably kept from forming an angle of-10 degrees to +10 degrees with the horizontal plane, so that the optimal incident angle for the reinforcement of the slope anchor rod is determined as follows:
(1) when t isdWhen the angle is larger than or equal to 10 degrees, the optimal incidence angle for reinforcing the slope anchor rod is alpha' ═ psid-θ；
(2) When t isdWhen theta is less than 10 degrees, the optimal incidence angle for reinforcing the slope anchor rod is alpha' which is 10 degrees;
step six, determining the ultimate bonding strength q of the rock anchorrQuantitative relation with uniaxial compressive strength Rc thereof;
step seven, determining the optimal anchoring length delta l of the prestressed anchor rodri；
Step eight, determining the optimal design total length of the prestressed anchor rodDegree lri。
2. The method for optimally measuring the reinforcement parameters of the prestressed anchor rod of the rock slope as claimed in claim 1, wherein the method for determining the quantitative relationship between the ultimate bonding strength of the rock anchor and the uniaxial compressive strength of the rock anchor is as follows: the relation curve of the ultimate bonding strength of the rock anchor and the uniaxial compressive strength of the rock conforms to an ln function curve, so that the ultimate bonding strength q of the rock anchor is assumedrThe function relation with the rock uniaxial compressive strength Rc is as follows:
qr＝aln Rc+b
the values of a and b in the formula are obtained by least square fitting.
3. The method for optimally measuring the reinforcement parameters of the prestressed anchor of the rock slope as claimed in claim 2, wherein the optimal anchoring length Δ l of the prestressed anchor is determinedriThe method comprises the following steps:
according to the technical specification of geotechnical anchoring and shotcrete support engineering (GB50086-2015) 4.6.10 item anchoring force calculation formula, the length delta l of each anchor rod optimized anchoring body can be determinedri：
Figure FDA0003007353350000031
In the formula: delta lriOptimizing the length (m) of an anchoring body for the i anchor rods in the r row; d is the diameter (mm) of the anchor rod anchoring body; q. q.srUltimate bond strength (MPa) between the surface of the anchor and the surrounding rock mass; delta friReinforcing the prestress value (kN) of the i anchor rods in the r-th row; k' is the bonding anti-pulling safety coefficient between the anchoring body and the surrounding rock mass, and the value is taken according to the table 3; n is the number of the steel bars or the steel strands; xi is the coefficient for reducing the bonding strength of the interface, and is 0.70-0.85; psi is the coefficient of influence of the anchoring length on the bonding strength.
4. The method for optimally measuring the reinforcement parameters of the prestressed anchor of the rock slope as claimed in claim 3, wherein the method for determining the optimal design total length of the prestressed anchor is as follows:
1) determining the distance from the slope of the rock body slope at each anchor rod construction position to the intersection point of the anchor rod and the potential slip surface as the length delta L of the free section of the anchor rodri：
Figure FDA0003007353350000041
2) Determination of the optimum overall design length l of the anchorri：
lri＝△Lri+△lri
In the formula: lriDesigning the total length of i anchor rods in the r-th row; delta Lri-the length of the free section of the i anchor rods in the r row; alpha' is the optimal incidence angle of the anchor rod; beta is the slope angle of the rock mass side slope; theta is the inclination angle of the plane damage potential slip plane of the rock slope; h isriThe slope height of the intersection point of the ith row of i anchor rods and the slope surface of the rock body.
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