CN117108327A - Supporting method for large-span IV-level broken rock mass roof - Google Patents
Supporting method for large-span IV-level broken rock mass roof Download PDFInfo
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- G06F30/20—Design optimisation, verification or simulation
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D11/00—Lining tunnels, galleries or other underground cavities, e.g. large underground chambers; Linings therefor; Making such linings in situ, e.g. by assembling
- E21D11/04—Lining with building materials
- E21D11/10—Lining with building materials with concrete cast in situ; Shuttering also lost shutterings, e.g. made of blocks, of metal plates or other equipment adapted therefor
- E21D11/105—Transport or application of concrete specially adapted for the lining of tunnels or galleries ; Backfilling the space between main building element and the surrounding rock, e.g. with concrete
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D20/00—Setting anchoring-bolts
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Abstract
The invention discloses a supporting method of a large-span IV-level broken rock mass roof, and belongs to the technical field of mining. The method is based on the span reduction effect and the combined arch effect, aims to improve the stress state of a top plate of a large-span IV-level broken rock mass and reduce the span of the top plate, and provides a combined supporting mode of anchor net, guniting, prestressed anchor rod and prestressed anchor cable; utilizing Mohr-Coulomb criterion, combining constitutive equation and geometric equation, and adopting secondary stress development of surrounding rock to make non-associated elastoplastic analysis; constructing analysis type of radius of the surrounding rock loosening area and the plastic deformation area by combining the partition boundary conditions, and determining a supporting range; the reasonable design is carried out on the guniting thickness of the top plate, the length of the prestressed anchor rods (ropes), the row spacing and the prestress size; the supporting method provided by the invention has an excellent supporting effect on the large-span IV-level broken rock mass roof, provides a reliable operation environment, ensures personnel and equipment safety, and has important theoretical research significance and higher popularization and application value.
Description
Technical Field
The invention relates to a supporting method of a large-span IV-level broken rock mass roof, and belongs to the technical field of mining.
Background
The broken rock body roadway (cave) has the advantages that the structural surface and the cracks are more, a large number of irregular bodies are contained, the mechanical property is poor, the mine pressure is violent under the combined action of the ground stress and the mining stress, the rock body is greatly deformed, the supporting is difficult, even in the short period of supporting, the roof collapses and falls off, and the mine production and the safety are seriously influenced. According to the division of spans in the railway tunnel design Specification (TB 10003-2016), the tunnel excavation spans 5-8.5 m are small spans, 8.5-12 m are medium spans and 12-14 m are large spans. According to the division of self-stabilization capability of a middleman Cheng Yanti in engineering rock mass grading standards (GBT 50218-2014), engineering spans of >5m are excavated in IV-grade rock mass, the self-stabilization capability is generally not available, loosening deformation and small collapse can occur in days to months, and then the engineering rock mass is developed into medium and large collapse.
For a long time, aiming at the extremely unstable rock mass roof support, a great deal of researches are developed by a plurality of scholars, and a plurality of engineering problems are solved. The Wang Weijun and the like provide a supporting scheme of 'high-strength anchor rod + strong anchor cable + surrounding rock grouting' aiming at the ultra-soft broken roadway support of the water head coal mine through field test and simulation test. Song Yijiang and the like analyze the surrounding rock destruction characteristics of the broken soft rock roadway, and provide a dynamic superposition supporting scheme consisting of reserved deformation quantity, anchor cable, anchor net spraying and secondary grouting, so that the supporting problem of Zhao Zhuangkuang pole broken roadway is successfully solved. And the left building is equal to analyze the deformation and damage mechanism of the surrounding rock of the large-section weak broken roadway, and provides a full-space truss anchor cable supporting technology. He Fulian and the like analyze surrounding rock deformation damage characteristics aiming at the stability control problem of the top plate of the deep broken rock roadway, reveal the essential cause of roof collapse, and provide a multi-level anchor net injection combined support technology. Sun Anjing and the like, a supporting principle of 'top control, side fixing and bottom protection' is provided, and a supporting technology of 'double-layer metal net + sprayed concrete + pre-supporting rectangular grid + contractible longitudinal connector' is provided according to the actual situation of a state coal mine. Ren Fenhua and the like quantitatively evaluate the asymmetric damage and the deformation characteristics of the broken rock roadway by utilizing FLAC3D, and provide a quantitative basis for the stability control of broken surrounding rocks. Peng Wenqing and the like are used for researching the stress distribution rule of a broken rock roadway, and deriving stress solution of a surrounding rock breaking area and a plastic area based on Karster and Kerster theory, so that a repairing scheme of anchoring anchor ropes at a roadway bottom plate and matching with roof anchor nets (ropes) and injection concrete and full-section grouting is provided.
Although the students have made a great deal of research and have obtained abundant results in the aspect of roof support of broken rock mass, the actual roof span depending on engineering is smaller, and the research on roof control of broken rock mass is relatively insufficient under the condition of large span. Under the condition of the same lithology, the larger the span of the roof is, the more difficult the maintenance is, and the less the large-span condition is involved in the research design of the support technology of the broken rock mass roof at the present stage. Therefore, in order to solve the stability problem of the large-span IV-level broken rock mass roof, based on the current situation of roof supporting mechanism research of roadways (chambers) at home and abroad, a combined supporting scheme of anchor net, guniting, prestressed anchor rod and prestressed anchor cable based on the span reduction effect and the combined arch effect is provided.
Disclosure of Invention
The invention aims to provide a large-span IV-level broken rock mass roof supporting method, which specifically comprises the following steps:
(1) And IV, selecting a reasonable supporting mode of a top plate of the crushed rock mass: aiming at the stability problem of the IV-level broken rock mass large-span roof, analyzing roof supporting difficulty, and based on the span reduction effect and the combined arch effect, aiming at improving the stress state of the IV-level broken rock mass roof and reducing the span of the roof, providing a combined supporting mode of anchor net, guniting, prestressed anchor rod and prestressed anchor cable; the supporting mode can improve the bearing capacity of the IV-level broken rock mass structure; the span of the top plate is reduced, and the stress state of the top plate is improved.
The anchor net and the guniting have the functions of timely sealing surrounding rock, preventing rock mass from further weathering, preventing live stone from falling off and providing supporting force.
The prestress anchor rod has the function of forming a combined arch structure in a loosening area and improving the self-stabilization capability of the rock mass. The prestress anchor cable has the function of mobilizing the bearing capacity of the deep rock mass and firmly fixing the combined arch formed by the broken rock mass to the deep stable rock stratum.
The compressive stress point at the tray at the end part of the prestressed anchor rod (rope) can be regarded as a fulcrum at the bottom of the combined arch, and plays a role in reducing the span of the top plate, so that the tensile stress of the top plate is reduced.
The stability problem of IV broken rock mass large-span roof is solved, and the key lies in two points: the bearing capacity of the IV-level broken rock mass structure is improved; the span of the top plate is reduced, and the stress state of the top plate is improved; in combination with the analysis of the supporting mechanism of the anchor rod (rope), the supporting of the IV-level broken rock mass large-span roof is based on the combined arch and the span reduction effect.
The basic principle is as follows: for the shallow broken rock mass, conical compressive stress areas are formed at the two ends of the anchor rod by utilizing the tensile stress generated by the pre-stress anchor rod after drawing and are mutually overlapped to form a combined arch structure, so that the broken rock mass is mutually extruded to form a whole, and the self-stabilizing capacity of the rock mass is improved as shown in figure 2; the roof surface layer is in the outer rock mass of toper compressive stress stack district, still exists the risk that drops, can adopt "anchor net + spouting" mode in time seal the country rock, prevents the rock mass further efflorescence to provide supporting force. The stress arches formed between the prestressed anchors are difficult to bear the whole load of the upper part, the deep rock mass is less in original rock stress diffusion impact caused by excavation, the stability is better, the bearing capacity of the deep rock mass is mobilized through the long prestressed anchor cable anchored into high strength, and the combined arches formed by the broken rock mass are firmly fixed to the deep stable rock stratum, as shown in figure 2. Meanwhile, the anchor rod and the anchor cable end tray form a compressive stress area on the top plate, which can be regarded as a fulcrum at the bottom of the combined arch, and plays a role in reducing the span of the top plate, reducing the bending stress and the deflection deformation of the rock stratum of the top plate, and comprehensively improving the bearing capacity of the top plate, as shown in figure 2; in summary, the large-span roof supporting mode of the IV-level broken rock mass is designed as the combined supporting mode of 'anchor net + guniting + prestressed anchor rod + prestressed anchor cable'.
(2) Determining the roof support range: utilizing Mohr-Coulomb criterion, combining constitutive equation and geometric equation, and adopting secondary stress development of surrounding rock to make non-associated elastoplastic analysis; and constructing analysis of radii of the surrounding rock loosening area and the plastic deformation area by combining partition boundary conditions, and determining thicknesses of the loosening area, the plastic strengthening area and the plastic deformation area so as to determine the supporting range.
Analyzing the secondary stress state and the elastic region distribution of surrounding rock, and being the length design basis of the anchor rods and the anchor cables; according to research results of rock mechanics, after the chamber is excavated, if the surrounding rock stress is smaller than the rock body yield strength, the surrounding rock is in an elastic state, if the surrounding rock stress exceeds the rock body yield strength, the surrounding rock is converted from the elastic state into a plastic state, the area where the surrounding rock in the plastic state is located is called a plastic deformation area, the plastic deformation area is a limited-range area, and the surrounding rock gradually transits to the elastic state along with the increase of the distance from the chamber, namely enters the elastic area; the area which is not disturbed by the secondary stress is called as a primary rock stress area, if the surrounding rock stress area is subdivided, the plastic deformation area can be divided into a loosening area and a plastic strengthening area, the loosening area is a stress reduction area, and the plastic strengthening area and the elastic deformation area are stress rising areas (bearing areas).
The Mohr-Coulomb rule is adopted, the surrounding rock is assumed to be a continuous isotropic homogeneous rock body, the plastic deformation zone should meet the balance equation and the plastic condition, the elastic zone should meet the balance equation and the elastic condition, and the plastic condition and the elastic condition should be met at the joint of the elastic zone and the plastic deformation zone, and the surrounding rock partition model is shown in figure 3; the model stress boundary conditions and contact conditions are as follows:
wherein:-radial stress of the loosening zone;
-plastic strengthening zone radial stress;
-elastic zone radial stress;
u c -loosening zone displacement;
u p -plastic strengthening zone displacement;
u e -displacement of the elastic zone;
a-excavating a chamber radius;
r is the distance from any point in surrounding rock to the excavation center;
p 0 -a supporting resistance;
p-primary stress;
R z -loosening zone radius;
R p -plastic deformation zone radius.
The constitutive equation is:
wherein: epsilon r -radial strain;
ε θ -hoop strain;
σ r -radial stress;
σ θ -hoop stress;
μ -poisson ratio of rock mass;
e-elastic modulus of rock mass;
r-distance from any point in the surrounding rock to the excavation center.
The geometric equation is:
wherein: u-rock mass displacement;
r-distance from any point in the surrounding rock to the excavation center.
Other parameters in the formula are as described above.
From the theory of plasticity, the plastic strain depends on the plastic potential phi, expressed as follows:
φ(σ r ,σ θ )＝σ θ -Hσ r (4)
wherein: phi (sigma) r ,σ θ ) -a plastic potential function;
h-material parameters.
Wherein:
wherein: h c -loosening zone material parameters;
H p -plastic strengthening zone material parameters;
ω c -a loosening zone expansion angle;
ω p -plastic strengthening zone expansion angle.
Other parameters in the formula are as described above.
Using the non-associated flow law:
wherein: lambda-side pressure coefficient.
Other parameters in the formula are as described above.
In the loosening area (a is more than or equal to R is more than or equal to R z ) A range; according to elastoplastic mechanics, the strength criterion satisfied by the equilibrium differential equation and stress under the axial symmetry plane strain is as follows:
wherein:-internal friction angle of rock mass.
-radial stress of the loosening zone;
-hoop stress of the loosening zone.
Other parameters in the formula are as described above.
The first expression of the boundary condition expression (1) is obtained by integrating the expression (7) and substituting the same:
wherein: c c -loose area rock mass cohesion.
Other parameters in the formula are as described above.
Analysis formula (8) shows that the internal stress of the loosening area is irrelevant to the stress of the original rock, and is only relevant to the size of a roadway, the rock property of the loosening area and the magnitude of supporting force.
The fractional strain expressions of the reuse formula (6), the formula (3) and the formula (8) are as follows:
wherein:-radial strain of the loosening zone;
-circumferential strain of the loosening zone;
u c -loosening zone displacement;
u-integration constant;
H c -loosening zone material parameters.
Other parameters in the formula are as described above.
Zeta in (9) c The expression is:
in the plastic strengthening zone (R z ≤r≤R p ) Within the scope, there are the following relationships:
wherein the parameters are as described above.
After the combination and integration of the formula (11), the formula (1) and the formula (8) can be substituted to obtain the formula (1):
wherein: r is R z -loosening zone radius;
c p -plastic strengthening of zone rock mass cohesion.
Other parameters in the formula are as described above.
Analysis (12) shows that the internal stress of the plastic strengthening zone is also irrelevant to the original rock stress, and only the rock properties of the loosening zone and the plastic strengthening zone, the chamber size, the radius of the loosening zone and the supporting force are relevant.
The strain expression of the plastic strengthening area can be obtained by using the formula (6), the formula (3) and the formula (12):
wherein:-plastic strengthening zone radial strain;
-plastic reinforcement zone hoop strain;
u p -plastic strengthening zone displacement;
R p -plastic deformation zone radius;
ζ p -plastic strengthening zone strain;
H p -plastic strengthening zone material parameters;
v-integration constant.
Other parameters in the formula are as described above.
Zeta in (13) p The expression is as follows:
the second and third formulas of the boundary contact conditional formula (1) can know that the displacement of the boundary positions of the loosening area and the plastic strengthening area and the boundary positions of the plastic strengthening area and the elastic area are continuous, so that the integral constant U and V can be obtained by combining formulas (9) and (13):
substituting the formula (15) into the formulas (9) and (13) yields a product containing R alone z 、R p Strain and displacement expressions of the loosening region and the plastic strengthening region.
In the elastic region (R p In the range of r.ltoreq.+.infinity), the following relationship exists:
after the combination and integration of the formula (16), the formula (1) is substituted into the third formula, the fourth formula and the formula (12) to obtain the first formula:
the formula (17) shows that the internal stress of the elastic zone has close relation with the properties of the loosening zone and the plastic strengthening zone, and the maximum main stress and the minimum main stress in the elastic zone are reduced and increased by the existence of the loosening zone and the plastic strengthening zone, so that the stability of surrounding rock of the elastic zone is improved.
The elastic region strain and displacement expressions are combined (6), formula (3) and formula (17):
at the junction of the plastic deformation region and the elastic region, the elastic stress also meets the plastic yield condition, namely the tangential stress is continuous, and the following stress relationship exists:
substituting the related expression can obtain:
the formula for simplifying the relation between the radius of the loosening area and the radius of the plastic deformation area in the formula (20) is as follows:
the surrounding rock strain is analyzed again, and at the boundary of the loosening zone and the plastic strengthening zone, the following boundary conditions exist:
the first expression of the combined formula (9) and the first expression of the formula (13) can be obtained by the following relation:
the radii of the loosening area and the plastic deformation area can be obtained by substituting the combined type (22) and (23) into the structural size of the chamber and the rock mechanical parameters.
In combination with the supporting scheme shown in fig. 2, the surrounding rock loosening area is the main object of prestress anchor bolt supporting, and the prestress anchor bolt needs to pass through the loosening area and be anchored in the plastic strengthening area; in order to fully mobilize the bearing capacity of the deep rock mass, the prestressed anchor cable needs to pass through the loosening area and the plastic strengthening area and be anchored into the elastic area; therefore, the determination of the range of the loosening area, the plastic strengthening area and the plastic deformation area is the basis for designing the length of the prestressed anchor rod and the length of the anchor cable.
The thickness expression of the loosening area is:
L P1 ＝R z -a (24)
wherein: l (L) P1 -loosening zone thickness;
R z -loosening zone radius;
a-the chamber excavation radius.
The thickness expression of the plastic strengthening zone is:
L P ＝R p -R z (25)
wherein: l (L) P -plastic reinforcement zone thickness;
R p -plastic deformation zone radius;
R z -loosening zone radius.
Thickness of plastic deformation zone
L P2 ＝R p -a (26)
Wherein: l (L) P2 -thickness of the plastic deformation zone;
R p -plastic deformation zone radius;
a-the chamber excavation radius.
(3) And (3) determining supporting parameters: according to the thickness analysis results of the loosening area, the plastic strengthening area and the plastic deformation area, the aim of guaranteeing stability of a large-span IV-level broken rock mass roof is fulfilled, and reasonable design is conducted on the row spacing between anchors, the concrete guniting thickness, the combined arch height, the prestress anchor rod tension standard value, the prestress anchor cable tension standard value, the prestress anchor rod tension design value, the prestress anchor cable tension design value, the prestress anchor rod cross section area, the prestress anchor cable cross section area, the prestress anchor rod diameter, the prestress anchor cable diameter, the prestress anchor rod anchoring section length, the prestress anchor rod length, the prestress anchor cable length, the prestress anchor rod prestress size and the prestress anchor cable prestress size.
The rock bolt row spacing determines the loading of the live rock as shown in fig. 4; the activity Dan Hezai determines the thickness of the concrete gunite; the relationship of the three times is shown as follows:
wherein: gamma-rock mass severity;
a 1 -pitch of the anchor bar rows;
d, the thickness of the guniting layer;
f ct -concrete design tensile strength;
M max -a mid-span maximum bending moment;
w is a section coefficient;
f-safety factor, required to be greater than 2;
σ max -maximum tensile stress of the gunite layer.
The relationship between the row spacing between the anchors and the combined arch height is as follows:
wherein: b-thickness of the combined arch;
L 11 -the effective length of the pre-stressed anchor is the thickness of the loosening zone;
a 1 -the pitch between the prestressed anchors;
the angle of action of the alpha-prestress anchor rod on the pressure stress of the fractured rock mass is 45 degrees.
The standard value of the tension of the prestressed anchor rod (cable) is calculated by adopting the following steps:
wherein: n (N) k -a pre-stressed anchor rod tension standard value;
N k1 -a standard value of the tension of the prestressed anchor cable;
L P1 -loosening zone thickness;
L P2 -plastic deformation zone thickness;
a 1 -the row spacing between the prestressed anchors;
a 2 -row spacing between pre-stressed anchor lines;
ρ—loose zone rock mass density;
g-gravitational acceleration.
The tension design value of the prestressed anchor rod (cable) is calculated by adopting the following formula:
wherein: n (N) d1 -prestressed anchorA lever tension design value;
N d2 -a pre-stressed anchor cable tension design value;
γ w -working condition coefficient of prestressed anchor rod (cable), generally 1.1;
N k1 -a pre-stressed anchor rod tension standard value;
N k2 -a standard value of the tension of the prestressed anchor cable;
the cross-sectional area of the prestressed anchor rod (cable) is calculated by adopting the following steps:
wherein: a is that s1 -prestressed anchor cross-sectional area;
A s2 -prestressed anchor cable cross-sectional area;
f py1 -design values of tensile strength of the prestressed deformed bars;
f py2 -design values of tensile strength of the prestressed steel strand;
N d1 -a design value of the tension of the prestressed anchor;
N d2 -design value of the pre-stressed anchor cable tension.
The diameter of the prestressed anchor rod (cable) is calculated by adopting the following steps:
wherein: d, d 1 -a pre-stressed anchor diameter;
d 2 -a pre-stressed anchor cable diameter;
A s1 -prestressed anchor cross-sectional area;
A s2 -prestressed anchor cable cross-sectional area.
The length of the anchoring section of the prestressed anchor rod (cable) is calculated by the following formula:
wherein: l (L) a1 -length of the prestressed anchor rod anchoring section;
L a2 -length of the pre-stressed anchor cable anchoring section;
N d1 -a design value of the tension of the prestressed anchor;
N d2 -design value of the pre-stressed anchor cable tension.
K 1 -the bonding anti-pulling safety coefficient between the grouting body of the anchoring section of the prestressed anchor rod and the ground layer;
K 2 -a bonding anti-pulling safety coefficient between the grouting body of the pre-stressed anchor cable anchoring section and the ground layer;
f mg1 -the standard value of the limit bonding strength between the grouting body of the anchoring section of the prestressed anchor and the stratum;
f mg2 -the standard value of the limit bonding strength between the grouting body of the anchoring section of the prestressed anchor cable and the stratum;
D 1 -the diameter of the drill hole of the anchoring section of the prestressed anchor;
D 2 -diameter of the drill hole of the anchoring section of the prestressed anchor cable;
φ 1 -the coefficient of influence of the length of the anchoring section of the prestressed anchor on the ultimate bond strength;
φ 2 -coefficient of influence of the length of the anchor section of the pre-stressed anchor cable on the ultimate bond strength.
The length of the prestressed anchor rod (cable) is calculated by the following formula:
wherein: l (L) 1 -a pre-stressed anchor length;
L 2 -pre-stressed anchor cable length;
L 11 -the exposed length of the prestressed anchor rod is equal to the thickness of the backing plate plus the length of the lock + (0.1-0.15 m);
L 21 -the exposed length of the prestressed anchor cable, which is equal to the thickness of the backing plate + the length of the lock + (0.1-0.15 m);
L 12 -the length of the free section of the prestressed anchor is the thickness of the loosening area;
L 22 -the free section length of the prestressed anchorage cable is the thickness of the plastic deformation zone;
L a1 -length of the prestressed anchor rod anchoring section;
L a2 -length of the pre-stressed anchor cable anchoring section.
The stress of the prestressed anchor is calculated by the following steps:
σ con1 ＝k 1 f fpk (35)
wherein: sigma (sigma) con1 -a pre-stress anchor pre-stress design value;
k 1 -taking 0.55 of the prestress design coefficient of the prestress anchor rod;
f fpk -standard value of yield strength of prestressed reinforcement.
The stress of the prestressed anchor cable is calculated by the following steps:
σ con2 ＝k 2 f ftk (36)
wherein: sigma (sigma) con2 -a pre-stressed anchor cable pre-stress design value;
k 2 -a pre-stressed anchor cable pre-stress design factor, taken to be 0.55;
f ftk -standard value of ultimate strength of steel strand.
The invention has the beneficial effects that:
(1) The method can accurately determine the stress distribution state and the partition range of the large-span crushing roof, and can provide theoretical basis for the design of the supporting scheme of the large-span crushing roof.
(2) The method can realize effective support of the large-span broken top plate, and has important effects on guaranteeing stability of the top plate and guaranteeing operation safety of personnel.
(3) The method provides an accurate design scheme for the large-span broken roof support, simplifies the roof support design program and reduces the design difficulty of engineering technicians.
Drawings
FIG. 1 is a process flow diagram of the present invention;
FIG. 2 is a schematic diagram of a large-span IV-class broken rock roof support;
FIG. 3 is a model diagram of a zonal surrounding rock;
FIG. 4 is a schematic representation of live stone area loading;
FIG. 5 is a top panel IV-level broken rock mass diagram of a certain ore body;
FIG. 6 is a top mining quasi-engineering layout of a certain ore room;
FIG. 7 is a schematic diagram of an original supporting scheme of a roof of a large-span IV-level broken rock mass of a certain mine;
FIG. 8 is a top plate caving diagram (original scheme) of a large-span IV-level crushed rock mass of a certain mine;
FIG. 9 is a plan view of a combined support scheme of anchor net, gunite, prestressed anchorage cable and prestressed anchorage cable;
FIG. 10 is a plan (new scheme) of roof support for large-span IV-level broken rock mass in a mining field 9# mining field;
FIG. 11 is a top slab guniting view of a large-span IV-level crushed rock of a certain mine 9# stope (new scheme);
FIG. 12 is a construction drawing (new scheme) of roof support of large-span IV-level broken rock mass of a certain mine 9# stope;
figure 13 is a diagram of the roof supporting effect of large-span IV-class crushed rock in a 9# stope of a certain mine (new scheme).
Detailed Description
The present invention will be described in further detail with reference to specific examples, but the scope of the present invention is not limited to the above.
Example 1
The invention relates to a supporting method for a large-span broken rock mass roof, which comprises the following specific embodiments:
(1) Description of the background
A certain ore main ore body, wherein a top plate is mainly made of marble and marble rock limestone, and the lithology of a bottom plate of the ore main made of siecarock and siecarock marble; according to the rock quality evaluation result, the ore body and the bottom plate belong to II-III rock bodies, and the integrity and the stability are good; the roof is a type IV rock mass, hard, relatively crushed-crushed, and poor in integrity and stability, as shown in fig. 5.
According to the mining technical conditions of ore bodies, a downward large-diameter deep hole lateral ore caving open stope subsequent filling method is designed and adopted, ore blocks are arranged along the trend, the length of the ore blocks is the trend length (north-south direction) of the ore bodies, the width of an ore room is 15m, and the height of the ore bodies is vertical.
The rock drilling level at the top of the ore house adopts a 'chamber plus point column' arrangement mode, the point columns are arranged at two sides of the rock drilling chamber, the point columns have the width of 3m, the length of 5m and the interval of 6m; the span of the west chamber is 7m, the eastern chamber is 5m, the width of the top plate of the non-point column is 15m, and the arrangement and the structural dimensions of the horizontal drilling engineering are as shown in figure 6.
In order to ensure the stability of the IV-level broken rock mass large-span roof, the mine is designed with a combined supporting scheme of anchor net, pipe seam type anchor rod, gunite and prestressed anchor cable. The length of the anchor net is 2m, the width is 1m, the diameter of the net rib is 6mm, and the net degree is 100mm multiplied by 100mm; the diameter of the pipe seam type anchor rod is 42mm, the length is 2m, and the interval is 1m multiplied by 1m; the guniting thickness is 100mm, and the concrete is marked with a C25; the anchor cable is 1X 7 (seven strands) steel stranded wire with diameter of 21.6mm, length of 8m, mesh length of 3m X3 m and prestress of 300N/mm 2 The method comprises the steps of carrying out a first treatment on the surface of the The support scheme is shown in fig. 7.
Even under this high strength supporting arm condition, the roof still appears large area to fall during the ore collapse process in the ore room, as shown in fig. 8. The mine safety production is seriously affected, a large amount of ores are lost and depleted, and stope stoping is difficult. The reason for this is that the selection of the supporting arm section is unreasonable, the stress state of the top plate is not effectively improved, the stability is still poor, the large-area disclosure of the roof plate of the ore room is not effectively supported, and then unconstrained asymptotic damage occurs; from the aspect of roof falling on site, the pipe seam type anchor rod is in falling off condition, which indicates that the depth analysis of the supporting area is insufficient; secondly, the pipe seam belongs to a passive supporting arm section, and the mechanical effect of the pipe seam mainly shows a suspension effect and a combined beam effect, so that the pipe seam is suitable for block rock mass and lamellar rock mass. The prestressed anchor cable belongs to an active supporting arm section, the mechanical effect of the prestressed anchor cable is mainly represented as span reduction, and the prestressed anchor cable is suitable for a large-span top plate. Because the pipe seam type anchor rod cannot play a good supporting role on broken rock mass, the load of the anchor cable is increased, and the prestress design of the anchor cable is smaller, so that the anchor cable supporting is invalid.
(2) Reasonable supporting mode selection of a roof of a large-span IV-level broken rock mass of a certain mine:
according to the stability problem of the roof of the large-span IV-level crushed rock mass of the mine. The scheme of combined support of anchor net, gunite, prestressed anchor rod and prestressed anchor cable is designed. For the rock mass in the loosening area, the tensile stress generated by the pre-stress anchor rod after drawing is utilized to form conical compressive stress areas at the two ends of the anchor rod to be mutually overlapped to form a combined arch structure, so that the crushed rock mass is mutually extruded to form a whole, and the self-stabilizing capacity of the rock mass is improved. The surrounding rock is timely sealed by adopting an anchor net and guniting mode, further weathering and falling off of the rock mass are prevented, and supporting force is provided. The bearing capacity of the deep rock mass is mobilized through the high-strength long pre-stressed anchor cable, and the combined arch formed by the broken rock mass is firmly fixed to the deep stable rock stratum. Meanwhile, the anchor rod and the anchor cable end tray form a compressive stress area on the top plate, can be regarded as a fulcrum at the bottom of the combined arch, plays a role in reducing the span of the top plate, reduces the bending stress and the deflection deformation of the rock stratum of the top plate, and comprehensively improves the bearing capacity of the top plate, as shown in figure 9.
(3) Support range analysis
Calculating the radius value of the rock loosening area and the radius value of the plastic deformation area of the mine roof surrounding rock by adopting a radius calculation formula of the loosening area and the radius calculation formula of the plastic deformation area shown in (21) and (22) and combining the structural size of a top chamber of the mine stope (equivalent circular chamber structural size) and the mechanical parameters of roof broken marble rocks; the calculated parameters are shown in table 1.
Table 1 chamber structural dimensions, rock mass mechanical parameters
| Excavation radius/m | Vertical stress/MPa | Cohesive force/MPa | cohesion/MPa | Internal friction angle/° | Elastic modulus/GPa | Poisson's ratio |
| 4.40 | 10 | 0.12 | 0.2 | 32 | 5 | 0.35 |
The radius of the loosening area is as follows:
R z ＝6.93m (37)
the radius of the plastic deformation zone is as follows:
R p ＝9.76m (38)
the thickness of the loosening area is as follows:
L P1 ＝R z -a＝6.93-4.40＝2.53m (39)
the thickness of the plastic strengthening area is as follows:
L P ＝R p -R z ＝9.76-6.93＝2.83m (40)
thickness of plastic deformation zone
L P2 ＝R p -a＝9.76-4.40＝5.36m (41)
(4) Support parameter design
The gunite thickness was calculated according to equation (27), and the calculated parameters are shown in table 2.
TABLE 1 calculation parameters of gunite thickness
| Concrete label | Compressive Strength/MPa | Row spacing/m between anchor rods | Row spacing/m between anchor cables | Gunite thickness/m |
| C20 | 1.10 | 1.0 | 3.0 | 0.065 |
The calculation results are as follows:
calculating the combined arch height using equation (28):
according to the calculation, the row spacing of the prestressed anchor rods is designed to be 1m multiplied by 1m, the row spacing of the prestressed anchor rods is designed to be 3m multiplied by 3m, the combined arch height is 1.53m, C25 concrete guniting is adopted, and the thickness is designed to be 6.5cm; the grouting method is combined with an anchor net, wherein the length of the anchor net is 2m, the width of the anchor net is 1m, the diameter of a net rib is 6mm, and the net degree is 100mm multiplied by 100mm.
The standard value of the tension of the prestressed anchor (cable), the design value of the tension, the sectional area, the length of the anchoring section and the design length are calculated by using the formulas (29), (30), (31), (32), (33) and (34), and the calculation results are shown in table 3.
TABLE 3 selection results of prestressed anchor rods and anchor cables
Designing anchor rod prestress by adopting a formula (35):
σ con1 ＝k 1 f fpk ＝1080×0.55＝594N/mm 2 (44)
designing anchor cable prestress by adopting a formula (36):
σ con2 ＝k 2 f ftk ＝1860×0.45＝744N/mm 2 (36)
according to the analysis result, a combined supporting scheme of anchor net, guniting, prestressed anchor cable and prestressed anchor cable is provided for the large-span IV-level broken rock mass roof of the mine, as shown in fig. 9; the guniting thickness is 100mm, and the concrete is marked with a C25; the length of the anchor net is 2m, the width is 1m, the diameter of the net rib is 6mm, and the net degree is 100mm multiplied by 100mm; the diameter of the anchor rod is 25mm, and the design value of tensile strength is 770N/mm 2 The length of the prestressed twisted steel is 3.2m, the anchoring length is 0.47m, the interval is 1m multiplied by 1m, and the prestress design value is 594N/mm 2 The method comprises the steps of carrying out a first treatment on the surface of the The anchor cable has diameter 21.6mm and designed tensile strength 770N/mm 2 1X 7 (seven strand) steel strand, length 8.0m, anchoring length 2.44m, spacing 3m, prestress design value 744N/mm 2 The method comprises the steps of carrying out a first treatment on the surface of the The tray is made of 20 steel, and has the length of 100mm, the width of 100mm and the thickness of 10mm.
(5) Industrial test
The roof rock mass of the 9# stope is most broken, the length of a stope room reaches 121m, the exposed area of the roof is 1815 square meters, and roof support design of the 9# stope is completed according to the design parameters, as shown in fig. 10, black points in the drawing are prestressed anchor cables, and circles are prestressed anchor rods.
When the roof cutting engineering is constructed, a short digging and short supporting mode is adopted, and shotcrete supporting is carried out every 5-6 m of digging. Firstly, installing an anchor net, wherein the length of the anchor net is 2m, the width is 1m, the diameter of a net rib is 6mm, the net degree is 100mm multiplied by 100mm, the overlap joint length of the anchor net is 100mm, and binding by using binding ribs is adopted; the anchor net is fixed by a pipe seam type anchor rod, the diameter of the pipe seam type anchor rod is 42mm, the length of the pipe seam type anchor rod is 1m, the interval row distance is 1m multiplied by 1m, the gunite thickness is 10cm, and the concrete reference number C25 is shown in fig. 11.
After the top plate guniting is completed, constructing a prestressed anchor rod drill hole by adopting a YT-28 rock drill, wherein the diameter of the hole is 40mm, the depth of the hole is 3.0m, and the interval is 1m multiplied by 1m; and (3) constructing prestressed anchor cable drilling by using a CYTJ45 (A) drilling trolley, wherein the diameter of the hole is 40mm, the depth of the hole is 7.8m, and the interval is 3m multiplied by 3m. The anchor rod is processed by adopting prestress screw steel with the diameter of 25mm, and the cutting length is 3.2m; cement rolls with a diameter of 30mm and a length of 0.25m were used for anchoring, 2 for each borehole. The prestressed anchor cable is purchased externally and is a steel strand with the length of 8m, the diameter of 21.6mm and the length of 1 multiplied by 7 (seven strands), cement slurry anchoring is adopted, the water cement ratio is 1:2, the anchor cable and the exhaust pipe are firstly sent to the hole bottom, the free section adopts a PVC pipe sleeve, and then full-hole grouting is carried out. After anchoring and curing the prestressed anchor rod (cable) for 28 days, installing a tray and a lock on the exposed section, wherein the tray is made of 20 steel by cutting, and has the length of 100mm, the width of 100mm and the thickness of 10mm; the clamping piece type single-hole lockset matched with 25mm screw steel and 21.6mm steel stranded wires is selected. The mining anchor cable stretching machine is loaded with prestress by adopting an MQ22-300-63, and the working parameters are shown in Table 4. The prestress design value of the anchor rod is 594N/mm 2 Load 291KN, the working oil pressure of the corresponding machine tool is 54MPa; the design value of the prestress of the anchor rod is 744N/mm 2 The load 273KN corresponds to the working oil pressure of the machine tool to be 51MPa. When stoping in a mining room, adopting large-diameter deep space side ore collapse, wherein the rock drilling equipment is a T150 down-the-hole rock drill, and the rock drilling equipment is supported and fixed by hydraulic pressure during operation, so that the exposed section of an anchor rod (cable) needs to be cut in order to ensure the drilling quality; the construction process is shown in fig. 12.
Table 4MQ22-300-63 mining anchor rope tensioning tool load versus oil pressure correspondence (description)
| Oil pressure | Load of | Oil pressure | Load of |
| 10MPa(100Par) | 54kN | 40MPa(400Par) | 216kN |
| 20MPa(200Par) | 108kN | 50MPa(500Par) | 270kN |
| 30MPa(300Par) | 162kN | 63MPa(600Par) | 324KN |
The 9# stope is built at the beginning of the period of 2022, 11 and 6, the construction of roof supporting and mining and cutting engineering is completed at the end of 2023, 2 and 17, the ore breaking is started at the beginning of 2 and 23, the stoping is finished at the end of 7 and 18, and roof falling is not seen in site monitoring and goaf scanning in the stoping process of a stope, as shown in fig. 13; the rationality and feasibility of the roof support scheme are fully proved.
Claims (6)
1. A supporting method of a large-span IV-level broken rock mass roof is characterized by comprising the following steps:
(1) The supporting mode of the large-span IV-level broken rock mass top plate comprises the following steps: selecting a combined supporting mode of 'anchor net + guniting + prestressed anchor rod';
(2) Determining the roof support range:
utilizing Mohr-Coulomb criterion, combining constitutive equation and geometric equation, and adopting secondary stress development of surrounding rock to make non-associated elastoplastic analysis; constructing analysis of radii of the surrounding rock loosening area and the plastic deformation area by combining partition boundary conditions, and determining thicknesses of the loosening area, the plastic strengthening area and the plastic deformation area so as to determine a supporting range;
(3) And (3) determining supporting parameters:
according to the thickness analysis results of the loosening area, the plastic strengthening area and the plastic deformation area, the aim of guaranteeing stability of a large-span IV-level broken rock mass roof is fulfilled, and reasonable design is conducted on the row spacing between anchors, the concrete guniting thickness, the combined arch height, the prestress anchor rod tension standard value, the prestress anchor cable tension standard value, the prestress anchor rod tension design value, the prestress anchor cable tension design value, the prestress anchor rod cross section area, the prestress anchor cable cross section area, the prestress anchor rod diameter, the prestress anchor cable diameter, the prestress anchor rod anchoring section length, the prestress anchor rod length, the prestress anchor cable length, the prestress anchor rod prestress size and the prestress anchor cable prestress size.
2. The method for supporting a roof of a large-span iv-scale crushed rock mass according to claim 1, wherein the thickness expression of the loose area in the step (2) is:
L P1 ＝R z -a
wherein: l (L) P1 -loosening zone thickness;
R z -loosening zone radius;
a-the chamber excavation radius.
3. The method for supporting a roof of a large-span iv-scale crushed rock mass according to claim 1, wherein the thickness expression of the plastic strengthening zone in the step (2) is:
L P ＝R p -R z
wherein: l (L) P -plastic reinforcement zone thickness;
R p -plastic deformation zone radius;
R z -loosening zone radius.
4. The method for supporting a roof of a large-span iv-scale crushed rock mass according to claim 1, wherein the thickness expression of the plastic deformation zone in the step (2) is:
L P2 ＝R p -a
wherein: l (L) P2 -thickness of the plastic deformation zone;
R p -plastic deformation zone radius;
a-the chamber excavation radius.
5. A method of supporting a roof of a large span iv-stage crushed rock mass according to any one of claims 1 to 3, wherein: the roof support range in step (2) can be represented by the following formula:
the relation expression of the radius of the loosening area and the radius of the plastic deformation area is as follows:
wherein:
wherein: r is R z -loosening zone radius;
R p -plastic deformation zone radius;
a, excavating a radius;
c c rock mass in loose areaCohesive force;
c p -plastic strengthening zone rock mass cohesion;
-internal friction angle of rock mass;
p 0 -a supporting resistance;
p-primary stress;
H c -loosening zone material parameters;
H p -plastic strengthening zone material parameters;
ω c -a loosening zone expansion angle;
ω p -plastic strengthening zone expansion angle;
μ -poisson ratio of rock mass.
6. The method for supporting the top plate of the large-span IV-class crushed rock mass, as claimed in claim 1, is characterized by comprising the following steps: the support parameters in the step (3) can be represented by the following formula:
the row spacing of the anchor rods and the concrete guniting thickness are expressed as follows:
wherein: gamma-rock mass severity;
a 1 -pitch of the anchor bar rows;
d, the thickness of the guniting layer;
f ct -concrete design tensile strength;
M max -a mid-span maximum bending moment;
w is a section coefficient;
f-safety factor;
σ max -maximum tensile stress of the gunite layer;
the combined arch height expression is:
wherein: b-thickness of the combined arch;
L 11 -the effective length of the pre-stressed anchor is the thickness of the loosening zone;
a 1 -the pitch between the prestressed anchors;
the angle of action of the alpha-prestress anchor rod on the pressure stress of the fractured rock mass is 45 degrees;
the tensile force standard value of the prestressed anchor rod is calculated by adopting the following formula:
wherein: n (N) k -a pre-stressed anchor rod tension standard value;
N k1 -a pre-stressed anchor cable tension standard value;
L P1 -loosening zone thickness;
L P2 -plastic deformation zone thickness;
a 1 -the row spacing between the prestressed anchors;
a 2 -row spacing between pre-stressed anchor lines;
ρ—loose zone rock mass density;
g-gravitational acceleration;
the tension design value of the prestressed anchor rod is calculated by adopting the following steps:
wherein: n (N) d1 -a design value of the tension of the prestressed anchor;
N d2 -a pre-stressed anchor cable tension design value;
γ w -the working condition coefficient of the prestressed anchor rod/cable is generally 1.1;
N k1 -a pre-stressed anchor rod tension standard value;
N k2 -prestressed anchorAn anchor cable tension standard value;
the sectional area of the prestressed anchor rod is calculated by adopting the following formula:
wherein: a is that s1 -prestressed anchor cross-sectional area;
A s2 -prestressed anchor cable cross-sectional area;
f py1 -design values of tensile strength of the prestressed deformed bars;
f py2 -design values of tensile strength of the prestressed steel strand;
N d1 -a design value of the tension of the prestressed anchor;
N d2 -a pre-stressed anchor cable tension design value;
the diameter of the prestressed anchor rod is calculated by the following formula:
wherein: d, d 1 -a pre-stressed anchor diameter;
d 2 -a pre-stressed anchor cable diameter;
A s1 -prestressed anchor cross-sectional area;
A s2 -prestressed anchor cable cross-sectional area;
the length of the anchoring section of the prestressed anchor is calculated by the following steps:
wherein: l (L) a1 -length of the prestressed anchor rod anchoring section;
L a2 -length of the pre-stressed anchor cable anchoring section;
N d1 -a design value of the tension of the prestressed anchor;
N d2 -prestressed anchorage cable pullForce design value;
K 1 -the bonding anti-pulling safety coefficient between the grouting body of the anchoring section of the prestressed anchor rod and the ground layer;
K 2 -a bonding anti-pulling safety coefficient between the grouting body of the pre-stressed anchor cable anchoring section and the ground layer;
f mg1 -the standard value of the limit bonding strength between the grouting body of the anchoring section of the prestressed anchor and the stratum;
f mg2 -the standard value of the limit bonding strength between the grouting body of the anchoring section of the prestressed anchor cable and the stratum;
D 1 -the diameter of the drill hole of the anchoring section of the prestressed anchor;
D 2 -diameter of the drill hole of the anchoring section of the prestressed anchor cable;
φ 1 -the coefficient of influence of the length of the anchoring section of the prestressed anchor on the ultimate bond strength;
φ 2 -the coefficient of influence of the length of the anchor section of the pre-stressed anchor cable on the ultimate bond strength;
the anchor length is calculated by the following formula:
wherein: l (L) 1 -a pre-stressed anchor length;
L 2 -pre-stressed anchor cable length;
L 11 -the exposed length of the prestressed anchor rod is equal to the thickness of the backing plate plus the length of the lock + (0.1-0.15 m);
L 21 -the exposed length of the prestressed anchor cable, which is equal to the thickness of the backing plate + the length of the lock + (0.1-0.15 m);
L 12 -the length of the free section of the prestressed anchor is the thickness of the loosening area;
L 22 -the free section length of the prestressed anchorage cable is the thickness of the plastic deformation zone;
L a1 -length of the prestressed anchor rod anchoring section;
L a2 -length of the pre-stressed anchor cable anchoring section;
the prestress of the prestress anchor is calculated by the following steps:
σ con1 ＝k 1 f fpk
wherein: sigma (sigma) con1 -a pre-stress anchor pre-stress design value;
k 1 -taking 0.55 of the prestress design coefficient of the prestress anchor rod;
f fpk -a standard value of yield strength of the prestressed reinforcement;
the prestress of the prestressed anchor cable is calculated by the following steps:
σ con2 ＝k 2 f ftk
wherein: sigma (sigma) con2 -a pre-stressed anchor cable pre-stress design value;
k 2 -a pre-stressed anchor cable pre-stress design factor, taken to be 0.55;
f ftk -standard value of ultimate strength of steel strand.
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