Research on the differentiated support technology for roadways based on the mechanical response of the plastic zone

With the advancement of coal resources mining to the deep part, the control of the surrounding rock of the roadway has become one of the main problems in the field of mining. At the present stage, the bolt support technology of the roadway in China still faces problems such as unclear support mechanism and poor support effect. Based on the mechanism of bolt support, through theoretical analysis and experimental research, this study proposes the differentiated support technology for roadways based on the mechanical response of the plastic zone and applies this method in the Gada Coal Mine. The results of the study showed that the plastic zones with different shapes have different mechanical responses. compared with other plastic zone shapes, the control method of the roadway with a butterfly‐shaped plastic zone is more complex. Consequently, the support design of a bolt should not only consider the scope of the plastic zone of support construction but also grasp the development law of the plastic zone. Effective support measures should be taken as early as possible for roadways with butterfly‐shaped plastic zones to prevent aggressive development of the butterfly‐shaped plastic zone. Field tests show that this support method realizes the ideal supporting effect in practical applications.


| INTRODUCTION
Bolt support has several uses in coal mines and various geotechnical applications and provides important technical support for roadways surrounding rock control and rock slope stability. 1However, the wide application of bolt support technology requires scientific and reliable support design methods.Generally, the support design methods of roadway bolts are mainly divided into four categories: engineering analogy, theoretical calculation, numerical simulation, and field monitoring. 2 These design methods have their own advantages and disadvantages.Therefore, in practical engineering, the results obtained by two or more design methods are often compared and analyzed and then the final support scheme is determined.
4][5][6][7] Xie et al. proposed a new "anchorage + pressure relief" collaborative control technology.It can help transfer the stress peak zones of the roadway sides to the deep surrounding rock without destroying the rock mass in the shallow anchorage zone. 8Wang et al. studied the stress evolution of the single mining support and the superposition effect of the repeated mining stress of broken surrounding rock under dynamic roadway, and proposed the surrounding rock control technology system with "improving stress environment + high-strength and high-prestress support + bottom angle support + lagging grouting" as the core. 9Pan carried out the anchor injection test of fractured rock mass, revealed the support mechanism of anchor injection of fractured rock mass, and proposed the anchor injection support technology of fractured surrounding rock. 10Rama et al. studied the deformation and damage characteristics of the surrounding rocks of the roadway under coal room and pillar mining methods. 11He et al. established and solved a mechanical model for calculating the working resistance of the rock bolt based on the rock bolt's tensile characteristics and the deformation of surrounding rock.This provides a theoretical basis for the supporting design of quadrilateral roadways. 12Batugin et al. studied the influence of the side rock bolt and anchor cable parameters on the mechanical properties of the anchorage body, and proposed a combined support technology for adjacent roadways. 13Ivan et al. studied the deformation characteristics of the perimeter rock of the roadway in auger mining and the effect of auger mining on the stability of the surrounding rock of the roadway in the affected area. 14Sun et al. studied the deformation and damage characteristics of the surrounding rock of the roadway in layered soft rock, and concluded that the damage modes of this type of roadway are mainly two kinds: layer bending fracture and layer slipping after excavation.Based on this, the damage mechanism of layered soft rock roadway is proposed. 15In some mining regions, the issue of roadways surrounding ground control has been properly resolved.However, the status of coal mine roadway bolt support in China still faces enormous challenges [16][17][18][19] mainly manifested as: on the one hand, most mines have excessive support, for example, support density is too high and bolt diameter is too large.Excessive support causes huge economic losses.On the other hand, deep dynamic pressure roadways still experience noncontinuous, noncoordination large deformation, largescale instability, and failure phenomenon.In many mining areas, the bolt support effect is poor, and roadways need to be frequently repaired. 20,21Obviously, bolt support still faces the problems of insufficient scientific basis and high support cost in practical engineering.This fundamentally stems from the inconsistency between the design method of bolt support and the actual engineering environment. 22,23Therefore, determining a scientific and optimal bolt support design method is very important for roadway surrounding rock control.
As is well known, the basis of bolt support design is to ensure that the bolt can function without failure, that is, the reliability of bolt support, 24 as well as the scientific optimization of support parameters to minimize the waste of support capacity, that is, the economy of bolt support.The reliability of bolt support requires that the strength of the bolt should be sufficiently high to ensure that the support structure cannot fail.Moreover, to ensure that the support structure can continue to support the rock mass, the bolt anchorage foundation should also stay stable.A bolt must be able to adapt to not only the stressful environment of the roadway during supporting construction but also to the potential mining and tectonic stresses throughout the entire service life of the roadway because the stress field of the roadway dynamically evolves.Additionally, the roadway plastic zone is not static.Especially, for a roadway in the state of two-way extremely unequal pressure, its surrounding rock usually has an unstable butterfly-shaped plastic zone.This type of plastic zone develops quite quickly, and the rock mass dilatancy in butterfly leaf has obviously increased.On the one hand, under conditions of particularly strong dilatancy, the rock mass in the plastic zone will squeeze the rock mass in the elastic zone inward, leading to the aggressive expansion of the plastic zone boundary.However, it will force the shallow shattered rock mass outward, causing significant deformation and instability of the road.On the other hand, it will squeeze the shallow broken rock mass outward, resulting in large deformation and collapse of the roadway. 25,26herefore, the scientific and optimal design of the roadway bolt support should be based upon the thorough understanding of the full-life failure law of the roadway.This study investigates the formulation of a scientific and optimal design method of the roadway bolt support by analyzing the mechanical response of the plastic zone.

| THE THEORY OF PLASTIC ZONE
Roadway instability and collapse are primarily caused by plastic zone formation and growth.Zhao 26 calculated the implicit equation of the circular roadway's plastic zone boundary in a non-axisymmetric stress field (Figure 1):   (1) Here, a is the radius of the roadway; p and λp are the horizontal and vertical principal stresses, respectively; the lateral pressure coefficient λ; r and θ are the distance and angle from any point to the origin of the coordinate in the polar coordinate system, respectively.
Figure 1 shows the mechanical model of the roadway.Taking the radius of the circular roadway a as 2 m, cohesion C as 0.7 MPa, internal friction angle φ as 30°, and the vertical principal stress p as 10 MPa, the plastic zone distribution and the variation of the maximum radius of the plastic zone R max under different principal stress ratios are obtained, as shown in Figure 2A.
In Figure 2A, once λ is near to 1, the plastic zone is circularly distributed, and increasing λ changes the plastic zone from round to oval.In the case of λ = 1.5, the plastic zone is oval.As λ continues to increase, the plastic zone develops rapidly in the direction of the shoulder and foot of the roadway.Thus, the roadway forms a "butterfly"-shaped plastic zone.As a result, three types: round, oval, and butterfly are used to describe the plastic zone following roadway excavation. 27n Figure 2B, when the lateral pressure coefficient reaches or is close to the critical value, only a very small increment of lateral pressure coefficient is needed to sharply expand the butterfly leaf, and the maximum radius of plastic zone will double or even increase by more than 10 times.When λp is 24 MPa and λ is 2.4, the maximum radius is 9.07 m.If λp increases by 24 MPa to 26.24 MPa, the plastic zone's maximum radius grows to 28.56 m, which is 3.15 times of the original.Thus, the morphological instability of the butterfly-shaped plastic zone is determined by its great sensitivity to micro stress. 28Owing to this special attribute of the butterfly-shaped plastic zone, it is one of the important sources of dynamic pressure disasters in coal mines.
Figure 3 shows the relationship between the horizontal principal stress and the maximum radius of the plastic zone of the surrounding rock for a certain vertical principal stress in the roadway.When the plastic zone is butterfly-shaped, as in Figure 3, its maximum radius grows exponentially as the primary stress rises.Unlike that of the butterfly-shaped plastic zone, the maximum radius of the circular or elliptical plastic zone grows very slowly with increasing principal stress.Additionally, the butterfly plastic zone's maximum radius will mutate when the lateral pressure coefficient reaches a crucial level, and this phenomena won't happen in the circular or elliptical plastic zones.As a result, the stable form of the roadway plastic zone is round or oval, whereas the unstable form is butterfly-shaped.[31]

| ENGINEERING BACKGROUND
The Gada Coal Mine's geological characteristics are extremely complex and heavily impacted by tectonic stress.The deformation of the roadway is extremely serious, and spalling and roof fall phenomena occur from time to time. Figure 4 is the rock strata histogram of the mining area.Figure 5 depicts the roadway's deformation and collapse conditions.

| Mineral composition analysis of the of rock mass
The mineral composition of the surrounding rock was obtained via core drilling and X-ray diffraction at the Gada Coal Mine's south wing track roadway.Table 1 shows the main minerals and their contents.The data in Table 1 show that quartz is the main component in the surrounding rock.Chlorite and siderite account for 17.75% and 10.28% of the total mineral content, respectively.Chlorite is a special soft rock, and its strength is higher than that of ordinary soft rock in the natural state.However, when it comes in contact with water, its mechanical strength suddenly decreases, exhibiting typical soft rock characteristics. 32,33I G U R E 3 Relation between the stress field and the maximum radius of different plastic zones.
F I G U R E 4 Regional rock strata histogram.
Therefore, the surrounding rock containing waterexpanding minerals to a certain extent exacerbated the failure of the roadway.However, the collapse of the roadway are still mainly caused by the stress environment.

| In-situ stress measurement
The south wing track roadway of the Gada Coal Mine is a rock roadway.The relation between the south wing track roadway and other roadways is shown in Figure 6.
To obtain the stress data of the south wing track roadway, in-situ stress measurements were conducted via a stress relief method in the mine.The rock strata of the south wing track roadway have developed cracks, are broken, and have poor integrity.As a result, the stable rock mass in the top portion of the roadway was equipped with the hollow inclusion needed for the in-situ stress measurement.The result of the in-situ stress measurement is shown in Table 2.
Comparison of the roadway azimuth and principal stress direction shows that the roadway is approximately excavated along the direction of the minimum horizontal principal stress.The intermediate principal stress of the roadway is approximated as vertical stress.The maximum principal stress of the roadway is approximated as the horizontal stress perpendicular to the roadway.The horizontal and vertical principal stresses perpendicular to the roadway axis are 21.1 and 10.2 MPa, respectively.Therefore, the lateral pressure coefficient of the roadway is about 2.07, and the roadway is in a two-way extremely unequal pressure stress environment.

| Broken state analysis of the roadway by drilling peeping
Drilling peep instrument YSZ (B) was used to observe the loosening and failure of the surrounding rock.There are two stations 25 m away from each other.Since the surrounding rock is broken, when the angle between the peephole axis and the horizontal direction is small or the peephole entrance is upward, the sludge water and gravel in the hole are difficult to discharge and block the observation channel; thus, the peep work cannot be completed.Therefore, the  peephole entrance of each station was arranged downwards.In Figure 7, you can see the specific arrangement.

| Numerical simulation of roadway plastic zone
The model size was 70 m × 70 m × 30 m (length × height × depth).The section size of the roadway was 4600 mm × 3600 mm (width × height).Normal displacement is constrained by the surroundings of the model.The model was divided into three layers: carbonaceous mudstone, argillaceous siltstone, and sandy mudstone.In Figure 12 and Table 3, respectively, the numerical model and specific parameters are displayed.
The model uses the Mohr-Coulomb constitutive model.The left and right boundaries of the model were fixed with normal displacement, the bottom was fixed, and the top was free.Due to the small angular error between the principal stress field and the rectangular coordinate system and considering the small influence of this error on the morphology and range of the plastic zone, to facilitate the modeling, the authors have simplified it here.3D directional stresses were applied inside the model to simulate the original stress of the rock mass: vertical stress szz = 10.2MPa, horizontal stress sxx = 21.1 MPa, and minimum principal stress syy = 9.3 MPa.At the initial equilibrium, the tensile strength and cohesion of the model were increased to avoid plastic damage.Once the initial geostress field had formed, the displacement and plastic zone generated by the first equilibrium were cleared, and the model parameters were assigned to perform the balance calculation.
Numerical simulations indicate that the plastic zone of the roadway is butterfly shaped, as shown in Figure 13.The depth of the plastic zone reaches a maximum of 6.05 m on the right shoulder.that the plastic zone of the south wing track roadway is formed like a butterfly, meaning that the depth of the plastic zone at the roadway's footing and shoulder is much deeper than that of the other areas.According to the in-situ stress measurement results, the lateral pressure coefficient of the roadway has reached 2.07, which is a two-way extremely unequal pressure roadway.The stress environment of the road has theoretically attained the fundamental requirements for the development of a plastic zone in the form of a butterfly shape.The results of field drilling and numerical simulation signify that the plastic zone of the south wing track roadway is butterfly shaped.In actual measurement and numerical simulation, the ratio of shoulder plastic zone depth to roof plastic zone depth was 2.42 and 2.71, respectively.2. Numerical simulation is performed based on certain assumptions, and there is a slight gap in the mechanics definition between the plastic and fracture zones.Therefore, some differences still exist between the scope of the surrounding rock fracture zone obtained by actual drilling peeping and the scope of the plastic zone obtained by numerical simulations.The main manifestations are as follows: in the actual measurement results, the plastic zone depths of the two shoulders were 5.68 and 5.30 m, respectively.In the numerical simulation results, they were 6.05 and 5.89 m, respectively.In the actual measurement and the numerical simulation results, the plastic zone depth of the roof was 2.35 and 2.23 m, respectively.

| Cause analysis of original support failure
The original support scheme of the roadway is mainly supported by a full section ordinary anchor + metal mesh + jet concrete and is supplemented by shallow broken rock mass grouting pipe grouting.Among them, the ordinary anchor specification is Φ17.8 mm × 6300 mm (diameter × length) and spacing is 700 mm × 700 mm.The grouting pipe using an ordinary circular iron pipe has a specification of Ф22 mm × 2200 mm (diameter × length) and the grouting material is cement mortar.Figure 14 displays the specific support scheme.
Cause analysis of the large deformation and collapse of the roadway under the original support scheme: 1.The bolt support parameters were not designed with the shape and scope of the plastic zone in mind.For instance, a long anchor with a length of 6.3 m was still employed despite the shallow plastic zone depth of the roof and rings.Despite the substantial failure of the floor, neither the footing nor the floor had any effective supporting measures in place.Furthermore, the substantial dilatation impact of the rock in the butterfly leaf was also not taken into account; only the choice of an ordinary anchor for the full-section uniform support was taken into account.2. The grouting method employed is not scientific enough.In the original support scheme, circular iron pipe grouting was adopted, which enhanced the | 677 mechanical strength of broken rock mass to a certain extent, but the degree of improvement was very limited. 34Additionally, a grouting pipe is different from a grouting bolt.A grouting pipe cannot provide an effective support force for the roadway.Therefore, the stress environment of shallow rock mass in roadway under low confining pressure was not effectively changed.The rock mass in the butterfly leaf squeezes the shallow anchorage rock mass under the action of strong dilatancy, which is bound to again destroy the shallow anchorage rock mass and squeeze it into the roadway space.However, the continuously expanding rib and shoveling floor not only increases the cost of roadway support but also aggravates the development of the plastic zone, rendering the original support bolt gradually ineffective.Moreover, the old scheme does not determine the grouting range according to the distribution characteristics of the plastic zone.Despite the fact that the rock mass at the butterfly leaf was broken, the original support scheme only utilized shallow grouting.The grouting depth was far insufficient.3. The selected grouting material is unreasonable.In accordance with the rock mass composition analysis, the roadway surrounding rock has a high proportion of water-expanding minerals.The original scheme used cement mortar as the grouting material, and cement mortar contains a lot of water.In the full section, grouting resulted in shallow broken rock coming in contact with water, which intensified the softening disintegration of the original broken surrounding rock.

| Roadway support method based on the mechanical response of plastic zone
The reliability of bolt support requires that the anchorage foundation of the bolt must always be in the rock mass.6][37][38] Figure 15 shows a schematic diagram of the roadway support method on the mechanical response of the plastic zone.
The roadway supporting method based on the mechanical response of plastic zone includes two main contents: 1. Scientific determination of the shape and scope of the roadway plastic zone (a) The mechanical properties of the rock mass, as well as the magnitude and direction of the roadway's principal stress, were determined utilizing field testing such as rock coring and in-situ stress measurement techniques.The mineral composition of rock mass was obtained via core X-ray diffraction.(b) The drilling peep test was conducted to obtain the failure characteristics of the rock mass in key parts of the roadway (roof and two shoulders).(c) The plastic zone scope was obtained by numerical calculation.(d) By comparing and analyzing the results of field tests and numerical simulations, the actual shape and scope of the plastic zone were determined.
2. Determining supporting parameters according to the mechanical response of the plastic zone Since the plastic zone has two forms of stable and unstable and they differ in shape and scope, their mechanical responses and development laws are also very different.Therefore, roadway support needs to be designed according to the type of plastic zone.
When a roadway is approximately in a two-way equal pressure environment or the ratio of the two-way principal stress is small (generally less than about 1.5), the shape of the plastic zone is usually round or oval.At this time, in the absence of external strong interference, these shape of the plastic zone usually does not continue to develop or develop very slowly, and the surrounding rock does not undergo large deformation and collapse.Therefore, the supporting parameters of the bolt need to be determined according to the scope of the plastic zone.
When the roadway is in a two-way extremely unequal pressure environment (usually greater than about 2), the plastic zone is butterfly shaped.Furthermore, the rock mass dilatancy in butterfly leaves has obviously increased.On the one hand, under conditions of particularly strong dilatancy, the rock mass in the plastic zone will squeeze the rock mass in the elastic zone inward, leading to the aggressive expansion of the plastic zone boundary.However, it will force the shallow F I G U R E 14 Original support scheme of the south wing track roadway.
shattered rock mass outward, causing significant deformation and instability of the road.On the other hand, it will squeeze the shallow broken rock mass outward, resulting in large deformation and collapse of roadway.Therefore, when designing the support mode of this kind of roadway, not only should the scope of the plastic zone be considered and the differential support mode be adopted but also the density and strength of bolt support at the butterfly leaf should be appropriately increased.When the rock mass is severely broken or the deviatoric stress is extremely strong, grouting reinforcement of the rock mass in weak area needs to be adopted to improve the rock mass strength.

| New support scheme and its parameters
The new support scheme was constructed using the data of the in-situ stress measurement and mineral composition determination of the rock mass, as well as the difference in the morphological properties of the plastic zone.Finally, a comprehensive control technology scheme with "grouting anchor + ordinary anchor" and "grouting bolt + metal mesh + sprayed concrete" as the support was adopted in the south wing track roadway.
1. "Grouting bolt + metal mesh + sprayed concrete" The "grouting bolt + metal mesh + sprayed concrete" technology condenses the broken surrounding rock around the roadway into a whole through slurry, which greatly improves the mechanical strength of the broken rock.The grouting bolt was a Ф22 × 2800 mm (diameter × length) left-handed nonlongitudinal rebar bolt.Each bolt had two anchorage agents, the anchorage force was greater than 70 KN, and the bolt interrow spacing was 700 mm × 700 mm.The tray of grouting anchor rod was composed of steel material.
2. "Ordinary anchor + grouting anchor" reinforcing support According to the field test and numerical simulation results, the plastic zone of the roadway was butterfly shaped.The rock mass dilatancy in the plastic zone's butterfly leaf has obviously increased.On the one hand, under conditions of particularly strong dilatancy, the rock mass in the plastic zone will squeeze the rock mass in the elastic zone inward, leading to the aggressive expansion of the plastic zone boundary.However, it will force the shallow shattered rock mass outward, causing significant deformation and instability of the road.On the other hand, it will squeeze the shallow broken rock mass outward, resulting in large deformation and collapse of roadway.Therefore, grouting anchors were arranged at the shoulder and footing of the roadway and high-water-content materials were used to fill the cracks and pores of the rock mass at the butterfly leaves.In addition to the special area arrangement of the grouting anchor, the roadway roof and floor and ring required a certain number of ordinary anchors.In Figure 16B, the shallow and deep rock masses of the roadway were strongly fastened by anchors to form a surrounding rock bearing structure with strong bearing capacity.
The size of the ordinary anchor was Φ17.8 × 3300 mm (diameter × length).The grouting anchor was Φ22 × 6300 mm (diameter × length) in size and had a grouting pipe inside.Anchors were arranged in 700 × 700 mm (column spacing × row spacing), and the anchors and bolts were arranged at intervals.The anchor tray was welded using 20 mm channel steel and 16 mm steel plates.The floor anchor ordinary anchors, with lengths of 3300 mm, and were arranged in 1500 × 1500 mm (column spacing × row spacing).
3. Subregional grouting with high-water-content materials in fractured rock areas Since the surrounding rock contains a high proportion of water-softening minerals, if conventional cement is used for grouting, the water in the cement slurry will fully contact the plastic zone rock mass through the crack under the action of the high-pressure grouting machine.Thus, the expansion and failure of rock mass in plastic zones will be aggravated.Subsequently, the grouting not only cannot play the purpose of strengthening the rock mass but also further deteriorates the mechanical properties of the rock mass.Therefore, the new support scheme employs high-water-content materials to replace conventional cement.
Additionally, due to the large scope of the fracture zone, the fracture sealing and reinforcement of the shallow surrounding rock were performed first (grouting bolt; grouting pressure 1.5 MPa).This solidified the slurry of the shallow rock mass; the deep hole grouting reinforcement created favorable conditions that prevented deep hole grouting slurry outflow.Thereafter, the rock mass in the butterfly plastic zone was grouted by the grouting anchor (the grouting pressure is appropriately increased, 2-3 MPa), so that the deep surrounding rock was completely cemented and the self-stability of the roadway was enhanced.

Grouting effect peep
The drilling peeping of the surrounding rock after grouting showed that the grouting effect was good in general, as shown in Figure 17.Clearly, the slurry vein distribution showed that the slurry can effectively penetrate into the cracks.Moreover, the distribution of the slurry veins varied in different regions.The shallow surrounding rock mass had a high degree of pore fracture development due to serious fragmentation.The amount of rock grouting in this area was large, and the slurry was distributed in crisscross pattern.As the hole depth increased, the number of cracks in rock mass and the size of cracks decreased.The rock mass in the middle area of the roadway was dominated by a slurry vein that is thick, long, and independent.When entering the deep rock mass, only a few tiny folds and fissures were observed.Figure 18 shows the infiltration of rock slurry at different depths.

Roadway deformation monitoring
The deformation monitoring of roadway was performed for 7 months after the new support technology was carried out.Three monitoring sections were selected, each with a distance of not less than 20 m, and the deformation data shown in Figure 19.The results indicated that the new   | 681 support method effectively reduced roadway deformation.Within 7 months after the new support method was implemented, the deformation of the roof and two rings were 86 and 115 mm, respectively, which meets the requirements of safe production.
1.The lateral pressure coefficient of the roadway was about 2.07, and the roadway was in a two-way extremely unequal pressure stress environment.Various research methods showed that the plastic zone of the south wing track roadway was butterfly shaped.In actual measurement and numerical simulation, the ratio of the shoulder depth of the plastic zone to roof depth was 2.42 and 2.71, respectively.2. Considering the differences in the mechanical response of different morphological plastic zones, and with the goal of preventing the plastic zone's aggressive development, a comprehensive control technology scheme was adopted in the south wing track roadway, taking "grouting anchor + ordinary anchor" and "grouting bolt + metal mesh + sprayed concrete" as support.3.According to the field observation results, after the implementation of the new support scheme, the deformation of the roof and the gangs decreased significantly compared with that under the original support scheme.The deformation of the surrounding rock of the roadway is effectively controlled, and the actual section of the roadway can meet the normal production requirements.

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I G U R E 1 Mechanical model of roadway.F I G U R E 2 Plastic zone shape and maximum radius evolution of the roadway.(A) Distribution of the plastic zone and (B) maximum radius of plastic zone.

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I G U R E 5 Roadway deformation and failure condition.(A) Roof subsidence and (B) roadway instability.T A B L E 1 Mineral composition and content.

Figures 8 , 9 , 7
and 10 illustrate, respectively, the fracture of the rock mass in the roof, two shoulders.The red color in the figure denotes areas where the rock mass is seriously broken.The orange color represents areas with a slightly broken rock mass.Gray represents areas where the rock mass is relatively complete.The number in the figure denotes the depth of the peephole.The depth unit is m.Comparison of Figures 8-10 shows that the failure mode of the rock mass are mainly the hole wall falling off, axial crack, circumferential crack, and different degrees of extrusion and dislocation.These fracture characteristics are mainly concentrated in the serious fracture zone, while the axial cracks occur more frequently in the deep micro fracture zone.Additionally, the test results also reveal that the fracture zone on the two shoulders of the roadway has T A B L E 2 Stress data of the regional stress field.Layout of the peephole.F I G U R E 8 Fracture of the rock mass of the roof (peephole 2).F I G U R E 9 Fracture of the rock mass of the left shoulder (peephole 1).FAN ET AL.| 675 a depth of 5.30 and 5.68 m, respectively, while the fracture zone directly over the roadway's roof has a depth of roughly 2.35 m.The fracture zone depth of the roof is markedly reduced than that of two shoulders.Because the surrounding rock is broken, it is impossible to directly observe the failure of the surrounding rock in the lower portion of the roadway.The schematic of the distribution of the fracture zone is drawn in accordance with the current distribution law of the fracture zone as determined by the results of the drill probe in the upper half of the roadway, as depicted in Figure11.

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I G U R E 10 of the rock mass of the right shoulder (peephole 3).F I G U R E Schematic of the roadway fracture zone.F I G U R E 12 Numerical model.

4. 3 | 4
Analysis of the shape and scope of the plastic zone 1.The results of the above various research methods show

T A B L E 3 5 F
Basic parameters.I G U R E 13 Distribution of the plastic zone.FAN ET AL.

F I U R E 15
Roadway support method based on the mechanical response of plastic zone.

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I G U R E 16 New support design scheme.(A) Grouting bolt and (B) ordinary anchor + grouting anchor.

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I G U R E 17 Drilling peep of grouting effect.F I G U R E 18 Slurry distribution in the surrounding rock.(A) Shallow fractured rock mass, (B) central fractured rock mass, and (C) deep fractured rock mass.

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I G U R E 19 Roadway deformation monitoring.