Patent Application
20170091355
The present invention relates to the design of underground excavations in general and more particularly to systems and methods of designing ground support systems for underground excavations.
Many different methods of designing ground support systems for underground excavations are known and have been used for decades to meet various performance and safety criteria. However, the design methods are typically iterative and require a significant amount of time and effort to select from among the numerous options available for determining support requirements under various conditions.
One embodiment of a design tool for allowing a user to develop on a computer a design for an underground excavation may include an excavation details tool. The excavation details tool receives information relating to the underground excavation to be developed. A stress estimator tool operatively associated with the excavation details tool receives information relating to stress calculation parameters. The stress estimator tool calculates ground stresses in a vicinity of the underground excavation based on the information relating to stress parameters and the underground excavation to be developed. A rock mass characteristics tool receives information related to geotechnical characteristics of rock mass adjacent the underground excavation. The rock mass characteristics tool also estimates a ground type category based on the information relating to the geotechnical characteristics. A ground support system schematic tool operatively associated with the excavation details tool and the ground support system schematic tool generates at least one schematic representation of the underground excavation to be developed. A wedge assessment tool operatively associated with the excavation details tool, the stress estimator tool, the rock mass characteristics tool, and the ground support system schematic tool estimates support requirements for the underground excavation to be developed and produces information relating to a kinematic stability of the underground excavation to be developed.
Also disclosed is a method of designing an underground excavation that involves the steps of: Developing a plurality of input parameters for the underground excavation; performing a first design iteration to determine an initial ground support system design; evaluating a kinematic and/or dynamic stability of the initial ground support system design; determining whether the kinematic and/or dynamic stability meets a predetermined factor of safety; and reiterating the initial ground support system design until the predetermined factor of safety is achieved.
A ground support design system may include a display system, an input system, and a computer system operatively associated with the display and input systems. The computer system further includes an excavation details tool that generates on the display system a plurality of input fields to allow the user to use the input system to input information relating to an underground excavation to be developed. A stress estimator tool operatively associated with the excavation details tool generates on the display system a plurality of input fields to allow the user to use the input system to input information relating to stress calculation parameters. The stress estimator tool calculates ground stresses in a vicinity of the underground excavation based on the input information relating to stress calculation parameters and the underground excavation to be developed. A rock mass characteristics tool generates on the display system a plurality of input fields to allow the user to use the input system to input information relating to geotechnical characteristics of rock mass adjacent the underground excavation. The rock mass characteristics tool estimates a ground type category based on the input information relating to the geotechnical characteristics. A ground support system schematic tool operatively associated with the excavation details tool generates on the display system at least one schematic representation of the underground excavation to be developed. A wedge assessment tool operatively associated with the excavation details tool, the stress estimator tool, the rock mass characteristics tool, and the ground support system schematic tool estimates support requirements for the underground excavation to be developed. The wedge assessment tool produces information relating to a kinematic stability of the underground excavation to be developed.
Illustrative and presently preferred exemplary embodiments of the invention are shown in the drawings in which:
One embodiment of a ground support design tool or system 10 is illustrated in
Briefly, the tools or modules 12 of ground support design system 10 may comprise an excavation module 22, a stress estimator module 24, a rock mass characteristics module 26, a ground support system schematic module 28, and a wedge assessment module 30. In addition, the ground support design tool 10 may also be provided with a number of additional modules or tools that may be utilized depending on a variety of factors. For example, in one embodiment, such additional modules or tools may include a depth of failure module 32, a bursting support design module 34, an intersection and an intersection design module 36. Intersection design module 36 may comprise design tools or modules 38 and 40 for both 3-way and 4-way intersections.
The ground support development tool 10 may also be provided with a number of supplemental tools or modules 13 to provide additional functionality. In the particular embodiment shown and described herein, the supplemental tools or modules 13 may comprise a ground support specifications module 42, a lookup sheet module 44, a stress estimate output module 46, a max IP module 48, and a min IP module 50.
Referring now to
With reference now primarily to
If the ground type category 52 is of one of the other types, e.g., Categories 2, 3, or 4, then process 20 proceeds to follow design iterations 58, 60, and 62, as depicted in
A significant advantage of the present invention is that it provides an single integrated system or tool 10 containing all of the analytical tools or modules required to develop a ground support system design that meets the requirements for given excavation, geotechnical, and stress conditions. Moreover, the information and data input to the various modules, as well as the calculations or computations performed by each module is automatically transferred or communicated among the various modules, thereby significantly streamlining the development process and significantly reducing the likelihood for errors to be inadvertently introduced during the development process. In addition, satisfactory and unsatisfactory ground support designs may be reflected immediately e.g., by the ground support system schematic tool 28. More specifically, unsatisfactory or poorly developed ground support system design elements may be indicated in the color red in the ground support schematic, thereby allowing the user to change the design ‘on-the-fly’ until a satisfactory indication (e.g., by use of the color green) is provided.
Still other advantages are associated with the development process 20. For example, the various design iterations or loops 54, 56, 58, 60, and 62 provide for an improved design methodology in which only those design iterations required to satisfy certain ground type categories are performed. Furthermore, the design methodology 20 provides a rationalized basis for situations for guiding a user to change or modify the underground excavation design when a satisfactory ground support design cannot be developed for a given initial underground excavation design.
Having briefly described one embodiment of the ground support design tool 10 and design process 20, as well as some of their more significant features and advantages, various embodiments and alternative configurations of the ground support design tool and design process 20 will now be described in detail. However, it should be noted that while the following description is directed to various embodiments and alternative structures and methods, other variations and modifications of the ground support design tool 10 and design process 20 will become apparent to persons having ordinary skill in the art after having become familiar with the teachings provided herein. Therefore, the present invention should not be regarded as limited to the particular structural arrangements, configurations, materials, and methods shown and described herein.
Referring back now to
As briefly mentioned earlier, the ground support system development tool 10 may comprise a plurality of tools or modules 12 that may be utilized in various combinations to assist the user in developing a ground support system design or configuration suitable for a proposed underground excavation. In the particular embodiment shown and described herein, the ground support design tool 10 may comprise an excavation detail tool or module 22, a stress estimator module tool 24, a rock mass characteristics module or tool 26, a ground support system schematic tool 28, and a wedge assessment tool 30. In addition, the ground support design tool 10 may also be provided with a number of additional modules or tools that may be utilized depending on a variety of factors. Those additional modules or tools may include a depth of failure module or tool 32, a bursting support design module or tool 34, and an intersection design tool 36. Intersection design tool 36 may comprise design tools 38 and 40 for both 3-way and 4-way intersections.
The ground support development tool 10 may also be provided with a number of supplemental tools or modules 13 to provide additional functionality. These supplemental tools or modules 13 also may be displayed on the display system 16 as one or more tabs (not shown), thereby allowing the user to readily access the various supplemental tools or modules 13 during the design process. In the particular embodiment shown and described herein, the supplemental tools or modules 13 may comprise a ground support specifications tool 42, a lookup sheet tool 44, a stress estimate output tool or module 46, a max IP tool 48, and a min IP tool 50.
Considering now the various tools or modules 12 and 13 in detail, the excavation detail module 22 may be configured to generate an underground excavation details window 66, as shown in
In the particular embodiment shown and described herein, the input data field area 68 includes fields for the Span, Height, Shape, Trend, and Plunge of the planned underground excavation. The input data field area 68 may also include fields for displaying the estimated equivalent radii of the roof and wall. The Span and Height of the proposed underground excavation are the width (i.e., from wall to wall) and height (i.e., from floor to roof) of the planned underground excavation. The excavation detail tool 22 may be configured to calculate or determine an equivalent radii of the roof and wall of the underground excavation based on the input values for the span and height. That is, because most underground excavations are roughly rectangular in shape (as shown in
The shape of the opening is used by other modules to calculate the tangential stresses around underground openings having certain defined shapes known in the art. In the example illustrated in
The stress estimator module 24 may be operatively associated with the excavation details module 22 so that information and data may be exchanged between the two tools or modules 22 and 24. The stress estimator module 24 accepts input from the user that relates to certain stress calculation parameters. The stress estimator tool 24 calculates ground stresses in a vicinity of the underground excavation based on the input information relating to the stress calculation parameters as well as on the information about the underground excavation to be developed.
Referring now to
The stress model query coordinates area 74 (
The excavation stress query area 76 (
The excavation stress compiler inputs area 78 (
The design stress state definitions area 80 (
As mentioned, the stress estimator module 24 may also produce and display information and data relating to various stress solutions. In one embodiment, the stress estimator module 24 may generate a principal stress solution area 82 and a 2D excavation stress solution area 84, as best seen in
The compiled data plots provided in area 82 present trends of the magnitude and orientation of the major (Sigma 1), intermediate (Sigma 2), and minor (Sigma 3) principal stresses by mining stage for the queried model locations. The error bars included in the magnitude plot correspond to the range defined by the minimum and maximum percentile values entered in the excavation stress compiler inputs area 78 of the stress estimator module 22. The line plots present mean values. Trend values are relative to the mine coordinate system. The plotted plunge data follows the same convention as the instantaneous values (up is positive).
Referring now primarily to
Sigma lip and Sigma 3ip represent the in-plane maximum and minimum stress, respectively, acting in the new, x′-z′ plane. This plane is oriented perpendicular to the excavation trend such that the x′-axis is horizontal and perpendicular to the underground excavation walls/ribs and the z′-axis is vertical and perpendicular to the underground excavation roof/back. The value labels also provide some indication of which in-plane stress is nearly horizontal (x′x′) and which is nearly vertical (z′z′). The y′-axis parallels the excavation trend and represents the orientation of the out-of-plane stress or that acting on the underground excavation end walls.
The instantaneous data portion of the plot presents the orientation of the in-plane stress as if looking along the excavation (y′-axis) orientation. The plot thus provides an indication of the orientation of the resolved in-plane stresses relative to the excavation roof/back and walls/ribs to assist in the interpretation of stress conditions.
For the compiled data types, area 84 may include a plot of underground excavation stress magnitudes. This plot presents the average of the truncated range (between the minimum and maximum percentiles) of in- and out-of-plane stresses by mining stage. The error bars represent the significant range of values defined by the minimum and maximum percentile values entered in the excavation stress compiler inputs area 78 (
Area 84 may also include a plot of underground excavation stress ratios and orientations. This plot includes the calculated in-plane and out-of-plane Ko values by mining stage based on the truncated average in- and out-of-plane stresses. Ko, is defined as the ratio of horizontal to vertical stress. Also plotted is the truncated average theta (θ) value which is the angular orientation of Sigma lip above horizontal. Similar to the plotted stress magnitudes, this value represents the average of the range of values between the minimum and maximum percentile values. Trends in these plotted values provide some indication of how the orientation of in- and out-of-plane stresses change through the mining sequence relative to the underground excavation surfaces. Finally, area 84 may also include a plot of Sigma lip and Sigma 3ip by stage. These plots provide a more detailed presentation of the distribution of the resolved in-plane stresses. They are included as a means to verify the trends plotted in the excavation stress magnitudes plot and minimize the potential for bias from outlier values when interpreting local stress conditions.
The rock mass characteristics module 26 may generate a plurality of input fields to allow the user to input information relating to the rock characteristics for the particular underground excavation that is being developed. In one embodiment, the various inputs used to calculate the quality of the rock mass may be based on the rock mass rating system developed by Z. T. Bieniawski, as published in Engineering Rock Mass Classifications, Bieniawski, Z. T., John Wiley & Sons (1989), hereinafter “RMR89”, and the ‘Q’ rating system system developed by the Norwegian Geotechnical Institute, in the publication entitled “Using the Q-System, Rock Mass Classification and Support Design,” Oslo, 2013, hereinafter “NGI.” An estimate of the Geological Strength Index (GSI), which may be obtained from “Predicting Tunnel Squeezing Problems in Weak Heterogenous Rock Masses,” Hoek, E., and Marinos, P., Tunnels and Tunneling International 32, no. 11, pp. 45-51 (2000), hereinafter “Marinos and Hoek,” is also required for the rock mass characteristic module 26. The input fields populated in this tab serve to define the geotechnical character of the rock mass an ultimately how the underground excavation will behave in response to in-situ and mining induced stress. In the particular embodiment shown and described herein, the rock mass characteristics module 26 estimates a ground type category 52 (
With reference now to
Referring now primarily to
The rock mass quality data area 90 and a rock mass rating data area 92 are best seen in
As mentioned earlier, the rock mass characteristics module 26 may also be used to estimate a ground type category 52. With reference now to
The ground support design schematic tool or module 28 receives information and data from the excavation detail tool 22 and causes the computer system 14 to display for the user (e.g., on display system 16) at least one schematic representation of the underground excavation to be developed. The user will typically make extensive use of the ground support design schematic module 28 during the iterative design process of method 20. The wedge assessment module 30 may be used to provide an assessment of the kinematic stability of the underground excavation to be developed.
The ground support design schematic module 28 may be configured to generate a design schematic window 96, as best seen in
Referring now to
The user may also input information and data relating to the Bolting Systems which may include two different bolting designs, designated herein as Bolting Designs 1 and 2. See also
In one embodiment, the data input into the fields for the various bolt design configurations may be immediately reflected in the cross-sectional view area 100 and the unfolded view area 102, as best seen in
Referring back now primarily to
This value represents the minimum design Factor of Safety (FS) based on the defined underground excavation use category using the following criteria:
This is the calculated support pressure for the ground support system. It is assumed that the shotcrete does not provide any active surface pressure, and is assumed to be a tie-in element.
This is the scaled support pressure based on a wedge with an apex height of ⅓ the span of the underground excavation. The term scaled means that the ‘true’ capacity of a bolt is that which is available from the length above the apex height of the wedge.
This is the max displacement value of the support system. The calculated value will appear in a color green if the ratio between it and the maximum required displacement is greater than or equal to the applicable design FS defined above. It will appear in a color red if the FS is less than the design criteria.
This is the estimated displacement/convergence of the roof/back taken from calculations in the depth of failure module 32. It represents the largest (i.e., maximum) estimated displacement value from the massive and heavily jointed rock mass cases.
This is the estimated displacement/convergence of the rib taken from calculations in the depth of failure module 32. It represents the largest or maximum estimated displacement value from the massive and heavily jointed rock mass cases.
This is the total scaled support capacity for the underground excavation roof/back. This value is calculated based on the scaled bolt capacity (i.e. capacity from length above the wedge) and the designed bolt spacing.
This is the required support capacity for a theoretical tetrahedral wedge with an apex height that is ⅓ the span of the underground excavation.
Calculated as the ratio of the available, scaled capacity to the required support capacity. The calculated value will appear in a color green on the display if it is greater than or equal to the FS design criteria calculated above. It will appear in a color red on the display if it is less than the design FS.
This is the calculated static capacity of the support system (not including shotcrete or mesh) in the underground excavation roof/back, scaled based on the maximum depth of brittle/spalling failure from the depth of failure module 32. In order for a bolt to have its maximum capacity it must have sufficient embedment to do so. Bolts that have a length less than the depth of spalling will have zero capacity.
This is the static capacity required for the roof/back calculated from the maximum depth of brittle/spalling failure from the depth of failure module 32 and defined rock density from the rock mass characteristics module 26.
Calculated as the ratio of the available roof/back depth of failure capacity to the required depth of failure capacity. The calculated value will appear in a color green on the display if it is greater than or equal to the FS design criteria calculated above. It will appear in a color red if it is less than the design FS.
This is the calculated static capacity of the support system (not including shotcrete or mesh) in the underground excavation ribs, scaled based on the maximum depth of brittle/spalling failure from the depth of failure module 32. In order for a bolt to have its maximum capacity it must have sufficient embedment to do so. Bolts that have a length less than the depth of spalling will be deemed to have zero capacity.
This is the static capacity required for the rib calculated from the maximum depth of brittle/spalling failure from the depth of failure module 32 and defined rock density from the rock mass characteristics module 26.
Calculated as the ratio of the available rib depth of failure capacity to the required depth of failure capacity. The calculated value will appear in a color green on the display if it is greater than or equal to the FS design criteria calculated above. It will appear in a color red if it is less than the design FS.
It should be noted that in most embodiments the inputs resulting in the presented values for Dynamic Capacity are somewhat subjective. Therefore, the Dynamic Capacity values will, in most instances, be useful primarily as guidelines.
This is the calculated energy capacity of the wall/rib support system. The scaled designation means that the support capacity is scaled based on the maximum depth of spalling damage. So in order for a bolt to have its maximum capacity it must have sufficient embedment to do so. Bolts that have a length less than the depth of spalling will be deemed to have zero capacity. Value is in kiloJoules (kJ) and is taken from the depth of failure module 32.
This is the estimated energy capacity required for an event in the rib taken directly from the depth of failure module 32.
Calculated as the ratio of the available energy capacity roof/back to the required energy roof/back capacity. The calculated value will appear in a color green on the display if it is greater than or equal to the FS design criteria calculated above. It will appear in a color red on the display if it is less than the design FS.
This is the calculated energy capacity of the roof/back support system. The scaled designation means that the support capacity is scaled based on the maximum depth of spalling. In order for a bolt to have its maximum capacity it must have sufficient embedment to do so. Bolts that have a length less than the depth of spalling will have zero capacity. Value is in kJ and is taken from the depth of failure module 32.
This is the estimated energy capacity required for an event in the roof/back taken directly from the depth of failure module 32.
Calculated as the ratio of the available energy capacity rib to the required energy rib capacity. The calculated value will appear in a color green on the display if it is greater than or equal to the FS design criteria calculated above. It will appear in a color red if it is less than the design FS.
As briefly mentioned earlier, ground support design tool 10 may also be provided with a number of additional modules or tools that may be utilized depending on a variety of factors and desired functionalities. In the particular embodiment shown and described herein, such additional modules or tools may include a depth of failure module or tool 32. The depth of failure module 32 may be utilized in certain instances wherein the geotechnical characteristics of the rock make certain failure modes more probable. For example, in the particular embodiment shown and described herein, the depth of failure module 32 is used when the estimated ground type category is other than Category 1, e.g., as may be determined by the rock mass characteristics module 26. The depth of failure tool 32 generates a plurality of input fields to allow the user to input certain information, including a spalling initiation threshold. The depth of failure module 32 may also receive or utilize certain information and data from the rock mass characteristics module 26. The depth of failure module 32 may then use this information and data to determine a depth of failure for a given set of rock mass properties and stresses. The calculations performed by the depth of failure module 32 may also analyze both massive and heavily jointed rock masses.
Referring now to
In the particular embodiment shown and described herein, the input data field area 108 includes a field for input data relating to Spalling Initiation Threshold. The Spalling Initiation Threshold is the ratio of the maximum induced stress, σmax, to the intact uniaxial compressive strength, σci, at which spalling is initiated. A higher threshold means that damage will be induced at a higher stress level. This value is utilized in calculating the Spalling Depth of Failure according to the techniques published in “Measurement of Spalling Parameters from Laboratory Testing,” Diederichs, M. S., and Martin, C. D., Rock Mechanics and Environmental Engineering, pp. 323-326, (2010), hereinafter “Diederichs and Martin.” Two other data input fields are for entry of the material constant (mi) for intact rock and the Disturbance Factor (D), as published in “Underground Excavations In Rock, Hoek, E. and Brown, E. T., Instn. Min. Metal, London, 1980, hereinafter “Hoek and Brown.” The material constant value is utilized in calculating the rock mass material constant mb. The Disturbance Factor ranges from 0-1 and represents that amount of damage induced into the underground excavation due to the excavation process itself. This value is used in calculating the depth of failure and anticipated strain in heavily jointed rock masses.
The remaining fields in the input data field area 108 include data automatically imported from the stress estimator module 24 and rock mass characteristics module 26, as previously described.
The depth of failure module 32 also includes fields for the Empirical Induced Stress Estimation and Empirical Rock Mass Strength Estimation, as depicted in input data field area 108. The various empirical estimates are determined by the depth of failure module 32 as follows:
For all terms within this section, the following variables are defined as follows:
This is the ratio of horizontal to vertical stress. A K0 value less than 1 indicates vertical stress is dominant while a K0 value greater than 1 indicates horizontal stress is dominant. It is calculated from the stress values entered in the stress estimator module 24.
This is the maximum tangential stress in the wall of the underground excavation based on the K0 ratio, the vertical stress entered in the stress estimator module 24, and the rotational angle θ relative to horizontal around the idealized, circular underground excavation:
σmax-wall=σv[(1+K0)+2(1−K0)cos 2θ] (3)
where θ=0 degrees.
This is the maximum tangential stress in the wall of the underground excavation based on the K0 ratio, the vertical stress entered in the stress estimator module 24, and the rotational angle θ relative to horizontal around the idealized, circular underground excavation:
σmax-roof=σv[(1+K0)+2(1−Kθ)cos 2θ] (4)
where θ=90 degrees.
Ratio σmax/σci—Wall:
This is the ratio of maximum tangential stress (measured in MPa) that is developed in the wall of the underground excavation, divided by σci. This ratio is utilized for assessing the depth of spalling in massive rocks.
Ratio σmax/σci—Roof/Floor:
This is the ratio of maximum tangential stress (measured in MPa) that is developed in the back of the underground excavation, divided by σci. This ratio is utilized for assessing the depth of spalling in massive rocks.
Stress Ration σmax-roof/σci (6)
This value is the anticipated maximum tangential roof stress (MPa) based on the shape of the underground excavation. The value is determined from the shape of the underground excavation that was selected in the rock mass characteristics module 26. The values are calculated based on the relationships provided in Hoek and Brown.
This value is the anticipated maximum tangential wall stress (MPa) based on the shape of the underground excavation. The value is determined from the shape of the underground excavation that was selected in the rock mass characteristics module 26. The values are calculated based on the relationships provided in Hoek and Brown.
Value is taken from the estimated value input in the rock mass characteristics module 26. It is used as input into the Hoek and Brown rock mass strength calculation.
This is the downgraded mi material constant for the rock mass, as published in “Hoek-Brown Failure Criterion—2002 Edition,” Hoek, E. et al., Proceedings of NARMS-Tac, pp. 267-273, (2002), hereinafter “Hoek et al.” This value is utilized in calculating the depth of failure and anticipated strain in heavily jointed rock masses. The value is calculated based on the GSI value.
Material constant for the rock mass, according to Hoek et al. This value is utilized in calculating the depth of failure and anticipated strain in heavily jointed rock masses. The value is calculated based on the GSI value.
Material constant for the rock mass, according to Hoek et al. This value is utilized in calculating the depth of failure and anticipated strain in heavily jointed rock masses. The value is calculated based on the GSI value.
This is the rock mass strength calculated in accordance with the equations defined in Hoek et al.
The massive rock assessment area 110 includes calculated fields that employ the same empirical formula for both the walls/ribs and roof/back, but differing excavation induced stress inputs; the wall/rib calculations reference the ‘Kirsch Solution—Wall’ value while the roof/back calculations reference the ‘Kirsch Solution—Roof/Floor’ value. A summary of the calculated fields in this area 110 is provided below.
Before proceeding it should be noted that all estimates of the depth of failure represent the condition with no support installed. The application of support provides confinement, suppresses the spalling, and acts to reduce the depth of failure. As such, these estimates are inherently conservative.
Spalling Depth—(Ratio σmax/σci):
This is the ratio of σmax/σci for the wall/rib or roof/back of the underground excavation. The value is calculated based on σci and respective Kirsch solutions.
This is the calculated depth of failure based on the equation provided in Diederichs and Martin. The spalling parameter, which determines at what σmax/σci ratio spalling initiates, can be adjusted to better correspond to site observations. The spalling parameter typically ranges from 0.4-0.5.
This value is the anticipated displacement on the rib of the underground excavation. To calculate closure multiply the value by 2. The calculation assumes that stiff ground support is installed, which reduces the anticipated dilation/bulking to 5%.
The heavily jointed rock area 112 also employ the same empirical formula for both the walls/ribs and roof/back, but excavation induced stress inputs vary based on the respective calculations. The wall/rib solutions make use of ‘In-plane Stress (Vertical) σv’ and ‘Kirsch Solution—Wall’ values, while the roof/back calculations use the ‘In-plane Stress (Horizontal) σR’ and ‘Kirsch Solution—Roof/Floor’ values. A summary of the calculated fields in this section of the tab are provided below.
This value is the anticipated depth of failure for a heavily jointed or soil like rock mass under static conditions. The value is calculated based on equations presented by Hoek and Marinos.
where:
The rock mass strength is determined based on Hoek et al. The internal support pressure value for the calculation comes from the ground support system schematic module 28. In the case of the roof/back calculation, the support pressure used is the scaled value, meaning that the support capacity is limited to the capacity provided by the portion of the tendon embedded beyond the largest theoretical wedge block (see the ‘Estimated Available Support Pressure (Scaled)’ field description in the ground support system schematic module 28.
This is the % closure strain value estimated using the following relationship presented in “Estimation of Tunnel Squeezing in Anisotropic Stress Fields using a FLAC-Based Neural Network,” Continuum and Distinct Element Numerical Modeling in Geomechanics-2011, (2011), hereinafter “DeGagne et al”:
where
This calculation converts the estimated % closure strain value to a closure dimension based on the respective original underground excavation dimension (span or height).
Another module may comprise a bursting support design module or tool 34. The bursting support design tool 34 may generate a plurality of input fields to allow the user to input (e.g., via computer system 14) information relating to a bulking factor, ejection velocity of a bulking event being assessed, and an energy capacity of a proposed floor support system. The bursting support design tool then determines or estimates demands imposed on the floor support system by rapid bulking. The primary calculations assume the dominant damage mechanism is bulking with ejection resulting from a strain burst event. If desired, the bursting support design tool 34 may also produce damage estimates resulting from a burst triggered by a remote seismic event, although such functionality is not required.
In one embodiment, the bursting support design module 34 generates or produces a bursting support design window 114 having a data input area 116, as best seen in
The data input area 116 provides fields for input and calculated data for failure mode assessment as follows:
The user enters the desired bulking factor to be used in subsequent bulking calculations. This allows the user to review the effects of the bulking factor on the support systems. The following values are recommended based on support type:
This value is the displacement resulting from the defined bulking factor and maximum depth of failure calculated by the depth of failure module 32 for the underground excavation roof.
This value is the displacement resulting from the defined bulking factor and maximum depth of failure calculated by the depth of failure module 32 for the underground excavation rib.
This value is the displacement resulting from the defined bulking factor and maximum depth of failure calculated by the depth of failure module 32 for the underground excavation floor. In one embodiment, this is assumed to be equal to the roof/back failure depth.
This is the acceleration due to gravity. The default value is 9.81 m/s2.
This is the anticipated mass of rock that could be ejected during a dynamic event. The mass is estimated from the depth of failure calculated by the depth of failure module 32.
This is the anticipated weight of rock that could be ejected during a dynamic event. The weight is estimated from the depth of failure calculated by the depth of failure module 32.
This is the anticipated mass of rock that could be ejected during a dynamic event. The mass is estimated from the depth of failure calculated by the depth of failure module 32.
This is the anticipated weight of rock that could be ejected during a dynamic event. The weight is estimated from the depth of failure calculated by the depth of failure module 32.
This is the ejection velocity of the bulking event being assessed. Experience from other mines has shown that velocities typically range from 1-3 meters per second (m/s). It is extremely difficult to predict whether ejection will occur, but some general rules of thumb can be used for assessing prior strain burst events underground. If material is ejected and is displaced beyond its angle of repose, the ejection velocity must be greater than 2 to 3 m/s. If velocities of greater than 3 m/s are anticipated a modified development sequence, distress blasting, or other method for reducing the ejection energy or likelihood of an event should be considered. Modern support systems in most cases will not survive an event with a velocity greater than 3 m/s.
This is the calculated ejection energy for an event that occurs in the back of the underground excavation. Ejection in the roof/back takes into account the effect of gravity.
E=0.5 mv2+am (10)
where
This is the calculated ejection energy for an event that occurs in the rib/wall of the underground excavation.
E=0.5 mv2 (11)
where
This is the calculated ejection energy for an event that occurs in the back of the underground excavation. Ejection in the floor takes into account the effect of gravity, which reduces the event energy.
E=0.5 mv2−am (12)
where
This is the calculated energy capacity of the respective roof/back and wall/rib support systems. The scaled designation means that the support capacity is scaled based on the maximum depth of spalling. In order for a bolt to have its maximum capacity it must have sufficient embedment to do so. Bolts that have a length less than the depth of spalling will have zero capacity.
This is the calculated energy capacity of the floor support system. This value needs to be entered by the user due to the fact support is not commonly installed in the floors of the underground excavation. The value entered in this cell should be scaled similar to the others mentioned above.
In the particular embodiment shown and described herein, the severity of calculated ejection energies are ranked and colored based on the classification scheme presented in the Canadian Rockburst Support Handbook, Geomechanics Research Centre/MIRARCO, (1996), hereinafter “Kaiser et al,” to provide a qualitative indication of the likely support system damage. The color/severity scale is outlined in the reference table 118. See
As best seen in
Ground support development tool 10 may also be provided with an intersection design tool 36. The intersection design tool 36 may generate a plurality of input fields to allow the user to input information relating to intersections in the underground excavation design being developed and determines information relating to a required number and type of support elements for the intersections. In one embodiment, the intersection design tool 36 may comprise design tools 38 and 40 for both 3-way and 4-way intersections.
Referring now to
This is the factor of safety that is utilized for assessing the number of tendons/rock bolts required to support a generalized, parabola shaped failure zone. See also
This is the density of the rock. The value is taken from the rock mass characteristics module 26. Value is in units of (kg/m3).
This is the unit weight of the material. Value is in units of (MN/m3).
This is the tendon/rock bolt type to be used to support the intersection. The selected type is used to determine the available support capacity and, ultimately, the number of bolts required.
This is the unit capacity of the support element selected. Value is in units of (MN/m2).
This is the width of the drift that is running up and down in the figure. The value is in units of (m).
This is the width of the drift that is intersecting drift A. Value is in units of (m).
This is the distance that the intersecting drift walls/ribs are cut back in order to make a 45 degree angle. A value of zero means that it is a 90 degree intersection.
This is the diameter of the inscribed circle used in the calculations in meters.
The loosening zone depth is estimated to be equal to ⅓ the inscribed circle diameter in meters.
This is the face area of the inscribed circle. Value is in units of (m2).
This is the volume of a parabola that has a height ⅓ the inscribed diameter. Value is in units of (m3).
This is the total weight of the failure zone calculated from the volume and density inputs in units of tonnes.
This is the total number of tendons/rock bolts required to support the parabola weight based on the input factor of safety and the capacity of the defined bolt type.
This is the tendon/rock bolt spacing in meters based on the parabola face area and Required Number of Tendons field.
This is the total number of tendons/rock bolts required in the inscribed circle estimate based on the calculated spacing and inscribed circle radius. This should be the same value provided in the Required Number of Tendons field.
This value is calculated by adding 1.5 meters to the estimated value provided in the Loosening Zone Depth field. The additional 1.5 meters is added to each tendon/rock bolt length due to general installation requirements and the need for adequate embedment to ensure full capacity.
With reference now primarily to
This is the factor of safety of the design depicted in
This is the number of tendons/rock bolts depicted within the circle in the intersection schematic.
This is the total number of tendons shown in the intersection schematic. As the drift approaches additional tendons should be installed outside of the circle to stabilize the intersection.
Optionally, the intersection design module 34 may also be configured to display one or more graphs 132, 134 of tendon/rock bolt spacing and length versus intersection span, as best seen in
As briefly described above, ground support development tool 10 may also be provided with a number of supplemental tools or modules 13 to provide additional functionality. These supplemental tools or modules 13 also may be displayed on the display system 16 as one or more tabs (not shown), thereby allowing the user to readily access or toggle between the various supplemental tools or modules 13 during the design process. In one embodiment, the supplemental tools or modules 13 may comprise a ground support specifications tool 42, a lookup sheet tool 44, a stress estimate output tool or module 46, a max IP tool 48, and a min IP tool 50.
The ground support specifications tool 42 may be provided with or include strength and deformability specifications for all the available ground support components. The lookup sheet tool 44 may be provided with or include all the lookup values and many of the calculations that are performed in the background. Lookup sheet tool 44 may also be provided with or include all the formulas and arrays that are required for the visualizations in the tool. The stress estimate output tool 46 may be provided with or include the output from a stress compiler macro that may be included in the stress estimator tool 24. The output values may be those referenced by to plots presenting the results by mining stage. A number of post-processing calculations may be included in this tool as well. The macro output values may be designated from the post-processed fields by text and cell fill color. The max and min IP tools 48 and 50 may include outputs from the stress compiler macro used to generate the in-plane (ip) maximum and minimum stress plots presented in the stress estimator tool 24.
Referring back now primarily to
As briefly mentioned above, design process 20 may comprise several design iterations or process loops 54, 56, 58, 60, and 62 in which a proposed ground support system design or configuration is evaluated and/or iterated to ensure that it meets the requirements for given excavation, geotechnical, and stress conditions. Design process 20 is hierarchical depending on the particular ground type category 52 and other factors, as described below. If the ground type category 52 is of type Category 1, then a ground support system design or configuration that meets certain requirements as to kinematic stability and static factor of safety will be deemed sufficient and the design process 20 complete. However, if the proposed initial ground support system design does not meet the requirements for kinematic stability and static factor of safety, then process 20 will proceed to the second design iteration loop 56. Thereafter, the user may adjust the initial ground support system design or configuration until the (now iterated or modified) ground support system design meets the requirements for kinematic stability and static factor of safety.
If the ground type category 52 is of one of the other types, e.g., Categories 2, 3, or 4, then process 20 proceeds to follow design iterations 58, 60, and 62 until the ground support system design or configuration for the proposed underground excavation design meets the various criteria associated with the respective design loops 58, 60, and 62. Once the ground support system design meets the various respective criteria, the design process 20 will then be complete. However, if the changes to the ground support system configuration made during the various design iterations 54, 56, 58, 60, and 62 are unable to produce a ground support system configuration that meets the various respective criteria, then the process 20 returns, as indicated by broken lines 21, 23, and 25, to initial step 64 in which the user may change the basic configuration of the underground excavation. Thereafter, design process 20 may be followed again until the support system design for the new underground excavation configuration satisfies the requirements.
A stepwise summary of the methods and evaluations that may be performed by the ground support design tool 10 is presented in the following sections. Prior to performing ground support design analyses, pertinent information related to underground excavation geometry, expected stress state(s), and the host rock geotechnical properties will need to be defined. These inputs are entered in various input fields generated by the various modules 12 within the ground support design tool 10.
For example, the excavation detail module 22 generates or includes input fields for entry of all details regarding the size, shape, and orientation of the underground excavation. This tool 22 may also include and/or display information regarding the version of the spreadsheet and space to document the date of evaluation, respective drawing number and assessment areas, and the user/designer.
The stress estimator tool 24 includes calculation tools for estimating the stresses likely to act normal to the underground excavation roof/back, ribs, and end walls through the mining sequence for the mine location under consideration. Inputs for these calculations may include the results of the mine-wide stress models and underground excavation orientation information, e.g., derived from numerical simulations.
In one embodiment, the general calculation steps may be as follows:
Rock mass characteristics are defined in the rock mass characteristics module 26. In one embodiment, the various inputs are used to calculate rock mass quality based on the RMR89 system and the NGI Q rating systems. An estimate of the Geological Strength Index (GSI) from Marinos and Hoek is also required in this module 26. The input fields generated (and populated) in this module 26 serve to define the geotechnical character of the rock mass and ultimately how the underground excavation will behave in response to in-situ and mining induced stress.
Once the analysis inputs have been defined, as described above, the empirical support design charts presented in the rock mass characteristics module or tool 26 can be used to develop an initial ground support system design. The system is constructed from available components in the ground support system schematic module or tool 28.
In the first design iteration 54, the initial design may then be checked for kinematic stability using the generic wedge calculations performed by the generic wedge assessment module or tool 30 and may be summarized in the ‘Support Capacity Checks’ area of the ground support system schematic module 28.
If site specific structural information is available, an analysis may be performed using the ‘Unwedge’ computer program available from Rocscience, Inc., of Toronto, ON (Canada) to verify the suitably of the initial support design. If the static factor of safety (FS) for this design iteration meets the respective design criteria for the excavation type, then the ground support system will meet the required demand and the design process is complete. If the static factor of safety (FS) does not meet the minimum criteria, then the second design iteration 56 is performed.
Commonly, adjusting support spacing and length will work to mitigate potential static failures. In the second design iteration 56, these inputs may be adjusted iteratively in the ground support system schematic module 28 until an acceptable factor of safety is achieved. If a reasonable combination of components cannot be determined, it may be necessary to adjust the dimensions, shape, and/or orientation of the underground excavation, as indicated by path 21.
As mentioned, if the combination of geotechnical and stress conditions indicates the ground type is Category 1 (i.e. structurally controlled failure mechanisms only), as estimated by the rock mass characteristics module 26, designing for a static, structurally controlled failure is all that is necessary. The process 20 is deemed complete. For the other ground support categories (Categories 2-4), additional evaluations or iterations 58, 60, and 62 are required.
Excavations in ground types other than Category 1 require an assessment of the potential for the induced stress to cause rock mass failure around the underground excavation. These steps may be performed in the third design iteration 58. Empirical estimates of the depth of rock mass failure are presented by the depth of failure module or tool 32. In the particular embodiment shown and described herein, calculated failure depths and associated displacements/closure are given for two mechanisms:
These two mechanisms represent the two end-members of stress induced failure and associated deformations. A review of the estimated ground type category and the qualitative damage scales provided for each of these mechanisms provides some indication of which is the more likely for the given conditions.
Once the predominate rock mass failure mechanism is identified, the tendon components of the ground support system should be adjusted to ensure adequate anchorage beyond the estimated failure depth for both the ribs and back/roof. As a general rule of thumb, the minimum anchorage length beyond the failure zone is considered to be ⅓ the total bolt length. It will be important to calibrate the estimated depths with site-specific experience and engineering judgement to ensure tendon lengths are adjusted appropriately.
Once the anchorage depths have been adjusted, the relative degree of potential for spalling/brittle failure may be assessed using the qualitative rating system defined for massive rock in the Depth of Failure module 32. If the indicated damage level is ‘Moderate to Major,’ it will be necessary to evaluate the dynamic demands on the ground support system. If the indicated damage level is ‘Moderate’ or less and the estimated ground type is not Category 3 or 4, then the current ground support system design will adequately meet the anticipated support demands. Again, design process 20 is deemed to be complete.
When the combined rock mass characteristics and stress conditions indicate potential for ‘Moderate’ to ‘Major’ brittle/spalling damage of massive rock, it is necessary to evaluate the dynamic capacity of the ground support system. These steps may be performed in the fourth design iteration 60. The calculated values presented by or in the bursting support design tool or tab 34 provide an empirical estimate of the ejection energy due to bulking associated with a potential strain burst in massive, brittle rock.
The estimated ejection energy is compared to the total absorption capacity of the support system to give a relative indication of dynamic suitability of the system. If significant disparity is indicated between the available dynamic capacity and the estimated ejection energy, the ground support system should be modified. The support system must be able to displace in order to contain the rapid onset of bulking. If the support system is too stiff, it will be overloaded and fail. Stiff support will suppress the bulking process, but offers little displacement capacity required for dissipating the energy associated with a dynamic event. Some guidance with regard to appropriate support systems for typical dynamic loadings is provided within the bursting support design module or tool 34.
In these evaluations of dynamic suitability it is also important to consider the respective risk associated with the underground excavation(s) under consideration. For instance, the risk to miners and equipment from a strain-burst in a drainage drift is low. Accordingly, it would not be practical to design a ground support system with high energy absorption capacity despite the damage rating estimated by the bursting support design module or tool 34.
It is also possible that a reasonable ground support system cannot be designed to address the dynamic support requirements for the given excavation, geotechnical, and stress conditions. Where this is the case, changes to excavation shape, size, and/or orientation may be necessary, as indicated by design path 23. Specialized excavation methods such as de-stress blasting may also need to be considered.
If the ground type estimation and results of the depth of failure module 32 indicate potential for squeezing rock mass failure it will be necessary to check that the design ground support system is capable of maintaining adequate support capacity at large strains. These steps may be performed in design iteration 62. This factor is most readily assessed by reviewing the displacement capacity check in the ground support system schematic module 28.
Similar to the case of dynamic, brittle/spalling type failure mechanism, it is possible that no combination of support elements will match the predicted underground excavation deformations. In these cases, it may be necessary to consider changes to underground excavation shape, size, and/or orientation, as indicated by design path 25. Alternatively, damage caused by squeezing conditions can also be managed by periodic support system rehabilitation. However, the intended underground excavation use and service life need to be considered when determining if periodic rehabilitation is a reasonable approach to managing large ground displacements.
The ground support design tool 10 may also be provided with an intersection design module 36 that will provide for the rapid evaluation of requirements for secondary support in 3-way and 4-way intersections. These analyses tools are included in respective intersection design (3-way) and intersection design (4-way) modules 38 and 40.
The input values and calculations in these modules estimate the number of secondary tendons needed in order to meet a specified factor of safety. It is assumed in this assessment that the surface elements assist in distributing the load to the tendons installed. The surface support does not significantly add to the integrated support system, and therefore may be ignored in the calculation. The calculation assumes that a zone of loosening/failure develops in the form of a parabola, which can be described by the following equation:
where:
Design iterations are conducted by varying the underground excavation and chamfer dimensions slightly until a reasonable distribution of tendons is indicated by the example layout, the calculated spacing is between 1.4 and 2 meters, and the actual factor of safety meets or exceeds the designated design factor of safety.
The tendon lengths have been determined based on the following definitions:
Tendon lengths have been extended by 2 meters past the anticipated depth of loosening to ensure there is sufficient bonded length to engage the full capacity of the support elements. As an example, an 8 meter span in good ground would require a tendon length of 4.6 meters. This can be rounded to 5 meters for operational ease of design and installation.
It is assumed in the calculations that the secondary support system works in combination with the surface support elements (mesh, shotcrete, etc.) in holding the mass of material in place. It is also assumed that the surface support elements do not significantly contribute to the overall capacity of the support system, but connect the various elements of the secondary bolting system so that loads are effectively distributed.
In the example, an additional row of secondary support may be installed just outside the measured span in each of the drifts that make up the intersection. This will ensure that the intersections do not become unstable due to ground movement in the near vicinity of the intersection. The spacing of the additional tendon should be the same as the those installed within the intersection span. A minimum of two (2) tendons must be installed in each of the adjoining drifts.
Having herein set forth preferred embodiments of the present invention, it is anticipated that suitable modifications can be made thereto which will nonetheless remain within the scope of the invention. The invention shall therefore only be construed in accordance with the following claims:
This application claims the benefit of U.S. Provisional Patent Application No. 62/233,719, filed on Sep. 28, 2015, which is hereby incorporated herein by reference for all that it discloses.
| Number | Date | Country | |
|---|---|---|---|
| 62233719 | Sep 2015 | US |
