Triaxial tests are conducted to determine the relationship between confinement and axial compressive strength. Depending on the confining stress applied to a core specimen, the failure process changes depending on the rock type’s internal composition (i.e. porosity, flaws, stiffness heterogeneity, grain shape, etc.). These failure process changes are not typically considered when planning a triaxial testing program or when processing triaxial test data. This paper summarises the changes in failure process that occur depending on the confining stress level for various rock types and outlines a procedure for processing triaxial data depending on the confining stress level for the determination of the Hoek-Brown strength envelop parameter mi and confidence intervals. For this, a triaxial and uniaxial dataset from Bingham Canyon is presented for a quartzite. The dataset is exceptionally complete in terms of the number of tests conducted (total of 217 uniaxial and triaxial tests) and the detail in test data quality and characterization of the specimens. The results show that triaxial data requires mi values outside (mi >50) the typically assumed range (mi ≤50). These high mi values appear to be needed to fit data at high confining stress levels (larger than about UCS/10). Based on the discussion in this paper; (1) the selection of confinement levels for testing purposes should include sufficient data in the confinement range of 0 to UCS/10 and UCS/10 to UCS/2; and (2) two sets of strength curves may need to be considered depending on the problem being assessed. One curve is valid for confinements of 0 to UCS/10 (representative of strengths near excavation boundaries) and the other for >UCS/10 to approximately the Mogi line (representative of strengths, for example, in wide pillars or mine abutments), after which a third envelop is needed. These changing envelop requirements are a result of changing failure mechanisms.
Recent developments in understanding brittle failure processes in hard brittle rocks (UCS>25MPa) has lead the authors to the realization that there are several deficiencies in how triaxial data is being treated to arrive at peak strength parameters. Furthermore, it is necessary to properly describe the uncertainty in test data. This paper aims at providing an understanding of how failure processes change as confinement increases, how this affects the failure envelop and thus how data should be interpreted to arrive at meaningful engineering parameters. Most importantly, as recently introduced by  it is necessary to differentiate strength envelops that are to be used for low confinement dominated problems (inner shell) and for those used to describe the behavior of rock at high confinement (outer shell).
The goals of this paper therefore are: (a) to review current practice for processing of triaxial data; (b) identify failure mechanisms that occur during loading at increasing confinement levels for different rock types and how they cause changes in the curvature of the strength envelop; and (c) provide suggested procedures for the formulation of triaxial data testing programs and the processing of triaxial testing results.
Nonlinear elastic wave propagation is related to the dependency of wave velocity on stress. In our studies, we investigated how the velocity depends on small amplitude stress oscillations. The oscillations aim to simulate a low frequency acoustic pulse used in a new two-frequency technique for measuring nonlinear elasticity. These controlled axial stress variations manipulate the elastic properties of rock, which are detected by the high frequency acoustic pulses. Here, the nonlinear propagation is examined for both P- and S-waves, which show the dependency of the wave propagation direction and polarization on the direction of applied stress. The sensitivity of the velocity gradient is investigated through given changes xternal stress and pore pressure. The impact of pore fluid type is tested on samples fully saturated with brine and kerosene, as well as dry samples. All our tests, preformed on Castlegate sandstone, indicate that the nonlinearity is mainly related to the rock structure and far less to the pore fluid. Moreover, it confirmed an idea of the micro- and macro-cracks as the primary source of nonlinear behavior of rock.
The tests presented in this paper concern an investigation of the still growing issue of the anonlinear elasticity of geomaterials. The interest in this phenomenon began several decades ago and has been investigated in numerous studies. Nowadays, literature provides a large number of experimental data that confirm a significant - compared to other materials - nonlinear elastic response of rocks . That places them in the mesoscopic class of the nonlinear materials, which are characterized by nonlinearity several orders of magnitude higher than that of materials belonging to the atomic elastic class like fluids and monocrystalline solids . This large difference in nonlinear elastic behavior is connected with its origin, and in case of rocks it is associated with the complexity and high heterogeneity of their structures. More precisely, the source of a nonlinearity in rock includes all compliant features present in a hard rock matrix. These soft features are the weakest parts of the rock'' structure, i.e. discontinuities such as pores, macro- and micro-fractures, joints, and grain-to-grain contacts. They determine rocks deformability and thus are the main, but not only, sources of nonlinearity. Another factor commonly quoted is saturation, where both the amount and type of pore fluid influence nonlinerity.
Nonlinear elastic response of rock is manifested in many different ways [3, 4] and revealed both in mechanical and acoustic experiments. The most common are : the nonlinear character of stress-strain curves, hysteresis (difference between stress-strain relation for loading and unloading paths), pulse distortion (generation of higher harmonics), side bands (appearance of new frequency), etc. That large number of nonlinear phenomena, as well as the high magnitude of nonlinearity, suggest that the nonlinear elasticity of rocks should not be neglected. Moreover, it should be treated as an attribute, since it brings additional information about the rock. Thus, many studies, including that discussed here, attempt to create a commercial method of rock testing based on the nonlinear elasticity alone, or on its combination with other methods. The most promising applications, particularly for the petroleum industry, are the detection of fractures  and determination of pore fluid content (saturation) .
The stress-strain relationship is essential for modeling coupled hydro-mechanical processes. This paper reviews our recent progresses in developing a general stress-strain relationship for elastic deformation in porous and fractured media. The relationship includes the following key elements. First, when applying Hooke’s law in natural rocks, true strain (rock volume change divided by the current rock volume), rather than engineering strain (rock volume change divided by unstressed rock volume), should be used, except when the degree of deformation is very small. Second, because of its inherent heterogeneity, rock can be divided into two parts, a hard part and a soft part, with the hard part subject to a relatively small degree of deformation compared with the soft part. The stress-strain relationship developed here allows for the derivation of constitutive relationships between stress and a number of mechanical/hydraulic properties. The remarkable consistency between these relationships and a variety of the corresponding empirical expressions and/or laboratory experimental data tends to support the validity of our theoretical development.
The stress-strain relationship is fundamental for modeling mechanical deformation and the associated coupled processes in porous and fractured rock. Hooke’s law has been generally used to describe this stress-strain relationship for elastic mechanical processes. Hooke’s law, an approximation for small deformations, states that the amount by which a material (e.g., rock) body is deformed (the strain) is linearly related to the force (stress) causing the deformation. Nevertheless, the current application of the Hooke’s law to porous and fractured rock is not without questions. Strictly speaking, the proportionality in the observed stressstrain relationship should be constant if the current application of Hooke’s law is perfectly valid. However, it is not unusual to see studies indicating that the proportionality is not always constant, but rather stressdependent in many cases [1,2]. A number of efforts have been made to relate this stress-dependent behavior to the microstructures of “cracks” in porous rock [3,4,5]. An excellent review of these efforts is provided in a chapter entitled Micromechanical Models in . Because it is generally difficult to characterize small-scale structures accurately and then relate their properties to large-scale mechanical properties that are of practical interest, it is desirable to have a macroscopic-scale theory that does not rely on the detailed description of small-scale structures, and that can physically incorporate the stressdependent behavior of relevant mechanical properties. This paper reviews our recent progress in developing a theory of this kind within the framework of Hooke’s law.
This paper is organized as follows. Section 2 describes the developed stress-strain relationship. Section 3 discusses its validation and applications. 2. THEORY
This section presents a new stress-strain relationship proposed in  for porous and fractured rock. For simplicity, we mainly consider the relationship here for the volumetric strain, although our results can be easily extended to other types of strains. Assume that a uniformly distributed force is imposed on the surface of a homogeneous and isotropic material body subject to elastic deformation.
Surface deformations generated as a result of oil production, waste or water reinjection can be applied to model reservoir deformations. This is referred to as inverse modeling. Inverse models presented in the literature are mostly based on the nucleus of strain approach, and apply one deformation data type (i.e., vertical displacements) as input. In this study, a new numerical model was developed based on the unidirectional deformation technique. In order to solve the inverse ill-posed problem, a regularization technique was developed. The main objective of this research was to study the effects of monitoring strategies on inverse simulation by applying combinations of surface deformation measurements as input. A detailed sensitivity analysis was therefore performed in order to optimize the data collection procedure. The sensitivity of the inverse simulation was examined based on the following parameters: observation area; geometry and number of benchmarks; and measurement error. The results indicated that adding benchmarks after a certain number did not significantly affect the simulation. The distribution pattern of benchmark points was also found to significantly affect the inverse simulation.
Ground surface deformations generated as a result of fluid/material injection or withdrawal, into or from the subsurface are easy to monitor and sensitive to subsurface pressure changes [1, 2, 3]. Induced surface deformation data can therefore be used to indirectly monitor subsurface deformations. This approach has considerable potential use in fast-paced projects, where continuous monitoring of reservoir deformation is vital: steam injection/steam-assisted gravity drainage, where the objective of screening is to monitor steam concentration zones in the subsurface; waste injection projects, in order to track and model induced deformations and fracture movements; general reservoir monitoring and optimization, where the objective is to monitor the behaviour of the reservoir with respect to production and reinjection processes. Applying surface deformation measurements in order to model subsurface deformation sources is referred to as solving for the inverse case. Direct and inverse models have been previously studied and reported on in the literature [4, 5, 6, 7, 8, 9, 10, 11, 12]. Previous studies on inverse modeling in the hydrocarbon industry are mostly based on the nucleus of strain approach , where subsurface deformation sources are simulated as point sources that expand or compact in all directions, representing expansion or compaction (e.g. [6, 10, 14, 15]). Most inverse simulations are developed based on one type of deformation data (i.e. vertical displacement measurements). Very few studies have focused on inverse simulation based on different combinations of surface displacement measurements (i.e., vertical displacements/tilt measurements) . It has been revealed that tilt measurements are more appropriate for inverse modeling compared to vertical displacements . The main focus of this paper was therefore, to numerically study the effect of the data collection procedure on reservoir inverse simulation, using combinations of surface tilt measurements.
Possibility of inducing shear fractures rather than tensile during and after the hydraulic fracturing operation is an important issue in stimulation of shale gas plays which could affect the fracturing pattern and in-situ stresses estimation. Therefore, the experimentally obtained geomechanical parameters are necessary for the shale material characterization and the numerical simulations of its stimulation processes. In this study, four double shear tests were conducted on the Montney’s samples to understand its behavior under different loading states and to measure its discontinuities strength parameters. During the experiments it was observed that samples sheared through the foliation planes as well as through the rock material. It showed that when the inclination of the discontinuity with respect to the normal stress approaches 90°, the sample would not necessarily shear along the discontinuity, but behaves like an intact material in which many factors such as stress conditions, discontinuity surface conditions, joints spacing, as well as the rock material by itself would play important roles in the final failure mode. From the results, the cohesion was found as 2 MPa and the peak friction angle was about 40°.
Shale gas is natural gas that is embedded in shale, a sedimentary rock that was originally deposited as clay and silt. Shale gas is one of a number of “unconventional” sources of natural gas, including coalbed methane tight sandstones, and methane hydrates. While the potential for Canadian shale gas production is still being evaluated, the principal Canadian shale gas plays are the Horn River Basin and Montney Shales in northeast British Columbia, the Colorado Group in Alberta and Saskatchewan, the Utica Shale in Quebec and the Horton Bluff Shale in New Brunswick and Nova Scotia. Located in a large area spanning the British Columbia and Alberta border, the Montney Formation is one of the largest economically feasible resource plays in North America (Fig. 1) . As new exploratory drilling continues to disclose the wide range of facies in the Montney, it adds to both the complexity and potential of this relatively distinctive formation in western Canada .
A tight gas reservoir is generally defined as any low permeability formation in which special well completion techniques, mostly hydraulic fracturing, are required to stimulate production. New technologies, such as multi-stage hydraulic fracturing, together with horizontal drilling, are making it easier and more reasonable to produce shale gas . Advances in logging and core evaluation techniques have improved our ability to understand the petrophysical characteristics of the complex reservoirs so far. Still, it is believed that with the addition of innovative technology based on the better understanding of geomechanical behavior of these reservoirs, the productive yield from application of hydraulic fracturing technique could be further enhanced. Predicting the geomechanical response of the shale gas material during hydraulic fracturing operation in the field needs better understanding of their geomechanical behavior under laboratory testing. Furthermore, understanding the geomechanical behavior helps optimize the planning and management of the hydraulic fracturing operation.
Possibility of inducing shear fractures rather than tensile during and after the hydraulic fracturing operation is an important issue which could affect the fracturing simulations and in-situ stresses estimation.
Akbari, B. (Memorial University of Newfoundland) | Butt, S.D. (Memorial University of Newfoundland) | Munaswamy, K. (Memorial University of Newfoundland) | Arvani, F. (Memorial University of Newfoundland)
A distinct element rock cutting model was implemented in which weight on bit and rotary speed could be simulated and the resultant penetration rate was recorded. Different scenarios of conventional rotary drilling and oscillatory changing weight on bit with constant rotary speed were investigated and the results showed that drilling penetration rate increases considerably by the addition of a superimposed oscillatory changing weight on bit in certain frequencies. Drill string vibration and instabilities resulting from cutter rock interaction was also investigated and some hazardous scenarios and possible causes were identified. The effect of bottom hole pressure on the rock surface was also simulated and the results showed that rate of penetration decreases proportional to the logarithm of bottom hole pressure and it also showed that by increasing the bottom hole pressure the positive effect of force oscillations on rate of penetration diminishes.
Cutter rock interaction is the primary area of study if prediction of drilling performance with respect to various parameters such as hydraulic system or hoisting system is the desired outcome.
There are; however, several drawbacks to such a study and those are relate to complications in rock failure models, contact models and coupling with hydraulic system and etc. These drawbacks have prevented development of a comprehensive model for rock bit interaction which is capable of predicting penetration rate and other drilling performance parameters with respect to various input parameters such as weight on bit, mud flow rate, bottomhole pressure and bit specifications.
The primary mechanism involved in rock cutting is chip formation which is a discontinuous process and involves formation of minor chips until a major chip forms. During the chip formation process horizontal and vertical forces acting on the cutter oscillate and reach to a maximum just before a major chip forms . This is a true conclusion in the sense that a fracture path in the rock in front of the cutter forms which produces the chip. And analytically they are similar to logarithmic spirals .
A nomenclature with respect to drag bit specifications is also suggested by Maurer , that introduces wedge angle as the cutter tooth angle and rake angle as the cutter tooth angle with the bit axis and several other parameters and related them to drilling performance and penetration mechanism.
Fairhurst and Lacabanne , proposed a simple mathematical model which relates the horizontal force applied to the rock as a function of torque on the bit and bit-rock friction coefficient and weight on bit and then relates these forces to the fracture path direction with respect to different cutter rake angles.
The works mentioned above and a few others [5-8], were the early attempts to study rock-bit interaction and mechanisms and rock failure modes. However, simplifying assumptions either in rock constitutive model and failure criteria and non-homogeneity and limitations in analytical solution methods made them unrealistic and not a comprehensive model for rock-bit interaction.
Zhen, Yang (Shool of Mines, China University Of Mining And Technology) | Chencheng, Huang (Shool of Mines, China University Of Mining And Technology) | Wang, Shugang (Department of Energy and Mineral Engineering, Penn State University)
Since several mine inundation on disasters happen in china andU.S. in the past, researchers have paid more and more attention to the In Seam Seismic (ISS) method which can be applied in detecting the uncertain boundaries in a coal seam. The uncertain boundaries are mapped by the reflected channel waves. Wave propagation has been studied for several decades, but is still remains very difficult to identify the reflected channel waves effectively in a coal seam due to the rock-coal-rock structure. SH wave plays an important role in the rock-coal-rock structure, so this paper focuses on modeling SH wave propagationin a rock-coal-rock structure with a Gaussian pulse as an explosion source. Our results show that the SH wave will be excited in different modes in a coal seam due to different positions of a seismic source and different angles of truncation, which is the key to map the uncertain boundaries to avoid disasters such as Quecreek and Wangjialing coal mine accidents. Finally, the rock-coal-rock is a natural filter for SH waves in a coal seam in practice, so it is still important to select the right filter before mapping uncertain boundaries based on the ISS technique.
Uncertain abandoned voids, old workings gobs, and faults are potential threats to live of coal miners and can also increase the cost of underground mining. Nine miners were trapped over 3 days in a mining accident after the continuous mining section cut into an abandoned mine accidently at the Quecreek Mine, Pennsylvania, in the United States, on July 24, 2002 . In china, 152 miners were trapped in the underground due to the water flooded into working area accidently, and 38 miners lost their lives in this mining accident on March 28, 2010 . If gas and water accumulations can be detected ahead of mining, the risk of mining can be reduced. Many different techniques have been developed to address such problems, but most havelimited usefulness or high cost. Drilling is the main exploratory method used ahead of working faces. It directly detects prospective coal area, but the information provided by sampling drilling may be incomplete or inaccurate. The technique of indentifying the differences of velocity and attenuation of seismic wave between the coal and the surrounding rocks has been used for coal exploration .Another method is to use transmitted waves between boreholes to determine void and discontinuities . Surface reflection is not a cost-effective and accurate method for detecting voids . Thus, the most effective method to locate the void in a coal seam may be the Seam Seismic Method.Wave propagation in a coal seam has been an interesting problem since last decade, because it is very difficult to identify the reflected channel waves . Since several mine inundated disasters happen in U.S. and China, researchers have paid more and more attention to ISS to explore how to detect the uncertain boundary in coal seam. The key of ISS is that the uncertain boundary is mapped by the reflected channels waves.
We have developed a complete seismoelectric theory based on the upscaling the Nernst-Planck and Stokes equations in water-saturated porous media. The coupling between the poroelastic deformation of the porous material (described by Biot''s theory) and the low-frequency limit of the Maxwell equation is electrokinetic in nature (due to the relative displacement between a charged mineral and the pore water). The total electrical current density is equal to a conduction term described by Ohm''s law and a source current density associated with the drag of the excess of electrical charge contained in the pore water by the relative velocity between the fluid and solid phases. This excess of electrical charges is due to the presence of the electrical double layer at the interface between the solid phase and the water phase. The complete set of equations is solved with the finite element code Comsol Multiphysics 3.5 in 2D. We consider then a seismic source described by a moment tensor and we compute the electromagnetic disturbances generated by the seismic source. Three types of signals are generated: (i) a signal directly generated by the source. This signal can be described by a multipole expansion and the resulting electrical field decreases therefore as a powerlaw function of the distance. (ii) seismoelectric conversions are generated at heterogenities of the electrical properties. (iii) Finally, co-seismic signals are generated and they propagate at the same speed as the P and S-waves. We will present synthetic seismograms and associated synthetic electrograms and magnetograms. We will discuss the possibility of a joint inversion of the seismic and electromagnetic information to locate the seismic source and to determine its moment tensor. Applications will be discuss about hydrofracturing in oil and gas reservoirs, geothermal systems, and to the monitoring of active volcanoes.
Observations of electric signals in relation with seismic wave propagation have been reported by many authors in the last decade [1-6]. Of most interest are the two seismoelectromagnetic phenomena described in  and [8-9]. The first one, called the direct field, is associated directly with the hydromechanical source. The second interesting effect corresponds to the electromagnetic interface response (also called the seismoelectric conversion) occurring when a compressional wave or a shear wave crosses an interface characterized by a drop in the mechanical or electrical properties. These two effects are created by the relative displacement between the charged solids phase and the pore water. Such a mechanism is one of the so-called electrokinetic effects in petrophysics. Electrokinetic effects are fundamentally related to the existence of the electrical double alyer at the pore water mineral interface. If the material deforms, this surface charge is fixed in a Lagrangian framework attached to the solid phase. This charge is shielded partly by the sorption of counterions in the Stern layer coating the surface of the minerals [10, 11]. Global electroneutrality at the scale of a representative elementary volume requires an excess of electrical charges located in the vicinity of the mineral/water interface, in the so-called electrical diffuse layer [12,13].
Jabbari, Hadi (Department of Geology and Geological Engineering, University of North Dakota) | Zeng, Zhengwen (Department of Geology and Geological Engineering, University of North Dakota) | Ostadhassan, Mehdi (Department of Geology and Geological Engineering, University of North Dakota)
In France, an underground research laboratory is constructed in a clay formation, called Callovo-Oxfordien argillites. In order to evaluate quantitatively the structure durability, it is necessary to achieve a good understanding of the long-term behavior of the material. Subcritical crack growth is one of main causes of time-dependent behavior in rock. In order to rigorous modeling of the time-dependent behavior of studied material, a micromechanical model incorporated subcritical damage propagation is proposed for Callovo-Oxfordien argillites in this paper. In the proposed constitutive model, the argillite is considered as a two phase composite: the Callovo–Oxfordian argillite matrix and the mineral inclusion (calcite and quartz grains). Based on experimental observations, the clay matrix is described by a coupled viscoplastic subcritical damage model and the mineral inclusions are described by a linear elastic model. The passage form the micro-scale to the macro-scale is done through a Hill type incremental homogenization method.
In the field of fracture mechanics, crack growth appears when the stress intensity factor reaches the fracture strength of the material. However, slow crack growth also arises when the stress intensity factor is less than the facture strength. This phenomenon is called subcritical crack growth.. For rocks, there are many reports which indicate that water is the corrosive agent. For example, Waza and al.  reported that the crack velocity in water-saturated rock was two to three orders of magnitude greater than the crack velocity in dry rock. Meredith and Atkinson  investigated the effect of water on subcritical crack growth in basic rocks and showed that the crack velocities under water environments were much higher than those under atmospheric. Subcritical crack growth is one of main causes of time-dependent behavior in rock . For this reason, count in the subcritical crack growth in the constitutive model of the rock is important for predict the long-term mechanical behavior of rock structures. T. Jiang. and al.  proposed to consider the argillite as a two phase composite: the clay matrix and the mineral inclusion (calcite and quartz grains). It has been observed on creep tests the dependency of time of argillite mainly due to the viscous behavior of the clay matrix. From the above, at present, the clay matrix is described by a coupled viscoplastic damage model and the mineral inclusions are described by a linear elastic model.
2. PROCEDURE OF THE HOMOGENIZATION FOR THE CALLOVO-OXFORDIAN ARGILLITE
2.1. Introduction of the Hill’s incremental method
In order to carry out the homogenization for nonlinear composite material, Hill proposed an incremental approach in 1965.
4. NUMERICAL SIMULATION OF EXPERIMENTATION
The objective of this section is to evaluate the correspondence between the simulation from this micromechanical model and the experimental data.
4.2 Triaxial creep test
For the simulation of time-dependent responses, we have used the values shown in Table 2. We can see that there is generally a good agreement between experimental data and our model’s prediction (Fig 2-3), the proposed model is able to correctly reproduce creep deformation.
Cemented Paste Backfill is gaining popularity as a method for filling underground mine stopes. However, the behavior of the paste is not well understood. This paper proposes a modeling method which represents the paste as a series of sequential layers. Layer size is controlled by the rise rate of the backfill in the stope. The time-dependent behavior of the fill is implemented as each layer can be aged and assigned the age appropriate material properties. These properties were obtained by a laboratory testing program summarized in the paper. The paper presents a brief validation exercise as well as a comparison between the model and in-situ instrumentation results.
Cemented paste backfill (CPB) is a popular backfilling method for underground mining operations due to its delivery speed and versatility, engineered strength, and for decreasing the area needed for and the amount of risk associated with surface disposal. However not much is known about how the CPB behaves in an underground opening, particularly during the early curing ages of the CPB. This lack of understanding poses several problems for mining engineers including how to design backfill barricades and backfilling procedures. For instance, most mines use a two staged pour which is divided into a plug pour and a final pour. There is a delay in-between the two pours, usually 3 to 7 days, to allow the paste in the plug to harden and gain strength. This delay and subsequent paste strengthening is used to protect the backfill barricade when the rest of the stope is filled. There is a large potential for a mine to save money if they can reduce their stope cycle times or move to a continuous pour procedure. Increased understanding of CPB behaviour would also decrease the uncertainty associated with the barricade fences themselves, allowing for better and cheaper fence designs. However, these cost savings cannot be realized unless a there is a reasonable and reliable method for determining what stresses the backfill barricade will experience. These stresses are dictated by a range of parameters including: binder content, binder type, tailings type, additional aggregates, filling rate, stope geometry, etc.
Numerical and analytical models have provided a starting point for investigating in-situ pressures within the stope and at the backfill barricade. However, there is a lack of in-situ stress measurements to test the validity of these models. The University of Toronto has established a large field project which involves the instrumentation of several test stopes at three mine sites: Barrick Gold Corporation’s Williams Mine, Inmet Mining Corporation’s Cayeli Bakir Mine, and Xstrata Copper Canada’s Kidd Mine. This paper presents a numerical modelling exercise of the 2010 test stope at the Williams Mine (Thompson et al, 2010).
The modelling was conducted using Itasca’s Flac3D modelling software and attempts to incorporate the stope filling rate , the time-dependent strength behaviour of the paste, and the actual 3D stope geometry. The model tries to match the actual filling strategy used to fill the stope and compares these results with the readings from the in-situ instrumentation.