Increasing stability of underground mine workings by forming new geotechnical properties of adjoining layers via roller compaction

The authors express their gratitude to the staff of the Department of Computer Material Engineering of Superhard Composite Materials at V. Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine for providing test instrumentation system.


INTRODUCTION
Seal polydisperse system is the main process for a variety of industries.In particular, the production of building materials and construction quality of seal mixtures identifies the main technical and operational performance of a product (Hopkinson, Myatt & Tajbakhsh, 2004).
Despite the existence of different ways of concrete mixtures sealing, the most effective are the methods of densification which makes it possible to create in a sealed environment a strained condition resulting from normal and shear stresses.One of the ways that implements the given principle is a method of roller compaction.This method proved itself in the construction of monolithic structures, in particular, hydraulic structures (Berga, 2003), roads (Vahedifard, Nili & Meehan, 2010).
The current stage of tunnel construction development is characterized by using a combination of multiple mounting with monolithic and prefabricated elements (Miura, 2003;Ramoni & Anagnostou, 2010).Roller compaction of monolithic structures can be used for creating of monolithic refinement layers (Zenunović & Folić, 2012; (Zinchuk, Mullarney & Hancock, 2004)).The new technology requires to study the process of sealing the tunnel by roller compaction method because of stresses occurring in the environment, which are linked by the way of interacting with roller working body.
The most approximate theoretical and experimental research into the process of roller compaction is described in the works devoted to the interaction of the wheel with the ground (Hambleton & Drescher, 2008;Chiroux, Foster, Johanson, Shoop & Raper, 2005;Hambleton & Drescher, 2008).
In these studies, the process is modeled by a rigid cylinder interacting with a semispace under the known value of power agitation or quantity of rainfall, where the material properties are represented by constant coefficients of models (Mohr-Coulomb, Drucker-Prager, Jung).

SIMULATION METHODOLOGY
During processing of adjoining layers by a roller, for the case of circular outline of tunnel construction, upon the completion of the process of adjacent circuit geotechnical properties formation, soil rock massive will be divided into layers in the form of concentric circles (Fig. 1).

RESULTS AND DISCUSSION
Sizes (radiuses) of adjacent contour layers of soil massive, in which there are various types of deformations: -slow deformation zone: -developed plastic deformation zone: (2) -elastic deformation zone: where: т R -radius of the tunnel; ( ) and max ІІІ h -maximum height of slow developed plastic deformation zone.
As a result of dissipating and attenuation of force impact of the working body, the density will gradually change along the depth of the soil layer.The highest density can be expected in the slow deformation zone, the lowest -on the boundary of the developed plastic and elastic deformation zones in the case when soil mass will be holistic.In the case of mass destruction to a depth greater than the total height of the developed plastic and elastic deformation zones, minimum value of density will be in elastic deformation zone.
Under the impact of the roller working body on the processed soil mass, environment, depending on the values of the resulting surface deformation, shows its elastic and plastic properties.Start of working body interaction (zone I, arc AB , I ϕ ) (Fig. 2) is accompanied by elastic and plastic mass deformations that match the phase of compaction and displacement (seals phase and local displacements) (zone I).A further effect of the working body leads to the formation of advanced plastic flow phase (phase of significant displacements) between the formed seal core (zone II) and sealing area that is formed by the core (zone III).

Figure 2. Scheme of rock mass processing by the roller: I -sealing zone of the working body; II -compaction core zone; III -compaction core zone of compaction
Soil and rock mechanics focusing on the compression zones formation was studied by K. Tsymerman, Jh.Ratie, Zh.Biarez and V. Kurdyumov.The basis of this research is the hypothesis of constant orientation of the displaced platform relative to indenter surface.In addition, it allowed to determine the height change of the slow deformation zone, the maximum height occuring at point E , where slip surfaces overlap: where: τ ϕ -angle of soil internal friction; R -working body radius; ϕ -angle of the load zone arc AEC ; γ -neutral angle.
It should be noted that the planes of displacement during soil compaction are spatially located.It will lead to lateral expansion with the formation of the core additional surface, which is oriented at an angle 2 4 τ ϕ π + to the generatrix contacting surface of the working body.Сompaction core shape under these conditions is shown in Figure 3.The described compaction process can take place only in the condition of the required amount of soil mixture determined by angle of capture φ (arc AC ).If the amount of soil exposed to the working body impact decreases, the formed compaction core is reduced and takes the shape of a rotation body with radius r and height h (Johnson, 1985): ( ) Distribution of compacted soil height across the contact area ( ) , for the case of inadequate amount of soil mixture , is shown in Figure 4. Obtained distributions of compaction core height allow to determine the sealing contact pressures, using the equations of soil mixture volume element equilibrium, derived from T. Karman's equation (Alexander, 1972).The equations for the conditions of geotechnical properties formation of underground mine marginal layer take the following forms: -advance zone (arc AE ): ( ) -lag zone (arc ED ): ( ) where ( ) Solution to differential equation of normal pressure distribution along the contact arc x ϕ by Euler numerical method with predictor-corrector is shown in Figure 5 as the pressure distribution surface in the contact zone for the composition of soil mixture with humidity: MPa.The resulting distribution of normal contact pressures has convex nature which is typical for interaction of hard indenter with plastic environment, with maximum values in the zone of tangential pressures changes.The values of obtained maximum stresses (1.6 -2.21 MPa) are sufficient for compaction of soils forming adjacent contour of transportation, hydraulic and collector tunnels of cities.
To test the proposed dependences of normal and tangential pressures distributions in the models of contact interaction of compaction environments with working bodies, the calculated and experimentally determined force impacts were compared.Figures 6 and 7 show the formation process and a typical graph presenting forces, arising during the impact on soil mixture which were determined by a device for measuring and recording the working body actions.
The graph shows gradual increase in measured parameters during soil mixture compaction at each pass.It confirms the importance of taking into account the distribution of strength and deformation characteristics along the contact zone.In all graphs, normal force N is 1.5 -2 times higher than the tangent force x Q , which corre- sponds to improved compacting conditions when pressing of the working body occurs due to displacement.The axial force y Q during roller compaction is virtually absent.The reason for the relatively low value of axial force, which equals about 4% of the normal, is formation of the lateral expansion zone at the final stage, while tangential pressures that shape the axial force are directed opposite to the direction of the working body axial movement.Thus, the resultant axial force of the lateral pressure zone balances the axial force of friction that occurs in advance and lag zones.
In measuring the force of working bodies impact on soil mixture, the data was partly obtained at the end of forming process without feeding mixture to the compaction zone.This was accompanied by the decrease in the contact zone, complete restoration of the deformable layer height and sharp reduction of force -up to 10% of the maximum value.It confirms the hypothesis about the plastic nature of deformation during roller compaction.
The components of force impact determined experimentally and on the basis of theoretically derived stress distribution diagrams for compacted soil mixture of different compositions and deformation velocities, are shown in Table 1 (component y Q was not theoretically determined).Comparison of the experimental and theoretical values of force impact components on soil mixture confirms theoretical conclusions.The difference between the results ranges from 9 to 14%.

CONCLUSION
Comparison of experimentally determined force impact components on the processed environment with theoretically established normal and contact pressures distributions allows to confirm suitability of the proposed models for describing the contact interaction of roller working bodies with soil mixture.It also allows to use these data to develop a method for engineering calculation of principal parameters of geotechnical properties formation on the basis of the proposed approach.

Figure 4 .
Figure 4. Compaction core form for the case of insufficient amount of soil mixture

Figure 5 .Figure 6 .
Figure 5. Distribution of normal pressures on the contact surface

Figure 7 .
Figure 7. Changing components of force -normal N, tangent Q x and axial Q у during compaction of the soil layer (▬▬ N; ▬▬ Q x ; ▬▬ Q у )