Numerical simulations of water flow and contaminants transport near mining wastes disposed in a fractured rock mass

A numerical tool, called Hydro-Geosphere, was used to simulate unsaturated water flow and contaminants migration around an open pit filled with mining wastes. Numerical simulations had been carried out to assess the influence of various factors on water flow and solute transport in and around the surface openings including recharge, properties of the waste material and presence of fractures in the surrounding rock mass. The effect of the regional hydraulic gradient was also investigated. The analyses were conducted by simulating various 2D cases using experimentally obtained material properties and controlled boundary conditions. The effects of the hydrogeological properties of the filling material(i.e., water retention curve and hydraulic conductivity function), fracture network characteristics and conductivity of the joints were assessed. The results illustrate that fractures control water flow and contaminants transport around the waste disposal area. A fracture network can desaturate the system and improve the regional gradient effect.

Numerical investigation of the stresses in backfilled stopes overlying a sill mat

Backfill is commonly used in underground mines to help increase the ore recovery rate and reduce the ore dilution. The use of a part of mine waste as underground backfill material also helps reduce the environmental impact of mining operations. After all, backfill is used to provide a working platform or safer working space. Its primary and most important role is to improve the rock mass stability around mine openings. However, most available solutions to stress analyses were developed for an isolated stope, without taking into account the influence of mine depth, or of adjacent stopes. In this paper,results from a numerical study carried out to evaluate the stresses in backfilled stopes overlying a sill mat are presented. Mine depth and excavation of the underlying stope below the sill mat(horizontal pillar)are both taken into consideration. The influence of stope geometry, backfill, sill mat and rock properties on the stresses is also evaluated. Compared with the case of a single isolated backfilled stope, the numerical results show that the stress magnitudes in the overlying backfill are considerably increased due to the excavation of the underlying stope. In general, the stresses also increase with mine depth and backfill stiffness, while these tend to decrease with an increase in the surrounding rock mass stiffness.These results suggest that existing solutions for backfill design may need to be revised.

A new concept of backfll design—Application of wick drains in backflled stopes

Backflling represents an environmentally friendly mining waste disposal technique.It is increasingly used in underground mines all over the world.However,its primary purpose remains to improve ground stability and to reduce ore dilution.Previous investigations have shown that fll drainage plays a key role in backfll and barricade design.With a poor drainage system in the backflled stope,the required dimension of barricade,which is constructed at the base of the stope near the drift entrance,has to be increased.A poor backfll drainage system can also lead to a signifcant increase in drainage waiting time and further reduction in mining productivity.In this paper,the drainage of conventional backfll design in backflled stopes is briefly reviewed.For the frst time,the application of the wick drain is introduced in the backfll within mine stopes.The drainage improvement from the introduction of the wick drain is illustrated using numerical modeling.

Experimental study of the shrinkage behavior of cemented paste backfill

Cemented paste backfill(CPB)is largely used in underground mine stopes worldwide.When a CPB is placed in a stope,an important task is to estimate the settlement associated with the shrinkage and selfweight consolidation of the CPB.This is closely related to the volume management to ensure the stability of barricades and tight contacts between the backfill and stope roof.Over the years,shrinkage studies were mostly performed on fine-grained soils(silts and clays),with only a few publications on the shrinkage behavior of uncemented tailings.No study has been published on the shrinkage behavior of CPB.To fill this gap,a series of shrinkage tests has been conducted on CPB with different cement contents,including zero cement content(uncemented paste backfill,uCPB).The results show that the shrinkage response of CPB is very different from that of uCPB.At a given initial water content,CPB exhibits a shorter normal shrinkage stage than uCPB.The unsaturation onset water content and void ratio,shrinkage limit and final void ratio of CPB are generally higher than those of uCPB.At a given cement content,the shrinkage behaviors of CPB and uCPB are significantly influenced by the initial water content.