Design Of Barricades Research Articles

An update of the 3D analytical solution for the design of barricades made of waste rocks

Stope backfilling is increasingly used in underground mines. Barricades are necessary to retain slurried backfill poured in mine stopes . In Canada, waste rock barricades (WRB) have been becoming more and more popular to retain paste backfill in stopes. A few solutions have been developed to size the WRB. Among them, a solution developed by Yang and coworkers in 2017 is particularly relevant. However, this solution was calibrated and validated by 2D numerical modeling . Its validity in 3D conditions remains unknown. In addition, the local stability analysis was made by considering a horizontal sliding plane while their numerical modeling clearly showed an inclined plane. In this study, the validity of the Yang et al. solution is first evaluated against a few numerical results obtained with FLAC3D. The subjectivity in evaluating the instability onset of a structure in numerical modeling is further reduced by considering the first occurrence between displacement jump and coalescence of current yield zones passing through a WRB structure from the downstream to upstream slopes. The results show that both the global and local stability analysis equations of the Yang et al. solution need to be updated. For the global stability analysis, the value of the earth pressure coefficient needs to be modified while an inclined sliding plane needs to be considered for the local stability analysis. These considerations result in a considerable improvement because the updated solution does not contain any empirical calibration coefficient. Good agreements are obtained between the results obtained with numerical simulations and those predicted by the updated 3D analytical solution. The proposed solution is then further validated by an experimental result recently available in the literature. It can be used to design WRB to retain fluid-like paste backfill at the preliminary stage of a project.

Experimental study of the evolution of pore water pressure and total stresses during and after the deposition of slurried backfill

Mining backfill is increasingly used in underground mines to fill stopes. Its successful application depends on the stability of barricades built to retain the backfill in stopes. The design of barricades requires a good estimation of pore water pressure (PWP) and total stresses during and after the deposition. On this regard, a large number of works have been published on analytical and numerical solutions. There are however very few experimental results with simultaneous measurements of PWP as well as horizontal and vertical total stresses that can be used to validate or calibrate the analytical and numerical solutions. For a specific project, field measurements are interesting in terms of representativeness to field conditions, but the results are very difficult to be correctly interpreted because the treated problem can involve a large number of uncertainties and the obtained results are due to combined effects of several influencing factors. Laboratory tests with simplified and well-controlled conditions are thus preferred. Until now, however, the most previous laboratory tests were conducted with dry backfill or with a tailings slurry instantaneously poured in a confining structure without simultaneous measurements of PWP as well as horizontal and vertical total stresses. Studies on the effects of filling rate and solid content of backfill on the variation of PWP and total stresses during the filling operation are absent. To fill these gaps, a series of column backfilling tests were conducted with simultaneous measurements of PWP as well as vertical and horizontal total stresses during and after the deposition of slurried backfill. When the filling rate is high, the test results showed that the PWP, horizontal and vertical total stresses increase at the same rate and equal to the iso-geostatic overburden pressure during the deposition of backfill slurry. Their peak values appear at the end of deposition. The backfill thus behaves like a liquid with little generation of effective stresses during the deposition. High filling rate and/or high solid content lead to high PWP and horizontal total stresses at the end of deposition. When the filling rate is small, the PWP and total stresses exhibit also peak values at the end of filling operation, but the vertical total stress at the center can continue increasing with time after the end of deposition due to the suspended sensor and occurrence of a phenomenon known as stress shielding effect. The results also showed that the settlement of settled backfill after the end of slurry deposition can generally exhibits a fast evolution rate stage, followed by a slow evolution rate stage. The duration of the fast evolution rate stage and the final settlement of the settled backfill increase as the solid content decreases. The final settlement after the end of slurry deposition is related to the solid content, not to the filling rate.

Experimental study of the “short-term” pressures of uncemented paste backfill with different solid contents for barricade design

The successful application of paste backfill in underground mines depends on the stability of a confinement structure, called barricades, constructed at the base of stopes to hold the backfill slurry in the stopes. The stability analysis of barricades needs the knowledge of the pressures during or shortly after the placement of the paste backfill exerted on the barricades. The recommendation of slight construction of barricades for paste backfill given in the few handbooks on paste backfill implicitly indicates that the paste backfill pressure is very small. This does not correspond to the field pressure measurements reported in the literature, which indicated that the pressures of paste backfill during and shortly after the placement can be as high as the iso-geostatic overburden pressure. To understand this dilemma, the difference between the paste backfill defined in the handbooks and that used in underground mines is for the first time highlighted. The former requires a high enough solid content and the backfill should be unsaturated. In practice, enough water has to be added in the backfill to facilitate its transportation by pipes. The solid content cannot be as high as that required in the handbooks. The dilemma between the recommendation of handbooks and field pressure measurement is for the first time solved. However, this analysis tends to indicate that the pressure of paste backfill depends on the solid content. To verify this hypothesis, a series of laboratory tests were conducted to measure the vertical total stresses of paste backfill having different solid contents at the end of filling operation. The results show that the vertical total stresses decrease as the solid content increases. The solid content should be taken into account in the pressure estimation of paste backfill for the design of barricades.

A solution to estimate the total and effective stresses in backfilled stopes with an impervious base during the filling operation of cohesionless backfill

SummaryMining backfill is commonly used in underground mines. A critical concern of this practice is to evaluate the pressures and total stresses in backfilled stopes to ensure a safe and economic design of barricades, constructed to retain the backfill. When a slurried backfill is placed in a mine stope, excess pore water pressure (PWP) can instantaneously generate and progressively dissipate. The dissipation of the excess PWP and consolidation lead to the development of effective stresses, which in turn lead to an arching effect in the backfilled stope. Until now, arching effect has been largely considered for stress estimation in dry or submerged backfill. The former corresponds to the final state at the end process of the drainage and consolidation of the backfill with a pervious while the latter with an impervious barricade. However, previous studies have shown that the most critical moment for the stability of barricades is during the stope filling. Therefore, the design of barricades requires a proper estimation of the pressure and total stresses during the filling operation. This in turn needs joint consideration of the arching effect and consolidation of the backfill. In this paper, a new solution is developed to evaluate the pressures and stresses in backfilled stopes during the filling operation of cohesionless backfill by considering the self‐weight consolidation and arching effect. The proposed solution is validated by numerical modeling with Plaxis2D. It can thus be used to evaluate the pressures and stresses in backfilled stopes during the stope filling with an impervious barricade.

Total and Effective Stresses in Backfilled Stopes during the Fill Placement on a Pervious Base for Barricade Design

Backfill is increasingly used in underground mines worldwide. Its successful application depends on the stability of the barricades built at the base of the stopes to hold the backfill in place, which in turn depends on the knowledge of the pore water pressure (PWP) and stresses during, or shortly after, the placement of the slurried backfill. Until now, self-weight consolidation is usually considered for the estimation of the PWP. There is no solution available to evaluate the total and effective stresses during, and shortly after, the filling operation. As excess PWP can simultaneously be generated (increased) and dissipated (decreased) during the backfilling operation, effective stresses can develop when the filling rate is low and/or hydraulic conductivity of the backfill is high. The arching effect has to be considered to evaluate the effective and total stresses in the backfilled stopes. In this paper, a pseudo-analytical solution is proposed to evaluate the effective and total stresses in backfilled stopes during the backfill deposition on a permeable base, by considering the self-weight consolidation and arching effect. The proposed solution is validated by numerical results obtained by Plaxis2D. A few sample applications of the proposed solution are shown.

Effect of Drainage and Consolidation on the Pore Water Pressures and Total Stresses within Backfilled Stopes and on Barricades

The pore water pressures (PWPs) and total stresses during the placement of a slurried backfill in underground mine stopes are the key parameters for the design of barricades, built to retain the backfill in the stopes. They can be affected by the drainage and consolidation of the backfill. Over the years, several studies have been reported on the pressure and stresses in backfilled stopes by accounting for the drainage and consolidation. Most of them focused on the pressure and stresses in the stopes, few specifically on the barricades. The effect of the number of draining holes commonly installed through the barricade has never been studied. In this paper, the influence of hydraulic properties and filling rate of the backfill, stope size, barricade location, and number of draining holes is systematically investigated with numerical simulations. The results show that the stresses in the backfilled stope and on the barricade largely depend on the filling rate, hydraulic conductivity, and Young’s modulus of the backfill. The draining holes can significantly decrease the PWP, but only slightly the total stresses on the barricades in short term.

A new concept of backfill design—Application of wick drains in backfilled stopes

Backfilling 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 fill drainage plays a key role in backfill and barricade design. With a poor drainage system in the backfilled 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 backfill drainage system can also lead to a significant increase in drainage waiting time and further reduction in mining productivity. In this paper, the drainage of conventional backfill design in backfilled stopes is briefly reviewed. For the first time, the application of the wick drain is introduced in the backfill within mine stopes. The drainage improvement from the introduction of the wick drain is illustrated using numerical modeling.

Mechanical Behaviour of the Interface Between Cemented Tailings Backfill and Retaining Structures Under Shear Loads

Understanding the shear behaviour of the interface between cemented tailings backfill and retaining wall structures (barricades, bulkheads) is important for the optimal design of barricades or bulkheads, and for mine operators to balance strength and safety against cost. However, our understanding of the shear behaviour of the aforementioned interface is limited. This paper is aimed at investigating the interfacial behaviour and properties of cemented tailings backfill-retaining wall structures, including stress–strain behaviour, cohesion, friction angle and shear stiffness through direct shear tests. Two different types of barricade or bulkhead materials (brick and concrete) are used in this study. Interface shear tests are performed at various curing times of the cemented backfill. Valuable results are obtained with regards to the interface shear behaviour of backfill-retaining structures. Based on these results, interfacial properties between cemented tailings backfill and barricades or bulkheads show a significant time-dependent variation.

Horizontal pressure on barricades for backfilled stopes. Part II: Submerged conditions

This paper presents a method to calculate the pressure generated by submerged backfill on barricades (or bulkheads) located in drifts at the base of mine stopes. The paper complements Part I (see companion paper, this isue), which presents an analytical solution for the pressure on barricades when the backfill is in drained conditions (after the pore-water pressure has dissipated). The solution presented here applies shortly after backfill deposition, for undrained conditions. In this case, the effect of pore pressure cannot be neglected as it may be critical for the response of barricades. The solution is developed for totally or partly submerged backfill (with the water table at various elevations). Experimental testing and numerical modelling results are used to validate the proposed equations. Both numerical and analytical results show that the total pressure on barricades can be significantly increased by pore pressure, while the effective stress is decreased in the access drifts (compared to dry or drained conditions). The proposed solution provides a simple method to obtain a realistic estimate of the total and effective stresses, and can thus be used as a basis for barricade design.

Developing a sound basis for the design of vented explosion barricades in chemical processes

AbstractMost commonly used barricade design methods are based on taking an explosion scenario and treating it as a “TNT equivalent.” A widely used approach in the chemical industry is documented in TM5‐1300. Although this may be a reasonable approach for explosives in cubical barricades, it may not always relate well to the reality of many chemical facilities. This paper discusses some of the limitations of the TM5‐1300 method, the need for a good definition of the hazardous event(s), and the use of computational fluid dynamics to define blast loads for barricade design. © 2005 American Institute of Chemical Engineers Process Saf Prog, 2005

The design of barricades for hazardous pressure systems

Procedures are given for the rational design of barricades for hazardous pressure systems. Methods are given for estimating the initial velocities of missiles produced by exploding pressure vessels, and for determining the penetrating effects of these missiles on materials normally used for barricade construction. Methods are also given for estimating effective blast pressures produced by the explosion of pressure vessels. Charts and diagrams to assist in performance of the calculations are included. Some checks of the design method against experimental data are presented.