Stress developments within a backfilled mine stope and the lateral loading on the barricade

Widisinghe, Sankha Darshanath (2014) Stress developments within a backfilled mine stope and the lateral loading on the barricade. PhD thesis, James Cook University.

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Abstract

Mine backfilling, filling of underground mined voids with processed tailings, is an integral process within the mining cycle and brings multiple benefits. Engineered barricades are constructed, to retain the backfill within the mined void (stope), across the horizontal drives before backfilling. Failure of such a slurry retaining barricade not only endangers the miners' lives but also has led to many financial losses. Correct engineered design of barricade would bring safety and efficiency to the mining operation. The purpose of this thesis is to critically assess the arching and stress developments within backfilled stopes and drives and to develop a methodology to estimate the loads onto barricades, synthesizing analytical, numerical and laboratory studies.

The arching theory is revisited and analytical equations are established, with limit equilibrium analysis method, for the vertical stress determination within the stope, considering the stope perimeter to the cross sectional areas as the basis. Numerical simulations were carried out to record the vertical stress at the bottom of the stope, which is a unique way of stress recording and has not been identified by previous studies. Although the lateral variation of vertical stress is well understood, there is a lack of simplified models to estimate the vertical stress at any point within the backfilled structure. Vertical stress isobars, were created with the use of numerical simulations, enable to estimate the vertical stress at any point within a backfilled structure up to a depth of six times the width. This has been extended to axisymmetric situations that can represent grain storage silos.

A novel laboratory model was developed to identify the factors affecting lateral load on barricade as well as to measure the variation of the barricade loads with the change of barricade location within the drive (offset distance) and the effect of barricade width. Transducers were used to measure the horizontal normal stress on the barricade and the vertical stress at the stope centre and the stope corner. With laboratory tests, it is observed that the barricade stress decreased with the offset distance and increased with the drive width. Then the barricade stress is estimated with modified analytical equation, which considers the equilibrium of a vertical layer element. Additionally, three dimensional numerical simulations were carried out to replicate the laboratory tests. The barricade stress estimated from analytical equations, numerical simulations and laboratory tests varied within a narrow range for all three approaches but the stress estimations were deviated at the stope entrance because of the continuum approach. Finally, an empirical equation to estimate the barricade stress in full scale mine backfilling situations was proposed with the test results, considering the offset distance, the drive width and the vertical stress at the stope centre.

In order to improve the understanding of the stress variation within a backfilled stope, the previous laboratory models were modified to measure the average vertical stress and the horizontal stress on the stope wall. The vertical stress variations from laboratory model tests showed two distinct regions of vertical stress deviation, the upper region showing an exponential variation followed by a linear variation in the lower region of the stope. In contrast, the arching theory as well as finite difference numerical simulations use the continuum approach and predict an asymptotic vertical stresses achieved at large depths. Additionally, laboratory model tests revealed that the lateral pressure coefficient is not a constant along the depth. The deviations occurred as the cohesionless granular material differs from the concept of continuum approach considered in arching theory as well as in finite difference numerical simulations. Therefore, an alternative analytical solution, considering the particulate approach and inter-particle forces, was proposed. The vertical stress variation within a backfilled stope or silo, as studied through laboratory model test, could successfully match the new analytical solution which considered the presence of intermediate arching conditions with the packing of cohesionless granular material.

Item ID: 41008
Item Type: Thesis (PhD)
Keywords: arching; backfilled mines; backfilling; backfills; barricades; earth pressure; geotechnical engineering; granular fill; Janssen’s effect; lateral loads; mathematical models; mine stopes; mining engineering; mining; numerical modelling; silos; stress concentration; stresses; trenches; vertical stress
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Widisinghe, Sankha, and Sivakugan, Nagaratnam (2014) Vertical stresses within granular materials in containments. International Journal of Geotechnical Engineering, 8 (4). pp. 431-435.

Widisinghe, S.D., Sivakugan, N., and Wang, V.Z. (2014) Loads on barricades in hydraulically backfilled underground mine stopes. In: Proceedings of the 11th International Symposium on Mining with Backfill, pp. 123-134. From: Mine Fill 2014: 11th International Symposium on Mining with Backfill, 20-22 May 2014, Perth, WA, Australia.

Sivakugan, Nagaratnam, Widisinghe, Sankha, and Wang, Vincent Z. (2014) Vertical stress determination within backfilled mine stopes. International Journal of Geomechanics, 14 (5). pp. 1-5.

Widisinghe, Sankha, and Sivakugan, Nagaratnam (2014) Vertical stress isobars for trenches and mine stopes containing granular backfills. International Journal of Geomechanics, 14 (2). pp. 313-318.

Widisinghe, Sankha, Sivakugan, Nagaratnam, and Wang, Vincent Z. (2013) Laboratory investigations of arching in backfilled mine stopes. In: 2013 Geotechnical Society of Singapore (GeoSS), pp. 741-746. From: 18th Southeast Asian Geotechnical Conference Cum Inaugural Agssea Conference, 29-31 May 2013, Singapore.

Sivakugan, Nagaratnam, and Widisinghe, Sankha (2013) Stresses within granular materials contained between vertical walls. Indian Geotechnical Journal, 43 (1). pp. 30-38.

Widisinghe, Sankha, and Sivakugan, Nagaratnam (2012) Vertical stresses within granular materials in silos. In: ANZ 2012 Conference Proceedings, pp. 590-595. From: Ground Engineering in a Changing World: 11th Australia - New Zealand Conference on Geomechanics, 15-18 July 2012, Melbourne, Australia.

Date Deposited: 29 Oct 2015 04:10
FoR Codes: 09 ENGINEERING > 0905 Civil Engineering > 090501 Civil Geotechnical Engineering @ 100%
SEO Codes: 87 CONSTRUCTION > 8704 Construction Processes > 870403 Industrial Construction Processes @ 50%
84 MINERAL RESOURCES (excl. Energy Resources) > 8402 Primary Mining and Extraction Processes of Mineral Resources > 840299 Primary Mining and Extraction of Mineral Resources not elsewhere classified @ 50%
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