Showing items 1 - 6 of 6

A borehole stability study by newly designed laboratory tests on thick-walled hollow cylinders

- Hashemi, Sam, Melkoumian, Nouné, Taheri, Abbas

  • Authors: Hashemi, Sam , Melkoumian, Nouné , Taheri, Abbas
  • Date: 2015
  • Type: Text , Journal article
  • Relation: Journal of Rock Mechanics and Geotechnical Engineering Vol. 7, no. 5 (2015), p. 519-531
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  • Description: At several mineral exploration drilling sites in Australia, weakly consolidated formations mainly consist of sand particles that are poorly bonded by cementing agents such as clay, iron oxide cement or calcite. These formations are being encountered when drilling boreholes to the depth of up to 200 m. To study the behaviour of these materials, thick-walled hollow cylinder (TWHC) and solid cylindrical synthetic specimens were designed and prepared by adding Portland cement and water to sand grains. The effects of different parameters such as water and cement contents, grain size distribution and mixture curing time on the characteristics of the samples were studied to identify the mixture closely resembling the formation at the drilling site. The Hoek triaxial cell was modified to allow the visual monitoring of grain debonding and borehole breakout processes during the laboratory tests. The results showed the significance of real-time visual monitoring in determining the initiation of the borehole breakout. The size-scale effect study on TWHC specimens revealed that with the increasing borehole size, the ductility of the specimen decreases, however, the axial and lateral stiffnesses of the TWHC specimen remain unchanged. Under different confining pressures the lateral strain at the initiation point of borehole breakout is considerably lower in a larger size borehole (20 mm) compared to that in a smaller one (10 mm). Also, it was observed that the level of peak strength increment in TWHC specimens decreases with the increasing confining pressure. © 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences.

An experimental study on the relationship between localised zones and borehole instability in poorly cemented sands

- Hashemi, Sam, Taheri, Abbas, Melkoumian, Nouné

  • Authors: Hashemi, Sam , Taheri, Abbas , Melkoumian, Nouné
  • Date: 2015
  • Type: Text , Journal article
  • Relation: Journal of Petroleum Science and Engineering Vol. 135, no. (2015), p. 101-117
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  • Description: Poorly cemented sands are mainly located in areas where layers of unconsolidated formations exist. Drilling a borehole in the ground causes stress perturbation and induces tangential stresses on the borehole wall. If the cohesion between sand particles generated by existing cementation is not high enough, the tensile stress concentration may cause grain debonding and, consequently, borehole breakout. In this study a series of solid and thick-walled hollow cylinder (TWHC) laboratory tests was performed on synthetic poorly cemented sand specimens. The applied stresses were high enough to generate breakout on the borehole wall. Simultaneous real-time monitoring and deformation measurement identified the development of localised breakout zones and compaction bands at the borehole wall during the tests. The results from the video recording of the tests showed that a narrow localised zone develops in the direction of the horizontal stress, where stress concentration causes the full breakout in specimens. Dilation occurred at lower confining pressures in TWHC specimens and contracting behaviour was observed during the onset of shear bands at higher pressures. Scanning electron microscopy (SEM) studies showed that sand particles stayed intact under the applied stresses and micro- and macrocracks develops along their boundaries. The SEM imaging was also used to investigate and characterize pre-existing microcracks on the borehole wall developed due to the specimen preparation. It showed that boring the solid specimen in order to produce a TWHC specimen could generate microcracks on the borehole wall prior to testing which affects the process of borehole failure development during the test. © 2015 Elsevier B.V.

Improved shear strength performance of compacted rubberized clays treated with sodium alginate biopolymer

- Soltani, Amin, Raeesi, Ramin, Taheri, Abbas, Deng, An, Mirzababaei, Mehdi

  • Authors: Soltani, Amin , Raeesi, Ramin , Taheri, Abbas , Deng, An , Mirzababaei, Mehdi
  • Date: 2021
  • Type: Text , Journal article
  • Relation: Polymers Vol. 13, no. 5 (2021), p. 1-21
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  • Description: This study examines the potential use of sodium alginate (SA) biopolymer as an environmentally sustainable agent for the stabilization of rubberized soil blends prepared using a high plasticity clay soil and tire-derived ground rubber (GR). The experimental program consisted of uniaxial compression and scanning electron microscopy (SEM) tests; the former was performed on three soil–GR blends (with GR-to-soil mass ratios of 0%, 5% and 10%) compacted (and cured for 1, 4, 7 and 14 d) employing distilled water and three SA solutions—prepared at SA-to-water (mass-tovolume) dosage ratios of 5, 10 and 15 g/L—as the compaction liquid. For any given GR content, the greater the SA dosage and/or the longer the curing duration, the higher the uniaxial compressive strength (UCS), with only minor added benefits beyond seven days of curing. This behaviour was attributed to the formation and propagation of so-called “cationic bridges” (developed as a result of a “Ca2+/Mg2+

Improving workability of cement paste backfill using new binders

- Taheri, Abbas, Zhao, Y., Soltani, Amin, Karakus M., Deng, A.

  • Authors: Taheri, Abbas , Zhao, Y. , Soltani, Amin , Karakus M. , Deng, A.
  • Date: 2019
  • Type: Text , Conference paper
  • Relation: 13th Australian New Zealand Conference on Geomechanics, 1-3 April 2019, Perth Australia
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  • Description: In this study effects of binder type and content and curing time on the compressive strength development of cement paste backfill (CPB) is investigated. Moreover, the effects of binder type and content and water content on the rheological properties of CPB material were studied. To undertake an experimental study, tailings of a copper mine in South Australia are mixed with binder and water. A new slag-cement called Mine Cement (MC) and ordinary Portland cement (PC) are used as the primary binder materials. Furthermore, fly ash (FA) is used as an additive to reduce the amount of the cement. Some CPB samples were cured under pressure to be more representative of the field conditions. MC exhibited better performance that PC regarding compressive strength development. Fly ash improved the compressive strength of CPB. However, this binder observed to be much less cementitious compare to MC. Strength performance of the CPB sample significantly improved when there were cured under pressure. Based on the results obtained from the test undertaken using a rheometer, it was found that increasing the water content results in lower yield stress. The results also show that MC improves the rheological properties of the CPB.

Shear failure analysis of a shallow depth unsupported borehole drilled through poorly cemented granular rock

- Hashemi, Sam, Taheri, Abbas, Melkoumian, Noume

  • Authors: Hashemi, Sam , Taheri, Abbas , Melkoumian, Noume
  • Date: 2014
  • Type: Text , Journal article
  • Relation: Engineering Geology Vol. 183, no. (2014), p. 39-52
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  • Description: Adopting an appropriate failure criterion plays a key role in the borehole stability analysis. In this paper the induced stresses on a vertical borehole wall were calculated based on the elastic theory. Then, to predict the stability of a borehole drilled through a poorly cemented sand formation, failure envelopes in different failure criterion domains were derived using the results from a series of precise laboratory tests conducted on solid and hollow cylinder specimens. The mixture used in specimen preparation was designed to simulate the properties of the samples collected from depths up to 200m at a drilling site in South Australia. The hollow cylinder test apparatus was developed by modifying a Hoek triaxial cell. These modifications allowed observing the process of debonding of sand grains from the borehole wall during the test and consequently, acquiring a better understanding on the failure mechanisms of a borehole drilled through poorly cemented sand formations. Three well-known failure criterion domains; Coulomb, Drucker–Prager and Mogi, were considered versus the laboratory test data to investigate their capability to predict the shear failure of a borehole using the data from hollow cylinder tests. The obtained results showed the significance of selecting an appropriate failure domain for predicting the shear failure behavior of poorly cemented sands near the borehole wall. The results also showed that the Coulomb criterion is not well suited for predicting the borehole failure when there is no pressure acting inside the borehole. A failure envelope based on the Mogi domain was developed which can be used for the far-field stress states. The introduced failure envelope allows predicting the stability of a borehole drilled in poorly cemented sands.

The failure behaviour of poorly cemented sands at a borehole wall using laboratory tests

- Hashemi, Sam, Melkoumian, Nouné, Taheri, Abbas, Jaksa, Mark

  • Authors: Hashemi, Sam , Melkoumian, Nouné , Taheri, Abbas , Jaksa, Mark
  • Date: 2015
  • Type: Text , Journal article , Technical Note
  • Relation: International Journal of Rock Mechanics and Mining Sciences Vol. 77, no. (2015/07/01/ 2015), p. 348-357
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  • Description: Borehole stability analysis is an important challenge for researchers in the field of geotechnical, mining and petroleum engineering. Several borehole instability problems during or after the completion of drilling, have been reported by a number of exploration companies in Australia. Many of these problems are reported in drilling projects in poorly cemented sand formations at depths of up to 200 m beneath the ground. The sand production problem, as it is known, has also been observed in weakly bonded sandstones where the debonding of sand grains can be triggered by fluid pressure and induced stresses leading to the failure of the sandstone at the borehole wall. The strength of a granular material formation is generated mainly by a natural cementing agent that bonds sand grains together.
  • Description: Borehole stability analysis is an important challenge for researchers in the field of geotechnical, mining and petroleum engineering. Several borehole instability problems during or after the completion of drilling, have been reported by a number of exploration companies in Australia. Many of these problems are reported in drilling projects in poorly cemented sand formations at depths of up to 200 m beneath the ground. The sand production problem, as it is known, has also been observed in weakly bonded sandstones where the debonding of sand grains can be triggered by fluid pressure and induced stresses leading to the failure of the sandstone at the borehole wall [1], [2]. The strength of a granular material formation is generated mainly by a natural cementing agent that bonds sand grains together [3].
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