Ayhan Kesimal

The effect of desliming by sedimentation on paste backfill performance

Abstract One of the most important characteristics of a backfill material is the particle size distribution. In this paper, the authors have focused the effect of deslimed mill tailings on paste backfill performance at a copper–zinc mine in northeast Turkey. The use of sedimentation methods to deslime has a widespread utilisation and regarded as a true fractional size analysis practice. The common laboratory method of beaker decantation was used for desliming in order to determine the optimum particle size distribution. For studying the beaker decantation, two mine tailings, namely tailings samples A and B are used which have particles 52 and 54 wt.% finer than 20 μm, respectively. The fines content (−20 μm) of each tailing were reduced to 15, 20, 25 and 30 wt.% via desliming. Deslimed tailings then were tested to investigate the relationship between particle size and strength gain. It was found that strength ranges of the deslimed tailings were from 12% to 52% higher than as-received mill tailings.

Prediction of unconfined compressive strength of carbonate rocks using artificial neural networks

The unconfined compressive strength (UCS) of intact rocks is an important geotechnical parameter for engineering applications. Determining UCS using standard laboratory tests is a difficult, expensive and time consuming task. This is particularly true for thinly bedded, highly fractured, foliated, highly porous and weak rocks. Consequently, prediction models become an attractive alternative for engineering geologists. The objective of study is to select the explanatory variables (predictors) from a subset of mineralogical and index properties of the samples, based on all possible regression technique, and to prepare a prediction model of UCS using artificial neural networks (ANN). As a result of all possible regression, the total porosity and P-wave velocity in the solid part of the sample were determined as the inputs for the Levenberg–Marquardt algorithm based ANN (LM-ANN). The performance of the LM-ANN model was compared with the multiple linear regression (REG) model. When training and testing results of the outputs of the LM-ANN and REG models were examined in terms of the favorite statistical criteria, which are the determination coefficient, adjusted determination coefficient, root mean square error and variance account factor, the results of LM-ANN model were more accurate. In addition to these statistical criteria, the non-parametric Mann–Whitney U test, as an alternative to the Student’s t test, was used for comparing the homogeneities of predicted values. When all the statistics had been investigated, it was seen that the LM-ANN that has been developed, was a successful tool which was capable of UCS prediction.

Utilization of industrial waste products as pozzolanic material in cemented paste backfill of high sulphide mill tailings.

In this study, the potential use of the industrial waste products including waste glass (WG), fly ash (FA), granulated blast furnace slag (GBFS) and silica fume (SF) as pozzolanic additive for the partial replacement of ordinary Portland cement (OPC) in cemented paste backfill (CPB) of sulphide-rich mill tailings was investigated. The influence of these industrial waste products on the short- and long-term mechanical performance of CPB was demonstrated. The rate of development of strength of CPB samples tended to slow down when the pozzolanic wastes were incorporated or increased in dosage in the binder phase. Severe losses (by 26%) in the strength of CPB samples produced from exclusively OPC occurred after an initial curing period of 56 days. The addition of WG (10-30 wt%) as a partial replacement of OPC was observed to aggravate further the strength losses of CPB samples. GBFS, FA and SF appeared to improve the long-term performance of CPB samples; albeit, only GBFS and SF could be incorporated into the binder phase only at certain levels i.e. up to 20 wt% GBFS and 15wt% SF in order to maintain a threshold strength level of 0.7MPa over 360 days. SEM studies have provided further insight into the microstucture of CPB and confirmed the formation of deleterious gypsum as the expansive phase. These findings have demonstrated that the industrial waste products including GBFS and SF can be suitably used as mineral additives to improve the long-term mechanical performance of CPB produced from sulphide-rich tailings as well as to reduce the binder costs in a CPB plant.

Effect of natural pozzolans as mineral admixture on the performance of cemented-paste backfill of sulphide-rich tailings

This paper presents the effect of the natural pozzolans as mineral additives on the short- and long-term strength and stability performance of cemented paste backfill (CPB) samples. Prior to their use in CPB studies, the natural pozzolans — the volcanic tuffs (Akkus Trass [AT] and Fatsa Trass [FT]) and pumice (KP) — were tested for their pozzolanic characteristics. These tests revealed that the pozzolanic activity of the natural pozzolans is closely inter-related with their content of reactive silica and, accordingly, KP has the highest pozzolanic activity. The addition, or increasing the amount, of natural pozzolans in the binder phase resulted in a slower rate of strength development of CPB samples. The deterioration in stability of CPB samples prepared from Portland cement (PC) alone (i.e. a strength loss of 24.6%) occurred following 56 days. The replacement of PC with FT and AT led to even higher losses in strength. However, the addition of KP (up to 30 wt%) mitigated, to a certain extent, long-term strength and stability problems with the losses in strength of CPB samples consistently lower than 20%. It can be inferred that the performance of the natural pozzolans as a mineral additive in CPB is dependent intimately on their pozzolanic characteristics.

Application of Generalized Regression Neural Networks in Predicting the Unconfined Compressive Strength of Carbonate Rocks

Measuring unconfined compressive strength (UCS) using standard laboratory tests is a difficult, expensive, and time-consuming task, especially with highly fractured, highly porous, weak rock. This study aims to establish predictive models for the UCS of carbonate rocks formed in various facies and exposed in Tasonu Quarry, northeast Turkey. The objective is to effectively select the explanatory variables from among a subset of the dataset containing total porosity, effective porosity, slake durability index, and P-wave velocity in dry samples and in the solid part of samples. This was based on the adjusted determination coefficient and root-mean-square error values of different linear regression analysis combinations using all possible regression methods. A prediction model for UCS was prepared using generalized regression neural networks (GRNNs). GRNNs were preferred over feed-forward back-propagation algorithm-based neural networks because there is no problem of local minimums in GRNNs. In this study, as a result of all possible regression analyses, alternative combinations involving one, two, and three inputs were used. Through comparison of GRNN performance with that of feed-forward back-propagation algorithm-based neural networks, it is demonstrated that GRNN is a good potential candidate for prediction of the unconfined compressive strength of carbonate rocks. From an examination of other applications of UCS prediction models, it is apparent that the GRNN technique has not been used thus far in this field. This study provides a clear and practical summary of the possible impact of alternative neural network types in UCS prediction.

A comparative study of Schmidt hammer test methods for estimating the uniaxial compressive strength of rocks

The Schmidt hammer is being widely used for estimating the uniaxial compressive strength (UCS) of rocks because of its simplicity, rapidity and portability. However, determination of the Schmidt hardness (R) in laboratory conditions is sometimes very difficult for weak rocks due to the fact that samples can be broken during the test, as well as sample scarcity. Additionally, some Schmidt hammer test procedures necessitate more readings for obtaining the average R values than others. For these reasons, this study aims to explore more practical and useful Schmidt hammer tests by reducing the rebound readings, especially for the UCS estimation of rock materials. Accordingly, three different trial methods (T1, T2 and T3) were studied on tested rock samples. T1 is obtained by recording six single impacts and averaging all the values. T2 is obtained by recording eight single impacts and discarding the lowest and highest value to obtain a mean rebound number. T3 is obtained by recording ten single impacts and discarding the lowest and highest two values to obtain a mean rebound number. For comparison purposes, Schmidt hardness values were also calculated from four other test procedures (R1–R4) recommended in the literature. Forty-seven rock samples were tested in this study, including igneous, sedimentary and metamorphic rock origins. Statistical equations were determined for estimating the UCS of rocks by using trial Schmidt hammer test methods and other test procedures. Correlation, ANOVA and percentage error analyses were performed between the measured and estimated UCS values. The UCS of rock materials can be reliably estimated from any of the Schmidt hammer methods (T1–T3, R1–R4), taking into account the correlation and ANOVA analyses results. This study, however, demonstrated that T1 is slightly more reliable and simpler to use than the other tested methods, giving a better representation of overall rock hardness, and hence a better prediction of UCS based on the percentage error analysis.

Evaluation of Indirect Tensile Strength of Rocks Using Different Types of Jaws

The Brazilian test is the most popular indirect tensile strength (ITS) test method because it can be used with conventional compressive test equipment (Hobbs 1964; Barla and Innaurato 1973). The test is widely accepted to be invented by Prof. Fernando LLB. Carneiro (Carneiro 1943; Fairbairn and Ulm 2002), who was a very popular Brazilian concrete consultant. As an interesting event, Tsunei Akazawa, a Japanese scientist, independently developed the splitting tension test and proposed its ITS determination method in the same year that Carneiro first announced his method (Akazawa 1943). The International Society of Rock Mechanics (ISRM) in 1978 suggested the splitting method as a standard testing method for determining the ITS of rocks (ISRM 1978). The Brazilian ITS (rtB) of rocks can be calculated using the Eq. 1, as suggested by ISRM (Muskhelishvili 1963; Ulusay and Hudson 2007):

A comparative assessment of indirect methods for estimating the uniaxial compressive and tensile strength of rocks

The uniaxial compressive and tensile strength of rocks are crucial parameters in the design stage of geotechnical structures. However, direct determination of these parameters is expensive, troublesome, time consuming, and sometimes requires high-quality core samples for tests. Therefore, this study aimed to determine the applicability of the point load strength index and Schmidt hammer hardness values to estimate the uniaxial compressive strength and tensile strength of rocks based on the regression analyses. Further, multiple regression analysis was used on datasets obtained from tested rocks. For these purposes, representative samples of volcanic, sedimentary, and metamorphic rocks were collected from 37 different points along a tunnel alignment in Northeast Turkey where hundreds of underground projects are being constructed. Results from the regression analyses showed the existence of satisfactory correlations. The results were also compared and discussed with the results obtained by other researchers conducted on different types of rocks.

Improved Performance of Rock Bolts using Sprayed Polyurea Coating

Cost of Polyurea Coat The deficiencies in tunnel supports led to improvements, including the use of new materials. Because underground water can substantially affect steel materials and decrease their load-bearing capacity, especially for long contact times and acidic water conditions, researchers have been trying to find economical ways to solve the problems of steel corrosion for many years (Ranasooriya et al. 1995; Li and Lindblad 1999; Komurlu 2012; Hassell and Villaescusa 2005). The application of a polyurea-type thermoset polymer coating was assessed in this study. Polyurea is an isocyanate-based copolymer used for surface treatment applications, such as liners for truck beds, tanks, ships, buildings, pools, and waste deposition isolation plants, beacause of its good water-resisting performance (Komurlu and Kesimal 2012). In addition, it is becoming popular for application on sewage walls because of its resistance to chemical degradation from sulphuric acid and hydrogen sulfide gas (Muynck et al. 2009). Polyurea is being used as spraying membrane in tunneling and a support called thin spray-on liner (TSL) (Tannant 2001). It is known that polyurea has good adhesion with rock, concrete and steel surfaces (Ozturk and Tannant 2010; Ozturk 2012; BASF 2009). Polyurea polymerizes owing to the chemical reaction between two liquid ingredients. The liquid phase time of mix can be chosen in accordance with the type of product. The material used in this study is immediately activated within two or three seconds after being blown out of the sprayer gun nozzle. To test the load-bearing capacities of polymercoated rock bolts (PCRBs) and the corrosion prevention performance of the polyurea coating, a copper mine in the northeastern region of Turkey was chosen as the case study area.

Core size effect on the dry and saturated ultrasonic pulse velocity of limestone samples.

This study presents the effect of core length on the saturated (UPVsat) and dry (UPVdry) P-wave velocities of four different biomicritic limestone samples, namely light grey (BL-LG), dark grey (BL-DG), reddish (BL-R) and yellow (BL-Y), using core samples having different lengths (25-125mm) at a constant diameter (54.7mm). The saturated P-wave velocity (UPVsat) of all core samples generally decreased with increasing the sample length. However, the dry P-wave velocity (UPVdry) of samples obtained from BL-LG and BL-Y limestones increased with increasing the sample length. In contrast to the literature, the dry P-wave velocity (UPVdry) values of core samples having a length of 75, 100 and 125mm were consistently higher (2.8-46.2%) than those of saturated (UPVsat). Chemical and mineralogical analyses have shown that the P wave velocity is very sensitive to the calcite and clay minerals potentially leading to the weakening/disintegration of rock samples in the presence of water. Severe fluctuations in UPV values were observed to occur between 25 and 75mm sample lengths, thereafter, a trend of stabilization was observed. The maximum variation of UPV values between the sample length of 75mm and 125mm was only 7.3%. Therefore, the threshold core sample length was interpreted as 75mm for UPV measurement in biomicritic limestone samples used in this study.