Kadir Karaman

Assessment of strength properties of cemented paste backfill by ultrasonic pulse velocity test

Ultrasonic pulse velocity (UPV) test is one of the most popular non-destructive techniques used in the assessment of the mechanical properties of concrete or rock materials. In this study, the effects of binder type/dosage, water to cement ratio (w/c) and fines content (<20 μm) of the tailings on ultrasonic pulse velocity (UPV) of cemented paste backfill (CPB) samples were investigated and correlated with the corresponding unconfined compressive strength (UCS) data. A total of 96 CPB samples prepared at different mixture properties were subjected to the UPV and UCS tests at 7, 14, 28 and 56-days of curing periods. UPV and UCS of CPB samples of ordinary Portland cement (CEM I 42.5 R) and sulphate resistant cement (SRC 32.5) initially increased rapidly, but, slowed down after 14 days. However, UPV and UCS of CPB samples of the blast furnace slag cement (CEM III/A 42.5 N) steadily increased between 7 and 56 days. Increasing binder dosage or reducing w/c ratio and fines content (<20 μm) increased the UCS and UPV of CPB samples. UPV was found to be particularly sensitive to fines content. UCS data were correlated with the corresponding UPV data. A linear relation appeared to exist between the UCS and UPV of CPB samples. These findings have demonstrated that the UPV test can be reliably used for the estimation of the strength of CPB samples.

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.

Utilizing the strength conversion factor in the estimation of uniaxial compressive strength from the point load index

The strength conversion factor (k) is the ratio between the uniaxial compressive strength (UCS) and the point load index (PLI). It has been used to estimate the UCS from the PLI since the 1960s. Many researchers have investigated the relationship between UCS and PLI for various rock types of different geological origins, such as igneous, sedimentary, and metamorphic rocks. In this study, the k values for subclasses of igneous (pyroclastic, volcanic, and plutonic), sedimentary (chemical and clastic), and metamorphic (foliated and nonfoliated) rocks were evaluated. For this purpose, UCS and PLI data for a total of 410 rock samples extracted from literature published around the world as well as UCS and PLI data obtained in this work for 80 rock samples taken from the Eastern Black Sea Region in Turkey were evaluated together to determine the k values of different rock classes. Strength conversion factors were obtained using zero-intercept regression analysis, formulation, and a graphical approach. This study confirmed that there is no single k value that is applicable to all rock classes. According to statistical analyses, k varied between 12.98 and 18.55 for the rocks studied. These findings demonstrate that the k values derived in this work can be reliably used to estimate the strengths of rock samples with specific lithologies.

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.

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.

Understanding the mechanism of slope failure on a nearby highway tunnel route by different slope stability analysis methods: a case from NE Turkey

The Arakli tunnel is located in the eastern Black Sea region where the most mass movement is observed in Turkey. Following the tunnel entrance portal excavations in basaltic tuffs on nearby the Konakonu residential area, an impending failure occurred. Because of the developed tension cracks and deformations on the ground, five houses and their gardens were damaged completely. The present study aims to investigate the mechanism of the failure. In order to do this, kinematic, limit equilibrium, and numerical stability analyses were carried out. Firstly, the kinematic analyses were performed taking into account the main joint sets for the slopes. The results of the kinematic analyses showed that planar and wedge failures were possible on the portal slope and no failure occurred on the cut slope. However, the limit equilibrium analysis showed that neither the planar nor wedge failures were expected to occur on the portal slope. The numerical stability analyses were performed to determine if circular failure is to occur in the slopes. The Phase2 programme was used in the numerical analyses, and the Strength Reduction Factors (SRF) of the slopes were determined. According to the numerical stability analyses, the failure mode for the portal slope is composite starting with a circular surface and following a linear surface and circular for the cut slope. The stability analyses indicated that the failure mechanism was not directly controlled by the joints and might be related to the low strength parameters of the rock mass and joints. Finally, precautions were determined to make the region stable using the Phase2 programme. After support installation, the SRF values for the portal and cut slopes increased from 1.21 to 1.63 and from 1.32 to 1.71, respectively. These results showed that the proposed support units prevent the effects of failure and were essential for the long-term stability.

İLERİ MİKROSKOPİ YÖNTEMLERİ İLE PARLAK KESİT ANALİZLERİ

Bu calismanin amaci pirit iceren kayaclarin parlak kesit analizlerini, yeni bir teknik olan trinokuler arastirma mikroskobuna entegre clemex goruntu analiz sistemi ve motorize tabla kullanarak yapmaktir. Motorize tabla ile butun kesitin patern olusturarak taranmasi mumkun olmustur. Clemex goruntu analiz sistemi ile cok kisa surede analizler yapilabilmistir. Bu nedenle manuel olarak yapilan analizlere gore daha guvenilir ve daha hizli oldugu anlasilmistir. Calisilan kayaclardaki pirit orani (%0.09-%2.13) ve pirite ait en kucuk (24µm), en buyuk (895µm) ve ortalama dane caplari (48µm-132µm)hesaplanmistir. Sonuc olarak daha kisa surede daha dogru sonuclar alma acisindan motorize tabla ve clemex gibi sistemlerin kullanilmasinin onem tasidigi anlasilmistir.

Geotechnical investigations and remediation design for failure of tunnel portal section: a case study in northern Turkey

Mass movements are very common problems in the eastern Black Sea region of Turkey due to its climate conditions, geological, and geomorphological characteristics. High slope angle, weathering, dense rainfalls, and anthropogenic impacts are generally reported as the most important triggering factors in the region. Following the portal slope excavations in the entrance section of Cankurtaran tunnel, located in the region, where the highly weathered andesitic tuff crops out, a circular toe failure occurred. The main target of the present study is to investigate the causes and occurrence mechanism of this failure and to determine the feasible remedial measures against it using finite element method (FEM) in four stages. These stages are slope stability analyses for pre- and postexcavation cases, and remediation design assessments for slope and tunnel. The results of the FEM-SSR analyses indicated that the insufficient initial support design and weathering of the andesitic tuffs are the main factors that caused the portal failure. After installing a rock retaining wall with jet grout columns and reinforced slope benching applications, the factor of safety increased from 0.83 to 2.80. In addition to slope stability evaluation, the Rock Mass Rating (RMR), Rock Mass Quality (Q) and New Austrian Tunneling Method (NATM) systems were also utilized as empirical methods to characterize the tunnel ground and to determine the tunnel support design. The performance of the suggested empirical support design, induced stress distributions and deformations were analyzed by means of numerical modelling. Finally, it was concluded that the recommended stabilization technique was essential for the dynamic long-term stability and prevents the effects of failure. Additionally, the FEM method gives useful and reasonably reliable results in evaluating the stability of cut slopes and tunnels excavated both in continuous and discontinuous rock masses.

Effect of Tunnel Blasting Operation on the Surface Penstock Pipe

This paper presents the investigation of the effect of ground vibration components induced blasting events in Ordu-Mesudiye Highway Topcam tunnel on the penstock pipe (PP) having 35-400 slopping of Topcam Hydro-Electrical Power Plant (HEPP). Until the tunnel excavation passed under the PP of HEPP, a total of 37 shots (26 upper halves and 11 lower half) were monitored and the ground vibration components (peak particle velocity, acceleration, displacement and frequency) were measured in two different stations. It was also examined whether the concrete platform under this PP had a crack, damage or etc. As a result of these workings, a maximum of 220 kg total charge was used and the charge weight per delay varied between 1.0-18 kg in the shots. The distance of shots to measurement station was between 78.04 and 170.16 m. 6 PPVs, 11 accelerations and a displacement value exceeded the threshold values determined. However, the vibration values were taken under control with changing the blasting parameters and it was provided that the tunnel excavation passed under the PP of Topcam HEPP.