Strength Index Tests Research Articles

Temperature effect on the mechanical behavior of shale: Implication for shale gas production

• The variation in mechanical strength parameters of shale at elevated temperatures. • Tensile strength, mode-I fracture toughness and point load strength investigation. • Mechanical strength attributes were supported with XRD and SEM analysis. • Micro-crack and thermal behaviour of minerals induced thermal behaviour of shale. Deformational shale attributes such as fracture toughness, tensile strength, and axial point load strength (PLS) index under elevated temperatures are crucial for the petroleum and gas industries. Here, an attempt has been made to investigate the thermal response of shale from room temperature to 400°C. Three-point bending (TPB) test using semi-circular bending (SCB) specimen, Brazilian tensile test, and the point load strength index test were conducted to evaluate mode-I fracture toughness, tensile strength, and PLS index, respectively, with varying temperatures. Additionally, the X-ray Diffraction (XRD) analysis was performed to determine the bulk rock composition and the resulting phase changes with increasing temperature. Furthermore, Scanning Electron Microscope (SEM) was used to study the induced microcracks in the sample due to thermal treatment. It was found that the mode-I fracture toughness increased from 25°C up to 100°C and, after that, a slight decline up to 400°C. The fracture toughness of the shale got increases from 0.256 MPa·m 1/2 to 0.454 MPa·m 1/2 in a transition from ambient room condition to 400°C. The same trend was obtained for tensile strength and PLS index. With the same temperature range, the tensile strength of the shale changed from 7.94 MPa to 9.75 MPa. The SEM images of the thermally treated samples demonstrate the formation of noticeable microcracks at 400°C.

Development of shear strength index test probe: its application on historic structures

PurposeMaterial properties, such as shear and compressive strength of masonry, have a crucial impact on the seismic analysis results of masonry structures. Considering that most of the historical buildings are masonry structures, the damage caused by obtaining shear strengths with known methods exceeds acceptable limits. Instead of traditional shear strength index tests, this paper presents a test technique that has been developed which causes less damage to the structure, to obtain mechanical properties in masonry structures.Design/methodology/approachA new approach to shear testing and a test probe has been developed to minimize the destructive effects of mechanical in situ testing on masonry structures. The comparison of the results obtained with reduced destruction level using the novel shear strength index test probe with those obtained from the traditional method is addressed. Masonry specimens were tested in the laboratory and in situ tests were carried out on 12 historical buildings.FindingsTest results obtained from the proposed probe shear strength index test were consistent with the results obtained from the conventional shear strength test both at the laboratory setting and in situ. Although a large number of data is needed for the validation of a method, satisfactory agreement with the conventional shear strength index test method was obtained.Originality/valueThe authors believe that the proposed method would give the opportunity to collect more mechanical strength data with much less destruction. The experimental work in the laboratory and in situ tests and their comparisons are the supportive and original values of this research.

Experimental Study on Mudstone’s Strength Characteristics in Deep‐Buried Coal‐Measure Formation: A Case Study of Permian Longtan Formation

To investigate the strength characteristics of mudstone in deep‐buried coal‐measure formation, four types of experiments have been conducted: (i) the X‐ray diffraction (XRD) test; (ii) the scanning electron microscope (SEM) scanning test; (iii) the point load strength index test; and (iv) the uniaxial compressive strength test. It was concluded that the mudstone of the deep‐buried coal measures in the Longtan Formation is dominated by chlorite, quartz, and albite using the XRD test, of which chlorite is primary, accounting for 74.3%. It was found that the three minerals in the mudstone are unevenly distributed using the SEM scanning test, albite is irregularly distributed in chlorite, and quartz is present in the albite and chlorite. Sixty‐five specimens were tested for the point load strength index. After processing the data using the method suggested by the International Society for Rock Mechanics and Rock Engineering(ISRM), it was found that the maximum value of Is(50) was 6.10 MPa, the minimum is 0.14 MPa, and 53% of the specimens’ Is(50) values are below 2.0 MPa. The RMT‐150C rock mechanics testing machine was used to conduct uniaxial compression tests on six specimens. The maximum uniaxial compressive strength (UCS) value is 59.26 MPa, the minimum value is 31.77 MPa, and the average is 45.64 MPa. Linear fitting and logarithmic fitting are carried out for the correlation between UCS and Is(50). The goodness of fit R2 of the linear fitting is 0.863, and that of the logarithmic fitting is 0.919, indicating a strong correlation between them. When it is challenging to make standard specimens, Is (50) can be used to estimate UCS.

BÜYÜK ÖLÇEKLİ KÖMÜR ARININDA GERÇEKLEŞTİRİLEN SCHMİDT SERTLİK İNDEKSİ VE NOKTA YÜKLEME DAYANIMI DENEY SONUÇLARININ DEĞERLENDİRİLMESİ

Kömür ve kömür damarı içerisinde konumlanan ara kesmelerin (t=0,5m) yerinde malzeme özelliklerinin belirlenmesine yönelik bu çalışma, TKİ-GLİ-Ömerler yeraltı maden ocağında gerçekleştirilmiştir. Kömür arın yüksekliği 3,5 m ve uzunluğu ise 110 m olan A1 hazırlık panosunda, yaklaşık 385 m2’ lik yüzey alanı üzerinde her biri yaklaşık 15 m2 olan 4 deney alanı belirlenmiştir. Bu deney bölgeleri arının iki kenar uç tarafında ve arın ortasında konumlanmıştır. Deney bölgeleri kendi içlerinde toplam 238 birim hücreye bölünmüştür. Birim hücrelerin orta noktasında en az üç kez tekrarlanmak kaydı ile Schmidt sertlik belirleme deneyleri yapılmıştır. Nokta yükleme dayanımı indeks deneyi için A1 panosunun kömür arını yaklaşık 5’ er metre aralıklar ile toplam 21 birim bölgeye ayrılmıştır. Her birim bölge ise kendi içerisinde beş alt birim hücreye bölünerek her bir alt birim hücreden alınan düzensiz örnekler ile toplam 563 adet nokta yükleme dayanımı belirleme deneyleri yapılmıştır. Sonuç olarak yapılması pratik olan Schmidt sertlik ölçümleri ile nokta yükleme dayanım deney sonuçları arasındaki mekanik ilişkiler ve bu deney sonuçlarına dayalı kazı kolaylığına ait bir sınıflama bu çalışmada önerilmiştir.

Stabilization of Lateritic Soil Admixed with Maize Husk Ash

Lateritic soil is one of the major construction materials in road pavement. However, obtaining lateritic soil with sufficient strength is difficult, which may necessitate its improvement by stabilization. Lateritic soil, in this study, was stabilized with upto 12% Maize Husk Ash (MHA) by weight of soil samples, with a view of improving its geotechnical properties and assessing it as subbase materials. Classification tests (particle size analysis, specific gravity, Atterbergs limits) and strength index tests (compaction, california bearing ratio (CBR), unconfined compression test (UCS) were performed on both the natural and the MHA-stabilized soil samples. The grain size analysis shows that the percentage passing No. 200 BS sieve was 47.7% for the natural lateritic soil and between 50 and 62.1% for MHA stabilized lateritic soil. The liquid limit, plastic limit and plasticity index are in the range of 61 to 76%, 28 to 53% and 16 to 37% respectively. Also, the maximum dry densities increased, while the optimum water content decreased with increase in the MHA content. The CBR value of the lateritic soil increased with MHA content up till 6% addition of MHA and thereafter decreased, while higher UCS value was obtained up till 3% and then decreased with increasing content of MHA. The results indicated that the MHA stabilized lateritic soil could only be used as subgrade and fill materials.

Estimate of Uniaxial Compressive Strength of Hydrothermally Altered Soft Rocks Based on Strength Index Tests

The purpose of this study was to clarify the relationships between results of index tests and uniaxial compressive strength (UCS) in hydrothermally altered soft rocks of the Upper Miocene, which are typical of the soft rock found in northeastern Hokkaido, Japan. Index tests were performed using point load testing machine and needle penetrometer with irregular lump specimens under forced-dry, forced-wet, and natural-moist states. The relationships between irregular lump point load strength (IPLS) index and UCS, and needle penetration (NP) index and UCS were “UCS = approximately 19 IPLS index” and “UCS = 0.848 (NP index)0.619”, respectively, in soft rocks with a UCS below 25 MPa. These relationships could be applied to on-site tests of rocks with natural moisture content. The UCS could be calculated from IPLS and NP tests on soft rocks only when UCS was below 25 MPa, using the equations obtained as a result of this study.

Assessment of Durability and Weathering State of Some Igneous and Metamorphic Rocks Using Micropetrographic Index and Rock Durability Indicators: A Case Study

Weathering and durability are the key factors of the rock in the suitability and usefulness of different construction materials, building materials and engineering structures. A single test never predicts the entire factor for suitability of rock stone and aggregate in different uses. Thus, variety of physical, mechanical and chemical tests and indices of rocks are widely used to estimate and evaluate the rocks for the suitability of the required purpose. In all the cases, knowledge of durability and weathering properties are the most important along with the strength of the rock. Micropetrographic index and rock durability indicators (dynamic and static) are the one of the best methods to evaluate the rock for weathering and durability. To estimate these indices, variety of tests are performed such as petrographic examination test, point load index, sulfate soundness test, water absorption test, modified aggregate impact value test and test for specific gravity. Slake durability index and impact strength index tests were also performed for correlation with static and dynamic rock durability indicators due to its application and usefulness in the durability and strength of the rock materials. Micropetrographic index was obtained by petrographic examination test and correlated with all the physical and mechanical properties used for find out the durability indicators. The present study is to express the usefulness of these three indices in the classification of weathering and durability classes and estimation of durability indices by slake durability index, impact strength index and micropetrographic index.

An Equation to Evaluate the Unconfined Compressive Strength of Rock from Splitting Tensile Strength Test Results

The unconfined compressive strength (UCS) of rock is a basic parameter for the design of foundations resting on rock. However, it is often very difficult to retrieve intact rock core specimens for the UCS test due to mechanical breaking or natural fracturing of the rock core during the drilling process. In such cases, it becomes obligatory to correlate UCS values based on the point load strength index test results. Correlation between the UCS and the point load strength index test results has been observed to be inconsistent in many instances and hence a need for another such correlation with a relatively higher degree of accuracy to predict UCS values of rock sample has been generated. An endeavor has been made to correlate the UCS value based on the test results of a splitting tensile strength test (STS) by conducting both the tests on various rock samples. Though the UCS test provides compressive strength and the STS test provides tensile strength of a rock, a dimensional analysis technique has been used to correlate these properties. The predicted UCS results are compared with the actual lab UCS test results to validate the mathematical equation thus developed. It has been observed from comparison that this equation can be used to predict UCS values from STS results with a fair degree of accuracy. Thus the Dimensional analysis has established a provisional rule-of-thumb to correlate the UCS with STS test results and further proved that, it is an easy and sufficiently accurate analytical tool.

The Influence of Microwave Preheating on Grindability of Low Rank Turkish Coal Using Impact Strength Index (ISI)

In this study, the effect of microwave treatment on grindability of low rank Turkish coal has been investigated. Coal samples (–9.52 + 3.18 mm) was treated by microwave at a frequency of 2.45 GHz with different residence time (15–180 sec). In order to determine the grinding resistance of lignite samples treated by microwave oven, the impact strength index test was applied for each treated and untreated sample and compared with each other. Experimental results have shown that significant increases in grindability without damaging the coal structure were achieved when the coal samples were exposed to microwave radiation. The impact strength index of samples decreased up to 265%.

An Evaluation of the Impact Strength Index as a Criterion of Grindability

In this study, Hargrove Grindability Index and Impact Strength Index values of coals collected from 17 coal seams in the Zonguldak Hardcoal Basin were determined. Then, the effect of the Impact Strength Index test on grindability was examined by investigating the relationship between Hargrove Grindability Index and Impact Strength Index values. The results indicated that the best relationship between Hargrove Grindability Index and Impact Strength Index values was found to be in the form of a parabolic function, i.e., coals with high values of Hargrove Grindability Index and low values of Impact Strength Index are much easier to grind. Furthermore, investigations have been conducted as to the effect of volatile matter and carbon contents as well as the rank and maceral composition of the samples on Hargrove Grindability Index and Impact Strength Index values. As a result, it has been proven that Impact Strength Index values can be assessed as a criterion of grindability.

The Uniaxial Compressive Strength of Soft Rock

Soft rock is a term that usually refers to a rock material with a uniaxial compressive strength (UCS) less than 20 MPa. This low strength range might be influenced by physical characteristics, such as size, saturation, weathering and mineral content. A number of uniaxial compression tests have been conducted onto soft rock samples. The results showed that the strength reduced significantly in saturation. The reduction was also caused by weathering, the strength of distinctly weathered rocks were lower than that of partially weathered rocks. In conjunction with the uniaxial compression test, point load strength index tests, IS(50), have also been conducted in order to obtain a correlation between the UCS and the point load strength index IS(50). The results showed that the IS(50) could well be correlated with the UCS. A conversion factor of 14 is proposed for soft rock materials.

A new portable rock strength index test based on specific energy of drilling

A new portable rock strength index test based on specific energy of drilling

Soil Strength Indices as Indicators of Consolidation

ABSTRACT SHEAR strength indices are often used to estimate soil characteristics related to erosion. The purpose of this study was to evaluate the effectiveness of using soil strength indices as indicators of soil changes caused by consolidation. Fall-cone, torvane shear, and pocket penetrometer measurements were obtained on clay, silt loam, and fme sand soils as a function of soil water stress history and time. Also, wet aggregate stability was measured for the clay soil. Prestress suction was the dominant mechanism for strengthening the three soils. Time effects were less pronounced. The fall-cone was the best indicator of consolidation and the pocket penetrometer was also effective with some limitations. The torvane shear device was the least effective index for detecting strength changes, although it worked well on the silt loam soil. The three index tests did not rank the three soils the same in order of increasing strength, suggesting that the validity of using index tests to rank or compare soils is questionable. The results of the study indicated that proper strength index tests may be effective in characterizing relative changes in stability of a given soil over time.

Fracture frequency in mudrocks: an example from the Queenston Formation of southern Ontario

In weathered surface exposures of the Queenston Formation (a red mudrock of Upper Ordovician age), an important fracture type appears as curved partings of generally low dip. Excavation of these fractures shows them to be continuous (for many metres), contorted, ranging in orientation from horizontal to vertical, and to be closely associated with small-scale slickensided surfaces. Evidence of water movement along these fractures is present. They are considered to be large soft sediment deformation shears, their present aperture being due to stress release.Detailed examination of core samples of the formation reveals numerous small slickensided shears, present throughout the unit but sometimes only revealed by core breakage. The frequency of these slickensides correlates directly with clay content and inversely with calcite content. In addition, their frequency is inversely correlated with point load strength index. Engineering geologists normally would not advocate the prediction of fracture frequency of a geological material from a strength index test or a compositional parameter. However, evidence presented here suggests that such a prediction is possible for certain fracture types in this, and perhaps other, red mudrocks. Key words: red mudrock, slickensided fracture frequency, point load test, calcite content.

Strength and Durability Properties of Core Lithologies from Coal-Bearing Tyonek Formation, Cook Inlet Region, Alaska: ABSTRACT

The Tyonek Formation (late Oligocene to middle Miocene) is a nonmarine unit of sandstone, siltstone, and claystone that contains large quantities of strippable subbituminous coal and lignite. The geotechnical properties, determined by field and laboratory tests on core from the Capps and Chuitna coalfields, dictate the equipment needs for excavation, determination of pit slope angle for mine planning, and durability of excavated spoil to weathering degradation. Point-load strength index tests are rapid and inexpensive field tests approximating the tensile and unconfined compressive strength of rock types. These tests, combined with laboratory uniaxial compression tests, were used to rank the formation lithologies in order of decreasing strength: coal (2,670 psi), carbonaceous claystone (825 psi), siltstone (435 psi), claystone (375 psi), and sandstone (145 psi). Except for coal, the lithologies range in hardness from soft soil to soft rock. Laboratory slake durability index tests, which measure the deterioration potential of rock masses as a result of cyclic wetting and drying, were used to rank lithologies in order of decreasing durability: claystone (49%), carbonaceous claystone (46%), siltstone (40%), and sandstone (20%). The cored Tyonek lithologies are noncarbonate, and their strength and durability increase with decreasing grain size and increasing clay-particle content. Compressional wave velocity, combined with point-load data, indicates that most of the rocks could be removed by bulldozers with ripping blades or by scrapers and shovels. However, coal (with rare exceptions, the strongest lithology tested) would require blasting before removal. End_of_Article - Last_Page 674------------

Comparison between the Strength Index Test and the Predicted Dynamic Strength Test in Predicting Motor Performance

Comparison between the Strength Index Test and the Predicted Dynamic Strength Test in Predicting Motor Performance