Schmidt Hammer Rebound Values Research Articles

Detection of internal defects of concrete structures based on statistical evaluation of healthy part of concrete by the noncontact acoustic inspection method

A noncontact acoustic inspection method was developed to perform measurements from a long distance (usually about 5 to 7 m but even over 30 m) and detect internal defects (up to 10 cm in depth) of concrete structures using a long-range acoustic device and a laser Doppler vibrometer. An algorithm was also proposed to detect internal defects of concrete by combining two acoustic features, the vibrational energy ratio and spectral entropy obtained by our measurement. However, in actual concrete structures, it is difficult to distinguish a boundary between a healthy part and a defective part owing to influences such as the shape of internal defects, age-induced deterioration, and the surface condition of concrete. Therefore, we propose a method to statistically evaluate the distribution of the healthy part of concrete and extract the healthy part to identify the defective part. By this proposed method, the actual concrete floor slab bridge was measured from 33 m away and some internal defects were detected and visualized. Furthermore, a result for a railroad tunnel was compared with the Schmidt hammer rebound value and elastic wave velocity to verify the validity of the proposed method.

Field estimate of paleoseismic slip on a normal fault using the Schmidt hammer and terrestrial LiDAR: Methods and application to the Hebgen fault (Montana, USA)

AbstractThe weathering characteristics of bedrock fault scarps provide relative age constraints that can be used to determine fault displacements. Here, we report Schmidt hammer rebound values (R‐values) for a limestone fault scarp that was last exposed in the 1959 Mw 7.3 Hebgen Lake, Montana earthquake. Results show that some R‐value indices, related to the difference between minimum and maximum R‐values in repeated impacts at a point, increase upward along the scarp, which we propose is due to progressive exposure of the scarp in earthquakes. An objective method is developed for fitting slip histories to the Schmidt hammer data and produces the best model fit (using the Bayesian Information Criterion) of three earthquakes with single event displacements of ≥ 1.20 m, 3.75 m, and c. 4.80 m. The same fitting method is also applied to new terrestrial LiDAR data of the scarp, though the LiDAR results may be more influenced by macro‐scale structure of the outcrop than by differential weathering. We suggest the use of this fitting procedure to define single event displacements on other bedrock fault scarps using other dating techniques. Our preliminary findings demonstrate that the Schmidt hammer, combined with other methods, may provide useful constraints on single event displacements on exposed bedrock fault scarps. Copyright © 2018 John Wiley & Sons, Ltd.

Effect of impact velocity, block mass and hardness on the coefficients of restitution for rockfall analysis

One of the most significant input parameters in rockfall trajectory modelling is the Coefficient of Restitution, which controls block rebound. In particular, in the design of rockfall barriers, it can significantly affect their height. In practice, the coefficients of restitution are acquired by field or laboratory tests, back analyses of known events, experience or, most commonly, suggested values connected to the slope material. Furthermore, to account for the effect of impact velocity or block mass, scaling factors are available. However, the suggested values are based on a qualitative description of the slope material, and the scaling factors are not well documented, nor do they account for the effects of impact velocity and block mass simultaneously. In this paper, a semi-empirical correlation is proposed that takes into account the Schmidt hammer rebound value of both the slope and block material as well as the impact velocity and block mass. This was derived by an extensive laboratory experimental study (445 impact tests) of a one-dimensional drop of spherical blocks onto planar surfaces. The semi-empirical correlation proposed adequately describes the responses observed under the circumstances imposed in the laboratory.

Evaluating the pull-out load capacity of steel bolt using Schmidt hammer and ultrasonic pulse velocity test

Steel bolts are used in the construction industry for a large variety of applications that range from fixing permanent installations to temporary fixtures. In the past much research has been focused on developing destructive testing techniques to estimate their pull-out load carrying capacity with very little attention to develop non-destructive techniques. In this regards the presented research work details the combined use of ultrasonic pulse velocity and Schmidt hammer tests to identify anchor bolts with faculty installation and to estimate their pull-out strength by relating it to the Schmidt hammer rebound value. From experimentation, it was observed that the load capacity of bolt depends on its embedment length, diameter, bond quality/concrete strength and alignment. Ultrasonic pulse velocity test is used to judge the quality of bond of embedded anchor bolt by relating the increase in ultrasonic pulse transit time to the presence of internal pours and cracks in the vicinity of steel bolt and the surrounding concrete. This information combined with the Schmidt hammer rebound number, R, can be used to accurately identify defective bolts which resulted in lower pull-out strength. 12 mm diameter bolts with embedment length of 70 mm and 50 mm were investigated using constant strength concrete. Pull-out load capacity versus the Schmidt hammer rebound number for each embedment length is presented.

Correlation relationships between mechanical parameters of Bulgarian crushed-rock aggregates utilized in railway construction

Crushed-rock aggregates from 11 railway ballast-producing quarries in Bulgaria have been investigated. The test materials consist of igneous and sedimentary rocks of different ages: basaltic andesite, trachyte, diabase, andesitic tuff, quartz-cemented sandstone, dolomite and five varieties of limestone. The standard laboratory tests (Los Angeles, micro-Deval and point load) and in-situ test (Schmidt hammer) were carried out for determination of the following mechanical properties of aggregates: resistance to fragmentation; wear resistance; strength; and rock hardness. Results show that Los Angeles coefficient (LA) values range from 11.9% to 28.4%. The micro-Deval coefficient (MDE) varies between 3.7% and 22.4%. The point load strength index (IS(50)) is between 4.0 MPa and 8.8 MPa. The Schmidt hammer rebound value (SHV) ranges from 34.4 to 60.2. The possibility of predicting the Los Angeles and micro-Deval coefficients from the Schmidt hammer rebound value and the point load strength index was studied. Regression analysis shows a strong correlation between Los Angeles coefficient and point load strength index (coefficient of determination R2=0.93), a good correlation between the Los Angeles coefficient and the Schmidt hammer rebound value (R2=0.62) and moderate correlation between the micro-Deval coefficient and the Schmidt hammer rebound value (R2=0.51).

Forensic Excavation of Rock Masses: A Technique to Investigate Discontinuity Persistence

True persistence of rock discontinuities (areas with insignificant tensile strength) is an important factor controlling the engineering behaviour of fractured rock masses, but is extremely difficult to quantify using current geological survey methodologies, even where there is good rock exposure. Trace length as measured in the field or using remote measurement devices is actually only broadly indicative of persistence for rock engineering practice and numerical modelling. Visible traces of discontinuities are treated as if they were open fractures within rock mass classifications, despite many such traces being non-persistent and actually retaining considerable strength. The common assumption of 100% persistence, based on trace length, is generally extremely conservative in terms of strength and stiffness, but not always so and may lead to a wrong prediction of failure mechanism or of excavatability. Assuming full persistence would give hopelessly incorrect predictions of hydraulic conductivity. A new technique termed forensic excavation of rock masses is introduced, as a procedure for directly investigating discontinuity persistence. This technique involves non-explosive excavation of rock masses by injecting an expansive chemical splitter along incipient discontinuities. On expansion, the splitter causes the incipient traces to open as true joints. Experiments are described in which near-planar rock discontinuities, through siltstone and sandstone, were opened up by injecting the splitter into holes drilled along the lines of visible traces of the discontinuities in the laboratory and in the field. Once exposed the surfaces were examined to investigate the pre-existing persistence characteristics of the incipient discontinuities. One conclusion from this study is that visible trace length of a discontinuity can be a poor indicator of true persistence (defined for a fracture area with negligible tensile strength). An observation from this series of experiments was that freshly failed surfaces through pre-existing rock bridges were relatively rough compared to sections of pre-existing weaker areas of geologically developed (though still incipient) discontinuities. Fractographic features such as hackle and rib marks were typical of the freshly broken rock bridges, whereas opened-up areas of incipient discontinuity were smoother. Schmidt hammer rebound values were generally higher for the rock bridge areas, probably reflecting their lower degree of chemical and physical weathering.

Applying soft computing methods to predict the uniaxial compressive strength of rocks from schmidt hammer rebound values

The uniaxial compressive strength (UCS) of rock is widely used in designing underground and surface rock structures. The testing procedure of this rock strength is expensive and time consuming. In addition, it requires well-prepared rock cores. Therefore, indirect tests are often used to estimate the UCS, such as the Schmidt hammer test. This test is very easy to carry out because it necessitates less or no sample preparation and the testing equipment is less sophisticated. In addition, it can be used easily in the field. As a result, comparing with uniaxial compression test, indirect test is simpler, faster, and more economical. In this paper, the application of soft computing methods for data analysis named support vector regression (SVR) optimized by artificial bee colony algorithm (ABC) and adaptive neuro-fuzzy inference system-subtractive clustering method (ANFIS-SCM) to estimate the UCS of rocks from Schmidt hammer rebound values is demonstrated. The estimation abilities offered using SVR-ABC and ANFIS-SCM were presented by using experimental data given in open-source literatures. In these models, the Schmidt hammer rebound values (T1–T3, R1–R4) were utilized as the input parameters, while the UCS was the output parameter. Various statistical performance indexes were utilized to compare the performance of those estimation models. The results achieved indicate that the ANFIS-SCM model has strong potential to indirect estimation of the UCS of rocks from the Schmidt hammer rebound values with high degree of accuracy and robustness.

Determination of Granite Rock Massif Weathering and Cracking of Surface Layers in the Oldest Parts of Medieval Mine Depending on Used Mining Method

Abstract The paper presents the use of selected non-destructive testing methods for the purpose of specifying information on weathering and cracking of surface layers of granite rock massif in the medieval Jeroným Mine (the Czech Republic). This mine has been declared the National Heritage Site of the Czech Republic and its opening as a mining museum to the public is gradually prepared. Geological and geomechanical evaluation documents the possibility to find all kinds of weathering grades of rock massif in this mine. Two non-destructive methods have been tested, namely the measurement of ultrasonic pulse velocity and the measurement of Schmidt hammer rebound value. Field measurements were performed in two selected galleries to verify the application of such methods in specific conditions of underground spaces. Used mining method is one of the parameters later influencing cracking of rock massif. In selected galleries, two different mining methods were used which means that a part of a gallery profile was mined out by hand tools in the Middle Ages and another part of the profile was later mined out by blasting. Measurements in these galleries have enabled to analyse the influence of used mining methods on cracking of rock massif in the impaired zone, and, consequently, on ongoing weathering processes in those zones.

Mechanical characterization of Trebisacce stone: preliminary results

Trebisacce stone is a building material employed in the past for the construction of structural elements of the historical centre of Trebisacce and for the realization of ornamental elements of the northern part of Cosenza province.The outcrops of Trebisacce stone belong to the Albidona Formation and are located in the area of Sibari. Lithotypes which have been investigated, limestones, come from historical outcrops situated in the old town of Trebisacce.The aim of this study is to characterize Trebisacce stone, a carbonate rock with good mechanical and durability properties, and to compare results obtained performing different techniques of analysis. Tests which have been performed belong to both non-destructive techniques (Schmidt hammer test) and to destructive techniques (uniaxial compressive strength test). Relationship between Schmidt hammer rebound values and uniaxial strength was analyzed using different equations. Results obtained demonstrate that Trebisacce stone has good mechanical properties. No-destructive tests performed show that the Schmidt hammer device could be a useful tool in estimating rock strength values for engineering applications. Furthermore, the comparison between direct and indirect uniaxial compressive values, demonstrate which of the relationships proposed by many authors, could be better for evaluating the uniaxial compressive strength as a function of unit weight and Schmidt hammer rebound.

Nondestructive Testing Procedure to Evaluate the Load-Carrying Capacity of Concrete Anchors

AbstractConcrete anchors are extensively used in the construction industry. Their applications range from erecting permanent objects such as sign poles, direction signs, lighting poles, and so on, to temporary support structures. Several destructive testing equipment types exist in the industry that can be used to evaluate the load-carrying capacity of concrete anchors. However, no nondestructive testing method has been proposed that can estimate their load-carrying capacity. This study develops a new relationship between the pull-out load-carrying capacity, P, of concrete anchors and Schmidt hammer rebound value, R. It was observed from experimentation that the load-carrying capacity of the concrete anchors depends on the embedment length, anchor diameter, concrete strength, and anchor alignment. The effect of anchor alignment was also observed during experimentation, and anchors with ill alignment of more than 5% can lead to lower load-carrying capacity. In addition, it is also possible to identify the ...

Drilling rate prediction of an open pit mine using the rock mass drillability index

Besides intact rock properties, structural parameters of rock mass have strong effect on drilling rate. In this research, 11 different zones of an open pit iron mine were studied precisely to classify the area based on rock drillability point of view. Laboratory tests were conducted on the rock samples to determine strength parameters. Geological mapping of the rock facies was carried out and rock mass structural parameters as joint inclination, spacing, aperture and filling were recorded along with net drilling times of drill holes. Using these data, an empirical relation was developed to predict drilling rate (DR) using the rock mass drillability index (RDi) and also a relation that can predict uniaxial compressive strength (UCS) of rocks in terms of Schmidt hammer rebound values at this mine. In conclusion, all 66 zones of the mine area were classified according to the RDi. It was observed that RDi can reasonably predict drilling rate of rock masses. A new penetration rate model is defined based on the measured data and then compared with previous model of penetration rate from literature. Since the new model which involves not only intact rock mechanical properties but also structural properties of rock masses could attain better predictions in relation to the previous model.

Estimation of strength characteristics of different Himalayan rocks from Schmidt hammer rebound, point load index, and compressional wave velocity

Various rock types—including highly deformed to undeformed quartzites, granites, granitic gneisses, gneisses, metabasics (meta-amphibolites and meta-dolerite), and dolomites—collected from different formations of the Lesser and Higher Himalayas were tested to evaluate correlations between the uniaxial compressive strength (UCS) and the point load test (PLI), Schmidt hammer rebound (SHR) value, and compressional wave velocity (Vp). Various equations between UCS and PLI, SHR, and Vp were obtained using regression analysis. It was found that there is high scatter in the data when all lithologies are considered together, whereas this scatter is reduced when the lithologies are considered individually. This was attributed to wide variations in the mineralogical and textural characteristics of different rocks. Furthermore, it was also noted that quartzites exhibit high scatter in their data points, even though they are monomineralic. Thin section studies revealed that different microfabrics have been produced in the quartzites, due to the actions of different deformational phases during tectonic activity in the area. Therefore, it is necessary to treat deformed and undeformed rocks separately when deriving such equations.

Time-dependant surface deterioration of glacially abraded basaltic boulders by Fláajökull, SE Iceland

he surface deterioration of glacially abraded basaltic boulders by Fláajökull, SE-Iceland, deposited since the Little Ice Age maximum, was assessed based on measurements of micro-roughness, weathering rind thickness and Schmidt hammer R-values in order to find indices of relative age of the moraines. Micro-roughness of boulders was analysed using a Handysurf E35-B electronic profilometer working with a vertical resolution of 0.01 μm, which is a new method in geomorphology. A pilot microscopic analysis showed heavy fracturing within the weathering rind developed in fine-grained basalts, which is interpreted as inherited from mechanical weathering and responsible for deterioration of rock surfaces. A weak to moderate correlation was observed between time-dependent moraine rank and studied indices. Surprisingly, no chemical alteration was observed in analysed rock samples subject to weathering for more than a century. Results indicate that 80 years of weathering cause gradual increase in selected micro-roughness parameters, weathering rind thickness and decrease in Schmidt hammer rebound value. However, these indices of surface deterioration do not change on older moraines, which is attributed to exfoliation. The results do not provide unequivocal arguments in the ongoing discussion about the timing of the LIA maximum of Fláajökull, but encourage further use of the Handysurf E35-B electronic profilometer as a tool in determining initial stages of rock surface weathering.

10Be exposure age chronology of the last glaciation in the Krkonoše Mountains, Central Europe

A new chronology of the last glaciation is established for the Krkonoše (Giant) Mountains, Central Europe, based on in-situ produced 10Be in moraine boulders. Exposure ages and Schmidt Hammer rebound values obtained for terminal moraines on the northern and southern flank of the mountains suggest that the oldest preserved moraines represent early phases of the Last Glacial Maximum (LGM). Large moraines at the outlet of the Snowy Cirques (Śnieżne Kotły) and in the middle part of the Úpa (Obří důl) trough were deposited around 21ka while a series of smaller moraines above the LGM deposits represent readvances that occurred no later than 18.1±0.6ka, 15.7±0.5ka, 13.5±0.5ka and 12.9±0.7ka. An exposure age of 13.8±0.4ka obtained for protalus ramparts at the foot of the Úpská jáma Cirque headwall indicates that glaciers advanced only in north- to east-facing cirques during the Lateglacial. The last glacier fluctuation was synchronous with the Younger Dryas cold event. The timing of local glacier advances during the last glacial episode correlates with the late Weichselian glacier phases in the Alps and in the Bavarian/Bohemian Forest.

Multiscale structural and lithologic controls in the development of stream potholes on granite bedrock rivers

Jointing, veins, dikes, and fracture patterns influence the genesis of potholes in bedrock rivers. We use measures of surface rock strength (Schmidt hammer readings, joint orientation, and spacing) and subsurface rock properties (ultrasound velocity) to analyze the spatial relationship between joints and potholes in three rivers of the Spanish Central System: the Tietar, Manzanares, and Alberche rivers. At each site, we measured the dimensions of between 45 and 77 potholes; at least 50 randomly located Schmidt hammer rebound values, as well as Schmidt hammer values in a 15×15cm grid around each pothole; and ultrasonic p-wave velocities measured in a 15×15cm grid around a subset of 12 of the potholes. Results support our hypotheses that most potholes correlate with joints (89% of potholes are related to joint sets), potholes exhibit preferred orientations associated with dominant joints, and pothole genesis correlates more strongly with variations in substrate resistance than with hydraulics. We classify potholes by morphology and present a genetic sequence for specific morphologies in relation to substrate characteristics.

Deterioration of different stones used in historical buildings within Nigde province, Cappadocia

The Cappadocia region hosts various historical buildings constructed by several civilisations from long in the past until more recently. Some of these are big and significant buildings and their artistic, cultural and aesthetical features are quite attention-grabbing. The stones used in most of these buildings have deteriorated due to various effects. The correct identification of the deterioration mechanisms is of fundamental importance to design retrofitting and restoration procedures. In this study we aimed to determine the engineering properties and deterioration of the stones widely used in the different historical buildings in the Nigde region that forms the southern boundary of Cappadocia. 17 block samples (2 marble, 2 travertine, 6 tuff, 5 ignimbrite and 1 andesite) were taken – in accordance with the obtained permits – from stones that had fallen from the buildings and could not be used again as part of any restoration. With the purpose ofidentifying the deterioration of the building stones due to their geological structure and external effects, chemical and petrographic analyses were conducted along with detailed field observations. To determine the geomechanical properties (dry unit weight, water absorption, effective porosity, P-wave velocity, uniaxial compressive strength, slake durability index, capillary water absorption, Bohme abrasion value and Schmidt hammer rebound value) of the stones comprehensive laboratory research was carried out. The main cause of the deterioration observed in ignimbrites (UK3) and tuffs (AK3) with low strength and high porosity was humidity, especially at the capillary level. Significant deterioration observed on some stone samples was also due to the use of stones that exhibited poorer properties than the rest, although they came from the same quarry. Adding the negative effects of ground and surface water on top of these, severe damage on the stones in the formof flaking, discolouration and loss of strength were observed.

Measure of a Limestone Weathering Degree Using Laser Scanner

The weathering degree of the building materials and natural stones is generally quantified as the decrement of some mechanical features that can be measured experimentally by means of compressive tests or point load tests in the laboratory or Schmidt hammer tests carried out in situ. Such destructive or damaging tests are unacceptable in case of cultural heritage since even small amounts of damage must be avoided. This work shows a correlation between Schmidt hammer rebound values and the reflectivity that is detected by means of terrestrial scanner laser; therefore it allows assessing the weathering degree of buildings or stones in situ. The results demonstrate that such an investigation could be a significant alternative representing an innovative and non-destructive technique.

The control of mineral constituents and textural characteristics on the petrophysical & mechanical (PM) properties of different rocks of the Himalaya

Petrophysical and mechanical (PM) properties of a rock are primarily controlled by its mineral constituents and various textural parameters. Similar rock types in different tectonic setups may be characterized by different mineralogical compositions and textural properties because they might have suffered different deformational processes. This paper presents a study on the mineralogical and textural control on various PM properties in quartzites, granitoids, gneisses, metabasics and dolomite collected from different tectonic set ups. The inter relationships among mineral constituents, various textural parameters, Unconfined Compressive Strength (UCS), Schmidt hammer rebound (R-) value, seismic wave (both P- and S-waves) velocity and their attenuation characteristics were obtained using regression analyses. It has been concluded that there exists no relation between UCS and seismic wave velocity in quartzite, granitoids and gneisses, moderate positive relationship in metabasics and strong negative relationship in dolomite. It has further been noted that in quartzite and dolomite (monominerelic rocks), grain size dominantly control the seismic wave velocity as the relatively coarser grained samples have higher seismic wave velocity, whereas UCS is strongly controlled by grain size as well as the quantity and the orientation of the weak minerals like muscovite, biotite, calcite etc. In gneisses and granitic gneisses, preferred orientation of minerals especially the mica minerals, although in present small quantity is the main factor controlling UCS and seismic velocity. Both these properties increase with the increase in intensity of preferred alignment of minerals, whereas in metabasics it is the presence of amphibole+pyroxene minerals/feldspar that dominantly controls the seismic wave velocity.

Schmidt-hammer exposure-age dating (SHD) of rock glaciers in the Schöderkogel-Eisenhut area, Schladminger Tauern Range, Austria

Schmidt-hammer rebound values ( R-values) enable relative-age dating of landforms, with R-values relating to degree of weathering and therefore length of exposure. This method – recently termed as Schmidt-hammer exposure-age dating (SHD) – was applied to date five rock glaciers (size range, 0.01–0.12 km2) and one recent rockfall deposit at the study area Schöderkogel-Eisenhut, in the Schladminger Tauern Range (14°03′E, 47°15′N), Austria. The rock glaciers consist of gneiss or high metamorphic series of mica-schist that are comparable in their R-values. Four of them are relict (permafrost absent) and one is intact (containing patches of permafrost). On each of the five rock glaciers, SHD was carried out at 4–6 sites (50 measurements per site) along a longitudinal transect from the frontal ridge to the root zone. Results at all five rock glaciers are generally consistent with each other sharing statistically significant R-values along transects. The range between the highest and the lowest mean R-value at each of the five rock glaciers is 9.9–5.2. Using rock glacier length and surface velocity data from nearby sites, the rock glacier development must have lasted for several thousand years. Furthermore, by using SHD results from rock glaciers of known age from other sites in the region with comparable geology, approximate surface ages of 6.7–11.4 ka were estimated. This indicates long formation periods for all five rock glaciers. Our results suggest that many of the 1300 relict rock glaciers in central and eastern Austria were formed over a long period during the Lateglacial and Holocene period.

The Influence of Weathering on the Engineering Properties of Dunites

Weathering processes cause important changes in the engineering properties of rocks. In this study, dunites in the Bursa region in western Turkey were investigated and the changes in engineering properties due to weathering were evaluated. The studies were initiated with field observations including measurement of the characteristics of discontinuities such as spacing, aperture, fill material, roughness, and Schmidt hammer rebound value. Subsequently, laboratory studies were conducted in two stages. The first stage comprised mineralogical, petrographic, and chemical analyses. The second stage included physicomechanical tests to determine specific gravity, unit weights, water absorption, effective porosity, uniaxial compressive strength, P-wave velocity, and slake-durability index. According to these evaluations, the changes in engineering properties were determined to be mostly related to serpentinization at every stage of weathering. The most suitable parameters for characterizing the degree of weathering of the studied dunites are loss-on-ignition values, specific gravity, unit weight, water absorption, and effective porosity.