Evaluation of damage to light structures erected on a fill material rich in expansive soil

The paper reports a study of the cause of defects in light structures and the toppling of a wall constructed on a fill material rich in Ankara clay. Laboratory tests were carried out on vertical and horizontal samples from boreholes and a trial pit was excavated near the damaged structures. The results showed that in the vicinity of the toppled wall, swelling pressures in the horizontal direction were greater than those measured in the vertical direction. The swelling properties of the fill material were higher than those of original Ankara clay as determined previously by other investigators, suggesting that breakdown of the cementing bonds and a change in the fabric are the main factors affecting the swelling pressure of disturbed and compacted expansive soils. The calculations to predict uplift showed a good agreement with the observations in the damaged structures. It is concluded that swelling was the main cause of the damage to the light structures at the study site and resulted from the highly expansive nature of the fill material, poor drainage, the semi-arid climate, poor construction methods and ineffective precautions. Some recommendations for minimizing the effects of swelling at the study site are briefly outlined.     

Seismic,ground motion and geotechnical characteristics of the 2011 Van-Erciş and Van-Edremit earthquakes of Turkey,and assessment of geotechnical damages

Two devastating earthquakes with moment magnitudes of 7.2 and 5.6 occurred on October 23, 2011 (Van-Erci? earthquake) and November 9, 2011 (Van-Edremit earthquake), respectively, in the Van Province of the eastern Turkey. The Van-Erci? and Van-Edremit earthquakes caused 604 and 38 fatalities, respectively, and heavy damage to buildings and other structures, particularly in Erci? town and Van City. In this study, characteristics of both main shocks and their geotechnical aspects, such as local site conditions, liquefaction phenomena and associated ground deformations and slope failures are evaluated. The failures of slopes and embankments and rock falls and ground liquefaction may also be indications of diluted ground deformation caused by the earthquake fault. It seems that a wedge-like body bounded by two fault planes was uplifted. As a result of this movement, the northern shoreline of Van Lake uplifted. The November 9, 2011 Van-Edremit earthquake was triggered due to the variation of crustal stresses induced by the October 23, 2011 earthquake. The effects of local site conditions have contributed to the damage of some parts of Erci? city and its vicinity; however, the ground liquefaction was not observed in the city as anticipated. With a magnitude of 5.6, the Van-Edremit earthquake is probably the smallest magnitude earthquake to cause liquefaction in Turkey so far.     

Geo-engineering properties and settlement of peaty soils at an industrial site (Turkey)

Peats consist of the partly decomposed remains of vegetation, which have accumulated in waterlogged areas. They are often unsuitable for supporting structures of any kind due to their high water content, high compressibility, low shear strength and high degree of spatial variability. The paper reports a preliminary study on peats from industrial sites in the city of Kayseri, Turkey. The soils in the study area are classified as peat to muck. The peats are fibrous at shallow depth and become amorphous as they extend to some 8 m depth. The ranges of geo-engineering properties are generally consistent with those reported in the literature, with some variation due to their higher mineral soil contents. The behavior of the peats is essentially frictional, with high friction and relatively small cohesion. The direct shear tests yielded higher shear strengths than those from the triaxial tests, due to the fact that the peat specimens used in the direct shear tests were rich in fibers and mineral soils. Back analysis of the settlement of heavy rolls of metal wires laid on the peat generally confirmed the consolidation properties of the soil determined in laboratory.     

Assessment of deformation modulus of weak rock masses from pressuremeter tests and seismic surveys

The deformation modulus of intact rock can be determined through standardized laboratory tests for heavily jointed rock masses but this is very difficult, while in situ tests are time-consuming and expensive. In this study, the deformation modulus of selected heavily jointed, sheared and/or blocky, weathered, weak greywacke, andesite and claystone were assessed, based on pressuremeter tests, geo-engineering characterization and seismic surveys. Empirical equations based on GSI and RMR values are proposed to indirectly estimate the deformation modulus of the greywackes. For the andesites, the spacing of the discontinuities is greater than the length of the pressuremeter probe hence the intact rather than rock mass deformation modulus is obtained. The pressuremeter test results from the claystones could not be correlated with the field data; the relationship between the ratio of rock mass modulus to intact rock modulus and RQD appears to give a better estimation of the deformation modulus.      

Empirical correlations between shear wave velocity and penetration resistance for ground shaking assessments

Prediction of the ground shaking response at soil sites requires knowledge of the soil, expressed in terms of shear wave velocity. Although it is preferable to measure this dynamic soil parameter in situ, this is often not economic at all locations. Existing correlations between shear wave velocity and penetration resistance have been assessed in this study and compared with correlations with SPT values obtained based on geotechnical and geoseismic data collected from a first-degree earthquake zone in Turkey. The results obtained support the findings of earlier studies that blow-count is a significant parameter in these correlations while type of soil has no important influence. The regression equations developed in this study compare well with most of the previous equations and exhibit good prediction performance. It is noted that better correlations are obtained when uncorrected blow-counts are used.      

Engineering geological characteristics of the 1998 Adana-Ceyhan earthquake, with particular emphasis on liquefaction phenomena and the role of soil behaviour

 The Adana-Ceyhan earthquake (M_s=6.2) occurred in the southern part of Turkey on 27 June 1998 and resulted in the loss of 145 lives and extensive damage to buildings in Ceyhan town and the settlement areas in its vicinity. Soil liquefaction, ground failure due to lateral spreading and rock falls occurred. The area of Adana is characterised by a large alluvial basin with a delta shape. Most of the basin is filled with Quaternary recent Holocene deposits. The recent rapid deposition of sediments and the very shallow groundwater table throughout the basin create conditions conducive to liquefaction. The results of a preliminary investigation of soil liquefaction caused by the earthquake and liquefaction assessments based on field performance data are presented together with evaluations concerning the likely contribution of the soils to the damage sustained by buildings. The results of the liquefaction susceptibility analysis indicated that the data from the liquefied sites were within the empirical bounds suggested by the field-performance evaluation method. It was also shown that shallow sand layers should have liquefied and the surface disruption observed on the site could be predicted by the bounds used for the relationships between the thickness of liquefiable sediments and the overlying non-liquefiable soil. Site-response analyses based on acceleration response spectra from the actual earthquake's strong motion records revealed that soil behaviour was one of the most significant factors in the damage to buildings caused by the earthquake. Received: 4 January 2000 · Accepted: 28 March 2000     

Relation between Kaiser effect levels and pre-stresses applied in the laboratory

This study aims to investigate the relation between the Kaiser effect (KE) levels and pre-stresses applied to rock samples in laboratory. For the purpose, a number of test specimens were obtained from different types of rock and a mortar block. Deformation and crack propagation stages were identified for each sample group. Based on the thresholds of these stages, the specimens were subjected to selected pre-stresses under uniaxial and axisymetric triaxial loading under laboratory conditions. Following the laboratory preloadings, acoustic emission (AE) experiments were carried out on the specimens under uniaxial loading conditions to determine the KE levels. The comparisons made between the laboratory pre-stresses and the KE levels suggest that the KE level is not equal to one of the pre-stress values or their differences, and should be related to combined effect of axial and confined pre-stresses, and some rock dependent characteristics.     

Water-induced variations in mechanical properties of clay-bearing rocks

This study presents the results obtained from laboratory tests carried out on different types of clay-bearing rock collected from various parts of Turkey, to quantify the effects of water content on mechanical properties of the rocks, and to develop a method for estimating the rock strength and deformability at any water content based on physical properties. For this purpose, in addition to physical properties of the rock types collected, needle penetration resistance, uniaxial compressive strength, tensile strength and modulus of elasticity were determined on a number of specimens with different water contents. The results suggest that with increasing the water content the reductions in the uniaxial compressive strength, modulus of elasticity and tensile strength are up to 90%, 93% and 90%, respectively, from oven-dried to saturated conditions. Based on a series of empirical models developed and the comparisons between the experimentally determined mechanical properties and those predicted from the models, it is concluded that the suggested models seem to be very practical tools to estimate the mechanical properties of the clay-bearing rocks at any water content using the coefficients related to some physical properties of the rock material such as dry unit weight, water absorption by weight and porosity. In addition, needle penetration test is particularly suitable for such rocks to indirectly estimate their uniaxial compressive strength.     

Empirical models and numerical analysis for assessing strength anisotropy based on block punch index and uniaxial compression tests

This study aims to investigate the strength anisotropy associated with discontinuity orientation by performing block punch index (BPI) tests and uniaxial compressive strength (UCS) tests, and to develop some empirical relationships for estimating the BPI and UCS in the strongest direction, and the UCS from the BPI determined at any angle between the loading direction and weakness plane. The experimental results obtained from six rock types show that these rocks fall into the moderate-to-low strength anisotropy classes. The comparison between the observed and predicted UCS values indicated that the prediction performances of the equations developed are quite good. Numerical simulations revealed that numerically estimated BPI values are very close to experimentally determined values for each angle between the loading direction and the weakness planes involved by the BPI specimens. As the angle between the weakness planes and loading increases, plastic zones become wider and unsymmetrical. The results of this study are also applicable to anisotropic rocks outside the strength ranges of the rocks studied by the authors, but their degree of anisotropy should be in the range of low-to-moderate.     

Modifications to the geological strength index (GSI) and their applicability to stability of slopes

Determination of the strength of closely jointed rock masses is difficult since the size of representative specimens is too large for laboratory testing. This difficulty can be overcome by using the Hoek–Brown failure criterion. Since its introduction in 1980, the criterion has been refined and expanded over the years, particularly due to some limitations in its application to poor quality rock masses. In the latest version, the geological strength index (GSI) was introduced into the criterion by its originators. However, the GSI classification scheme, in its existing form, leads to rough estimates of the GSI values. Another particular issue is the use of undisturbed and disturbed rock mass categories for determining the parameters in the criterion, for which clear guidelines are lacking. Furthermore, the data supporting some of these revisions, particularly the latest one, have not been published, making it difficult to judge their validity. In this study, in order to provide a more quantitative basis for evaluating GSI values, some modifications are suggested by introducing easily measurable parameters with their ratings and/or intervals which define the blockiness and surface condition of discontinuities. In addition, a method is proposed to assess the influence of disturbance on rock mass constants due to the method of excavation. The modifications to the GSI and the suggested method have been applied to slope instability case histories selected from Turkey by performing back analysis, to discuss the validity of the criterion and the methodology of parameter estimation. It was shown that the failure conditions in each case were confirmed, i.e. the analysed failure surfaces satisfied factors of safety of unity, when the suggested modifications and disturbed rock mass condition are considered. On the basis of the results, a chart to assess the effect of disturbance in terms of method of excavation was also suggested. The back analysis of a spoil instability indicated that spoil pile materials consisting of blocky and angular rock pieces could be categorized as a disintegrated rock mass in the GSI classification and the criterion seemed to be applied to such materials. The method suggested herein must, however, be verified by additional data from slope failures before more precise guidelines can be formulated.