Zeynal Abiddin Erguler

A simple test and predictive models for assessing swell potential of Ankara (Turkey) Clay

Abstract During the past three decades, damage due to swelling action of Ankara Clay has been observed more clearly in some parts of Ankara where rapid expansion of the city led to the construction of various kinds of structures. In this study, a comprehensive research program has been conducted (i) to investigate the effect of remoulding and desiccation on the swelling behavior of Ankara Clay and its swelling anisotropy, (ii) to estimate depth of active zone, (iii) to develop a simple technique in determining the magnitude of swelling based on water content of the soaked specimen after 24 and 72 h ( w max24,72 ), and (iv) to produce predictive models which could be used to estimate the swelling potential of Ankara Clay from its mineralogical and simply measured engineering characteristics. A laboratory testing program was carried out using both undisturbed, and remoulded and desiccated samples selected from 20 different locations. Montmorillonite was identified as being the main clay mineral present. Based on the moisture content variation with depth, the active expansive zone was considered to be about 2 m. The test results suggest that swelling pressure of the clay considerably decreases and/or dies out when the water content is greater than 30%. It is also noted that the measured lateral swelling is significantly in excess of the vertical equivalent indicating an anisotropy with respect to swelling. Statistical assessments indicate that a new parameter ( w max24,72 ) from a simple test, suggested in this study, is a very strong parameter for predicting swelling parameters of Ankara Clay. Based on 60 empirical predictive equations with coefficients of correlation between 0.96 and 0.66 from multiple regression analyses, w max24,72 , methylene blue value, liquid limit, dry unit weight and smectite content are the most important index and mineralogical properties to predict the swelling parameters of Ankara clay with small deviations from the measured values.

Swelling Properties of Ankara (Turkey) Clay with Carbonate Concretions

Geology, sedimentation, and arid climate influence the formation of the expansive soil in Ankara, the capital of Turkey. The soil called Ankara clay locally bears carbonate concretions at shallow depths in the western parts of the city. To better understand the swelling properties of the soil, a detailed investigation was conducted at the Beytepe Campus area of Hacettepe University, where Ankara clay with carbonate concretions is typically observed. The principal aims of this investigation were to study the engineering properties, mineralogical composition, and swelling characteristics of the clay; to investigate the effect of carbonate content on the swelling behavior of Ankara clay; to develop empirical relationships for predicting the swelling pressure and swelling percentage of the clay from its index and mineralogical properties to be used when it contains carbonate concretions; and to generate swelling maps of the site for further engineering practice. Test results indicate a strong relationship between the presence of carbonate content and swelling parameters. Statistical assessments suggest that the empirical equations developed in this study exhibit superior prediction performance compared to those based on a data set using Ankara clay samples generally free from carbonate concretions and nodules. One of the prediction equations using only three parameters also was applied to the data set from Turkey and other countries. This equation showed acceptable performance for a cheap first cut, particularly for field engineers who need to make decisions based on limited data. In addition, swelling maps of the study site were generated based on the swelling data derived from the proposed predictive equations.

ISRM Suggested Method for the Needle Penetration Test

Estimation of mechanical properties of intact rock is usually required for assessment of the stability of rock structures. They are also important elements of the rock classifications used in empirical assessment of rock masses. Measurement of these properties requires laboratory testing, which must be performed on samples of certain dimensions to fulfill testing standards and/or suggested methods. Laboratory tests are also time-consuming due to sample preparation, as well as experimental procedures often require high-capacity loading devices. High-quality core samples recommended by standards and/or suggested methods for the laboratory tests cannot always be obtained, particularly from weak and clay-bearing rocks. For these reasons, some simple and inexpensive index test methods have been developed to indirectly estimate the mechanical properties of intact rock (ISRM 2007). However, even preparation of smaller samples from weak and clay-bearing rocks for some index tests is still troublesome. In addition, geo-engineering and/or restoration studies on natural and man-made historical rock structures and monuments or buildings built with masonry construction techniques may require the determination of mechanical properties of intact rock. Sampling from such ancient sites is not allowed due to preservation, and environmental and other concerns resulting in the lack of mechanical data for those studies. To overcome the above-mentioned difficulties, a portable, lightweight and non-destructive testing device, called needle penetrometer, was developed in Japan and released as a suggested method by the Rock Mechanics Committee of the Japan Society of Civil Engineers (JSCE-RMC 1980). Similarly, Public Works Research Institute (PWRI 1987) published a draft manual of the test for weak rock mass Please send any written comments on this ISRM Suggested Method to Prof. Resat Ulusay, President of the ISRM Commission on Testing Methods, Hacettepe University, Department of Geological Engineering, 06800 Beytepe, Ankara, Turkey.