Abdallah I. Husein Malkawi

Uncertainty and reliability analysis applied to slope stability

In this paper, reliability analysis of slope stability is presented using two methods of uncertainty first-order second-moment method (FOSM) and Monte Carlo simulation method (MCSM). The results of these methods are compared using four recognized methods of slope stability. These are Ordinary method of slices, simplified Bishops method, simplified Janbus method and Spencers method. Two illustrative examples are presented in this paper: one is homogenous slope and the other is non-homogeneous layered slope. The study shows that the reliability index (β) is independent of the seed random number generator and a sample size of 700 or greater is a good choice for MCSM. In the case of homogeneous slope a good agreement is observed between the calculated (β) using FOSM and MCSM for both the Ordinary and the Bishops method. However, slight difference in (β) is observed between the two uncertainty methods whether Janbus method or Spencers method is used. In the case of the layered slope good agreement is obtained between the two uncertainty methods for Ordinary, Bishop and Janbu methods. Similar to example 1, Spencers method shows also slight difference in (β) between FOSM and MCSM methods. Model uncertainty is addressed by evaluating the relative performance of the three slope stability methods i.e. Ordinary, Bishop and Janbu methods as compared to Spencers method.

Swelling-shrinkage behavior of natural expansive clays

Abstract The swell-shrinkage behavior of expansive clays was investigated in four soils of different plasticity cyclic swelling. To simulate drying temperatures typical of site conditions, two shrinkage schemes were adopted, partial and full shrinkage. After each cycle, the expansive characteristics of the soils were assessed. Furthermore, the physical and microstructural changes due to cyclic swelling were also studied, respectively, through an ultra-sonic investigation and scanning electron microscope observations. The results showed that cyclic swelling and shrinkage has a marked influence on the expansive behavior of clays. Generally speaking, a decrease in the swelling ability of the clays, corresponding to a reduced water absorption capability, was observed when the soils were alternately wetted and partially shrunk. On the other hand, an increase in the swelling potential was noted when the soils were fully shrunk. In either case, equilibrium can be attained after several cycles. As the number of cycles increase, further destruction of large aggregates and disorientation of structural elements takes place. Approximately after the fifth cycle, the fabric becomes almost disoriented, consequently further changes in expansibility disappear. The scanning electron microscope analysis showed that for partial shrinkage the structural elements exist mainly as edge to face contacts with a tendency to form a turbulent flocculated system while a horizontal clay particle orientation was observed when the specimens were cyclicly wetted the fully shrunk. In parallel, the ultrasonic wave transmission velocity increased with the number of cycles in the first case, and decreased when transmitted through a fully shrunk soil sample.

Effects of organic matter on the physical and the physicochemical properties of an illitic soil

The main thrust of this study is to investigate the effects of organic matter on the physical and the physicochemical properties of illitic soils. For this purpose, organic matter (peat) was added to inorganic illitic clayey soil at eight levels (0%, 5%, 10%, 12.5%, 15%, 17.5%, 20%, and 30% by weight). The physicochemical properties of the resulting soils were determined using a Grain Size Analyzer (GSA) with specific surface area measurement, Scanning Electron Microscopy (SEM), and Infrared Spectroscopy (IR). The physical properties of the mixtures were determined by conducting a series of laboratory tests including Atterberg limits, compaction, unconfined compressive strength, and swell characteristics tests. The results showed that at low organic contents (in general less than 15%) the soil particles tend to aggregate, whereas at higher organic contents the soil particles tend to disperse. Also, the IR tests showed that direct chemical interactions took place between the organic and the inorganic fractions of the mixtures. The tests on the physical properties showed that at low organic content (up to 10%) the plasticity index slightly increased then after, the plasticity index decreased with increasing organic content. Organic matter has shown to decrease the maximum dry density and increase the optimum water content, nevertheless, although organic matter decreased the soils compactability, the feasibility of compaction of slightly organic content soils still exists. Moreover, it was shown that organic matter decreased the peak strength values and increased the water contents at these peak strengths. The final free swell for illitic soils increased with increasing levels of added organic matter.

Reliability-based optimization of laterally loaded piles

A general approach to the reliability-based analyses and the optimum designs of laterally loaded piles (LLOP) is presented. This approach takes into consideration all behavior and side constraints specified by standard specifications for piles. Additionally, the casual effect of corrosion of piles with time is considered in formulation with limiting state functions. The solution to reliability-based problems is obtained by a computer program (RELLOP). A general reliability based methodology is developed and implemented in the developed computer program (RELLOP) for both element and system limit states. Numerical examples demonstrating the feasibility of considering multiple limit states and system reliability requirements in the design of laterally loaded piles are presented. Effects on the reliability-based design solution of allowable reliability levels, and time of exposure to corrosion are also illustrated.

Locally derived earthquake ground motion attenuation relations for Jordan and conterminous areas

Abstract The most recent catalogue of earthquakes in Jordan and conterminous areas is used to derive formulae for the principal seismic ground motion parameters of peak ground acceleration (PGA), surface wave magnitude (Ms), Mercalli intensity (I0(MM)), and epicentral distance (R). In this context, empirical relations characterizing earthquake ground motion attenuation in Jordan are developed. The main purpose of this paper is to assist engineers in estimating ground motion parameters in the pre-planning and design stages of construction as well as to help seismologists in decisions concerning the installation and operation of earthquake strong motion instrumentation around the country.

The Aqaba Earthquake of November 22, 1995

This study concentrates on the assessment of the structural damages caused by the Aqaba earthquake and attempts to give a better understanding of the geological, geotechnical and structural response following an earthquake event, through focusing on the understanding of the dynamic response of local site conditions to strong shaking and assessing structural performance. Furthermore, this paper calls for future efforts toward enforcing the seismic code provisions for all structures and improving the construction practices in a seismic prone region.

Probabilistic seismic hazard zonation of Syria

Earthquake hazard maps for Syria are presented in this paper. The Peak Ground Acceleration (PGA) and the Modified Mercalli Intensity (MMI) on bedrock, both with 90% probability of not being exceeded during a life time of 50, 100 and 200 years, respectively are developed. The probabilistic PGA and MMI values are evaluated assuming linear sources (faults) as potential sources of future earthquakes. A new attenuation relationship for this region is developed. Ten distinctive faults of potential earthquakes are identified in and around Syria. The pertinent parameters of each fault, such as theb-parameter in the Gutenberg-Richter formula, the annual rateλ4 and the upper bound magnitudem1 are determined from two sets of seismic data: the historical earthquakes and the instrumentally recorded earthquake data (AD 1900–1992). The seismic hazard maps developed are intended for preliminary analysis of new designs and seismic check of existing civil engineering structures.

Probabilistic Seismic Hazard Zonation and Dynamic Site Periods Mapping for Major Cities in Jordan

Seismic hazard maps were developed for major cities in Jordan (Amman, Zarka and Irbid). These maps show the Peak Ground Acceleration (PGA) on bedrock with 90% probability of not being exceeded for an economical life time of 50, 100 and 200 years respectively. The probabilistic (PGA) values were calculated based on a rupture fault model incorporated in the computer program FRISK (McGuire, 1978). Ten distinctive seismic sources are identified in Jordan and vicinity. The pertinent parameters of each sources, are determined from two sets of seismic data : the historical earthquake records up to 1899 and the instrumentally recorded earthquake data covering the period from 1900 A.D. to December 1992. Acceleration attenuation relationship given by Husein Malkawi and Fahmi, (1995) and the rupture relationship based on empirical relationships of historical fault ruptures published by Ambraseys (1988) were used to estimate the peak ground acceleration. Maps of dynamic site periods for the three major cities under study were developed by using the computer program SHAKE (Schnabel et al, 1972) in which earthquake time histories of the following strong earthquakes were used in the analysis : El-Centro, Taft and Erzangan and Dead Sea Earthquakes. The maps developed in this study are intended for preliminary analysis of new designs and seismic check of existing civil engineering structures as well as for recommending land-use regulations in the cities investigated.

Geotechnical Study of Landslides Resulting From a Highway Construction in Jordan

Landslides in Jordan have caused numerous problems during the past 40 years. The most critical slides occurred during the period of 1991/1992 after exceptional heavy rain and snowfall. Many disastrous landslides occurred along the newly reconstructed international highway that links Amman, Jerash and Irbid. Causes for these slides are attributed mainly to the lack of a comprehensive overview and geotechnical understanding of the problem.Many investigators have been interested in this problem of finding an adequate solution to such landslides in Jordan either by using theoretical analysis or by using computer software to solve the slope instability problems. A detailed study was conducted at the Jordan University of Science and Technology to investigate the potential causes and measures for this problem. Seven landslides along the mountainous section of this international highway were reviewed. One of these landslides was thoroughly investigated using a three-dimensional computer program called JUST-SLOPE introduced at the Jordan University of Science and Technology campus. Results of this study indicate that landslides at this site could have been predicted had this technique been applied prior to the occurrence of this slide.

Application of extreme value statistics to annual maximum magnitudes in Jordan employing a mixture distribution

The concept of extreme value mixture distribution (EV mix ) has been implemented in this study to estimate maximum earthquake magnitude occurrence. The EV mix model is applied to annual maximum earthquake magnitude occurrence in Jordan and conterminous regions spanning over the period 1918 to 1997. The maximum likelihood method, in conjunction with the two optimization methods, was employed for determining the statistical parameters of the Gumbels asymptotic distribution, i.e., GI, and the extreme value distributions EVIII and EV mix . The Simplex method of Nelder and Mead (1965) was found to be more successful in obtaining the maximum likelihood estimators of the three given distributions than the Newton-Raphson method. The difficulties inherent to the Newton-Raphson method were overcome by the Simplex method. It is shown in this study that the EV mix model fits the observed annual maxima far better than GI and EVIII models. In addition, the maximum likelihood estimators obtained using the Simplex method were used to calculate the earthquake risk for a given return period and a design lifetime of structures.