Korhan Adalier

Stone columns as liquefaction countermeasure in non-plastic silty soils

In many cases densification with vibro-stone columns cannot be obtained in non-plastic silty soils. Shear stress re-distribution concepts [1] have been previously proposed as means to assess stone columns as a liquefaction countermeasure in such non-plastic silty soils. In this study, centrifuge testing is conducted to assess the performance of this liquefaction countermeasure. Attention is focused on exploring the overall site stiffening effects due to the stone column placement rather than the drainage effects. The response of a saturated silt stratum is analyzed under base dynamic excitation conditions. In a series of four separate model tests, this stratum is studied first without, then with stone columns, as a free-field situation, and with a surface foundation surcharge. The underlying mechanism and effectiveness of the stone columns are discussed based on the recorded dynamic responses. Effect of the installed columns on excess pore pressures and deformations is analyzed and compared. The test results demonstrate that stone columns can be an effective technique in the remediation of liquefaction induced settlement of non-plastic silty deposits particularly under shallow foundations, or vertical effective stresses larger than about 45 kPa (1000 psf) in free field conditions.

Structural engineering aspects of the June 27, 1998 Adana–Ceyhan (Turkey) earthquake

Abstract On June 27, 1998, an earthquake measuring 5.9 on the Richter scale rocked the Adana–Ceyhan region of Turkey, an important industrialized and agricultural area of about two million population. It resulted in 145 deaths, more than 1,500 injuries and significant damage to more than ten thousand structures. In this paper, the observed structural damages are analyzed in view of the strong ground motion characteristics, the geological conditions and the building codes. Geotechnical aspects such as soil liquefaction and site amplification effects that considerably influenced the damage patterns at many areas are also briefly discussed. It is believed that the information presented herein is important to the engineering community as the observed seismic performance of the structures in this earthquake gives a good indication as to the aseismic strength of the whole Turkish building stock.

Seismic response of adjacent dense and loose saturated sand columns

Abstract Compaction or densification of loose saturated soils has been the most popular method of reducing earthquake related liquefaction potential. Such compaction of a foundation soil is only economical when limited in extent, leading to a case of an ‘island’ of improved ground (surrounded by unimproved ground). The behavior of the densified sand surrounded by liquefied loose sand during and following earthquakes is of great importance in order to design the compacted area rationally and optimize both safety and economy. This problem is studied herein by means of dynamic centrifuge model tests. The results of three heavily-instrumented dynamic centrifuge tests on saturated models of side-by-side loose and dense sand profiles are discussed. The test results suggest the following concerns as relates to ‘islands’ of densified soil: (1) there is a potential strength degradation in the densified zone as a result of pore pressure increase due to migration of pore fluid into the island from the adjacent loose liquefied ground; (2) there is a potential for lateral deformation (sliding) within the densified island as the surrounding loose soil liquefies.

Numerical analysis of embankment foundation liquefaction countermeasures

Computational simulations are presented for a unique series of centrifuge tests conducted to assess the performance of liquefaction countermeasure techniques. In these centrifuge tests, the dynamic response of an embankment supported on a liquefiable foundation (medium sand) is investigated. The experimental series included: (i) a benchmark test without a liquefaction countermeasure, (ii) foundation densiflcation below the embankment toe, and (iii) use of a sheet-pile containment enclosure below the embankment. This series of experiments documents a wide range of practical liquefaction response mechanisms (including countermeasure implementation). In order to numerically simulate the above centrifuge tests, a new calibrated soil stress-strain constitutive model is incorporated into a two-phase (solid-fluid) fully coupled Finite Element formulation. Comparison of the computational and experimental results demonstrates: (i) importance of post-liquefaction dilative soil behavior in dictating the dynamic response and deformation characteristics of the embankment-foundation system, and (ii) capabilities and limitations of the numerical modeling procedure.

Liquefaction of over-consolidated sand : A centrifuge investigation

A centrifuge testing study is conducted to investigate the effect of over-consolidation on liquefaction in clean saturated sand deposits. Thirty-four shaking tests on 11 level-ground models are performed. Soil models with Over-Consolidation Ratios (OCRs) of 1, 2, and 4 at relative densities of 35%, 50%, and 70% are tested. Model response to dynamic base shaking is monitored with accelerometers, pore pressure transducers, and displacement gauges. Test data show that the potential for liquefaction decreases with the increase in OCR, relative density, and prior shaking. The threshold peak acceleration needed to induce excess pore pressure increases as the OCR increases. Over-consolidated sand layers subjected to lower levels of excitation do not experience any excess pore pressure buildup even when shaken for a long duration. For acceleration marginally above the threshold, pore pressure buildup may be mild and liquefaction may be unlikely. As such, preloading can be a practical cost-effective liquefaction remedial technique in sandy soils under earthquake loading scenarios resulting in peak acceleration of up to about 0.15 g.

Liquefaction during the June 27, 1998 Adana-Ceyhan (Turkey) Earthquake

On June 27, 1998, a moderate earthquake measuring 5.9 on the Richter scale struck the alluvial plains of Cukurova in the Adana-Ceyhan region of Turkey. The earthquake resulted in 145 deaths, about a thousand injuries and significant damage to more than ten thousand structures. The coincidence of the projected location of the release of energy along the earthquake fault with a very vulnerable geological surface formation (the thick alluvial deposits of Ceyhan River containing loose sand layers) resulted in liquefied sediments of substantial thickness and extensive areal distribution. Liquefaction associated ground deformations such as lateral spreading, flow failures, ground fissures and subsidence, sand boils, and slope failures were observed. This paper presents and analyses the geotechnical aspects of this earthquake with the main emphasis on the observed liquefaction and associated ground deformations, together with the earthquake characteristics. The observed liquefaction mechanisms provide valuable information on the seismic response of the alluvial soils covering most of the Cukurova plains, an area of industrial and agricultural importance with more than 2 million inhabitants. The observations from this earthquake also provide us with an opportunity to further improve our understanding of the observed phenomena and their effects that can be expected during other future earthquake events around the world.

Ocean Rise Instability in Coastal Clay Slopes and Possible Countermeasures: A Centrifuge Modeling Study

Increase in saturation in natural clayey slopes along coastal zones as a result of tsunamis or storm surges may cause flow slides or failures. One of the common treatments is to increase the overall stability by soil replacement and/or re-compaction, which is often difficult to implement, expensive, and, most importantly, damages the natural vegetation. In this paper, remedial effectiveness of a relatively economical and environmentally friendly method involving insertion of geotextile strips with drainage capability into natural clayey slopes is evaluated through a series of centrifuge tests. The test results demonstrate the effectiveness of the employed technique to increase the stability of slopes and their drainage capability as well as to reduce the deformations under surcharge loadings.

On the Important Mechanical Properties of Rubber-Sand

More than a billion rubber tires are discarded annually around the world. Growing piles of discarded tires create fire and environmental hazards. Current disposal methods are mostly wasteful and costly. Tires possess high tensile strength, are chemically very stable, practically non-destructible and light in weight. All of these properties make tires a potentially useful geo-material. This paper presents the results of an extensive laboratory testing study investigating the potential of using shredded tires mixed with sandy soils (rubber-sand) as lightweight fill and backfill material in road construction. The results show that rubber-sand has significant promise for use as an earthwork fill material. In addition to its engineering benefits, such use of scrap tires would significantly contribute to solving the ever-growing tire disposal problem.

Alternative Remedial Techniques for Sheet-Piled Earth Embankments

This paper proposes two different remediation techniques, slightly different from conventional-type sheet-piled earth embankments, to reduce adverse effects induced by foundation liquefaction. A total of four centrifuge tests were conducted without and with countermeasure techniques, all involving model sheet-piles. The effectiveness of each countermeasure were compared and discussed based on the recorded displacements, accelerations, pore water pressure measurements and post-earthquake deformations. The tests showed that conventional sheet pile retrofitting method may not be fully adequate to reduce the distress in the embankment cased by liquefaction. However, the utilization of proposed countermeasures was found to be more significant in reducing the embankment settlement, deformation and cracking. Besides, they are practical and can be easily applied with less expense to existing structures.

Seismic Retrofit of Coastal Dikes

Soil liquefaction and associated ground failures have caused much damage to coastal and waterfront structures in the past major earthquakes. The prevalence of liquefaction in the coastal environment necessitates the development of appropriate remediation countermeasures. This paper presents an experimental study involving centrifuge physical modeling to assess the earthquake performance of countermeasure retrofit techniques for a liquefiable marine foundation under an existing coastal dike-embankment. Currently, such testing results offer a valuable alternative to studying actual full-scale dynamic response, since such data is virtually non-existent for retrofitted dikes. The response of a cohesive dike supported on a loose saturated sand layer is analyzed under dynamic base excitation conditions. In a series of four separate heavily instrumented model tests, this embankment foundation system was studied first without, and then with, the following three foundation liquefaction countermeasure-retrofit techniques: crushed gravel (drain) walls, cemented soil walls, and sheet-pile enclosure. The underlying mechanism and effectiveness of each countermeasure is discussed, based on the recorded dynamic response. All of the implemented countermeasures were found to significantly reduce embankment deformations. In some cases, cracking and lateral spreading of the dikes were practically eliminated.Copyright