Increase In Liquefaction Resistance Research Articles

Role of geofoam inclusions on the liquefaction resilience of transportation geostructures

Though the effectiveness of geofoam buffers for improving the dynamic load response and seismic performance of road embankments and retaining walls is well-established, their role on soil liquefaction is not investigated by many. This study explores the potential of Expanded Polystyrene (EPS) geofoam inclusions for liquefaction mitigation in sands through a series of stress-controlled constant volume cyclic simple shear tests. The study quantifies the increase in liquefaction resistance of sand with geofoam inclusions and reduction in modulus degradation and shear deformations and increase in energy dissipation with loading cycles. Effects of geofoam density and thickness of the layer on the liquefaction response were also investigated through systematic series of experiments with geofoam of three different densities and two different thicknesses. Findings from this experimental study suggest that providing a thick low-density geofoam layer provided the maximum benefit among all the inclusions. Fundamental mechanisms governing this improved response are explored through a series of bender element tests. Results from this study confirm the effectiveness of geofoam buffers in mitigating liquefaction in granular soils and recommend their use in road embankments and retaining walls being constructed in zones of high seismicity to avoid liquefaction and associated lateral spreading failures in these structures.

Improvement of cyclic liquefaction resistance induced by partial saturation: An interpretation using wave-based approaches

Methods to estimate the liquefaction resistance in sandy soils have been proposed in the literature, involving correlations between cyclic resistance ratio and seismic wave velocities measured by in situ and laboratory tests. However, the applicability of these correlations has not been validated in sands improved with the induction of partial saturation. This study addresses the assessment of cyclic liquefaction resistance improvement induced by partial saturation using wave-based approaches. For this purpose, an experimental plan comprising cyclic triaxial and bender elements was carried out in a Portuguese natural sand. The studied soil is TP-Lisbon sand, a historically liquefiable soil collected in the ‘Terreiro do Paço’ site — next to the Tagus River in the centre of Lisbon. Notwithstanding, the results presented herein are compared against other liquefiable sands from Japan. The induced partial saturation was controlled by P-wave velocity measurements, which were contrasted against theoretical predictions performed in the light of Biot’s theory. The results confirmed the increase in liquefaction resistance by inducing partial saturation. Experimental results revealed that P-wave velocity provides a reliable prediction of liquefaction resistance in partially saturated conditions rather than S-wave velocity. The suitableness of these approaches was attributed to the presence of occluded air bubbles in partially saturated soils, which can be detected by the P-wave and not by the S-wave.

Cyclic Liquefaction Resistance of an Alluvial Natural Sand: A Comparison between Fully and Partially Saturated Conditions

Earthquake-induced liquefaction is one of the major causes of building damage as it decreases the strength and stiffness of soil. The liquefaction resistance of soils increases significantly as the degree of saturation decreases, making soil desaturation an effective measure for the mitigation of this phenomenon. This paper presents a comparative analysis of liquefaction resistance of an alluvial sand from Aveiro (Portugal) under fully and partially saturated conditions. For this purpose, an in situ characterisation based on CPTu and a laboratory series of cyclic triaxial tests were carried out. The cyclic triaxial tests were conducted under undrained conditions on remoulded specimens with different degrees of saturation, including the full saturation. On the other hand, the triaxial apparatus was instrumented with Hall-effect transducers to accurately measure the strains during all testing phases. In addition, it was equipped with piezoelectric transducers to measure seismic waves velocities, namely P-wave velocity, for evaluation of the saturation level of the specimen in parallel with the Skempton’s B parameter. Hence, relations between the B-value, and P-wave velocity and cyclic strength resistance are presented. The number of cycles to trigger liquefaction, considering the pore pressure build-up criterion, is presented for the different degrees of saturation. Results confirmed the increase in liquefaction resistance for lower degrees of saturation in this soil.

Influence of Fines Contents on Soil Liquefaction Resistance in Cyclic Triaxial Test

Liquefaction is the most detrimental ground failure caused by strong earthquakes. Ground liquefaction leads to associated foundation and superstructure failures due to loss of bearing capacity and excessive deformation. An appropriate assessment of liquefaction is critical to the seismic safety evaluation of foundations and super structures. In this study, a series number of isotropically consolidated undrained cyclic triaxial test have been performed to evaluate influence of fines contents on soil liquefaction resistance. A total of 96 cyclic triaxial test was run on the uniform medium Monterey No. 0/30 sand with six different percentages of fine content. A total of 198 cyclic triaxial test was performed on the uniform medium concrete sand with five different percentages of fine content. Four different relative densities of 30%, 45%, 50% and 60%, two confining pressure of 103kpa and 207 kpa, six stress ratios (0.2, 0.25, 0.3, 0.35, 0.4 and 0.45) have been used for series of cyclic triaxial tests on two different soil types. Laboratory cyclic triaxial tests were conducted systematically to produce liquefaction potential curves.At a constant overall void ratio and PI, the increase in fines content up to 12% in the clean sand causes a decrease in liquefaction resistance. Beyond 20%, the further increases in fines content results in increase in liquefaction resistance. The threshold fines content, which is in the range of 12–20%, observed from nearly 300 of laboratory test results in this study. Statistical analyses were performed to formulate functional relationships for predicting liquefaction resistance of soils containing fines. For evaluating liquefaction potential for soils containing fines content, soil with 12–20% of fines content should be paid more attention.

Effects of Fly Ash on Liquefaction Characteristics of Ottawa Sand

This paper presents the results of effects of non-plastic fines (Class F fly ash) on liquefaction behavior of Ottawa sand. Stress-controlled cyclic triaxial tests were performed on clean Ottawa sand, fly ash, and sand–fly ash mixtures containing 10, 20, 25, 30, 50, and 70% of fly ash. For the evaluation of the effects of confining pressure on liquefaction resistance, three series of tests were conducted at 34.48, 68.96, and 103.42 kPa initial effective confining pressures, except for pure fly ash. In the case of pure fly ash, tests were conducted only at an effective confining pressure of 34.48 kPa. The reversible shear stress was applied systematically by varying Cyclic Stress Ratio from 0.1 to 0.5. Addition of fly ash to sand resulted in decrease in liquefaction resistance initially and then increase in liquefaction resistance for fly ash contents up to about 20–25%. Increase in fly ash content beyond 25% was seen to decrease the liquefaction resistance.

Liquefaction triggering and post-liquefaction deformation of laminated deposits

As part of dynamic stability evaluations of earth embankments founded on laminated sand and clay deposits, the need to characterize their cyclic resistance became critical for the assessment of the embankment behavior and subsequent decisions on liquefaction mitigation measures. Due to lack of experimental and case history data on the effective stress behavior of such deposits, which are typically encountered in tidal and alluvial depositional environments, advanced laboratory tests on high quality undisturbed samples and numerical simulations using advanced constitutive models were performed to gain insight on liquefaction triggering and post-liquefaction accumulation of deformations under level and sloping ground conditions of such formations. Results indicated that the presence of clay laminations within sand deposits tends to increase the liquefaction triggering resistance. The increase in liquefaction resistance becomes more pronounced as the percentage of clay laminations increases. Numerical analyses results also indicated that void redistribution effects, often related to strain localization effects, tend to reduce as the thickness of sand laminations decreases, or as the clay lamination percentage increases.

Disasters – Special Focus on Earthquake Induced Soil Liquefaction

Disasters disrupt progress and destroy the developmental efforts, often pushing nations back by several decades. Disaster due to soil liquefaction is also one of them. A parametric study is taken up for disaster caused by soil liquefaction in present work. Tests had been conducted on saturated sand in the shake table at different accelerations varying from 0.1 g to 0.3 g. Uniaxial geogrid had been used to reinforce the fine sand. The rise of excess pore pressure is responsible for liquefaction and experiments have been done with reinforced sand. The liquefaction resistance of sand increases due to addition of geogrid layers. For 0.1 g at 35% density the average increase in liquefaction resistance is about 17.87%. Further by increasing acceleration to 0.3 g the liquefaction resistance further increase to 20.67%. In present paper efforts had been made to see the effect of reinforcement against liquefaction. There was decrease in rise of excess pore pressure with use of geogrid in shake table. Thus punching shear foundation failure of structures can be prevented. Thus geogrids can be used as anti soil liquefaction measure. Keywords: Disaster, Earthquakes, Goegrids, Liquefaction, Soil

Liquefaction Resistance of a Silty Sand Deposit Subjected to Preshaking Followed by Extensive Liquefaction

The effect of extensive liquefaction on the liquefaction resistance of heavily preshaken saturated silty sand is studied using a centrifuge experiment. The base of a 6-m homogeneous deposit was subjected to a total of 91 shaking events of different horizontal base accelerations and durations. Three event types were used in alternating patterns: mild preshaking Events A, stronger preshaking Events B, and strong liquefying Events C. The experiment was divided in two stages. In Stage One, reported in a previous publication, 66 preshaking Events A and B, were applied. In Stage Two, which is the focus of this paper, 25 additional shakings were applied which included two Events C in addition to continuing the same pattern of Events A and B. Stage One resulted in a significant increase in liquefaction resistance of the deposit. In Stage Two, extensive liquefaction produced by Events C resulted in a dramatic immediate reduction in liquefaction resistance of the deposit to a level comparable to that before preshaking. These findings are consistent with other reported field observations and laboratory results.

Cyclic liquefaction behaviour of a moderately cemented grouted sand under repeated loading

The aim of this paper is to provide an insight into the effects of a previous cyclic history “triggering” full liquefaction on the subsequent undrained cyclic behaviour of a moderately cemented grouted sand in terms of strength, deformability and pore pressure response. The research was conducted on sand specimens stabilized by a commercial mineral based chemical grout (“Silacsol”), capable of imparting unconfined compression strength (UCS) values ranging between 500kPa and 700kPa. Monotonic shear strength parameters of treated specimens were preliminary assessed through a series of isotropically consolidated drained triaxial tests (TX-CID). Afterwards, stress-controlled undrained cyclic simple shear (SS) tests were conducted on both treated and untreated sand specimens in order to evaluate the improvement provided by the grout on the liquefaction resistance of the sand. A significant beneficial effect of the grout was observed, regardless of the initial density of the pure sand. Finally the influence of a cyclic large preshearing on the undrained cyclic behaviour of the grouted sand was investigated by subjecting the specimens to a sequence of two cyclic loadings with the same stress ratio (CSR). After the first loading in which specimens were brought to full liquefaction, they were allowed to reconsolidate in approximately K0 conditions and then subjected to the second loading. An increase in liquefaction resistance induced by cyclic history was clearly apparent on treated specimens.Excess pore pressures build-up during the first cyclic loading on treated specimens followed a different trend compared to that observed on untreated ones. A significant difference was also observed on the excess pore pressure trends developed in the second loading compared to that developed in the primary loading. A simple model for the prediction of pore water pressure build-up of grouted sands during cyclic loading is proposed.

Liquefaction behavior of reinforced saturated sand under dynamic conditions

For reduction in liquefaction potential in liquefiable soils, the common practices are densification of strata, draining, vibroflotation, etc. For densification, the deployment of large plant and machinery is involved. Reinforced earth techniques may simplify the densification technique. The behavior of reinforced soil is well known. In the present paper, efforts had been made to see the effect of reinforcement against liquefaction. Uniaxial geogrid had been used to reinforce the fine sand. Tests had been conducted on the shake table at different accelerations varying from 0·1 to 0·3g. For particular value of acceleration, the densities of the sample were also varied from 35 to 65%. It was observed that after inclusion of 4 Nos. geogrid layers, the reduction in liquefaction potential was 17–20% at different values of acceleration on 35% density. At higher densities, the average increase in liquefaction resistance was 25%. Effect of surcharge was also studied on reinforced sand to simulate field conditions. For surcharge conditions at 50–65% densities, it is observed that average liquefaction resistance increased 28–45% at 0·3g for reinforced soil.

液状化対策地盤の巨視的動的応答特性とその調査法に関する検討

Sand compaction pile, SCP, is widely adapted to reclaimed ground as a counter-measure against liquefaction of ground during earthquake. However, many case studies imply that the current design with evaluation of improvement effects by N-value is, considerably conservative. In this paper, we propose a new evaluation method for the over-all dynamic properties of the improved ground in terms of a finite difference analysis and a non-linear seismic response analysis with homogenization theory. The finite difference simulation of seismic waves shows that both share wave and surface wave propagate with constant velocity, which can be estimated by homogenization method, even if in heterogeneous improved ground. The overall evaluation including the lateral earth pressure increase around SCP showed that the improvement effects were controlled not only by an increase in liquefaction resistance, but also by an decrease in dynamic amplitude and the natural period; these results are valid for the seismic resistant design for reclaimed grounds.

Numerical simulation of liquefaction behaviour of granular materials using Discrete Element Method

In this paper, numerical simulation of 3-dimensional assemblies of 1000 polydisperse sphere particles using Discrete Element Method (DEM) is used to study the liquefaction behaviour of granular materials. Numerical simulations of cyclic triaxial shear tests under undrained conditions are performed at different confining pressures under constant strain amplitude. Results obtained in these numerical simulations indicate that with increase in confining pressure there is an increase in liquefaction resistance.

Study of the liquefaction resistance of a saturated sand reinforced with Geosynthetics

This article presents various tests using a cyclic triaxial instrument, on samples of saturated Hostun RF sand, reinforced with circular sheets of geosynthetic material. Tests performed with different types of geosynthetics of different compressibility, rigidity and roughness characteristics indicate a significant increase in liquefaction resistance for samples reinforced with compressible, non-woven geotextiles. The undrained behaviour of saturated Hostun RF sand reinforced with non-woven geotextiles is analysed on the basis of different test series. This analysis highlights the influence of reinforcement compressibility on interstitial pressure distribution in the sample, thus showing the role of this type of inclusion in the increase in liquefaction resistance.