Results Of Cyclic Simple Shear Tests Research Articles

Application of Critical State Approach to Liquefaction Resistance of Sand–Silt Mixtures under Cyclic Simple Shear Loading

An extensive experimental program of constant-volume (undrained) cyclic simple shear tests was undertaken on Ticino, Italy, sand with different contents of nonplastic fines, ranging from 0% to 40%. The samples were reconstituted by moist tamping and tested with different initial states, including void ratios and effective vertical stresses. Test results confirmed that the concept of equivalent granular void ratio e* is appropriate for the interpretation of the undrained cyclic behavior of sand with different amounts of fines up to the limiting fines content. Because a single trend for critical state (CS) data points was observed in the e*-log(p′) plane (EG-CSL) for different amounts of fines, the cyclic simple shear test results were analyzed within a unified critical state soil mechanics (CSSM) framework in terms of an alternative state parameter, Ψ*. A unique correlation between undrained cyclic strength (CRR) and Ψ* was found, irrespective of the fines content and initial state. Although a correlation between the cyclic resistance ratio and the conventional state parameter Ψ works as well, the procedure based on Ψ* has the advantage that the cyclic behavior of a certain sand with different contents of non plastic fines is described by a single reference curve (EG-CSL). In contrast to previous investigations in the literature, which mainly used triaxial tests, the CRR-Ψ* correlation proposed in the present study is based on cyclic simple shear tests, which better represent the real ground conditions under seismic loading.

Capacity degradation method for piles under cyclic axial loads

Piles used for jacket type foundation of offshore wind turbine are subjected to highly cyclic tension and compressive loading. The pile capacity under cyclic tension loading decreases with increased number of loading cycles due to reduction of the pile shaft resistance. A numerical simulation scheme is presented, which allows the calculation of the pile capacity degradation (CDM) due to cyclic loading for driven steel piles. The volume compaction of soil near the pile surface during the cyclic loading is determined from the cyclic simple shear test results and then applied to the pile-soil system.From the limited number of tests available, interaction diagrams have been developed, which give the number of load cycles leading to failure dependent on the mean load and the amplitude of the cyclic load portion, which are both related to the static pile capacity. However, such diagrams cannot account for different soil conditions or pile geometry and pile stiffness. The calculation results for different piles in sandy soil under cyclic axial loading are presented and compared with existing interaction diagrams. Finally, recommendations regarding further investigations and improvements of the method are given.

Recent advances in pore water pressure and liquefaction characteristics of low plasticity silty sands subjected to cyclic loading

Low plasticity sand-silt mixtures are very common in Italy either in natural depositional environment or in man-made earth-fill, hence the knowledge of their behavior is a crucial aspect in many practical applications. Due to higher compressibility features, significant strains and strength loss may be triggered by earthquakes. The results of a laboratory-based investigation undertaken on undisturbed samples of low plasticity silty-sandy soils recovered from a bank stretch after the 2012 Emilia Romagna earthquake in Italy, when serious damages and widespread liquefaction events were observed, are herein presented. Special emphasis was given to susceptibility to liquefaction and pore water pressure response in presence of an initial static shear stress. As part of the present work, the results of undrained cyclic simple shear (CSS) tests carried out on reconstituted specimens of sand-fines mixtures, covering a range of non plastic fines contents from 0% to 40%, were used for predicting undrained cyclic resistance through the concept of equivalent granular void ratio, e*. The conceptual framework based on e* appears appropriate for streamlining the effect of fines on cyclic liquefaction resistance of these intermediate soils, provided that fines content is less than a limiting value. Since an important stage in the assessment of liquefaction potential is to predict excess pore water pressure during cyclic loading, the results of CSS tests were also utilized for analysing pore water pressure generation models of silty sands over a wide range of fines contents.

Liquefaction potential of sands at the Krško-Brežice field, Slovenia

The Krsko-Brežice field is one of the most seismically active areas in Slovenia. The most damaging recorded earthquake with an intensity of VIII (EMS) occurred on 29th January 1917. It caused damage and claimed two lives. In the last 100 years, 9 earthquakes with intensity higher than VI (EMS) have been recorded. At the investigated area, a top layer up to 5 m thick, consisting of recent deposit of very loose silts and sands (ML, SM, SP), covers the medium dense to dense Quaternary gravel, beneath which there are over-consolidated, uncemented Miocene silts and marls. The top layer could be prone to liquefaction, as reported for the close surroundings of Brežice, where the liquefaction phenomenon was observed during the Zagreb earthquake in 1880 and during the Kupa Valley earthquake in 1909. The paper presents the results of laboratory index tests, cyclic simple shear tests and field investigations (SPT, CPT, (S)DMT, vs measurements), which were carried out to assess the liquefaction potential of the top layer at the location of the Brežice Hydroelectric Power Plant (HPP). All results show that the top layer is prone to liquefaction for an earthquake with a 475 year return period. Cyclic simple shear test results show that the liquefaction potential of horizontal ground for an earthquake with a 475 year return period can be reduced by the densification of the top layer to at least 95% of maximum Proctor density.

폐기물 매립장 접촉면의 동적 전단거동특성

최근 늘어나고 있는 폐기물량에 따라 폐기물 매립장의 건설이 증가하고 있으며, 매립장 내 폐기물의 격리, 보호 및 환경오염방지를 위하여 토목섬유가 널리 활용되고 있다. 토목섬유는 주변의 흙과 접촉면을 형성하여 폐기물 매립장의 전단 거동에 영향을 미치게 된다. 폐기물 침출수에 포함된 화학적 요소는 이러한 접촉면 거동에 중요한 영향을 미치며, 지진과 같은 동적하중 또한 접촉면 거동에 미치는 화학적 영향을 가속화시킬 수 있다. 따라서 본 연구에서는 화학적 영향을 고려한 접촉면 전단강도 감소효과를 반영하여 수치해석을 수행하였다. 반복 단순전단시험 결과를 바탕으로 수치해석을 수행한 결과, 접촉면 전단강도 감소를 미 고려시 폐기물 매립장의 동적 안정성을 과대평가할 수 있다고 판단된다. The number of the waste landfill site increases continuously in recent years. Various types of geosynthetics have been utilized in the waste landfill site for encapsulating, isolating, protecting, and so on. Geosynthetics compose the interface with soil and affect the shear behaviors of waste landfill system. The chemical aggressors in the leachate also play a critical role in the interface and it is known that the dynamic loading is able to accelerate manifestation of the effects of chemical attack. In this research, numerical analysis was conducted considering shear stress degradation in the geosynthetic-soil interface due to dynamic load with chemical effect. Cyclic simple shear test results was reviewed and applied to the numerical modeling as well. Consequently, the stability of waste landfill site could be overestimated without considering the shear stress degradation of interface.