Predicting the safety factor of ash impoundment against liquefaction (original) (raw)
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A developed procedure for predicting the risk of liquefaction: A case study of Rasht City
Soil liquefaction is one of the most important and complex seismic geotechnical and engineering topics. Most experimental methods in the study of liquefaction have been based on deterministic analysis, and parameters, such as soil resistance and earthquake loads, have been considered without dispersion and fault. Statistical analysis, particularly reliability analysis, is a new and comprehensive approach used to solve and evaluate problems, as well as entering of uncertainties in calculations. In this study, information on 50 boreholes were obtained using a database of Standard Penetration Test (STP), and diverse experimental procedures, such as NCEER2001, Idriss and Boulanger, Highway bridge of Japan, OCDI and reliability approach, were used in the evaluation of soil liquefaction in Rasht and finally, the results were compared with each other. By comparing the different methods, it was observed that these methods do not correspond with clay soils and their results were different from each other. Also, safety factor of greater or lesser than one is the mean of safety and occurrence of liquefaction, therefore, reliability analysis was used to ensure the probability of liquefaction. Finally, two empirical relationships based on the probability of liquefaction (PL) and safety factor (FS) were proposed from which the liquefaction potential can be calculated directly. Soil liquefaction risk can be assessed by the proposed relationship between (PL) and (FS) based on deterministic approaches.
IOP Conference Series: Earth and Environmental Science
Institut Teknologi Sumatera (ITERA) is the only state institute in Sumatera, specifically located in South Lampung region, which is a coastal area with dominant sandy soil type. It soil type can allow liquefaction. The purpose of the research is to analyze the mitigation potential of liquefaction with the deterministic method. It is expected that the research result could be used as a reference in planning of the ITERA future development. This analysis takes into account deterministic data that compares Cyclic Resistance Ratio of the soil (CRR) with Cyclic Stress Ratio (CSR) caused by an earthquake. CSR depends on the depth of soil layer, total vertical pressure, effective vertical pressure, earthquake magnitude and maximum acceleration in each layer of soil. CRR is obtained from the empirical correlation with the Cone Penetration Test (CPT) results. Judging from the results of the CPT test, the soil type in ITERA is loose sand and clay. Based on earthquake parameters and CPT test data at 12 points, ITERA is in the category of medium liquefaction potential with a safety factor value of less than 2.
Correlation of CBR and Resilient Modulus in Subgrade Stabilization Using Fly Ash
The objective of this study was to acquire the correlation between California Bearing Ratio (CBR) and Resilient Modulus (MR) of subgrade soil stabilizes using chemical stabilization which is Fly Ash (FA). The research was conducted at various content of FA obtained from electric generator system Kapar and soil samples were taken from Tanjung Harapan, Klang. To determine the optimum moisture content (OMC) and maximum dry density (MDD), compaction test was conducted using Standard Proctor Test. The stabilized soil samples were prepared by mixing the 4% of FA, 10% of FA and 20% of FA by weight of soil of each sample. The strength of the samples was tested using Unconfined Compressive Strength (UCT). Four (4) samples from different percentage of FA at OMC were tested for CBR value and MR value curing in 7 days and 28 days. The result shows increases in the CBR and MR value by addition of FA where the presence of FA in different percentage affected by different curing time period increased the value of CBR and MR differently. By using Pearson Correlation, the correlation between CBR and MR for 7 days is 0.625, 28 days is 0.648 and for overall data consists of both 7 and 28 days curing period is 0.553.
CONSTITUTIVE MODELING OF COAL ASH USING MODIFIED CAM CLAY MODEL
Coal ash is a by-product from coal-fired power plants that generates electricity. These waste materials most of the time is kept in storage facilities. Due to the growing demand in electricity generation, storage facilities can no longer accommodate the waste materials. Instead of disposing the waste materials, it can be used as a construction material. A promising civil engineering structure that can use coal ash as a construction material is land reclamation. The structure needs huge volume of materials and this can maximize the usage of coal ash. In the Philippines, most land reclamation projects are conducted at the sea. From this, distilled water was replaced with sea water to have a better evaluation of the strength properties of coal ash. Consolidated drained test was performed having three conditions with respect to sea water exposure. First condition is no exposure, second condition is immediate exposure and third condition is prolonged exposure. Results show that coal ash exposed to seawater, immediate and prolonged, has smaller shear strength. On the other hand, it still has reasonable strength suitable for land reclamation projects. Constitutive modeling using Modified Cam Clay model is incorporated in the study to be able to predict its behavior and failure in terms of mean effective stress, deviator stress and specific volume.
Liquefaction Hazard Assessment andBuilding Foundation Safety for Chennai City, India
ABSTRACT. Chennai is India’s 4th largest metropolitan city has a multi-dimensional growth in development of its infrastructures and population. The city is prone for moderate seismic activity and the anticipated earthquake is with magnitude of 6.5 based on past earthquake history. The Chennai city is with variety of geological deposits and the geotechnical characteristics of sediment deposits have its own importance on ground movements. Liquefaction is one of the most destructive phenomena caused by earthquake and especially in loose saturated sand deposit. Hence there is a need to prepare liquefaction hazard map which will enable urban planners to design earthquake resistant structures and strengthen existing unstable structures. In this study, SPT data from 666 boreholes used to evaluate the liquefaction potential. A Liquefaction Hazard Map is prepared and the result has been correlated with various geological deposits. It shows that the marine deposits has higher liquefaction hazard comparatively to that of fluvial deposits. Among marine deposits, the paleo tidal litho unit is more prone for liquefaction compared to strand flat and tidal flat litho units. The result shows that the liquefaction layer thickness varies from 1m to 10m. The Severity of Liquefaction (SL) is calculated for Very Severe and Severe categories of Factor of Safety (FS) and utilized to arrive the pile diameter for preventing of buckling of building foundation piles. In this study, over 50,000 buildings from 3 to 14 stories have been studied to evaluate the foundation stability against the sand layer thicknesses of liquefiable zones. Generic recommendations for shallow foundation and deep foundation of multi-storied buildings have been suggested to mitigate against the effect of liquefaction hazard for building foundation safety.
E3S Web of Conferences
Liquefaction is a hazardous and temporary phenomenon by which water saturated soil loses some or all of its resistance. The undrained conditions linked to the cyclic load increase the pores water pressure inside the soil and consequently reduce effective stress. As a result, the soil can no longer resist or hold the shear forces, and lead to enormous deformations that directly influence the stability of structures and infrastructures foundations. Since 1964, several semi-empirical methods have been invented to evaluate the liquefaction potential using the in-situ test results. This study is based on the correlation between experimental data results of Menard pressuremeter and SPT dynamic penetrometer tests. Samples used in this test come from the Rhiss dam located in the North of Morocco, 24 kilometers as the crow flies from the town of Al Hoceima and south of the foundations of a calcareous ridge. The studied area have high seismic activity and a high percentage of fine soil elemen...
Journal of Physics: Conference Series, 2020
To evaluate soil resistance against liquefaction, a simplified procedure has been developed based on directly field soil testing. There are four recommended field tests, including CPT and SPT. Soil resistance to liquefaction is measured by the safety factor SF, which is the ratio between the capacity of the soil to resist liquefaction cyclic resistance ratio (CRR) and the soil stress occurs due to an earthquake cyclic stress ratio (CSR). If SF <1, liquefaction occurs. This research was carried out at Sanur area, Southeast Denpasar City, Bali, by conducting 6 pairs of CPT and SPT tests, each of 6-meter depth. The Ground Water Level (GWL) at this area is 1.5 meter below the soil surface. The soil type is silty sand to sandy silt, with the unit weight between 1.617 to 1.837 g/cm^3. The calculation results, both with CPT and SPT, show that the soil layer did not experience liquefaction with earthquake magnitude Mw = 4.0. At Mw = 5.0, liquefaction occurs in most soil layers, except th...
Strength Characterstics of Stabilized Embankment Using Fly Ash
Infrastructure projects such as highways, railways, water reservoirs, reclamation etc. requires earth material in very large quantity. In urban areas, borrow earth is not easily available which has to be hauled from a long distance. Quite often, large areas are covered with highly plastic and expansive soil, which is not suitable for such purpose. Extensive laboratory / field trials have been carried out by various researchers and have shown promising results for application of such expansive soil after stabilization with additives such as sand, silt, lime, fly ash, etc. As fly ash is freely available, for projects in the vicinity of a Thermal Power Plants, it can be used for stabilization of expansive soils for various uses. The present paper describes a study carried out to check the improvements in the properties of expansive soil with fly ash in varying percentages. Laboratory tests like 1) grain size analysis 2) atterberg limits 3) standard compaction 4) permeability test have been carried out on soil and CBR (California bearing ratio) test is conducted on soil sample mixed with fly ash in various proportions and results are reported in this paper. One of the major difficulties in field application is thorough mixing of the two materials (expansive soil and fly ash) in required proportion to form a homogeneous mass. The fly ash is mixed with soil in required proportion until the CBR value for the embankment is achieved.
Liquefaction Hazard Mapping of Chennai, India using SPT Data
Liquefaction hazard is one of the major concerns for earthquake geotechnical engineering. In this paper an attempt has been made to assess liquefaction potential of Chennai city using SPT N values. Chennai is located between 12.75° to 13.25° N and 80.0° to 80.5° E on the southeast coast of India and in the northeast corner of Tamil Nadu. To understand the liquefaction possibility of Chennai city, about 650 Borelogs have been collected from different geotechnical agencies and used for the analysis. These boreholes were drilled for different projects in Chennai, most of them were drilled up to hard stratum and a minimum depth of 10m. SPT borehole data contains information about depth of water table, the classification of soil and the field observed 'N' values, index properties, rock depth. These borehole information are used to prepare N corrected table by applying the universally followed correction factors for liquefaction study. These corrected N values are further used to estimate the factor of safety against liquefaction of soil layer. Based on the factor of safety, the regional liquefaction hazard maps have been developed for depths of 1.5m, 3.0m, 6.0m and 10.0m. To represent the worst scenario, least factor of safety has been identified for each borehole location and mapped. Further the estimated factor of safety against liquefaction is used to estimate liquefaction potential index by considering depth of layer. These results are analyzed and compared in this paper.