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Reanalysis of Failure of Soil-Nailed Shoring System and Remedial Measures
Abstract
Support systems in urban areas for temporary excavations are necessary to keep the sides of excavation nearly vertical, to minimize the excavation area and to ensure that the excavation is stable from stability as well as deformation criteria and will not lead to any damages in the surrounding area. In the present study, the paper discusses the cause for the failure of excavation of 11.65 m deep supported by nailing. The serviceability requirements and factors of safety are evaluated using finite element analysis. Further, it discusses the revised design for a temporary support system. The paper highlights the importance of pull out tests in the preliminary stage as well as during execution which are useful in design and performance assessment of the shoring system. The revised system is implemented in the field and is performing well.
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Field pullout testing of soil nails is identified as the appropriate method for studying the nail-soil interaction and assessing the performance of soil nail walls. The primary objective of this study is to highlight the importance and practical applications of field pullout tests in the design and performance assessment of soil nail walls. Bond strength of soil-nail interface is the essential parameter in the design of soil nail walls. Field pullout tests provide valuable inputs for the selection of appropriate design bond strength. In this paper, a reliability based methodology for the evaluation and selection of appropriate field pullout tests is proposed for the determination of the design bond strength. The proposed methodology is illustrated with reference to the field pullout tests on soil nails conducted at a local site. J. Ross Publishing, Inc.
In India, soil nail walls are being extensively used for supporting vertical excavations below ground level to accommodate construction of one-or two-storied basements. Generally, the depth of excavations for basement construction ranges from 10 m to 15 m. For such large depth of excavation, variability of in-situ soil properties has significant influence on the stability of the soil nail walls. In the present study, using reliability analysis, an attempt is made to study the influence of variability of in-situ soil properties on the stability of soil nail walls. For better understanding, a case of 10 m high soil nail wall constructed to support a vertical cut is considered for the study and its stability is evaluated for various failure modes. Additionally, the influence of correlation among soil parameters on soil nail wall stability is assessed. In-situ soil friction angle and correlation between in-situ soil cohesion and angle of friction are found to influence soil nail wall stability significantly. In general, reliability analysis provided a better insight into the assessment of stability of soil nail wall.
Pullout failure of reinforcement is one of the very important criteria in the ultimate limit sate analysis of internal stability of reinforced soil retaining wall. This is particularly of critical importance in upper layers of wall where the normal pressure on the reinforcement is low. Cellular reinforcement is found very effective and better performing for reinforced soil applications. However, pullout experimental study of such reinforcement has not been focused till date. Therefore, in the present paper, full scale laboratory pullout test set up has been designed, fabricated and developed to test the pullout resistance of cellular reinforcement. A series of pullout test was carried out with different heights of reinforcement, under low normal pressures of 25 kPa and 50 kPa. Deformation patterns of all reinforcement in pullout are studied. Finite element simulation is used to verify the experimental pullout response and found in good agreement with experimental load-displacement relationships. Suggested reduction factor 'k' is found decreasing with increase in height of reinforcement; yet, ultimate pullout resistance is found increasing with increase in the reinforcement height, to the height of 20 mm to 30 mm; after which, greater interference between the transverse members caused decrease in pullout resistance. Pullout interaction factor for cellular reinforcement is found increasing with increase in the reinforcement height. J. Ross Publishing, Inc.