Allowable limit of soil nail wall deflection based on damage level of adjacent structures

Damage probability of structures caused by excavation wall movement is an important design aspect of support system in urban areas. This will be more important, if the adjacent structure be old or have low strength parameters. Frame distortion and crack generation are signs of building damage to excavation-induced ground movements which is a challenge in projects involving deep excavations. These highlight the importance of evaluation of building response in excavation projects. The aim of estimation and evaluation of building response is to establish limiting criterion for excavation support system design to certify the structure safety against undesirable damage. Thus, limiting criterion prepares a framework to determine the damage level of building based on excavation induced ground movements. Mentioned limiting criterion also is named Damage criterion or Damage model. Damage models are too practical before design progress of nailing wall. Based on uncertainty in data from excavation project and variability of the many factors that contribute to the response of nearby structures, existing Damage models are rare and generally need special instrumentation of excavation wall and nearby structures, so they cannot prepare a simple framework to use in practical situation.
This paper describes a study of building response to excavation-related ground movements and provides procedure for damage assessment of building near excavation projects. This study uses field data based on 10 case studies and 90 calibrated 3D FEM models in addition to probabilistic analysis to establish new simple damage criterion for design consideration of excavation supported by soil nail wall technique. Presented Damage model simply relates the damage level of structure to maximum displacement of excavation wall.To create this paper following stages are used:1.Case studies:31 deep excavation (16.7-31 meters) from expert companies are studied in first stage.2.First filtering of the collected data: part of collected data (14 projects of 27 projects) is eliminated from data base because of inaccuracy in the results of monitoring, unfavorable results in displacement caused by nearby galleries or underground facilities, inappropriate execution and etc. 3.Evaluation of the structures in the excavation-affected zone (EAZ). 4.Second filtering of database: part of first-filtered data is eliminated from data base because of non-deductible conditions of structure in EAZ, mismatch between damage level and results of monitoring and etc. At the end of this stage only ten masonry structures (TMS) were selected to continue case studies. 5.Creating and calibrating FE models: at this stage, FE models are included excavation wall and adjacent structure were extended for each of TMS and were calibrated based on field results. 6.Idealization of calibrated TMS’s FE model (ICTM): each of calibrated TMS’s FE models were modified and idealized by removing water table, modification of excavation condition, simplification of structure frames and etc.7.Development of damage levels: in the last stage, DPI calculated from ICTM for each frame of structure and then compared with the value of excavation wall deflections. Finally, damage levels developed based on resulted database.