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Finite element results show both systems, especially uncroppped overhang cases, depend critically on available rotational restraint, otherwise continued settlement and recurrent cracking may occur.",{"@graph":14,"@context":72},[15,34,55],{"@type":16,"itemListElement":17},"BreadcrumbList",[18,23,27,31],{"item":19,"name":20,"@type":21,"position":22},"https://docshare.wps.com","Home","ListItem",1,{"item":24,"name":25,"@type":21,"position":26},"https://docshare.wps.com/document/","Document",2,{"item":28,"name":29,"@type":21,"position":30},"https://docshare.wps.com/document/research-report/","Research & 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problem does the paper address after underpinning installation?","Question",{"text":62,"@type":63},"It addresses cases where remedial underpinning work failed to stop footing settlement and crack development in residential houses.","Answer",{"name":65,"@type":60,"acceptedAnswer":66},"Which two underpinning systems are compared in the study?",{"text":67,"@type":63},"The study compares the RCSS system with 1.5\" anchors installed at a 5° angle and the RS system with 3.5\" diameter piles installed with or without batter, with or without cutting off the footing projection.",{"name":69,"@type":60,"acceptedAnswer":70},"What key factor governs the post-installation performance according to the simulations?",{"text":71,"@type":63},"Finite element simulations indicate performance depends critically on the rotational restraint available to the footing, and insufficient restraint can lead to anchor deformation, lateral pile movement, continued settlement, and crack 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Ashkinadze, Consulting Engineer, Edmonton, AB, Canada, Ph. 780-945-9746, email@k[the-eng.com](the-eng.com)  \nABSTRACT  \nThe paper investigates post-installation performance of residential concrete foundation underpinning systems with helical (screw) piles, following claims by clients of two recent underpinning projects that the remedial work done “failed to stop the footing settlement and crack development” in their houses. Although screw pile-based underpinning systems have been extensively studied in recent years, most of the studies focused on the anchors and supporting brackets, not the “foundation” side of the underpinning arrangement. Two systems were considered: (i) the Rounded Corner Square Shaft (RCSS) system with 1.5\" (38 mm) anchors installed at a 5° angle to vertical, and (ii) the Round Shaft (RS) system with 3.5″(89 mm) diameter piles, installed with or without batter, cutting and not cutting off the projection of the strip footing at the location of the pile. As a result of finite element simulations, the performance of both systems, but especially the one where the footing overhang was not cut off, was found critically dependent on the available rotational restraint of the footing. If it is not sufficient, the anchors will exhibit post-installation deformation by bending and lateral movement of the pile shafts, which may cause continuing settlement of the supported foundation and reoccurrence of cracks in the interior finishes.  \nKeywords: Deformability, eccentric, foundation, helical pile, residential, screw pile, settlement, strength, underpinning.  \nINTRODUCTION  \nUnderpinning with helical (screw) piles is one of the most popular technologies of repair of failed residential and commercial building foundations (Carville and Walton 1995) . In many regions of North America, the native surface soils are prone to local subsidence due to changing weather conditions and groundwater regime, desiccation by tree roots, construction activities in the proximity of the foundation. Underpinning strives to resupport the existing foundation off deeper soil strata, unaffected by these factors. However, since the foundation is already in place, it is difficult to put the anchors directly underneath the footing. Rather, the anchors are installed at the side of the foundation and are connected toit by underpinning brackets (more frequently) or poured reinforced concrete caps. The steel brackets are more technological and are considered further in this paper.  \nTwo underpinning systems, commonly used in the practice of underpinning residential foundations in Alberta, are investigated. The first system is a Rounded Corner Square Shaft (RCSS); the arrangement of the helical anchors and angular brackets is shown in Fig. 1. The piles are 1.5\" (38 mm) square solid section with rounded corners, installed with a slight angle to vertical (a.k.a. batter) . The projection of the strip footing is cut off at the pile location to reduce the eccentricity of the support.  \nThe other system considered is a Round Shaft (RS) system using tubular anchors (3.5\" OD × 0.25\" thick pipe section; 89 mm OD × 6 mm in metric), which provides for heavier-duty underpinning. The current design of the bracket in this system only allows vertical installation and the footing overhang is not being cut off (Fig. 2) . Notably the design procedure in this system does not account for the installation eccentricity in the anchor design other than the 3\" (76 mm) pile installation tolerance.  \nFig. 1. Underpinning arrangement with battered piles and cut-off footing projection (RCSS) .  \nFig. 2. Underpinning arrangement with vertical piles without cutting off the footing projection (RS) . LITERATURE REVIEW  \nThe behaviour of eccentric underpinning brackets for foundation walls and the resulting settlement of the footing has not been adequately researched. ","cbCaieccTZ6gcP7H","https://ap.wps.com/l/cbCaieccTZ6gcP7H","pdf",242806,"English","# Abstract\n# Introduction\n## Background and regional soil conditions\n## Two investigated underpinning systems (RCSS and RS)\n# Literature Review\n## Eccentric bracket behavior and settlement\n## Prior studies and limitations\n## Force transfer considerations","[{\"question\":\"What problem does the paper address after underpinning installation?\",\"answer\":\"It addresses cases where remedial underpinning work failed to stop footing settlement and crack development in residential houses.\"},{\"question\":\"Which two underpinning systems are compared in the study?\",\"answer\":\"The study compares the RCSS system with 1.5\\\" anchors installed at a 5° angle and the RS system with 3.5\\\" diameter piles installed with or without batter, with or without cutting off the footing projection.\"},{\"question\":\"What key factor governs the post-installation performance according to the simulations?\",\"answer\":\"Finite element simulations indicate performance depends critically on the rotational restraint available to the footing, and insufficient restraint can lead to anchor deformation, lateral pile movement, continued settlement, and crack recurrence.\"}]","POST-INSTALLATION PERFORMANCE OF ECCENTRIC SCREW PILE UNDERPINNING SYSTEMS FOR RESIDENTIAL FOUNDATIONS | PDF",1792836313,25]