Developing a Risk Assessment Model for Trenchless Technology: Box Jacking Technique Babak Mamaqani, Ph.D., P.E., M.ASCE 1 ; Mohammad Najafi, Ph.D., P.E., F.ASCE 2 ; and Vinayak Kaushal, Ph.D., A.M.ASCE 3 Abstract: Overcut is required during bore excavation in the box jacking (BJ) technique to facilitate steering of culverts and to reduce friction. BJ is a trenchless construction technique to install rectangular box culverts under existing facilities such as highways and railroads. In this method, box culverts are pushed through the ground using the thrust power of a hydraulic jack. Soil may collapse into the annular space during project execution and cause surface or subsurface settlement. Several investigations have examined this phenomenon in pipe jacking (PJ) and tunneling. Although some aspects of BJ are similar to PJ, there are significant differences between the two methods. The objective of this paper is to investigate surface settlement and determine the associated risk for BJ projects in sandy soil. In this research, finite-element modeling (FEM) software, PLAXIS 2D, was used as the main tool to simulate BJ. Since FEM results are limited to a specific project, artificial neural network and multiple linear regression analysis were adopted in conjunction with PLAXIS 2D to understand the effects of different parameters on determining surface settlements. It was concluded that soil cohesion, box culvert depth from the surface, and overcut size have the highest impact on determining a surface settlement, and their associated risk was determined. The analytical results were validated through two case studies. DOI: 10.1061/(ASCE)PS.1949-1204.0000484. © 2020 American Society of Civil Engineers. Introduction and Background Box culverts and drainage structures play important roles in rail- road, highway, and road construction and maintenance since they transfer stormwater from upstream to downstream with minimum hydraulic head effect. The box jacking (BJ) method is a unique trenchless technology method for installing a box culvert under- ground from a drive shaft to its receiving shaft beneath critical facilities, such as railways, major highways, and airport runways without surface disruption (Hung et al. 2009). The basic process of installing a box culvert includes setting a box culvert in a launch shaft and then jacking into the ground with excavation taking place within an open-face shield (Najafi 2013). Fig. 1 shows a BJ project. The pipe/box jacking (PJ/BJ) method is a cyclic method that uses the thrust power of hydraulic jacks to propel each segment of a pipe/box culvert through the ground (Najafi 2010). Installing box culverts underground, like other trenchless methods, will disturb the ground and may cause surface settlements and, conse- quently, damage road pavement or railroad embankments. As a re- sult, the need to better understand ground movements induced by the BJ process is important. The box culvert jacking method involves underpass construc- tion and has been widely used all over the world (Chapman et al. 2007). As a subsurface structure (Zhang et al. 2018; Lai et al. 2016; Nie et al. 2018; Ren et al. 2018; Wang et al. 2018; Wang and Sun 2019; Ma et al. 2019), the box culvert is an important component of urban infrastructure. According to the literature, numerous studies have been conducted of the box culvert structure and have focused on the following aspects: (1) structural response and load distribution under vehicle load and earth pressure (Acharya et al. 2016a, b; Abdel-Karim et al. 1993; Bennett et al. 2005; Chaurasia et al. 2013; Chen and Sun 2014; McAffee and Valsangkar 2008; Oshati et al. 2012; Pimentel et al. 2009; Zhang et al. 2015); (2) structural stability analysis under seismic loads (Abuhajar et al. 2015a, b; Wang et al. 2005); and (3) response of overlying pavement (Kavanagh et al. 2016; Park et al. 2015; You et al. 2001). With regard to box culvert jacking construction, much attention has focused on the engineering case presentation (Allenby and Ropkins 2004; Powderham et al. 2004; Barker 2012; Ogborn et al. 2011), electrohydraulic system and jacking force (Mi et al. 2012; Zhang 2008), and ground surface deformation during the jacking operation (Du et al. 2006; Mamaqani and Najafi 2014; Prakoso and Lase 2014). With the constant innovation in underpass jacking technology, a novel method of box culvert shield jacking has been developed in recent years, which combines the principles of box jacking and shield tunneling (Cheng et al. 2018; Fang et al. 2018; Yan et al. 2018). This method utilizes a steel structure, known as a shield, that is installed in front of the box culvert for the purpose of excavation, support, and orientation. It breaks the embankment soil into three parts for a gridded excavation (Luo et al. 2018, 2019; Zhang et al. 2018, 2019), minishield excavation, column excavation, and central soil excavation; this approach pro- vides maximum protection for existing roads. Compared with other jacking constructions, the advantages of the box culvert shield jacking method are threefold: (1) the shield is a temporary steel frame structure installed in front of the box culvert for stabilizing the surroundings and reduces the need for 1 Project Manager, PB&A, Inc., 810 Fifth Ave. #100, San Rafael, CA 94901. Email: babak.mamaqani@pbandainc.com 2 Professor and Director, Center for Underground Infrastructure Research and Education, Dept. of Civil Engineering, Univ. of Texas at Arlington, P.O. Box 19308, Arlington, TX 76019. Email: najafi@uta.edu 3 Adjunct Professor and Postdoctoral Research Associate, Center for Underground Infrastructure Research and Education, Dept. of Civil Engi- neering, Univ. of Texas at Arlington, P.O. Box 19308, Arlington, TX 76019 (corresponding author). ORCID: https://orcid.org/0000-0001-7922-2746. Email: vinayak.kaushal@mavs.uta.edu Note. This manuscript was submitted on May 17, 2019; approved on April 24, 2020; published online on June 24, 2020. Discussion period open until November 24, 2020; separate discussions must be submitted for in- dividual papers. This paper is part of the Journal of Pipeline Systems En- gineering and Practice, © ASCE, ISSN 1949-1190. © ASCE 04020035-1 J. Pipeline Syst. Eng. Pract. J. Pipeline Syst. Eng. Pract., 2020, 11(4): 04020035 Downloaded from ascelibrary.org by Vinayak Kaushal on 06/24/20. Copyright ASCE. For personal use only; all rights reserved.