Remediation of Slope Failure by Compacted Soil-Cement Fill Jason Y. Wu, P.E., M.ASCE1; Kaiming Huang2; and Munira Sungkar3 Abstract: Remediation of a complete destroyed slope is often difficult because of various geotechnical challenges and different constraints at the site. Many solutions have been developed; however, not all stabilization methods are appropriate for every type of slope failure. In addition to the technical considerations, aesthetic concerns and sustainability have also become significant issues during the past decades because of global environmental concerns. The principle of multiple-criteria decision analysis (MCDA) will be helpful in the consideration of these alternatives when all criteria are considered simultaneously. In this study, it was concluded that compacted soil-cement would be the best solution for the site after MCDA procedures. This paper presents a detailed report to demonstrate the benefits of utilizing compacted soil- cement for the restoration of slope failure. Traditionally, compacted soil-cement stabilization has been used worldwide for embankment constructions to mitigate the constraints of problematic sites. When it is applied in a slope remediation, the stability of the reconstructed slope can be improved with the increased strength of the cemented material. The experience described herein indicates that slopes treated with compacted soil-cement not only successfully meet all the site criteria, they also display sustainable performance. Compared to slopes con- structed with traditional stabilization methods, the slope in this case demonstrates superior performance. Based on field monitoring to date, the slope in the described case continues to maintain its structural stability and safety. The utilization of compacted soil-cement fill is a valuable and sustainable solution, particularly for those sites that have concerns with the disposal of impracticable silty debris waste. DOI: 10.1061/(ASCE)CF.1943-5509.0000998. © 2017 American Society of Civil Engineers. Author keywords: Slope failure; Remediation; Compacted soil-cement; Sustainability. Introduction environmental protection and sustainable development also have become significant issues because of concerns about extreme Landslides of unsaturated slopes, triggered by rainfall infiltration and climate and global warming. Ways of reducing negative human im- reduction of matric suction, have become a major worldwide concern pact or using eco-friendly solutions are often mandatory for many over the past few decades (Rahardjo et al. 2001; Wu and Wang environment-sensitive sites (Jefferis 2008; Keaton 2014; Kil et al. 2011). The increase in unit weight and loss in strength due to severe 2016). At times, because of other nontechnical influences, the final rainfall have caused many slopes to disintegrate, leading to piles of decision may not even be made by the design engineer. Therefore, debris and rubble at the site. The rehabilitation of such failures is the determination of treatment for a landslide appears to have no difficult, especially for slopes that consist of silty or clayey soils with definitive rule to follow. Experts recommend that the factors to be high water content. Reconstruction of these materials for the repair of considered for the selection of correct remediation include safety, slopes is also difficult because of fines. The removal and disposal of construction scheduling, availability of materials, site accessibility, the collapsed debris can be particularly troublesome because of envi- equipment availability, aesthetics, environmental impact, political ronmental restrictions in the metropolitan areas. issues, and labor considerations (Abramson et al. 2002; Corkum There are many solutions for landslide rehabilitation. Common and Martin 2004; Brencich 2010; Costa and Sagaseta 2010). A principles used are unloading, drainage, reinforcement, retaining multitude of variables are required to develop the best or the most structures, and surface vegetation (Cornforth 2005). However, appropriate solution, but integrating all variables together generally Abramson et al. (2002) and Brencich (2010) indicate that not all results in an ambiguous or controversial solution. One of the more stabilization methods are appropriate for every type of slope failure; effective methods is using the principle of multicriteria decision the most expensive treatment may not always be the most effective, analysis (MCDA), a valuable method in making important deci- and vice versa. Recently, in addition to technical considerations, sions that cannot be easily decided (Sánchez 2005; Sabzi and King 2015; Kil et al. 2016). Downloaded from ascelibrary.org by Iowa State University on 02/21/17. Copyright ASCE. For personal use only; all rights reserved. Compacted soil-cement fill is a highly compacted mixture of 1Professor, Dept. of Civil Engineering, Chung Hua Univ., Hsinchu, Taiwan 30012, Republic of China (corresponding author). E-mail: soil, cement, and water that has been used for decades to meet en- [email protected] gineering purposes for a variety of infrastructures to improve 2Ph.D. Candidate, Dept. of Civil Engineering, Chung Hua Univ., unsuitable subgrade or to modify soft soil properties (Bergado et al. Hsinchu, Taiwan 30012, Republic of China. E-mail: mkm_huang@rrb. 1996; PCA 2016). By compacting a mixture of cement and soil to a gov.tw designated density, both shear strength and durability of the 3 Ph.D. Candidate, Dept. of Civil Engineering, Chung Hua Univ., Hsinchu, material increase substantially. Cement stabilization improves soil Taiwan 30012, Republic of China. E-mail: [email protected] structure by increasing intercluster cementation bonding and reduc- Note. This manuscript was submitted on May 8, 2016; approved on October 17, 2016; published online on February 15, 2017. Discussion ing the pore space (Horpibulsuka et al. 2010). Therefore, it can be period open until July 15, 2017; separate discussions must be submitted used to construct embankments or rebuild failed slopes (Gill and for individual papers. This paper is part of the Journal of Performance Bushell 1992; Abramson et al. 2002). In comparison with other of Constructed Facilities, © ASCE, ISSN 0887-3828. remedial solutions, compacted soil-cement fill presents many © ASCE 04017022-1 J. Perform. Constr. Facil. J. Perform. Constr. Facil., -1--1 Fig. 1. Plan view of the sliding area (adapted from Wu et al. 2016, © ASCE) advantages. It can use on-site materials and therefore reduces the Site Description need for debris disposal. It does not need a retaining wall and thus provides more space and a more attractive appearance. It eliminates As shown in Fig. 1, the site is located in the eastern vicinity of Hsinchu City near Baoshan Reservoir in Taiwan. The hill slope excess moisture problems and promotes easier workability for silty is located at the northwest wing of a residential community. A soils. Its cost and construction time are also competitive compared 4-m-wide access road alongside a curved side hill alignment to other solutions. and a 6-m-high concrete retaining wall along the road were at This study aims to present a solution by using compacted soil- the toe of the slope. A landslide occurred during a strong typhoon cement to successfully rehabilitate a landslide in a congested res- when torrential rainfall hit Taiwan. The slope failure was approx- idential area. Associated with the major study objectives are the 2 imately 2,750 m in plan dimensions, with a height of approxi- remedial measures undertaken for the treatment, such as construc- mately 27 m from the toe to the top of the head scarp. The tion procedures and environmental concerns. The experiences pre- landslide resulted in three to four slumped terraces that caused a sented herein can be beneficial and valuable for cases with similar complete collapse of the upper and lower retaining walls (Figs. 2 conditions. and 3). The slide debris also buried the access road, rendering it completely inaccessible to local traffic. The lower margin of the displaced material just barely stopped in front of several residential Downloaded from ascelibrary.org by Iowa State University on 02/21/17. Copyright ASCE. For personal use only; all rights reserved. Fig. 2. Collapsed lower slope and retaining wall (reprinted from Wu et al. 2016, © ASCE) Fig. 3. Collapsed upper slope and retaining wall (image by Jason Y.Wu) © ASCE 04017022-2 J. Perform. Constr. Facil. J. Perform. Constr. Facil., -1--1 houses. Residents were evacuated to prevent any further life- Laboratory Testing threatening conditions. Laboratory test results indicated that the silty sand contained plastic As an immediate short-term response, the area around the head fines varying from 36 to 43%. Material based on the Unified Soil scarp was covered with a plastic vinyl sheet to minimize ingress of Classification System (ASTM D2487), the sand can therefore be surface water into cracks in the slide area. Several emergency classified as SC-SM (silty clayey sand) material (ASTM 2011a). ditches were installed to divert the surface water from the slide Field water contents ranged from a low of 15.3% to a high of location. 32.6% at the surface. Moisture unit weight varied from 19.6 to 20.5 kN=m3. The quick direct shear strength parameters for sam- ples obtained at depths of 5–9 m ranged from 13 to 39 kPa for Geotechnical Evaluations cohesion and 17–19° for angle of shearing resistance. Site Investigation Slide Assessment The site is composed of interbedded sandstone,