Durability Studies on Native Soil-Based Controlled Low Strength Materials

The Integrated Pipeline Project (IPL) is a collaborative effort between the Tarrant Regional Water District (TRWD) and Dallas Water Utilities (DWU), which bring additional water supplies to the Dallas / Fort Worth area. As part of a sustainability initiative, several studies were conducted to assess the reuse potential of excavated materials along the IPL project. One of these studies involved using the excavated material as an ingredient in Controlled Low Strength Material, often known as CLSM or flowable fill. This flowable fill can be used as bedding and haunch material in pipeline construction. These CLSMs meet the specifications in the short-term; however their long-term performance should be verified in order to be successfully used in the field, especially when these materials are subjected to seasonal changes such as wetting and drying. Hence, durability studies were conducted on CLSMs from two different geologic formations, namely Eagle Ford and Queen City formations. The variations in retained strength and volumetric strain changes, along with the amount of stabilizer leached out of the CLSM samples at different durability cycles, are presented in this paper. It was observed that Eagle Ford soil CLSM lost more than 50% of its initial strength while Queen City sand CLSM lost approximately 50% of its initial strength when subjected to durability studies. The loss in strength was attributed to both volume change and stabilizer loss in case of Eagle Ford soil while stabilizer loss alone caused the loss of strength in the case of Queen City sand

Geotechnical Evaluations of a Tailings Dam for Use by a Molybdenum and Copper Mine Project in Southern Idaho

A proposed mining project in Boise County, Idaho for the extraction of copper, molybdenum, and silver deposits, required investigations into a possible tailings dam construction that will be built using the processed material from the mine. The mine is located southwest of Lowman Idaho, northeast of Pioneerville Idaho, and directly north of Jackson Peak Mountain. The total area for the proposed project is approximately 12 square kilometers and the estimated material to be excavated is about 1.99 billion cubic meters (BCM) (USDA 2013). Typical investigations into the construction of a tailings dam consist of identifying the types of ore contained within the mine, identifying a suitable location for the dam based on topography, and conducting an analysis of the geotechnical aspects of constructing the dam. In this project, construction of the tailings dam will adequately model a cut and fill operation where the excavated waste material will be used to construct the tailings dam. Construction of the tailings dam will happen in stages, with a starter dam followed by successive additions to accommodate the need for reservoir capacity. Several aspects such as excavation depth, the types of excavated soil and rock, the ore processing methods, and mechanical properties of the waste material, have been considered for properly conducting an analysis of the tailings dam. Also, aspects including the slope stability of the tailings dam, seepage velocities through the tailings dam, and slope stability after a seismic event have also be studied. This paper discusses the geotechnical aspects of the tailings dam construction including the stability of the dam under both hydrological and seismic conditions

Strength and Stiffness Characterization of Controlled Low-Strength Material Using Native High-Plasticity Clay

A research attempt was made to design a controlled low-strength material (CLSM) mix that can be used as bedding and haunch material for a pipeline by using the native soil as fine aggregate. Several CLSM mix designs were attempted using native high-plasticity clay as fine aggregate material. Comprehensive material characterization studies including flowability to strength tests were performed. These results were analyzed to address the applicability of each mix to serve as pipe bedding/backfilling zones in a pipeline construction. Both flowability and density test results are first evaluated, and as a result, several mixes are formulated. These mixes were further subjected to engineering characterization-related studies, and this paper presents these test results. Setting time, strength, and stiffness results as well as excavatability evaluations of these mixtures are covered as a part of these studies. These results indicate that the CLSMs can be produced using native high-plasticity soils with strength properties always matching specified requirements. Certain relaxation on setting time periods could further help in developing economical mix designs. CLSMs that meet project specifications are recommended for field implementation

A Practical Framework to Assess the Sustainability and Resiliency of Civil Infrastructure

Research within civil engineering is focusing on newer ideas and philosophies such as sustainability and resiliency (S&R). This is evident in the development of frameworks for assessing the sustainability or the resiliency of civil infrastructures. Several frameworks have been developed by researchers to quantify the S&R of civil infrastructures. It is evident that the S&R are not mutually exclusive, and it is important to assess these aspects at the same time and that frameworks are able to accommodate simultaneous assessments. While there are other frameworks that follow a unified approach to S&R assessments, they do not account for the risk of the hazard as part of the framework. In the proposed framework, an attempt was made to include the risk of the hazard as part of the assessment to gain a realistic perspective of the hazard impact. This paper presents explicit steps to use the framework, along with an example of using the framework in assessing an earthen dam subjected to two types of hazards, earthquakes and floods. The novel aspects of this framework revolve around the simplicity and flexibility of the framework. Major input parameters are user-defined, which allows for a wide range of variables to be considered when determining the overall quality of the infrastructure

Flowability and Density Characteristics of Controlled Low Strength Material (CLSM) Using Native High Plasticity Clay

In pipeline construction projects when high plastic clayey soils are encountered in the excavated trench material, they are typically landfilled and better quality materials are imported from outside quarry sources for use as bedding and haunch zone materials. This practice has detrimental environmental and cost impacts; therefore, an efficient reutilization of this high plastic excavated material to produce controlled low strength materials (CLSMs) to use as bedding and haunch zone materials will have major sustainability benefits. As a part of an on-going research study, novel CLSM mix designs were developed by utilizing native high plastic clayey soils from the excavated trench material. Due to the high plasticity nature of the soils, it is essential to address both flowability and density property requirements prior to validating them against other engineering properties. Hence, several CLSM mixtures with the native clayey soils as ingredients were initially designed as per flowability criterion to establish the optimum quantities of chemical binders and water quantities. Later, these mixes were verified for satisfying density property criterion. This technical note presents the step by step procedure followed in preparing these mixes along with test results obtained from various mixes designed as a part of the testing program. Based on these results it was evident that CLSM mixes with high plastic clays can be developed that meet both flowability and density criteria. The success of this research has enhanced the sustainability efforts in pipeline construction projects as this study showed excavated clayey soils can be successfully reused in CLSM applications than landfilling them

Evaluating the Applicability of Biostimulated Calcium Carbonate Precipitation to Stabilize Clayey Soils

Clayey soils with medium to high plasticity are prevalent in several parts of the world, causing billions of dollars in damage annually to various civil infrastructures. Several ground-improvement techniques can be employed to counteract this issue. However, these methods are impractical in certain situations and unsustainable in others due to their economic and environmental impacts. Microbial-induced calcite precipitation (MICP) could provide a more sustainable alternative. Researchers have successfully used MICP to alter specific geotechnical properties of sands and silts. This research investigates the applicability of MICP via biostimulation to treat clayey soils with low to high plasticity. The goal is to determine the viability of this technique to alter the engineering behavior of clayey soils, especially given the low permeability of these soils. For this purpose, four soils were selected from four different locations in Idaho and Montana. The soils were selected such that their plasticity varied from low to high to study the effect of plasticity index on the effectiveness of MICP treatments. In addition to the four soils, three additional artificial mixes were studied to study the effect of clay content on MICP effectiveness. Both macroscale and microscale studies were conducted on untreated and biostimulated soils to observe strength gain, swelling reduction, and calcium carbonate precipitation. The results show that MICP via biostimulation would be a promising method to treat problematic clayey soils

Addressing Clay Mineralogy Effects on Performance of Chemically Stabilized Expansive Soils Subjected to Seasonal Wetting and Drying

Premature failures in chemically stabilized expansive soils cause millions of dollars in maintenance and repair costs. One of the reasons for these failures is the inability of existing stabilization design guidelines to consider the complex interactions between clay minerals and the stabilizers. It is vital to understand these complex interactions, as they are responsible for the strength improvement and swell/shrink reduction in these soils, in turn affecting the overall health of the infrastructure. Hence, this research study examined the longevity of chemically stabilized expansive soils subjected to wetting/drying conditions with a major focus on clay mineralogy. Eight different natural soils with varying clay mineralogy were subjected to wetting/drying durability studies after stabilizing with chemical additives including quicklime and cement. Performance indicators such as volumetric strain and Unconfined compressive strength trends were monitored at regular intervals during the wetting/drying process. It was observed that clayey soils dominant in the mineral Montmorillonite were susceptible to premature failures. It was also noted that soils dominant in other clay minerals exhibited early failures at lower additive contents. Also, an attempt was made for the first time to address the field implications of the laboratory studies by developing a correlation that predicts service life in the field based on clay mineralogy and stabilizer dosage

Evaluating the Effectiveness of Soil-Native Bacteria in Precipitating Calcite to Stabilize Expansive Soils

The use of chemical additives to stabilize expansive soils is a common practice. However, the environmental concerns associated with the greenhouse gas generation during the production of these chemicals have launched engineers in search of sustainable stabilization alternatives. Microbial induced calcite precipitation (MICP) is a bio-cementation technique that could be a potential solution to this problem. Typically, MICP is achieved via bio-augmentation; however, bio-stimulation was argued to be a more realistic alternative due to its field implementation potential. Hence, in this research study, two expansive soils with varying plasticity characteristics were examined to understand the potential of MICP in treating expansive soils. These two soils were subjected to MICP treatments using enrichment and cementation solutions. The treatment effectiveness was studied via response measures such as Atterberg limits, unconfined compressive strengths, one-dimensional swell test, and calcium carbonate precipitation. The results indicate that MICP has potential in stabilizing expansive soils and further research is warranted to explore this idea

Swell and Shrinkage Characterizations of Unsaturated Expansive Clays from Texas

Expansive soils have long been recognized as problematic because they cause failure to civil structures constructed above them. The main problem of these soils can be attributed to poor understanding of the volume changes caused by moisture fluctuations. Current swell and shrinkage characterization models are limited by both the lack of standardized tests and tests that employ volume changes in uniaxial direction. In the present research, a comprehensive laboratory investigation was undertaken to study the volume change related swell–shrinkage behaviors of five different types of expansive clayey soils sampled from various regions in Texas, USA. Extensive experimental programs consisting of basic, chemical and mineralogical soil properties were first determined. Three-dimensional free swell and shrinkage tests were performed on all soils at various compaction moisture content conditions. Soil–water characteristic curves (SWCCs) of all test soils were determined by studying the suction potentials of these soils over a wide range of moisture contents. Volume change measurements of soils showed a good correlation with soil properties, including plasticity and soil compaction properties. SWCC results also showed a clear variation in SWCC profiles of soils with respect to soil plasticity. Overall, a large database of soil properties was developed and is presented here. It includes physical and mineralogical properties, as well as engineering swell, shrinkage and SWCC test results

Optimizing Fiber Parameters Coupled with Chemical Treatment: PROMETHEE Approach

In order to combat issues related to expansive soils, chemical stabilization augmented with use of synthetic fibers is gaining focus in recent times. However, in most of these applications, the practicing field engineers face difficulty in selecting the right mix of fiber size, fiber dosage and stabilizer content. The decision becomes more typical, as the target is to achieve or enhance multiple geotechnical properties which differ with fiber dosage and stabilizer content based on governing mechanisms. Addressing these issues, in this study an attempt is made to present an approach for selecting fibre dosage and lime mix for a typical expansive semi-arid soil. In this article, the effect of randomly oriented polypropylene fiber inclusion in enhancing various geotechnical properties of a typical expansive semi-arid soil is studied. The addition of lime is considered in order to ensure proper bonding between clay particles and discrete fiber elements. PROMETHEE is adopted in order to assist in multi-criteria decision-making process. The approach evaluates multiple geotechnical properties for possible alternatives viz., untreated soil; lime treated soil and other including combinations of fiber dosage and fiber size in the presence of lime. The response measures being the targeted geotechnical properties which include, linear shrinkage tests, unconfined compression strength test, California Bearing Ratio behavior, compressibility characteristics and hydraulic conductivity. The study revealed the best possible alternative considering all the selected response measures