Swell and Shrinkage Strain Prediction Models for Expansive Clays

A comprehensive laboratory investigation was conducted to study volume change behaviors of five different types of expansive clayey soils sampled from various regions in Texas, USA. The laboratory test results, which were presented in an earlier paper, are analyzed here to evaluate existing correlations that can be used to predict swell and shrink-related displacements in these soils. The test database is also used to develop newer and practical models for predicting volume change-related soil properties. Models developed here used soil plasticity and compaction properties as independent variables. Newer models, that rely on seasonal compaction moisture content variations in the subsoils, were introduced to estimate both volumetric and vertical swell and shrinkage-induced soil deformations expected under civil infrastructure. The developed correlations, along with the existing models, were then used to predict vertical soil swell movements of four case studies where swell-induced soil movements were monitored. This comparison analysis showed that the model dependency on the volume change test procedural information and moisture content variation due to seasonal changes will lead to better prediction of swell movements in subsoils. Future research directions and recommendations are provided on implementation of the developed models in a realistic estimation of swell movements of infrastructure construction projects

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

Shrinkage and Consolidation Characteristics of Chitosan-Amended Soft Soil: A Sustainable Alternate Landfill Liner Material

Kuttanad is a region that lies in the southwest part of Kerala, India, and possesses soft soil, which imposes constraints on many civil engineering applications owing to low shear strength and high compressibility. Chemical stabilizers such as cement and lime have been extensively utilized in the past to address compressibility issues. However, future civilizations will be extremely dependent on the development of sustainable materials and practices such as the use of bio-enzymes, calcite precipitation methods, and biological materials as a result of escalating environmental concerns due to carbon emissions of conventional stabilizers. One such alternative is the utilization of biopolymers. The current study investigates the effect of chitosan (biopolymer extracted from shrimp shells) in improving the consolidation and shrinkage characteristics of these soft soils. The dosages adopted are 0.5%, 1%, 2%, and 4%. One-dimensional fixed ring consolidation tests indicate that consolidation characteristics are improved upon the addition of chitosan up to an optimum dosage of 2%. The coefficient of consolidation increases up to seven times that of untreated soil, indicating the acceleration of the consolidation process by incorporating chitosan. The shrinkage potential is reduced by 11% after amendment with 4% chitosan and all the treated samples exhibit zero signs of curling. Based on the findings from consolidation and shrinkage data, carbon emission assessments are carried out for a typical landfill liner amended with an optimum dosage of chitosan. In comparison to conventional stabilizers like cement and lime, the results indicate that chitosan minimized carbon emissions by 7.325 times and 8.754 times, respectively

Safety Evaluations for Skewed Intersections on Low-Volume Roads: Case Study

Safety on low-volume roads is a major concern. It has been reported that the traffic fatality rate is more than three times higher on rural roads than on other roads. Some of these fatalities occur at inter sections, and the safety risks increase when the intersections are skewed or have an elevation difference. In Idaho, some skewed intersections (e.g., those on SH-39 and US-91 in eastern Idaho) are the result of highways having been built parallel to rivers or railroad lines and local roads having been built later on a grid with a north–south or east–west orientation. In an attempt to improve the safety of existing intersections, the Idaho Transportation Department\u27s District 5 performed a systematic and comprehensive evaluation of all of the intersections on the state highway system in southeastern Idaho. In total, 125 intersections along US-91 and 194 intersections along SH-39 were evaluated, and safety improvements were made. These improvements resulted in a reduction in the overall number of crashes along these two highways. This paper presents the results of these evaluations and the recommendations that followed

Microbial-Facilitated Calcium Carbonate Precipitation as a Shallow Stabilization Alternative for Expansive Soil Treatment

Expansive soils generally recognized as swell-shrink soils have been a problem for civil infrastructure for a long time. Engineers are in search of sustainable stabilization alternatives to counter these problematic soils. Microbial-induced calcium carbonate precipitation (MICP) is a promising biocementation process that can improve the properties of expansive soil through calcium carbonate precipitation. Past research has shown promise for the use of MICP in mitigating swelling distress from expansive soils. In this research, MICP via biostimulation was attempted by mixing enrichment and cementation solutions with soils in an effort to develop a new alternative to shallow chemical stabilization. Three soils with varying clay contents (30%, 40%, and 70%) and plasticity characteristics were selected, and soils were treated by mixing with enrichment solutions followed by cementation solutions. Five different mellowing periods, three different curing periods, and two types of cementation solutions were studied to optimize the method. Treatment effectiveness was evaluated using unconfined compression tests, calcium carbonate tests, and free swell index tests. Results showed that an increase in the mellowing period beyond two days was not beneficial for any of the three soils tested in this research. It was determined that the best improvement was observed at two days of mellowing and seven days of curing

Utilizing Site Investigation and Load Tests to Predict Drilled Shaft Design Parameters and Capacities for Various Geological Formations

An accurate prediction of design capacities of a drilled shaft on weak rock formations is vital for a better design of deep foundations. Irregularities in rock formations due to weathering cause high inconsistency in actual bearing capacities. The assessment of bearing capacity of these rocks typically requires frequent in situ field tests such as drilled shafts load test at smaller intervals (multiple gauges) that are time consuming and expensive. The current design charts that being used in few states such as Texas and Oklahoma do not distinguish between the various types of rock or degradable materials such as intermediate geomaterials (IGM) or shale formations. This study documents several load tests such as Statnamic and bi-directional (O-cell) load cell testing (Osterberg) that were performed across the United States. The principal goal of this research is to improve methods to predict drilled shaft design capacities by accounting for the geologic formations and learning from past projects. This research developed predictive equations to shaft capacities for various rock formations

Effect of fibre reinforcement on CBR behaviour of lime-blended expansive soils: reliability approach

The use of synthetic fibres as reinforcement to stabilise expansive soils is gaining momentum. As a contribution towards this growing field of research two different types of synthetic fibres, Fiber Mesh® and Fiber Cast®, were evaluated as a stabilisation alternative for expansive soils in the presence of lime. California bearing ratio (CBR) is chosen as a performance indicator as it is a good pointer towards pavement effectiveness. Variables such as length and amount of the fibres as well as curing period were studied. Both deterministic and probabilistic (or reliability) analyses is presented in this paper. While the deterministic analysis helps in understanding the measured experimental data, the probabilistic approach accounts for the stochastic nature of the experimental data and provides a better rationale for the design methods. The deterministic approach showed that the improvement in CBR increased with higher fibre contents and longer lengths and the effect was prominent when lime was used as a stabiliser. There were some exceptions to this behaviour, which were noted in the paper. The probabilistic analysis showed that the amount and lengths of fibres were important factors in CBR strength. It was also determined that the variation in the target CBR value had a considerable effect on optimising the length and amount of the fibres

Safety Evaluations for Skewed Intersections on Low-Volume Roads

Safety on low-volume roads is a major concern. It has been reported that the traffic fatality rate is more than three times higher on rural roads than on other roads. Some of these fatalities occur at inter sections, and the safety risks increase when the intersections are skewed or have an elevation difference. In Idaho, some skewed intersections (e.g., those on SH-39 and US-91 in eastern Idaho) are the result of highways having been built parallel to rivers or railroad lines and local roads having been built later on a grid with a north–south or east–west orientation. In an attempt to improve the safety of existing intersections, the Idaho Transportation Department\u27s District 5 performed a systematic and comprehensive evaluation of all of the intersections on the state highway system in southeastern Idaho. In total, 125 intersections along US-91 and 194 intersections along SH-39 were evaluated, and safety improvements were made. These improvements resulted in a reduction in the overall number of crashes along these two highways. This paper presents the results of these evaluations and the recommendations that followed