Tejo V. Bheemasetti

Numerical Modeling of a Highway Embankment Using Geofoam Material as Partial Fill Replacement

Geofoam material has been used as a partial replacement for conventional fill material in a highway embankment in Texas, USA, to mitigate bridge-approach slab settlements. The embankment under current focus was constructed more than a decade ago and has experienced nearly 405 mm (16 in.) of settlement since its construction. Several treatment methods were attempted in mitigating the settlement, which were proven to be ineffective. One of the primary causes of the settlement was attributed to embankment and its self-weight. To reduce the weight, part of the embankment fill was replaced with a lightweight EPS geofoam material. This site was extensively instrumented with horizontal inclinometers at different locations for monitoring the settlements after rehabilitation. Settlements occurring in the field have been monitored periodically. To understand the settlement patterns occurring in the field and also to identify the long-term performance of this section, numerical and analytical hyperbolic modeling were attempted. Both these models are used to predict the approximate long-term settlements. Prediction results indicate that the settlements predicted by the hyperbolic model are higher when compared with the same predicted by numerical model.

Spatial Mapping of Soluble Sulfate Concentrations Present in Natural Soils Using Geostatistics

AbstractSulfate heaving has had a major impact on civil engineering infrastructure for the past few decades. Past researchers have attributed the provenance of this heaving mechanism to the chemical reactions between soluble sulfates and calcium-based stabilizers, but despite the increase in studies related to sulfate heaving, very little effort has been made to address the variability of sulfate concentrations in the field. The natural deposition of sulfate pockets causes inevitable problems to chemical stabilization techniques. Because of the high variability of sulfate concentrations present in nearby locations, it is possible that engineers may mischaracterize the sulfate concentrations or not able to design appropriate stabilization measures in the field. In this study geostatistical analysis was used to quantify and map sulfate concentrations along a mega water pipeline project located in north Texas. Various soil samples, originating from six different geological formations along the pipeline align...

Assessment of Measurement Errors of Piezocone Penetration Test in Soft Clay

Uncertainty evolved through in situ testing, such as measurement error, is a major concern in the characterization of soft clays that suffer from the low strength and high sensitivity of soil properties. In this research, 20 piezocone penetration tests (CPTUs) in a laboratory calibration chamber and 25 CPTUs performed in marine soft clay in Lianyungang, Jiangsu province, China, are considered for characterizing various in situ measurement errors. Equipment error, calibration error, penetration pause effect, and random measurement error are identified as the four main sources of measurement errors based on comprehensive literature review and field observations. Laboratory studies revealed that a coefficient of variability (COV) of 4 % was recorded for uncertainties associated with calibration of the device. Analyses performed on the in situ measurements showed that the COVs of penetration pause effects on cone tip resistance values varied from 0 % to 8 %. The methods of moments and maximum likelihood approach were used to estimate the random measurement error of qt profiles based on the analysis of correlation structure. Both methods showed that COVs of random measurement error of qt ranged from 0 % to 12 %. Using the second-moment statistics, the COVs of the total measurement errors comprising of calibration and equipment error, penetration pause effects and random measurement errors were estimated to vary from 5 % to 15 %. Consequently, a representative CPTU sounding example was used to demonstrate the influence of measurement error on the tip resistance measurements. Overall, this research presents a rational method to improve the accuracy of CPTU measurements in marine soft clay by separating the uncertainties associated with measurement errors.

Effect of Constant Energy Source on Coherence Function in Spectral Analysis of Surface Waves (SASW) Testing

The quality and acceptability of a waveform data collected during spectral analysis of surface waves (SASW) testing is judged based on the coherence function over the measured range of frequencies. However, many trials and repetitions are required during SASW testing to obtain data with acceptable coherence value (>0.95). This makes the test time-consuming, and in most cases, only small portion of the collected data that satisfies the acceptable coherence criteria can be used for analysis. In this research study, an attempt was made to study the effect of using an impact source of constant energy on the coherence function as compared to the use of traditional handheld hammers. Laboratory experimental studies were performed on sandy clay soil bed filled in a metal box of dimensions 1.5 m × 0.61 m × 0.45 m. Also, a series of field tests were performed to validate the applicability of the laboratory findings. In both laboratory and field testing, a 2.5 kg hammer was used with height of fall as variable parameter. Two sets of tests were performed. One with random height of fall that is similar to current practice and the other with fixed height of fall of 0.13 m to simulate impacts with same energy conditions. Test results depicted that unlike the conventional procedure of testing, the use of constant energy of impact leads to coherence close to 1 over a significantly large frequency bandwidth. This research highlights the effect of using constant and varying impact energy on coherence value over a wide range of frequencies obtained during SASW testing.

Quality Assurance Studies for Ground Improvement Projects

In situ QA/QC studies play a crucial role in the civil engineering projects, especially in ground improvement projects related to geotechnical engineering. These studies are of paramount importance in geotechnical engineering projects as they not only enhance the overall quality of the project but also ensure that the project is being constructed as per standards. In this research paper, QA/QC studies that were performed on two different ground improvement techniques including chemical stabilization using native high plasticity clays, and deep soil mixing (DSM) technique are discussed. These solutions on all the projects discussed provided a new approach on analysing the geotechnical engineering data.

Analysis and Interpretation of Inclinometer and Pressure Cell Data on a Soil-Geofoam Embankment

This paper presents analysis and interpretation of monitored vertical settlements and pressures of a rehabilitated bridge approach slab located in Johnson County, Texas. Four horizontal inclinometer casings and pressure cells (equipped with thermometers) were installed at the test site during the rehabilitation process. In this paper, collected data from the inclinometers, pressure cells, and thermometers were employed in an attempt, to understand the effect of climate changes on the vertical settlements and pressures of the approach slab. It has been observed that with an increase in temperature, the bridge structure enforced the movements of the geofoam blocks causing vertical settlement. Whereas, the bridge structure movements after a temperature decrease, induced vertical swelling at the top of the geofoam blocks. The pressure cells that were installed at the top and bottom of the geofoam embankment revealed that the stresses observed at the top of the geofoam were significantly reduced. Also, the pressure cells installed at the sides of the bridge and geofoam structure to evaluate the lateral pressure response lost contact and provided negative results. The loss of contact can be a response to the movement of the structure with respect to thermal changes in the structure. This research highlights the important observations of a bridge structure and its approach soil-geofoam embankment movements with respect to temperature and precipitation variations.

Geotechnical Data Visualization and Modeling of Civil Infrastructure Projects

Geomaterial data analysis and visualization are important tools as they can provide geotechnical information in a visualized way that will help design and practice engineers understand the site to materials conditions in a holistic manner so they can make prudent decisions on foundation infrastructure to ground improvement options. With the advancements made in the computational arena, the use of material property sets including those of large data sets, one can expect a nicer presentation of site to material characterization if they are presented in a visual manner. GIS-based visualization tools are often used in many areas of the geotechnical engineering including terrain digital elevation modeling, subsurface material characterization, infrastructure monitoring and hazard mapping. Tests including laboratory and field studies on geomaterials, sensor instrumentation, remote sensing and photogrammetry studies, and others have provided geomaterial characterization to performance details in the visualization models. This paper highlights a few of these highlights and advancements made for better understanding of construction and performance of infrastructure using geospatial and visualization tools. Case studies ranging from data captured from photogrammetry-based measurements using unmanned aerial vehicles (UAVs) platforms to material characterizations to in-situ cone penetration tests are described to illustrate the significance of 2-Dimensional and 3-Dimensional based visualization analyses. Future applications are also briefly covered.

Assessment of Guar Gum Biopolymer Treatment Toward Mitigation of Desiccation Cracking on Slopes Built with Expansive Soils

Expansive soil embankments are prone to shallow slope failures caused by associated swell–shrink movements. Previous studies have confirmed that seasonal changes and corresponding volumetric changes are responsible for desiccation cracking, which is a major factor behind shallow slope failures of highway embankments. For the past few years, soil stabilization proved to be an effective way to mitigate the swell–shrink property of expansive clays. The current study addresses the feasibility of guar gum biopolymer in mitigating the swell–shrink behavior of clays and in turn making it possible to adopt them as stable geomaterials. The sustainable benefits of biopolymers far exceed the environmental benefits from conventional stabilizers that contractors typically use. This paper presents a comprehensive laboratory study, followed by finite difference modeling analysis, on biopolymeric guar gum–remediated expansive soils collected from shallow slope failure-prone areas. For this study, two dam locations, at Grapevine Lake and Joe Pool Lake, Texas, that were originally constructed with expansive soils, were considered. The engineering performance of biopolymer-treated soils was evaluated and an optimum dosage was recommended for mitigating desiccation cracking at the test sites. Slope stability analyses were conducted using Fast Lagrangian Analysis of Continua in Three Dimensions software by adopting laboratory-determined strength parameters to determine the range of the factor of safety for the slopes. The variation of the factor of safety computed with the inclusion of enhanced engineering parameters from guar gum treatments revealed the advantages of adopting this treatment.

A rational approach to select the number of field tests required to determine subgrade properties

Abstract This paper presents a rational approach to answer the questions of how many field tests need to be performed at a test site to determine its subgrade strength properties, and what inferences can be drawn from limited number of field tests. MATLAB simulations were performed to generate various data sets that corresponded to site variability, with the coefficient of variation (CoV) ranging from 10 to 80%. Studies were performed based on coefficient of variation (CoV) and regression analysis. This study provides two important charts for evaluating subgrade properties at test sites: (1) to determine the number of field tests to be performed, after which there would not be any significant change in the inferences drawn from the test results; (2) inferences pertaining to subgrade soil property of a field test site, based on a limited number of tests. In order to demonstrate the applicability of the charts developed through this research, light weight deflectometer (LWD) spot tests that were performed at a test site, were considered. The results were used to draw inferences about the modulus of the subgrade material and the possible variability of the test site, in addition to the maximum number of tests that might be performed.

Design of Sustainable High-Volume Pavements Using Controlled Low-Strength Material from Native Soil

Long-term performance and durability of a pavement structure built on expansive soils are mainly dependent on the effective stabilization of the subgrade and the compaction techniques adopted during construction. Recent studies proved that the self-compacting, controlled low-strength materials acted as an effective bedding material for pipelines. A major portion of highways and low-volume traffic intersections are underlain by pipelines and other culvert structures. In this research study, an attempt was made to investigate the effectiveness of controlled low-strength material (CLSM) as a pavement subgrade material. For this study, CLSM mix designs were investigated by using native high-plasticity soil and Type 1 portland cement. From these mix designs, two high-performing mixes were selected on the basis of their setting time, flowability, and density. A series of resilient modulus tests and durability tests was conducted on the samples cast in the laboratory. Alternate wetting–drying cycles were conducted on laboratory cast specimens to address the long-term stability of the proposed mixtures. These test results were analyzed. A sustainable mix design is recommended for the design of high-traffic pavement roads. It was observed that Mix Design 2, with 10% cement, showed significant improvement in terms of strength and durability and thereby showed promise as a subgrade material for high-volume roads.