Haifeng Zou

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.

Evaluation of Liquefaction Potential of Saturated Sands Based on Resistivity Piezocone Penetration Testing

The liquefaction of saturated soils is a major concern for the earthquake damage of foundation. Due to the difficulty and cost constraint in obtaining high-quality undisturbed samples, in-situ testing is commonly applied to evaluating the potential of soil liquefaction. In high risk projects, a comprehensive evaluation based on various methods is usually adopted, and thus the research on new method to evaluate the liquefaction is still necessary. In this research the feasibility of using resistivity piezocone penetration test (RCPTU) for predicting liquefaction resistance is investigated. The resistivity of saturated silts and sands is measured using RCPTU at a test section of Suqian-Xinyi expressway. First, the relationship between normalized cone tip resistance and resistivity is analyzed and can contribute to the evaluation of soil liquefaction based on resistivity. Second, the study on combination of resistivity and soil behavior type index to directly calculate the cycle resistance ratio (CRR) is conducted with the CRR from Robertson modified liquefaction evaluation model as reference. The influence of thin cohesive layers and transition zones is also analyzed. It is shown that the resistivity and soil behavior type index can be used for effective evaluation of liquefaction potential of saturated soils.

Multivariate Correlations Among SCPTU Parameters of Jiangsu Cohesionless Soils

Estimation of Vs from other testing indices has gained increasing interest over the decades. The enhanced seismic piezocone penetration testing (SCPTU) provides a convenient method to measure Vs simultaneously with other three indices including the cone tip resistance, sleeve frictional resistance and pore water pressure in a close proximity. In this study, a database containing 612 sets of data points is compiled for the stress-normalized SCPTU parameters of the Jiangsu cohesionless soils. An approach based on the multivariate distribution method is utilized to develop the multivariate correlations among the normalized shear wave velocity (Vs1) and other three indices. It is shown that the correlations are reliable to describe the dependence of the Vs1 on other three indices for the Jiangsu cohesionless soils. However, caution shall be taken when these correlations are applied in other soils.

Evaluation of Liquefaction Potential of Saturated Sands Based on Resistivity Piezocone Penetration Testing—A Case Study

The liquefaction of saturated soils is a major concern for the earthquake damage of foundation. Due to the difficulty and cost constraint in obtaining high-quality undisturbed samples, in situ testing is commonly applied to evaluating the potential of soil liquefaction. At present, numerous methods based on the cone penetration test (CPT) have been developed, but none of them has been accepted to be the most reliable one. In high risk projects, a comprehensive evaluation based on various methods is usually adopted, and thus the research on new method to evaluate the liquefaction is still necessary. In this research the feasibility of using resistivity piezocone penetration test (RCPTU) for predicting liquefaction resistance is investigated. The resistivity of saturated silts and sands is measured using RCPTU at a test section of Suqian-Xinyi expressway. The study on combination of resistivity and soil behavior type index to directly calculate the cycle resistance ratio (CRR) is conducted with the CRR from Robertson modified liquefaction evaluation model as reference. The state parameter (Ψ) to directly calculate the cycle resistance ratio (CRR) is also analyzed. It is shown that the resistivity and soil behavior type index and the in situ state parameter (Ψ) are two good methods that used for effective evaluation of liquefaction potential of saturated soils.

Application of the Piezocone Penetration Testing to Assess Flow Characteristics of Marine Clay

Parameters from piezocone test (CPTU) are commonly used for soil profiling and geostratigraphy, along with the parameters used for assessment of geotechnical design. CPTU provides near-continuous measurements of tip resistance, sleeve friction and pore pressure at the shoulder, or face, or shaft of the cone. The dissipation results in CPTU soundings are used to evaluate the coefficient of consolidation and permeability of soil at intermittent depth. Recently, however, several approaches based on CPTU data to assessing the hydraulic conductivity of soils continuously are developed to avoid the time-consuming dissipation of excess pore pressure. This paper presents an experiment, centered on the use of piezocone tests, to determine the flow characteristics of cohesive soils on the engineering background of design of a transformer substation in Lianyungang, China. Three methods (two continuous and one discontinuous) are applied to obtain the coefficient of permeability of soils, and the results are compared with those from laboratory tests. This study confirmed the potential for use of piezocone tests to obtain valid predictions for flow characteristics of soils.