Sarah L. Gassman

Leak detection in pipes by frequency response method using a step excitation

This paper presents a new procedure utilizing transient state pressures to detect leakage in piping systems. Transient flow, produced by opening or closing a valve, is analyzed in the time domain by the method of characteristics and the results are transformed into the frequency domain by the fast Fourier transform. This method is used to develop a frequency response diagram at the valve end. The frequency response diagram of a system with leaks has additional resonant pressure amplitude peaks (herein called the secondary pressure amplitude peaks) that are lower than the resonant pressure amplitude peaks for the system if there were no leaks (herein called primary amplitude peaks). The location of a leak is determined from frequencies of the primary and secondary pressure amplitude peaks and the leak discharge is determined from the maximum and minimum discharge amplitudes. This method is applicable for practical values of the friction factor over the range 0.01 to 0.025 and can be used to detect leaks in real-life pipe systems conveying different types of fluids, such as water and petroleum. It can be used directly by comparing the frequency response diagram of a modeled system without leaks to the frequency response diagram developed by gradually opening or closing a valve at the downstream end of a pipe and taking measurements of pressure head and discharge at only one location.

Damage Assessment of Concrete Bridge Decks using Impact-Echo Method

This study presents results of a nondestructive evaluation (NDE) testing program performed to assess the damage in concrete bridge decks subjected to full-scale static and dynamic loading using the impact-loading method. The bridge decks were removed from a bridge built in 1953 in South Carolina. While in service, the concrete decks were retrofitted with FRP composite materials to repair extensive damage. Two slabs were tested by NDE in the lab after removal of the reinforcement layer. Impact-echo tests (IETs) were performed concurrently with full-scale static and dynamic load tests. The first slab was statically loaded to failure, and the second was tested dynamically with cyclic loading. IETs were performed before and after the loading sequence for each slab and between each application of cyclic loading for the second slab. Results from tests on the statically loaded slab detected a significant reduction in propagation wave velocity after failure, indicating a reduction in the slab stiffness. IETs on the dynamically loaded slab quantified the degradation of the slab during dynamic testing. Significant damage was detected earlier than by visual observance and before the slab reached service failure.

LONG-TERM STRENGTH DEVELOPMENT OF CONTROLLED LOW-STRENGTH MATERIAL

This paper presents results of an experimental study conducted to evaluate the combined effects of prolonged mixing time, late water inclusion, and variations in total water content on the long-term compressive strength of controlled low-strength material (CLSM). Long-term strengths refer to strengths measured after 600 days of curing. To evaluate strength development in moist ground conditions, sampled specimens were continuously cured in water. The main aim of the research was to determine the effects of mixing and water content variables on the long-term strength development of the immersed CLSM mixture as measured by unconfined compression testing. Findings are discussed.

Characterizing the Liquefaction Resistance of Aged Soils

The occurrence of liquefaction in soils is often evaluated using the simplified procedure originally proposed by Seed and Idriss based on in situ indices. Although numerous studies have been conducted to improve and extend this procedure, the effect of age on liquefaction resistance is still poorly understood and correction factors have not been generally accepted. Nine published studies on the effect of age are reviewed in this paper. A regression line representing the average variation in liquefaction strength grain with time was developed from cases where strength was expressed based on recommended liquefaction resistance curves. This regression line is considered an update of the previously proposed relationship by Arango et al. The results indicate that commonly used liquefaction evaluation procedures can be overly conservative in many natural soil deposits.

Methods for Field and Laboratory Measurement of Flowability and Setting Time of Controlled Low-Strength Materials

Flow consistency and setting time are two important properties of controlled low-strength materials (CLSM). This paper describes and evaluates several standard and non-standard methods to measure these properties. Several mixtures with a range of water-to-binder ratios were investigated through a series of field and laboratory experiments. A linear relationship was observed between the flowability measured by the flow cylinder method (ASTM D 6103) and the inverted slump cone method. Pocket penetrometer and Torvane measurements were compared to the Kelly Ball method (ASTM D 6024) for estimating sufficient bearing capacity. Pocket penetrometer resistance correlates well, but its capacity was often exceeded. Volume stability should be controlled to avoid softening of the surface and subsequent delays in measured hardening time.

Effect of Soil Aging on Assessing Magnitudes and Accelerations of Prehistoric Earthquakes

Increase in strength due to aging of sands is reflected in higher blow counts and tip resistance values in penetration resistance measurements. This affects the magnitudes and peak ground acceleration estimates of prehistoric earthquakes obtained from an analysis of geotechnical observations at paleoliquefaction sites in the South Carolina Coastal Plain. In this study, corrections were made to account for the effects of soil aging, which were neglected in earlier estimates. The results show that when the effects of aging of soils on their geotechnical properties are incorporated, the resulting back-calculations reduced earlier magnitude estimates of prehistoric earthquakes by about 0.9 units. The peak ground acceleration estimates were reduced by about 15% for those earthquakes originally estimated at approximately 0.15 g. For those earthquakes whose original estimates were greater than 0.2 g, there was no noticeable change when a correction was made for the aging of soils.

Environments for fostering effective critical thinking in geotechnical engineering education (Geo-EFFECTs)

This paper describes the development, implementation, and assessment of instructional materials for geotechnical engineering concepts using the Environments for Fostering Effective Critical Thinking (EFFECTs) pedagogical framework. The central learning goals of engineering EFFECTs are to (i) improve the understanding and retention of a specific set of concepts that provide core knowledge and (ii) encourage students to recognise and develop critical thinking skills that lead to growth in engineering judgement. The practice of geotechnical engineering deals with complex and uncertain soil conditions, where critical thought and judgement are imperative. Three geo-EFFECTs were created in the context of levee reconstruction, levee permeability, and settlement of a tower structure. Students often provided inaccurate estimates to driving questions set in those contexts; when given opportunities for self-exploration and self-correction in the EFFECT structure, students often achieved more accurate final solutions. Overall, results suggest that EFFECTs have a measurable, positive impact on student learning.

Performance Evaluation of High-Density Polyethylene Culvert Pipe

A study has been performed to evaluate the field performance of existing high-density polyethylene (HDPE) pipe used for drainage applications on highway projects. Forty-five HDPE pipes were inspected at sites in South Carolina. The sites were statistically selected based on geographical location, pipe diameter, use, and age, and the condition of each pipe was not known before selection for inspection. Pipe performance was evaluated with respect to AASHTO and ASTM specifications, measurements of pipe deflection with a mandrel set to 5% deflection, and visual inspections using a video camera. The video camera inspections revealed circumferential cracks in 18% of the pipes, localized bulges in 20% of the pipes, and tears or punctures in 7% of the pipes. Deflections greater than 5% were observed in 20% of the pipes. Most of this observed damage was considered minor because the pipes were maintaining a relatively round shape with limited structural distress and still performing near to the original installation purpose. Installation problems such as poor preparation of bedding soils, inappropriate backfill material, and inadequate backfill cover contributed to the excessive deflection and observed internal cracking in pipes with observed damage. More pipes backfilled with Class IV soils did not pass the mandrel test than those backfilled with Class II or III soils. In addition, cracks were more apparent in Class IV backfilled pipes than they were in pipes backfilled with Class II or Class III soils. Forty-four percent of the pipes had less than the recommended height of soil cover. Appropriate installation procedures are essential to achieving high-quality performance.

Effect of resilient modulus of undisturbed subgrade soils on pavement rutting

Abstract This paper presents the results from a test program to characterise resilient modulus (M R ) of subgrade soils for different geographic regions in South Carolina. For this study, Shelby tube samples of subgrade soils were collected from existing pavements in different regions: SC-93 in Pickens county (Upstate Area), US-521 in Georgetown county (Coastal Plain), and US-321 in Orangeburg county (Coastal Plain, near the fall line). Resilient modulus model parameters were obtained using both the bulk stress model and the generalised constitutive resilient modulus model. Statistical analysis was performed to develop M R estimation models for undisturbed soils using soils index properties. A correlation between laboratory measured M R with the modulus from Falling Weight Deflectometer tests was also developed. Finally, the effects of M R on subgrade rutting were studied using MEPDG. Results showed that the developed models offer higher reliability than the universal Long-Term Pavement Performance models in estimating the resilient modulus of undisturbed soils and predicting subgrade rutting for South Carolina.

Magnitudes of Prehistoric Earthquakes at the Hollywood, South Carolina Site

Pleistocene soil deposits show an increase in liquefaction resistance compared to younger deposits; thus, semi-empirical procedures for evaluating liquefaction potential that are derived from databases of young Holocene soils may not be applicable to aged soils. In this study, the minimum earthquake magnitude and peak ground acceleration required to initiate liquefaction were computed for soils estimated to be about 120,000 to 130,000 years old at the Hollywood site located in the South Carolina Coastal Plain. Discovered sandblows at this site are associated with earthquakes that date back to 11,000 years before present. In-situ geotechnical data, including SPT and CPT with pore water pressure measurements, were used with empirical methods that account for the age of the soil deposit to back analyse the minimum earthquake magnitude and peak ground acceleration at the time of the prehistoric earthquakes. When the age of the earthquake was not considered, the magnitude ranged from 7 to 7.2 and the corresponding acceleration ranged from 0.23 to 0.35g. The earthquake magnitude at the time of earthquake was found to be lower when accounting for age; for the most recent prehistoric earthquake with the age of 546±17, the magnitude was reduced and ranged from 5.7 to 6.7 with corresponding acceleration ranging from 0.17 to 0.30g.