Boo Hyun Nam

Evaluation of the Use of Recycled Concrete Aggregate in French Drain Systems

Recycled concrete aggregate (RCA) is often used as a replacement for virgin aggregate in road foundations (base course), embankments, hot-mix asphalt, and Portland cement concrete. However, the use of RCA in exfiltration drainage systems, such as French drains, is still uncommon. The primary concerns with using RCA as drainage media are excessive fines and calcite precipitation that can cause a reduction in permeability performance. This study investigates the potential benefits of RCA as drainage material. This paper presents and discusses: (1) the results of a nationwide survey on current practices and policies, (2) physical and chemical properties, (3) effective fine-removing methods, (4) re-cementation potential, (4) permeability (under varied fine content), and (5) long-term drainage performance of RCA as drainage material. Test results indicate that RCA No. 4 gradation does not restrict the flow of water, but the RCA fines being generated during aggregate handling process (e.g., stockpiling, placing and transporting) may cause clogging buildup over time.

Investigation on Clogging Potential of Recycled Concrete Aggregate in French Drain Systems

Recycled concrete aggregate (RCA) has been used as replacement for virgin aggregates in road foundation, embankment, portland cement concrete, and hot-mix asphalt. The use of RCAs in drainage systems (i.e., base/subbase layer and French drain) has not received much attention because of the poor drainage performance of RCAs. Two major causes are (1) the accumulation of excess fines precipitated on geotextile and (2) deposition of calcite precipitation over time. To date, not many studies have been conducted on the drainage performance of RCAs. This limited and unavailable information hinders the use of RCA as drainage materials although there are many benefits to these in promoting sustainability in geotechnical and pavement engineering systems. In this paper, the drainage performance of RCA, No. 4 gradation used in a French drain system, has been investigated. Physical properties (i.e., abrasion resistance, gradation, absorption, etc.) of RCA were investigated, and a number of permeability (constant-head) tests were conducted. With the permeability test, the effect of fines (less than 75 µm) on the RCA permeability was evaluated. Lastly, accelerated calcite precipitation testing was devised and conducted to evaluate long-term performance of RCA associated with the calcite precipitation that can reduce permittivity of geotextile.

Effect of Cyclic Loading on the Lateral Behavior of Offshore Monopiles Using the Strain Wedge Model

This paper presents the effect of cyclic loading on the lateral behavior of monopiles in terms of load-displacement curves, deflection curves, and - curves along the pile. A commercial software, Strain Wedge Model (SWM), was employed, simulating a 7.5u2009m in diameter and 60u2009m long steel monopile embedded into quartz sands. In order to account for the effect of cyclic loading, accumulated strains were calculated based on the results of drained cyclic triaxial compression tests, and the accumulated strains were combined with static strains representing input strains into the SWM. The input strains were estimated for different numbers of cycles ranging from 1 to 105 and 3 different cyclic lateral loads (25%, 50%, and 75% of static capacity). The lateral displacement at pile head was found to increase with increasing number of cycles and increasing cyclic lateral loads. In order to model these deformations resulting from cyclic loading, the initial stiffness of the - curves has to be significantly reduced.

Methodology to Improve the AASHTO Subgrade Resilient Modulus Equation for Network-Level Use

AbstractFalling weight deflectometer (FWD) testing is commonly used to estimate subgrade resilient modulus (MR) by using back calculation and/or the AASHTO MR equation. Considering the availability of limited information in the pavement management information system (PMIS) database, the AASHTO MR approach is suitable for subgrade assessment at a network level because of its simplicity. An adjustment factor is commonly applied to the AASHTO MR equation because of the difference between laboratory-measured MR and estimated MR. However, large variations in the adjustment factor have been observed with different geographical locations and climate conditions. Thus, using a fixed value of the adjustment factor has led to inaccurate assessment of subgrade soil MR. This paper presents a methodology to improve the accuracy of the existing AASHTO MR equation by constructing an MR adjustment factor based on the correlation of back-calculated ER and AASHTO MR. This study also investigated the effects of subgrade soil...

Physical and Numerical Analysis on the Mechanical Behavior of Cover-collapse Sinkholes in Central Florida

The behavior of cover-collapse sinkholes in Central Florida was investigated in this research by both physical and numerical methods. In the physical model, a head drop between the unconfined aquifer and the confined aquifer was applied, and the cavity propagation due to a fracture at the boundary between the two aquifers was visually monitored. The cavity grew upwards in an inverted triangle shape until ground surface collapse occurred. The same cavity shape was then incorporated into the numerical study. A stress-seepage coupled analysis was carried out using GeoStudio modules: SEEP/W and SIGMA/W, simultaneously. The stress conditions during sinkhole formation were assessed at different groundwater conditions and cavity sizes. Stress redistributions were observed around the cavity due to soil arching. The effective stress significantly increases at the corners of the cavity to compensate for a stress reduction above the center of the cavity. Highest recharge values and seepage forces occur around the cavity corners. The stress paths at the corners show that the stability decreases when the cavity height increases, even when the overburden thickness decreases. Additionally, the side angles of the cavity affect the stress conditions around it. Introduction Sinkholes are a common geohazard in karst terrain which threaten human life and infrastructure throughout the world approximately 20% of the United States has karst features where residual soils are underlain by soluble carbonate rocks. Cavities develop at the interface between the residual soils and bedrock by a soil erosion process which ultimately leads to ground failure (Newton & Hyde, 1971; Newton, 1976, 1984; Williams & Vineyard, 1976). According to the USGS, the most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania. Florida Geological Survey classifies sinkholes in Florida into three major types: covercollapse, cover-subsidence, and dissolution. The most dramatic type is the cover-collapse due to its abrupt behavior. The collapse occurs when a subterranean cavity grows until the overburden thickness above the cavity becomes too thin for soil arching to be maintained. In Florida, the groundwater flow triggers the growth of subterranean cavities by erosion and increases the instability of the system by seepage forces. Florida’s aquifer system consists of an unconfined surficial aquifer (residual soil layer) overlying the confined Upper Floridan Aquifer (bedrock layer) which is the main source of groundwater withdrawn for usage purposes. The water level in the surficial aquifer is highly influenced by the rapid infiltration of rainwater due to the relatively high hydraulic conductivity of this soil layer. However, the hydraulic conductivity in the Upper Floridan Aquifer, which is mainly composed of limestone, is relatively low. Therefore, the head of water in the residual soil (surficial aquifer) is usually greater than that in the limestone (Upper Floridan Aquifer) which results in downward seepage (recharge). Wilson and Beck (1992) observed that 85% of new sinkholes in the Orlando area occurred within areas of high groundwater recharge. Whitman and his team (1999) examined the spatial interrelationships of head difference between Moataz H. Soliman Department of Civil, Environmental, and Construction Engineering, University of Central Florida, 4000 Central Florida Blvd, Orlando, FL 32816, U.S.A, moatazhs@knights.ucf.edu Adam L. Perez Department of Civil, Environmental, and Construction Engineering, University of Central Florida, 4000 Central Florida Blvd, Orlando, FL 32816, U.S.A, alperez87@knights.ucf.edu Boo Hyun Nam Department of Civil, Environmental, and Construction Engineering, University of Central Florida, 4000 Central Florida Blvd, Orlando, FL 32816, U.S.A, boohyun.nam@ucf.edu (corresponding author) Ming Ye Department of Scientific Computing and Geophysical Fluid Dynamics Institute, Florida State University, Tallahassee, FL 32306, U.S.A, mye@fsu.edu

An Optimized Data Interpretation for Marshall Flow and Stability Test

Due to its simple and quick manner in testing, Marshall Stability and Flow test method is still widely used over the world. Testing method provides useful information such as strength, deformation, and stiffness represented by Stability, Flow, and Martial Quotient (MQ) respectively. However, an initial error in load-displacement curves can generate significant misleading in those mechanical properties. This paper presents an optimized data processing method for data interpretation. Previous researches and specifications related to MQ are reviewed to identify limitations of the exiting data interpretation methods. Laboratory experiments were performed to verify the limitation of the current methods. This study illustrates that a non-resistive section of specimen causes an “initial delay” in the load-deformation curve, resulting in misleading of the mixture properties. Lastly, the automated algorithm to offset the initial delay and determine the best MQ was devised.