John J. Bowders

Controlled low-strength material using fly ash and AMD sludge.

Controlled low-strength material (CLSM) is a cementitious material with properties similar to stabilized soil. After hardening, CLSM provides adequate strength in bearing capacity and support but can also be easily excavated. To be classified as a CLSM, the material must have a compressive strength between 450 kPa (65 psi) and 8400 kPa (1200 psi). Typical CLSM contains coal-combustion fly ash (FA), cement, water and fine or coarse aggregate. In this paper, physical and strength properties of CLSM formed by combining sludge, a by-product from the treatment of acid mine drainage (AMD), with Class F FA are investigated. The sludge is a lime-based waste product that when combined with FA, exhibits self-hardening characteristics similar to cement. A main focus of this research is to develop a CLSM mix in which by-product material utilization is maximized while satisfying workability and performance requirements. A mixture of 10% AMD sludge, 2.5% Portland cement (PC), 87.5% Class F FA (dry wt.%) with water provided unconfined compressive strength values within the range for classification as CLSM. This mixture satisfies the excavatability and walkability requirements as well as the hardening time and stability criteria.

ENGINEERING PROPERTIES OF RECYCLED PLASTIC PINS FOR SLOPE STABILIZATION

An ongoing demonstration project has shown the feasibility of using slender (90 mm × 90 mm × 2.4 m) recycled plastic pins (RPPs) for in situ reinforcement of slopes and embankments. The technique uses RPPs driven into the face of the slope in a grid pattern to intercept the sliding surface and “pin” the slope. The engineering properties of the RPPs, including the compressive, tensile, and flexural strength along with creep behavior, dictate the design and construction practice. Constituent materials and manufacturing processes are highly variable among the more than 30 U.S. manufacturers. A specification for acceptance of the members is needed; however, before an effective specification can be developed, the appropriate engineering properties and design requirements for the RPPs must be determined. The engineering properties and driving performance of four different types of members were evaluated and are reported on. Additional evaluations are under way.

Sidewall leakage in hydraulic conductivity testing of Asphalt concrete specimens

Asphalt specimens with irregular sidewalls can require special testing considerations when measuring hydraulic conductivity in a flexible wall permeameter. The hydraulic conductivity of laboratory prepared, dense asphalt concrete with high asphalt cement content (6–8.5% asphalt cement) was measured in the laboratory. Hydraulic conductivities were found to be excessive and were shown to be caused by sidewall leakage. Applying a thin layer of silicone vacuum grease to the sides of the asphalt specimens arrested the sidewall leakage, thereby permitting more accurate measurement of the hydraulic conductivity of the asphalt concrete.

Stabilization of Surficial Slides Using Recycled Plastic Reinforcement

Surficial slope failures, or nuisance slides, constitute a significant economic and manpower burden for many transportation agencies because of the frequent and recurring nature of the slides. TRB recently estimated that annual costs for stabilization of nuisance slides exceed the costs for repair of major landslides; this estimate suggests that annual costs for repair of nuisance slides on the National Highway System alone exceed

Field Performance of Embankments Stabilized with Recycled Plastic Reinforcement

100 million. Recent work has shown the feasibility of using slender recycled plastic members for in situ reinforcement of surficial slides in slopes and embankments. This paper describes the activities performed to evaluate the technique and the results and conclusions derived from the work. Topics covered include the description of five instrumented field test sites, material properties of the recycled plastic members used, construction equipment and techniques used to install the members, general performance observed at the field test sites, and the costs of the technique as compared with other methods.

Sealed Double-Ring Infiltrometers for Estimating Very Low Hydraulic Conductivities

The performance of earth slopes reinforced with arrays of slender reinforcing members is currently being investigated. The reinforcing members used are fabricated from recycled plastics and other waste materials to form sections 90 mm (3.5 in.) × 90 mm (3.5 in.) × 2.4 m (8 ft) long. A design methodology was adopted to estimate the limit resistance provided by each member, which is then incorporated into conventional limit equilibrium slope stability analyses to calculate the improvement in the factor of safety under various reinforcement scenarios. Four field test sites were stabilized using recycled plastic reinforcement to demonstrate the effectiveness of the stabilization scheme and to evaluate the load transfer mechanisms between the soil and the reinforcement. One additional site was stabilized with similarly sized steel pipe members for comparison with the recycled plastic members. The stabilized slopes are performing well, whereas several control sections have experienced failures. The performance of each site is being monitored with field instrumentation to monitor lateral movements, pore pressures, strains within the reinforcing members, and the lateral loads applied to the members. Observations to date indicate that the slopes are performing well and that the reinforcing members have significant remaining capacity to maintain the stability of the slopes.

Prefabricated vertical drains for use in soil vapor extraction applications

The goal of this paper is to document the issues relating to measurement of in situ hydraulic conductivity of very low hydraulic conductivity materials, particularly asphalt concrete using sealed, double-ring infiltrometers (SDRIs). A new flow volume measurement device known as a constant head board (CHB) was developed and used alongside with flexible bags to measure the infiltration rate of the asphalt concrete barrier test pad. The design, construction, and use of the SDRI are presented followed by the design and operation of the CHB. A method to determine the hydraulic gradient based on the total flow quantity and air void content of the liner are presented. Flow quantity measurement, infiltration rate, and calculated hydraulic conductivity based on flexible bag and CHB options are presented and discussed.

Geotextile Separators for Dust Suppression in Unbound (Gravel) Roads

Soil vapor extraction (SVE) is an effective and cost-efficient method of removing volatile organic compounds and petroleum hydrocarbons from unsaturated soils. However, SVE becomes ineffective in soils with low permeability—for example, soils with air permeabilities less than 1 Darcy. Prefabricated vertical drains (PV drains) have been used to dewater finegrained soils for more than 20 years. For the last 5 years, PV drains have been used for soil flushing applications to remove contaminants below the groundwater table. Incorporating PV drains in an SVE system can extend the effectiveness of SVE to lower permeability soils by shortening the airflow paths and ultimately expediting contaminant removal. An advantage of using PV drains in place of conventional SVE wells is that they can be installed relatively inexpensively. The objective is to effectively incorporate PV drains into an SVE remediation system and to demonstrate a PV drain-enhanced SVE system at full scale.

Shear Behavior of Compacted Silty Loess

Dust is a health concern because of its potential to contain respirable particles, especially particles less than 10 microns in diameter (PM10). It is also a nuisance issue for residents living in the vicinity of unbound, unsealed (gravel) roads. Numerous techniques are used in attempts to reduce the dust generated from unbound roads, but all have limitations. Anecdotal evidence suggests that dust from unbound roads can be reduced for roads that incorporate a geotextile separator. A program to document the effect of the geotextile separators quantitatively is under way, with several test sections in central Missouri. A test section including a nonwoven, needle-punched geotextile; a non-woven, spun-bonded geotextile; and a new aggregate-only layer was installed; dust measurements were made over a 6-month period, during which the road experienced more than 3,600 vehicle passes. Dust levels were lowest immediately following the placement of new aggregate for the unbound layer and increased with time (traffic passes). Initially the sections containing a geotextile separator produced slightly less dust than the control (no geotextile) section. After 6 months of service, dust levels from the geotextile and control sections were similar, but the percentages of fines in the unbound layer above the geotextiles were about one-half that in the control section. Geotextile separators are likely to reduce dust for unbound roads when the source of particulate is fines migrating from the subgrade into the unbound layer. When the fines are developed because of degradation of the aggregate in the unbound layer, geotextile separators may be less effective in reducing dust from the roadway.

Sensitivity Study of a Ground Probing Radar System

Loess, a uniform-sized, wind-blown, cohesive soil can be problematic in geotechnical engineering applications. Natural deposits have high strength and exhibit stable vertical slopes; however, dramatic collapse can occur when loess becomes saturated. In remolded, compacted applications, the behavior of loess is less well known. Regionally (central USA), embankments of compacted loess can exhibit deformation and slope failure after years of service. The initial phase of a larger effort to characterize the strength behavior of compacted loess is reported herein. This phase is limited to assessing the short-term, undrained shear strength of compacted loess. Undrained strengths of compacted loess were measured to be up to 500 to 650 kPa. Higher compactive effort, dry of optimum water content, maximizes the undrained strength. Modified Proctor energy increased undrained shear strength by up to 2.5 to 3.0 times higher than loess compacted at the same water contents using standard energy. Loess compacted at or greater than optimum moisture content, as determined in the standard Proctor test, had similar undrained strength (100 to 200 kPa) regardless of the compactive effort. In order to maximize short term strength of compacted loess, use the greatest compactive effort and compact the soil well dry of optimum moisture content.