Alamitos Gap: A Case Study Using the Trench Remixing and Deep Wall Method

The trench remixing and deep wall method (TRD) is a one-phase process for excavation and in situ mixing of a vertical barrier. While the TRD method was developed and has been widely employed in Japan for more than a decade, it has only recently been used in the United States. Since the TRD method mixes the entire depth of the vertical profile, this method can be used to construct a more homogeneous wall than other in situ methods. Using a large revolving chain and cutter bar, the TRD equipment simultaneously excavates and mixes in situ soils and added slurry resulting in a continuous soil mixed wall. The blend of slag, Portland cement and clay-water slurry is added as the excavation moves along the alignment of the barrier and produces continuous vertical mixing of in situ soils with the added blend. This paper presents a case study of the first TRD project in the United States involved the construction of closed cells to allow full evaluation of the method. This installation was part of a larger evaluation of the use of a vertical passive barrier to prevent the intrusion of salt water into fresh ground water aquifers in Southern California. The paper describes the site characterization, an extensive laboratory study conducted to investigate the appropriate mix design, field construction and post-construction testing. The case study shows the methodology used to develop design mixtures and presents information showing the successful completion of a barrier wall by the TRD method

Design and Evaluation of IoT-Enabled Instrumentation for a Soil-Bentonite Slurry Trench Cutoff Wall

In this work, we describe our approach and experiences bringing an instrumented soil-bentonite slurry trench cutoff wall into a modern IoT data collection and visualization pipeline. Soil-bentonite slurry trench cutoff walls have long been used to control ground water flow and contaminant transport. A Raspberry Pi computer on site periodically downloads the sensor data over a serial interface from an industrial datalogger and transmits the data wirelessly to a gateway computer located 1.3 km away using a reliable transmission protocol. The resulting time-series data is stored in a MongoDB database and data is visualized in real-time by a custom web application. The system has been in operation for over two years achieving 99.42% reliability and no data loss from the collection, transport, or storage of data. This project demonstrates the successful bridging of legacy scientific instrumentation with modern IoT technologies and approaches to gain timely web-based data visualization facilitating rapid data analysis without negatively impacting data integrity or reliability. The instrumentation system has proven extremely useful in understanding the changes in the stress state over time and could be deployed elsewhere as a means of on-demand slurry trench cutoff wall structural health monitoring for real-time stress detection linked to hydraulic conductivity or adapted for other infrastructure monitoring applications

Hydraulic Conductivity of Model Soil-Bentonite Backfills Subjected to Wet-Dry Cycling

The potential for changes in hydraulic conductivity, k, of two model soil-bentonite (SB) backfills subjected to wet-dry cycling was investigated. The backfills were prepared with the same base soil (clean, fine sand) but different bentonite contents (2.7 and 5.6 dry wt %). Saturation (S), volume change, and k of consolidated backfill specimens (effective stress = 24 kPa) were evaluated over three to seven cycles in which the matric suction, Ym, in the drying stage ranged from 50 to 700 kPa. Both backfills exhibited susceptibility to degradation in k caused by wet-dry cycling. Mean values of k for specimens dried at Ym = 50 kPa (S = 30-60 % after drying) remained low after two cycles, but increased by 5- to 300-fold after three or more cycles. Specimens dried at Ym ≥ 150 kPa (S \u3c 30 % after drying) were less resilient and exhibited 500- to 10 000-fold increases in k after three or more cycles. The greater increases in k for these specimens correlated with greater vertical shrinkage upon drying. The findings suggest that increases in hydraulic conductivity due to wet-dry cycling may be a concern for SB vertical barriers located within the zone of a fluctuating groundwater table

Lessons Learned from the Macon County Slurry Wall

A soil-bentonite slurry trench cutoff wall was installed as part of landfill improvements at the Macon County Landfill located in Decatur, Illinois. In order for a soil-bentonite barrier to be continuous and defect-free, a homogeneous, well-graded backfill needs to displace the slurry used to maintain trench stability. Historically, specifications required that the backfill have a unit weight of 15 pounds per cubic foot (pcf) higher than the unit weight of the in-trench slurry and the slurry have a maximum density of 85 pcf. More recently, specifications have also required that the sand content of the slurry, not exceed 10 to 15%. During the course of construction, difficulties arose which gave rise to post-construction investigations of the integrity of the completed cutoff wall. A program of field sampling and testing, which included Osterberg sampling, modified Osterberg sampling, and sonic-core borings, was developed to investigate the integrity of the wall. Since state-of-the-practice quality assurance and quality control measures are based upon field measurements and sampling during construction coupled with laboratory measurements of field-prepared backfill samples, detailed investigations of the in-situ, as-constructed wall are relatively uncommon and even more uncommonly documented in the literature. This paper presents these investigations, findings, conclusions derived from the investigations and provides recommendations for slurry wall design and construction derived from these studies

Soil-Bentonite Slurry Trench Cutoff Wall Proposal

This is the proposal to the National Science Foundation for a soil-bentonite slurry trench cutoff wall. The proposal includes a project summary, description of the project, and the resources implemented on the project

National Science Foundation Soil-Bentonite cutoff Wall Award Abstract

This award abstract describes the purpose of constructing a soil-bentonite cutoff wall as well as the tests that were performed to analyze the performance of the wall

The Impact of Mental Illness Status on the Length of Jail Detention and the Legal Mechanism of Jail Release

Objective: This analysis investigated whether persons with serious mental illnesses have longer jail detentions than other detainees and whether they are released by different legal mechanisms. Methods: Jail records and mental health service records from a Medicaid database were matched for all admissions to the Philadelphia jail system in 2003. Survival analysis techniques were used to compare length of jail stays of persons with and without serious mental illnesses (N=24,290). Serious mental illness was defined as a diagnosis either in the schizophrenia spectrum (DSM-IV code 295.XX) or of a major affective disorder (DSMIV code 296.XX) recorded in Medicaid records (2001–2003). Mechanisms of release were also examined for those with release dates before September 1, 2005 (N=20,573) Results: Just over 50% of the 1,457 persons with serious mental illnesses were released from jail within 30 days of incarceration, compared with 56% of the other detainees. Mental illness status was not found to be a significant predictor of longer detentions. Forty-nine percent of those with serious mental illnesses were released from jails through unpredictable release mechanisms, such as bail, release from court, or withdrawal of a bench warrant, whereas only 19% were released through mechanisms that had release dates that allowed adequate time for discharge planning. Conclusions: The findings suggest that reentry programs and other jail-based interventions for persons with mental illnesses should ensure that they have the capacity to rapidly identify and serve clients with shorter and more unpredictable stays or risk not being responsive to the needs of a substantial proportion of this population