Urban Institute Ireland Research Collection

Construction related dewatering in urban areas often induces damage of existing structures. The following forensic investigation highlights the complexities of such a phenomenon. Somerset plantation, a national historic landmark located in northeastern North Carolina is currently exhibiting distress. At many locations, these wooden structures on brick piers are experiencing sufficient differential settlement to impact building functionality. Heavy visitor traffic was proposed by the site staff as the cause of the building displacements. Given a perched aquifer located within a fatty clay, dewatering based settlement was suspected. Two potential sources of ground water change were investigated – (1) general drought conditions or (2) a nearby mining operation.

Sample disturbance effects in the laminated facies at the Bothkennar soft clay research site are examined by comparing the results of laboratory tests on specimens obtained from three fixed piston tube samplers. A significant feature of the results is that the sampling process associated with the conventional piston tube used in the UK and Ireland appears to increase the post yield stiffness and the CAUC triaxial undrained strength, reduce the preconsolidation stress, the pore pressure coefficient at failure and induce a strong tendency for dilatant behaviour post peak when compared to tests on specimens from a sampler with a modified (sharper) cutting edge angle. It is reasoned that these findings are caused by material destructuration during the sampling process with the conventional tubes. Increased densification of these specimens caused both by sampling and during anisotropic consolidation may also contribute to these effects. The results are supported by reference to recent analytical work and data for three other soils. It is recommended that the use of these conventional thin walled tubes with a crude cutting edge is abandoned and that some with improved cutting edge geometry replaces them.

A gravel-based tidal flow reed bed system was operated with three different strategies in order to investigate its optimal performance for the treatment of high strength agricultural wastewaters. According to the three strategies, individual reed beds of the system were saturated and unsaturated with the wastewaters for different periods while steady hydraulic and organic loadings were maintained. Experiment results demonstrated that the system produced highest pollutant removal efficiencies with relatively short saturated period and long unsaturated period, highlighting the importance of O2 transfer into reed bed matrices during the treatment of high strength wastewaters. Significant removals of some major organic and inorganic pollutants were achieved with all the three operation strategies. Nitrification was not the major route of NH4-N removal when the system was under high organic loading. Due to the filtration of suspended solids and accumulation of biomass, gradual clogging of the reed bed matrices took place. The clogging caused concerns over the long-term efficiency of the current tidal flow reed bed system.

Problems concerning the management and utilization of sludge derived from water treatment processes are still not fully solved. A common approach is direct discharge to a landfill site. This study provides experimental data to demonstrate the effectiveness of a combination of gypsum (CaSO4x2H2O) and an organic polymer in alum sludge conditioning and dewatering. Experimental results demonstrated that the filterability of dually conditioned alum sludge was significantly improved by the addition of gypsum at a 1:1 ratio (WT/WT) to original sludge solids. Dewatering tests showed that a further decrease of almost seven percentage of sludge cake equilibrium moisture content was achieved by the involvement of gypsum compared to the situation of single polymer conditioning. The importance of this study lies in the possible application of dewatered alum sludge to land use or as a filter medium in constructed wetland for wastewater treatment, providing a positive solution to the problem of alum sludge disposal.

Sustainability in the construction industry can only be achieved through a radical rethinking of building construction and reuse. This paper outlines the problems and offers innovative solutions that embrace technological innovations, advances in manufacturing and distribution, and integration of building and land use concepts through:1) application of a dismountable and reconfigurable structural system, 2) promotion of the concept of kitting, and 3) reconceptualization of the relationships between construction management, engineering, supply chain configurations, environmental modeling, design, and urban planning. Basic components are described with the modeling and research agenda needed to make these solutions both viable and adoptable.

Settling behaviour of polymer conditioned water-treatment sludge was investigated in this study for the purpose of a better understanding of a so-called “CML30 method”, which was developed in previous study to evaluate the optimum polymer dosage in sludge conditioning. The “CML30 method” is on the basis of a 30 min settling test in 100 ml measuring cylinders. In this study, the series of settling tests in 100, 500 and 1000 ml measuring cylinders were respectively performed and the settling curves (interfacial height to dose and time) were the main focuses for presentation and analyses in great detail in this paper. According to the experimental data presented in this study, settling behaviour may be controlled by both the growth of large sized floc and progressively decreased viscosity. The “speed-up” phenomenon in small polymer dose range obviously enhances the settlement and plays a critical role for the settling set in a 100 ml measuring cylinder at a special dose and at the settling time interval 5-30 min. It is such special observation that leads to the success of so-called ad hoc “CML30 method”. However, sludge settling behaviour could be controlled by the formation of networked structure which is involved in excess polymer during the large range (say over 10 mg/l for the case tested) of polymer doses. The higher liquid viscosity values derived from excess polymer will increase the drag force for the resistance of the settlement. In addition, wall effects are likely to interplay with the internal networked structure in large dosed region.

On the basis of experiments carried out using an image analysis system and static zone settlement, the alum sludge floc structure and the floc packing status with varied polymer dosages were examined in greater detail to reveal the link with the settling behaviour manifested in the “CML30 method”. The results of image analysis lead to the findings of the floc size with a pattern in initially great increase with low polymer dose and finally a plateau being reached at higher amount of polymer addition. Meanwhile, a polymer dosage in the range of 2.0 – 20.0 mg/l (for sludge SS = 4,595 mg/l) can result in the increase of the floc fractal dimension (DF) up to an average value of 1.72 (raw sludge DF being 1.06), indicating greater compactness of the floc solids. These floc features control the settling behaviour of the “CML30 method”, especially in small polymer dosages. However, in large polymer doses, the controlling factor is derived from the floc 'packing' status (referring to the inter – floc contact manner). This 'packing' status may associate with viscosity of settling medium (supernatant) and the excess polymer in bulk solution. All these affect the sludge floc networked structure in overdosing range.

Two separate sets of reed bed systems were operated in parallel for the purpose to study a comparative behaviour of high strength animal wastewater treatment. Each system consisted of five-stage gravel-based reed beds. The only difference between the two systems lies in the gravel arrangement within the beds. One system employed single sized gravel as bed medium (termed as mono-sized bed) while the other used two layers of gravel with coarse grain as the upper layer (termed as anti-sized bed). It was demonstrated that both the systems have the strong capacity for animal wastewater treatment but no significant difference with regard to pollutants‟ removal efficiency. However, anti-sized system showed a clear advantage in its ability to retard the clogging phenomenon exhibited during the system operation and avoid the impairment of its long-term functioning and sustainability. Clogging development was monitored via daily record of evolution of water level after the reed bed fill-up step in tidal flow operation strategy. According to present study, anti-sized reed bed experienced more than 2-fold operating period without clogging as compared with mono-sized reed bed in their parallel operation. In addition, a conceptual model to predict the clogging time was attempted and its utility was demonstrated via the data of this study.

Several recent articles and discussions in GIN, by Penman (2002), Thomann et al. (2003), Ridley (2003) and Sellers et al. (2003) highlight the importance of pore water pressure and suctions and in particular the difficulties associated with measuring suction. This article outlines some recent experience in measuring suctions, which were developed in cut slopes in a very stiff glacial till during the Dublin Port Tunnel (DPT) project in Ireland. A particular feature of the project was the execution of a fully instrumented 12m deep trial excavation (Menkiti et al., 2004). Initially some background to the project and to the problem will be given. Then some details of the specification, installation technique and some examples of the measurements obtained will be outlined. Finally some conclusions will be made on the lessons learned and recommendations will be made for future similar applications.

The purification capacity of a laboratory scale tidal flow reed bed system with final effluent recirculation at a ratio of 1:1 was investigated in this study. In particular, the four-stage reed bed system was heavily loaded with strong agricultural wastewater. Under the hydraulic and organic loading rates of 0.43 m3/m2.d and 1055 gCOD/m2.d, respectively, the average removal efficiencies obtained for COD, BOD5, SS, NH4-N and P were 77%, 78%, 66%, 62% and 38%, respectively. Even with the high loading rates, about 30% of NH4-N was converted into NO2-N and NO3-N from the mid-stage of the system where nitrification took place. The results suggest that the multi-stage reed bed system could be employed to treat strong wastewater under high loading, especially for the substantive mass removal of solids, organic matter and ammoniacal-nitrogen. Tidal flow combined with effluent recirculation is a favourable operation strategy to achieve this objective.

The fate of ammoniacal-nitrogen (NH4-N) was studied in a lab-scale downflow reed bed system treating an artificial landfill leachate. Individual reed beds were submerged by the leachate, then drained and rinsed by tap water. It was discovered that NH4-N was removed by a two-staged process, adsorption onto the reed bed media followed by nitrification into nitrite-nitrogen (NO2-N) and nitrate-nitrogen (NO3-N). A drop of NH4-N level of the leachate was observed when the reed beds were submerged. By rinsing of the beds, part of the NH4-N adsorbed inside the bed matrices was re-released into the rinse water. The presence of NO2-N and NO3-N in the rinse water demonstrated that nitrification process took place while the NH4-N was being retained inside the bed matrices. For artificial leachates with NH4-N levels of 150±5 mg/l, an average removal rate of 43.8% in a three-hour treatment was achieved; mass balance analysis indicated that processes of adsorption, and transformation into NO2-N and NO3-N accounted for 63.7%, 4.3% and 24.4% of the NH4-N removal, respectively. This study also demonstrated that in general greater recirculation rate of effluent around the downflow reed beds gives higher NH4-N removal.

Despite being considered one of many seventeenth century American wall insulation systems, brick nogging emerges as a prevalent construction type throughout all of original colonies. Used in both framed and hewn-log structural systems, brick nogging is most typically found beneath clapboard siding. Because clapboard ultimately becomes a style in its own right, the presence of brick nogging beneath such clapboards becomes an unexpected complication for modern preservation and intervention efforts. The technique of placing fired and unfired bricks mortar, clayed, and dry laid, although poorly documented extends well into the nineteenth century increasing the anticipated weight of the structure by ten percent. Similarly, the presence of brick nogging substantially changes the structure’s wall stiffness. Identifying clapboard covered, brick nogging structures is not straightforward as their emergence was influenced by historical, fiscal and social factors in addition to engineering considerations.

The characteristics of pre-regulated American cements differ fundamentally from those manufactured afterwards, both in terms of physical and chemical properties and with regard to cement consistency. This paper presents an overview of cementitious products available in America from 1875 to 1909. Historical testing data is compared to that expected of modern materials. The data presented show that a lack of consistency and a less rigorous manufacturing processes resulted in an original product much inferior to modern expectations regarding the compressive capacity of concrete and that this was true for both natural and Portland cements.

This study describes a numerical projection of pre- and post-retrofitted conditions of telecommunication poles subjected to seismic hazards. The absence of explicit guidelines for the rehabilitation of existing poles motivated the investigation of the effectiveness of steel jack-eting for the retrofitting of self-supporting steel and reinforced concrete (RC) communication poles. Effects of mast flexibility, variable damping on dynamic response, and significance of period on base shear amplification were investigated. The overall effectiveness of retrofitting against base excitation was assessed for RC and steel poles through the application of modal analyses and response spectrum approach based on a set of strong motion accelerograms record-ed during the 1994 Northridge earthquake. Based on a serviceability approach, the analysis of results shows effectiveness of the steel jacketing in increasing load carrying capacity of the poles by enabling stress redistribution.

This study investigated the efficiency of a four-stage tidal flow constructed wetland system for the removal of organic matter and ammoniacal-nitrogen from diluted piggery wastewater. The results demonstrated that the operation of tidal flow enhanced the transfer of oxygen into wetland matrices. The overall oxygen consumption rate in the tidal flow system (357 gO2/m2∙d) was considerably higher than the rate obtainable in conventional wetlands. Most oxygen consumption (99%) was due to the decomposition of organic matter. The total supply of oxygen into the wetlands (473 gO2/m2∙d) exceeded the demand for the treatment. The percentage removal of BOD5 and NH4-N was improved by effluent recirculation at a ratio of 1:1. Immobilization by microbial cells and adsorption were found to be the main routes for the removal of ammoniacal-nitrogen. Significant nitrification could not take place under the treatment condition of the experiment.

Since the September 11, 2001 terrorist attacks in the United States (U.S.), there has been a marked increase in both public and private sector demand for increased blast-mitigation for existing buildings. To adequately address these new performance requirements, a rational and cost-oriented policy is needed to help building managers and owners make fiscally intelligent decisions regarding the retrofitting of existing structures. This paper presents a cost-rationalized approach to blast-mitigation retrofitting decision making, with respect to a building’s criticality to the surrounding community. The proposed method addresses current approaches to blast assessment, typical blast-related vulnerabilities (structural and non-structural), and possible solutions for vulnerability mitigation. Special emphasis is given to non-gravity based loadings, post-incident functionality requirements, and transient versus permanent/semi-permanent loading.

The experimental procedures and results are presented for a one-tenth scale laboratory investigation of changes in achievable grouted zones through alterations in helical pier parameters. The parameters investigated were the location of the grouting holes with respect to the position of the helices, the grouting pressure and the rate of helical pile installation. The results showed that the total treated volume was 40% to 158% greater than the grouted volume and that the thickness of the treated zone beyond that which was strictly grout was 15% to 61% of the radius of the grouted, cross-sectional area, which was largely controlled by the diameter of the bottom helix. Increases in pressure generate non-linear improvements with increasing effectiveness at higher pressures. The placement of grout holes beneath the bottom helix was shown to be more effective in grout delivery than the standard industry practice of placing the holes above the helix.

The progressive settlement of a plantation in North Carolina is explored through a post-damage inspection. If a building is experiencing settlement or other deleterious movement, the underlying causes must be established to prevent further damage and ensure effective repair. This article outlines a methodology for the forensic investigation of historic structures experiencing what may appear to be structural distress and provides a case history exemplifying the effectiveness of the proposed method for establishing settlement-related movements. Through simple and straightforward engineering principles, a logical and methodical approach can be applied to determine contributing factors to historic-building distress. Key elements of this method include documentation of the history of architectural damage and apparent distress, consideration of initial and existing structural loading capacity (including both the structural system and specific materials), exploration of soil conditions, and investigation of groundwater factors.

This research assessed the use of gypsum (CaSO4.2H2O) as a skeleton builder for sludge dewatering since polymer conditioning of sludge affected only the rate of water release, not the extent of dewatering. The use of gypsum as a physical conditioner, in association with a polymer, could improve sludge filterability. More significantly, gypsum serves as a skeleton builder, forming a permeable and rigid lattice structure that can remain porous under high positive pressure during the compression step after the cake growth of the filtration, thereby maintaining the size of the micro-passages through which water is expressed. Experiments using a high pressure cell apparatus showed that a further decrease of two to seven percent of the equilibrium moisture content of the sludge cake was achieved, for sludge thicknesses for dewatering of 1 to 10 cm, by the addition of gypsum with 60% of the original sludge solids when compared to the single polymer conditioning. The importance of the addition of gypsum in alum sludge dewatering is not only the improvement in the extent of dewatering, but also the potential application of transforming dewatered alum sludge from ‘waste’ for landfill to useful ‘fertilizer’ or to be used as filter medium/adsorbent for wastewater treatment engineering.

Although three-dimensional laser (3DLS) scanning has been used to document and monitor individual excavation walls and structures on a limited basis, impediments remain to its use for major infrastructure projects. This paper outlines current technological opportunities and obstacles for using 3DLS to predict excavation-induced, damage prediction. Specifics are provided as to limitations regarding cost, optical resolution, processing time requirements, data set convergence, data conversion, and data mining. Specific solutions are proposed to advance the state-of-the-art.