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By R. Gerritsen, Erwin de Jong, E. van der Velde, C. te Boekhorst

"In recent years the market for Mixed-In-Place soil mix techniques in the Netherlands has been growing rapidly. Initially the technique was used to create cut-off walls near river dikes and as a vibration free method to create retaining walls for building pits. Studies have been undertaken and projects are executed in order to strengthen the dike itself by the use of Mixed-In-Place techniques. In February 2012 Bauer Funderingstechniek started the construction of the first polder in the Netherlands with their approved Mixed-In-Place cut-off walls. This article explains the background of the use of this cost-effective and durable construction method and discusses how the challenging requirements from the client were fulfilled, both in design and execution. The quality assurance and quality control consisted of preliminary soil and mixture investigations, extensive measurements during construction and leakage detection through geophysical methods. The information is presented in 3 case histories, all subprojects of a large infrastructural project ‘Leeuwarden Vrij-Baan’ in the Netherlands.INTRODUCTIONThe Netherlands have a worldwide reputation in creating their own country by reclaiming land from the sea. Since the 15th century the Dutch have been creating “polders”, areas of reclaimed land below sea level, surrounded by dykes and with a mechanically maintained water level. In the 20th century the use of artificial polders became an interesting construction method for creating underpasses below motorways and canals using watertight geomembranes to create an impermeable layer that separated the polder from its surroundings. These kinds of structures have one big disadvantage, they need a lot of space. The main idea of such a structure is that the upward water pressure under the geomembrane has to be in balance with the remaining soil on top of it. For this reason, the geomembrane has to be placed at a depth significantly deeper than the polder surface, depending on the hydraulic head in the aquifer. Slopes of 1:3 (1 vertical : 3 horizontal) are most commonly used, resulting in very large open excavations and massive earthworks, even for relatively small underpasses. Special measures can be taken to reduce the spatial use with vertical limits, but these measures will increase the building costs (Gerritsen et al. 2014)."

Jan 1, 2015

By Tara Schenk-McFarland, Mark Bliss

Echo Dam, located near Coalville, Utah, is a facility that provides storage for irrigation and municipal use. Original construction of the dam was completed in 1931. Because of seismic concerns, the spillway crest structure and upper chute section, founded on old landslide and colluvial material, were recently replaced. Prior to replacement of these structures, jet grouting of a block of the loose and potentially liquefiable soils, directly beneath the spillway crest structure was selected as the preferred alternative to address the potential for settlement and cracking of the spillway crest structure. The replacement or alteration of the in-place soil reduces the likelihood of seismic-induced excess pore pressure development and subsequent settlements. Core drilling and sample recovery of the production jet grouted columns was completed to verify compliance with the specifications. It was recognized that due to the larger rock sizes within the deposits that full homogeneity of the jet grouted zone was unlikely to be achievable. However, the purpose of this jet grouted section was to strengthen enough of the soil so that widespread liquefaction does not occur. During the jet grouting production many instances of ground fracturing occurred. Fracturing was evident based on grout/air bubbles exiting the surface near some of the grout holes during jet grouting, air bubbles appearing in the spoil pits, and lifting of the ground surface in the vicinity of the monitor during the jet grouting process while the system was pressurized. In one instance, a section of the upstream spillway slab, which was left in place, was cracked due to pressurized grout escaping beneath the slab. The overall results of the jet grouting were satisfactory despite difficulties encountered. The cause of the fracturing is hypothesized and a recommendation is included to reduce the likelihood of this occurring on future jobs.

Jan 1, 2017

By Sumantra Sengupta

"Northeast Frontier Railway (NF Railway) intends to connect Imphal, the capital of Manipur (bordering Myanmar) with Assam by railway link. They have planned a 125km long railway line that passes through steep rolling hills of Patkai region, eastern trail of Himalaya, and as a result large number of tunnels and bridges need to be designed. While the high mountains are penetrated by tunnel, the deep gorges between the mountain ridges are connected by tall bridges. The tallest of such bridges connects a gorge at about 140m above its bed level with an overall length about 700m at rail level. In all, five such bridges with tall piers are now under construction. With extensive study on possible alternate arrangement of the bridges considering the effect of high seismicity of the area, moderately to highly weathered siltstone/ sandstone as ground bed material, slope of the hills etc it was decided that bridge will be founded on 1.5m diameter bored cast in situ piles with length varying from 20m to 30m depending on the location. The substructures are RCC hollow pier and superstructures are steel open web through type girder of 103.5m span. Considering absence of any major construction work in the vicinity, it was decided that prior to design work, Site-specific spectrum study will be carried out and design will be carried out considering the varying stiffness of the tall piers, each of different height. Interesting results were obtained regarding behavior of piles under lateral loads generated by high seismic conditions. The paper discusses in detail the design of Pile foundations and the effect of bed material along the steep slope on which the piles are being constructed.INTRODUCTIONIndian Railway has undertaken the construction work of connecting the North-Eastern states of India through railway line. The major stretches of the area passes through hilly terrain and as a result the line passes through tunnels and bridges in succession. The tall mountains are being penetrated with tunnels and immediate after deep gorges are crossed with high level bridges. The entire area is under high seismically active zone. The bed material below the ground level of the sloped hill is 4 to 10 meter of mixed soil of sand, gravel, pebbles etc underlain by moderately to highly weathered sandstone, siltstone at the higher level and moderately weathered sandstone, siltstone at lower level. Considering all the aspects like constructability, maintainability, geological and geotechnical aspect, seismicity, stability, safety, functional aspect and cost it was finally decided that the bridges will be simply supported structure with open web through type steel superstructure of maximum span 103.5m and hollow cylindrical discretely varying RCC substructure with 1.5m diameter group of piles as foundation. The paper discusses on the design aspect of the pile foundation in the rocky strata in the hill slope. The codes and standards that have been followed for design are IRS (Indian Railway Standard), IS (Indian Standard), IRC (Indian Road Congress), AREMA (American Railway Engineering and Maintenance-of-way Association), UIC (International Union of Railway) provisions."

Jan 1, 2015

By Glen R. Andersen

"Two of the greatest challenges we face in managing our aging infrastructure are to perform accurate condition assessments and to realistically predict the risk of non-action. The aim of this paper is to discuss common pitfalls we face in performing accurate condition assessments of our aging infrastructure using the case history of a recent near miss at the Lake Manatee Dam in Central Florida. The dam was placed into service in 1967 and was inspected every couple of years by dam safety engineers beginning in 1978. Although there was substantial and repeated evidence of a serious piping and internal erosion problem in each of these inspections, the problem was overlooked by most of the inspection teams. In 2012, the inspection team concluded that: “the Lake Manatee Reservoir Dam is well maintained and is in very good overall condition.” However, in 2013 a new team inspected the dam from an entirely different perspective, identified potentially serious conditions, performed an integration of the historical inspection data and concluded that: 1) the Lake Manatee Dam was in a severely distressed state; and, 2) without an immediate intervention there was a high risk of an uncontrolled release of the reservoir most likely following a large rainfall event and prolonged opening of the service spillway. This case history highlights human factors contributing to the near miss including group think and focusing on changes from prior inspections. The integration of historical inspection data is recommended for managing our aging infrastructure.INTRODUCTIONThe engineering analytical techniques most appropriate for assessing an aging infrastructure can be distinct from those used for the original design. To adequately manage our aging infrastructure it is necessary to change our perspective from anticipating failure mechanisms and designing to prevent them to assessing condition, detecting the presence of potential failure mechanisms, and assessing the potential risks. In many circumstances the failure mechanisms currently active may not have been anticipated by the original design team.We have developed a substantial body of experience in the design of our infrastructure. Full scale and laboratory testing coupled with the application of scientific principles to model behavior has led to many powerful design tools. The continued serviceability of our infrastructure as its elements reach their design lives stands as a legacy to our profession. However, under the sustained effect of limited resources for maintenance and rehabilitation parts of our infrastructure are in a highly deteriorated state. Unfortunately, the condition of some of these has not been properly assessed. This paper focuses on the Lake Manatee Dam in Central Florida and the process used to clearly identify its highly deteriorated state. While there are many factors that contributed to the lack of a proper assessment of its condition, the focus herein will be on human factors and in particular how “Group Think”, “Aversion to Bad News”, and “Condition Assessments Based on Changes to Prior Condition” may have contributed to not properly identifying the development of a serious failure mechanism."

Jan 1, 2017

By Brian Wilson, Franz-Werner Gerressen

"Cutter Soil Mixing, also known as CSM, was developed in Europe as an alternate method of Deep Mixing to the more traditional single and multiple auger techniques, and brought to market by Bauer Maschinen GmbH (Bauer), towards the end of 2003. Initial development of the technique had been completed in a joint venture between Bauer and Bachy Soletanche. In 2004 the concept was introduced to the North American market. Continued development of the method and demonstration of its versatility, both in terms of applications and applicable soil types has seen a steady growth in the number of designs incorporating the approach, and contractors offering the technique. This paper provides a brief overview of the variety and size of projects and applications where the method has been adopted, discusses some lessons learned with respect to equipment operation as well as the improvements that have been introduced to the equipment, and briefly reviews the current state of practice, as well as some of the associated on-going research and development.BACKGROUNDCutter Soil Mixing (CSM) is a technique for deep soil mixing that was initially developed as a collaborative effort between Bauer Maschinen (Bauer) and Bachy Soletanche, but which ultimately resulted in the separate development of two somewhat different brands of CSM tool. The Bauer brand of CSM entered the European market in 2004, and was first promoted in the North American market in late 2004, with the first project starting in 2005. The Bachy Soletanche brand, sometimes referred to as “Geomix” was first marketed in Europe in 2005 and the first model introduced in North America in 2007.The development of the Cutter Soil Mixing technique utilized the experiences gained from Trench Cutter/Hydrofraise equipment, developing a technique that incorporates two cutting wheels rotating about a horizontal axis as opposed to the more conventional deep soil mixing approach which utilizes augers and mixing paddles rotating about vertical axes. Whereas the Trench Cutter/Hydrofraise technique excavates the soil from within a panel, and supports the open hole using a bentonite slurry, the CSM technique cuts and displaces the soil whilst pumping a slurry/grout directly into the soil through a port located between the wheels. The combination of cutting the soil while introducing an appropriate volume of slurry effectively fluidizes the column of soil around and above the cutter head. While this process achieves a high degree of mixing, even on the downward cutting stroke, thorough in-situ mixing typically occurs on the withdrawal stroke, when most of the slurry is added."

Jan 1, 2015

By Abid Adekunte

"Engineers and developers have witnessed the growing popularity of deep basement structures as components of urban commercial and residential developments. This is often attributed to inadequate surface parking facilities in urban centres and a somewhat popular belief that underground parking facilities improve both commercial and aesthetic values of urban structures. For many years, diaphragm walls and sheet pile walls have been widely accepted as effective deep excavation support systems for basement construction in urbanised zones. However, these are now being replaced by bored pile retaining walls as preferred earth retention systems of choice on many projects for several reasons, which may include economy, faster installation process, reduced space requirement for machinery and ancillary equipment, flexural rigidity and axial capacities.However, there are complexities associated with the use of bored pile retaining walls on urban developments. These include; limitations due to vertical and horizontal installation tolerances, which is a major issue when wall is required to provide groundwater cut-off for multi-level basements as tolerances are difficult to achieve for deep piles, uncertainty associated with the prediction of wall axial capacity as piles are rarely tested, difficulties in using temporary props as wall restraint due to restricted working spaces in urbanised zones and difficulties in adopting ground anchors as restraint due to the existence of adjacent sensitive structures in built-up areas. Such complexities have resulted in cases of failure, non-serviceability and abandonment of basement construction schemes. Therefore, overcoming the intricacies associated with the application of bored pile walls is becoming a priority to the present day basement engineer.This paper is centred on the numerical modelling, design, construction and monitoring aspects of four recent case histories of multi-level basement and marine engineering construction schemes in the United Kingdom and the Republic of Ireland, which involved the use of bored pile retaining walls. The paper highlights the various customised approaches and innovative novel solutions adopted on the sites, to mitigate risks and ultimately overcome the intricacies associated with the earth retention techniques. Simple empirical equations for developing the geometry of secant pile walls for effective groundwater cut-off are presented and validated. An alternative approach for predicting axial capacities of bored pile walls is also presented; this is shown to be considerably less conservative than a common routine design approach, while also in good agreement with observations made in a recent series of laboratory-based scale model tests."

Jan 1, 2017