Foundation For Investigation Research Articles

Developing the 3D geological model for Crossrail 2, London, UK

A 3D geological model, referred to as the Project Stratigraphic Model, has been developed for Crossrail 2, a proposed £30 bn railway linking Surrey and Hertfordshire via 27 km long tunnels through London. The British Geological Survey 1:50 000 scale 3D model of the London Basin was adopted as the initial baseline. Over 1000 boreholes were collated, together with information from existing publications, such as tunnel face excavation records, to review and develop the Project Stratigraphic Model. Digital tools such as ArcGIS and Leapfrog Works facilitated the efficient development, interrogation and dissemination of the c. 40 km 2 model and helped to communicate geological uncertainty. The Project Stratigraphic Model was a key tool in identifying geological hazards along the route, designing the vertical alignment, informing early design decisions for the proposed structures and estimating third-party building foundation depths for obstruction risk assessments. Further refinement of the model will continue into future design and construction stages, including the addition of project-specific ground investigation, geotechnical parameters and construction data, and will provide an invaluable geotechnical risk management tool for the project. Thematic collection: This article is part of the Ground models in engineering geology and hydrogeology collection available at: https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology

Determination and Mapping of the Bearing Capacity of Subsurface Soil: A Case Study of Moi University, Eldoret Kenya

Ground investigation is a prerequisite for any construction work that ultimately transfers its loads to the earth. Geotechnical investigation eliminates the uncertainties of ground conditions and can be planned for and considered accordingly during actual design and construction. In Kenya, ground investigation is not given the weight it deserves since most players in the sector use their experience and physical inspection to judge on the soil conditions. This is however very risky especially for high-rise buildings. Moi University, the case study, is one of the institutions that has in its plan, a series of construction developments. This study aimed at investigating, determining and mapping of index properties and bearing capacity of subsurface soil. Direct shear box and tri-axial tests results were used to map soil bearing capacity by geospatial interpolation within geographical information system platform (GIS). 9 trial pits mapped by triangulation and visual inspection were excavated and soil samples obtained at a depth of up to 3 m. The soil samples were tested for soil index and engineering properties and classified using the USCS approach. A relationship between tri-axial and direct shear box test results was developed by correlating soil bearing capacity results from the two tests. This paper provides a thematic map of the bearing capacity for the study area derived from spatial interpolation. Four geospatial interpolation methods namely; Ordinary Kriging (OK), spline, Natural Neighbour (NN) and Inverse Distance Weighting (IDW) were used. In this paper, the most suitable method for interpolating the soil bearing capacity of the four methods is provided. Six of nine sample test results were used for interpolation and the other three used for validation and error correction. Ordinary Kriging generated satisfactory results for soil bearing capacity for the study area with a relative error of 2.23 % and R 2 of 0.9993. From the safe bearing capacity map, the ground conditions of the study area varied gradually with the bearing capacity ranging from to . Generally, the amount of clay in the soil within the area affected to a large extent, the soil bearing capacity. Keywords: Soil bearing capacity, Geospatial interpolation, Deterministic interpolation, correlation. DOI: 10.7176/CER/12-7-05 Publication date: July 31 st 2020

Rates of oxygen-depletion in granular Lambeth Group strata and evidence for barometric pumping

Laboratory experiments have been performed to demonstrate significant levels of oxygen depletion within samples of Upnor Formation of the Lambeth Group deposits. These have been used to explain the reasons for several incidences of confined space hypoxia during underground construction within the stratum beneath London. Further investigation, using a relatively small-scale field pump-out test, revealed the rapid effects of dewatering on the generation of hypoxic gas (within the ground) and that the amount of oxygen falls to fatal levels within a very short time after commencement of pumping. Monitoring of boreholes during ground investigation for the Thames Tideway Tunnel has indicated barometric control on the release of hypoxic gas from installations within granular deposits of the Lambeth Group, namely the Upnor Formation, as well as channel sand deposits within the Laminated Beds. In these, reduced levels of oxygen coincide with low and/or falling barometric pressure. Continuous 24-hour monitoring demonstrates that the reduction is almost instantaneous and has serious implications for the Health and Safety of underground construction personnel.

Acceleration of the Pissouri landslide, Cyprus

The residential development of Limnes in Pissouri, Cyprus was constructed on a slope formed by a pre-historic landslide. Reactivated ground movements within this landslide, first noticed by residents in 2012, continue to cause significant damage to property. The rates of movement, already observed to be accelerating between 2014 and 2017, increased by up to a factor of three during and following the very wet winter of 2018–19. The outcome has been a marked increase in architectural and structural damage to some properties, as well as building rotation in the both vertical and horizontal planes. An interpretation of the most recent InSAR results suggests that the area behind the back scarp may also now be undergoing displacement and this, to an extent, is borne out by observed cracking to some buildings and paved surfaces in the vicinity. Uncertainties remain over the depth(s) of sliding and the groundwater regime within the landslide mass that can only be resolved through further ground investigation and subsurface monitoring.

Infrastructure Damage Due to Dewatering Without Considering Land Use History

Geotechnical processes such as subsidence, seepage, scouring, extreme temperatures as well as geological events pose constructional challenges even despite advancements in design codes, ground investigation techniques and numerical analysis. This paper analyses a case record where subsidence and damages to existing structures occurred adjacent to a location where dewatering works were being carried out for a new pipeline. Initially, the damages were thought to be solely linked to the dewatering effects, but it was still a puzzle as to why the problems only occurred at particular locations and not over the entire dewatered area. To solve the puzzle, forensic ground investigation and geophysics were performed. Based on borehole and CPT results, the ground profile was interpreted and compared with results from two parallel geophysical methods. Both of these revealed that the problem area was part of an old channel that had been dredged decades earlier and reclaimed by filling with loose material. This was corroborated by theoretical calculations of ground subsidence, which was found to be consistent with values of 600–700 mm measured on site. This work therefore demonstrates the importance of thorough consideration of past site history as part of design of new works or analysis of dewatering effects on existing structures.

Research on calculation and optimal allocation of groundwater resources in Rizhao coastal area

In this paper, the calculation and optimization of groundwater resources in Rizhao coastal area are realized by means of ground investigation, geophysical prospecting, pumping test, water level measurement and sampling test, groundwater recharge, diameter, drainage and other factors. According to the calculation and analysis of groundwater resources in the investigation area, the hydrochemical types in the investigation area can be divided into eight categories Cl, HCO3, HCO3⋅Cl, HCO3⋅SO4, HCO3⋅NO3, NO3Cl, SO4, and NO3. The mineralization degree is mostly above 0.3g/l. The groundwater recharge in the investigation area is 8638.40×104m3/a, and the groundwater consumption is 6017.12×104m3/a. Furthermore, on the basis of calculation and analysis of groundwater resources, this paper delimits the prohibition and restriction zones of the investigation area by groundwater resources exploitation and hydrochemical properties, and puts forward reasonable exploitation opinions, such as building underground seepage interception dams and constructing groundwater reservoirs, so as to realize the optimization of groundwater resources in the investigation area. This not only guarantees the groundwater resources demand of Rizhao City, but also has certain reference and application value for the rational utilization evaluation of groundwater resources in other regions.

The 2nd Hanrahan Lecture: Geotechnical properties of Irish compressible soils

The objectives of this paper are to provide an update on work done and the development of knowledge on Irish compressible soils since Eamon Hanrahan's book on the topic. Eamon subdivided these soils into three categories; namely, alluvial, estuarine and lake-bed deposits, and he termed them ‘troublesome soils’. A brief background geology will initially be presented. The complexity of the deposits both on a macro- and micro-scale will be highlighted. Sites that have been well studied will be summarized and the engineering solutions used to construct on these sites will be reviewed. Although work on these sites presents a significant engineering achievement, some important lessons were learned. The remainder of the paper deals with how these lessons might be addressed in the future; for example, how to use modern ground investigation techniques to best characterize these complex deposits and what are the best techniques for examining important detailed aspects of 1D consolidation behaviour such as the identification of the apparent preconsolidation stress, the sometimes rapid rate of consolidation and creep, and also how to characterize the undrained shear strength of the soils. The work will be benchmarked against experience of the behaviour of Scandinavian soft soils.

Identification of risk zone area of declining piezometric level in the urbanized regions around the City of Kolkata based on ground investigation and GIS techniques

The falling piezometric level of groundwater is one of the major concerns, because of its immense importance especially in areas where treated surface water is not easily accessible. An attempt is made to identify the areas of maximum depletion of groundwater in KMC area by studying the post monsoon groundwater level data for the years 1991–2010. The Arc GIS software is used for the representation of the secondary data and also for the easy comparison of data. The study is done to find the groundwater trough in the region by predicting the groundwater level for post monsoon 2018 and validating the result with the data collected from the field. The result thus obtained is analysed with the help of the said software using the IDW (Inverse Distance weightage) technique. Thus, it is seen that GIS forms an excellent platform for the analysis of groundwater data and is very helpful in the present study. A comparative analysis has been made and it is seen that at maximum places in KMC region the water level is receding-places like Narendrapur, Chitpur, Sinthi, Ballygunge, Park Street, Jadavpur all show a receding trend, few places being exception like Mukundapur, Kalikapur where there has been a slight rise in the groundwater level, over the years. With the advancement in the surface water supply by the Kolkata Municipal Corporation and with the decrease in population density, there is no respite in the groundwater level recession in the city. Blessed with river Hooghly alongside, the potable water issue is solved to a greater extent but still the southern Kolkata shows dependence on groundwater. Due to the falling groundwater level the chances of land subsidence is seem to be high in the city.

GIS-Based Study of Prioritized Gully Erosion and Flood Locations in Ebonyi State

Gully erosion and flood is a major environmental disaster in south eastern part of Nigeria. This study adopts Geographic Information System (GIS) as a tool in the identification of flood and gully erosion locations in Ebonyi State. 31 flood and erosion locations were identified using GPS receiver and field ground investigation. Gully erosion and flood severity map was produced using the SRTM (Shuttle Radar Topographic Mission), which was imported into the ArcGIS platform. The result shows that gully erosion sites were well dispersed around Ajali Sandstone geological Formation. The slope characteristic was ascertained to be greater than 15 o which encourages flood and gully erosion activities. The flood and erosion severity map produced showed risk and vulnerability of settlements and infrastructure while the observation on site showed loss of properties, economic trees, biodiversity and obstructed access; thus endangered human existence. This study therefore recommended public enlightenment on their role in flood and erosion control, enlistment of geologists, environmental managers and other experts in flood and erosion control planning for better understanding of the terrain before adopting any measure of control. Also the production of gully and flood severity map for other areas within the south-eastern Nigeria is necessary to enable better control of these environmental hazards. Keywords : Gully Erosion, Flood Locations, GIS DOI: 10.7176/JEES/10-2-11 Publication date: February 29th 2020

Post-20th century near-steady state of Batura Glacier: observational evidence of Karakoram Anomaly

Stable or marginal mass loss dominating in Karakoram has been reported widely through satellite and ground investigations. This work aimed to verify the variation in glacier mass by collecting ground-based data. By tracking profiles from the first survey by China–Pakistan Batura Glacier Investigation Group in 1974–1975, we revisited Batura Glacier and conducted an updated comparable measurement of the glacier surface elevation and ice thickness of this large valley glacier of Karakoram, in August 2017. Results of ground penetrating radar (GPR) measurement were used to improve the accuracy of an ice thickness distribution model (GlabTop2). The model calculation agreed reasonably with the measurement when the optimal basal shear stress (100 kPa for clean ice to 140 kPa for heavy debris cover) and shape factor (0.9) were used. We then used a glacier bed topographies map to calculate the ice flux. By subtracting the glacier surface topographies from the remote-sensing measurements, we observed a marginal thinning in Batura during 2000–2016, with a rate of variation in glacier surface elevation of −0.12 ± 0.27 m a−1. It indicated that the mass gain in the accumulation area nearly compensated the mass loss in the ablation area. In addition, both ground and satellite remote measurement reveal a steady rate of decrease in surface of the Batura tongue, implying an absence of significant variation during the past 40 years. Moreover, the mass conservation equation was applied to the Batura tongue, in combination with surface elevation variation and ice flux evolution. The tongue-averaged mass balance diminished by more than half from the 1970s to the 2010s. In summary, we inferred a near-steady state of Batura Glacier post 2000 based on the above-mentioned evidence of “Karakoram Anomaly”.

Assessment on liquefaction potential of seabed soil in Chang-Bin Offshore wind farm considering parametric uncertainty of standard penetration tests

Liquefaction potential analysis is a required task in the foundation design process of offshore wind turbine in Taiwan. The standard penetration test (SPT) is mostly used in the preliminary soil investigation of the pilot offshore wind farm in Chang-Bin, Taiwan. Due to the different experimental conditions and operating conditions, the N value (SPT-N) of SPT varies greatly. This study applies statistical methods in conjunction with the New Japan Road Association simplified-empirical method (NJRA method) to incorporate the uncertainty of SPT-N values into the offshore liquefaction potential assessment to quantify the risk of seabed liquefaction. The study statistics the field experimental geotechnical parameters SPT-N and determines the probability density function of the SPT-N distribution of each layer of soil in the offshore wind farm. In order to quantify the risk of seabed soil liquefaction potential, the Monte Carlo random sampling method is used, and by the NJRA method to carry out the seabed liquefaction potential in Changhua, Taiwan. After comparing, the results obtained by the current SPT-based soil liquefaction potential assessment by deterministic approach are conservative. In the ground investigation of offshore wind farm development, the method proposed in this paper can access the thickness of liquefiable soil layers under any given probability for optimizing offshore wind turbine foundation design.

Crossrail project: the impact of 4–18 Bishop's Bridge Road on the new Elizabeth line, London, UK

This paper describes the interaction of the Crossrail project to deliver London's new Elizabeth line in the UK with a building situated directly over the machine-bored tunnels, close to Paddington station. The initial scheme called for the demolition of the existing building at 4–18 Bishop's Bridge Road, including extraction of existing piles, which would have had a considerable impact on the local area. Changes in the design of the Elizabeth line station at Paddington allowed a revised strategy to be considered, whereby the building could be kept, reducing construction costs to the project considerably. A combination of desk study and ground investigation works was used to identify the likely extent of the piling under the building, and to predict the risk of clashes with the tunnels. The results of analyses considering the impact of construction works on the building, and associated monitoring results are presented. The decision not to demolish produced numerous benefits aside from the reduction in cost, including a considerably reduced impact on those using the building and adjacent areas.

Chapter 12 Subsidence – chalk mining

Abstract Old chalk and flint mine workings occur widely across southern and eastern England. Over 3500 mines are recorded in the national Stantec Mining Cavities Database and more are being discovered each year. The oldest flint mines date from the Neolithic period and oldest chalk mines from at least medieval times, possibly Roman times. The most intensive period for mining was during the 1800s, although some mining activities continued into the 1900s. The size, shape and extent of the mines vary considerably with some types only being found in particular areas. They range from crudely excavated bellpits to more extensive pillar-and-stall styles of mining. The mines were created for a series of industrial, building and agricultural purposes. Mining locations were not formally recorded so most are discovered following the collapse of the ground over poorly backfilled shafts and adits. The subsidence activity, often triggered by heavy rainfall or leaking water services, poses a hazard to the built environment and people. Purpose-designed ground investigations are needed to map out the mine workings and carry out follow-on ground stabilization after subsidence events. Where mine workings can be safely entered they can sometimes be stabilized by reinforcement rather than infilling.

Improved near-surface resolution in geotechnical applications using very early AEM time gates

ABSTRACTIn a majority of geotechnical projects and in geohazard studies, knowledge of sediment thickness is crucial, along with information about sediment types such as possible occurrence of sensitive clay. We test the recently improved system response (SR) method on data from an airborne electromagnetic (AEM) survey carried out in Norway to support ground investigations for linear infrastructure projects. In geotechnical projects, especially the upper metres are important to resolve. The acquisition systems, calibration and data processing and inversion are continuously improved to increase the sensitivity of the AEM systems. SR is applied in the inversion of time-domain AEM data making it possible to utilise the very earliest time gates, which provide information about the shallower layers, aiming to increase the near-surface resolution of the models. We test this new method on data from a site where comparably small resistivity contrasts (5–10 Ωm embedded in 10–50 Ωm) are crucial to resolve, to successfully identify hazardous quick clay. The AEM field data inverted with the full SR provide models with more pronounced structures in the near surface, better reflecting true structures observed in resistivity borehole measurements. We see the same outcome when conducting synthetic modelling. In the synthetic models where these early gates were included, thinner layers with smaller resistivity contrasts are resolved. This is a promising result considering to further use AEM in projects where high resolution in the near surface is essential.

On the Validation of Satellite Microwave Remote Sensing Data under Soil Salinity Conditions

The results of a comparative analysis of the underlying surface brightness temperature obtained from the SMOS satellite and calculated with the use of ground-based measurements of moisture and the laboratory measurements of dielectric characteristics of samples of saline soils and saline water from test sites of the Kulunda Steppe are presented. The values of the underlying surface brightness temperatures calculated with the use of ground investigations and the laboratory studies correlate satisfactorily with the values of brightness temperatures measured from the SMOS satellite. The deviations can be caused by the seasonal drying of highly mineralized shallow lakes, which results in a significant change in the areas occupied by lakes and the appearance (instead of a water surface) of wetlands with a high content of mineral salts, whose radio emission characteristics differ from the characteristics of the water surface and the soil cover.

Parameter variability of undrained shear strength and strain using a database of reconstituted soil tests

During construction, the mobilization of undrained shear strength must be limited to avoid soil failure. Soil strains must be controlled to avoid compromising structural serviceability. To assess foundation performance by strength mobilization, an understanding of soil strains at various levels of strength mobilization is required. In practice, ground investigation data are often limited, and assessment of the expected variation of stress–strain and undrained shear strength is improved with empirical correlations calibrated with a database. The new database RFG/TXCU-278 contains data of 278 consolidated–undrained triaxial tests on reconstituted fine-grained soil samples compiled from the literature. Analysis of the database to evaluate the variability of undrained strength ratio (cu/[Formula: see text]) and a reference shear strain with shear mode is undertaken in this paper. The new database provides evidence that shear strain (like undrained shear strength) is sensitive to the consolidation (isotropic or K0) and shear mode (triaxial compression or extension) applied in the test. For the materials included in the database, the strength mobilization parameters obtained from a triaxial compression test can be used to predict the corresponding triaxial extension parameters to a reasonable accuracy.

Towards Multiscale and Multisource Remote Sensing Mineral Exploration Using RPAS: A Case Study in the Lofdal Carbonatite-Hosted REE Deposit, Namibia

Traditional exploration techniques usually rely on extensive field work supported by geophysical ground surveying. However, this approach can be limited by several factors such as field accessibility, financial cost, area size, climate, and public disapproval. We recommend the use of multiscale hyperspectral remote sensing to mitigate the disadvantages of traditional exploration techniques. The proposed workflow analyzes a possible target at different levels of spatial detail. This method is particularly beneficial in inaccessible and remote areas with little infrastructure, because it allows for a systematic, dense and generally noninvasive surveying. After a satellite regional reconnaissance, a target is characterized in more detail by plane-based hyperspectral mapping. Subsequently, Remotely Piloted Aircraft System (RPAS)-mounted hyperspectral sensors are deployed on selected regions of interest to provide a higher level of spatial detail. All hyperspectral data are corrected for radiometric and geometric distortions. End-member modeling and classification techniques are used for rapid and accurate lithological mapping. Validation is performed via field spectroscopy and portable XRF as well as laboratory geochemical and spectral analyses. The resulting spectral data products quickly provide relevant information on outcropping lithologies for the field teams. We show that the multiscale approach allows defining the promising areas that are further refined using RPAS-based hyperspectral imaging. We further argue that the addition of RPAS-based hyperspectral data can improve the detail of field mapping in mineral exploration, by bridging the resolution gap between airplane- and ground-based data. RPAS-based measurements can supplement and direct geological observation rapidly in the field and therefore allow better integration with in situ ground investigations. We demonstrate the efficiency of the proposed approach at the Lofdal Carbonatite Complex in Namibia, which has been previously subjected to rare earth elements exploration. The deposit is located in a remote environment and characterized by difficult terrain which limits ground surveys.

Classification of tree species and stock volume estimation in ground forest images using Deep Learning

Tree species classification and estimation of stock volume are two very important tasks in forest management. Currently, Ground Surveys’ Development (GSD) is the basic and most common approach employed by foresters. However, GSD is time-consuming and inefficient as it requires great human effort. In this research, digital cameras have been used, to obtain images of the ground forest. The classification and accumulation of tree species is performed, by considering extracted relevant image information. The purpose of this effort is not only to improve research efficiency, but to reduce the consumption of human and material resources as well. This research uses the UNET network which is pre-trained by the VGG16 model. The aim is to semantically segment the image containing the ground forest and the species and then to accurately identify the number of trees contained in the image. The proportion of the number of pixels in the trunk of each segment is estimated by considering the total number of pixels in the image. The nonlinear mixed effect model is used to estimate the growing stock volume. The differences in the growing stock volume caused by different forest types, are resolved by using the growing stock volume estimation equations, related to different tree species. The experimental results show that the tree species’ classification accuracy in testing is 96.03% and the average IoU (Intersection over Union) is 86%. The R2 and RMSE of the growing stock volume prediction model are equal to 80.70% and 30.539 (m3/ha) respectively. Therefore, it is concluded that the method proposed in this research can be used as an effective tool for tree species’ image segmentation and classification, and that the growing stock volume is predicted accurately by the extracted tree pixel information. The combination of the two approaches provides a new method for forestry ground investigation work.

Wind turbine construction in and around Carsington Pasture in Derbyshire; overcoming the challenges posed by difficult ground conditions

During construction of four 2.05 MW wind turbines at Carsington Pasture the ground conditions revealed a complex and highly variable geology much worse than had been anticipated. Preliminary investigations and ground assessment carried out at the conceptual planning stage for the development by other parties had identified the nature and discussed the likely extent of the complexities. These preliminary findings had concluded that the site was located in an area of known karst weathering, with extensive ancient mine workings for lead, and abandoned silica sand pits. The preliminary studies and investigations had confirmed shallow head deposits overlying dolomitic bedrock with a variably pinnacoidal interface, and presence of occasional large pocket deposits consisting of unconsolidated sediments. These finding concluded by optimizing the siting locations for each structure. During development, the ground conditions revealed at each location differed significantly and it was realized early on that no single ground remedial solution would be possible to adequately reinforce and suitably improve the bedrock foundation base for the envisaged design life. The challenging ground conditions necessitated extensive non-intrusive ground investigation followed by shallow and deep intrusive investigation to better define the ground conditions. The paper describes the unexpected and unusual combination of ground conditions that were encountered and their implications for foundation development, and examines the development of the bespoke engineered ground solutions developed for each of the four turbines. The experience at Carsington Pasture provided direction for the successful development of a further two wind turbines in an adjacent site located at Ryder Point situated over equally complex ground conditions. The paper concludes with discussion of how the experience of the combination of difficult ground conditions encountered at Carsington Pasture and their management served to guide the investigation, foundation development and successful construction of wind turbines in the adjacent area, and demonstrates the wider value of project examples and experience afforded by case studies.

A large impact crater beneath Hiawatha Glacier in northwest Greenland

We report the discovery of a large impact crater beneath Hiawatha Glacier in northwest Greenland. From airborne radar surveys, we identify a 31-kilometer-wide, circular bedrock depression beneath up to a kilometer of ice. This depression has an elevated rim that cross-cuts tributary subglacial channels and a subdued central uplift that appears to be actively eroding. From ground investigations of the deglaciated foreland, we identify overprinted structures within Precambrian bedrock along the ice margin that strike tangent to the subglacial rim. Glaciofluvial sediment from the largest river draining the crater contains shocked quartz and other impact-related grains. Geochemical analysis of this sediment indicates that the impactor was a fractionated iron asteroid, which must have been more than a kilometer wide to produce the identified crater. Radiostratigraphy of the ice in the crater shows that the Holocene ice is continuous and conformable, but all deeper and older ice appears to be debris rich or heavily disturbed. The age of this impact crater is presently unknown, but from our geological and geophysical evidence, we conclude that it is unlikely to predate the Pleistocene inception of the Greenland Ice Sheet.