Search

How did the geology and geomorphology of a site become the way it is today? And what are the practical engineering geological applications of that knowledge to civil engineering and environmental projects? The answer is much more than a description of the materials logged in an excavation or a borehole, or a description of a site's geological history. It requires a mental time machine that enables us to investigate and understand the conditions, processes and materials that occur over geological time and recently (including human-induced, anthropogenic impacts). In this paper, by means of some short case study examples, I explore and describe how the application of a time machine approach is an essential tool for engineering geologists, both in the field and back at their desks. (A recording of my lecture, which I gave at the Royal Institution, London on 24 November 2021, is available on YouTube: Glossop Medal Lecture, 2021, https://youtu.be/CAJDtSrrA4w. The lecture is about 65 minutes long.) [ABSTRACT FROM AUTHOR]

The Thames Water ring main extension is a 4·5 km long tunnel from Stoke Newington, in the London borough of Hackney, to New River Head in Finsbury, in the London borough of Islington. The 2·85 m i.d. tunnel was excavated by an earth pressure balance tunnel-boring machine (TBM) at depths between 40 and 60 m below the surface. Surface settlements along the route were measured by precise levelling, and were found to be small. It was therefore even more important to measure these settlements as accurately as possible, in order to provide informed estimates of subsurface movements induced in third-party underground structures much closer to the tunnel horizon. Because of the relatively large magnitude of the background movements measured, when compared with the small tunnel-induced settlements, it was necessary to adopt a rigorous statistical method to fit a Gaussian curve to the data. This exploited the analogy of the 'error function' to define the Gaussian curve parameters and . In all, 13 tunnels were underpassed successfully by the TBM, all within the 'conservative expected value' predictions, and without incident. The predictions and structural monitoring schemes undertaken for the High Speed 1 tunnels near Corsica Street and the Northern line tunnels near Angel station are described in the paper. It was found that the surface and subsurface trough width parameter did not vary with depth as predicted: therefore a new relationship is proposed. [ABSTRACT FROM AUTHOR]

The redevelopment of London Underground's King's Cross St Pancras Station in central London is being carried out to increase capacity from the current 55000 passengers per hour during the morning peak to an anticipated 82000, following the construction of the adjacent Channel Tunnel Rail Link (CTRL) terminus. The work will be undertaken in two phases: phase I works, currently nearing completion, which comprises a new western ticket hall and upgrade of the existing tube ticket hall; and phase II, which will comprise a new northern ticket hall and tunnelled links between the existing underground stations. This paper reviews the considerable amount of geotechnical work carried out for the project and will focus principally on three key areas: (a) developing an understanding of the potential hazards related to the stratigraphy of the site; (b) the use of advanced numerical methods; and (c) the role of instrumentation and monitoring within the design and risk management process. [ABSTRACT FROM AUTHOR]

The City of Pittsburgh, PA is located west of the Appalachian Mountains in the Appalachian Plateaus Province. The relatively flat surface of the plateau is dissected by drainage from the three principal rivers of the region, the Allegheny, Monongahela, and Ohio. The formation of Pittsburgh's three rivers and drainages has a long history dating back to before the Pleistocene Epoch, linked closely to the advance and retreat of continental glaciation. Western Pennsylvania is associated with the westernmost formation of the Appalachian Mountain chain with deformation in the form of a series of nearly flat-lying, gently warped Paleozoic sedimentary rocks. Rocks cropping out in the region range in age from Devonian to Permian. Pennsylvanian strata are dominated by thin cyclic sequences of sandstone, shale, claystone, coal, and limestone. Most of the geologic hazards present in the region include slope instability, expansive shales and slags, mine subsidence, acid mine drainage, pyritic acid rock and flooding. The region also has an abundance of natural resources including coal, natural gas, oil, salt, limestone, sand and gravel and water. Pittsburgh's strategic location helped shape westward expansion during the formation of the Nation, largely because of the rivers, which served as an inexpensive, yet efficient means of transportation. Infrastructure was always significant in Pittsburgh. However, the existing aging infrastructure are deteriorating. Today, Pittsburgh has transcended the legacy name, "Steel City" and has revitalized itself with nationally-recognized universities and medical centers and a resurgence in natural gas exploration. However, many environmental legacy issues still burden the area. [ABSTRACT FROM AUTHOR]

The creation of the Olympic Park, commenced with the formation of the development platform, on which the venues and infrastructure was built. This was part of the enabling works, and included 2 million m of excavation, and the remediation of contamination. To enable the contaminated soils to be reused, a number of soil treatment techniques were adopted: soil washing, bioremediation, chemical stabilisation and material sorting. Soil washing was the main technique, treating around 700 000 m of soil by mixing it with water. This removed the fine grained fractions on which the contaminants were predominantly based, creating a filter cake, typically around 20% of the total volume of soil washed. Bioremediation and chemical stabilisation together treated less than 100 000 m of soil. A regime of chemical testing was established to test the materials at the excavation stage, manage the treatment and finally validate the final material. With the exception of the final validation, testing was carried out off site in MCERTS accredited laboratories, the bulk of the testing was undertaken in the site laboratory, which also handled geotechnical testing. [ABSTRACT FROM AUTHOR]

A detailed borehole investigation has recently been undertaken for an extension to the Thames Water ring main in north London. Results of this were presented in a preconstruction geological model. This formed the basis for tunnel designers to assess ground conditions prior to construction and implement mitigation design and/or contingency plans in the event of adverse geological conditions being encountered. Previous sections of the ring main were constructed using open-faced tunnelling techniques. These allowed for inspection and continuous record of ground conditions at the tunnel face, enabling an identification of the geology and prediction of potentially adverse ground ahead. In facilitating such close geological supervision, tunnelling benefited from significant programme savings - in particular, a reduction of risk to the health and safety of underground personnel. In constructing the tunnel extension, a closed-face tunnel boring machine was opted for; this largely concealed the exposure of geology in situ during the excavation cycle. Apart from a limited number of tunnel face inspections, an indication of the geology was formed from observation and logging the spoil arising from the tunnelling machine, aided by an assessment of the performance of the machine itself in response to changes in geology over the alignment. These activities were necessary in validating the preconstruction geological model and in providing assurances to the on-site design and construction teams. [ABSTRACT FROM AUTHOR]

A site in central London called One New Change is currently being redeveloped. The new development has a basement that extends to approximately 14 m below ground level. Demolition of the building that formerly occupied the site, excavation of the new basement and construction of the new development have caused unloading and subsequent reloading of the ground. This change of loading has resulted in displacements occurring to the nearby London Underground Central Line tunnels that run parallel to the northern boundary of the site. The crowns of the tunnels vary from approximately 20 to 25 m below ground level. The piles and retaining wall for the proposed works are located at least 7 m clear distance to the south of the tunnel closer to the site boundary. The results of analyses carried out to assess the effects on the tunnels indicated that the imposed distortions caused by the proposed works were within tolerable limits. Monitoring was proposed to check that ground and structural movements were within the range of calculated values, and contingencies were identified in the event of agreed trigger levels being exceeded. Displacements measured during the demolition, excavation and construction phase of the project are presented. Conclusions are drawn from comparing the measured displacements with the tunnel deformation calculations. [ABSTRACT FROM AUTHOR]

A trial strain-monitoring system using Brillouin optical time-domain reflectometry (BOTDR) technology was set up to monitor joint movements in the concrete tunnel lining in an existing London Underground tunnel. The BOTDR strain sensor system allows the measurement of strain distribution along an optical fibre using the reflective technique, requiring access to only one end of the fibre. Measurements were obtained by a strain-sensing optical fibre installed along the tunnel lining. The joint movements were captured by measuring the strain along the fibre across the segment joints. The results show that there is good agreement between the joint movements evaluated by the BOTDR strain sensor system and those by conventional vibrating-wire strain gauges. Whereas conventional strain measurement gauges monitor the strain variations at discrete locations, a BOTDR strain sensor can provide a continuous strain distribution of the tunnel lining. The results demonstrate the practicality of using the BOTDR strain-sensing system to monitor the movement of tunnel linings. [ABSTRACT FROM AUTHOR]

Copyright of Géotechnique is the property of Thomas Telford Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

INTERVIEW Engineering beats Pisa's problem John Burland has been professor of soil mechanics at Imperial College London for 20 years and is recognized as a distinguished figure in geotechnical engineering. David Smith talks to him about his work. [ABSTRACT FROM AUTHOR]