Site Investigation Methods Research Articles

Subsidence hazards caused by the dissolution of Permian gypsum in England: geology, investigation and remediation

Abstract About every three years natural catastrophic subsidence, caused by gypsum dissolution, occurs in the vicinity of Ripon, North Yorkshire, England. Holes up to 35 m across and 20 m deep have appeared without warning. In the past 150 years, 30 major collapses have occurred, and in the last ten years the resulting damage to property is estimated at about £1000000. Subsidence, associated with the collapse of caves resulting from gypsum dissolution in the Permian rocks of eastern England, occurs in a belt about 3 km wide and over 100 km long. Gypsum (CaS0 4 .2H 2 0) dissolves rapidly in flowing water and the cave systems responsible for the subsidence are constantly enlarging, causing a continuing subsidence problem. Difficult ground conditions are associated with caves, subsidence breccia pipes (collapsed areas of brecciated and foundered material), crown holes and post-subsidence fill deposits. Site investigation methods that have been used to define and examine the subsidence features include microgravity and resistivity geophysical techniques, plus more conventional investigation by drilling and probing. Remedial measures are difficult, and both grouting and deep piling are not generally practical. In more recent times careful attention has been paid to the location for development and the construction of low-weight structures with spread foundations designed to span any subsidence features that may potentially develop.

Engineering in weathered rock

Abstract The potential problems to be faced when engineering in zones of weathered rock are reviewed. Difficulties in formulating realistic geotechnical models by standard methods of site investigation and routine testing are emphasized and the consequences of being wrong are illustrated by examples. Alternative approaches for delineating weathered zones for design are presented. The constraining influence of particular characteristics of weathered zones on methods of construction are discussed with reference to brief case histories.

Engineering Geophysics — A Civil Engineer’s Veiwpoint

Engineering geophysical methods are a useful site investigation tool in Civil Engineering provided they are applied by experienced personnel, and in conjunction with geological and other site investigation methods. Seismic refraction methods (P and S wave) and resistivity methods have the greatest application. Use of seismic refraction method with geological factors can allow estimation of the rippability of rock by bulldozers, but the methods available are only approximate. Contracts should recognise this limited accuracy and allow for separate rates for excavation of rippable and non-rippable rock.

Marine geotechnical engineering in Canada : Clark, J I; Guigne, J Y Can Geotech JV25, N2, May 1988, P179–198

Marine geotechnical engineering in Canada is over one hundred years old, having started with overwater drilling and testing for bridges and nearshore structures. Its growth has been sporadic, with not much attention being directed to the geotechnical properties of marine soils until the late 1970's when design of artificial islands made up of large caissons started to develop. For about the last 15 years, marine geotechnical engineering has been driven by the oil and gas industry. Most of the action has been in the Beaufort Sea, where complex site conditions have necessitated detailed geotechnical field drilling, sampling programs, and in situ testing. Very little geotechnical engineering research work or site invesigation has been carried out off the east coast except for the Hibernia site on the Grand Banks. In the coming years we can expect to see dramatic changes in site investigation methods. The use of robotics and expert systems coupled with innovative geophysical techniques could dramatically change our methods of site charcterization and measurement of geotechnical properties.

Twenty-fifth anniversary special paper: Marine geotechnical engineering in Canada

Marine geotechnical engineering in Canada is over one hundred years old, having started with overwater drilling and testing for bridges and nearshore structures. Its growth has been sporadic, with not much attention being directed to the geotechnical properties of marine soils until the late 1970's when design of artificial islands made up of large caissons started to develop. For about the last 15 years, marine geotechnical engineering has been driven by the oil and gas industry. Most of the action has been in the Beaufort Sea, where complex site conditions have necessitated detailed geotechnical field drilling, sampling programs, and in situ testing. Very little geotechnical engineering research work or site investigation has been carried out off the east coast except for the Hibernia site on the Grand Banks. In the coming years we can expect to see dramatic changes in site investigation methods. The use of robotics and expert systems coupled with innovative geophysical techniques could dramatically change our methods of site characterization and measurement of geotechnical properties. Key words: marine geotechnical engineering, Beaufort Sea, Grand Banks, Scotian Shelf, in situ testing, geophysical – geotechnical relationship, future trends.

Marine Site Investigations and BS 5930

Abstract Marine site investigations are reviewed briefly, in terms of suitable drilling platforms and craft for various conditions, requirements for permissions and service locations, marine ground investigation methods and marine survey methods including geophysical profiling. The wide range of marine site investigation methods is illustrated and the appreciable differences from land site investigation methods are noted. It is suggested that BS 5930 does not give sufficient guidance on marine site investigations and that this situation should be rectified.

Investigations into the role of groundwater in promoting floor heave in coal mine gateroads

ABSTRACT The geological environment of two South Wales collieries at which site investigations were carried out is summarised. This is followed by a review of identified geological parameters and their effects on floor heave under the headings of discontinuities, mineralogy, and groundwater. Methods of underground site investigation, laboratory testing, and data treatment are summarised. The effect of an increase of groundwater content on mechanical parameter values was quantified for laboratory tested rock cores, and in situ interbedded strata sections. The extent to which groundwater affects floor heave was found to be controlled by the mineralogical and structural nature of the floor strata.

Foundation Densification for Fossil Plant Loads

A case history is presented in which foundation soils in excess of 50 ft (15 m) deep, were densified in place to the degree required to support the loads of a coal-fired electric generating plant. The use of drop-weight compaction and compaction grouting techniques resulted in a significant savings when compared to a more conventional pile foundation system. The application of deep densification techniques has gained increased popularity in recent years. However, even when the soil conditions on a major project are appropriate for in-place densification, the implementation of a deep densification foundation plan may be difficult. A large portion of this difficulty is attributed to the required deviation from the traditional methods of site investigation, contract preparation and construction management. The case history considers how the foundation plan was developed to allow deep densification to be a viable foundation preparation alternative and, ultimately, part of a successful foundation system.

The geometry of slip surfaces beneath landslides: predictions from surface measurements

A knowledge of the slip surface profile beneath a landslip is essential for stability analysis and for the design of remedial works. This note sets out to demonstrate the accuracy of a technique that utilizes the measurement of surface displacements to predict the position and shape of the slip surface. The proposed technique is tested in model studies of all major classes of landslip and is used on three large landslips for which corroboratory evidence of the position of the slip surface, located by traditional site investigation methods, is available. The results indicate that, from a knowledge of ground surface displacements alone, the depth of the slip surface can be confidently predicted to within 2% of the distance between ground stations. The usefulness of this technique for planning and costing-feasibility studies, site investigation programmes, and prospective remedial measures is also discussed.

Observation on chemical grouting today : Hughes, F H Civ Engng, London, Sept 1982, P43–51

With more concern being shown in matters concerning safety and environmental pollution, developments described in the field of chemical grouts have been aimed at the formulation of less toxic materials. The article details two main groups of grouting materials for near-surface soil stabilization: particulate grouts which contain cement, clay or other coarse particles; and, true fluid grouts having no shear strength and a controllable gelling time. This second group includes most chemical grouts of the following types: silicate systems; acrylamide-based formulations; phenoplast resins; and, other polymer grouting mixtures. The main features and applications of this group of grouting mixtures are briefly described. For near-surface construction work the higher viscosity silicate systems offer strength and economy, while the acrylamide and acrylate grouts have low viscosity and quick gelling times. Methods of site investigation and of controlling grout mixing procedures are also detailed. (TRRL)

A seismic refraction survey for an expressway project in Singapore

Geophysical methods of site investigation have been used in civil engineering for many years. Of these methods, seismic refraction survey is perhaps the most highly developed. This paper describes such a survey which was carried out for a proposed expressway in Singapore. The proposed 11 km expressway runs through the Bukit Timah Granite Formation. Acid rocks including granite, adamellite and granodiorite together with various hybrids, which were the results of the assimilation of basic rock within the granite, are present in the formation. Because of the local geological formations, the limited accessibility of the site, and the need for speed and economy, seismic refraction survey had been selected for the subsoil investigation. The study aimed to establish the depth of rockhead level, the type of subsoil materials and the foundation conditions for the planning and construction of the expressway and its flyovers and tunnels. Multi-channel equipment was used for the seismic survey. The energy source was explosives. This paper describes the field procedures and the techniques used for interpreting the results. The problems encountered and the limitations of this survey are discussed. In addition, the findings of the seismic survey are compared with the logs from the boreholes sunk into the bedrock along the expressway alignment. Generally, the results of the seismic survey were found to be satisfactory.

Shear Mechanisms of Vane Test In Soft Clays

Although the vane shear test has become a widely used site investigation method for saturated soft clays, its shear mechanism is very complicated and consequently the significance of the resulting vane strength is not necessarily clarified. In this paper, the shear mechanism of vane test in soft clays is investigated, mainly focussing the stress states on the vertical shear plane. Two types of laboratory vane tests are carried out for the normally Ko-consolidated clays, involving total stress and pore water pressure measurements around shear plane. Also, finite element analysis of vane test is carried out, using a technique of multi-dimensional elasto-plastic consolidation analysis developed by the authors elsewhere. Based on both the experimental and analytical results, some important implications for the vane shear mechanism are shown through considerations of stress distributions and stress path behaviors.

Consolidation of soil using vertical drains

The use of vertical drains is examined critically in view of the fact that in half a century of use there have been a large number of occasions when vertical drains have failed to promote a more rapid consolidation of the soil under load. The mode of operation of the drain is discussed and it is shown that an understanding of this has affected the design of the more recent band-shaped drains. The effects of smear and drain resistance are also discussed. Reference is made to a three-dimensional finite difference computer program, modelling the flow of excess pore water in the drain and the surrounding soil which is used to aid in the drain design. Specific cases which can also be analysed by published techniques have been used to check the validity of the model. Consideration is also given to the methods of site investigation which should be employed to obtain the appropriate soil parameters for design. Cases are cited where a lack of data on the soil parameters has restricted the design of the vertical drainage schemes. L'utilisation de drains verticaux fait l'objet d'une analyse critique car au cours d'un demi-siècle de service, les drains verticaux se sont révélés, à maintes reprises, incapables de permettre une consolidation plus rapide du sol sous chargement. L'article décrit le mode de fonctionnement d'un drain et montre comment la compréhension de ce mode a influencé la conception des drains récents en forme de bande. Il étudie également les effects de l'étalement et de la résistance des drains. L'article se réfère à un programme informatique à différences finies tridimensionnel qui model isele débit de l'eau interstitielle excédentaire dans le drain et le sol environnant; celui-ci sert à faciliter la conception des drains. Des cas spécifiques qui peuvent également être analysés à l'aide de techniques existantes déjà publiées ont été utilisés pour vérifier la validité du modèle. L'article traite également des méthodes d'exploration in situ qui doivent être utilisé eb pour obtenir des paramètres du sol appropriés en vue de la conception. Il présente des cas où un manque de données concernant les paramètres du sol a considérablement limité la conception de systèmes de drainage vertical.

Experience in site investigation for dam construction

Most of the site investigation methods are satisfactorily well known to the engineering geologists and engineers. In sprite of this, individuals engaged in site investigations are less accquainted with the limitations and with the advantages and disadvantages of these methods.