Routine Site Investigation Research Articles

Piezocone penetration test-based site characterisation of Chong–Qi Bridge project, China

The piezocone penetration test (CPTU) provides an advanced way of characterising soil deposits in routine site investigation. This paper presents a synthesised application of CPTU in the site characterisation of Chongming–Qidong Bridge project in China, including soil classification, soil property evaluation and pile capacity estimation. Sixteen CPTU soundings and 31 borehole drillings were performed at the testing site, and their results were compared. Four CPTU-based soil classification charts were used to determine the soil types at the testing site, and their accuracy is discussed. Formulas for predicting the overconsolidation ratio and undrained shear strength of soft soils at the testing site were analysed. Six existing CPTU-based methods for assessing the ultimate capacity values of axially loaded piles were evaluated based on a database containing 14 pile load tests collected at the testing site. Practical recommendations for and implications of the use of the CPTU technique in deep-foundation projects are finally summarised.

In‐situ‐Versuche mit Flat Dilatometer und seismischem Dilatometer

AbstractIn the last decades there has been a massive migration from laboratory testing to in situ testing, to the point that, today, in situ testing is often the major part of a geotechnical investigation. In particular direct‐push in situ tests, such as Cone Penetration Test (CPT) and the Flat Dilatometer Test (DMT), are fast and convenient in situ tests for routine site investigation. The scope of this paper is to describe the DMT and its recent updates, in particular the Seismic Dilatometer Test (SDMT) for measuring shear and compression wave velocities and the automated dilatometer probe (Medusa DMT). An Example of SDMT test results and its application to derive soil stiffness parameters are shown, as well as the result of a class‐A prediction of an anchor pull‐out test, which was calibrated with the SDMT profile.

CHD pile performance: part II – numerical modelling

A set of simple finite-element modelling procedures that can be used to estimate the load–settlement behaviour of continuous helical displacement (CHD) piles in sand is presented. The approach makes use of a stress- and strain-dependent non-linear soil model that can be parameterised using basic soil data that can be determined through routine site investigation. The procedures are validated against a database of physical model tests (reported in a companion paper), where they are shown to be suitable for estimating the load–settlement behaviour of CHD piles within the serviceability range. In this way they are complementary to the analytical method reported in the companion paper for estimating the ultimate capacity of a CHD pile. In this paper, the finite-element method and analytical model are applied to four historical load tests on CHD piles conducted at three different sand sites. The modelling is further validated and used to discuss potential savings in pile material and therefore cost due to additional confidence in performance determination at both ultimate and serviceability limit states.

Spatial correlation length of normalized cone data in sand: case study in the north of Denmark

The main topic of this study is to assess the anisotropic spatial correlation lengths of a sand layer deposit based on cone penetration testing with pore pressure measurement (CPTu) data. Spatial correlation length can be an important factor in reliability analysis of geotechnical systems, yet it is rarely estimated during routine site investigations. Results from two different sites in the north of Denmark are reported in this paper, indicating quite strong anisotropy due to the depositional process, with significantly shorter spatial correlation lengths in the vertical direction. It is observed that the normalized cone resistance is a better estimator of spatial trends than the normalized friction ratio.

An improved steady-state apparatus for measuring thermal conductivity of soils

The thermal conductivity of soil is among the most critical parameters required to design ground heat exchangers, which are widely used as a renewable technology for providing heating and cooling for buildings. This paper describes the development of new test apparatus that can be used for soil specimens obtained from routine site investigation as well as reconstituted specimens. The design of the apparatus is based on the application of Fourier’s law where one directional uniform heat flux is generated through two identical specimens, producing a measurable temperature gradient that is used to calculate the thermal conductivity of the specimen. A new concept of minimizing the radial heat losses using a thermal jacket as a heat insulation barrier was examined. It was found that the no-radial heat losses condition can be achieved with thermal jacket temperature approximately equal to the average value of the ambient temperature and average specimen temperature. All parameters that can affect the measurements have been tested and the results showed a good performance with margin of error upto 5%. An application of the new test procedures involved conducting several experimental tests on undisturbed and reconstituted soil samples highlighted the simplicity of this apparatus in measuring thermal conductivity of soil under different conditions.

Aftershocks and the whole-life seismic performance of granular slopes

Shallow embankment slopes are commonly used to support elements of transport infrastructure in seismic regions. In this paper, the seismic performance of such slopes in non-liquefiable granular soils is considered, focusing on permanent movement and dynamic motion at the crest, which would form key inputs into the aseismic design of supported infrastructure. In contrast to previous studies, the evolution of this behaviour under multiple sequential strong ground motions is studied through dynamic centrifuge, numerical (finite-element, FE) and analytical (sliding-block) modelling, the centrifuge tests being used to validate the two non-physical approaches. The FE models focus on the specification of model parameters for existing non-linear constitutive models using routine site investigation data, allowing them to be used routinely in design and analysis. Soil-specific constitutive parameters are derived from shearbox and oedometer test data, and are found to significantly outperform existing empirical correlations based on relative density, highlighting the importance of specifying a suitably detailed site investigation. An improved sliding-block (‘Newmark') approach is also developed for estimating permanent deformations during preliminary design, in which the formulation of the yield acceleration is fully strain-dependent, incorporating both material hardening/softening and geometric hardening (re-grading). The site-specific (improved) FE models and the new sliding-block approach are shown to outperform considerably existing FE parameters and sliding-block models in capturing the permanent deformations of the slope under virgin conditions, and further, only the improved FE and sliding-block models are found to capture correctly the behaviour of the ‘damaged' slope under subsequent earthquakes (e.g. strong aftershocks). The FE models can additionally accurately replicate the settlement profile at the crest and quantify the dynamic motions that would be input to supported structures, although these were generally overpredicted. The FE procedures and sliding-block models are therefore complementary, the latter being useful for preliminary design and the former for later detailed design and analysis.

Model specification to determine thermal conductivity of soils

Developments in technology have led to an increasing interest in alternative sources of energy, which includes the ground and, in particular, the zone of influence of building foundations. The temperature in that zone in northern Europe is about 10–13°C, which is about the mean air temperature. It is possible to take advantage of this stable temperature to cool/heat buildings by circulating liquid through a closed loop within this zone and passing it through a heat exchanger or heat pump connected to a circulation system within the building. The number of loops required depends on the difference in temperature between the building and the ground, and on the thermal properties of the ground. This paper describes a model specification for determining the thermal characteristics of soils and rocks obtained from routine site investigations. Tests on cylindrical specimens have been used to develop the equipment, test procedure and analysis. The results indicate that the technique is simple, reliable, and produces typical results for sand and clays.

Diameter Effects on Pile Head Lateral Stiffness and Site Investigation Requirements for Pile Foundation Design*

The effect of pile shaft diameter on unrestrained pile head lateral and rotational stiffnesses of long piles is considered in relation to required site investigation data. Analysis of field test data for lateral load tests on piles of different diameters published in the literature led to the suggestion that the modulus of subgrade reaction appears to increase with increasing pile shaft diameter. This is contrary to the usual understanding that the modulus of subgrade reaction is independent of pile shaft diameter. This puzzle is resolved in the realization that as the pile diameter increases the depth of soil which contributes to the lateral stiffness also increases. If the soil stiffness increases with depth, then the pile head lateral stiffness will be greater than would be predicted on the basis of lateral load testing of smaller diameter piles. Included in the article is discussion of the effect of the variation with pile shaft diameter of the unrestrained pile head lateral and rotational stiffnesses for three distributions of soil modulus with depth, as well as the effect of the pile head moment to shear ratio. A corollary of the article is that accurate estimates of pile head stiffness during foundation design require better than routine site investigation data.

The Second James K. Mitchell Lecture Undisturbed sand strength from seismic cone tests

During routine site investigations, high-quality sampling and laboratory testing of sands are not feasible because of inevitable sample disturbance effects and budgetary constraints. Herein, a select database is compiled for calibration of cone penetration test (CPT) interpretative methods, primarily from undisturbed frozen sand samples at 15 sites in Japan, Canada, Italy, Norway, and China. The database is used to evaluate the peak secant friction angle in terms of the normalized cone tip resistance using two analytical approaches: (i) spherical cavity expansion theory with an operational rigidity index , and (ii) a limit plasticity formulation with appropriate angle of plastification . Backfigured values of and are found correlated to the normalized small-strain stiffness . Thus, with measurements taken of both the initial shear modulus and shear strength, seismic cone tests offer the opportunity to derive the entire stress–strain–strength response of sands at all depths.

Spatial Variability of Non-Aqueous Phase Liquid Chemicals in Soil--Implications for Source Zone Mass Estimates

Small-scale spatial variability of chemical concentrations in soil samples can introduce substantial uncertainty in the calculation of average concentrations and chemical mass in non-aqueous phase liquid (NAPL) source zones. Centimeter-scale sampling and analysis of a 2.5-m-long soil core from an experimental release of dense NAPL into a sandy aquifer at Canadian Forces Base Borden, Ontario, Canada, yielded chemical concentrations that varied by a factor of 1,000 times over a vertical distance of less than 0.5 m. Simulations to assess the effect of meter-scale sampling more typical of routine site investigations illustrated that there will be substantial uncertainty in average chemical concentrations calculated from less frequent sampling. For soil sampling at a 0.5-m interval, there would be only a 55 percent likelihood that the calculated average perchloroethylene (PCE) concentration would be within ±50 percent of the average calculated by detailed sampling. For sampling at a 1.25-m interval, there would be only a 30 percent likelihood that the calculated average PCE concentration would be within ±50 percent of the average calculated by detailed sampling. This degree of uncertainty is substantial in the context of designing an in situ treatment remedy or evaluating the performance of a mass removal remedy. Based on these results and the spatial variability in chemical concentrations anticipated in most NAPL source zones, the soil sampling and analysis performed for most routine site investigations will be of limited value in making useful estimates of contaminant mass.

Rehabilitation of industrial areas: case histories from England and Germany

Contaminated and possibly hazardous ground represents a problem in all of the industrialized countries of the world. The investigation of a site that is suspected of being contaminated differs somewhat from a routine site investigation. Sampling of soils, groundwater and gas-producing material may be required. Various precautions may be necessary in doing this and operatives may have to wear protective clothing. Four case histories have been chosen to illustrate different aspects of the rehabilitation of abandoned contaminated land, namely, investigation, assessment, ground treatment and redevelopment. The first comes from Leeds in West Yorkshire, England, and outlines how a site investigation was undertaken and the nature of the contamination present, together with a note on the suggested redevelopment. The remaining three case histories are taken from the heavily industrialized district of the Ruhr in Germany, where extensive mining of coal and associated industries were developed from the mid-19th century onwards. The first considers the site of the former Graf Moltke mine near Essen. In this instance, the somewhat novel methods of data assessment and ground treatment are dealt with. The Mont Cenis site at Herne-Sodingen is one of the more notable old mining/industrial sites undergoing redevelopment in the state of North Rhine Westphalia. Hence, the case history concentrates of this aspect of rehabilitation. This involves not only the construction of new and interesting structures but an attempt to reduce energy consumption in an attempt to effect the concept of sustainable development of an urban area. The last example deals with the abandoned site of the Minister Achenbach mine at Lunen, where the ground conditions were further complicated by the presence of old bomb craters that had been filled with a variety of materials. In addition, because of the suspected presence of former foundation structures in the ground an electromagnetic survey was carried out across part of the site, the areas of high conductivity suggesting their presence.

A survey of contaminated ground with illustrative case histories

Contaminated ground represents a problem in all the industrialized countries of the world. Contaminated ground may give rise to hazards and that implies a degree of risk which also involves a problem of definition. The investigation of a site which is suspected of being contaminated differs somewhat from a routine site investigation. Sampling of soils, groundwater and gas producing material may be required. Various precautions may be necessary in doing this and operatives may have to wear protective clothing. The first case history considered involves a site investigation for a relief sewer in Glasgow, Scotland. As the site investigation progressed it ran into made-ground which contained chemical waste. The presence of this waste meant that the nature of the investigation changed and much more stringent safety precautions had to be taken. It also meant that the initial location of the sewer tunnel had to be repositioned at greater depth in uncontaminated sandstone rather than in the superficial deposits above. Two further case histories associated with coal mining in the Ruhr district of Germany are included. The methods involved in investigating these two sites are described, as is their rehabilitation. Copyright © 2000 John Wiley & Sons, Ltd.

Characterizing Pavement Subgrades in Texas

Severe pavement distortions were found at several places along State Hignways 6 and 21 (SH 6 & SH 21) in Texas, USA. The heaves had a spacing of about 30m and an amplitude of over 0.3m. Routine site investigation before construction did not reveal underlying soil conditions that could produce the types of pavement distresses occurring relatively soon after completion of construction. Possible causes of this roughness are: (1) poor drainage from median and roadside ditches; (2) gravel lenses under the pavement; and (3) lime-sulphate-clay reaction. This paper presents a field investigation and site investigation procedures to determine which problems needed to be solved, and which methods should be used in the future to prevent problems of this type from recurring. Ground penetrating radar (GPR) and soil suction profiles were used to find out which causes were most likely and where they were located. Several laboratory tests were conducted to estimate the volume change and unsaturated flow properties of the pavement subgrade; they included Atterberg limits, water content, dry density, and soil particles finer than 75 microns and 2 microns. The soil's sulphate content was estimated by field electrical conductivity tests. Drainage water entering through the surface was found to be a main cause of the pavement problems.

Forensic Investigation of Pavement Distortions Using Soil Suction

State Highway 6 in Brazos County, Tex., is experiencing significant changes in surface profile at several locations. The changes in surface profile were noticed within a few months after construction. They quickly became severe enough to adversely affect vehicle safety. The longitudinal distance between the peak of the undulations is usually greater than 30 m. Patching to maintain a reasonably safe surface profile has been performed at least annually since construction. Routine site investigations prior to construction did not reveal underlying soil conditions that could produce these kinds of pavement distresses that appeared relatively soon after the pavement subgrade was stabilized with lime. In this study, the area was investigated using soil suction profiles to determine the origin(s) of the pavement distresses manifested at the surface. Findings indicated the swells were not caused by lime stabilization of sulfate bearing soils but were the result of surface water flowing through deep cracks and/or permeable soil layers to highly plastic expansive clays. Researchers used soil suction profiles to analyze the problem and recommended remedial measures to reduce subsequent swelling.

Contaminated ground and contaminated estuary sediment illustrated by two case histories

Contaminated ground forms a problem in all of the industrialized countries of the world. Contaminated ground may give rise to hazards and that implies a degree of risk which also involves a problem of definition. The investigation of a site which is suspected of being contaminated differs somewhat from a routine site investigation. Sampling of soil, groundwater and gas-producing material may be required. Various precautions may be necessary to do this and personnel may have to wear protective clothing. The first case history considered involves a site investigation for a relief sewer in Glasgow. As the site investigation progressed it ran into made-ground which contained chemical waste. The presence of this waste meant that the nature of the investigation changed and much more stringent safety precautions had to be taken. It also meant that the initial location of the sewer tunnel had to be repositioned at greater depth in uncontaminated sandstone rather than in the superficial deposits above. The other case history considers the contamination of sediments in the Forth Estuary. When trace metals are released into the water column they can be transferred rapidly to the sediment phase by adsorption onto suspended particulate matter, followed by sedimentation. Intertidal flats may be considered as important trace metal sinks since they accumulate large amounts of suspended matter. Hence, in polluted estuaries the deposition of suspended particles on intertidal flats may thus cause severe contamination. The Forth Estuary has unique contamination for British estuaries; it is experiencing significant Hg pollution. In addition, due to the presence of a nuclear submarine base in the Forth Estuary, 60Co is detectable in the intertidal sediments. Temporal and spatial contamination patterns were analysed in relation to historical and present pollution point sources. The effect of fluvial and marine sediment mixing on trace metals and other processes controlling contaminant levels is reviewed. Preliminary results on quantifying sediment accretion rates using Caesium levels are discussed.

Contaminated Land: The British Position and Some Case Histories

Contaminated ground may give rise to hazards and that implies a degree of risk which also involves a problem of definition. The attitudes of different states to contaminated ground and its redevelopment vary appreciably. The investigation of a site which is suspected of being contaminated differs somewhat from a routine site investigation. Samples of soils, ground water and gas producing material may be required. Various precautions may be necessary in doing this and operatives may have to wear protective clothing. Three case histories are given which involve site investigation. Two are fairly standard investigations of suspected contaminated land, the third involved some of the latest methods of contaminant detection. (A)

Ground probing radar applications in site investigation : Fenning, P J; Jack, A G; Veness, J K Non-destructive Testing in Civil Engineering, Liverpool (United Kingdom), 14–16 Apr 1993. Vol. 2, pp 113–140. Edited by J H Bungey. The British Institute of NDT (1993)

Although early experiments in the application of Ground Probing Radar to site investigation occurred in the early part of this century, it is only in the last ten years that this geophysical method has been used as a routine site investigation technique. All too often this technique has been misapplied and has led to disappointing results, often of little use to the Geotechnical Engineer. The reasons for this are examined and it is suggested that the introduction of Ground Probing Radar systems which are based on proven seismic reflection methodology will overcome some of the misapplications of the past. Reference is made to the requirement for radar signal propagation velocity determination to be made on site and the pre-survey requirement of assessing theoretical ground radar applicability before commencing a radar survey. Examples of case histories are given. (A) For the covering abstract see IRRD 861706.