Geophysical Tests Research Articles

The Western Australia Modeling project — Part 2: Seismic validation

Large-scale 3D modeling of realistic earth models is being increasingly undertaken in industry and academia. These models have proven useful for various activities such as geologic scenario testing through seismic finite-difference (FD) modeling, investigating new acquisition geometries, and validating novel seismic imaging, inversion, and interpretation methods. We have evaluated the results of the Western Australia (WA) Modeling (WAMo) project, involving the development of a large-scale 3D geomodel representative of geology of the Carnarvon Basin, located offshore of WA’s North West Shelf (NWS). Constrained by a variety of geologic, petrophysical, and field seismic data sets, the viscoelastic WAMo 3D geomodel was used in seismic FD modeling and imaging tests to “validate” model realizations. Calibrating the near-surface model proved to be challenging due to the limited amount of well data available for the top 500 m below the mudline. We addressed this issue by incorporating additional information (e.g., geotechnical data, analog studies) as well as by using soft constraints to match the overall character of nearby NWS seismic data with the modeled shot gathers. This process required undertaking several “linear” iterations to apply near-surface model conditioning, as well as “nonlinear” iterations to update the underlying petrophysical relationships. Overall, the resulting final WAMo 3D geomodel and accompanying modeled shot gathers and imaging results are able to reproduce the complex full-wavefield character of NWS marine seismic data. Thus, the WAMo model is well-calibrated for use in geologic and geophysical scenario testing to address common NWS seismic imaging, inversion, and interpretation challenges.

Practical considerations for array-based surface-wave testing methods with respect to near-field effects and shear-wave velocity profiles

An important constraint with geophysical testing methods based on the propagation of surface waves (active surface wave testing methods) comes from the filtering criteria that are used to avoid near and far-field effects. Such criteria suggest the use of a large receiver spread length to calculate accurate dispersion curves. However, for geotechnical investigations, the use of such a wide array is at best not desirable due mainly to site constraints and to the nature of the soil profile whose dynamic properties tend to vary laterally. The effectiveness of using smaller arrays of receivers covering limited distances to calculate accurate Rayleigh-waves dispersion curves and shear-wave velocity profiles is investigated. The methods used to compute the phase velocities are based on both group and phase velocity estimates. It is shown that the proposed method reduces the effects of body waves and the possibility of mode misidentification in the near and far-fields even when a limited number of traces covering relatively small distances are used. Also, the properties of the signal processing technique used to calculate the dispersion curves are shown to have a significant impact on the near and far-field effects. Numerical and experimental data are used to show the potential benefits of using shorter arrays of receivers to characterize the properties of different soil profiles with laterally varying properties.

Deformation Modeling of Flexible Pavement in Expansive Subgrade in Texas

The tendency of expansive subgrade soil to undergo swelling and shrinkage with the change in moisture has a significant impact on the performance of the pavement. The repeated cycles of wet and dry periods throughout a year lead to considerable stress concentration in the pavement subgrade soil. Such stress concentrations leads to the formation of severe pavement cracks. The objective of the research is to develop a prediction model to estimate the deformation of pavement over expansive subgrade. Two pavement sites—one farm to market road and one state highway—were monitored regularly using moisture and temperature sensors along with rain gauges. Additionally, geophysical testing was performed to obtain a continuous profile of the subgrade soil over time. Topographical surveying and horizontal inclinometer readings were taken to determine pavement deformation. The field monitoring data resulted in a maximum movement up to 80 mm in the farm to market road, and almost 38 mm in the state highway. The field data were statistically evaluated to develop a deformation prediction model. The validation of the model indicated that only a fraction of the deformation was reflected by seasonal variation, while inclusion of rainfall events in the equation significantly improved the model. Furthermore, the prediction model also incorporated the effects of change in temperature and resistivity values. The generated model could find its application in predicting pavement deformation with respect to rainfall at any time of the year.

Two-dimensional image of seismic refraction tomography and electrical resistivity tomography survey in a proposed geophysical test site at Shika, Ahmadu Bello University Zaria, Nigeria

Due to the advancement in technology being applied in geophysics, it is of importance that a geophysical test site center is established for calibration, training, and demonstration of such equipment. An integrated geophysical survey of the area has been conducted, with the aim of characterizing the subsurface structures and lithology. Thereafter, different types of objects that respond to all geophysical techniques will be buried at different depths in the site. Seismic refraction and electrical resistivity tomography were used, using the seistronix RAS 24 seismograph and SAS 4000 ABEM Terameter equipment. These two survey methods were adopted due to the pictorial image they give of the subsurface, enabling a clear view of subsurface structures. A total of five profiles were taken at a total length of 300 m and an inter-profile spacing of 45 m. The results of this survey in correlation with borehole data revealed three distinct layers; overburden, weathered and fresh basement. The overburden consists of the topsoil and lateritic clay, averaging a depth of 3 to 6 m and having a seismic velocity of 100 to 700 m/s and resistivity range of 370 to 750 Ωm. Underneath the overburden is the weathered basement, consisting of brownish fine to medium grained coarse sand, gravel and some disintegrated schistose material, averaging a depth of 6 to 30 m and having a seismic velocity of 700 to 2100 m/s and resistivity range of 56 to 370 Ωm. The depth to the third layer (fresh basement) suggested less compact subsurface of depth >45 m. A close examination of the velocities with depth shows higher velocities at deeper depths (2100 to 3200 m/s) and resistivity > 1500 Ωm.

About seismic observations on Sakhalin with the use of molecular-electronic seismic sensors of new type

To conduct complex geophysical observations in the area of the Central Sakhalin Fault, an experimental geophysical test site was created, including a broadband molecular electronic type station and a new development of the Molecular Electronics Center - molecular electronic hydrophone. A module for placing a molecular-electronic seismometer at the test site has been developed and arranged. The noise level of the seismometer was analyzed and compared with the reference data. The results of hydroacoustic observations of weak earthquakes in the area of the Central-Sakhalin fault using a molecular-electron hydrophone are presented. The characteristics of the recorded acoustic emission signals from earthquakes perceived by the hydrophone station (frequency spectrum, arrival times of seismic waves) are investigated. The issues of operation and maintenance of molecular-electronic sensors with seismic signal data logger at various stages of seismological observations (setting up equipment, acquisition and storing data) were considered. The analysis of recording capabilities of seismic equipment was performed. Conclusions about the advantages and disadvantages of molecular-electronic sensors and their use on Sakhalin are made.

Assessment of the Performance of Stone Columns through the Seismic Wave Test: A Review

The geophysical testing is increasingly being employed in many geotechnical applications. It is preferred in monitoring the mechanical characteristics of the ground because of its economy, not time consuming and non-destructive nature. Seismic wave test is one of the geophysical methods which showed a potential in observing the general behaviour of the reinforced soil with stone columns. Findings in most cases showed that the seismic wave measurements was integrated with or compared to the conventional tests such as standard penetration test or cone penetration test. There was a noticeable success in identifying the enhancement achieved to the ground upon the strengthening with the column, specifically when the associated surveys can produce a clear image of the underground which interprets the variation in the soil properties not prior to the soil treatment only, but even after the treatment occurring. However, from practical point of view, there were still some restrictions with applying such a method, specifically relating to the extent of data gathered, technical concerns and the difficulty of measuring the waves or interpreting results with the presence of ground water. This paper summarizes the recent publication work concerning this technique with a key focus on advantages and limitations within this type of ground improvement.

Model-data fusion for spatial and statistical characterization of soil parameters from geophysical measurements

A recently developed PDE-constrained stochastic inverse analysis algorithm for spatial and statistical characterization of soil parameters from geophysical measurements, considering uncertainty due to limited measurements and sensor noise, is exemplified and validated. A 60m × 60 m geotechnical site in Garner Valley, CA is used as the validation testbed. Advanced geophysical test measurements – in terms of velocity waveforms at a few locations on the surface due to surface excitations using a mobile shaker – are available for the site. The algorithm inversely analyzes the available measurements to probabilistically estimate the elastic parameters of the soil at the site up to a depth of 40 m. The algorithm relies on (1) hypothesizing the soil parameters to be heterogeneous, anisotropic random fields, (2) making prior assumptions on them, (3) numerically simulating the geophysical experiment using the finite element method in conjunction with a stochastic collocation approach, and (4) fusing simulated measurements with experimental measurements using a minimum variance framework to update the prior assumptions on the soil parameter random fields. The estimated elastic parameters of the soil are presented in terms of marginal mean and marginal standard deviation profiles of the soil's P- and S-wave velocities as well as their correlation structures in the x-, y-, and z-direction. In ascertaining the accuracy of the inverse analysis algorithm, the geophysical experiment is numerically re-simulated with the estimated P- and S-wave velocity profiles and the model predicted velocity waveforms are compared against the field observations at all the measurement locations. Comments are made at appropriate places regarding several aspects of the algorithm in highlighting the lessons learned through this validation effort towards accurate stochastic full waveform inversion of geophysical measurements.

Evaluation of Dynamic Soil Properties for Alluvial Plain of Bejaia Using Field Data and Laboratory Tests

This paper deals with the evolution of the shear modulus G and the damping D as a function of the shear deformation of the soil, using data from field and laboratory tests. The studied experimental site is located in port area of the city of Bejaia (Algeria), which has already been the subject of numerous geotechnical and geophysical investigation campaigns as part of construction of important industrial projects. In a first step, the geological, tectonic and hydrological contexts of the region are described, as well as the results of the geophysical and geotechnical tests. The result of this first step is the development of a database from field and laboratory tests. In a second step, monotonic and cyclic triaxial tests are performed to identify the dynamic properties on a reconstituted silty clayey sand soil in the laboratory with a characteristic relatively close to the ground in place. In a third step, a numerical analysis is carried out using a FLAC2D code. The nonlinear elastic model proposed by Ramberg–Osgood and limited by the Mohr–Coulomb criterion is used. The comparison between the numerical results and the experimental data shows the applicability of the Ramberg–Osgood model to describe the dynamic behavior of muddy silty sand and muddy sands of Bejaia.

Depth of influence of rolling dynamic compaction

The depth of influence of rolling dynamic compaction (RDC) was investigated in a field trial using a four-sided impact roller. Earth pressure cells (EPCs) were placed at varying depths at a site consisting of homogeneous soil conditions. EPCs measured pressures imparted by RDC at 3·85 m depth; however, the largest magnitudes of pressure were confined to the top 2 m beneath the ground surface. These results were complemented by field density data, penetrometer and geophysical testing. A number of published case studies using the 8 t four-sided impact roller, for either improving ground in situ or compacting soil in thick layers, are summarised in this paper. Finally, equations are presented that predict first, the effective depth of improvement, appropriate for determining the depth to which the ground can be significantly improved in situ, and, second, the depth of major improvement for RDC, appropriate for thick-layer compaction.

Assessment of Geothermal Resources in Petroliferous Basins in China

In order to speed up the development and utilization of hydrothermal energy, it is essential to assess the potential of geothermal resources in petroliferous basins. In this paper, the distribution of reservoirs (aquifers) and the characteristics of geothermal fields have been studied systematically based on geological, geophysical, well drilling, temperature, and sample test data obtained from the major petroliferous basins of China. It has been found that some of the porous sandstone formations in these petroliferous basins are major geothermal reservoirs and are extensively thick and widely distributed. In general, the geothermal gradient in China is higher in the eastern basins and lower in the western basins. On average, the geothermal gradient is above 30 °C/km in the Bohai Bay, Songliao, and Subei basins. The geothermal resource abundance is also higher in eastern China and in the Beibuwan basin in southern China, and the geothermal source forming condition is better, followed by the Ordos, Qaidam, and Sichuan basins in Central China. Other potential basins include the Tarim and Junggar basins in western China, where the geothermal gradient ranges between 21 and 22 °C/km, on average. In this paper, three methods, stochastic simulation, unit volumetric, and analogy, were used for the assessment of geothermal resources. Using the stochastic simulation and unit volumetric methods, the geothermal resources, annual recovered geothermal resources, geothermal water resources, and thermal energy of water in 11 basins or blocks of up to 4000 m deep were calculated. Grading evaluation criteria were established by considering the heterogeneity of geothermal reservoirs. The results showed that the petroliferous basins are very rich in geothermal resources. The annual recoverable resources reach 1626.8 × 106 tons of standard coal, in which grade I, grade II, and grade III resources are 641.9 × 106, 298.6 × 106, and 686.3 × 106 tons of standard coal, respectively. The results demonstrate that the development and utilization of geothermal energy in oilfields has a huge potential for industrial production and family use, and a great significance for the development of green oilfields. With the high demand of heat, the eastern oilfields with high geothermal resource abundance should be the first to be considered for the production and utilization of geothermal energy, followed by the central and western oilfields.

Characterization of shear wave velocity profiles for South Carolina Coastal Plain

The Atlantic Coastal Plain is a geological formation along the east coast of the United States that consists of unconsolidated sediments as thick as 1000 m underlain by very hard rock with shear wave velocity, V s of over 2600 m/s. In South Carolina, this very hard rock layer is located close to or at the ground surface in the central part of the state, and increases in depth towards the coast, and from north to south. The deep sediments are mostly Cretaceous and younger in age and consist of unlithified sediments with weakly lithified units. The deep sediments are unique geological and geotechnical conditions that pose significant challenges to seismic hazard analyses. Having an accurate V s profile for the deep sediment is critical for predicting the level of ground shaking at a particular site. Geotechnical borings were drilled at two locations to depths of approximately 150 m and 190 m for borehole geophysical testing, undisturbed sampling, and soil/rock coring. Geophysical testing was conducted independently by groups of experts at both locations and included P-S suspension logging, a combined multi-channel and spectral analysis of surface waves, and a combined multi-channel analysis of surface waves and microtremor array measurement methods. This paper presents a comparison between field testing results from the different methods and visual classification of soil and rock samples to evaluate uncertainties of deep soil profiles obtained by different methods. In addition, soil samples collected at both sites were tested using the resonant column method to evaluate dynamic properties. The shear wave velocities measured in the lab for soil and rock samples were compared with results from the field measurements. Cementation was found to be one of the important factors affecting the shear wave velocity measurements.

Improving Rigidity of Clay by Using Explosives and Proofing by Multichannel Analysis of Surface Waves (MASW)

The construction foundation problem in complex conditions with specific types of soils (peat and organic sediment, sludge, soft clay, etc.) is relevant at the present time. Excessive moisture, low bearing capacity, high compressibility, and other negative qualities of these soils make the process of foundation more expensive and complicated. To improve the properties of granular soil can be applied explosive compaction (EC) technology, which has been used for more than 80 years, but mostly for the compaction of gravels, sands and silts. This paper documents the successful application of EC for the compaction of clay soils. To cause compaction, the sequential detonations were performed using explosives placed in boreholes. To investigate the efficiency of explosive compaction on cohesive clay soil, geophysical testing was performed. Applied geophysical testing methods were a Multichannel analysis of surface waves (MASW) and seismic down-hole, whose test results are shear wave velocities (Vs) in depth. The shear modulus (Go) at small deformation, which is directly related to the Vs, were used to determine the degree of soil improvement. From a comparing of results of pre- and post-blast testing, the positive effects are evident.

The geotechnical test site in the greater Lisbon area for liquefaction characterisation and sample quality control of cohesionless soils

In the greater Lisbon area, widespread alluvial sandy deposits can be found that, due to its geology, geomorphology and high seismicity satisfy the criteria to trigger soil liquefaction if subjected to a cyclic action. Within the scope of a research project on liquefaction (LIQ2PROEARTH), an extensive geological, geotechnical, and geophysical database was established, including specific site investigation campaigns in four testing locations, in the municipalities of Benavente and Vila Franca de Xira, near Lisbon. In particular, the campaigns focused on the performance of SPT, CPTu, SDMT and geophysical tests, as well as on the collection of high-quality soil samples using advanced sampling techniques. This paper addresses the geotechnical characterization of a test site and describes the advanced sampling processes for liquefaction assessment. High-quality samples were retrieved by means of three different samplers: Mazier, Dames & Moore and Gel-Push. Preliminary assessment of the sampling quality of the collected samples has been made through the comparison of normalised field and laboratory measurements of shear wave velocity, emphasising the divergences between the different samplers. A comparative analysis of the results is presented and discussed, highlighting the identification of the layers with higher liquefaction susceptibility.

Geotechnical characteristics of sensitive Leda clay at Canada test site in Gloucester, Ontario

In 1954, the Canadian Geotechnical Research Site No. 1 was established as a testing and experimentation site for the soft and highly sensitive Leda clays that were deposited within the now-drained Champlain Sea. The Gloucester test site has a shallow groundwater table taken as hydrostatic at 0.8 m and is underlain by a sequence of leached marine sediments that make-up the Leda clays and extend about 22 m below grade. Below that are dense glacial tills and limestone bedrock. Previous research studies at the site have included full-scale construction, monitoring, and instrumentation of shallow foundations, embankments, drilled shafts, and driven pilings. Recently, a series of in-situ tests in 2012 and 2014 included type 1 and 2 piezocone soundings, porewater dissipations, and both conventional downhole tests and continuous-interval shear wave velocity measurements have been undertaken. Selected results obtained from laboratory, in-situ testing, and geophysical tests over the past six decades are presented.

Importance of coherence between geophysical and geotechnical data in dynamic response analysis

The demand for a precise evaluation of shear wave velocity Vs, is gaining interest in the field of geotechnical engineering due to its importance as a key parameter required to properly evaluate typical characteristics of soils. Nowadays, Vsmeasurements are performed on the field using different methods, such as SCPT tests and various geophysical methods. However, the effectiveness of these field measurements is not guaranteed and rather depends on how they are analyzed. Furthermore, a proper analysis is critical since the collected data may be used in liquefaction evaluation or earthquake ground response analyses. In these situations, it is recommended to verify the coherence between the obtained geophysical (Vs) and geotechnical (N-SPT, qc-CPT) measurements using alternative methods (e.g., Vs-correlations, H/V method, etc...). In some situations, the correlation between the different measurements makes it easier to unambiguously define seismic wave profiles. In other cases, geophysical and geotechnical tests would provide different resolutions for Vsmeasurements, an issue that complicates the decision of the practitioner. In this paper, we first demonstrate the importance of the shear-wave velocity in liquefaction potential analysis. A case study performed in eastern Canada is also presented where we show the importance of the method used to calculate Vsprofiles (MASW, MMASW).

Use of Dynamic Geophysical Tests to Assess the Hazard Associated with Landfills of Solid Industrial and Domestic Waste

Use of Dynamic Geophysical Tests to Assess the Hazard Associated with Landfills of Solid Industrial and Domestic Waste

The Application of the Generalized Finite Difference Method (GFDM) for Modelling Geophysical Test

The possibility of using a nodal method allowing irregular distribution of nodes in a natural way is one of the main advantages of the generalized finite difference method (GFDM) with regard to the classical finite difference method. Moreover, this feature has made it one of the most-promising meshless methods because it also allows us to reduce the time-consuming task of mesh generation and the numerical solution of integrals. This characteristic allows us to shape geological features easily whilst maintaining accuracy in the results, which can be a source of great interest when dealing with this kind of problems. Two widespread geophysical investigation methods in civil engineering are the cross-hole method and the seismic refraction method. This paper shows the use of the GFDM to model the aforementioned geophysical investigation tests showing precision in the obtained results when comparing them with experimental data.

Analysis of failure in landfill construction elements

The paper presents issues related to the failure of construction elements on landfills. The study investigates threats deriving from landfills, which are the result of emergency events. It reviews landfill failures of different types, showing how they may affect the natural environment, human health and safety. The research is aimed at identifying the causes of these events and at presenting the schedule of remedial works and methods of removing the effects of failures occurring in a selected landfill. Based on the analysis, the use of the geophysical testing method to identify the origin and extent of the failure has been demonstrated as a method crucial for the design of repair works.

Hydrogeological Parameter Determination in the Southern Catchments of Taiwan by Flow Recession Method

The understanding of hydrogeological characteristics and groundwater flow processes in aquifers is crucial for the determination of sustainable groundwater resource development as well as hydrological management and planning. In the past, information on hydrogeological characteristics was mainly acquired through point field measurement such as borehole geophysical techniques and field aquifer hydraulic testing. However, in view of the cost limitations and scale applicability of these methods, low-flow recession analysis techniques that utilize streamflow data can be used as alternative low-cost methods to reversely back-calculate hydrogeological parameters based on the hydrological processes by which groundwater from aquifers is naturally discharged to rivers. We chose Southern Taiwan as the study area for the estimation of the recession index (K), which is representative of catchment discharge behavior during both the dry and wet seasons, to determine seasonal differences in the aquifer flow regime and to estimate the following three hydrogeological parameters: hydraulic conductivity (k), specific yield (Sy), and transmissivity (T). Based on the field test reports of the locations of groundwater observational wells on the Chianan and Pingtung plains, the study area was divided into the Chianan sub-area (Zengwun, Yanshui, and Erren river basins) and the Kaoping sub-area (Kaoping, Donggang, and Linbian river basins). The estimation results of the present study were compared to the field test results. The results showed significant differences in the recession index K between the dry and wet seasons. Slight differences between the estimated hydrogeological parameters and the field test results were also observed for the two sub-areas because of differences in scale. Furthermore, regional differences in the estimation results were found to be consistent with the distribution of geological structures, which indicates a high degree of feasibility in the application of flow recession methods for catchment-scale hydrogeological parameter determination.

Measurement of static and dynamic properties of municipal solid waste at Mavallipura landfill site, India

Municipal solid waste (MSW) landfills have been widely constructed around the world for proper dispose of MSW. Geotechnical properties of MSW are difficult to determine because the heterogeneity, wide variation in particle size distribution and time dependent degradation. Knowledge of geotechnical properties of MSW is essential for the design and operation of landfills. Geotechnical properties of the MSW from landfills is very limited. The design of MSW landfills requires the selection of representative MSW material properties. Static and dynamic properties of emplaced MSW from landfill sites at Bangalore, India are evaluated. A comprehensive field and laboratory studies are conducted on MSW disposed at Mavallipura landfills that are in operation for about 12 years. Laboratory studies included: waste composition, water content, hydraulic conductivity, shear behavior for evaluation of static MSW properties. Field measurements included: cyclic plate load test and geophysical testing (multichannel analysis of surface waves) to assess the dynamic MSW properties at landfill site. Also, results obtained from cyclic plate load test is compared with numerical simulation like PLAXIS 2D. In additional, this paper presents a method for extrapolation of Vs30 for MSW site where subsurface data does not extend to a depth of 30 m. Based on the detailed field and laboratory test data, characterization of the small strain shear modulus and the shear wave velocity of MSW is an integral component of various seismic analyses, including site classification, analysis seismic response of landfill. The results in this study will provide guidance in the design and operation of the landfills in India.