Interpretation of Resistivity Piezocone Tests in a Contaminated Municipal Solid Waste Disposal Site

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Resistivity piezocone for geo-environmental site characterization: Two case histories from Brazil

This paper presents two case histories from Brazil where geophysical and resistivity piezocone tests were carried out to detect contamination. At the first one, the site investigation program was carried out to detect salt-water intrusions in a superficial sedimentary aquifer, at the Paranaguá harbor, in Paraná State. The second case history is a sanitary landfill from Bauru City, São Paulo State. In both sites, superficial geophysical tests were interpreted to detect and delineate the shape of contamination plume, helping to locate the resistivity piezocone tests. It was found that the interpretation of resistivity piezocone tests is straightforward to assess salt-water intrusion in sedimentary sands. For tropical soils, this technique presented some limitations since the groundwater table sometimes is deeper than the layer penetratable to the cone. Moreover, the genesis of those soils affects soil behavior and soil and water sampling is required to support interpretation.

The use of slot filter in piezocone tests for site characterization of tropical soils

The use of piezocone tests with a slot filter filled with automotive grease for site characterization of tropical soils is assessed. Laboratory tests using the slot filter filled with automotive grease as well as the conventional porous piezo-element saturated with glycerin were carried out to evaluate the pore pressure (u 2) transducer response. CPTu tests using piezo-elements saturated with glycerin and the slot filter filled with grease were pushed side by side in different research sites in Brazil. Estimates of mechanical and hydraulic soil parameters were made based on pore pressure dissipation curves from using both techniques. Laboratory test results indicate that the pore pressure response using the slot filter with grease was delayed when compared to the piezo-element saturated with glycerin, since grease has a higher viscosity. For tropical soils, the records of u2 in piezocone tests using slot filter with grease presented larger peaks than with porous element saturated with glycerin. Records of u2 using the slot filter above the groundwater table suggest the increase of the degree of saturation in unsaturated zone, where porous filter can be desaturated by suction. The slot filter can be used to help the interpretation of the soil profile with deep groundwater level as well as to help detecting its position for some studied soils. The results shown high repeatability for all study sites. This technique is much easier to handle, especially for tropical soils, where the groundwater table is usually deep and pre-drilling is expensive and time consuming. © 2009 IOS Press.

The resistivity piezocone for high resolution geo-environmental site investigation: A Brazilian example

A suit able decision-making on managing a contaminated site characterization program is strongly dependent of the diagnosis process. A detailed diagnosis can be done based on a Conceptual Site Model (CSM) elaboration using high resolution site characterization tools. The piezocone (CPTu) test is a high resolution tool which allows attaching several specific sensors, like the resistivity probe. This hybrid device is called the resistivity piezocone (RCPTu). A simulated geo-environmental site characterization program was performed on an erosion site using different tools (direct push tools soil samplers, hollow stem auger (HSA) drilling and RCPTu tests) to develop the CSM for a site similar to the Brazilian conditions. It was observed a good agreement between the site profiles interpreted by the different methods. The resistivity sensor attached to the piezocone improved the interpretation and the decision-making process on site was significantly better for the CSM elaboration. The RCPTu test data also allowed identifying the hydrogeological heterogeneities. The present study shows that the RCPTu test is also a useful and powerful tool to development an accurate CSM in a Brazilian condition, especially in an approach that prioritizes high resolution geo-environmental investigation. © 2013 Taylor & Francis Group.

Investigação geoambiental com tomada de decisão em campo utilizando o piezocone de resistividade como ferramenta de alta resolução: Marcos Tanaka Riyis. -

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Piezocone de resistividade: primeiros resultados de investigação geoambiental em solos tropicais

Pós-graduação em Engenharia Mecânica - FEB

O ENSAIO DE PIEZOCONE E DE MINICONE NA INVESTIGAÇÃO DO SUBSOLO: ALGUNS EXEMPLOS DE APLICAÇÃO.

O ensaio de penetração do cone elétrico e do piezocone pertence a um grupo de ensaios de campo, cuja utilização vem sendo cada vez mais difundida. Tanto o avanço da eletrônica como a rápida evolução da informática têm proporcionado equipamentos mais apropriados, menores, mais robustos e mais econômicos, permitindo a incorporação de diversos sensores a essa ferramenta de investigação. Isto contribuiu para que esse ensaio se consagrasse para a descrição contínua do perfil geotécnico, a definição do nível de água e para estimativa de parâmetros mecânicos do solo. Neste artigo faz-se uma breve apresentação do piezocone e do minicone elétrico: o primeiro vem sendo utilizado nos últimos anos, especialmente em geotecnia ambiental, e o segundo, na investigação da infra-estrutura de transportes. Apresentam-se e discutem-se exemplos de emprego do piezocone para identificação de regiões do maciço contaminadas e do minicone para detectar a superfície de ruptura de uma seção de um talude de aterro, para avaliar sua estabilidade através de retroanálises. Concluise o trabalho fazendo-se algumas considerações sobre a utilização dessa tecnologia moderna e recente em solos tropicais que ocorrem no Brasil.

Geotechnical characterization of mixed sandy and silty soils using piezocone tests: Analysis of partial drainage phenomena and rate effects on the experimental soil response

The cone penetration test (CPT), together with its recent variation (CPTU), has become the most widely used in-situ testing technique for soil profiling and geotechnical characterization. The knowledge gained over the last decades on the interpretation procedures in sands and clays is certainly wide, whilst very few contributions can be found as regards the analysis of CPT(u) data in intermediate soils. Indeed, it is widely accepted that at the standard rate of penetration (v = 20 mm/s), drained penetration occurs in sands while undrained penetration occurs in clays. However, a problem arise when the available interpretation approaches are applied to cone measurements in silts, sandy silts, silty or clayey sands, since such intermediate geomaterials are often characterized by permeability values within the range in which partial drainage is very likely to occur. Hence, the application of the available and well-established interpretation procedures, developed for ‘standard’ clays and sands, may result in invalid estimates of soil parameters. This study aims at providing a better understanding on the interpretation of CPTU data in natural sand and silt mixtures, by taking into account two main aspects, as specified below: 1)Investigating the effect of penetration rate on piezocone measurements, with the aim of identifying drainage conditions when cone penetration is performed at a standard rate. This part of the thesis has been carried out with reference to a specific CPTU database recently collected in a liquefaction-prone area (Emilia-Romagna Region, Italy). 2)Providing a better insight into the interpretation of piezocone tests in the widely studied silty sediments of the Venetian lagoon (Italy). Research has focused on the calibration and verification of some site-specific correlations, with special reference to the estimate of compressibility parameters for the assessment of long-term settlements of the Venetian coastal defences.

Estudo da resistência não drenada de solo de baixa consistência por meio de ensaios de campo e laboratório

A variabilidade natural dos solos torna complexo o conhecimento de suas propriedades na elaboração de projetos geotécnicos, sendo a determinação da resistência ao cisalhamento não drenada um parâmetro importante nas análises de estabilidade de solos moles. Os ensaios de laboratório de cone e palheta, não convencionais, os ensaios de campo de palheta e piezocone e os ensaios de compressão simples e triaxial não adensado e não drenado foram utilizados para mensurar a resistência não drenada de uma camada de argila marinha mole localizada na planície costeira central brasileira. Os ensaios de laboratório foram realizados em amostras indeformadas coletadas com amostradores de pistão estacionário em vertical próxima à realização dos ensaios de campo. O sítio foi investigado preliminarmente por sondagens de simples reconhecimento, sendo apresentado o perfil estratigráfico por meio de modelagem computacional. Foram também realizados ensaios para caracterização física (análise granulométrica, teor de umidade, limites de liquidez e plasticidade, densidade real dos grãos) e mineralógica (difração de raios X), e ensaios de adensamento para obtenção do histórico de tensões e classificação de qualidade das amostras indeformadas. Os valores de resistência não drenada obtidos pelos ensaios de laboratório foram comparados ao perfil contínuo de resistência determinado empiricamente pelo ensaio de piezocone, com fator de cone Nkt calibrado pelo ensaio de palheta de campo, apresentando boa concordância, com a variabilidade natural do solo influenciando de forma preponderante a qualidade das amostras na variação entre os resultados. Os valores de resistência obtidos pelos ensaios de laboratório de cone e palheta foram comparados entre si, apresentando boa compatibilidade. Ambos, quando comparados ao ensaio de palheta de campo, não apresentaram boa concordância. Os resultados de resistência obtidos pelos ensaios de compressão simples e triaxial apresentaram boa compatibilidade com os resultados do ensaio de laboratório de cone, o que não ocorreu com os resultados do ensaio de laboratório de palheta. Na comparação entre a resistência normalizada pela tensão de sobreadensamento obtida pelos diversos métodos e algumas correlações empíricas da literatura internacional, foi observado para as amostras de solo com índice de plasticidade superior a 60% boa concordância com as correlações de Mesri (1975) e Jamiolkowski et al (1985). Os ensaios não convencionais apresentaram boa confiabilidade, que aliado a simplicidade e agilidade de execução, justificam a difusão destes na prática da investigação geotécnica brasileira como método alternativo para complementar e dar suporte às estimativas de resistência não drenada de solos moles.

Nova metodologia de execução do ensaio SCPTu com avaliação da influência da fonte sísmica quanto à sua dimensão e afastamento

O objectivo deste trabalho consiste na determinação das Ondas de Corte, onda S, através de uma nova metodologia de ensaio do piezocone sísmico, SCPTu. A nova metodologia adoptada de aquisição de dados, consiste na aquisição da onde de corte no movimento ascendente de remoção de varas, após execução do já conhecido ensaio CPTu, ao invés da tradicional aquisição, no movimento descendente, previamente ao acréscimo de nova vara. Além da introdução de uma nova metodologia de aquisição sísmica, tentou-se avaliar a influência da dimensão da fonte geradora da onda de corte e a influência do afastamento das mesmas ao ponto de cravação, do ensaio de penetração estática mencionado. Na avaliação das influências foram usadas três fontes de madeira de secção rectangular, com uma chapa de ferro a topo e diferenciadas entre si pelas dimensões de 1m, 2m e 3m e afastamentos até 4m.

Geoenvironmental site investigation using different techniques in a municipal solid waste disposal site in Brazil

Different geoenvironmental site investigation techniques to assess contamination from a municipal solid waste disposal site in Brazil are presented here. Superficial geophysical investigation (geoelectrical survey), resistivity piezocone penetration tests (RCPTU), soil samples collected with direct-push samplers and water samples collected from monitoring wells were applied in this study. The application of the geoelectrical method was indispensable to identify the presence and flow direction of contamination plumes (leachate) as well as to indicate the most suitable locations for RCPTU tests and soil and water sampling. Chemical analyses of groundwater samples contributed to a better understanding of the flow of the contaminated plume. The piezocone presented some limitations for tropical soils, since the groundwater level is sometimes deeper than the layer which is impenetrable to the cone, and the soil genesis and unsaturated conditions affect soil behavior. The combined interpretation of geoelectrical measurements and soil and water samplings underpinned the interpretation of RCPTU tests. The interpretation of all the test results indicates that the contamination plume has already overreached the landfill's west-northwest borders. Geoenvironmental laboratory test results suggest that contamination from the solid waste disposal site has been developing gradually, indicating the need for continuous monitoring of the groundwater.

Specific depth cone resistivity measurements to determine soil engineering properties

The University of British Columbia (UBC) began performing piezocone penetration tests (CPTU) with electrical resistivity measurements (RCPTU) in 1989. Since then, RCPTU research at UBC has focused on obtaining geo-environmental parameters such as fluid resistivity and soil engineering properties such as porosity and degree of saturation from measurements of bulk soil electrical resistivity using the empirical relationship proposed by Archie (1942). Within this framework, the paper illustrates and discusses important design and calibration issues for resistivity modules such as the use of isolated circuitry to achieve linear calibrations over large ranges of resistivity. The suitability of RCPTU measurements for determination of geo-environmental and geotechnical parameters are assessed using typical ranges of soil and groundwater properties and methods of isolating individual factors for study are discussed. Illustrative examples of RCPTU research efforts including the environmental characterization of mine tailings, delineation of saline water intrusions in fresh water aquifers and the quality control of geotechnical ground densification are presented throughout the text. It is shown that groundwater temperature and hence ion mobility is not significantly altered by frictional heat generated during piezocone penetration and that ratio-based approaches to monitoring soil porosity can be used to eliminate the requirement for extensive groundwater sampling programs. Lastly, it is shown that RCPTU measurements above the water table can only be made using resistivity modules that are stable over a large range of resistivities and that such measurements are the most difficult to interpret because of grain surface conduction effects and generally unknown fluid resistivities.

Investigação de Intrusão de Água Salgada em Aqüífero Superficial a Partir de Medidas de Resistividade Elétrica

A site investigation program was carried out to detect salt-water intrusions in a shallow sedimentary aquifer based on electrical resistivity measurements. The site is located close to Paranaguá harbor, in the Paraná State, Brasil. At this site, high chloride concentration contaminated shallow water wells used to supply water for local industries. The site investigation program included a fieldwork, dipole-dipole electrical profiling, resistivity piezocone tests, physical-chemical analysis of sampled water and interpretation of borehole logs. The resistivity piezocone tests provided two simultaneous information; the soil stratigraphy at a very detailed level and a quasi-continuous resistivity profile. Both information adequately complemented dipole-dipole electrical profiling test data. The integration of all test data allowed identifying the contaminated areas as well as guided the location of new water wells to be installed in this area.

Development of a new TDR probe for determining soil water content and dry density

A few traditional methods for determining water content in the field are either inaccurate or time consuming. As an alternative, the time domain reflectometry (TDR) technology has been used in the determination of the soil water content for geotechnical applications. This paper presents the preliminary results on the development of a new TDR probe for determining soil water content and dry density at different depths. This new probe is intended to be pushed into the ground using piezocone equipment. Different from the standard TDR probes with straight rods, the new probe consists of two parallel copper stripes coiled around a PVC-steel core. The probe diameter is the same as the standard 10 cm2 piezocone diameter. Through laboratory calibrations, it is possible to establish expressions relating the soil apparent dielectric constant and the bulk electrical conductivity with the gravimetric water content and the dry density. Copyright ASCE 2007.

Developing a system for down-hole seismic testing together with the CPTU

This paper presents a system for performing down-hole seismic test together with the piezocone test in order to determine the shear wave velocity (Vs) and for calculating the maximum shear modulus (Go); a basic parameter for analyzing the dynamic soil behavior and a reference value of the soil stiffness. The system components are described and tests results for checking the geophone response are also presented, both before and after installation into the probe. The system was used in down-hole tests carried out at three experimental research sites located in the interior of Sao Paulo State, Brazil, where in situ seismic test results are available. The Vs values measured in down-hole tests carried out with this system were consistent with those determined in cross-hole tests and with a commercial seismic piezocone, which enabled to validate the developed system.