Marek Bajda

The use of resistivity and seismic cone penetration tests for site characterization

The use of resistivity and seismic cone penetration tests for site characterization The use of resistivity and seismic cone penetration tests for site characterization. Recent application of cone penetration tests to geotechnical and environmental site characterization has generated a wide collection of new sensors. This paper presents methods of interpreting geotechnical in situ investigations carried out by electrical resistivity (RCPT) and seismic (SCPT) cones. It contains some fundamental equations and the description of in situ electrical resistivity and shear wave velocity measurements and presents the results of SCPT and RCPT investigations at the experimental Stegny site in Warsaw. The aim of the paper is to present the approach to determination of shear wave velocity and porosity of clayey soils. According to the test results obtained, it can be concluded that both applied techniques are very useful to estimate the distribution of clay deposits and some of their geotechnical parameters. Obecnie obserwuje się dynamiczny rozwój zastosowań badań geotechnicznych, w tym zwłaszcza sondowań, do oceny stanu środowiska. W związku z tym można zaobserwować zapotrzebowanie na specjalistyczne badania podłoża gruntowego, mogące pomóc w określeniu różnych parametrów stosowanych w geotechnice środowiskowej, takich jak np. temperatura gruntu, oporność elektryczna, odczyn pH gruntu, potencjał redoks i innych. W niniejszym artykule przestawione zostały wyniki sondowań geotechnicznych stożkiem wyposażonym w moduł do pomiaru oporności elektrycznej gruntu (RCPT) oraz stożkiem sejsmicznym (SCPT). W artykule przedstawiono podstawowe informacje na temat techniki badań, opis stosowanych urządzeń oraz wyniki badań na terenie poligonu badawczego na Stegnach w Warszawie. Celem pracy było określenie zależności empirycznych pomiędzy parametrami uzyskanymi z badań sondami RCPT oraz SCPT a porowatością i prędkością fali poprzecznej badanych gruntów spoistych. Na podstawie przeprowadzonych badań można wnioskować, że zastosowane urządzenia pozwalające na pomiar oporności elektrycznej i prędkości rozchodzenia się fali poprzecznej w gruncie mogą być z powodzeniem wykorzystane do rozpoznania budowy geologicznej podłoża i określania pewnych parametrów gruntu.

Small strain stiffness in overconsolidated Pliocene clays

Abstract Small strain stiffness in overconsolidated Pliocene clays. A huge development of technical infrastructure, including the construction of many high-rise buildings, roads, railroads and extension of subway lines, took place over the recent years in Poland. Therefore, numerous planned investment projects require geotechnical data documenting the variation of soil parameters found in the subsoil. The shear wave velocity is one of the most important input parameters to represent the stiffness of the soil deposits. This paper focuses on the methods and devices using measurements of the shear wave velocity to estimate the initial shear modulus in cohesive soil. It is preferable to measure VS by in situ wave propagation tests, however it is often economically not feasible in all regions of Poland. Hence, a reliable correlation between shear wave velocity and parameters measured in triaxial cell or static penetration parameters would be a considerable advantage. This study shows results obtained from the bender elements tests and field techniques - seismic cone penetration test and seismic flat dilatometer, performed on overconsolidated cohesive soils in Warsaw. On the basis of the test results possible correlations between shear wave velocity (initial shear modulus), mean effective stress and void ratio are considered and four original empirical relationships are proposed. Moreover, the proposed formulas by two different techniques using triaxial apparatus and also RCPT cone were examined. The proposed formulas show a reasonable agreement with direct shear wave velocity profiles for clays and might be incorporated into routine laboratory and field practice

Analysis of yield stress ratio and overconsolidation ratio as parameter determination preconsolidation in eemian gyttja

Abstract The preconsolidation stress is an important phenomenon that determines the value of stress history exerted in the past on the subsoil in the geotechnical engineering. Overconsolidation ratio (OCR) is one of the main criteria conditioning soil behaviour and its characteristics. Here thought, the yield stress ratio (YSR) is used to determine the value of preconsolidation stress resulting from mechanical overburden than can be changed by many post depositional processes like secondary and tertiary compressibility, cementation, aging, temperature change and others. The yield stress ratio (YSR) is defined as the relationship between vertical yield stress (σ’vy) to the effective vertical stress (σ’v0). The eemian gyttja was used as a foundation in the engineering construction. In practical geotechnical engineering, evaluation of stress history is usually based on the overconsolidation ratio (OCR). The yield stress ratio (YSR) was used in the laboratory as one of the basic parameters for the geotechnical design of the structure. To know the relation between geological background, history and mechanical behaviour in long-time process of the soil aims a knowledge that can help engineers who often have to predict soil behaviour based upon the soil geological history and a few geotechnical data. In order to evaluate the yield stress ratio of eemian gyttja it is necessary to restore this soft, organic soil as much as possible to the in situ conditions. The laboratory tests were used to determinate the vertical yield stress and then the yield stress ratio. The laboratory tests were made in the automatic oedometer and the in situ tests were carried out on the dilatometer test (DMT). The comparison between the determination the yield stress ratio of eemian gyttja from the laboratory and the overconsolidation ratio from in situ test has been done. The studies have shown that the values of the overconsolidation ratio determinate from the laboratory tests are a little higher than determinate from the in situ tests.

The overconsolidation ratio of eemian gyttja determination

Abstract The overconsolidation ratio of eemian gyttja determination. The overconsolidation ratio is an important parameter that determines the value of stress history exerted in the past on the subsoil in the geotechnical engineering. Overconsolidation ratio (OCR) is one of the main criteria conditioning soil behavior and characteristics. To know the relation between geological background, history and mechanical behavior of the soil, aims a knowledge that can help engineers who often have to predict soil behavior based upon the soil geological history and a geotechnical data. In order to evaluate the overconsolidation ratio of eemian gyttja, it is necessary to restore this soft soil as much as possible to the in situ conditions. The eemian gyttja is an organic soft soil from the “Zoliborz channel” located in Warsaw. These soils are used as a base construction in the foundation engineering. In practical geotechnical engineering, evaluation of stress history is based on the overconsolidation ratio. The overconsolidation ratio is one of the basic parameters for the geotechnical design of the structure. Determination of this parameter using for example dilatometer tests, is usually based on empirical formulas which were established in different countries. Therefore, regional geotechnical conditions could have substantially affected on the empirical relationships. The laboratory tests are used to determinate the preconsolidation pressure and then the overconsolidation ratio. The laboratory tests were made in the automatic oedometer and the in situ tests were carried out on the dilatometer test (DMT). The paper presents results of determination the overconsolidation ratio of eemian gyttja from the laboratory and in situ tests. The studies have shown that the values of the overconsolidation ratio determination from the laboratory tests are a little higher than determination from the in situ tests.

Impact of the moisture content in medium sands on CPTU test results

Abstract Soils occurring in the soil “active zone” are in contact with the surface and are directly influenced by external factors (mainly climatic changes) that cause variation in their parameters over time. Dynamic and uncontrolled changes of soil properties e.g. due to rainfall and evapotranspiration processes may affect field test results leading to the misinterpretation of the obtained data. This paper presents investigations on the influence of moisture content changes in sandy soils on CPTU results. For this purpose, a field ground model has been constructed and five CPTU tests with a different moisture content of soil were carried out. During the investigations, the tip resistance (qc), friction on sleeve (fs), and pore water pressure (u2) were measured. Moreover, a TDR probe was applied to determine the distribution of the moisture content in the studied soil columns. Differences between CPT results obtained in saturated and unsaturated soils have been shown. Furthermore, a simple equation to correct the tip resistance value due to the impact of the degree of saturation has been proposed.