Seismic Dilatometer Tests Research Articles

Evaluation of deformation and strength parameters of organic soils for the design of geotechnical structures

The evaluation of deformation and strength parameters of Holocene organic soils obtained from DMT dilatometer tests based on empirical relationships and ANN Artificial Neural Networks is presented. The evaluation of undrained shear strength τfu, deformation modulus E0.1% and initial shear modulus G0 of Eemian organic soils obtained from DMT dilatometer tests and SDMT seismic dilatometer tests is given, and then its comparison with the values obtained from triaxial tests for the design of underground structures supported by diaphragm walls of the stations of the underground line II in Warsaw, is shown.

Stiffness decay characteristics and disturbance effect evaluation of structured clay based on in-situ tests

The structure of the sedimentary clay influences its mechanical behavior in non-negligible ways. This paper proposes an effective approach for investigating the in-situ stiffness characteristics from shear modulus and strain decay curves (G–γ curves) based on self-boring pressuremeter and seismic dilatometer tests. To evaluate the excavation disturbance effects on the structured clay, the stiffness parameters from pre-bored pressuremeter tests are compared with the results of self-boring pressuremeter tests. The result indicates that the complete in-situ G–γ curves can be acquired by integrating the strain-dependent tangent shear modulus Gt from self-boring pressuremeter tests and the small-strain modulus G0 from seismic dilatometer tests. Simultaneous observations of the G–γ curves with hyperbolic shapes in semi-logarithmic coordinates at the same strain scale show the similarity of the stiffness decay mode of the soil at different depths. The increase in the measured values of Gt and G0 with depth can be attributed to the improved consolidation pressures and cemented strength in the structured clay. Additionally, the G/G0–γ curves measured by the in-situ tests generally agree well with the results predicted by the Stokoe model. The excavation disturbance weakens the stiffness of the structured clay, as evidenced by Gt from the pre-bored pressuremeter data being significantly smaller than that from self-boring pressuremeter tests at the same depth. Based on quantitative analysis, the disturbance degree computed from the measured results has a low sensitivity to the soil depth and a strong negative correlation with the strain level of the soil. This study provides an effective method for predicting the stiffness parameters of structured soil based on in-situ tests.

Geotechnical characterization of the estuarine deltaic deposits in the Guayaquil city through in situ and laboratory tests

According to previously available research and seismic microzonation studies a large area of the Guayaquil (Ecuador, South America) sits on estuarine deltaic deposits which consist of weak and highly compressible clays with diatoms. The nature of these fine-grained deposits may determine difficulties in a proper estimation of the soil properties. In this respect, the paper provides a detailed geotechnical and geophysical characterization of these soft clays, carried out in the estuarine complex of the Ecuadorean city. Borehole logs, standard penetration tests (SPT), piezocone tests (CPTu), a seismic dilatometer test (SDMT), a non-invasive geophysical survey, and laboratory tests were performed and then compared to analyze the static and dynamic geotechnical parameters of these deposits. The interpretation of the results highlighted the higher reliability of CPTu and SDMT rather than SPT and characterization lab testing to estimate soil shear strength, compressibility and stress history due to the soft nature of these clays, underlining also a certain sensitivity to the presence of the diatoms.

Determination of Relative Density and Degree of Saturation in Mineral Soils Based on In Situ Tests.

Based on the results of dynamic probing (DP), time-domain reflectometry (TDR/MUX/MPTS), resistivity cone penetration tests (RCPT), Marchetti dilatometer tests (DMT), and seismic dilatometer tests (SDMT), it is possible to develop a relationship to calculate the relative density (Dr) and degree of saturation (Sr) of selected sandy soils. Compiled databases from documented research points for selected sandy soils were used to construct and develop direct correlations between the measured pressures p0 and p1 from DMT and shear wave velocity (Vs) from SDMT, along with pore water pressures (u0) and atmospheric pressure (Pa). The results allowed us to make a preliminary prediction when evaluating the parameters. Further, they allowed limiting the use of an additional device, especially in the case of multilayer heavy preconsolidated subsoils. Moreover, soil physical and mechanical characteristics (temperature, humidity, pressure, swelling, salinity) measured from TDR/MUX/MPTS (laboratory/field-operated meter for simultaneous measurements of soil moisture, matric potential, temperature, and salinity—bulk electrical conductivity) were assessed. The main achievement of this paper is the original proposal of using a new nomogram chart to determine the relative density and degree of saturation based on DMT and SDMT tests.

APPLICATION OF SEISMIC DILATOMETER FOR CEMENTATION ANALYSIS IN RESIDUAL GNEISS SOIL

Residual soils have different properties and behavior from sedimentary soils. Aspects related to the processes of origin and formation directly impact these geotechnical particularities. One of the characteristic properties of this material is cementation. Cementation is an additional resistance that occurs in the solid skeleton due to weathering actions on these materials. In a residual soil profile, different cementation levels occur between the grains, these differences are due to different types of matrix rock, decomposition mechanisms involved in the process and anthropic actions. This article evaluated changes in the degree of cementation in residual soil horizons using the Marchetti Seismic Dilatometer (SDMT). The research was carried out in a residual gneiss soil in the State of Santa Catarina. The evaluation of the cementation degree was based on the relationships obtained with the Go (shear modulus with small strain) and other field geotechnical indices. The results show that the interpretation of the correlations from the results obtained by the SPT (Standardized Penetration Test), CPT (Cone Penetration Test) and SDMT tests allow the identification of layer boundaries with different degrees of cementation in residual gneiss soils. . In the present work, the limits between the saprolitic and the lateritic layers were identified and, finally, it was concluded that the studied residual soil presents a low level of cementation between the particles.

Combined P- and S-Wave Measurements by Seismic Dilatometer Test (SPDMT): A Case History in Bondeno (Emilia Romagna, Italy)

Abstract A new seismic dilatometer (SPDMT) has been developed to combine the measurements of the flat dilatometer (DMT) geotechnical parameters with both P- and S- waves velocities. This new SPDMT is composed of the traditional mechanical DMT and four sensors for measuring the body waves velocities placed above the DMT blade. This SPDMT device is presented here, and the test procedure and the interpretation of P- and S-wave measurements are discussed. Results of the application of this new instrument are reported in a test site located in Bondeno (Emilia Romagna, Italy). Here, challenging water table conditions offer the opportunity to evaluate the advantage of a combined measure of the two propagation velocities, together with DMT geotechnical parameters, with the same apparatus for the porosity evaluation and a more calibrated liquefaction assessment.

Maximum shear modulus evaluation based on continuous wavelet transform of bender element test

Maximum shear modulus (Gmax) is a crucial parameter in the prediction of ground deformation and performance of seismic design. Practically, the Gmax parameter could be obtained from specific laboratory test or seismic field test. Bender element (BE) test is nondestructive laboratory test, which is simple yet reliable method in determining Gmax of soil. This study focuses on application; processes and analysis of Gmax values obtained from BE laboratory test using continuous wavelet transform (CWT) method. The Gmax values were validated with results from field seismic dilatometer test (sDMT) conducted at the same site of soil sampling for BE laboratory test. BE laboratory tests were conducted on undisturbed Auckland residual clay at various effective confining pressures (ECP) under fully saturated condition. The Gmax values analysis between CWT and field sDMT data were based on the overburden pressures values that matches with ECP applied in the BE laboratory test. In summary, the comparison between CWT analysis of laboratory and field sDMT data indicated good consistency of Gmax values. Thus, confirmed the reliability of CWT method in estimating Gmax parameter from BE laboratory test.

Comparative analysis of liquefaction susceptibility assessment methods based on the investigation on a pilot site in the greater Lisbon area

In Portugal, particularly in the greater Lisbon area, there are widespread alluvial sandy deposits, which need to be carefully assessed in terms of liquefaction susceptibility and risk zonation. For this purpose, a pilot site has been set up, as part of the European H2020 LIQUEFACT project. An extensive database of geological and geotechnical reports was collected and a comprehensive site investigation campaign was carried out, including boreholes with standard penetration (SPT), piezocone penetrometer and seismic dilatometer tests as well as geophysical methods, complemented by undisturbed soil sampling for laboratory characterisation. The assessment of liquefaction susceptibility based on field tests was made using the simplified procedure, considering the factor of safety against liquefaction (FSliq), which relates the cyclic resistance ratio (CRR) with the cyclic stress ratio (CSR). While the computation of the CSR is relatively straightforward, the reliability of the CRR strongly depends on the adopted in situ testing technique. Alternative approaches to liquefaction assessment have been proposed, based on quantitative liquefaction damage indexes, namely the Liquefaction Potential Index (LPI) and Liquefaction Severity Number. In this paper, the geotechnical field data is integrated in these distinct approaches to liquefaction assessment. A comparative and in-depth analysis of the conventional approach is presented and the inclusion of specific information on soil type, as a means to overcome the observed differences, is discussed particularly for SPT and VS results. The combination of these criteria enabled to clearly identify the most critical layers, in terms of liquefaction potential and severity.

Stiffness Decay in Structured Soils by Seismic Dilatometer

The small-strain stiffness modulus G0 is not directly applicable to evaluate deformation in most practical engineering problems, and therefore, nonlinear soil behavior curves have been developed in terms of Young modulus E or shear modulus G. These curves were successfully obtained for sedimentary soils, while for residual soils, the available data from intertional community is still scarce. Residual soils are considered structured soils and often classified as problematic soils since they do not fit into the behavior of remolded or unstructured soils. In fact, the role of bonding and fabric affects both the strength and the stiffness of the soil. This article illustrates the use of the seismic dilatometer test (SDMT) for the determination of in situ stiffness decay curves with strain level (G-γ curves or similar) in a granitic residual soil of the Northeastern region of Portugal (Guarda), showing its adequacy to solve these kinds of problems. In situ and laboratory tests were performed on these granitic residual soils. The adopted approach relies on the ability of SDMT to provide a small-strain modulus G0 (from the shear wave velocity Vs) and a “working strain” modulus GDMT (derived from the constrained modulus MDMT in accordance with the theory of elasticity). Thus, in situ G-γ decay curves were tentatively constructed by fitting curves through these two points using a hyperbolic model. However, it was observed that the results obtained by the hyperbolic model for the cemented soils are not satisfactory. Based on the SDMT parameters, a logistic curve was derived for the reproduction of reference stiffness curves obtained from the triaxial test results.

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.

Evaluation of the Undrained Shear Strength in Preconsolidated Cohesive Soils Based on the Seismic Dilatometer Test

The undrained shear strength in cohesive soils can be evaluated based on measurements obtained from the standard dilatometer test (DMT) using single- and multi-factor empirical relationships. However, the empirical relationships presented in the literature may sometimes show relatively high values of the maximum relative error. The add-on seismic module to the seismic dilatometer test (SDMT) extends parameters measurable in a standard dilatometer test by the shear wave velocity Vs as an independent variable. Therefore, a method for evaluating the undrained shear strength in cohesive soils based on data obtained from the seismic dilatometer test is presented in this study. In the method proposed, the two-factor empirical relationship for evaluating the normalized undrained shear strength τfu/σ’v is used based on independent variables: The normalized difference between the corrected second pressure reading and the corrected first pressure reading (p1 − po)/σ’v and the normalized shear wave velocity Vs/100. The proposed two-factor empirical relationship provides a more reliable evaluation of the undrained shear strength in the tested Pleistocene and Pliocene clays in comparison to the empirical relationships presented in the literature, with a maximum relative error max RE at about ±20% and the mean relative error RE at about 8%.

A proposed method to determine in-situ shear modulus and shear strain decay curves in different structured soil

This paper illustrates the application of the self-boring pressuremeter test and the seismic dilatometer test to acquire the in-situ decay curves of stiffness with shear strain level (G-γ decay curves) of three types of structural soil, which are granite residual soil, structural soft soil and expansive soft rock. The proposed approach in combines the functions of SBPT and SDMT to provide the high standard of accuracy for the small-strain stiffness (from SDMT) and the major attenuation stage of stiffness (from SBPT). Using the proposed mathematical model can properly describe the tendency in typical in-situ G-γ decay curves based on the data of tests. To analyse the suitability of the proposed approach, the G-γ curve obtain from the resonant column test of granite residual soil is also employed to compare with the in-situ curves. The shear modulus G obtained from laboratory tests is found to be smaller and the stiffness attenuation rate is found to be faster than the curve of the in-situ test, which reflects the process of sampling, transporting and preparation of soil samples could cause unrecoverable damages in soil.

Monitoring Ground Improvement Using the Seismic Dilatometer in Christchurch, New Zealand

This article illustrates the use of the seismic dilatometer test (SDMT) in combination with the piezocone test (CPTu) to monitor the effects of ground improvement by different techniques at seven test sites in Christchurch, New Zealand. The results of SDMTs carried out in treated soils and in adjacent natural soils are compared in order to assess the effectiveness of different ground improvement techniques (Rammed Aggregate Piers, Low Mobility Grout, Stone Columns, Deep Soil Mixing) aimed at reducing the liquefaction susceptibility. Moreover, the article presents the variation of significant parameters obtained from parallel SDMT and CPTu soundings in treated versus natural soils. SDMT and CPTu results are also used in combination to estimate the overconsolidation ratio and the at-rest lateral earth pressure coefficient (K0) before and after the treatment. The effectiveness of the different ground improvement techniques is also evaluated in terms of the variation of the before and after integral liquefaction vulnerability indicators, such as the liquefaction potential index and the liquefaction severity number, which are calculated using different methods based on CPTu, the DMT horizontal stress index (KD), and the shear wave velocity (VS) for a design earthquake. The results confirm that the DMT, as well as the CPTu, is sensitive to changes in stress/density in sands and silty sands and is, therefore, well suited to detecting improvements in these soils, while VS provides less evident results.

Deeper Vs profile constraining the dispersion curve with the ellipticity curve: A case study in Lower Tagus Valley, Portugal

Shear wave velocity profile and bedrock depth are key parameters for seismic site response estimation and a reliable tool to evaluate liquefaction potential in soil deposits. They can be determined using in-situ geotechnical tests such as the seismic Cross-Hole (CH), seismic Cone Penetration Test (SCPT), seismic Dilatometer Test (SDMT), or through geophysical surface wave methods. The main advantages of surface wave methods are their non-invasive nature and the ability to characterize the shear wave velocity of the soil at a larger scale. However, the investigation depth in general is less than 20 m. Using the Rayleigh ellipticity curve to constrain the dispersion curve from active and/or passive measurements, deeper Vs-profile is obtained.In this study, the Vs profile of the soil at a site located over Lower Tagus alluvial Valley was obtained using different surface wave methods. For this purpose, ambient vibration measurements using a single three-component seismic station were made, to complement active and passive linear measurements. The Rayleigh wave ellipticity curve was computed from the single station recordings using the RayDec method and dispersion curves were estimated with the array recordings processed using f-k based methods: MASW, ReMi and conventional f-k method for non-linear array data. A joint inversion procedure was applied to the data and the results were compared with Vs profiles obtained from direct measurements with Cross-Hole and SDMT tests. The results show that considering the passive ellipticity curve in the joint inversion process with the dispersion curve, it is possible to obtain deeper and less scattered Vs profiles.

Seismic amplification in a fractured rock site. The case study of San Gregorio (L'Aquila, Italy)

The village of San Gregorio (SG), eight kilometres away from L'Aquila (central Italy), was severely damaged by the April 6, 2009 L'Aquila earthquake (MW 6.1). A coseismic fracture zone was mapped along SW-dipping fault segments crossing SG, which is situated at the base of a carbonate relief bounded by the Aterno river alluvial plain. An interdisciplinary approach was used to investigate the seismic response of the area based on geological-structural, geophysical and seismic analyses. We integrated our data with available information from the recent microzonation studies. SG is partly built on alluvial fan deposits constituted by cemented gravel, and partly on jointed carbonate bedrock. An extensive survey of noise measurements showed strong and polarized peaks in the horizontal-to-vertical spectral ratios (H/V), both on soft and rock sites in the 2–10 Hz frequency band. Further, we checked the stability with time of H/V ratios at three sites of SG. An analysis on local earthquakes confirmed the results of noise measurements. To understand the influence of rock mass jointing condition on site effects, we performed structural surveys on carbonate bedrock. We also evaluated the propagation velocities at rock sites using seismic active and seismic dilatometer test (SDMT) surveys. Our analysis showed low values of compressional (VP) and shear wave (VS) velocities of the outcropping rock, where we also observed strong H/V spectral peak and high-density rock fracturing.

In Situ Tests—Predicted vs. Observed Settlements: A Comparative Case Study

This paper aims to deal with the comparison of the estimated settlements derived by in situ tests with the observed settlements in site, in order to evaluate the accuracy of settlement prediction by in situ tests, in comparison not only with site observation by topographic means, but also with the values of settlements derived by numerical analysis by means of PLAXIS 2D and 3D. The site where are carried out the tests and periodically are observed the settlements since the beginning of construction process, is located in the Oil Product Terminal, at the industrial park of Porto Romano, Durres, Albania. The main purpose of this project was the ground improvement by using preloading method in order to prevent liquefaction process and settlements. The data used to conduct this study are taken by the site investigation done after inserting into the soil vertical drains made of columns of free—draining gravel (gravel pile drains) until 14 m depth and center-to-center spacing of 2 m, and wick drains (premanufactured) until 25 m depth and center-to-center spacing of 1.8 m. The observed settlements are periodically measured by topographic equipments. This paper will present the conclusions derived by settlement analyzes from in situ tests and site observations. constructions in soft and sensitive soils. One of these case studies is presented in this paper. The aim of this study is to evaluate the settlement by using the data obtained by a series of piezocone tests and seismic dilatometer tests (hereafter mentioned as CPT and DMT), including also the comparison of CPT and DMT—calculated vs. observed settlements, in order to evaluate the accuracy of settlement predictions based on these tests.

Characterisation of collapsing loess by seismic dilatometer

Structural collapse and sudden volume changes represent a major geotechnical issue, particularly in loess soils. There are different criteria for assessing collapse potential based on laboratory test results, which require the collection of undisturbed samples from test pits. This can be a complicated and costly procedure, often financially unjustified for smaller projects. This paper presents the results of seismic dilatometer tests (SDMT) performed at a single location in a loess soil in Belgrade, in addition to the results of single oedometer collapse tests performed on high quality samples from test pits.After comparing laboratory test results it was possible to determine that in samples collected from boreholes, dry unit weight is approximately 20% higher than in block samples taken from test pits, while moisture content is between 1 and 4% higher. Unit weight estimated from DMT is on average 15% higher than the unit weight obtained from block samples.The constrained modulus (MDMT) determined by DMT are highly compatible with oedometer modulus (Eoed) obtained from samples at natural moisture content. This paper presents two possible ways of identifying collapsing loess based on intermediate DMT parameters and the ratio of G0/MDMT. The tests results indicate that if the ratio between the material index (ID) and the horizontal stress index (KD) is greater than 5, the danger of collapse is imminent. Simultaneous observation of the changes of ID and KD with depth on a semi-log graph in the same scale is recommended. In this way the relative distance between them may be clearly noticed; the larger the distance becomes, the greater the risk of collapse. In the collapsing loess ratio G0/MDMT is found to be higher than 21 for KD less than 0.6, while in non-collapsing loess G0/MDMT is less than 21 for higher values of KD. In terms of DMT, loess is considered as underconsolidated soil, which is one of the most common “definitions” of loess.

Analysis of the liquefaction phenomena in the village of Vittorito (L’Aquila)

This paper describes a case-history of liquefaction occurred near the village of Vittorito after the April 6, 2009 L’Aquila earthquake (moment magnitude Mw = 6.3), approximately 45 km far from the epicentre. In the document, first, an estimation of the seismic motion in the area has been made. Thereafter, the performed geotechnical investigation is described, followed by the application of some fast assessment criteria for the occurrence of liquefaction, recently proposed by the new Italian Building Code. A careful assessment of all the parameters involved in conventional Seed and Idriss (1971) liquefaction analyses is considered. The cyclic resistance ratio CRR is evaluated by cone penetration tests CPT and by in situ seismic dilatometer tests SMDT; in the latter case CRR is evaluated by different empirical correlations with shear wave velocity Vs and horizontal stress index KD. Analytical data confirmed the observed occurrence of the liquefaction in Vittorito, even if the acceleration field in the area, produced by the L’Aquila earthquake, was very low.

Seismic Flat Dilatometer Tests in Connecticut Valley Varved Clay

Abstract Downhole shear wave velocity measurements have been incorporated within a “Marchetti” flat dilatometer by placing a velocity transducer in a connecting rod just above the blade. The hybrid of combining downhole seismic with flat dilatometer, termed the seismic dilatometer test (SDMT), has the superior advantages of determining both the routine estimates of soil properties and stratigraphic information, while also measuring the small-strain stiffness within a single sounding. The SDMT is rapid, simple, and cost effective, requiring essentially no more time than a conventional dilatometer sounding. Results of seismic dilatometer testing in clays at the National Geotechnical Experimental Test Site (NGES) in Amherst, Massachusetts are presented and compare favorably with results from companion series of seismic cone penetrometer tests.