Small-strain Stiffness

Fine-grained sedimentary deposits can bear an increased risk for building settlements due to their moderate stiffness and strength properties, as well as high groundwater tables. However, some buildings, e.g., situated on shallow foundations in Alpine basins, show only relatively small settlements because the formation of carbonate cement can create bridging bonds between the detrital soil particles, leading to increased stiffness. These weak bonds can be damaged through dynamic loads and high static loads, causing a weakening of the soil’s microstructure and resulting in large settlements in several cases. However, the environmental controls and mechanistic processes underlying the formation versus damaging of microstructure in fine-grained, postglacial sediments are, to date, poorly understood. In the present study, fine-grained sediments are artificially cemented by calcium carbonates (CaCO3) to investigate (i) the influence of a mild and sustainable cementation process on the st...

A series of cyclic triaxial tests illustrated the definite increase of the cyclic strength of silty sands with prestress. This effect is found to be similar to that measured by other researchers. Relationships giving the proportional increase of the cyclic strength in the free field with the overconsolidation ratio are proposed. Conclusions are drawn regarding the potential of using preloading to reduce the liquefaction danger in the free field.

The complex cyclic shear stress path experienced by the soil during an earthquake, which could also induce liquefaction phenomena, can be approximated in the laboratory only by using sophisticated testing apparatuses. Cyclic triaxial tests have been widely used, especially for coarse grained soils, as in this study. In the framework of the design for the seismic retrofitting of the ‘‘Ritiro viaduct’’ foundations along the A20 motorway connecting Messina with Palermo (Italy), a soil liquefaction study was also carried out. With this aim, a detailed geological and geotechnical characterization of the area was performed by in situ and laboratory tests, including seismic dilatometer Marchetti tests (SDMTs), the combined resonant column (RCT) and cyclic loading torsional shear tests (CLTSTs), and undrained cyclic loading triaxial tests (CLTxTs). In particular, the paper presents the results of cyclic triaxial tests carried out on isotropically consolidated specimens of a sandy soil. The ...

The Marchetti Dilatometer test is a non-destructive in situ test that can be used to determine the geotechnical properties of soils. This paper presents the results of a study that investigated the correlations between the parameters obtained from the Marchetti Dilatometer test and geomechanical parameters for soft soils, mainly organic soils, obtained in the laboratory. The study was conducted in the El Garrochal sector in Southern Quito, Ecuador. The results of the study showed that there are significant correlations between the Marchetti Dilatometer test and the undrained shear strength, modulus of elasticity, and density of soil. The equations that were developed in this study can be used to estimate these geomechanical parameters from the results of the Marchetti Dilatometer test for the South Quito sector, which are valuable for geotechnical engineers to design structures in these types of soils. The equations that were developed in this study can be used to improve the accura...

ABSTRACT: Flat dilatometer tests were carried out at three relatively well-studied tropical research sites in the state of São Paulo, Brazil. Test results are presented and interpreted according to the traditional approach for site characterization of conventional soils. The results were compared to laboratory and others in situ tests. Soil description in terms of grain size distribution had to be confirmed with soil sampling. Correlations to estimate geotechnical parameters have to consider soil genesis. In this manner, some adjustment is necessary, especially for the soils with higher clay content. In tropical soils this approach appears to be an interesting way to achieve all requirements for an appropriate site characterization based on DMT testing.

The purpose of this paper is to present geotechnical parameters of the variegated soils from the São Paulo Formation, aiming in particular to establish correlations between stress history parameters, earth pressure coefficients at rest, deformability modules and resistance obtained through piezocone and dilatometer tests. The performance of in situ tests has, as the major advantage over laboratory tests for obtaining soil parameters of the project site, minimization of sample disturbance effects. Using data from geotechnical investigation carried out during the basic design of the Green Line expansion for the Metrô – SP it was possible to obtain preconsolidation pressure (σ’p), over consolidation ratio (OCR), earth pressure coefficients at rest (K0), Young’s module (Ei), initial shear module (G0), constrained module (M) and undrained shear strength (su) for the variegated soils of the São Paulo Formation. These soils are characterized by interlayered levels of clays and sands, const...

The Marchetti Dilatometer test is a non-destructive in situ test that can be used to determine the geotechnical properties of soils. This paper presents the results of a study that investigated the correlations between the parameters obtained from the Marchetti Dilatometer test and geomechanical parameters for soft soils, mainly organic soils, obtained in the laboratory. The study was conducted in the El Garrochal sector in Southern Quito, Ecuador. The results of the study showed that there are significant correlations between the Marchetti Dilatometer test and the undrained shear strength, modulus of elasticity, and density of soil. The equations that were developed in this study can be used to estimate these geomechanical parameters from the results of the Marchetti Dilatometer test for the South Quito sector, which are valuable for geotechnical engineers to design structures in these types of soils. The equations that were developed in this study can be used to improve the accura...

Soil stiffness constitutive model parameters are required when investigating and/or modeling stress-related deformations in geotechnical problems. The seismic dilatometer test (SDMT) can be used to determine various stiffness related parameters. This paper discusses utilizing SDMT to determine the hardening plasticity parameters for the tangent modulus from primary oedometer loading (Eoed), secant modulus in drained triaxial test (E50) , and unloading/reloading modulus (Eur), along with the nonlinear small strain stiffness input parameters for the initial reference shear modulus (G0) at very small strains and shear strain (γ0.7) at which Gs=0.722G0. The SDMT also provides evaluations of the soil strength and stress history for input into numerical simulations.

This paper illustrates the procedure for obtaining measurements of the shear wave velocity Vs by seismic dilatometer (SDMT) in backfilled boreholes in non-penetrable soils. The possibility of such measurement descends from the fact that the path of the shear wave from the surface to the upper and lower receiver includes a short path in the backfill of very similar length for both receivers. The SDMT equipment/test procedure and the borehole backfilling technique are briefly described. The validation of the method by comparison of parallel profiles of Vs obtained in the "virgin" soil and in a backfilled borehole is presented. Vs profiles obtained by SDMT in backfilled boreholes at two test sites in central Italy, Sulmona (coarse gravel) and L'Aquila (calcareous breccia), are compared to Vs profiles obtained by the traditional Down-Hole technique and related to the stratigraphic profiles of the subsoil.

An extensive geological, geotechnical and geophysical investigation was undertaken for the seismic microzonation of Avezzano, the main town of Fucino plain (L'Aquila province, Italy). Here, during the 1915 Fucino earthquake evidences of liquefaction were detected. The present study focuses on the lique-faction hazard assessment based on in-situ tests like piezocone (CPTu), dynamic penetration (standard SPT and super heavy DPSH tests), and seismic dilatomer SDMT tests. Results at the test site of Pozzone area have been reported and discussed hereafter. Preliminary results of liquefaction analyses carried out using simplified methods are illustrated, compared and discussed throughout the paper. According to these first outcomes, the SDMT and CPTu investigation methods show similar values of liquefaction susceptibility.

The Sarapui II research test site is a soft clay deposit located in a swampy area on the left bank of the Sarapui river, near the city of Rio de Janeiro in Brazil. The test site is very well documented with both in situ and laboratory test data. DMT measurements were performed with traditional pneumatic equipment, providing acceptable single pressure readings p0 and p1, but unacceptable scatter for Δp = p1 p0 and for all the geotechnical parameters deriving from this difference. In September 2018 the tests were repeated using the Medusa DMT equipment, a new device able to hydraulically operate the standard dilatometer blade at depth. The pressure is generated and measured in the probe at depth, eliminating any pressure equalization problem at the opposite ends of the pneumatic cable. The automated membrane inflation and the incompressibility of the pressurizing fluid enables the Medusa to enforce the standard rate of membrane inflation with high precision and repeatability. The resu...

To make accurate settlement predictions, the engineer must measure the soil’s stiffness. Dilatometer tests statically deform the soil at intermediate strain levels and have excellent correlations with the constrained deformation modulus of the soil. Standard penetration tests and cone penetration tests that engineers sometimes use do not have good correlations with deformation modulus because they are penetration tests that strain the soil to failure. One hundred and twenty nine case studies show buildings that were redesigned with shallow spread footings based on the dilatometer test data saved $25,053,000 than the original overly conservative design based on other less accurate tests.

This paper illustrates the procedure for obtaining measurements of the shear wave velocity VS by seismic dilatometer (SDMT) in backfilled boreholes in non-penetrable soils. The possibility of such measurement descends from the fact that the path of the shear wave from the surface to the upper and lower receiver includes a short path in the backfill of very similar length for both receivers. The SDMT equipment/test procedure and the borehole backfilling technique are briefly described. The validation of the method by comparison of parallel profiles of VS obtained in the "virgin" soil and in a backfilled borehole is presented. VS profiles obtained by SDMT in backfilled boreholes at two test sites in central Italy, Sulmona (coarse gravel) and L'Aquila (calcareous breccia), are compared to VS profiles obtained by the traditional Down-Hole technique and related to the stratigraphic profiles of the subsoil.

This paper illustrates the use of the seismic dilatometer (SDMT) to assess the decay of in-situ stiffness with strain level in different soil types. The approach adopted in this study relies on the ability of the SDMT to provide routinely at each test depth both a small strain stiffness (G0 from VS) and a working strain stiffness (constrained modulus MDMT derived from the usual DMT interpretation). At various test sites, working strainDMTmoduli are compared with reference stiffness decay curves back-figured from (i) the behavior observed under a full-scale test embankment (at Treporti) or footings (in Texas), (ii) from laboratory tests (at L’Aquila, Fucino plain and Po plain) and (iii) various combinations of insitu and laboratory testing techniques (Western Australia). Typical ranges of the shear strains �DMT associated with working strain DMT moduli are inferred to assist construction of stiffness - strain decay curves for different soil types.

An extensive geological, geotechnical and geophysical investigation was undertaken for the seismic microzonation of Avezzano, the main town of Fucino plain (L'Aquila province, Italy). Here, during the 1915 Fucino earthquake evidences of liquefaction were detected. The present study focuses on the lique-faction hazard assessment based on in-situ tests like piezocone (CPTu), dynamic penetration (standard SPT and super heavy DPSH tests), and seismic dilatomer SDMT tests. Results at the test site of Pozzone area have been reported and discussed hereafter. Preliminary results of liquefaction analyses carried out using simplified methods are illustrated, compared and discussed throughout the paper. According to these first outcomes, the SDMT and CPTu investigation methods show similar values of liquefaction susceptibility.

This study focuses on the back analysis of a geotechnical laboratory test with nonlinear finite element modeling using the Ramberg-Osgood material model. This model has been used by several authors recently for nonlinear ground response analysis and it has been implemented by Midas into their commercial finite element code Midas GTS NX 2014. The verification of the model for 1D nonlinear site response analysis can be found in the documentation of the software package. In this study, Torsional Simple Shear tests were modeled and a comprehensive study was performed to provide verification of the material model for static torsional loading and axisymmetric conditions.

The work described in the paper is an experimental investigation of the effects of anisotropic stress states and histories on the small-strain shear stiffness of reconstituted clays as measured with bender element tests. A brief review is made of previous work dealing with the dependence of small-strain shear modulus on stress state and history in isotropic conditions of confinement, and the rational link that exists between void ratio, e, effective stress, σ′, and overconsolidation ratio, OCR, is considered. Under isotropic stress conditions, only two out of the three variables e, σ′ and OCR are required to describe the dependence of the small-strain stiffness of a clay on current state and history. The same approach proved useful in the analysis of the data from tests with anisotropic stress conditions. The values of the small-strain shear modulus of reconstituted samples compressed along stress paths with constant triaxial effective stress ratios were higher than those measured o...

Natural cementation affects the properties of soils, the interpretation of in situ and laboratory test results, and the selection of criteria for geotechnical design. In this paper, published experimental studies are reviewed, a microscale analysis is presented of the effect of cementation on small-strain stiffness for distinct stress-cementation histories, and the effect of cementation on small-strain velocity and damping is experimentally studied. Observations include the prevailing effects of cementation over effective stress, the coexistence of frictional and viscous losses, and the effects of decementation when the medium is unloaded from the level of confinement prevailing during cementation.Key words: wave velocity, seismic response, stiffness, damping, sampling effects, loading history.

ABSTRACT: In Slovenia first DMT tests were performed in the beginning of 2003. Slovenia is a small country, covering only 20 500 km, but with very complex geology. The assessment of ground properties is therefore a demanding task and methods that provide profiles of material properties rather than individual material data are very important. A CPT test with pore pressure measurements has been extensively used in the past. Ménard pressuremeter tests have also been used to complement CPT. Marchetti flat dilatometer tests have proven to be a fast and reliable tool when material properties are required for the assessment of stability and settlements for different geotechnical structures. The paper presents some first comparisons of DMT results with other soil investigation techniques, including laboratory and in situ tests, such as vane test, CPT and Ménard pressuremeter. Measured and predicted settlements are compared at three locations. During the first three years of the use of DMT t...