Dissipation tests with the BAT probe at the Sarapuí Ⅱ soft clay

Dissipation tests are carried out with two main purposes: the estimation of the horizontal coefficient of consolidation, ch, and the evaluation of the equilibrium pore pressure. Regarding the first case, even in soft clays the duration of the test doesn´t need to be more than 40 minutes, in most situations. However, in the latter case a long time is needed to reach equilibrium, even when probes with small diameters are used. The present paper presents results of long-term dissipation tests performed in a soft clay layer, aiming at the decision of executing or not an underpinning of shallow foundations of a damaged warehouse which suffered significant settlements.

Dissipation tests are carried out with two main purposes: the estimation of the horizontal coefficient of consolidation, ch, and the evaluation of the equilibrium pore pressure. Regarding the first case, even in soft clays the duration of the test doesn´t need to be more than 40 minutes, in most situations. However, in the latter case a long time is needed to reach equilibrium, even when probes with small diameters are used. The present paper presents results of long-term dissipation tests performed in a soft clay layer, aiming at the decision of executing or not an underpinning of shallow foundations of a damaged warehouse which suffered significant settlements.

Interpretation of horizontal permeability from piezocone dissipation tests in soft clays

In situ dissipation tests provide a means of evaluating the in situ coefficient of horizontal consolidation and horizontal hydraulic conductivity of soft clays. Dissipation tests by means of piezocone (CPTU), dilatometer (DMT), self-boring pressuremeter (SBPT) and BAT permeameter (BAT) were utilized in the characterization of the coefficient of horizontal consolidation and horizontal hydraulic conductivity of Singapore marine clay at Changi in a land reclamation project. Dissipation tests were carried out prior to reclamation as well as after ground improvement with vertical drains to compare the changes in the coefficient of horizontal consolidation and horizontal hydraulic conductivity prior to and after ground improvement. Tests were carried out in a vertical drain area as well as in an adjacent untreated control area after 23 months of surcharge loading, for comparison purposes. The purpose of this research is to determine the horizontal consolidation parameters of Singapore marine clay prior to reclamation as well as after 23 months of surcharge loading with and without vertical drains by means of in situ dissipation tests.

A geotechnical investigation comprised 13 CPTu and 23 dissipation testing were performed on a site in East Kalimantan due to landslide triggered by 15 to 30m thick soft clay underlying 75m high overburden embankment. The investigation covers an area of about 250m x 275m wide on the area next to the toe of the embankment. From geological map, the site situated at borders of Balikpapan Formation (Tmbp) and Kampung Baru Formation (Tpkb) with Alluvium (Qa) formation from Heliosen period nearby. Measurement from penetration showed high pore-water pressure higher than the hydrostatic pressure. Result from dissipation testing showed that the soft clay is still consolidating with residual excess pore pressure (uf) still exist. Rahardjo (2016) Method was developed using CPTu data as its basis especially soft clay data to determine overconsolidation ratio (OCR). However, it can also be used to determine the degree of consolidation. The method uses Pore Pressure Ratio (Bq) value, excess pore pressure divided by net cone resistance – Bq = Δu/(qt – σv0), which was obtained when performing CPTu test. The formula proposed was 1/(1.2Bq+0.1). The method stated that the value of Bq=0.75 equals to OCR=1 which is showing a normally consolidated clay. Bq value higher than 0.75 will show a degree of consolidation of a consolidating soil and for Bq value lower than 0.75 will show an OCR value of overconsolidated soil. Applying Rahardjo (2016) Method to the dissipation data performed showed an agreement on soft clay where the soil is still consolidating. However, when applied to over consolidated soil near surface this method will show a greater OCR value.

During a pause in cone penetration in fine-grained soils, pore-water pressure dissipation tests are performed to evaluate the coefficient of consolidation. For standard piezocones with shoulder filter elements, soft clays and silts show a monotonically decreasing response with time; however, dissipation tests performed in heavily overconsolidated silts and clays show dilatory behavior, with the pore-pressure behavior increasing from the initial measured value to a maximum, and then decreasing to hydrostatic values. This paper presents a theoretical framework which combines cavity-expansion theory and critical-state soil mechanics with an analytical solution to the radial consolidation equation. The method is able to describe the pore-pressure response curve for dissipation tests performed in soils which demonstrate either monotonically decreasing or dilatory pore-pressure behavior.Key words: cavity expansion, consolidation, piezocone, pore pressure.

A 42-inch pipeline traverses a predominantly flat right-of-way (ROW), running from south to north in East Kalimantan. Adjacent to the ROW, a coal mine concession was located on the western side, while the Mahakam River lies a further 3 km to the east. A mining waste dump has been constructed since 2010, situated in an area underlain by soft alluvium soil (Qa). The waste was stacked, reaching heights of up to 75 meters, with its toe approximately 200 m from the edge of the ROW. In 2016, a failure occurred in the ROW, causing the 42-inch pipeline to shift a maximum of 6.8 m horizontally, and rise by 2.0 m within a 300 m span. A geotechnical investigation was then conducted, consisting of 7 CPTu with dissipation testing. The CPTu results indicated high pore pressure, with a layer of soft clay ranging from 15 to 32 m thickness found in the ROW area. A hypothesis was formulated suggesting that the soft clay was not fully consolidated. Hence, the failure of the pipeline was possibly caused by the migration of excess pore water pressure accumulated during the construction of the waste dump. Results of the investigation indicated that the permeability coefficient was 2.5 times greater in the horizontal direction compared to the vertical ones (kh/kv = 2.5), allowing the pore water pressure to migrate more easily in the horizontal direction. This study aims to elucidate how the migration of excess pore water pressure in the horizontal direction influences ground stability. The analysis was conducted using finite element software MIDAS GTS NX, with the kh/kv varying from 2.5 to 100 times to explore excess pore pressure movement behaviors. The results of this study confirm that excess pore pressure migration can occur horizontally if the horizontal permeability coefficient is larger than its vertical counterpart. Thus, this study highlights that the greater the permeability coefficient and the larger the ratio, the further the excess pore pressure travels. Moreover, the horizontal displacement increases with the permeability coefficient ratio.

This paper presents a discussion about vertical (cv) and horizontal (ch) coefficients of consolidation of Guaratiba’s very soft clay, located at the lowlands of the West Zone of Rio de Janeiro city, Brazil. Due to the thickness of the deposit, high compressibility of the clay, and low undrained strength, the settlement stabilization, even with vertical drains, are known to take of about 30 months to occur at these lowlands. Thus it is essential to know cv, ch and ch/cv relationship in order to predict when settlement stabilization will occur. The variability of cv and ch values is very high, probably due to the wide range of organic matter, sand lenses and the sand content throughout the soft soil deposit. The aim of the paper is to compare these values of coefficients of consolidation obtained from the dissipation tests and from the consolidation tests and to discuss an approach to determine them for design considering their variability.

This paper presents a discussion about vertical (cv) and horizontal (ch) coefficients of consolidation of Guaratiba's very soft clay, located at the lowlands of the West Zone of Rio de Janeiro city, Brazil. Due to the thickness of the deposit, high compressibility of the clay, and low undrained strength, the settlement stabilization, even with vertical drains, are known to take of about 30 months to occur at these lowlands. Thus it is essential to know cv, ch and ch/cv relationship in order to predict when settlement stabilization will occur. The variability of cv and ch values is very high, probably due to the wide range of organic matter, sand lenses and the sand content throughout the soft soil deposit. The aim of the paper is to compare these values of coefficients of consolidation obtained from the dissipation tests and from the consolidation tests and to discuss an approach to determine them for design considering their variability.

This paper describes the results of piezocone testing that was carried out in underconsolidated soft marine clay in Osaka Bay. The obtained profiles of the tip resistance and the pore-water pressure were quite different from those for clay strata of normally consolidated state. It was apparent that a different approach is needed to interpret the test results for underconsolidated clay. The dissipation tests with the piezocone were performed at different elevations and indicated the excess pore-water pressures remaining in the stratum.The depth profile of excess pore pressure of underconsolidated clay is of special importance to the understanding of the degree of consolidation of the stratum. An effort was made in this paper to assess the excess pore pressures remaining in the clay based on the piezocone data obtained during penetration. An examination was made of available piezocone data of similar marine clays, of both normally consolidated and underconsolidated states. Based on this, a method was proposed for predicting the profile of pore-water pressure in underconsolidated clay using the piezocone data obtained during penetration. Key words: piezocone, field test, underconsolidated clay, excess pore-water pressure, interpretation.

The piezoball, a ball penetrometer featuring pore pressure measurements, is a relatively new device that is potentially superior to the more commonly used piezocone for profiling fine-grained soils. This is due to lower uncertainty in how to derive soil strength from the net penetration resistance and the option of measuring consolidation characteristics during pauses in the penetration, potentially more quickly than in a piezocone test. This paper presents results from a series of piezoball tests undertaken at a soft clay test site using a piezoball that measures pore pressure concurrently at the ball equator, tip and half-way between the tip and equator, the so-called mid-face position. Analysis of the test data provides strong arguments for measuring pore pressure at both the equator and mid-face positions. The coefficient of consolidation derived from piezoball dissipation data using recently developed numerical solutions is shown to be highly comparable to that deduced from a piezocone dissipation test. This paper shows that the penetration resistance varies significantly with the rate of penetration due to either viscous rate effects or increasing degrees of partial consolidation during penetration, both of which influence the estimation of undrained shear strength and hamper interpretation of dissipation data. Guidance on assessing the drainage response during a piezoball penetration test is provided. Finally, dissipation test data presented in the paper are added to a database formed from centrifuge and field tests that is used to form a new empirical method for estimating the coefficient of consolidation.

The present research concerns a comparative analysis of the possible methods for estimating soft silty clay permeability to be used in the analysis of consolidation. For this purpose the consolidation response of a thick and homogeneous, instrumented soft silty clay deposit, on which an embankment was constructed, is back-analyzed using the finite-element method. To model the consolidation process, permeability data are carefully determined both from laboratory and in situ piezocone tests. One-dimensional and triaxial permeability test data are compared with the results of piezocone dissipation tests, the latter interpreted using four different solutions. The effects of anisotropy on permeability characteristics influencing the consolidation rate are also discussed.Key words: consolidation, embankment, finite-element analyses, permeability, piezocone, soft silty clay.

The test sites analyzed here consist of clay deposits located in the Jacarepaguá Lowlands in Rio de Janeiro, characterized by high plasticity, high compressibility and low undrained shear strength. The deposits are made up of lightly overconsolidated aged clays, montmorillonite being the predominant clay mineral. Soft clay deposits are usually superficial, with thicknesses generally varying between 6 m and 17 m and geologically recent and originated from marine regressions and transgressions, that occurred between 6000 and 3500 years ago. The objective of this study is to analyze a large database of undrained shear strength measurements obtained by 461 vane tests performed at 15 different sites. In general, most of the data correspond to very soft clays, with undrained shear strength values lower than 25 kPa. The undrained shear strength measurements are correlated with plasticity index and with maximum excess pore pressure, measured with piezocone tests. The method for estimating the undrained shear strength su(DT) of soil from the excess pore pressure generated during piezocone dissipation tests proposed by Mantaras et al. (2015) was validated against the vane test database.

Determination of Thermal Conductivity of Soil Using Standard Cone Penetration Test

The Nerang Broadbeach Roadway (NBR) embankment in Australia is founded on soft clay deposits. The embankment sections were preloaded and surcharged-preloaded to limit the post-construction deformation and to avoid stability failure. In this paper, we discuss the NBR embankment’s geology, geotechnical properties of the subsurface, and long-term field monitoring data from settlement plates and piezometers. We demonstrate a comparison of cone penetration test (CPT) and piezo cone dissipation test (CPT-u) interpreted geotechnical properties and the NBR embankment’s foundation stratification with laboratory and field measured data. We also developed two elasto-viscoplastic (EVP) models for long-term performance prediction of the NBR embankment. In this regard, we considered both the associated and the non-associated flow rule in the EVP model formulation to assess the flow rule effect of soft clay. We also compared EVP model predictions with the Modified Cam Clay (MCC) model to evaluate the effect of viscous behavior of natural Estuarine clay. Both EVP models require six parameters, and five of them are similar to the MCC model. We used the secondary compression index of clay in the EVP model formulations to include the viscous response of clay. We obtained numerical models’ parameters from laboratory tests and interpretation of CPT and CPTu data. We observed that the EVP models predicted well compared with the MCC model because of the inclusion of soft clay’s viscosity in the EVP models. Moreover, the flow rule effect in the embankment’s performance predictions was noticeable. The non-associated flow rule EVP model predicted the field monitoring settlement and pore pressure better compared to the MCC model and the associated flow EVP model.