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Characterisation of highly fractured and weathered rock masses within the young Tuang Formation in Sarawak, Malaysia is challenging, mainly due to the difficulties in extracting intact samples for conventional rock testing. Pressuremeter test was used as a viable alternative since it is performed in-situ, hence eliminating the need for sample extraction. A methodology was developed to interpret pressuremeter test results in highly fractured and weathered phyllite using an analytical approach, from which useful strength and stiffness parameters can be obtained. The interpretation method was based on the fundamental theory of cylindrical cavity expansion, which was originally established for soils. The results of the interpretation were in terms of commonly known Mohr–Coulomb strength parameters, which were subsequently used for assessment of frictional pipe jacking forces through back-analysis method. The results of the back-analysis showed the reliability of the developed methodology in analysing pressuremeter test results within highly fractured and weathered phyllite. Highlights In-situ pressuremeter testing was proposed for strength characterisation of weathered geology. Equivalent Mohr-Coulomb strength parameters were developed from pressuremeter testing through cavity expansion theory. Jacking forces from two pipe jacking drives were back analysed, corroborating that the drives were well-lubricated. Application of the Mohr-Coulomb parameters validated the use of in-situ pressuremeter testing for pipe jacking.

Economical geotechnical design requires proper sub-soil characterization by means of its consistency, compressibility and strength. In this respect, conventional borehole (BH) accompanied by standard penetration test (SPT) and laboratory tests is commonly conducted in the geotechnical investigation. Pressuremeter test (PMT) may be used to characterize the sub-soil profile by two parameters, i.e., limit pressure (PL) and pressuremeter modulus (EPMT). It is necessary to predict a standard range of these parameters of the sub-soil formation. In the present study, correlation between PL, EPMT with standard penetration value (SPT N) and EPMT/PL with the liquidity index (LI) for the cohesive (silty clay/clayey silt) sub-soil of Kolkata, India, are proposed. Further, a reference range of PL, EPMT and EPMT/PL is predicted for the same type of soil. Forty-eight numbers of PMT tests are carried out adjacent to the conventional boreholes, at three different sites, located in and around Kolkata city. The comparison of PL and EPMT with SPT N and EPMT/PL with the liquidity index (LI) is made for each site. Finally, a typical range of PL and EPMT for different SPT N values along with the range of EPMT/PL for different value of LI is established.

Landslides frequently occur at expansive soil slopes with characteristics of gradualness and chronicity that are related to the time-effect deformation, so it is crucial to study the creep behavior of expansive soils. Menard pressuremeter was used to conduct short-term tests and long-term creep tests on expansive soils at Nanyang, China, in order to analyze the in-situ behavior of expansive soils. The results of short-term tests show that the initial pressure, yield pressure, and limit pressure all increase with the increase of testing depth. The results of long-term creep tests show that: (1) Under low applied pressure, only instantaneous deformation and decay creep occur. However, when the pressure level reaches a certain value, the soil fails owing to excessive deformation within a few minutes, and different from the results of triaxial loading creep tests, there is no apparent accelerated deformation stage before the failure. (2) The expansive soil has nonlinear creep characteristics, and the boundary pressure of the linear and nonlinear characteristics is around the yield pressure. Besides, a nonlinear creep model for the pressuremeter test is proposed, which can well describe the in-situ creep behavior of expansive soils. This model can also give the critical pressure for the failure of expansive soils, which is between yield pressure and limit pressure. Hence, it is advised to monitor the pressure to be lower than the yield pressure, and to monitor the deformation of expansive soil slope in practical engineering projects to avoid disasters caused by excessive deformation.

The pressuremeter test (PMT) and plate load test (PLT) are principal in-situ experiments for measuring soil stiffness and deformation parameters. Although the PLT can be costly and complicated at great depths the PMT can be easily done in a borehole. Empirical equations linking the parameters from these tests can be useful for cross-checking the parameters obtained by the two methods and can reduce costs. In the present study, PMTs and PLTs were carried out on fine-grained soil from two sites in Iran. The pressuremeter modulus ( E PMT ) and limit pressure ( P L ) from the PMT and plate load modulus ( E PLT ), subgrade reaction modulus ( K ) and reload modulus ( E r ) from the PLT were determined and the relationships between them were investigated. A reliable and significant statistical model for these empirical equations has been was proposed. It was found that the average E PMT was about 25% higher than that of the E PLT and an exponential relationship could be determined linking the parameters at each site. A logarithmic relationship has been proposed between E r and E PLT . The mean absolute percentage error (MAPE) for calculation of the E PLT , K and E r for both sites was less than 15.14, indicating that the proposed equations estimated their values with good accuracy. Comparison of data from PLTs and PMTs in another area recorded a MAPE of less than 13.08.

Understanding the elastic stiffness evolution of Opalinus Clay is necessary for predicting ground deformation during the construction and operation of radioactive waste repositories. The elastic stiffness is stress dependent, and it degrades when a deviatoric stress/strain threshold is exceeded. A series of multi-staged triaxial tests is used to examine the elastic stiffness evolution of the Opalinus Clay at pre- and post-peak stages. With eight material parameters, a phenomenon-based constitutive model is proposed to account for stress-dependent elastic stiffness, damage, and plasticity in this rock type. The model is further implemented in a finite element (FE) code to predict borehole response during drilling unloading and pressuremeter testing using three proposed stress-dependent stiffness functions, respectively, in the minimum principal stress, the mean stress, and the full stress tensor. The use of the latter function predicts stress-induced anisotropy and explains the nonlinear variations of the elastic stiffness observed in both laboratory and in-situ tests. The FE analysis using the model parameters calibrated from the triaxial tests in this study, however, does not predict the unloading-induced damage in the borehole nearfield as indicated by the borehole ultrasonic survey. Possible reasons are provided concerning the representativeness of the laboratory data and the simplified borehole model for in-situ conditions. The impact of the borehole damage on the pressuremeter measurement is studied using the modified damage and failure parameters. The results show that the measured pressuremeter shear modulus is overall reduced and cannot be fully recovered under pressuremeter loading. Despite the limitation of reproducing the realistic damage behavior of Opalinus Clay using a continuum approach, this study effectively quantifies laboratory and in-situ measurements under a simple constitutive framework.HighlightsAn effective constitutive model is developed to assess the elastic stiffness evolution of Opalinus Clay in a multi-stage triaxial test.The model is implemented in a finite element code to capture the nonlinearity of borehole response in Opalinus Clay during pressuremeter testing.The unloading-induced borehole damage can potentially affect the interpretation of the modulus measured in a pressuremeter test.

Pressuremeter modulus ( E M ) and limit pressure ( P L ) are used for the calculation of the settlement and bearing capacity of foundation respectively. As the determination of these parameters from pressuremeter test ( PMT ) is relatively time-consuming and expensive, various empirical correlations have been proposed to correlate the E M and P L to other soil parameters. For the existing equations are incapable of estimating these PMT parameters well, in present research group method of data handling type neural network is used to estimate the E M and P L of clayey soils. The E M and P L were modeled as a function of three variables including the moisture content ( ω ), plasticity index and corrected SPT blow counts ( N 60 ). A database containing 51 data sets have been used for training and testing of the models. The performances of proposed models are compared with those of existing empirical equations. The results demonstrate that appreciable improvement with respect to the other correlations has been achieved. At the end, sensitivity analysis of the obtained models has been performed to study the influence of input parameters on model outputs and shows that the N 60 is the most influential parameter on the PMT parameters.

The main purpose of this paper is to obtain the rock mass rating (RMR) from different methods considering either the elastic modulus of intact rock specimens (Ei) and the modulus of deformation of andesitic rock mass (EM) or only the value of the in situ modulus of deformation, and to compare these values. This paper also presents comparisons between the values of deformation modulus obtained from pressuremeter tests in andesitic rock mass and the values of elastic modulus of intact rock core specimens retrieved from the same boreholes and depths at which pressuremeter tests have been carried out. The pressuremeter tests were conducted on weathered and fractured andesites observed along the İzmir subway route. Correlations between in situ moduli of deformation gathered from 32 pressuremeter test points and calculated RMR values for the andesites at the railway elevation of the İzmir subway were obtained as follows: EMPT = 0.0237 × e (0.0975 × RMR), R2 = 0.848 and RMR = 38.043 × EMPT(0.3291), R2 = 0.77. Finally, the results of comparisons between the modulus of deformation obtained from pressuremeter tests and the geomechanical quality of the rock mass, discontinuity effect, and the basic intact rock properties such as uniaxial compressive strength (UCS) and elastic modulus (Ei) have been discussed. In addition, engineering geological conditions of the andesitic rock masses located at the railway elevation of the İzmir subway were determined in detail.

The paper presents a numerical analysis of pressuremeter test in unsaturated cohesive soils. In practice, pressuremeter is commonly expanded up to 10–15% cavity strains. At these strains, limit pressure is not usually reached, and its value is estimated by extrapolation. Accordingly, authors suggest using cavity pressure at 10% strain ( P 10 ) for the interpretation of pressuremeter test rather than limit pressure. At this strain, it is also assured that plastic strain occurs around the cavity, which is crucial for the interpretations. In unsaturated soils, the moisture at which a soil is tested has a noticeable influence on the pressuremeter cavity pressure, and consequently, on the magnitude of P 10 . In this paper, unsaturated soil behaviour has been captured by Barcelona basic model (BBM), and the influence of each BBM parameter on the P 10 value is explored. Next, relative weight analysis technique is performed to investigate the relative importance of BBM parameters in prediction of P 10 . Artificial intelligence technique of genetic programming is used to develop a relationship to predict the P 10 value in unsaturated soils from BBM parameters. Finally, the application of the proposed equation is shown through illustrative examples.

Higher complexity of modern constitutive models often results in an increase of number of input parameters and time requirements for their calibration. Optimization methods provide a possible solution for this problem. A program application based on the metaheuristic optimization method Particle swarm optimization (PSO) is presented in the paper. The application consists of two parts: a subroutine with the PSO algorithm and a subroutine involving a finite element (FE) model of an analyzed construction. The subroutine with PSO governs input parameters modifications and evaluation of the objective function. Modified values of input parameters are then used in the FE model subroutine for calculation. Different alternatives of the PSO method are reviewed and tested in the first part of the paper. In the second part, a synthetic numerical experiment of pressuremeter test is used for automatically driven determination of input parameters for two constitutive models: Mohr - Coulomb, Hardening soil. The procedure is able to perform fully automatic determination of input parameters values. However, when only single test is used, several combinations of input parameters might get to the same result. Future research will be therefore focused on a combination of multiple measurements (e. g. from different depths) used during the optimization task.

Three types of marls can be found in the Tabriz area (Iran): yellow, green, and gray/black marls. In the present paper, strength and deformation characteristics of Tabriz marls and their stress–strain behavior are investigated by various in situ and laboratory tests. In order to study the deformation behavior of these marls, various experiments such as the pressuremeter test, plate loading test (PLT), seismic wave velocity test, uniaxial compression test, standard penetration test (SPT), and direct shear test were carried out. Ranges of strain at the elastic and failure points were determined. Young’s and shear modulus were obtained. Test results showed that the strength characteristics increase with depth. The value of deformation modulus determined by the pressuremeter test was in good agreement with those obtained from the PLT. This implies that pressuremeter is a suitable in situ test for characterizing the deformation modulus of marl. Deformation modulus obtained from pressuremeter and plate loading tests were approximately 4–5 times the results of uniaxial compressive test and the deformation modulus obtained from seismic data was about 30–50 times the static deformation modulus. Stress–strain curves showed that the maximum value of strain at the elastic and failure points and the minimum value of strength and deformation modulus are corresponding to the yellow marls while the minimum value of strain and the maximum value of strength and deformation modulus are corresponding to the gray/black marls. Some empirical relationships between different characteristics of Tabriz marls were also derived.