Predicting Vp and constrained modulus reduction curve based on Vs and shear modulus reduction curve in accordance with poroelastic theory

The compression wave velocity (Vp) of sediments plays a key role in seismic wave amplification of vertical motion and is required in site response analysis. However, such information is usually lacking during field exploration (e.g., surface wave method) because only shear wave velocity (Vs) is obtained. This study aims to predict Vp based on Vs empirically and theoretically, especially focusing on saturated conditions. The empirical approach is to establish the Vp correlation dependency on Poisson's ratio and Vs, and the theoretical approach is based on poroelastic theory that accounts for the interaction between fluid and soil skeleton. The Engineering Geological Database for the Taiwan Strong Motion Instrumentation Program and the Kiban Kyoshin Network database in Japan are adopted to establish an empirical model and validate poroelastic theory. The validated poroelastic approach is used to develop a constrained modulus reduction curve dependency on the porosity, Vs, Poisson's ratio, and degree of saturation with a shear modulus reduction curve. The proposed approach can be used to develop generic Vp profiles and constrained modulus reduction curves for the site response to vertical motion given a site specific Vs profile.

Load-Settlement Response of A Footing Over Buried Conduit in A Sloping Terrain: A Numerical Experiment-Based Artificial Intelligent Approach

Settlement estimation of a footing located over a buried conduit in a sloping terrain is a challenging task for practicing civil/geotechnical engineers. In the recent past, the advent of machine learning technology has made many traditional approaches antiquated. This paper investigates the viability, development, implementation, and comprehensive comparison of five artificial intelligence-based machine learning models, namely, multi-layer perceptron (MLP), Gaussian processes regression (GPR), lazy K-Star (LKS), decision table (DT), and random forest (RF) to estimate the settlement of footing located over a buried conduit within a soil slope. The pertaining dataset of 3600 observations was obtained by conducting large-scale numerical simulations via the finite element modelling framework. After executing the feature selection technique that is correlation-based subset selection, the applied load, total unit weight of soil, constrained modulus of soil, slope angle ratio, hoop stiffness of conduit, bending stiffness of conduit, burial depth of conduit, and crest distance of footing were utilized as the influence parameters for estimating and forecasting the settlement. The predictive strength and accuracy of all models mentioned supra were evaluated using several well-established statistical indices such as Pearson’s correlation coefficient (r), root mean square error (RMSE), Nash-Sutcliffe efficiency (NSE), scatter index (SI), and relative percentage difference (RPD). The results showed that among all the models employed in this study, the multi-layer perceptron model has shown better results with r, RMSE, NSE, SI, and RPD values of (0.977, 0.298, 0.937, 0.31, and 4.31) and (0.974, 0.323, 0.928, 0.44 and 3.75) for training and testing dataset, respectively. The sensitivity analysis revealed that all the selected parameters play an important role in determining the output value. However, the applied load, constrained modulus, unit weight, slope angle ratio, hoop stiffness have the highest strength with the relative importance of 18.4%, 16.3% and 15.3%, 13.8%, 11.4%, respectively. Finally, the model was translated into a functional relationship for easy implementation and can prove useful for practitioners and researchers in predicting the settlement of a footing located over a buried conduit in a sloping terrain.

Methods Development for the Constrained Elastic Modulus Investigation of Organic Material in Natural Soil Conditions

Compressibility is one of the most important mechanical properties of soil. The parameter that characterizes compressibility is the constrained modulus of elasticity. Knowledge of this is important to calculate the settlement of a structure foundation on peat material. According to soil classification by EN ISO 14688-2, peat is an organic soil that contains min. 20% organic matter. It is a highly organic type of soil. Peat material has large compressibility. The value of the constrained elasticity modulus for peat is ca. 400 kPa, while it may be ca 1.0–1.6 MPa for consolidated peat. Due to the extensive range of the modulus, experimental research in this field is proposed. It is suggested to load the peat material layer with an embankment and to determine its total settlement. Based on this, a program was developed to determine the settlement–strain relationship. The authors propose an approach according to two models: the first is based on constant stress distribution in the soil with an oedometer test. The second considers the variability of stresses in the soil and the influence of the loaded area. Both methods were tested based on numerical simulations, and then an experimental field in Szczecin was used. The formulae for the constrained modulus of elasticity measurement were derived; in practical conditions, a uniaxial deformation state can be used with the combination of the total settlement.

Evaluation of the Organic Soil Compressibility from In-Situ and Laboratory Tests for Road Application

Organic soil is characterised by high compressibility and should be improved so that it can be used for construction. The use of every method of soil improvement requires knowledge of the compressibility parameters. One of these parameters is the constrained modulus. The constrained modulus can be determined using laboratory or in-situ tests. In this study, the constrained modulus of organic soil was determined using oedometer and piezocone tests (CPTU). The author analysed subsoil under an approximately 250 m section of a designed road in north-eastern Poland. The constrained modulus of organic soil sampled from four different depths was determined in oedometer tests. Piezocone tests were conducted at 18 points located every 15 m along the length of the section concerned. To determine the constrained modulus based on the cone resistance from CPTU tests, the knowledge of the α and αM coefficients is needed. For the tested soil, the optimal range of the α coefficient from 0.4 to 0.7 was determined. The αM coefficient ranged from 0.4 to 0.8. The value of the constrained modulus of organic soil obtained from the oedometer tests, depending on the effective stress, ranged from approximately 100 kPa to 400 kPa. The constrained modulus of the tested soil decreased with depth, which both research methods proved.

Evaluation of geotechnical properties, petrographic characteristics and ultrasonic wave velocity of weak sandstones

Several new settlements have been constructed in the desert areas of Egypt. These new settlements are composed of many new types of problematic formations that creating many geological and engineering challenges. One of the most problematic formations is weak sandstones that are characterized by low mechanical strength and bearing capacity as well as high deformability and fracturing. The physico-mechanical characteristics of these sandstones are the most crucial parameters in design and stability evaluation of any surface and underground engineering structures. The determination of these parameters is complicated, difficult and time consuming as well as is required a great accuracy in sample preparation and testing procedure, and is considered as expensive testing. The objective of this study is analyzing the shallow marine weak sandstones to determine the best and significant correlations of petrographic characteristics and physical engineering index properties that may be useful for estimating unconfined compressive strength (UCS), uniaxial pore volume compressibility (mv), compressional P-wave velocity (Vp) and dynamic constrained modulus (Es). As well as predicting the UCS and mv from compressional P-wave velocity test and estimating the petrographic parameters from the physical engineering index parameters. The present study revealed that the studied samples are high to very high porous sandstones with very low to moderate density, and classified as extremely weak to weak rocks with very high deformability and very low wave velocity. In this study, the physical properties form non-significant linear relations with UCS, Vp, and Es as well as there are moderately strong to strong correlations between P-wave velocity, constrained modulus, unconfined compressive strength and compressibility characteristics. Based on the regression analysis, the dolomite cement and matrix contents, quartz and rock fragments contents, packing density and proximity, sorting, roundness, mean grain size, and grain to cement contact exhibited weak to strong statistical correlations with mechanical properties of the studied sandstones. These relationships revealed that due to the mineralogical, textural, and microstructure variations of the studied recycle origin sandstones, the non-significant to significant relations are resulted. In this study, the backward multiple regression was applied to predict the UCS, mv, Vp and Es of the studied sandstones by selecting some physical and petrographic characteristics which exhibit statistically significant correlations with them. The results of this study were presented in the form of predictive models and equations.

Compacted Anthropogenic Materials as Backfill for Buried Pipes

Buried pipe design requires knowledge about the fill to design the backfill structure. The interaction between the backfill envelope and the pipe impacts the structural performance of the buried pipe. The backfill material and compaction level respond to the backfill’s overall strength and, therefore, for pipe-soil interaction. The strength of backfill material is described in terms of modulus of soil reaction E’ and constrained modulus Eode. As the E’ is an empirical parameter, the Eode can be measured in the laboratory by performing the oedometer tests. In this study, we have performed extensive oedometric tests on five types of anthropogenic materials (AM). Three of them are construction and demolition materials (C–D materials) namely, recycled concrete aggregate (RCA), crushed brick (CB), and recycled asphalt pavement (RAP). Two of them are industrial solid wastes (ISW) namely, fly ash and bottom slag mix (FA + BS) and blast furnace slag (BFS). The results of the tests revealed that AM behaves differently from natural aggregates (NA). In general, the Eode value for AM is lower than for NA with the same gradation. Despite that, some of AM may be used as NA substitute directly (RCA or BFS), some with special treatment like CB and some with extra compaction efforts like RAP or FA + BS.

Investigation of small- to large-strain moduli correlations of normally consolidated granular soils

The establishment of correlations between the small-strain shear modulus (Go) and other soil parameters (such as the oedometer constrained modulus, Moedo) at large deformations constitutes an important step toward more precise modeling of soil deformation behavior. In this study, the shear wave velocities (Vs) of 22 different granular soils of various physical characteristics were measured experimentally using the piezoelectric ring-actuator technique (P-RAT) incorporated in the conventional oedometer cell. For each sample tested, the development of Moedo with the development of relative density (Id), as well as the void ratio (e), was recorded. Then, the obtained Vs and Moedo/Go trends were correlated to the physical parameters of the tested granular soils with the development of e and Id. A practical application employing the achievements in geotechnical engineering design was also evaluated. Based on the proposed correlations, geotechnical designers can easily estimate in situ stress–settlement behavior from the predicted Moedo and Id values using simple in situ measurements.

Regression Analysis of Small Strain Shear and Constrained Modulus Measurements on Sands with Fines: Effect of Different Void Ratio Functions Used

The article is focused on a regression analysis of small strain shear and constrained modulus measurements of 15 different natural sands with plastic fines from the Pannonian basin. Measurements done within this work are supported by additional data on sands with plastic and non-plastic fines gathered from the literature in order to demonstrate the versatility of the approaches used and behavior observed. Bender / extender element techniques are used in this study for measuring the small strain shear and constrained modulus of sands with fines. Three void ratio functions, which are commonly used in predictive empirical equations for predicting small strain stiffness, with corresponding fitted parameters are presented, and their effect on the accuracy of the regression procedure is studied. It is assumed that all the void ratio functions tested provide nearly the same degree of accuracy and that the fitted models are able to predict the values of the parameters measured within an acceptable range of errors. Finally, proposed constant regression constants for sands with plastic fines are given.

Use of functional cluster analysis of CPTU data for assessment of a subsoil rigidity

This paper shows an example of the grouping of piezocone penetration test (CPTU) characteristics using functional data analysis, together with the results of clustering, in the form of a subsoil rigidity model. The subsoil rigidity model was constructed based on layer separation using the proposed method, as well as the k-means method. In the construction of the subsoil rigidity model, the constrained modulus M was applied. These moduli were determined from empirical relationships for overconsolidated and normally consolidated soils from Poland based on cone tip resistance.