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.

Effects of current suction ratio and recent suction history on small-strain behaviour of an unsaturated soil

Although the small-strain shear modulus of saturated soils is known to be significantly affected by stress history, consisting of the overconsolidation ratio (OCR) and recent stress history, the effects of suction history on the small-strain shear modulus of unsaturated soils have rarely been reported. In this study, the effects of suction history, which refers to current suction ratio (CSR) and recent suction history, on both the very-small-strain shear modulus (G0) and shear modulus reduction curve of an unsaturated soil, are investigated by carrying out constant net mean stress compression triaxial tests with bender elements and local strain measurements. In addition, the effect of suction magnitude on G0 and the shear modulus reduction curve is also investigated. At a given suction, G0, elastic threshold strain (εe), and the rate of shear modulus reduction all increase with CSR. On the other hand, the effect of recent suction history on G0 is not significant. The effect of direction of recent suction path (θ) on the shear modulus reduction curve is not distinct. However, the magnitude of recent suction path (l) affects the shear modulus reduction curve significantly when θ = –90°.

Comparative analysis of some methods for deriving the expected flood reduction curve in the frequency domain

This article compares the results of three different models, namely empirical, geomorphoclimatic and stochastic, proposed in the literature for synthesising the reduction curve of average river discharges, of given frequency, over different durations. The analysis used observed reduction ratios inferred for twelve recording gauge stations with known rating curves, situated on central Italian watercourses all of which flow into the Adriatic sea. Particular emphasis was laid on the difficulties encountered in the parameterisation of the models, on the relations between the different formulations and on the existence of a link between the model parameters and the characteristic response times of the basins.

Alternative Method of Determining Resilient Modulus of Compacted Subgrade Soils Using Free-Free Resonant Column Test

An alternative procedure of determining the resilient modulus ( MR) of compacted subgrade soils using a free-free resonant column (FF-RC) test is proposed. The FF-RC test was used to determine a small-strain Young’s modulus ( Emax) and Poisson’s ratio on the basis of the elastic wave propagation theory. Resonant column (RC) and torsional shear (TS) tests were performed to investigate the effects of loading frequency and strain amplitude on the resilient modulus of subgrade soils. By performing FF-RC, RC/TS, and MR tests on the synthetic specimens of known stiffnesses, the feasibility of using the FF-RC test to measure the MR was evaluated and the MR testing equipment was calibrated. Moduli of subgrade soils determined by FF-RC tests match well with values obtained from RC and TS tests at small strains, indicating that the FF-RC test can provide a reliable estimation of Emax, if the effects of loading frequency are considered. In the proposed method, Emax obtained from the FF-RC test can be combined with the effect of loading frequency and the modulus reduction curve determined by the data base of the RC and TS tests for the compacted subgrade soils of various plasticity indexes. Moduli obtained from the proposed method overlapped nicely with MR values determined by standard MR testing, showing the capability of the proposed method being used in determining MR values, provided that the effects of loading frequency and modulus reduction curve are considered.

Friction and Lubrication Effects in Open Die Impact Forging

A horizontal forging machine, Impacter, was used to determine coefficients of friction under different conditions of forging 1020 steel and 2014 T-4 aluminum. Short cylinders were open die forged with repeated blows and the reduction of height determined for one to eight blows. The area under a calculated forging force versus reduction curve was related to available energy in the impellers so that a theoretical reduction for each blow could be determined for different coefficients of friction.