Zheng-Yi Feng

DYNAMIC PROPERTIES OF GRANULATED RUBBER/SAND MIXTURES

Processed waste tires mixed with soils are applicable in lightweight fills for slopes, retaining walls, and embankments that may be subjected to seismic loads. Rubbers high damping capacity permits consideration of granulated rubber/soil mixtures as part of a damping system to reduce vibration. The dynamic properties of granulated rubber/soil mixtures are essential for the design of such systems. This research investigates the shear modulus and damping ratio of granulated rubber/sand mixtures using a torsional resonant column. Specimens were constructed using different percentages of granulated tire rubber and Ottawa sand at several different percentages. The maximum shear modulus and minimum damping ratio are presented with the percentage of granulated rubber. It is shown that reference strain can be used to normalize the shear modulus into a less scattered band for granulated rubber/sand mixtures. The normalized shear modulus reduction for 50% granulated rubber (by volumme) is close to a typical saturated cohesive soil. Empirical estimation of maximum shear modulus of soil/rubber mixtures can be achieved by treating the volume of rubber as voids.

A NUMERICAL STUDY OF PILED RAFT FOUNDATIONS

Abstract This paper presents raft‐pile‐soil interaction for a vertically loaded flexible piled raft on layered subsoil using a two‐dimensional finite difference numerical tool. The subsoil is modeled as a linear elastic material and the raft is modeled as a beam structure under plane strain. In addition, the piles are simulated by a series of pile elements considering the pile/soil interface behavior. In the simulations, the required input parameters of soil, pile and interface are determined by back analyses of pile loading tests. Settlement, bending moment, both in pile and raft, as well as effects of raft flexibility for vertical uniform loading in the subsoil were examined. It is found that even though for vertical uniform loading, a relatively high bending moment may be induced in the piles due to lateral displacement of the stressed subsoil. For the case of a piled raft placed over a soft clay layer at ground surface the contact pressure at the raft‐soil interface is merely 4 ∼ 6% of that developed in the unpiled raft. Nevertheless, the contact pressure may reach 15 ∼ 25% of that of the unpiled raft if the piled raft is resting on a sand layer at the ground surface. This implies that the loading carried by the pile group could be reduced by almost 1/4 of the design load and it could eventually reduce the cost of pile group construction to a certain extent.

Hyperspectral Image Classification Using Fast and Adaptive Bidimensional Empirical Mode Decomposition With Minimum Noise Fraction

The scattered pixel problem in hyperspectral images caused by atmospheric noises and incomplete classification can lead to unsatisfactory classification; this problem remains to be solved. This letter reports the application of minimum noise fractions (MNFs) combined with fast and adaptive bidimensional empirical mode decomposition (FABEMD) as a two-step process to improve the classification accuracy of airborne visible-infrared imaging spectrometer hyperspectral image of the Indian Pine data set. With dimensional reduction by using MNF, FABEMD, considered as a low-pass filter, decomposes a hyperspectral image into several bidimensional intrinsic mode functions (BIMFs) and a residue image. The first four BIMFs are removed and the remainder BIMFs are integrated to reconstruct informative images that are subsequently classified through a support vector machine classifier (SVM). The classification results show that the proposed approach can effectively eliminate noise effects and can obtain higher accuracy than does traditional MNF SVM.

The characteristics of the seismic signals induced by landslides using a coupling of discrete element and finite difference methods

Landslide seismic signals support researchers to estimate magnitudes and locations of landslides. They can serve as a crucial data for landslide warning systems. However, the randomness of landslide locations makes the acquisition of landslide-induced seismic signals difficult and limits the number of available field data. The objectives of this study are to establish a numerical modeling approach to examine the characteristics of seismic signals induced by landslides and perform parametrical study. The two-dimensional particle flow code (PFC) and Fast Lagrangian Analysis of Continua (FLAC) are coupled to simulate the landslide process. The force and velocity data at the coupled interfaces of FLAC and PFC are transferred back and forth via a Socket I/O connection. Four locations were monitored for the induced vertical seismic signals, including velocity, acceleration, and stress histories. The signals were analyzed by Hilbert-Huang transform to obtain the time-frequency spectrograms for examining the characteristics of the signals. The particle size, wall friction, particle friction, and parallel bond of PFC input parameters were parametrically investigated. The Xiaolin landslide in 2009 was successfully simulated, and the characteristics of the seismic signals were studied and compared with the data from a broadband seismic station. These results demonstrate that terrain and transition in the movement type of a complex landslide do influence the seismic signals. A landslide with larger rock particles generates lower-frequency content seismic signals. Also, there can be approximately 40 s to escape before a large-scale landslide hits if seismic instrumentation is installed. The method proposed can be further applied for studies on many other large-scale rock avalanches to verify recorded signals and further correlate the signals with the landslide characteristics.

Damping capacity of bulk wheat

Results of resonant column tests on 23 specimens of bulk wheat, showing effects of strain amplitude, confining stress, wheat type (hard and soft red winter wheat), wheat density, and moisture content on wheat damping capacity are presented, along with models relating damping capacity to shear strain amplitude and to corresponding shear stiffness. Damping capacity is a primary property of bulk wheat needed to compute the seismic response of metal bins filled with wheat. Test results are presented to validate the use of staged testing procedures. Staged testing is desirable because it allows measurement of damping versus strain and damping versus shear modulus relationships for several different stress levels using a single specimen.

Stability Analysis of Landslide Dam under Rainfall

Failure of a landslide dam might occur by river discharge or rainfall. A rise of the upstream water level of a landslide dam and rain infiltration into the dam body increase pore water pressure and the weight of the dam. In this study, transient seepage analysis of rainfall infiltration and dam stability analysis are performed. A two-phase flow simulation using the FLAC finite difference code is adopted to analyze unsaturated seepage flow in transient fluid-mechanical calculations. The safety factor of dam stability is evaluated using the shear strength reduction technique. The parameters discussed in this study include the rising speed of the water level, rain infiltration, and the hydraulic conductivity of soil. The results show that the time to slope failure of the dam is approximately 247 min. when only the effect of the rising upstream water level of the dam is considered. The failure time decreases to 189 min. when the rain infiltration and rising upstream water level of the dam are considered. The results also indicate that the hydraulic conductivity of the dam affects dam failure time.

Landslide hazard zoning based on numerical simulation and hazard assessment

ABSTRACT This study conducted terrain analysis and remote sensing image interpretation to determine the distributions of historical and potential landslides in Shang-an Village and elucidate the characteristics of landslide development within the area. Using the discrete element method, we constructed a digital model of the study area in order to explore the landslide movement processes and determine the scope of influence with regard to deposition. The scope of influence was then used to perform hazard zoning in the creation of a landslide hazard map for use as a reference in future land planning and disaster prevention. Our results revealed 13 potential landslide masses in the study area, 92% of which are on unstable slopes with limited landslide activity. These areas should be the focus of future monitoring and remediation projects. Direct impact from falling rock is the main concern in the area roughly 50 m around the sliding masses in the source areas of the study region and approximately 30 m around the creek beds upstream. In contrast, being buried by debris flow is the concern in the lowland areas roughly 30 m from creek channels in the middle and lower reaches.

Using Continuous Wavelet Transform to Construct the Dispersion Image for Soil Layers

This study used a time-frequency domain analysis for estimating the dispersion curve of a Rayleigh wave by using two receivers. The signals were first transformed using continuous wavelet transform. A similar slant stack procedure was used to analyze the wavelet transform signals and extract a dispersion image. This method is advantageous because it requires no empirical judgment in phase unwrapping and few receivers. To examine the applicability of the method for evaluating the dispersion curve for soil layers with lateral heterogeneity, three synthetic examples and an experience example were investigated. In these examples, numerical simulations of the surface wave seismic test were performed using the finite difference FLAC code. The results revealed that the estimates of the surface wave dispersion curve, obtained using the method, coincide with those of the theoretical values. A high-resolution dispersion image is generated by increasing the spacing of receivers. The method is applicable for extracting a dispersion image for lateral heterogeneous soil layers.

Estimation of 2D Shear Wave Velocity Profile of Soil Layers Using Surface Wave Seismic Tests

The 2D shear wave velocity profile of strata is estimated using the active and passive surface wave seismic tests. The experimental dispersion curves were obtained after the recorded signals were transformed by the slant stack procedure. The phase velocity in the relatively high frequency range can be obtained using the dispersion curves deduced from the active tests. On the other side, dispersion curves obtained from the passive tests can be used to estimate the phase velocity in the relatively low frequency range. From the higher frequency portion of the dispersion curves that stand for the fundamental mode, we obtained the phase velocities about 190 m/s for the sandy surface fill. Theoretical dispersion curves can be constructed by the thin-layer-stiffness-matrix method. For theoretical dispersion curves, the soil layers of the test site were modeled as the sandy surface fill overlying a half space soil layer. A real-parameter genetic algorithm was programmed to minimize the difference between the theoretical and experimental dispersion curves. We prove that the real-parameter genetic algorithm is capable to reduce the error between experimental and theoretical dispersion curves. The estimated 2D geometry of the sandy surface fill using the active and passive surface wave seismic tests was verified with the borehole data.

Numerical Analyses of Dynamic Responses of an Earth Dam during 1999 Chi-Chi Earthquake in Taiwan

The Pastor and Zienkiewicz (P-Z) model was adopted here as the constitutive model to study the dynamic responses of the Liyutan dam subjected to the Chi-Chi earthquake. For numerical simulation, the shell materials of the earth dam are assumed to satisfy the P-Z model. The optimal material parameters of P-Z model were judged according to the experimental results by Center Region Water Resource Office in Taiwan. Staged construction, seepage, static equilibrium and dynamic response are sequentially analyzed. A comparison is performed between the P-Z model and Mohr-Coulomb model through the dynamic analysis of the Liyutan dam under Chi-Chi earthquake. The influence of permeability of shell on the generation of pore water pressure under earthquake loading was studied. The results show that the large horizontal permanent movements at the upstream shell were resulted and the larger vertical settlement took place at the top of dam after the earthquake. The Mohr-Coulomb model results in higher pore water pressure compared to those obtained of the P-Z model during the earthquake shaking. The pore pressure parameter in upstream shell slightly decreases with the increase of the permeability of shell.