The Effect of Compaction Effort on Shear Strength Parameters of Low/High Plasticity Clay Soils
M.Yamin, M. F. Attom, S. Atabay, and R. Vandanapu
ABSTRACT: This paper investigates the effect of compaction effort on shear strength parameters of clay. Four clayey soils, two with high plasticity and two with low plasticity were used in this study. The initial physical properties of the clay such as gradation, optimum moisture content, maximum dry density, and Atterberg limits were determined in accordance with American Standard for Testing and Materials (ASTM) standard procedures. All soil specimens were remolded at five different compaction levels at three different water contents: dry, optimum and wet conditions. Empirical formulae were suggested to obtain optimum moisture content and maximum dry unit weight at an energy level utilizing the results obtained from the standard Proctor test. The shear strength parameters of the prepared specimens were determined using direct shear test. Another set of empirical formulae were also suggested to obtain the cohesion and friction angle at an energy level utilizing the cohesion and friction angle obtained from direct shear test at maximum dry unit weight and optimum moisture content from standard Proctor test.
KEYWORDS: Compaction energy, Cohesion, Angle of internal friction, Shear strength.
Using a Stochastic Model to Study the Ground Motion of Comprehensive Subsurface Structure
C. H. Hsu, S. J. Chao, S. G. Chern, and H. Hwang
ABSTRACT: The seismic response analysis of buildings and bridges use earthquake acceleration time histories as input data. But there is always a lack of earthquake time histories in regions where buildings are constructed, which makes ground motion simulation is one of the most important problems in civil engineering domain. In this study, the strong motion stations of boring log data collected within Lanyang plain have been combined with the subsurface layers of Lanyang plain obtained by using geophysical method to construct a comprehensive subsurface structure of Lanyang plain. Available papers and reports on nonlinear dynamic soil characteristics have been reviewed to determine appropriate soil parameters for representing soils in Lanynag plain. In this research, the stochastic seismic model developed by Boore (1983, 2005) will be used to simulate a set of rock-outcrop synthetic acceleration time histories. The acceleration time histories at the rock-outcrop from this study will be compared with the real earthquake record for all the soil sites, the acceleration time histories at the ground surface will be generated from nonlinear site response analyses using the computer program SHAKE91. For the strong motion station, we compare the earthquake spectrum and real earthquake spectrum to investigate the appropriateness in the Ilan area. These ground motions may be used in the field of disaster reduction, such as the calculation of the ground response subject to earthquakes using the SHAKE computer program or the evaluation of the safety of buildings and bridges.
KEYWORDS: Synthetic ground motion, Response spectra, Comprehensive subsurface structure.
The Effect of the Inclined Core of the Earth Fill Dam on the Settlement Rate
A. M. Ghaemi, B. K. Ahangari, C. A. Noorzad, and D. K. Goshtasbi
ABSTRACT: Since the constituent material of the earth fill dams are granular, they have little resistance to tensile stresses and are undergoing deformations as settlement. A large number of parameters affect the performance of dams. The aim of this paper is to evaluate the effect of the inclined core of earth fill dam as a parameter that is less regarded for the dam settlement rate. Therefore, considering the different angles for the core (60°, 75°, and 90°), the dam settlement (Case Study: Sardasht dam) was investigated. In this study, numerical and statistical methods (fuzzy set) were used to analyze the results, first analyses were conducted by numerical modeling using PLAXIS software, and then a settlement criterion was obtained using existing techniques in statistics. Then, to obtain the considered relationship, the fuzzy linear regression model was used. Finally, after dynamic and static analysis with the mentioned methods, it was observed that with increasing core slope, the dam settlement decreases. The outcomes of fuzzy regression equations also confirm this issue.
KEYWORDS: Settlement rate, Inclined core, Body slope, Numerical modelling, PLAXIS, Fuzzy set regression.
The Boundary Condition of a 3D Continuum Model for a Quasi 2D Plane Strain Condition
S. Chaiyaput and M. Sugimoto
ABSTRACT: The half-model has been used in the finite element analysis, based on the symmetric condition against the tunnel’s longitudinal, vertical plane, but this design concept cannot apply to a staggered lining. Therefore, the authors have proposed a multi-ring model to present the segmental lining behavior of a 3D continuum ground model in the case of staggered building, but the proposed 12-ring model shows the different axial force distributions in circumferential directions between the center of the model and the end of the model, especially in cases of soft soil. Accordingly, to make clear, the mechanism of the above difference and to establish the analysis condition of the proposed model for quasi 2D plane strain condition, this paper evaluates the influence of boundary condition on the transverse cross section at the end of the segmental lining on the segmental lining behavior, based on the analyzed axial force and bending moment in soft and stiff ground conditions using both the 2-ring model and a 12-ring model. As a result, it was confirmed that the proposed 2-ring model could simulate the segmental lining behavior under quasi 2D plane strain condition.
KEYWORDS: Segmental lining, Staggered arrangement, Continuum ground model, 3D FEM, Boundary condition.
3D Evaluation of PWP Development Due to Tunnel Excavation in an Over Consolidated Clay
D. L. Vettorello, F. A. M. Marinho, and P. D. G. Orlando
ABSTRACT: The stress relief promoted by the excavation process may induce the reduction of the pore water pressure within the soil when an undrained condition occurs. According to the magnitude of the stress relief and the initial hydrostatic pressure, the pore water pressure reduction may generate suction in the soil, thus increasing the soil shear strength. Effects of the stress relief promoted by a circular tunnel excavation process in stiff clay was investigated by means of a series of 3D numerical analyses. These analyses considered a NATM unsupported excavation advance of a shallow and small diameter tunnel in a saturated soil mass. The results highlight the development of a suction zone in front of the tunnel face where the soil shear strength is increased. The extension of this suction zone and its dissipation rate through time, however, are influenced by the soil massif coefficient of earth pressure at rest, and hydraulic conductivity, respectively.
KEYWORDS: Tunnels, 3D Numerical model, Pore water pressure development, Stress relief, Overconsolidated clay.
Seismic Behaviour of Complex H-Shaped Buried Structures
B. Salehi, A. Bahmanpour, and M. Derakhshandi
ABSTRACT: Seismic loading parameters are always characterized by high complexity and uncertainty. The uncertainty increases in complex structures, which makes the process more complicated, particularly for structures that are partly buried deep and partly at the surface. In this research, the seismic behavior and stress changes of complex H-shaped structures have been studied using 2D FE analysis. Five points in the geometry of the model were selected at which the normal and shear stresses were extracted. Granular soil with variable strength parameters was investigated in the sensitivity analysis. The structures had height-to-width ratios of 1, 1.5 and 2. The results show that the stress increased in structures under near-field earthquake records. A decrease in shear stress was observed for all structural ratios with an increase in the internal friction angle. A rise in the internal friction angle at the midpoint of the wall also increased the shear stress. This growth was observed for all far-field earthquake records up to an internal friction angle of 35° and then descend. At a constant friction angle, climbing structure ratio H/L from 1 to 1.5 improved the shear stress at least 20%. However, as H/L changed from 1.5 to 2, the minimum stress increase was 85%. For far-field earthquakes, the stress values depended on the horizontal acceleration and H/L because they are influenced by the frequency content and internal friction angle.
KEYWORDS: Time history, Finite element method, Complex structure, Shear stress.
Settlement’s Prediction of Piles in Tropical Soil
P. H. L. Bezerra, A. S. Moura, F. C. da Silva Filho, F. V. C. G. Filho, and E. Cerqueira Junior
ABSTRACT : The prediction of deep foundation settlements remains challenging due to the scarcityofstudies about it. This paper aimed to evaluate the accuracy of the usage of load transfer methods in predicting the settlement of bored piles in granular soil in Brazil’s Northeast. For this, two small piles were installed and submitted to load tests, a small amount of expansive polystyrene was placed under one of the pile’s tips to evaluate the load distribuition of the elements.. For the settlement’s prediction, methods based on load transfer functions, such as analytical and numerical (using RSPile and UniPile ), were employed. The comparinson of the predicted values with the experimental measurements showed agreement in the elastic zone of soil’s behavior for all the methods. For higher loads, discrepancies occurred. The method proposed by Massad (1992) was the most effective among the used methodologies. Using the mentioned programs, results were close to the experimental values.
KEYWORDS: Settlement prediction, Load transfer, Bored piles.
Cyclic Resistance of High Plasticity North Java Clays and Silt
E. Rismantojo, E. Ginting, and M. Ochoa
ABSTRACT: In an attempt to develop a database of the cyclic resistance of fine-grained soils in Indonesia a series of cyclic triaxial test was performed on fine-grained soils collected from two locations near shore of north Java Island, Indonesia. These samples were classified as fine-grained soils with clay-like behavior and, according to various liquefaction criteria, they are non-liquefiable. Our study used a cyclic triaxial test to apply multistage cyclic axial stresses in a form of sinusoidal stress with a frequency of 1 Hz. All specimens are isotropically consolidated passing their preconsolidation stress in order to achieve a normally consolidated state with OCR of about 1. Our findings suggest that cyclic resistance of North Java clay-like fine-grained soils follows the SHANSEP concept and could be normalized at OCR of 1. At fifteen cycles of uniform sinusoidal loading the tested clay and silt samples have a normalized cyclic strength, , or a cyclic resistance ratio (CRR) of approximately 0.31 and a cyclic strength ratio, , of 0.70.
KEYWORDS: Clay-like behavior, Cyclic resistance ratio, Cyclic strength ratio, Plasticity index, Water content to liquid limit ratio.
Durability of Erosion Control Geomesh of Paddy by ‘Accelerated Biodegradation Test’
S. Halkude and R. Katdare
ABSTRACT: Paddy straw is abundantly available as crop waste and has a sacrificial quality to biodegrade early, which can be advantageously utilized to develop a low-cost Paddy Straw Geomesh (PSG) to control rain-induced surface erosion of a newly constructed embankment for the critical period of few months of the rainy season. The present study reports employing, ‘Accelerated Biodegradation Test’ to quickly estimate the test time of PSG specimens in the laboratory to reach its durability in comparison with the field test time which is generally longer due to slow disintegration of organic material in climatic conditions. This acceleration is achieved by increasing fungi spore concentration with respect to field fungi concentration, using various concentrations ranging from 3.29 x 105 through 3.29 x 109 spores per gram of soil while taking ‘Accelerated Biodegradation Test’. The findings of ‘Accelerated Biodegradation Test’ report 40% decrease in test time of PSG in a laboratory, using higher fungi spore concentration in soil embodiments, as compared to those in the field.
KEYWORDS: Accelerated biodegradation test, Laboratory embedment, Paddy straw geomesh, Fungi spore concentration, Tensile strength.
Stability Analysis of an Overall Failure Excavation Case in Hang Zhou
T. N. Do
ABSTRACT: In this paper, stability of an overall failure excavation case in Hang Zhou, China was analyzed using the finite element method (FEM). The retaining system of the excavation was fully modelled, including walls, horizontal struts, and vertical center posts. For comparison, the structural elements were simulated using plates with both elastic and elastoplastic behaviors. The soil response nesar failure was assumed to follow the Morh-Coulomb model. Results showed that the FEM using the elastoplastic retaining system gave a more reasonable estimate of stability of the excavation than that using the elastic support system. With the elastoplastic retaining system, yielding firstly occurred on the wall and then on the struts, which caused large movement of surrounding soil toward the excavation. On the other hand, with the elastic retaining system, failure of the excavation was only due to the great plastic heave of soil at the excavation bottom. The predicted movement of soil and wall was nearly one meter as using the ealstoplatic support system but several meters as using the elastic one.
KEYWORDS: Deep excavations, Stability analysis, Finite element method, Failure mechanism.
