Abstract
Researches have been done to discover ways to strengthen peat soil deposits. In this model study, fibrous peat that is the most compressible types of peat has been reinforced with precast peat columns stabilized with ordinary Portland cement and polypropylene fibres. Rowe cell consolidation tests as well as plate load tests (PLTs) were conducted on various types of test samples to evaluate the strength and deformation of untreated peat and peat reinforced by various types of columns. PLTs were conducted in a specially designed and fabricated circular steel test tank. The compression index (Cc) and recompression index (Cr) of fibrous peat samples reduced considerably upon use of precast columns. Also, PLT results confirmed the results obtained from Rowe cell tests. Use of polypropylene fibres added to cement further decreased (Cc) and (Cr) and increased load bearing capacity of untreated peat. Finite element method (FEM) using Plaxis 3D was carried out to evaluate the stress distributions along various types of tested samples and also, to compare the deformations obtained from FEM analysis with the actual maximum deformations found from PLTs. FEM results indicate that most of the induced stresses are taken on the upper portion of tested samples and reach their maximum values below the loading plate. Also, a close agreement was found between actual deformation values obtained from PLTs and values resulted from FEM analysis for various types of tested samples.
Key Words
precast stabilized peat columns; compression index; recompression index; Rowe cell; Plate load test; FEM
Address
Civil Engineering Department, Hormozgan University, Bandar Abbas, Iran.
Abstract
By means of finite element numerical simulation and pseudo-static method, the shallow-buried bilateral bias twin-tube tunnel subject to horizontal and vertical seismic forces are researched. The research includes rupture angles, the failure mode of the tunnel and the distribution of surrounding rock relaxation pressure. And the analytical solution for surrounding rock relaxation pressure is derived. For such tunnels, their surrounding rock has sliding rupture planes that generally follow a "W" shape. The failure area is determined by the rupture angles. Research shows that for shallow-buried bilateral bias twin-tube tunnel under the action of seismic force, the load effect on the tunnel structure shall be studied based on the relaxation pressure induced by surrounding rock failure. The rupture angles between the left tube and the right tube are independent of the surface slope. For tunnels with surrounding rock of Grade IV, V and VI, which is of poor quality, the recommended reinforcement range for the rupture angles is provided when the seismic fortification intensity is VI, VII, VIII and IX respectively. This study is expected to provide theoretical support regarding the ground reinforcement range for the shallow-buried bilateral bias twin-tube tunnel under seismic force.
Address
(1) Xin-Rong Liu, Dong-Liang Li, Zhen Wang:
School of Civil Engineering, Chongqing University, Chongqing 400045, China;
(2) Xin-Rong Liu, Dong-Liang Li, Zhen Wang:
Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing 400045, China;
(3) Jun-Bao Wang:
School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, 710055, China.
Abstract
Millions of scrap tires are discarded annually in Turkey. The bulk of which are currently landfilled or stockpiled. These tires consume valuable landfill space or if improperly disposed, create a fire hazard and provide a prolific breeding ground for rats and mosquitoes. Used tires pose both a serious public and environmental health problem which means that economically feasible alternatives for scrap tire disposal must be found. Some of the current uses of scrap tires are tire-derived fuel, creating barrier reefs and as an asphalt additive in the form of crumb rubber. However, there is a much need for the development of additional uses for scrap tires. One development the creation of shreds from scrap tires that are coarse grained, free draining and have a low compacted density thus offering significant advantages for use as lightweight subgrade fill and backfill material. This paper reports a comprehensive laboratory study that was performed to evaluate the use of a shredded tire-sand mixture as a backfill material in trench conditions. A steel frame test tank with glass walls was created to replicate a classical trench section in field conditions. The results of the test demonstrated that shredded tires mixed with sand have a definite potential to be effectively used as backfill material for buried pipe installations.
Key Words
tire rubber; backfill material; HDPE flexible pipe
Address
(1) Niyazi U. Terzi, C. Erenson:
Aksaray University, Engineering Faculty, Department of Civil Engineering, Geotechnics Division, Aksaray, Turkey;
(2) Murat E. Selçuk;
YıldızTechnical University, Civil Engineering Faculty, Department of Civil Engineering, Geotechnics Division, Istanbul, Turkey.
Abstract
Three-dimensional simulation of flow through dam foundation is performed using finite element (Seep3D model) and artificial neural network (ANN) models. The governing and discretized equation for seepage is obtained using the Galerkin method in heterogeneous and anisotropic porous media. The ANN is a feedforward four layer network employing the sigmoid function as an activator and the back-propagation algorithm for the network learning, using the water level elevations of the upstream and downstream of the dam, as input variables and the piezometric heads as the target outputs. The obtained results are compared with the piezometric data of Shahid Abbaspour's Dam. Both calculated data show a good agreement with available measurements that demonstrate the effectiveness and accuracy of purposed methods.
Key Words
seepage; dam foundation; finite element method; neural network; Seep3D model
Address
Department of Civil Engineering, Shahid Bahonar University of Kerman, P.B. 76169133, Kerman, Iran.
Abstract
This article describes a new in-situ load test called the Hydraulic Cylinder Test (HCT) and its application to determine the geotechnical properties of soil-rock mixtures. The main advantages of the test are its easy implementation, speed of execution and low-cost. This article provides a detailed description of the equipment and the test procedure, and examines a case study of its application to determine the geotechnical properties of an earth-filled dam for a tailings pond. The containment dams of the ponds are made from blocks of gypsum and marl, obtained from the excavation of the ponds, mixed in a matrix of sands and clays. The size of the rocks varies between 1 and 30 cm. The HCT is particularly useful for determining the geotechnical properties of this type of soil-rock mixture. Nine HCTs were carried out to determine its strength (c, φ) and deformation (B, G) properties. The results obtained were validated using the Bim strength criterion, recently proposed, and some pressure meter tests carried out beforehand. The properties obtained are used to analyze the stability of the dam using computer simulations and a modification to its design is proposed.
Key Words
hydraulic cylinder test (HCT); earth-filled dams; soil-rock mixture; bim strength criterion; back analysis
Address
(1) Roman F. Rodriguez:
Research Group of Ground Engineering, Mining Engineering School, University of Oviedo, Oviedo, Asturias, Spain;
(2) Celestino G. Nicieza:
Department of Exploitation and Prospecting Mines, Mining Engineering School, University of Oviedo, Oviedo, Asturias, Spain;
(3) Fernando L. Gayarre:
Department of Construction and Manufacture Engineering, Engineering School of Gijon, Viesques Campus, Gijon, Asturias, Spain;
(4) Francisco L. Ramos Lopez:
Department of Physics, Engineering School of Gijon, Viesques Campus, Gijon, Asturias, Spain.
Abstract
The creep property of salt rock significantly influences the long-term stability of the salt rock underground storage. Triaxial creep tests were performed to investigate the creep behavior of salt rock. The test results indicate that the creep of salt rock has a nonlinear characteristic, which is related to stress level and creep time. The higher the stress level, the longer the creep time, the more obvious the nonlinear characteristic will be. The elastic modulus of salt rock decreases with the prolonged creep time, which shows that the creep damage is produced for the gradual expansion of internal cracks, defects, etc., causing degradation of mechanical properties; meanwhile, the creep rate of salt rock also decreases with the prolonged creep time in the primary creep stage, which indicates that the mechanical properties of salt rock are hardened and strengthened. That is to say, damage and hardening exist simultaneously during the creep of salt rock. Both the damage effect and the hardening effect are considered, an improved Maxwell creep model is proposed by connecting an elastic body softened over time with a viscosity body hardened over time in series, and the creep equation of which is deduced. Creep test data of salt rock are used to evaluate the reasonability and applicability of the improved Maxwell model. The fitting curves are in excellent agreement with the creep test data, and compared with the classical Burgers model, the improved Maxwell model is able to precisely predict the long-term creep deformation of salt rock, illustrating our model can perfectly describe the creep property of salt rock.
Key Words
salt rock; creep model; damage; hardening
Address
(1) Jun-Bao Wang, Xin-Rong Liu, Zhan-Ping Song, Zhu-Shan Shao:
School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, China;
(2) Jun-Bao Wang, Xin-Rong Liu:
School of Civil Engineering, Chongqing University, Chongqing, China.
Abstract
Commonly, the base stability of sheeted excavation pits against seepage failure by heave is evaluated by using two-dimensional groundwater flow models and Terzaghi's failure criterion. The objective of the present study is to investigate the effect of three-dimensional groundwater flow on the heave for sheeted excavation pits with various dimensions. For this purpose, the steady-state groundwater flow analyses are performed by using the finite element program ABAQUS 6.12. It has been shown that, in homogeneous soils depending on the ratio of half of excavation width to embedment depth b/D, the ratio of safety factor obtained from 3D analyses to that obtained from 2D analyses FS(3D)/FS(2D) can reach up to 1.56 and 1.34 for square and circular shaped excavations, respectively. As failure body, both an infinitesimal soil column adjacent to the wall (Baumgart & Davidenkoff's criterion) and a three-dimensional failure body with the width suggested by Terzaghi for two-dimensional cases are used. It has been shown that the ratio of FS(Terzaghi)/FS(Davidenkoff) varies between 0.75 and 0.94 depending on the ratio of b/D. Additionally, the effects of model size, the shape of excavation pit and anisotropic permeability on the heave are studied. Finally, the problem is investigated for excavation pits in stratified soils, and important points are emphasized.
Key Words
seepage failure; heave; sheeted excavation pit; three-dimensionality; finite element method
Address
Department of Engineering Geology and Hydrogeology, RWTH Aachen University, Lochnerstr. 4-20, D-52064 Aachen / Germany.
