Abstract
Adhesion in geotechnical engineering is the interaction between cohesive soil and a solid surface which can cause clogging in mechanized tunnelling through clayey formations. Normal piston pull out and modified direct shear tests were performed on clayey soil samples to determine which type of adhesion stress, normal or tangential, could be most effectively measured. Measured values for normal adhesion ranged from 0.9 to 18 kPa. The range of tangential adhesion was 2.4 to 10 kPa. The results indicate normal adhesion results were more accurate than those for the modified direct shear test that measure tangential adhesion. Direct shear test on identical samples did not show any correlation between measured cohesion and normal adhesion values. Normal adhesion values have shown significantly meaningful variation with consistency index and so are compatible with the base of field clogging assessment criteria. But tangential adhesion and cohesion were not compatible with these assessment criteria.
Key Words
clogging; tunnelling; normal adhesion; tangential adhesion; clayey soils
Address
(1) Amir Khabbazi Basmenj, Mohammad Ghafoori:
Department of Engineering geology, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran;
(2) Akbar Cheshomi, Younes Karami Azandariani:
Department Engineering geology, Faculty of Sciences, University of Tehran, Tehran, Iran.
Abstract
The purpose of this paper is to study the propagation of Rayleigh waves in an anisotropic heterogeneous crustal layer over a gravitational semi-infinite sandy substratum. It is assumed that the heterogeneity in the crustal layer arises due to exponential variation in elastic coefficients and density whereas the semi-infinite sandy substratum has homogeneous sandiness parameters. The coupled effects of heterogeneity, anisotropy, sandiness parameters and gravity on Rayleigh waves are discussed analytically as well as numerically. The dispersion relation is obtained in determinant form. The proposed model is solved to obtain the different dispersion relations for the Rayleigh wave in the elastic medium of different properties. The results presented in this study may be attractive and useful for mathematicians, seismologists and geologists.
Key Words
rayleigh waves; heterogeneity; elasticity; sandy substratum; anisotropy
Address
(1) Rajneesh Kakar:
163/1, C-B, Jalandhar-144022, India;
(2) Shikha Kakar:
Department of Electronics, SBBS University, Padhiana.
Abstract
A total of 104 laboratory model tests on a square footing subjected to eccentrically inclined loads supported by sand reinforced with randomly distributed polypropylene fibers were conducted in order to compare the results with those obtained from unreinforced sand and with each other. For conducting the model tests, uniform sand was compacted in a test box at one particular relative density of compaction. The effect of percentage of reinforcement used, thickness of the reinforced layer, angle of inclination of load to vertical and eccentricity of load applied on various prominent factors such as ultimate load, vertical settlement, horizontal deformation and tilt were investigated. An improvement in ultimate load, vertical settlement, horizontal deformation and tilt of foundation was observed with an increase in the percentage of fibers used and thickness of reinforced sand layer under different inclinations and eccentricities of load. A statistical model using non-linear regression analysis based on present experimental data for predicting the vertical settlement (sp), horizontal deformation (hdp) and tilt (tp) of square footing on reinforced sand at any load applied was done where the dependent variable was predicted settlement (sp), horizontal deformation (hdp) and tilt (tp) respectively.
Key Words
geosynthetics; eccentrically inclined loading; fiber reinforced sand; model tests; ultimate load; tilt
Address
(1) Arshdeep Kaur:
Department of Civil Engineering Technology, University of Johannesburg, Doornfontein Campus, Johannesburg 2028, South Africa;
(2) Arvind Kumar:
Department of Civil Engineering, Dr. B.R. Ambedkar National Institute of Technology, Jalandhar 144011, India.
Abstract
The construction of a new cavern modifies the state of stresses and displacements in a zone around the existing cavern. For multiple caverns, the size of this influence zone depends on the ground type, the in situ stress, the cavern span and shape, the width of the pillar separating the caverns, and the excavation sequence. Performances of underground twin caverns can be unsatisfactory as a result of either instability (collapse) or excessive displacements. These two distinct failures should be prevented in design. This study simulated the ultimate and serviceability performances of underground twin rock caverns of various sizes and shapes. The global factor of safety is used as the criterion for determining the ultimate limit state and the calculated maximum displacement around the cavern opening is adopted as the serviceability limit state criterion. Based on the results of a series of numerical simulations, simple regression models were developed for estimating the global factor of safety and the maximum displacement, respectively. It was proposed that a proper pillar width can be determined based on the threshold influence factor value. In addition, design charts with regard to the selection of the pillar width for underground twin rock caverns under similar ground conditions were also developed.
Key Words
influence factor; ultimate and serviceability performances; pillar width; global factor of safety; maximum displacement
Address
(1) Wengang Zhang, Anthony T.C. Goh:
Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing 400045, China;
(2) Wengang Zhang:
School of Civil Engineering, Chongqing University, Chongqing 400045, China;
(3) Wengang Zhang:
School of Civil and Environmental Engineering, Nanyang Technological University, 639798 Singapore.
Abstract
Soils are subjected to additional stresses due to the loads transferred by the foundations of the buildings. The distribution of stress in soil has great importance in geotechnical engineering projects such as stress, settlement and liquefaction analyses. The purpose of this study is to examine the shear stresses on horizontal plane below the rectangular foundations subjected to biaxial bending on an elastic soil. In this study, closed-form analytical solutions for shear stresses in x and y directions were obtained from Boussinesq\'s stress equations. The expressions of analytical solutions were simplified by defining the shear stress influence values (I1, I2, I3), and solution charts were presented for obtaining these values. For some special loading conditions, the expressions for shear stresses in the soil below the corners of a rectangular foundation were also given. In addition, a computer program was developed to calculate the shear stress increment at any point below the rectangular foundations. A numerical example for illustrating the use of the presented solution charts was given and, finally, shear stress isobars were obtained for the same example by a developed computer program. The shear stress expressions obtained in this work can be used to determine monotonic and cyclic behavior of soils below rectangular foundations subjected to biaxial bending.
Abstract
Granulated coal ash (GCA), a mixture of the by-product from milling processes with a small amount of cement added, has recently come to be used as a new form of geomaterial. The shear strength and deformation behaviours of GCA are greatly determined by its relative density or void ratio. A series of drained triaxial compression tests were performed on cylindrical specimens of GCA at confining pressures of between 50 kPa and 400 kPa at initial relative densities of 50%, 70% and 80%. Experimental results show that a rise in relative density increases the peak shear strength and intensifies the dilation behaviour. The initial tangent modulus and secant modulus of the stress-strain curve increase with increasing initial relative density, whereas the axial and volumetric strains at failure decrease with level of initial relative density. The stress-dilatancy relationships of GCA at different relative densities and confining pressures display similar tendency. The dilatancy behaviour of GCA is modelled by the Nova rule and the material property N in Nova rule of GCA is much larger than that of natural sand.
Abstract
Settlement of foundations in permafrost regions primarily results from three physical and mechanical processes such as thaw consolidation of permafrost layer, creep of warm frozen soils and the additional deformation of seasonal active layer induced by freeze-thaw cycling. This paper firstly establishes theoretical models for the three sources of settlement including a statistical damage model for soils which experience cyclic freeze-thaw, a large strain thaw consolidation theory incorporating a modified Richards' equation and a Drucker-Prager yield criterion, as well as a simple rheological element based creep model for frozen soils. A novel numerical method was proposed for live computation of thaw consolidation, creep and freeze-thaw cycling in corresponding domains which vary with heat budget in frozen ground. It was then numerically implemented in the FISH language on the FLAC platform and verified by freeze-thaw tests on sandy clay. Results indicate that the calculated results agree well with the measured data. Finally a model test carried out on a half embankment in laboratory was modeled.
Key Words
settlement; frozen ground; freeze-thaw; thaw consolidation; creep
Address
(1) Songhe Wang, Fengyin Liu:
Institute of Geotechnical Engineering, Xi'an University of Technology, Xi'an Shaanxi, 710048, China;
(2) Jilin Qi:
College of Civil and Transportation Engineering, Beijing University of Civil Engineering and Architecture, Beijing 100044, China;
(3) Fan Yu:
State Key Laboratory of Frozen Soil Engineering, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou Gansu 730000, China.
Abstract
In this paper, based on understanding the design theories on soil stabilization, a series of soil stabilizers were prepared with different kinds of industrial wastes such as calcined coal gangue (CCG), blast furnace slag (SS), steel slag (SL), carbide slag (CS), waste alkali liquor (JY), and phosphogypsum (PG). The results indicated that when the Portland cement (PC) proportion was lower than 20% in the stabilizer, for the soil sample selected from Wuhan (WT) and Beijing (BT), the unconfined compress strength (UCS) of the stabilized soil specimens could increase 4.8 times and 5.4 times respectively than that of the specimens stabilized only by PC; compared with the UCS of the specimen stabilized only by PC, the UCS of the specimen which was made from soil sample WT and stabilized by the stabilizer composed only by CCG, CS, and PG increased 1.5 times, and UCS of the specimen which was made from soil sample BT and stabilized by the stabilizer composed only by SS, JY, and PG increased 4.5 times.
Key Words
industrial wastes; character classification; scientific combination; stabilizer; soil stabilization
Address
(1) Hao Yu, Xin Huang, Yongsheng Zhao:
Department of Civil Engineering, Beihang University, Beijing, China;
(2) Jianguo Ning:
Key Laboratory of Mine Disaster Prevention and Control, Shandong University of Science & Technology, Qingdao, Shandong province, China;
(3) Zhanguo Li:
Key Laboratory of Urban Security and Disaster Engineering, Ministry of Education, Beijing University of Technology, Beijing, China.
