Supporting the Observational Approach in Construction through Bayesian Analysis
by C.W. Boon and L.H. Ooi
ABSTRACT: The validation of design assumptions, as construction works are being carried out, is a vital component in geotechnical engineering. The feedback can be in terms of either the prescribed quality control tests, instrumentation and monitoring, or other site observations. As most of these can be evaluated through systematic logic, the use of data science methods or machine learning procedures is rarely necessary. There are, however, exceptions especially for cases in which: (i) there are several possible causes to the problems which are hard to pinpoint precisely, (ii) the quantum of data is overwhelming, and (iii) there is scatter in the of observed outcomes. Where these features are encountered, it is generally more efficient to process the data using a computer. This paper presents a possible way of interpreting the feedback obtained through observations in construction, via Bayesian programming, which is one of the many methods in machine learning. A case history discussing the performance of ground anchors in a deep excavation project is discussed.
KEYWORDS: Observational approach, Bayesian, Probability, Ground anchors, Artificial intelligence.
Effect of Shape of Footing on Coefficient of Elastic Uniform Compression of Polypropylene Fibre Reinforced Fine Sand
by C.N.V. Satyanarayana Reddy and G.V. Usha Rani
ABSTRACT: Synthetic fibre reinforced granular soils, particularly fine to medium sands have the benefits of improved shear strength and permeability and as a result found wide application as fill and backfill material. However, not much work is reported on coefficient of elastic uniform compression (Cu) of fibre reinforced sand. Cu is used in determination of soil spring stiffness and is an important essential parameter in design of machine foundations and structures subjected to cyclic loads. Hence, in the present study, the effect of addition of polypropylene fibre in fine sand is assessed by conducting small scale cyclic load tests in the laboratory. The study is also intended to evaluate the effect of shape of loading plate on Cu of fibre reinforced sand. Fibres of 6 mm and 12 mm length in proportions of 0.5%, 1.0% and 1.5% by weight are mixed with fine sand in the study. The study yielded the optimum percentage of fibre for stabilization as 1%, with 12 mm fibre more effective than 6 mm fibre. No shape effect on Cu of fibre reinforced fine sand is observed in contrast to unreinforced fine sand for which Cu of circular plate is 0.85 times the Cu of square plate of same size.
KEYWORDS: Fine sand, Coefficient of elastic uniform compression, Polypropylene fibre, Shape of footing.
Numerical Analysis for Appropriate Buried Depth of Cold-Proof Drainage Hole of a Tunnel
by Zhao Mao-Long and Zhu Wei
ABSTRACT: Based on the MIDAS/GTS finite element analysis software, taking a tunnel in Qinghai province as an example, fixing the position of main tunnel and holing through, just adjusting the buried depth of the cold-proof drainage hole, the change rules of displacement, stress and plastic zone in different buried depths of cold-proof drainage hole are analyzed. The influence of different buried depths for cold-proof drainage hole on the structure of main tunnel is revealed. The result shows that (1) the influence between main tunnel and cold-proof drainage hole is mutuality; (2) from the point of displacement change rule, the optimal effective buried depth for the cold-proof drainage hole of a tunnel in Qinghai province is from 5 m to 6 m; (3) from the point of stress change rule, the optimal effective buried depth for the cold-proof drainage hole is also from 5 m to 6 m; (4) bases on the stress homogeneity of the support and the material, from the point of plastic zone change rule, the optimal effective buried depth for the cold-proof drainage hole is from 4 m to 6 m; (5) eventually, on the basis of comprehensive consideration of the largest frozen depth, requirements of safe and economy, and influencing factors of construction of tunneling engineering area, the proper effective buried depth of the cold-proof drainage hole is confirmed to be 5 m, i. e., the proper buried depth of the cold-proof drainage hole is confirmed to be 8 m.
KEYWORDS: Tunneling engineering, Buried depth, MIDAS/GTS, Cold-proof drainage hole, A tunnel in Qinghai province.
Microstructural Change of Clay under Compression
by Riqing Xu, Jiaqi Jiang, Yuming Huang, and Jianlin Yu
ABSTRACT: Triaxial test and SEM test are combined to investigate the microstructural variation of Zhejiang marine clay during compression. SEM images are processed and analysed quantitatively, employing an improved determination for threshold. Then the concept of critical threshold is proposed. The test results show that: during compression, it was the pores with middle and large size which were mainly compressed. 2D porosity and fractal dimension showed a decreasing trend, indicating that pore morphology tended to be uniform. A linear relationship between 2D porosity and real porosity can be observed. Similarly, a positive correlation was established between real porosity and fractal dimension. No obvious orientation was found for both clay particles and pores. Finally, the ellipticity distribution of clay particles were stable and concentrated in the interval of 0.4~0.6. some of the macroscopic properties, such as isotropy and internal friction angle, can be a reflection of these variations in microstructure.
KEYWORDS: Triaxial compression, SEM, Microstructure, Critical threshold, Quantitative analysis.
Reliability of ULSD Theory in Geotechnics
by P. Koudelka
ABSTRACT: The article discusses the theory of ultimate limit state design (ULSD) and its consequences. An influence of definitions both characteristic and design values of soil parameters of EN 1997-1 (Code) is analyzed. The article has two basic theoretical aims: a) To demonstrate the incorrectness of ULSD in geotechnics and due to it in-effectivity and risk. b) To present a concept of a more plausible and correct design theory which is simpler and in compliance with mathematical principles. A case of slope design is chosen from basic geotechnical problems because slope masses are most sensitive. Slope designs based on the design approaches of the Code are compared with a direct design value definition-based approach. Slope analysis exploits the results of a statistical analysis of an extensive database of soil material properties. The analysis is based on data sets of sandy and fine-grained soils and demonstrates the risk of homogeneity for ULS designs. Another simple geotechnical design concept suitable also for advanced numerical methods is suggested and a procedure example is presented.
KEYWORDS: Design theory reliability, Design value definition, Soil property database, European standard EN 1997-1, Slope design.
Cyclic Parameters of Gas Oil Contaminated Fine Soils
by Fatemeh. Mir Mohammad Hosseini, S. M. Mir Mohammad Hosseini, and Hamidreza Jahangard
ABSTRACT: Extensive demands of societies to different oil products and the presence of these materials in large sectors of industrial and non-industrial regions may lead to pollute the shallow soil layers. Due to numerous obstacles and high expenses regarding remediation of these sites, knowing its altered properties may provide an adequate basis to more reliable land use of these sites for engineering purposes. In the present research, extensive studies regarding dynamic properties of gas oil contaminated sites consisting of pure and mixed kaolinite clay with fine sand contaminated by different gas oil contents ( up to 16%) have been carried out on remolded soil samples. Based on the results, the presence of gas oil up to a certain content (8-10%) leads to an increase in the dynamic shear modulus and decrease in damping ratio of cohesive soils. The presence of some fine sand in clayey soils would cause the above gas oil content to increase to 12%.
KEYWORDS: Gas oil, Clayey soil, Shear modulus, Damping ratio, Contamination.
Study on the Failure Pattern of Layered Soil using Finite Element Method
by Moumita Goswami and Arunav Chakraborty
ABSTRACT: In geotechnical engineering, it has always been a tough yet herculean task and also a subject of concern to carry out the stability analysis of slopes, since numerous failures of slopes and large settlements have been taking place causing a huge destruction of property and life. In this paper, various non-homogenous soil slopes with different layers of soil have been considered. A rigorous limit equilibrium method of slices i.e. Morgenstern-Price method is used to analyse the stability of the slope. Finite element shear strength reduction technique is also used for displacement calculations and comparison with limit equilibrium method. The soil parameters (c and φ) were kept as constants in each soil model. Thus, considering different slope angles of the soil mass, the Factor of Safety for each slope, pattern of formation of the slip surfaces along with the vertical, horizontal and total displacement has been studied.
KEYWORDS: Non-homogenous slope, Mohr-Coulomb failure, Finite element method, Factor of safety, Critical failure surface.
A Numerical Approach to Cyclic Consolidation of Saturated Clays
by Shay Haq, Tian Ho Seah, Kuo-Chieh Chao, and Cholachat Rujikiatkamjorn
ABSTRACT: A finite-difference numerical code is written in MATLAB to predict excess pore pressures and settlements under stepped/square wave cyclic loads. The numerical code is developed by approximating the Terzaghi’s 1D consolidation equation under time-dependent loading using the Crank Nicolson scheme. A method of applying the stepped/square wave cyclic loads is proposed. The code considers the nonlinear inelastic stress ~ strain relationship and can be used for both homogeneous and heterogeneous layers. The code is validated by comparing the results with analytical, experimental, and field monitoring data in the literature. A good agreement of the results shows that the code is well developed and can be used in predicting the settlements in practice. The analyses show that the maximum steady-state degree of consolidation calculated based on settlement and the maximum steady-state average degree of consolidation calculated based on dissipation of excess pore pressures decrease as the time period decreases. Below a specific time period, both remain unchanged. For a specific time period, both increase as the percentage of loaded portion in a cycle increases. Besides, the maximum steady-state degree of consolidation based on settlement, for a specific time period, increases with an increase in stress levels, which is due to the nonlinear stress ~ strain behavior.
KEYWORDS: Consolidation, Cyclic loads, Finite difference, Crank Nicolson, Settlements.
CPT & SPT Tests in Assessing Liquefaction Potential
by Ripon Hore, Sudipta Chakraborty, M. R. Arefin, and M. A. Ansary
ABSTRACT: The purpose of this research is to estimate the earthquake induced liquefaction potential of selected reclaimed areas of Dhaka city based on both Cone Penetration Test (CPT) and Standard Penetration Test (SPT). CPT and SPT data have been collected from ten (10) selected reclaimed areas of greater Dhaka city. The filling depth of the reclaimed areas varies from 1.5 to 13.5 m from the existing ground level (EGL). The values of peak ground acceleration (amax) and the magnitude (M) have been taken as 0.15g and7.5 respectively for the liquefaction analyses. The range of SPT-N, Cone tip resistance (MPa), local friction (kPa) and friction ratio varies between 1~42, 0.17~18.58, 0~273.2 and 0~9.34 respectively of the ten (10) selected sites of Dhaka city. Liquefaction potential has been estimated based on both CPT and SPT data. It has been observed that in reclaimed areas of Dhaka city especially for the locations reclaimed by dredged soil up to a filling depth of 1.5 to 4.5m there is high probability of liquefaction occurrence. In most of the cases, liquefaction zone for CPT have been observed in two different depth zones. On the other hand, liquefaction zone for SPT have been observed in only one zone. The highest value of Liquefaction Potential Index (LPI) for CPT and SPT are 21 (Bramangaon) and 28 (Purbachal) respectively. The lowest value of Liquefaction Potential Index for CPT and SPT are 3 (Kawran Bazar) and 1 (Kawran Bazar) respectively. The low liquefaction potential zone value has been found along the center and north south alignment of Dhaka City. The high potential zone has been found in the outer periphery of the study area.
KEYWORDS: Liquefaction potential, Soil profile, CPT, SPT, Cone tip resistance, Sub soil characteristics.
Properties of an Unsaturated Residual Soil behind a Failed Slope in Sri Lanka
by N. Vasanthan and S.A.S. Kulathilaka
ABSTRACT: Rain-induced slope failures are common in Sri Lanka. With the infiltration of rainfall, the matric suction at upper levels of the slopes reduces, perched water table develops, ground water table rises and the shear strength diminishes making the slopes vulnerable. Basic characteristics such as; Soil Water Characteristic Curves (SWCC), permeability function and unsaturated shear strength parameters have not been established for typical residual soil slopes in Sri Lanka. Undisturbed samples of soil obtained behind the scar at the location of a failed slope at Welipenna in the Southern Expressway were used in this study. Direct shear tests and permeability tests were done and matric suctions were measured with a miniature tensiometer. Pressure plate apparatus was used to obtain the SWCC. The SWCC obtained by alternate techniques and empirical procedures were in reasonably good agreement. Contribution of matric suction to the shear strength found to be in agreement with finding of other researchers.
KEYWORDS: Soil water characteristic curve, Permeability function, Tensiometer, Unsaturated residual soil, Matric suction.
Improvement of Soil Cohesion Using Microbial Acitvity
by Yustian Heri Suprapto, Budi Susilo Soepandji, Wiwik Rahayu, and Puspita Lisdiyanti
ABSTRACT: Bio-cementation process or commonly known as MICP (Microbial Induced Calcite Precipitation) on soil is strongly influenced by urease enzyme activity. High of urease activity the precipitation of urea and calcium chloride into calcite particles will also increase. The urease enzyme is obtained from B.subtilis bacteria with isolate number P3BG41 and P3BG43. The bacteria was grown under B4 urine medium at 37oC and pH +7 for five days observation. The B.subtilis was then daily measured its optical density and urease activity. The bacteria and combination of urea (CO(NH2)2) and calcium chloride (CaCl2) were daily injected into the sand to obtain the optimum results from the calcite precipitation. The highest value of urease enzyme activity occurs on the second day incubation. While the optical density was reduced on the second day, the soil cohesion reaches the highest value at that day. However, the friction angle value on the second day has the lowest point compared to the other day.
KEYWORDS: B.subtilis, Calcium chloride, Cohesion, Friction angle, Urea.
Estimation of Vibration Parameter for Blast Based on Shear Strength
by Ranjan Kumar, Pravin Prakash Yerunkar, and Kapilesh Bhargava
ABSTRACT: The topic of blast loads on structures has received considerable attention of researchers and various site specific empirical models for blast induced vibration parameters such as Peak Particle Velocity (PPV) already exist. However, these empirical models do not consider the variation in soil property namely shear strength. In this paper, a total of 166 blast data from various soil sites have been collected and used to propose a generalized empirical model to estimate PPV in terms of shear strength. The presented empirical model has been compared with the models of other researchers. It has been found that the presented model, having maximum coefficient of correlation and minimum standard error, can be directly used in calculation of PPV. In the absence of field blast vibration data, the present model will be very useful to evaluate blast vibration parameter by using only basic soil property specified in terms of shear strength. The present model has also been validated for various degrees of saturation of soil. It is concluded that the present model predicts slightly higher values (i.e. critical values for design purposes) for partially saturated alluvium and sand, and predicts fairly for partly saturated tuff, wet tuff, saturated alluvial and loess.
KEYWORDS: Disaster engineering, Geotechnical engineering, Safety & hazards.
Solution for Partially Penetrated Vertical Drain with Anchor Plate
by Trong Nghia-Nguyen, Le Thanh Cuong, Le Gia Lam, Phuoc H. Dang, and Phu-Cuong Nguyen
ABSTRACT: This paper presents a solution for partially penetrated prefabricated vertical drains (PVD) with less computational time and more accuracy than previous analytical solutions. A new impermeable boundary region at drain’s end is introduced to simplify boundary conditions and reduce the number of variables. Moreover, Laplace transform technique is utilized in this solution which could help to estimate smooth excess pore pressures with depth even in the early stage of consolidation. Results of the new modified solution have been verified against results of the current literatures. A case study by vacuum consolidation technique is presented to verify the current solution. Excess pore water pressure in the soil and the drain and are well agreement with the proposed solution. Derived degree of consolidation from field settlements shows not much differences than current approach. Those verifications indicate that the proposed solution is an effective tool in solving the consolidation problems of partially penetrated vertical drain.
KEYWORDS: Partially penetrated prefabricated vertical drain, Anchor plate, Analytical solution, Laplace transform technique, Soft soil.
Post-liquefaction Settlement Evaluation Method of Non-plastic Silty Sand
by Mei Hsun Chang, Jing Wen Chen, and Wei Feng Lee
ABSTRACT: Although the soil liquefaction potential has been the focus of considerable research, post-liquefaction subsidence has not yet received equal attention. In addition to this, non-plastic silty sand is observed in areas where severe earthquakes have occurred in Japan, Taiwan, and New Zealand, and thus the soil liquefaction engineering properties of such soil need to be investigated immediately. In the past five years, the authors applied the new sampling techniques to obtain high quality soil samples, and a series of soil tests were performed to determine the dynamic properties and post-liquefaction volumetric strain behaviours of non-plastic silty sand. In this study, the applicability of the current settlement evaluation methods in Taiwan is discussed based on relevant research results first. Then, for the convenience of use, the formulation of analysis process of the current evaluation methods is proposed. Finally, considering the influence of the volumetric strain behaviour of non-plastic silty sand, the modifications to current evaluation methods of the silty sand post-liquefaction settlement were then proposed using case verifications. It is considered that analysis results using the suggested modifications proposed in this study are more consistent than those of the previous methods.
KEYWORDS: Non-plastic silty sand, Post-liquefaction volumetric strain, Evaluation method.
End-Bearing Granular Pile-Effect of Non-Linearity of Soil and Granular Pile
by Prof. J.K. Sharma and Dr. Pooja Guptag
ABSTRACT: The solutions for consideration of linear and non-linear non-homogeneity of floating granular pile in homogeneous soil conditions are available, still solutions are not available for non-homogeneous end-bearing granular pile in non-homogeneous soil conditions. The present paper deals with the mathematical solution, for calculating the top displacement, normalized shear stresses, normalized axial load and percentage load transferred to the base for the non-homogeneous end-bearing granular pile in non-homogeneous soil conditions based on the elastic continuum approach. The contemplation of non-homogeneity of the granular pile in the stiffness range of stone columns/ granular piles in non-homogeneous soil mass is more realistic and could represent true in-situ behavior. The analysis concludes that with the increase of the degree of non-homogeneity of granular pile, the settlement influence factor decreases significantly for the shorter length of granular pile (L/d ≤ 20) because of higher values of deformation modulus of a granular pile at all depths as compared to modulus of longer ones. With the increase of soil non-homogeneity, the shear stresses decrease in the top 15 % and bottom 10 % portions of the granular pile while they increase in the rest (middle part) of its length. A comparative study has been made for present analysis and average analysis and it was found that by average analysis the values of settlement influence factors are underestimated in comparison to exact analysis therefore the average analysis is not suitable.
KEYWORDS: End-bearing granular pile, Relative stiffness of bearing stratum, Relative stiffness of granular pile, Settlement influence factor.
Hypoplastic Model with Intergranular Strain: Dependence on Grain Properties and Initial State
by S. Nagula and Prof. Dr. Ing.,J. Grabe
ABSTRACT: The Hypoplastic model is introduced and the procedure to determine the model parameters along with intergranular strain parameters is discussed in detail. Static trial tests and load/displacement controlled oedometer tests are performed to determine the hypoplastic model parameters. The dependence of the hypoplastic model parameters on initial density of granular materials is studied. Intergranular strain parameters are conventionally determined by resonant column tests. An innovative method based on static triaxial setup coupled with stress path test method is employed to determine the intergranular strain parameters. Parameters are determined for 5 different naturally existing sands. The dependence of the model parameters, on density, stress state and grain assembly properties of the sand is studied. The elastic strain range within which the incremental stiffness remains constant after strain reversal is studied in conjunction with the grain properties and the validity of the assumption that the governing parameter is a material independent constant is commented upon. The model parameters are verified against results of standard element tests.
KEYWORDS: Hypoplastic, Intergranular, Strain reversal, Incremental stiffness, Sand.
Effect of Permeability Variation in Vacuum Consolidation
by Van-Tuan Vu, Yu-you Yang, and Anh-Tuan Vu
ABSTRACT: The varying coefficient of permeability plays a major role in increasing the accuracy of the numerical prediction results. This paper aims to evaluate the range of deviation of numerical results if the varying coefficient of permeability is not used during the consolidation time. Four models, one with constant permeability and the others with the varying coefficient of permeability corresponding to different values of Cc/Ck, were used to simulate an axisymmetric single vacuum wellpoint. Comparing those predicted values together and to the measured values, the results show that: the settlement value and the decrease in pore water pressure value of the model which did not consider the change in permeability coefficient were higher than those of the models which considered the change in permeability coefficient during the consolidation process; the bigger the Cc/Ck ratio, the smaller the settlement and the smaller the decrease in pore water pressure.
KEYWORDS: Soft ground, Vacuum consolidation, Vertical drain, Vacuum wellpoint systems, Finite element method.
Test Equipment and Application of Compression Properties of MSW
by Gang Zeng, Feng Quan, Dan Hu, Jing Wang, Jun Ma, and Xinminnan Hui
ABSTRACT: In order to study the compression characteristics of municipal solid waste (MSW), a set of test device was independently developed. Five kinds of loading methods were analyzed, and the physical loading method using two levels of levers was selected. The experimental methods and operation process of the device were introduced. The laboratory test of compression characteristic of MSW by using self-developed device was carried out. Test application results show that the device can realize all pre-designed functions, and have the advantages of convenient operation, stable loading and small occupied floor space. As the stress is 100 kPa, 200 kPa, 300 kPa, 400 kPa, the strain of MSW is 42.4%, 49%, 54.1% and 59.25% respectively. The compression amount of the first 6 days reaches about 80% of the total compression. The compression amount of the pre-test specimen increases with the increase of the pressure, while the deformation rate of the later stage decreases. The instantaneous strain of MSW is basically linear to the pressure. The research results enrich the experimental equipment for studying the compression characteristics of municipal solid waste so as to provide data support for the subsequent research on the settlement model of landfill.
KEYWORDS: MSW, Compression properties, Test equipment, Laboratory test.
The Durability of Soil-Cement Columns in High Sulphate Environments
by Pham Van Ngoc, Brett Turner, Jinsong Huang, and Richard Kelly
ABSTRACT: Soil-cement column is a geotechnical solution used for ground improvement in coastal areas. However, after long periods of exposure, the strength of these columns may decrease to below their designed safe bearing capacity, ultimately resulting in failure. In this paper, the effects of high sulphate concentrations (100%, 200%, 500% and 1000% that of seawater) on the durability of soil-cement samples were examined. In addition, the simple simulation model was applied to predict the deterioration depth and long-term strength of the soil-cement columns. The results show that the deterioration is more pronounced and occurs deeper in the presence of high sulphate concentrations. For instance, the strength of a 0.5 m diameter column exposed to 200% seawater will fall below the minimum design strength after 75 years. For higher sulphate environments (5 to 10 times that of normal seawater) the same column would never reach the minimum design strength requirement. Consequently, this has significant implications on soil-cement column when used to stabilise soils in high sulphate environments.
KEYWORDS: Soil-cement column, High sulphate environment, Long-term strength, Needle-penetration test.
Causes of Damage of Rural Road in Coastal Areas of Bangladesh
by Md. Jahangir Alam, Mohammed Emdadul Karim, and Md. Shamsul Hoque
ABSTRACT: Developing countries spend a lot of budget each year for elevating, widening or repairing the existing coastal rural roads. These rural roads are constructed for a design life of 10 years. But these low volume roads loose serviceability within two or three years. To find out the reasons of less sustainability, different rural road sites in coastal region were visited by the authors and sandy soil (used for Improved Subgrade) and clayey soil (borrow pit soil used for side slope and shoulder) were collected from 28 sites. Grain size analysis, liquid limit and plastic limit of collected samples were determined. Fineness Modulus (FM) of sandy soils ranged from 0.00 to 0.50 and the most borrow pit soils are lean clay. Dynamic Cone Penetration (DCP) tests were conducted on pavement and shoulder. The test results were analyzed and compared with the Local Government Engineering Department (LGED) recommended DCP values for rural road by employing the AfCAP LVR-DCP software. It is found that the DCP values of base under pavement and shoulders were inadequate. Several reasons were identified which are responsible for less sustainability of rural roads. The reasons are use of unsuitable material, poor compaction, borrow pit location at toe, vehicle movement over soft shoulder, consolidation settlement due to soft soil under road embankment, inadequate design of palisading and slope protection, erosion of side slope by wave action. A new road widening methodology is proposed for making sustainable rural road in coastal areas of Bangladesh.
KEYWORDS: Unconfined compression test, Shear strength, Lime, Fly ash, Slag, Rural road, Compaction, DCP.
Laboratory Study on Natural Fibre Amended Fly Ash as an Expansive Soil Stabilizer
by B. Soundara, S. Selvakumar, and S. Bhuvaneshwari
ABSTRACT: Expansive soil subgrade pose major problems for the pavements due to their volume change characteristics. In the present investigation, the suitability of fibre reinforced fly ash on the stabilisation of expansive soil is studied. Coconut fibre is chosen as natural reinforcing fibre with a cut length of 10 mm and used in different percentages such as 0.25, 0.5 and 1% along with fly ash content of 20% of dry weight of soil. Laboratory tests includes standard Proctor tests, swelling pressure tests and California Bearing Ratio (CBR) tests were conducted to determine the maximum dry density (MDD), optimum moisture content (OMC), swelling pressure and strength of the soil with and without fibre reinforced fly ash matrix. With the addition of admixtures, the OMC is decreased and MDD is increased, the swelling pressure is decreased drastically and CBR values increased with the addition of admixtures showing an optimum improvement for soil with 0.5% fibre and 20% fly ash content. Thus the test results favoured the utilisation of waste materials such as fly ash and natural coconut fibre to enhance the suitability of stabilized expansive soil as subgrade for pavements.
KEYWORDS: Stabilization, Coconut fibre, Fly ash, Expansive soil, Subgrade.
Soil Model Effects on Deep Excavations Analysis
by S. Ghaffarpour Jahromi and H. Ataeeian Dehkordi
ABSTRACT: Nowadays, excavation is considered as one of the sensitive and important steps of urban construction that engineers are always attempting to analyze, design, and construct it by selecting various methods. The importance of this subject is conspicuous when the analysis of displacement and deformations around the excavation is necessary according to the national building regulation due to the presence of buildings in this area, which are of high sensitivity to asymmetric settlement. Therefore, in addition to the stability analysis of excavation, engineers are also dealing with the assessment and prediction of deformations and displacements of its surrounding by using geotechnical site specifications, excavation geometry, surrounding overloads, and simulating the excavations stages. The analysis of displacement and deformation is highly dependent to the constitutive soil model and the use of an appropriate model that imitates the actual behavior of the soil is of significant importance in the simulation of soil behavior in numerical software. In the present study, a comparison investigated between the results obtained from hardening-soil and Mohr-Coulomb constitutive models for a case study of a 16.5m deep excavation in Tehran city with the numerical method of finite element analysis. The results show that the soil behavior and the excavation operations induced displacements are more similar to the reality if the hardening-soil constitutive model is selected compared to the Mohr-Coulomb constitutive model.
KEYWORDS: Excavation, Soil model, Stability, Deformation, Analysis.
A Review on Rock Slope Stability: Failure Mechanisms, Stabilization Techniques and Implications for Mining Engineering
by William Ngaha Tiedeu, Deyi Jiang, Jie Chen, and Jinyang Fan
Abstract: Mines worldwide are now exploited at very large depths to recover minerals lying within the rock strata. The increase in the mining depth often leads to real risk of large-scale stability failure. This would further be aggravated by mining companies seeking to realize large profits by often operating at the steepest possible slope. As the slope angle increases, its stability decreases and in case of collapse, casualties are often immense. It is therefore crucial to conduct a thorough analysis when designing slopes. In this review paper, we have gathered the most relevant and updated information regarding rock slope stability and its practical application in the field of mining engineering. Specifically, after reviewing the principle underlying rock slope stability, we have presented a clear procedure for geological data collection and computational techniques used for slope analysis. Stabilization and protection techniques used in rock slope have also been presented and in the end, we have analyzed how these different technologies are applied in the field of mining engineering through bench design in open-pit mines and shaft design in underground mining.
KEYWORDS: Slope analysis, Discontinuities, Data collection, Computer analysis, Mine design.
Permeabilities of Cement-Treated Geomaterials Subjected to Varying Water-Cement Ratios
by Hai-lei Kou, Meng Yang, Wang-chun Zhang, Jing-kui Wang, and Qing-ming Song
ABSTRACT: The effect of cement-grouting plays an important role in the engineering property of cement-treated sands. To investigate the effect of different water-cement (w/c) ratios on sand cementation, one dimensional seepage test was conducted with different particle size in this study. The permeability coefficient and uniaxial compressive (UC) strength of treated samples were studied respectively. Test results indicated that with the increase of w/c ratio, the increase of permeability coefficient of sands with particle size 1.25-2.50 mm is larger than that of sands with particle size 2.50- 5.00 mm after 7 days curing time. The UC strength of treated samples decreases with the increase of w/c ratio. The larger the particle size, the smaller the reduction of UC strength. These phenomena are closely related to the formed bond strength between sand particles.
KEYWORDS: One-dimensional seepage test, Water-cement ratio, Permeability coefficient, Porosity, Uniaxial compressive strength.
Tunisian Phosphogypsum Challenges
by Hajer Maazoun and Mounir Bouassida
ABSTRACT: The accumulation of phosphogypsum (PG) produced till 2015 makes its management a real challenge to the Tunisian authorities and put the Tunisian Chemical Group (TCG) to face a challenge at large scale as the specified storage embankments knew considerable extensions in terms of heights and areas. Several studies were elaborated subsequently in 2007, 2012 and 2013 to focus on the stability of Sfax and Skhira PG embankments’ and showed two different chemical and mechanical behaviours according to the experienced deposition process. In 2012, it was revealed that the wet PG embankment of Sfax City with 56m height, 53Ha area and 32° slope can attain 70m maximum height. This embankment can reach 100m in height if a reinforcement technique will be used. This deposition process is well recommended to ensure a better interaction between the embankment and the existing ground surface. Using the dry deposited process, the area of the PG embankment of Skhira City covers 112Ha and presents two elevation levels of 25m and 55m in 2013. However, the dry deposited process results in a damaged embankment profile, significant settlements and lateral displacements. Therefore, a PG embankment of 100m height cannot be targeted. A reinforcement of the embankment by High Density Polyethylene geotextile (HDPE) layers at increments of 4m from 55m elevation allows reaching 130m of height. Comparative study was raised between the wet and the dry process and resulted in favour of the wet process from both industrial and geotechnical perspectives. Thus, the TCG expects turning all its deposition processes to the wet one. A characterization of Tunisian Phosphogypsum was carried out based on the previous studies performed on Phosphogypsum embankments of Sfax and Skhira Cities and on the experimental tests performed on dry deposited Phosphogypsum. A numerical model is built in an attempt to propose an optimized solution to the PG specified storage areas.
KEYWORDS: Embankment, Phosphogypsum, Stability, Environment, Height, Slope.
Shaft Capacity Assessment of Recharge Impulse Technology
by Wafi Bouassida, Essaieb Hamdi, Mounir Bouassida, and Yuri Kharine
ABSTRACT: This paper discusses the performance of Recharge Impulse Technology (RIT) in increasing the shaft capacity of deep foundation systems regarding classical set-up processes. Based on the major contributors behind such performances: the shape effect and the electrical discharge installation, a case study is analyzed in view of highlighting that the coupling of these two components leads to a reasonable estimation of RIT shaft capacity with reference to in situ loading tests. A related design chart estimating the contribution of the shape effect in the increase of the shaft capacity had been drawn and a mean power law was proposed through a parametric study on the adhesion factor.
KEYWORDS: Load test, Pile, Recharge impulse technology, Shaft capacity.
Back Analyses of Historical Ground Subsidence Induced by the Lowering of Groundwater Table
by R.N. Hwang and Z.C. Moh
ABSTRACT: Numerical analyses were conducted to correlate the ground settlements observed in the central area of the Taipei Basin with the variations of the piezometric levels in the Jingmei formation. The relationship of the historic changes of the piezometric levels and the ground settlements induced by the consolidation of the Songshan formation was established by matching the results of the analyses with the observed settlements. The influence of replenishing water from rivers and infiltration of surface water into the Songshan formation was accounted for by assuming a linear distribution of water pressures with zero pressure at a level of replenishment and a pressure corresponding to the piezometric level in the Jingmei formation at the bottom of the Songshan formation.
The records of the ground settlement and piezometric levels in the Jingmei formation obtained in the Beimen area were used in the analyses and the results of analyses indicated that the ground could have settled by 0.38 m before the initial reading of settlement was taken in 1950, giving a total settlement of 2.55 m, instead of 2.17 m reported in literature (Wu 1987). It has also been found that consolidation of the sandy layers contributed to more than half of the settlement.
KEYWORDS: Taipei Basin, Jingmei formation, Songshan formation, Groundwater pumping, Dewatering, Ground settlement, Consolidation.
Deliberate Failure of Slurry Trench Excavations in Soft Clay
by E. DiBiagio, F. Myrvoll, A .S. Balasubramaniam, J. M. N. S. Jayasiri, G. Aas, and E. Oh
ABSTRACT: The instrumentation used and the observations made on full scale field tests carried out in two slurry trench excavations in soft marine clay (at Vaterland, Oslo) are presented and discussed. The excavations were 1 m x 5 m and 1 m x 1.8 m in internal cross section and 20 m deep. The testing program was carefully planned to obtain information which could confirm the overall stability of the trenches using water instead of expensive special slurries. The instruments used included a precision settlement gauge, numerous settlement reference points and electrical piezometers, slope indicator casings and specially designed hydraulic gauges for instantaneous measurement of the inward movement of the vertical walls of the trenches. This project illustrates the importance of large-scale tests and instrumentation in Geotechnical Engineering.
KEYWORDS: Full-scale test, Slurry trench excavation in soft clay, Geotechnical instrumentation, Stability, Deliberate failure.
