Prediction of Piled Raft Foundation Settlement – A Case Study
By Phung Duc Long
ABSTRACT: Piled raft foundation is an effective foundation method. For the last few decades, the rapid growth of cities all over the world led to a tremendous increase in the number as well as the height of high-rise and super high-rise buildings, even in unfavourable subsoil conditions. Piled raft foundation concept, in which piles are only used for reducing the settlement, not for carrying the whole load from the structure, has been successfully applied for many projects. In this paper the result from the Author’s experimental study, which strongly supports the concept of settlement-reducing piles is reviewed. Basing on the experiment, which is surprisingly in good agreement with the monitoring results of case histories many years later, a simplified design method is proposed. In this paper, the method is used for conceptual design of a large high-rise complex. In combination with FEM analyses using Plaxis 3D, the simplified method is a reliable tool for conceptual design of piled-raft.
KEYWORDS: Piled-raft, Pile foundation, Field model test, Simplified method, FEM, Plaxis 3D
Geotechnical Adaptation to the Vietnamese Coastal and Riverine Erosion in the Context of Climate Change
By K. Yasuhara, M. Tamura, Trinh Cong Van and Do Minh Duc
ABSTRACT: Climate change related disasters such as erosion along riverine and coastal areas of the Mekong Delta in south and the Red River Delta in north are expected to be exacerbated by land subsidence, sea-level rise (SLR), and magnified typhoons. Adaptation to severe erosion is expected to respond to regional circumstances and the demands of local residents. Based on the expectations outlined above, for soft adaptation, attempts were made to conduct perception surveys of local residents, in addition to field surveys of erosion at riverside and coastal areas using an un-crewed aerial vehicle (UAV). Furthermore, for hard adaptation, a proposal is made to conduct pilot field tests at the coast for reinforcing coastal dykes using the combined technique of locally available materials with cost-saving eco-geosynthetics in addition to application of ICT. This paper explains the possibility of smart adaptation combining soft and hard adaptation to reduce severe coastal and riverine erosion in the Vietnamese deltas.
KEYWORDS: Climate change, Erosion, Adaptation, Geosynthetics, Natural fibers, UAV, Dyke
Bidirectional Tests on Two Shaft-Grouted Barrette Piles in Mekong Delta, Vietnam
By H. M. Nguyen, B. H. Fellenius, A. J. Puppala, P. Aravind, and Q. T. Tran
ABSTRACT: The piled foundation design of the 40-storey Exim Bank Building in Ho Chi Minh City, Vietnam, included bidirectional static loading tests on two shaft-grouted barrette piles tested in September 2013. The soil profile consisted of organic soft clay on silty sand with some gravel and silty clay. The cross-section area of the barrette piles, TP1 and TP2, was 2,800 mm by 800 mm. They were excavated to 65-m and 85-m depth, respectively, using grab-bucket excavation techniques with bentonite slurry and guide wall advanced ahead of the hole. For each pile, the bidirectional cell assembly was installed 16 m above the pile toe level and the reinforcing cage was instrumented with diametrically opposed vibrating wire strain-gages at three levels below and five (TP1) to eight (TP2) levels above the cell level. Shaft grouting was carried out along a 40-m length above the TP1 pile toe and along a 20-m length above the TP2 pile toe. The static loading tests were performed 23 and 25 days, respectively, after the piles had been concreted. Analysis of strain-gage records indicated Young’s modulus values of about 27 GPa on the nominal cross section of the piles. Simulation of the measured load-movement response indicated that the shaft resistance response was hyperbolic. The test schedule was interrupted by unloading/reloading cycles, which disturbed the gage data and included uneven load-holding durations which exacerbated the analysis difficulty.
KEYWORDS: Bidirectional tests, Barrette piles, Shaft grouting, Analysis of strain-gage records
Soil Characterization and Land Subsidence Prediction for the First MRT Line in HCM City
By Pham Huy Giao and Ta Thi Thoang
ABSTRACT: The Mass Rapid Transit (MRT) system is being constructed in HCM city to meet the transportation needs of a fast growing population and rapid urbanization. Being located in the Sai Gon-Dong Nai delta HCM city area has low elevations and is underlain by a sequence of clayey, silty and sandy soil layers. Land subsidence due to groundwater extraction had been suspected and observed in HCM city. With the increasing groundwater pumping, land subsidence is unavoidable and its effect on infrastructure development of the city has to be seriously considered and controlled at certain degree. The presence of the underlying thick and soft clay layer is another important factor to contribute to land subsidence of the city. In this study, geotechnical characterization of the subsoil along the first MRT line was carried out. Prediction of land subsidence along this MRT line was conducted using a FEM consolidation code. As a result, a subsoil profile of 9 soil layers was characterized, including a soft and compressible clay layer located on top of the soil profile from surface to the depth of more than 20 m. The land subsidence analysis results found that the soft clay layers are vulnerable to drawdown caused by groundwater extraction.With a drawdown of 5.5 m in the second aquifer for a period from 1999 to 2009 a total subsidence of 0.35m can be reached after 20 years at Km. 2.0, the junction zone between the underground metro segment and the elevated train segment, while a maximum subsidence of 0.45 m could be found after 20 years at Km 3.0 where the very soft and soft clay layer is thickest.
KEYWORDS: HCM City, Subsoil database, Land subsidence, MRT line, Groundwater extraction, Soft clay, Sai Gon- Dong Nai delta
Soft Ground Improvement by Deep Cement-Mixing Technique in Southern Vietnam
By Dinesh Raj Shiwakoti and Ryuji Manai
ABSTRACT: This paper examines the application of deep cement-mixing technique in improving engineering properties of soft grounds at nine different sites in southern Vietnam’s typical soft soil deposits. The exercise consisted of running a series of laboratory tests on undisturbed soil samples and their mix designs with cement, and of field trials followed by field application of 500,000 m of the cement treated columns having 600mm diameter. The field treatment was done using Dry Jet Mixing (DJM) technique. After the field trials and applications, cores were extracted from the treated grounds to evaluate improvement in their engineering characteristics. Both the laboratory and the field results revealed a drastic enhancement in strength, stiffness, and permeability of the treated soft soils, thus establishing the deep cement-mixing technique’s capability to treat southern Vietnam’s soft grounds.
KEYWORDS: Deep cement-mixing technique, Dry mixing method, Soft ground, Uniaxial compressive strength, Stiffness, Permeability
Over Consolidation Feature of Clayey Soils in Southern Vietnam According to Piezocone
By Bui Truong Son, Le Hong Quang, Lam Ngoc Qui
ABSTRACT: Over-consolidation ratio (OCR) is an important geotechnical parameter for predicting undrained shear strength, lateral pressure ratio and settlement of clayey ground. Based on the reliable data of consolidation test results of samples taken by piston tube and piezocone, relationship between over-consolidation ratio and normalized penetration resistant is established and analyzed. The results show that the relationship of the two quantities can be presented by linear function with coefficient k*, which ranges from 0.17 to 0.22. Using the normalized cone resistance Qt allows analyzing behavior and stress state of over-consolidated clay more reasonable than the corrected resistance qt.
KEYWORDS: Soft soil, Over-consolidation ratio, Piezocone, Relationship
Ground Improvement Using Soil-Cement Method: A Case Study with Laboratory Testing and In-Situ Verification for a Highway Project in Southern Vietnam
By Phan To Anh Vu
ABSTRACT: This article presents the experimental unconfined compressive strength results of soil-cement columns to improve the soft soil gained by Tan Son Nhat-Binh Loi Outer Ring Road Project, located in Ho Chi Minh City, Vietnam. Initially, in the laboratory, two cement materials were chosen to stabilize the soil with different depths, including Stable Soil cement and tower (60%) slag cement. The specimens were prepared by mixing method. Three trial ratios of cement content (i.g. 160 kg/m3, 200 kg/m3, and 240 kg/m3) mixed into soil which obtained from 3m, 6m, 9m, 12m and 15m depths from in-situ. All specimens were cured at the age of 7-, 14-, 28-day with the temperature of 20±3°C. The laboratory test results revealed that the Stable Soil cement has a greater unconfined compressive strength than tower (60%) slag cement and it was suitable with soil condition in this area, irrespective of the curing time and depth. Based on obtained results from three trial cement ratios, the target cement content of 240 kg/m3 was satisfied not only a required compressive strength (≥ 24 kgf/cm2) but also a low-cost. In site, the deep mixing method was applied to produce soil-cement columns. The unconfined compressive strength of core specimens was tested at various depths of 3m, 6m, 9m, 12m, and 15m for test piles and official piles. The obtained results are expected to provide an experience for further design and construction in Ho Chi Minh city and its vicinity.
KEYWORDS: Soil-cement method, Sable Soil cement, Tower slag cement, UCS
Wide Storage Tanks on Piled Foundations
By Bengt H. Fellenius and Mauricio Ochoa
ABSTRACT: Foundation designs benefit from correlation to well-documented case histories. However, for the design of wide tanks storing liquids, in particular those requiring piled foundations, only few well-documented case histories exist. The authors have found five papers reporting settlement of wide tanks or large groups and have reanalyzed the records. The reanalyzes show that a large piled foundation can be modeled as a flexible raft placed at the pile toe level with the foundation load distributed according to Boussinesq stress distribution, and, for large piled foundations, that the capacity of an individual pile is not relevant to the foundation performance. The findings are used to address the analysis of a hypothetical large piled foundation for an 84 m diameter LNG tank at a site with a 60 m thick soil profile, consisting of clay, sand, and clay deposited over competent dense gravel. The differential settlement between the perimeter and interior piles and the effect of drag force and downdrag are discussed. The limitation of drag force as affected by the pile spacing and the weight of the soil in between the interior piles is addressed.
KEYWORDS: Wide storage tanks, Piled foundations, Settlement analysis
Discrete Modelling of Excavation in Fractured Rock by NSCD Method
By Tran Thi Thu Hang and Frederic Dubois
ABSTRACT: The presence of the network of discontinuities on intact rock is a special feature of nature rock masses. Non Smooth Contact Dynamics method (NSCD), a discrete numerical method with many strong advantages of the study on granular materials and has been recently used in rock engineering. LMGC90, the open-sourced numerical tool of NSCD, has demonstrated robust capacity in the modelling and mechanical analysis of diverse environments, masonry and rock included. In this study, a numerical modelling of a multi-phaseexcavation in fractured rock was realized. The simulation of the tunnelling was conducted with the consideration of the state of the excavation and its neighbouring rock blocks. The obtained mechanical behaviours of the model were analysed, and three failure mechanisms of the excavation vicinity during the tunnelling were aimed. The observed phenomena showed typical effects of two components of the rock mass (rock structure and rock material) to the stability of the excavation and the host rock mass.
KEYWORDS: Fractured rock, NSCD, LMGC90, Multi-phase-excavation, Simulation
A Method for Estimating Pile Group Settlement Considering Distribution of Pile Shaft Friction (SDF) – Application for Pile Groups in Vietnam
By Duong Diep Thuy, Pham Quang Hung, and Le Thiet Trung
ABSTRACT: Pile bearing capacity and settlement of pile groups are two most important considerations when design a pile foundation. The prediction of pile group settlement is always a difficult task. A model for pile group settlement considering distribution of friction along the pile, named SDF, is presented in this paper. Applications of the model for a full scaled experimental model by Koizumi et al (1967), Phung
(1993) and two major projects in Vietnam (Camau Fertilizer Plant and – Ecopark Tower 2) are presented to illustrate the proposed model. Comparison of the calculated settlements with the results using other methods and the measured data shows that the SDF method provided the best prediction for all these cases.
KEYWORDS: Pile group, Settlement, Friction along pile, Vietnam
Mechanical behaviour of Hai Duong Medium Sand in Triaxial Test and its DEM Simulations
By Nguyen Quang Tuan and Heinz Konietzky
ABSTRACT: This paper presents mechanical characteristics of Hai Duong medium sand – sampled from Chi Linh, Hai Duong – obtained from some laboratory tests. This sand is a typical constructional soil material and widely used in Northern Provinces of Vietnam. Specimens, obtained from compaction tests, were remoulded with dry unit weight of 95% of maximum dry unit weight. The drained triaxial compression tests on these dense sand specimens were performed under different confining pressures. Numerical simulations of the triaxial tests were carried out using the three dimensional particle flow code (PFC3D) with a non-linear contact model. Numerical results were directly compared with the corresponding laboratory test results. The simulations show, that the particle based code PFC3D is able to capture the mechanical behaviour of medium dense sand. Peak strength and stiffness of the sand specimens were well reproduced by the use of spheres with a simple rolling resistance model. The simulations also reveal the influence of the microscopic parameters of the model on the macroscopic behaviour of the sand.
KEYWORDS: DEM, Triaxial test, Sand
Influence of Geometrical Parameters of Soil-Cement Columns on the Average Settlement of Embankment on Reinforced Soft Soil – Numerical Analysis
By Tran The Truyen, Nguyen Van Hung, and Tran N. Hoa
ABSTRACT: This article contributes to analyze the behavior of foundation on soft soil improved by soil-cement columns (SCC). Axisymmetric model is used in foundation settlement analysis by finite element method with geotechnical characteristics gathered from some typical projects in Viet Nam. Influence of geometrical parameters such as SCC diameter, SCC spacing and SCC length are considered
in these evaluations. The results clarify the behavior of reinforced ground base and offer recommendations for the choice of relevant geometrical scheme of SCC system to improve soft soil in transportation projects in Viet Nam.
KEYWORDS: Soil-cement columns, Model, Embankment, Soft soil, Strain, Stress, Settlement, Viet Nam, Spacing, Length, Diameter.
Evaluation of Performance of Diaphragm Walls by Wall Deflection Paths for Deep Excavations in Central Ha Noi
By Benson Hsiung, Dao Sy Dan, and William Cheang
ABSTRACT: The objective of this paper is to evaluate the performance of diaphragm walls by wall deflection paths for deep excavations in Central Ha Noi. The commercial software PLAXIS 2D was used as a numerical tool for 2D finite element analyses in this paper. A deep excavation in Central Ha Noi is adopted as a basis for numerical analyses in this study. A benchmark analysis was firstly conducted on the excavation to verify the validity of material models and their input parameters for predicting wall deflections; following that the reference envelopes of wall deflection paths were delivered for various conditions of deep excavations in Central Ha Noi. Considering the current prediction, up to 72 mm of the maximum lateral wall displacement for an excavation have a 21.9 m of excavation depth. However, some assumptions made have to be further confirmed by comparing data observed later on. Reference envelopes of excavations have been developed and discussed in various conditions of the excavation. It is first found that the maximum lateral wall displacement at the first stage of excavation is roughly inversely proportional to the Young’s moduli of soils. In conclusion, changing wall thickness leads to the limited difference in reference envelope at shallow excavation stage, but it may not be true when the excavation goes deeper.
KEYWORDS: deep excavation, wall deflection, wall deflection path, reference envelope, PLAXIS 2D.
Effect of Vacuum Pressure Distribution on Settlement Analysis Results for an Improved Thick Soft Clay Deposit at Sai Gon-Hiep Phuoc Terminal Port, South of Vietnam
By Hoang Hiep and Pham Huy Giao
ABSTRACT: In the recent years ground improvement with preloading, PVD and vacuum pressure has become commonly used for many projects in Southern Vietnam, including that of Sai Gon-Hiep Phuoc (SGHP) terminal port. At this project site a very soft to soft clay layer was improved by a combination of three techniques as mentioned above. As the clay deposit is very thick, extending from the surface to the depth of 35m, the effect of vacuum pressure along the PVD and the immediately surrounding soil is of particular interest in term of its influence on the settlement analysis among other parameters, commonly considered in settlement analysis, such as soil properties, smear zone, PVD spacing etc. In this study, the effect of ratio between vacuum pressure at the bottom and the top of the drain (kp) on the settlement analysis results, was investigated using a Fortran code. It was found that kp varied from 0.85 to1.0 and its value could affect the matching of the calculated settlement curve with monitoring data if not properly chosen. In addition, the smear effect with RS equal to 3.0 and a PVD spacing of 1.0 m were found as optimal values for settlement analysis at the SGHP site.
KEYWORDS: Sai Gon-Hiep Phuoc port terminal, Soft clay, Ground improvement, Vacuum pressure, Settlement analysis
Characteristic of Unsaturated Soil of Earth Fill Dams in Vietnam
By Nguyen Thi Ngoc Huong and Trinh Minh Thu
ABSTRACT: In Vietnam, earth dams are generally used with in-situ soils having low clay content (especially earth dams at the central part of Vietnam). The knowledge, experience, theory for calculation, apparatus for unsaturated soils in Vietnam are still very limited, especially the studies of the influences of the shear strength of unsaturated soils to the stability of earthen structures. Therefore, the research to study the soil-water characteristic curve, shear strength and coefficient of permeability versus different matric suction on Vietnamese soil is an urgent issue and it has big scientific and practical meaning. This research shows that when the matric suction in the soil changes, the effective cohesion c’ would change, however the internal friction angle, f’, is almost unchanged for some type of soil in Vietnam. The experimental results would be applied to study the affect of unsaturated soil to the factor of safety of the slope.
KEYWORDS: Unsaturated soils, Earth fill dam, Seepage, Slope stability, Shear strength, Soil-water characteristic
Settlement management for urban tunnels: an example from France
By Alain Guilloux and Hervé Le Bissonnais
ABSTRACT: The TOULON highway tunnel is located in a very dense urban environment, and a much complex geology. The excavated section is about 120 m2 and the depth is in the range 15-35 m. The aim of the paper is to show how a great attention was paid to the settlements control: at the design stage through soils investigations, survey of existing constructions in regards to their sensibility to tunnel induced settlement, definition of settlements thresholds, and choice of ground pre-reinforcement techniques; during the construction, by heavy monitoring of deformations and continuous adaptation of the supports to the actual settlements and buildings behavior. This case history is an illustration of how the settlements induced by tunneling can be managed for any urban tunnel, mainly in old cities.
KEYWORDS: Tunneling, Settlements, Monitoring, Compensation grouting
