Estimating Pile Axial Bearing Capacity by c-Φ Derived from Pressuremeter Test
by T-L. Gouw
ABSTRACT: Due to its rather brittle nature, retrieving undisturbed samples of Jakarta cemented greyish stiff clay, often found at a depth of 30 to 120 m, is very difficult. Good and reliable effective shear strength parameters, i.e., c’ and Φ’ values, obtained from triaxial test are hardly available. By modifying cavity expansion theory, Gouw (2017) was able to derive these effective shear strength parameters through Pressuremeter in situ test stress strain curve. It was found Jakarta cemented clay exhibiting a drained behaviour when loaded. Its effective cohesion, c’, values are linearly increasing with depths, averaging from around 95 kPa at 20 m to around 475 kPa at 100 m depth, while its effective friction angle Φ’ values are within 20o – 30o, averaging to around 24o. The values found to be similar to the values derived from CIU triaxial compression test from relatively good undisturbed samples. This paper presents the methodology in deriving the shear strength parameters and then applying the derived Pressuremeter c’ and Φ’ values to estimate the pile axial bearing capacity through finite element simulation and comparing it with the commonly known SPT method applied in Jakarta.
KEYWORDS: Pressuremeter, Modified cavity expansion theory, Effective shear strength parameters, Pile axial capacity.
Volcanic Cohesive Soil Behaviour under Static and Cyclic Loading
by W. O. Sumartini, H. Hazarika, T. Kokusho, and S. Ishibashi
ABSTRACT: The objective of this study is to evaluate the behavior of reconstituted (disturbed) samples of volcanic soil under static and cyclic loading using a series of undrained static and cyclic tests. The static test results show that under low confining pressure, the disturbed sample is contracted and then dilated with no sign of temporary liquefaction. On the contrary, the undisturbed sample is dilated under low confining pressure and becomes contracted when reaching the peak of the soil strength. However, under high confining pressure, both disturbed and undisturbed samples show a contraction. The cyclic test results show cyclic mobility behavior under an investigated cyclic stress ratio. At a low cyclic stress ratio, the shear strain increases slowly, and after a certain number of cycles, the shear strain significantly increases. Conversely, the shear strain increases gradually at a high cyclic stress ratio. These results indicate a contradictive behavior of the soil under different confining stress and cyclic stress ratios.
KEYWORDS: Static triaxial test, Cyclic triaxial test, Volcanic soil, Reconstituted samples, Soil behavior
Reliability Assessment on Deep Braced Excavations Adjacent to High Slopes in Mountain Cities
by R. H. Zhang, W. G. Zhang and Z. J. Hou, and W. Wang
ABSTRACT: Due to rapid urbanization, the land available for city construction and development becomes more and more scarce. Within a built-up environment, the construction safety of a deep excavation becomes more crucial with the ever-increasing building density. For deep excavations in mountain cities, the areas of the foundation pit to be excavated are generally the passive soil pressure zones for the upper existing slope. Construction disturbance, weakening of the passive area, as well as the formation of even higher slope through the superposition of foundation pit to the existing upper slope, will result in more deformation and even failure of the slope. This study numerically investigates the influences of excavation geometries, the system stiffness and the distance between the excavation and slope and develops simplified ultimate and serviceability limit state surrogate models with regard to the overall factor of safety and the maximum lateral wall deflection of the supporting system, respectively. Considering the uncertainties of the design parameters, a probabilistic framework combining the estimation models with First-Order Reliability Method (FORM) is proposed to determine the probability that a threshold factor of safety or the pre-defined maximum wall deflection is exceeded. The study presents preliminary guidelines for reliability assessment of ultimate and serviceability limit state designs for deep braced excavations adjacent to high slopes in mountain cities.
KEYWORDS: Braced excavation, Upper slope, Wall deflection, Factor of safety, Reliability assessment.
Effect of Compaction Ratio, Frequency, Stress Amplitude and Cyclic Stress Ratio on the Dynamic Characteristic of Sea Sand Material under Vehicle Loading
by C.L. Nguyen, H.H. Nguyen, Q.P. Nguyen, D.H. Ngo, and D.M. Nguyen
ABSTRACT: Haiphong city is situated on the North-Eastern coast of Vietnam. This city has a large coastal and sea area, which is an advantage for marine economic development. However, in order to reclamation the coastal area, river sand material is much demand which leads to face some environmental problems due to the exploitation of river sand. Thus, the intensive laboratory experiments were conducted including physical, chemical and mechanical tests of river sand and sea sand to evaluate the potential use of sea sand in road embankment in Haiphong city. The samples were prepared by compacting to value of 90% and 95% of maximum density defined by the Standard Proctor test. Consolidated undrained cyclic triaxial tests were conducted for sea sand samples and river sand samples. The cyclic triaxial test results showed that all samples are not liquefied under normal vehicle conditions which corresponding to cyclic deviator stress about 8 kPa and frequency of 1 Hz. In addition, sea sand samples were not liquefied when increasing the compaction effort to 95% of maximum density. Therefore, it is possible to use sea sand instead of river sand in some cases for reclamation land in the Haiphong area.
KEYWORDS: Dynamic properties, Road embankment, CU cyclic triaxial test, Liquefaction.
The Use of the Observational Method in Deep Excavations for the Realization of a Residential Compound in a Complex Hydrogeological Context
by M. Carassini, F. Bucci, and A. Antiga
ABSTRACT: The urban redevelopment works of the “Railway Station Area ex-Boschi”, was developed on an area of nearly 17.0000 m2, it entailed the execution of deep excavations in a difficult geotechnical and hydrogeological context. In order to overcome these critical issues a design based on an observational approach was developed. This design considered several possible hydrogeological scenarios and staged excavations over small areas.
The Observational Method has been successfully extended from the more traditional case of tunneling works to the less usual case of deep excavations in large construction areas.
KEYWORDS: Observational method, Deep excavations, Diaphragms.
Performance of Helix Piled Raft Foundation in Tropical Fibrous Peat Soil Under Traffic Loads
by A. Arsyad, A. B. Muhiddin1, T. Harianto, E. Budianto, P. Sangle, and A. B. Firmansyah
ABSTRACT: This paper presents the investigation of settlement based performance of helix piled raft foundation under traffic load through analytical and numerical methods. The analytical method is based on the concept of PDR analysis of piled raft where the stiffness of helix piled raft is computed from the stiffness of helix pile and raft with a certain helix piled – raft interaction factor. In this study, the stiffness of helix pile to peat soil is estimated by using a modified Randolph and Wroth equation, incorporating the mechanical behavior of helix pile. On the other hand, the stiffness of raft is determined by using Richart et al equation. In the numerical model, 3-dimension FEM model of helix piled raft is undertaken in which helix pile is modeled as fixed end anchor, and raft as a plate above soft peat soil. The effect of helix pile number on the bearing capacity and settlement of helix piled raft foundation system is investigated. The results reveal that the stiffness of helix pile is too small compared to the stiffness of raft with the ratio from 1/6 to 1/4. The helix pile stiffness is much influenced by the number of helice and the radius of helice in a single helix pile. Since the stiffness of helix pile is small, such critical number of helix piles is needed to have effect on the foundation system. Below this number, helix pile is insignificant to have effect in the helix piled raft foundation system, and the elasticity of the raft plays important role. In general, however, it is obvious that the increasing number of helix piles can decrease the elastic settlement of helix piled raft foundation when it is subjected with traffic load. In the stiffness ratio of helix pile to raft at 1/6, the increasing number of helix pile can reduce the settlement up to 80%, whereas that in the stiffness ratio helix pile to raft at ¼ can reduce the settlement by 65%. These finding s would beneficial for development of alternative helix piled raft foundation for road infrastructure in tropical fibrous peat soil.
KEYWORDS: Tropical fibrious peat soil, Helix piled raft, Stiffness, Elastic settlement.
Application of Distributed Fibre Optic Sensor (DFOS) in Bi-directional Static Pile Load Tests
by S. C. Lee, B.P. Tee, M. F. Chong, H. Mohamad, K. A. Ang, and P. P. Rahardjo
ABSTRACT: This paper describes a case study of a bi-directional load test on a working pile located at limestone formation area. The test pile was instrumented with Distributed Fibre Optics Strain Sensors (DFOS) to measure the change in strain and to determine the pile shaft friction and end bearing. This paper highlights the advantages and limitations of DFOS in measuring the continuous strain profile of a test pile. Interpretation on the anomalies detected through the DFOS results is discussed. The paper aims to introduce to the industry, the superior information obtained using the innovative fibre optic technology for geotechnical testing and monitoring.
KEYWORDS: Bidirectional static load test, Distributed fibre optic strain sensor, Pile load test.
Numerical Study of Ground Surface Settlement Induced by Diaphragm and Buttress Installation
by A. Lim and P. Hsieh
ABSTRACT: In construction practices, diaphragm walls are a cast-in-situ reinforced concrete retaining wall that is constructed using a slurry supported trench method. The installation process includes slurry supported trench excavation, placing the reinforcement cage, concrete casting and curing. This installation process would modify the in-situ stress state in the soil close to the trench and generate ground surface settlements, which might be significant compared to those induced by the main excavation. Also, the construction of buttress walls, a concrete wall that perpendicular to diaphragm walls, might generate additional ground surface settlement, and this issue has not been investigated. For clarify this issue, a series of three-dimensional finite element analysis was performed to quantify the amount of ground surface settlement induced by the diaphragm and buttress walls installation process using the Wall Installation Modeling (WIM) method. Results show that the installation of buttress walls inside or outside the excavation zone did not yield significant additional ground surface settlement outside the excavation zone because the diaphragm wall was completed first before the construction of the buttress wall. But, the construction of outer buttress walls could widen the settlement zone.
KEYWORDS: Excavation, Settlement, Installation, Buttress wall, Diaphragm wall.
New Solutions to Geotechnical Challenges for Coastal Cities
by J. Chu, S.F. Wu, H. Chen, X.H. Pan, and K. Chiam
ABSTRACT: Coastal cities like Singapore and Jakarta have undergone rapid economic development in the past decades. There is an increasing demand for infrastructure upgrading. With climate changes and population increase, geotechnical design and construction are getting more and more challenging for coastal cities. We need to develop new technologies and new solutions to tackle the challenges and enhance our ability to fight disasters such as earthquake and flood. In this paper, four different solutions pertinent to geotechnical engineering for coastal cities are presented. The first is the establishment of a web-based 3D geological map to make better use of geological and geotechnical data and information for more reliable geotechnical design. The second is a new method for using dredged slurry or soft materials for land reclamation, as there is a shortage of granular fill materials in many cities. The third is the technology for construction of seawalls using suction caissons. The last solution is the biogas desaturation method for mitigation of soil liquefaction which is becoming the most cost-effective solution for prevention of liquefaction for a large area.
KEYWORDS: Coastal cities, Geological model, Geotechnical engineering, Land reclamation, Liquefaction, Underground construction.
An Investigation of the Elastic Modulus of Cement-Stabilised Soil by Wet Mixing Method for Sand Ground
by H-D. Do, V-N. Pham, A-D. Pham, P-N. Huynh, and E. Oh
ABSTRACT: This paper presents the results of the experimental study to determine the correlation between the elastic modulus (E50) and the unconfined compressive strength (qu) of cement-treated soil by wet mixing method. Laboratory experiment program was conducted for four soil types: clayey sand, fine sand, medium sand and coarse sand with the amount of cement from 150 to 350 kg cement per cubic meter of natural soils. The unconfined compression tests were conducted, and stress-strain curves were recorded by Trapezium 2.24 software to determine qu in all cases at the ages of 7, 14, 21, 28, and 56 days. Bayesian Model Averaging method (BMA) was used to analyse the effect of cement content, soil type, curing time to the elastic modulus E50 and determine the linear regression equations between E50 and qu. The results can be applied for determining of the elastic modulus E50 of cement-treated sand by a wet-mixing method in order to calculate and design soil-cement columns bearing load for a high-rise building foundation.
KEYWORDS: Cement-treated soil, Elastic modulus (E50), Unconfined compressive strength (qu), Stress-strain curves, Soil-cement columns.
Jack-in Pile Design and Construction for High-rise Buildings – A Malaysian Consulting Engineer’s Perspective
by C. M. Chow and Y.C. Tan
ABSTRACT: Large diameter jack-in pile foundation for high-rise buildings has been successfully adopted in Malaysia since the 1990s and currently, large diameter spun piles of up to 600 mm in diameter with working load up to 3200 kN have been successfully adopted for high-rise buildings of up to 45-storeys. This paper summarises some Malaysian experience in design and construction of high capacity jack-in pile system which has been successfully adopted for high-rise buildings in weathered granite and weathered sedimentary formation. Experiences gained throughout the years will be summarized including advantages and limitations of the system. Some results of static maintained load tests will also be presented illustrating clear differences in performance in different ground conditions. Recommendations on empirical correlations between ultimate shaft resistance (fsu) with SPT’N’ and preliminary guidance on ultimate end-bearing resistance (fbu) will also be discussed.
KEYWORDS: Jack-in pile, Weathered granite, Weathered sedimentary, Shaft resistance, End-bearing resistance.
Compressibility Behaviour of Sapric Peat in Double Drainage Constant Rate of Strain (CRS) Test
by D. N. D. Unoi, A. Hasan, A. G. Amuda, and F. Sahd
ABSTRACT: Peat is highly compressible, and it creeps significantly after primary consolidation. Hence, the knowledge of peat settlement characteristics is crucial for sustainable construction on peat. This paper presents the compressibility behaviour of the reconstituted tropical sapric peat specimens obtained via Constant Rate of Strain (CRS) tests by controlling back pressure equal to zero. This technique is found to be helpful to expedite the test. The specimens are compressed one-dimensionally under five different strain rates, from 0.5 %/ hour to 20 %/ hour. Three sets of conventional oedometer tests are also conducted for comparison and verification purposes. The primary compression index values obtained from the specimens vary from 3.021 to 4.146 and are found to be at the lower range for peat in the literature. It is found that the effect of strain rates in the observed range of excess pore water pressure ratio on the compressibility properties of the peat is insignificant.
KEYWORDS: Consolidation, Constant rate of strain, Strain rate, Tropical sapric peat.
