Soft Soil Improvement by Geosynthetics for Enhanced Performance of Transport Infrastructure
B. Indraratna, S. Atapattu, C. Rujikiatkamjorn, J. Arivalagan, and N. Jing
ABSTRACT:Increasing demand for transportation has forced new infrastructure to be built on weak subgrade soils such as estuarine or marine clays. The application of heavy and high-frequency cyclic loads due to vehicular movement during the operational (post-construction) stage of tracks can cause (i) cyclic undrained failure, (ii) mud pumping or subgrade fluidisation, and (iii) differential and excessive settlement. This keynote paper presents the use of prefabricated vertical drains (PVDs) to enhance the performance of tracks. A series of laboratory experiments were carried out to investigate the cyclic response of remoulded soil specimens collected from a railway site near Wollongong, NSW, Australia. The results of the laboratory tests showed that beyond the critical cyclic stress ratio (CSRc), there is an internal redistribution of moisture within the specimen which causes the top portion of the specimen to soften and fluidise. The role that geosynthetics play in controlling and preventing mud pumping was analysed by assessing the development of excess pore water pressure (EPWP), the change in particle size distribution, and the water content of subgrade soil. The experimental data showed that PVDs can prevent the EPWP from building up to critical levels. PVDs provide shorter-radial drainage for EPWP to dissipate during cyclic loading, resulting in less accumulation of EPWP. Moreover, PVDs cause soil to behave in a partially drained rather than an undrained condition, while geotextiles can provide adequate surficial drainage and effective confinement at the ballast/subgrade interface. Partially drained cyclic models were developed by adopting the modified Cam clay theory to predict the behaviour of soil under cyclic loadings. The Sandgate Rail Grade Separation project case study presents a design of short PVDs to minimise the settlement and associated lateral displacement due to heavy-haul train loadings.
KEYWORDS: Case history, Cyclic loads, Prefabricated Vertical Drains, and Subgrade.
Development of the Jet Grouting Method: Evolutionary History, Mechanism Insights, Innovative Approaches, and Future Prospects
J. Yamazaki, K. C. Chao, K. N. Wong, and I. M. Wang
ABSTRACT: The development of the jet grouting method has been a significant breakthrough in the field of geotechnical engineering. This construction method was initially developed in Japan in the 1960s and has undergone various improvements to enhance its effectiveness and efficiency. The jet grouting method involves the injection of a cement-based grout material into the ground through a high-pressure jet. It has many excellent features, such as a wide range of applicable soils, high improvement strength, and the ability to construct using small-diameter boreholes. This technique enables the creation of a solid column of grout material that can provide support to unstable soil or rock formations. However, the quality of the improved ground is influenced by various factors, including the quality of the injection flow, the lifting speed, the rotation frequency, and the soil conditions. Over the years, there have been efforts to develop new construction methods that can improve the performance of the jet grouting method. These efforts have led to the development of advanced equipment and techniques that can achieve higher grouting pressures and faster injection rates, resulting in a more efficient and cost-effective construction process. In this paper, the history of the development of the jet grouting method will be reviewed, and the basic improvement mechanism of the method and case studies that the authors have worked on will be discussed. Furthermore, the development of new methods and future challenges and prospects for the jet grouting method will be discussed.
KEYWORDS: Jet Grouting, V-Jet Method, Rapidjet Method, and Jet Wave Monitoring System.
Evaluation of the Impact of Having of Expansive Clay Core on the Stability of an Earth Dam
K. C. Chao, F. Shah, and S. Soralump
ABSTRACT: The study focuses on the changes in seepage and stability of the dam with a clay core constructed with expansive soils. Heave potential of the expansive clay core was also evaluated in the study. Laboratory testing was conducted to evaluate the swelling potential and hydraulic properties for the compacted expansive soils under various dry unit weights and initial water contents. Numerical modeling was conducted to evaluate the changes in seepage flow and slope stability due to the heaving of the expansive clay core for the dam. The findings suggest that to reduce seepage flow, the swelling soil should be compacted to a lower degree of compaction at a moisture content exceeding the optimum moisture content (OMC), which effectively reduces soil swelling and consequently minimizes seepage. Conversely, if stability is the primary concern, the swelling soil should be compacted to a relatively higher degree of compaction at a moisture content lower than the OMC, providing enhanced strength to the dam. In conclusion, the study demonstrates that for expansive soil used in dam cores, the same traditional compaction conditions utilized for seepage and stability in normal clayey soil can be applied. However, it is crucial to consider the specific characteristics of the swelling soil during the compaction process. By implementing suitable compaction techniques based on the desired outcome, seepage control, and dam stability can be effectively managed when utilizing swelling soil in dam construction. The findings offer valuable insights to engineers and practitioners involved in dam design and construction, aiding in informed decision-making and optimal compaction practices when incorporating swelling soils in dam cores.
KEYWORDS: Expansive clay core, Expansive soil, Seepage, Stability, Heave potential, and Time rate of heave.
Evaluating Bentonite Sludge Suitability for Landfills and Developing a Coefficient of Permeability Prediction Model
N. Prongmanee, T. Boonyarak, S. Chea, N. Thasnanipan, Z. Z. Aye, and A. Noulmanee
ABSTRACT: Construction in Bangkok, Thailand, often requires bentonite slurry for stabilization during deep foundation and diaphragm wall construction due to this region’s thick, soft clay layers. However, the bentonite slurry creates environmental and logistical challenges after construction as it becomes a waste product. Thus, this study first examined the feasibility of repurposing flocculated bentonite sludge, treated with anionic polyacrylamide from deep foundation construction, for landfill construction. The research compared the physicochemical, swelling, and hydraulic properties of the bentonite sludge with the original bentonite powder, using the free swelling index and consolidation testing. The test results indicated that the microstructure of bentonite sludge, altered by the polyacrylamide, had reduced the swelling and barrier properties compared to the original material. Although unsuitable for the core material of geosynthetic clay liners, bentonite sludge could still be an effective compacted clay liner material with appropriate design and construction. Secondly, this study developed a more rapid method than the consolidation test to estimate permeability values based on the liquid limit and void ratio test results, providing a user-friendly, time-efficient approach. This research identified a sustainable solution for waste management in Bangkok or other similar regions with thick, soft clay layers, as well as offering a practical method for quick permeability estimation in landfill applications.
KEYWORDS: Bentonite sludge, Deep foundation, Landfill, Prediction, and Permeability.
Effect of Soil Slope on Lateral Response of Piled Raft Foundations in Cohesive Soil
S. Lateh, T. Chub-Uppakarn, P. Jongpradist, T. Chompoorat, S. Swasdi, and W. Srisakul
ABSTRACT: The advantages of the piled raft foundations system over conventional pile group foundations have been demonstrated in previous studies. In a pile raft foundation, the raft load capacity is extensively investigated in level ground conditions; its behaviour in a soil slope is limited. In the present study, three-dimensional finite element analyses using PLAXIS 3D software were performed to examine the effect of the soil slope on the lateral response of the piled raft foundation. The study showed that the lateral capacity of piled raft foundations decreases when installed within a certain distance (less than 8 times the pile diameter) from a slope. Furthermore, the enormous effect of slope occurs at distances nearer than 4D. Despite a decrease in lateral capacity when installed near slopes, the effect on the piles is insignificant, especially the rear piles. As a result, the distance between the piled raft foundations and the slope is a key factor that needs to be considered to improve design guidance to reduce construction costs.
KEYWORDS: Piled raft foundation, Soil slope, Lateral resistance, 3D Finite element, and Raft load sharing.
Equivalent-Linear and Nonlinear Seismic Ground Response Analysis of Important Sites in Amaravati Capital Region, Andhra Pradesh, India
R. Satyannarayana, B. G. Rajesh, and S. K. Yamsani
ABSTRACT: The characteristics of bedrock motion are examined using seismic ground response analysis to determine the impact of the regional soil layers overlaying the bedrock, with the use of two programs, DEEPSOIL and SHAKE. The diversity in the seismic ground response is investigated for a variety of input parameters, including soil geometry, the use of various shear moduli, damping curves, and analytical techniques. The present study attempted to study the local site effects for important towns like Amaravati, Velagapudi, Nekkallu, and Abburaju Palem in the Amaravati capital region by adopting both the equivalent linear and non-linear approaches. The ground responses are observed for the synthetic accelerograms obtained from 2001 Bhuj earthquake motion as seed accelerogram and results are presented in the form of response spectrum, acceleration time histories, and Amplification ratio. The peak ground acceleration and amplification factor for the Velagapudi soil site are found to be the highest among the four soil sites with a value of 0.149 g. The maximum surface acceleration obtained for Amaravati, Nekkallu, and Abburaju Palem is 0.09 g, 0.084 g, and 0.128 g respectively for a given input motion. The amplification ratio for maximum acceleration is found to be 4 at a frequency of 2.5 Hz for Velagapudi, 3.5 at a frequency of 5.5 Hz for Abburaju Palem, 3.4 at a frequency of 3.5 for Amaravati and 3.85 at a frequency of 10 Hz for Nekkallu town respectively. The mean spectral values obtained by equivalent linear analysis are found to be higher than that of the non-linear analysis.
KEYWORDS: Equivalent linear ground response analysis, Non-linear ground response analysis, Pseudo spectral acceleration, Fourier amplification ratio, Maximum surface acceleration, and Amaravati capital region.
2D Dynamic Numerical Modelling of a Tunnel – Soil – Building System Subjected to Seismic Loading
Z. He and S. P. G. Madabhushi
ABSTRACT: It is important to determine dynamic tunnel behaviour under cyclic loading for the seismic underground structural design. The dynamic response of tunnels is further complicated when considering the interaction with surface buildings. This paper investigates a series of 2D plane-strain numerical models to study the dynamic response of a shallow cut-and-cover rectangular tunnel in loose, cohesionless soil. Both dry and saturated conditions are considered. Input motion includes sinusoidal waves with 10 cycles of shaking. A raft foundation with a 50 kPa structural surcharge is adopted to simulate the effect of the surface building. Soil displacements, wave propagation, earth pressures and tunnel lining structural response are determined. These results show that the soil liquefaction introduced by accumulated excess pore pressures causes the attenuation of soil horizontal acceleration, reduction of soil effective stresses and promotes tunnel flotation. The existence of a building not only reduces the liquefaction ratio of sub-surface soil right below the foundation but also effects the earth pressure distribution on the adjacent tunnel sidewall. In addition, the presence of the tunnel may affect adversely the rotation of the foundation especially in saturated soils.
KEYWORDS: Tunnel Flotation, Liquefaction, Cut & Cover Tunnel, and Soil-Structure Interaction (SSI).
Development of IoT Slope Monitoring System and its Applications for Kratu-Patong Road Landslide in Phuket, Thailand
A. Jotisankasa, W. Praphatsorn, V. Siriyakorn, P. Sanposh, I. Janthong, Y. Tipsuwan, A. Sawangsuriya, and P. Jitareekul
ABSTRACT: This paper presents an on-going development of Internet-of-Things (IoT) slope monitoring for landslide early warning system in Thailand. The current system employs a variety of sensors, namely MEMs-based tensiometers, piezometers, soil moisture sensor, tiltmeter, in-placed inclinometer and tipping bucket raingauge, all connected to Arduino-based microcontroller which relied on Narrowband, NB-IoT, protocol for data transmission to the cloud server. A specially designed application platform was developed to convert the sensor readings to engineering unit and ultimately geotechnical parameters, such as factor of safety, which enable engineers to readily understand the situation and make an informed-decision based on such parameters. A weighted approach was proposed in calculating the overall landslide hazard level based various kinds of sensor readings. A case history of Kratu-Patong Road Landslide in Phuket, Southern Thailand, taking place in Year 2022 was presented to demonstrate how the developed IoT system was used real-time together with geotechnical analysis to aid in traffic management during the critical time. The warning event primarily stemmed from spikes in slope movement, spurred by heightened traffic intensity. Rapid slope movement during the incident was characterized by a tilting magnitude of -2 to 1.2 degrees and a velocity ranging from -1.7 to 1.8 degrees per hour. Notably, the calculation of the warning index based on tilting magnitude provides a continuous warning message, in contrast to an intermittent message based on tilting velocity. The tensiometer effectively detected the decrease in suction caused by slope movement, while the piezometer only registered changes in pore-water pressure when the groundwater table rose above the measurement point. Finally, an Artificial Neural Network (ANN) model was used to predict the pore-water pressure at different depths based on 5 rainfall parameters, namely, 5-min, 1-hour, 1-day, 3-day and 7-day antecedent rainfalls. The model demonstrated satisfactory predictive accuracy (R² = 0.644, RMSE = 3.637 kPa), offering promising potential for integration with the IoT platform in the future.
KEYWORDS: IoT slope monitoring system, Slope stability, Landslide early warning, and Pore-water pressure.
