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Smear effects due to the installation of prefabricated vertical drains were studied in the laboratory using special equipment and in the field using a full‐scale test embankment. The prefabricated vertical drains were installed by two... more
Smear effects due to the installation of prefabricated vertical drains were studied in the laboratory using special equipment and in the field using a full‐scale test embankment. The prefabricated vertical drains were installed by two different sizes of mandrel. The test results showed that the smear zone can be assumed to be twice the equivalent mandrel diameter and the horizontal permeability coefficient in the smeared zone, kh′, was approximately equal the vertical permeability coefficient in the undisturbed zone, kv. A faster settlement rate and higher amounts of compression were observed in the small mandrel area than in the large mandrel area, suggesting lesser smear effects in the former than in the latter. The total settlement prediction using the method of Skempton and Bjerrum of 1957, with stress distribution using Poulos's 1967 method, yielded reasonable agreement with the observed values. More accurate settlement‐rate predictions can be obtained using Asaoka's 1978 method when the prediction w...
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Natural fiber was fabricated into woven geotextile called limited life geosynthetics (LLGs) used for ecological ground improvement purposes. This chapter focuses on the performance of two real-field applications of kenaf in soil... more
Natural fiber was fabricated into woven geotextile called limited life geosynthetics (LLGs) used for ecological ground improvement purposes. This chapter focuses on the performance of two real-field applications of kenaf in soil reinforcement and water hyacinth in soil erosion control, respectively. Laboratory tests were performed to investigate interface strength properties of kenaf consisting of large-scale direct shear tests and pullout tests. The kenaf-reinforced embankment system was instrumented to monitor its behavior during and after construction and, thereby, evaluate its performance. The surface settlements, subsurface settlements, excess pore water pressures, and deformations of kenaf reinforcement were monitored and predicted. For soil erosion control purposes, water hyacinth was selected and investigated in the laboratory using index and hydraulic tests. A field soil erosion control test embankment was conducted to confirm the performance of water hyacinth with and without grass covering. From soil reinforcement application using kenaf, it was found that there was close agreement between the measured and predicted settlements as well as pore pressures. Higher deformations were observed in the middle portions of the reinforcements following the settlement pattern. In the case of soil erosion control by water hyacinth, the surface runoff was reduced when using water hyacinth cover combined with grass, which was further reduced with increasing growing periods. In the absence of grass, the smaller opening size has better erosion resistance than the larger opening size when runoff was similar for both opening sizes. It can be concluded that the kenaf LLGs’ natural fibers can be used for temporary reinforcement and the water hyacinth LLGs’ natural fibers combined with grass covering can be applied for erosion control of slopes.
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ABSTRACT No Yes
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This paper focuses on the behaviour of a full-scale test embankment with silty sand backfill on soft ground reinforced with kenaf limited life geotextiles (LLGs). Slide 5·0 software is used to analyse the stability of the embankment with... more
This paper focuses on the behaviour of a full-scale test embankment with silty sand backfill on soft ground reinforced with kenaf limited life geotextiles (LLGs). Slide 5·0 software is used to analyse the stability of the embankment with kenaf LLGs and indicates a higher factor of safety than without kenaf LLGs. Surface settlements, subsurface settlements, excess pore water pressures and deformations of kenaf LLGs reinforcement are monitored and predicted. The predicted settlements agree well with measured values in the field but are overestimated by the Terzaghi one-dimensional consolidation method, as expected. There is close agreement between the measured and predicted settlements by Asaoka's method, as well as the predicted pore pressures using Skempton–Bjerrum predictions. Deformations are observed for LLG reinforcements which mobilised reinforcement tension up to 20 kN/m following the settlement pattern. After construction, the rates of settlement increase up to 250 days o...
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ABSTRACT For the first time, woven Kenaf Limited Life Geosynthetics (LLGs) were used for short term reinforcement of full scale embankment constructed on soft clay and their behavior is presented. The observed data in terms of... more
ABSTRACT For the first time, woven Kenaf Limited Life Geosynthetics (LLGs) were used for short term reinforcement of full scale embankment constructed on soft clay and their behavior is presented. The observed data in terms of settlements, excess pore water pressures and deformations or stresses in the reinforcements were compared with the simulated data. Two types of Kenaf LLGs were utilized, namely: coated and not coated with polyurethane. The coating can reduce water absorption and increase their life time. Subsequently, numerical simulations were performed on the behavior of Kenaf LLGs reinforced embankment using 2D and 3D finite element software. The rates of settlement from FEM 2D method overestimated the observed settlements data while the FEM 3D predictions agreed with observed settlements due to the three-dimensional geometrical loading of the embankment with length to width ratio (L/B) of 1.0. Regarding the maximum excess pore-water pressures at the locations of 3 m and 6 m depth, the FEM 2D analyses overestimated while the FEM 3D simulation yielded satisfactory agreement with the observed data. The reinforcement deformations and stresses in both coated and non-coated Kenaf LLGs reinforcement have higher values at the middle portions of the embankment and the predicted results from FEM 3D simulation yielded closer deformations of Kenaf LLGs reinforced than the FEM 2D simulation. Consequently, FEM 3D simulation captured the overall behavior of the Kenaf LLGs reinforced embankment with more reasonable agreement between the field observations and the predicted values compared to the FEM 2D simulation. The behavior of the sections on coated and non-coated LLGs were similar. The Kenaf LLGs can be applied for short term embankment reinforcement in order to improve the stability of embankment on soft clay.
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... day landfill with emphasis on proper simulation of field conditions and subsequent use of these ... The bottom shear box was moved relative to the fixed upper shear box under a constant normal ... The normal loads applied in the... more
... day landfill with emphasis on proper simulation of field conditions and subsequent use of these ... The bottom shear box was moved relative to the fixed upper shear box under a constant normal ... The normal loads applied in the direct shear tests for this study are approximately 155 ...
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... Vacuum preloading and groundwater lowering by pumping was used at the other test section (Woo et al., 1989). ... While there is some difference in opinion concerning quantitative criteria for satisfactory filters, the following rules... more
... Vacuum preloading and groundwater lowering by pumping was used at the other test section (Woo et al., 1989). ... While there is some difference in opinion concerning quantitative criteria for satisfactory filters, the following rules are widely used: (1 ... On effectiveness of sand drains. ...
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Field data observed from the full-scale test embankments and excavations at 8 different locations have been analyzed to evaluate the useful engineering parameters and field behavior in soft Bangkok clay. Change of excess pore pressures,... more
Field data observed from the full-scale test embankments and excavations at 8 different locations have been analyzed to evaluate the useful engineering parameters and field behavior in soft Bangkok clay. Change of excess pore pressures, ground movements, ground improvement, land subsidence, slope stability analysis and probablistic analysis are the main topics in this paper. Recent theory considering the concept of local yielding and critical stress in the settlement prediction has been used and reasonably good agreements with the measured value were obtained. Stability analysis with shear strengths at large strain, i.e. critical state, yielded values of safety factor near unity at failure. In addition, abundance of test data in soft Bangkok clay enabled the establishment of probability distributions of strength and compressibility characteristics using Monte Carlo simulation. Consequently, relationships are established between the probability of failure, conventional safety factors, and safety margins. Further, the use of sand drains and lime column techniques for improving the soft Bangkok clay did not have reliable positive results so far. Finally, the effect of land subsidence and the consequent results such as negative skin friction of long piles, differential settlements of structures and the hazardous effects of floods seem the most urgent problem in the Bangkok area at present. For the covering abstract of the conference see IRRD 287689. (Author/TRRL)
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11 comprehensive invited lectures on site investigations, engineering behavior of soils, ground improvements, pile foundations, settlement of structures, landslides, environmental geotechnics.
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Engineering Behavior of Cement-Treated Bangkok Soft Clay. K Uddin, AS Balasubramaniam, DT Bergado GEOTECHNICAL ENGINEERING 28, 89-119, ASIAN INSTITUTE OF TECHNOLOGY, 1997.
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The interaction behaviour between steel grid reinforcements and a clayey sand has been studied in laboratory and field pullout tests. The clayey sand is potentially useful as cheap, low quality, locally available and cohesive-frictional... more
The interaction behaviour between steel grid reinforcements and a clayey sand has been studied in laboratory and field pullout tests. The clayey sand is potentially useful as cheap, low quality, locally available and cohesive-frictional backfill in the construction of mechanically stabilized earth walls and embankments, especially in coastal areas. The laboratory tests were conducted under undrained conditions at three compaction moisture conditions. The field tests were conducted on dummy reinforcements embedded at different elevations in a full-scale test embankment resting on soft clay foundation. The laboratory tests revealed that the moisture content of the compacted soil, compaction stress, applied normal stress level, diameter and spacing to diameter ratios of the transverse members of the steel grid, all affect the soil-reinforcement interaction, and thereby, also the magnitudes of the pullout resistances. Interferences between the bearing transverse members of the grid were...
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... This intentional increase in water content is to simulate water content increase taking place in wet method of dispensing cement admixture in deep mixing and the significant increase in water contents taking place in jet grouting. The... more
... This intentional increase in water content is to simulate water content increase taking place in wet method of dispensing cement admixture in deep mixing and the significant increase in water contents taking place in jet grouting. The clay along with Type I Portland cement at ...
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In this paper, the analyses and design using conservative limit equilibrium methods (AASHTO simplified and FHWA structure stiffness methods) were compared with the working stress methods called K-stiffness method (original and modified... more
In this paper, the analyses and design using conservative limit equilibrium methods (AASHTO simplified and FHWA structure stiffness methods) were compared with the working stress methods called K-stiffness method (original and modified K-stiffness methods). Moreover, the predictions from the K-stiffness methods were confirmed from the observed data for a reinforced embankment on a hard foundation. Furthermore, since the reinforcement loads increased due to post-construction settlements for reinforced embankments on soft foundation, a further modification of the K-stiffness method is proposed. This further modification is concerned with the proposed settlement factor (Φs). The validity of this further modification is demonstrated by the good agreement between the maximum measured reinforcement loads and the recalculated maximum reinforcement loads from further modified K-stiffness method.
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This paper presents the performance of a full-scale test embankment constructed on soft Bangkok clay with prefabricated vertical drains (PVDs) at the site of the new Bangkok International Airport in Thailand. The embankment was square in... more
This paper presents the performance of a full-scale test embankment constructed on soft Bangkok clay with prefabricated vertical drains (PVDs) at the site of the new Bangkok International Airport in Thailand. The embankment was square in plan with a maximum height of 4.2 m, 3H:1V side slopes, and base dimensions of 40 m by 40 m. The piezometric level with depth is characterized by negative drawdown starting at around 8-10 m depth caused by excessive withdrawal of groundwater. Instrumentation was provided to monitor both horizontal and vertical movements of the test embankment. The measured increases in undrained shear strengths with depth are in agreement with the values calculated from the SHANSEP technique. The secondary compression ratio, Cα, was 0.018, or within the normal values for marine clays. The coefficient of horizontal consolidation measured in the field, Ch(field), was higher for soil at 4 and 10 m depths than for the weakest soil at 6 m depth. The back-calculated Ch(fi...
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The response of reconstituted soft Bangkok clay to electroosmotic consolidation was investigated using the small cylinder electro-osmotic cell and the large consolidometer. Test results indicated that employing electro-osmosis to induce... more
The response of reconstituted soft Bangkok clay to electroosmotic consolidation was investigated using the small cylinder electro-osmotic cell and the large consolidometer. Test results indicated that employing electro-osmosis to induce consolidation produced a 3 to 4´4 times faster rate of consolidation. An 11´6±58% increase in shear strength with the reduction of water content was achieved for treated samples. In contrast, only 9´8±19´5% increase in shear strength was achieved without treatment. It was found that the 120 Vam voltage gradient and the 24 h duration of polarity reversal interval had maximum effect on the shear strength distributions and settlements between the electrodes.
Due to its high compressibility, clay will consolidate and generate significant settlement when subjected to loading. This consolidation settlement causes detrimental effects on the overlying structures. Furthermore, with its low... more
Due to its high compressibility, clay will consolidate and generate significant settlement when subjected to loading. This consolidation settlement causes detrimental effects on the overlying structures. Furthermore, with its low permeability, the clay takes longer to achieve primary consolidation. To solve this problem, vertical drains are installed with a preloading pressure to shorten the drainage path and, subsequently, to reduce consolidation time. Consequently, water can be discharged much faster through the drain towards the drainage layers. Recently, prefabricated vertical drains (PVD) have gained popularity because of low price and short installation time. However, although PVD has desirable effects in accelerating the consolidation of soft foundations and thereby increasing soil strength, it was deemed necessary to conceptualize another way as to how PVD can function more efficiently and economically. The development of the use of PVD can be enhanced by the electro-osmosis technique for the transport of water and moving chemical species within fine-grained and low-permeability soil. Electro-osmotic transport of water through clay is the result of diffuse double-layer cations in the clay pores being attracted to a negatively charged electrode or cathode upon the application of electric fields. Water molecules orient themselves around ions in the pore space as water of hydration. As these cations move through the pore space towards the cathode, they bring with them associated hydration water or water molecules that clump around the cations as a consequence of their dipolar nature. Consolidation results when water is drained at the cathode but not replaced at the anode. It has been proven to be effective in stabilizing and consolidating soils both in the laboratory and in the field (Chappell and Burton 1975; Mitchell and Wan 1977; Shang et al. 1996; Shang and Ho 1998). The electro-osmotic consolidation induced the reduction of moisture content and increase in shear strength (Bjerrum et al. 1967; Lo et al. 1991; Shang and Dunlap 1996). This process can also be used in remediation of contaminated soils and groundwater (Acar et al. 1994). The purposes of this paper are to evaluate the electro-osmotic effects generated on both undisturbed and reconstituted Bangkok clay using the combination of electrodes with PVD and to compare the efficiency of using copper and carbon as electrodes. The experimental data are obtained from Sasanakul (2000), which is the continuation of the work by Bergado et al. (2000). Electro-Osmotic Consolidation If, in a compressible soil, electro-osmosis draws water to a cathode where it is drained away and no water is allowed to enter at the anode, consolidation of the soil between the electrodes occurs in an amount equal to the volume of water removed. As water movement away from the anode causes consolidation in the vicinity of the anode, the effective stress must increase. Because the total stress in the vicinity of the anode remains essentially unchanged, the pore water pressure must decrease. On the other hand, there is no consolidation at the cathode since water flows towards it. This means that there is no change in total, effective, and pore water pressures. As a result, a hydraulic gradient develops that tends to push water back from cathode to anode. Consolidation continues until the hydraulic force that drives water back toward the anode exactly balances the electro-osmotic force driving water toward the cathode (Mitchell 1993).
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This paper presents the results of an experimental investigation carried out to study thermally induced volume changes under drained heating condition and thermally induced excess pore water pressures under undrained heating condition of... more
This paper presents the results of an experimental investigation carried out to study thermally induced volume changes under drained heating condition and thermally induced excess pore water pressures under undrained heating condition of soft Bangkok clay. The clay was heated up from room temperature (25 °C) to 90 °C using a modified oedometer and a triaxial test apparatus, respectively. The clay was
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Soft ground improvement techniques have become most practical and popular methods to increase soil strength, soil stiffness and reduce soil compressibility including the soft Bangkok clay. This paper focuses on comparative performances of... more
Soft ground improvement techniques have become most practical and popular methods to increase soil strength, soil stiffness and reduce soil compressibility including the soft Bangkok clay. This paper focuses on comparative performances of prefabricated vertical drain (PVD) using surcharge, vacuum and heat preloading as well as the cement-admixed clay of Deep Cement Mixing (DCM) and Stiffened DCM (SDCM) methods. The Vacuum-PVD can increase the horizontal coefficient of consolidation, C h, resulting in faster rate of settlement at the same magnitudes of settlement compared to Conventional PVD. Several field methods of applying vacuum preloading are also compared. Moreover, the Thermal PVD and Thermal Vacuum PVD can increase further the coefficient of horizontal consolidation, C h, with the associated reduction of k h /k s values by reducing the drainage retardation effects in the smear zone around the PVD which resulted in faster rates of consolidation and higher magnitudes of settlements. Furthermore, the equivalent smear effect due to non-uniform consolidation is also discussed in addition to the smear due to the mechanical installation of PVDs. In addition, a new kind of reinforced method, namely: Stiffened Deep Cement Mixing (SDCM) pile is introduced to mitigate the problems of the Deep Cement Mixing (DCM) pile due to the low flexural resistance, lack of quality control in the field and, consequently, unexpected failures. The SDCM pile consists of DCM pile reinforced with precast reinforced concrete (RC) core pile. The full scale test embankment on soft clay improved by SDCM and DCM piles was studied. Numerical simulations using the 3D PLAXIS Foundation finite element software have been done to understand the behavior of SDCM and DCM piles. The simulation results indicated that the surface settlements decreased with increasing lengths of the RC core piles, and, at lesser extent, increasing sectional areas of the RC core piles in the SDCM piles. In addition, the lateral movements of the embankment decreased by increasing the lengths (longer than 4 m) and, the sectional areas of the RC core piles in the SDCM piles. The results of the numerical simulations closely agreed with the observed data and successfully verified the parameters affecting the performances and behavior of both SDCM and DCM piles.
A full-scale reinforced earth embankment was designed and constructed by the Department of Highways of Thailand on a hard foundation in Phitsanulok Province, Thailand. Two types of reinforcement were used in the embankment. One side was... more
A full-scale reinforced earth embankment was designed and constructed by the
Department of Highways of Thailand on a hard foundation in Phitsanulok Province,
Thailand. Two types of reinforcement were used in the embankment. One side was
reinforced with polymeric reinforcement consisting of polyester (PET), polypropylene
(PP) and high-density polyethylene (HDPE) and referred to as a reinforced steep slope
(RSS), with an angle of 70° from horizontal. On the other side, the embankment was
reinforced with metallic reinforcement consisting of metallic strips (MS) and steel wire
grids (SWG) combined with vertical segmental concrete facing and referred to as a
mechanically stabilised earth wall (MSEW). The behaviour of the reinforced soil slope
and the mechanically stabilised earth wall on a hard foundation were observed and
compared with predictions from the PLAXIS 3D software. The lateral displacements
and settlements were very small in the case of the MSEW with inextensible reinforcement.
The corresponding lateral and vertical deformations in the RSS were much larger
due to its extensible reinforcing materials. The stiffnesses of the reinforcing materials
decrease in the following order: MS, SWG, PP, HDPE and PET. The results obtained from
three-dimensional (3D) finite element method simulations (using PLAXIS 3D) were in
good agreement with the field measurements in terms of vertical and lateral deformations
and strains in the reinforcement.
Department of Highways of Thailand on a hard foundation in Phitsanulok Province,
Thailand. Two types of reinforcement were used in the embankment. One side was
reinforced with polymeric reinforcement consisting of polyester (PET), polypropylene
(PP) and high-density polyethylene (HDPE) and referred to as a reinforced steep slope
(RSS), with an angle of 70° from horizontal. On the other side, the embankment was
reinforced with metallic reinforcement consisting of metallic strips (MS) and steel wire
grids (SWG) combined with vertical segmental concrete facing and referred to as a
mechanically stabilised earth wall (MSEW). The behaviour of the reinforced soil slope
and the mechanically stabilised earth wall on a hard foundation were observed and
compared with predictions from the PLAXIS 3D software. The lateral displacements
and settlements were very small in the case of the MSEW with inextensible reinforcement.
The corresponding lateral and vertical deformations in the RSS were much larger
due to its extensible reinforcing materials. The stiffnesses of the reinforcing materials
decrease in the following order: MS, SWG, PP, HDPE and PET. The results obtained from
three-dimensional (3D) finite element method simulations (using PLAXIS 3D) were in
good agreement with the field measurements in terms of vertical and lateral deformations
and strains in the reinforcement.
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Smear effects due to the installation of prefabricated vertical drains were studied in the laboratory using special equipment and in the field using a full-scale test embankment. The prefabricated vertical drains were installed by two... more
Smear effects due to the installation of prefabricated vertical drains were studied in the laboratory using special equipment and in the field using a full-scale test embankment. The prefabricated vertical drains were installed by two different sizes of mandrel. The test results showed that the smear zone can be assumed to be twice the equivalent mandrel diameter and the horizontal perme-ability coefficient in the smeared zone, k', " was approximately equal the vertical permeability coefficient in the undisturbed zone, k v. A faster settlement rate and higher amounts of compression were observed in the small mandrel area than in the large mandrel area, suggesting lesser smear effects in the former than in the latter. The total settlement prediction using the method of Skempton and Bjerrum of 1957, with stress distribution using Poulos's 1967 method, yielded reasonable agreement with the observed values. More accurate settlement-rate predictions can be obtained using Asaoka's 1978 method when the prediction was based on settlement data having at least 60% consolidation.