Soft Bangkok Clay Research Articles

Pore Pressure : Stress Ratio Relationship for Soft Bangkok Clay

ABSTRACT A series of triaxial tests was performed on undisturbed samples of soft Bangkok clay, which were consolidated under different constant stress ratios, to study the pore pressure development under monotonic loading conditions. The test results are interpreted through a pore pressure : stress ratio relationship. The behaviour of isotropically consolidated samples in the normally consolidated state shows a linear relationship between the pore pressure and the stress ratio under monotonic loading conditions and the same patterns were also established for other clays such as kaolin, Drammen clay and Boston Blue clay. Overconsolidated samples, and anisotropically consolidated samples showed bi-linear variation on the same plot. The linear/bilinear variation in the pore pressure-stress ratio relationship was used to develop simple expressions for the undrained stress paths for different initial conditions of the samples, using simple soil constants.

Behavior of a welded wire wall with poor quality, cohesive–friction backfills on soft Bangkok clay: a case study

A full-scale and extensively instrumented experimental mechanically stabilized earth (MSE) wall with steel grid reinforcements was built on soft clay foundation. Three different locally available poor to marginal quality backfills were used in each of three sections along its length. The soft Bangkok clay in the subsoil is about 6 m thick, overlain by a surficial 2 m thick weathered clay crust and underlain by a layer of stiff clay. It was observed that the amount of subsoil movement greatly influenced the variation in the vertical pressure beneath the wall, as well as the tension in the reinforcement. Pullout resistances in the field were also found to be very much affected by the arching effects due to the presence of inextensible reinforcement in combination with the subsoil movements. The wall showed no signs of instability both during construction and in the postconstruction phases, despite the large settlements and lateral movements. Its overall performance has been satisfactory. It was concluded that the steel grid reinforcement can be effectively used to reinforce poor to marginal quality backfill in walls and embankments on soft clay foundations. Key words: mechanically stabilized earth, inextensible reinforcements, soft clay foundation, poor quality backfills, base pressures, settlements, lateral movements, lateral pressures, compaction, arching.

Prediction of Embankment Settlements by In-Situ Tests

Abstract The compressibility of soft Bangkok clay preloaded with an instrumented test embankment was studied using the results of a series of in-situ and laboratory tests. In the field, eight screw plate and eight pressuremeter tests were performed at four test levels in the subsoil. In the laboratory, twelve Rowe cell consolidation tests were carried out. The method of Asaoka (1978) was used in determining the coefficient of consolidation from the screw plate test. It was found that Cv values obtained from the Rowe cell consolidation tests were twelve times smaller compared to those derived from the screw plate tests. The soil parameters obtained from the two types of in-situ tests conducted in this study were then used to predict the settlement behavior of the two test embankments, one improved by prefabricated vertical drains (PVD), and the other, on unimproved ground. The difficulty associated with the proper choice of the drained modulus values are highlighted, and it was found that the predicted settlement magnitudes using elastic theory can vary considerably for the ratio of drained and undrained soil moduli, E′/Eu, ranging between 0.25 to 0.50. The undrained modulus from the screw plate test corresponding to the fitted data was found to be 1.38 times the undrained modulus from the pressuremeter test. General agreement with the observed settlement was found using the graphical procedure of Asaoka (1978) and adopting the coefficient of consolidation from the screw plate test.

Application of an inter-active computer-aided probabilistic slope stability assessment for embankment on soft Bangkok clay : Bergado, D T; Chang, J C Proc International Symposium on Computer and Physical Modelling in Geotechnical Engineering, Bangkok, 3–6 December 1986P25–52. Publ Rotterdam: A A Balkema, 1989

Application of an inter-active computer-aided probabilistic slope stability assessment for embankment on soft Bangkok clay : Bergado, D T; Chang, J C Proc International Symposium on Computer and Physical Modelling in Geotechnical Engineering, Bangkok, 3–6 December 1986P25–52. Publ Rotterdam: A A Balkema, 1989

Deformability and consolidation characteristics of soft Bangkok clay using screw plate tests : Bergado, T, Chong, C, Daria, P A M, Alfaro, M C Can Geotech JV27, N5, Oct 1990, P531–45

Deformability and consolidation characteristics of soft Bangkok clay using screw plate tests : Bergado, T, Chong, C, Daria, P A M, Alfaro, M C Can Geotech JV27, N5, Oct 1990, P531–45

Improvement of soft Bangkok clay using vertical geotextile band drains compared with granular piles : Bergado, D T; Singh, N; Sim, S H; Panichayatum, B; Sampaco, C L; Balasubramaniam, A S Geotext GeomemV9, N3, 1990, P203–231

Improvement of soft Bangkok clay using vertical geotextile band drains compared with granular piles : Bergado, D T; Singh, N; Sim, S H; Panichayatum, B; Sampaco, C L; Balasubramaniam, A S Geotext GeomemV9, N3, 1990, P203–231

Deformability and consolidation characteristics of soft Bangkok clay using screw plate tests

This study centred on the performance of the screw plate test (SPLT) to determine the deformability and consolidation characteristics of soft Bangkok clay. For comparison, a series of stress-path-controlled triaxial consolidation tests (tri) were carried out on good quality samples of Bangkok clay taken from the same testing sites and imposed with the same loading conditions as the screw plate tests. Undrained and drained moduli and coefficients of consolidation were obtained from the stress-path-controlled triaxial consolidation tests and were compared with the corresponding values of the screw plate test. In addition, the ultimate bearing capacity was derived from the pressure–deformation relationships of the screw plate test results. A graphical method was used to compute the coefficient of consolidation from the screw plate tests and from stress-path-controlled triaxial consolidation test results. The compressibility data were also obtained from conventional oedometer tests (oed). Both cv (SPLT)/cv (tri) and cv (SPLT)/cv(oed) ratios compared favorably with the cv (field)/cv (laboratory) ratio obtained from past investigations. The data from pressure–settlement–time relationships of the screw plate tests were used to successfully predict values that compared favorably with the measured values at each stress level. The pressure–deformation–time relationship from stress-path-controlled triaxial consolidation tests were also evaluated, and they indicated behaviour similar to that of the screw plate test results. Soil parameters obtained from screw plate tests were subsequently used to predict the settlement of two test embankments, giving fairly close agreement with the observed values. Key words: soft clay, settlement, deformation, consolidation, screw plate test, triaxial test, embankment, prediction, stress path.

Improvement of soft Bangkok clay using vertical band drains based on full scale test

Improvement of soft Bangkok clay using vertical band drains based on full scale test

Settlements of Bagna-Bangpakong highway on soft Bangkok clay : Bergado, D T; Ahmed, S; Sampaco, C L; Balasubramniam, A S J Geotech Engng Div ASCEV116, N1, Jan 1990, P137–155

Settlements of Bagna-Bangpakong highway on soft Bangkok clay : Bergado, D T; Ahmed, S; Sampaco, C L; Balasubramniam, A S J Geotech Engng Div ASCEV116, N1, Jan 1990, P137–155

Influence of different vane types on undrained strength of soft Bangkok clay, Technical note : Kietkajornkul, C; Vasinvarthana, V Soils FoundV29, N2, June 1989, P146–152

Influence of different vane types on undrained strength of soft Bangkok clay, Technical note : Kietkajornkul, C; Vasinvarthana, V Soils FoundV29, N2, June 1989, P146–152

Undrained Strength of Underconsolidated Clays and Its Application to Stability Analysis of Submarine Slopes Under Rapid Sedimentation

Of several triggering mechanisms of submarine slope instability, the effect of rapid rate of sedimentation is focused on. When subjected to rapid sedimentation, the clayey material in the seabed is in a state of incomplete consolidation or underconsolidation. In order to understand the undrained behaviour of underconsolidated clay, triaxial compression tests were conducted on laboratory-reconstituted samples of soft Bangkok clay which were consolidated Under various total pressures and degrees of consolidation. The test results indicated that the undrained strength of the clay increases with the degree of consolidation, while the cohesion and friction angle in terms of effective stress are independent of the degree of consolidation. It was revealed also that the underconsolidated clay develops a slightly greater amount of excess pore water pressure during shear than the normally consolidated clay. Using the above findings, a finite element program was developed to analyze the stability of submarine slopes undergoing rapid sedimentation and increasing height with time. It was shown by an example calculation that the degree of consolidation of the slope decreases with time, eventually resulting in a failure.

Settlements of Bangna‐Bangpakong Highway on Soft Bangkok Clay

Time‐settlement data of more than 30 different sections of the 55‐km long Bangna‐Bangpakong Highway in Thailand are analyzed. The deformation parameters, namely: undrained modulus, Eu; drained modulus, E′; and coefficient of consolidation, Cv, are backfigured from the field performance of the highway embankment, and the following correlations are found: Eu/Suv=150; E′/Suv=15; and Cv(field)/Cv(lab)=26; where Suv is the uncorrected vane shear strength. It was also found that Cv values are overestimated by the method of Asaoka when the during‐construction time‐settlement curve is used, and are best estimated when backfigured from postconstruction performance. It is also found that for construction settlements, the method proposed by Cox, which is a combination of the method of D'Appolonia et al. for immediate settlements and that of Leroueil et al. for consolidation settlements, underpredicts settlements at some sections but yields conservative estimates when considering secondary settlements since the begin...

Improvement of soft Bangkok clay using vertical geotextile band drains compared with granular piles

For the first time, improvement of the soft Bangkok clay by accelerated consolidation has been studied by constructing two full-scale, instrumented, test embankments. In one, consolidation was accelerated by vertical band drains and in the other, by granular piles. The embankment on granular piles, initially 2·4 m high, was later raised to a height of 4 m after 345 days, to impose the same level of applied stress as the other embankment on vertical band drains. The actual settlements and pore pressure build-up have been constantly monitored for both embankments since their construction in 1985. Relative comparison with previous embankment performance on umimproved ground demonstrated the effectiveness of the vertical drains to accelerate the consolidation process and increase the shear strength of the soft clay. The installation of vertical band drains at 1·5 m spacing on a triangular pattern, resulted in achieving 90% consolidation after 430 days using 4 m high embankment preloading. In contrast, the embankment on granular piles indicated reduction in settlements by as much as 20–40%. The results suggested that the granular piles seemed to reinforce the soft clay rather than draining it, increasing the bearing capacity up to four times and increasing the slope stability safety factor by up to 25%. Comparison of actual and predicted values using different methods of settlement predictions are presented. It was found that for the embankment on vertical drains, best agreement between the observed and predicted settlments were obtained using the Asaoka method adopting back-analyzed parameters. The Skempton & Bjerrum method yielded good agreement with the observed data except at the initial stages of loading, where overestimation of settlement could be seen. In addition, underestimation of settlements resulted using the one-dimensional method. Settlement reduction due to the presence of granular piles were calculated using the equilibrium (Aboshi et al.; Barksdale) and finite element (Balaam et al.) methods. The equilibrium method resulted in overestimation of settlements while Balaam's finite element formulation yielded good agreement with the observed data.

Application of an interactive computer-aided probabilistic slope stability assessment for embankments on soft Bangkok clay : Bergado, D T; Chang, J C Proc Symposium on Computer Aided Design and Monitoring in Geotechnical Engineering, Bangkok, 3–6 December 1986P184–246. Publ Bangkok: AIT, 1986

Application of an interactive computer-aided probabilistic slope stability assessment for embankments on soft Bangkok clay : Bergado, D T; Chang, J C Proc Symposium on Computer Aided Design and Monitoring in Geotechnical Engineering, Bangkok, 3–6 December 1986P184–246. Publ Bangkok: AIT, 1986

Influence of Different Vane Types on Undrained Strength of Soft Bangkok Clay

This paper concerns the effect of using the different in-situ vane types performed in the same site. The first equipment is the VANE TYPE I which conducted without casing and preboring, and the other is the VANE TYPE II carried out in preboring type hole. The results indicate that the undrained shear strength from the VANE TYPE I is higher than the other about 20-30%. In addition, the unconfined compression tests yield approximately the same undrained strengths with those from VANE TYPE II. The difference in strengths between these tests are believed partly dependent upon the effects of disturbance during sampling. Despite the large variation of plasticity index in Bangkok area, the normalized corrected VANE TYPE I strength based on Bjerrum (1972) and the measured VANE TYPE II strength (Cu/σ'v0) show the unique curve when they are plotted versus OCR.

Full scale load test of granular piles with different densities and different proportions of gravel and sand on soft Bangkok clay. Technical note : Bergado, D T; Lam, F L Soils FoundV27, N1, March 1987, P86–93

Full scale load test of granular piles with different densities and different proportions of gravel and sand on soft Bangkok clay. Technical note : Bergado, D T; Lam, F L Soils FoundV27, N1, March 1987, P86–93

Undrained Deformability and Strength Characteristics of Soft Bangkok Clay By the Screw Plate Test

Abstract Eighteen screw plate tests were carried out using 10-in. 25.4-cm diameter plate, and three types of laboratory test were performed, namely, 18 unconfined tests, 31 unconsolidated-undrained triaxial tests, and 18 one-dimensional consolidation tests. The sampling and testing were carried out at three sites inside the campus of the Asian Institute of Technology in the soft clay layer. At each site, six screw plate tests were performed at depths of 2.50, 4.50, and 6.00 m, and three boreholes were made to take 60-cm-long Shelby tube samples at the test levels. The screw plate test results were calibrated with unconsolidated-undrained (UU) triaxial test results and the bearing capacity factor Nc was found to be 11.00 while the undrained modulus factor K was found to be 0.61. The screw plate test results were also correlated with the unconfined compression (UC) test and one-dimensional consolidation test in this study as well as with the vane shear test and pressuremeter test results from previous investigations. Furthermore, the pressuremeter-settlement-time relationship was evaluated, and it was found that the logarithm of settlement rate, log s, decreased linearly with the logarithm of time, log t, and increased linearly with the logarithm of the stress level, log P′.

Full Scale Load Test of Granular Piles with Different Densities and Different Proportions of Gravel and Sand on Soft Bangkok Clay

The behavior of granular piles with different densities and different proportions of gravel and sand on soft Bangkok clay was investigated. A total of 13 piles were installed with 0. 30 m diameter and 8. 0 m long using a non-displacement cased borehole method with 1. 20 m spacing in a triangular pattern. The piles were grouped into 5 categories. Groups 1, 2, and 3 with 3 piles each, were constructed using sand compacted at 20, 15, and 10 hammer blows per layer, respectively. Group 4 was made of gravel mixed with sand in the proportion on 1:0. 30 by volume and group 5 was constructed with gravel; both groups consisted of two piles each were compacted at 15 blows per layer. Four active and 2 dummy piezometers were installed for monitoring pore pressures. The soil properties were investigated by the field vane and pressuremeter tests. The ultimate capacity of each granular pile was determined by using full scale plate load tests. Using the pressuremeter results and the method by Hughes et al (1975), the predicted ultimate pile capacity and load-settlement curve agreed well with the experimental data. The maximum bulge in the pile was observed to be about one pile diameter from the ground surface. It was found that the pile made of gravel with 15 blows per layer (Group 5) yielded the maximum ultimate pile capacity closely followed by the piles constructed out of sand with 20 blows per layer (Group 1). In an earlier investigation (Bergado et al, 1984), it was found that the ultimate pile bearing capacity was 3 to 4 times greater than that of the untreated ground and that the piles acted independently when the spacing was 3 pile diameters or greater.

Reliability assessment of test embankments on soft Bangkok clay by variance reduction and nearest-neighbor methods

This paper presents the application of probabilistic slope stability model based on variance reduction method on the Nong Ngoo Hao (NNH) test embankment and the probabilistic settlement evaluation of AIT test embankment using the nearest-neighbor method. The NNH embankment was constructed to failure. Sample autocorrelations were obtained from corrected vane shear test data as well as from the Dutch cone test data in both horizontal and vertical directions. The results showed that using a design criteria of probability of failure of 10 −3, a design safety factor of 1.12 is recommended for 3-D analysis. In 2-D analysis, the variance reduction method yielded lower probabilities of failure compared to an earlier work based on Monte Carlo method. For the AIT test embankment, the statistical data for the occurrence of fine sand and silt lenses in the soft Bangkok clay were obtained and the inclusions were probabilistic settlement prediction in conjunction with the method of Skempton and Bjerrum and Lacasse's approximation showed reasonable agreement with the observed values.

Skin friction tests on driven piles in soft Bangkok clay : Brenner, R P. Balasubramaniam, A S Proc 6th Budapest Conference on Soil Mechanics and Foundation Engineering, Budapest, 2–5 October 1984P327–334. Publ Budapest: Akademiai Kiado, 1984

Skin friction tests on driven piles in soft Bangkok clay : Brenner, R P. Balasubramaniam, A S Proc 6th Budapest Conference on Soil Mechanics and Foundation Engineering, Budapest, 2–5 October 1984P327–334. Publ Budapest: Akademiai Kiado, 1984