Dense Silt Research Articles

Experimental study on the bearing property of the composite foundation with stiffened deep cement mixing pile based on the PHC pile

Inserting a prestressed high-intensity concrete pipe pile into a cement–soil mixing pile can form a new composite pile named the composite foundation with stiffened deep cement mixing (SDCM) pile. The Huanghuai alluvial stratum in China is selected to carry out the in situ test for the SDCM pile, and the bearing capacity of the SDCM pile is tested by the slow-speed maintenance load method. The results show that for an SDCM pile with dense silt and fine sand as the bearing layer, the characteristic value of bearing capacity can reach 2,300 kN, which means an SDCM pile with a length of 8.0 m meets the load requirement of a general high-rise building. Further analysis shows that the SDCM pile saves more than 40% of the cost compared with the traditional CFG pile and has better quality control advantages at the same time. This research can provide basic data and design references for similar site foundation projects.

Experimental Study on Silt Liquefaction by Shaking Table Test

Based on the shaking table test, the liquefaction of silt under earthquake load and the earthquake damage after liquefaction are studied. The test results show that the lower silt is relatively dense, the pore pressure increases slowly, and the pore pressure ratio can not reach the initial liquefaction state. However, under the stronger earthquake action, the dense silt may also produce liquefaction, which indicates that the increase of pore water pressure has a great relationship with the compactness and earthquake intensity under the earthquake load. Because the permeability coefficient of silt is relatively low, the increase and dissipation of pore pressure are relatively slow. After the earthquake, he pore pressure of silt continues to rise, and the liquefaction will be further aggravated.

BEHAVIOR OF A DENSE NONPLASTIC SILT UNDER CYCLIC LOADING

Density of granular soils is increased after being subjected to seismic loading, leading to settlements in deeper layers. Foundation systems and shallow buried structures are affected from possible damage due to settlements induced by seismic action. Since studies on liquefaction behavior of silts is limited, it was considered to carry out an experimental study for evaluation of strength behavior of dense silts under cyclic loading conditions. All the tests were performed on specimens at a relative density of 80%, by application of constant level sinusoidal stresses under a frequency of 0.1 Hz. As a consequence, cyclic behavior of a dense silt is experimentally determined and evaluated by application of ten different cyclic stress ratio values.

Load Transfer Calculation and Analysis of Large-Diameter Bored Piles According to Rules Based on Test Pile Measurement

This study aims to establish an appropriate method to calculate the bearing deformation of large-diameter bored piles in alluvial deposits with soils characterized mainly by medium-dense to dense silt, fine sand, and plastic to hard plastic silty clay in the middle and lower reaches of the Yellow River. According to the field measurement results of 18 large-diameter bored piles in six sites of the third-ring expressway project in Zhengzhou, this study discusses the action laws of pile shaft friction with pile-soil shear displacements and pile tip resistances with pile end displacements. A pile shaft load transfer model and pile tip bearing model are then established for large-diameter bored piles. The calculation parameter values are also given. The feasibility and rationality of the calculation method are verified by an engineering example. According to the engineering example and by changing the parameters of the pile diameter and pile length, the properties of bearing capacities and deformations of the large-diameter bored piles under this site condition are further analyzed. Results show that the inflection point of the pile Q~s curve is obvious for large pile diameters. The pile bearing capacity and deformation property are significantly improved by increasing the pile diameter under a small load. The increase amplitude of the pile bearing capacity and deformation property obviously decreases with the increase in pile length. This result indicates that the improvement of the pile bearing capacity and deformation property by increasing the pile length is not effective. The pile without grouting shows an obvious puncture damage model. Moreover, the settlement of the pile without grouting is small with a large pile diameter or short pile length. The effective length and bearing capacity of a large-diameter bored pile can be greatly increased by pile tip post grouting. The increased value of the pile bearing capacity is high with a large pile diameter and pile length under pile tip post grouting conditions.

Effect of dry density on the liquefaction behaviour of Quaternary silt

Quaternary silt is widely distributed in China and easily liquefies during earthquakes. To identify the influence of the dry density on the liquefaction behaviour of Quaternary silt, 40 cyclic triaxial liquefaction tests were performed on loose silt (dry density ρd=1.460 g/cm3) and dense silt (ρd=1.586 g/cm3) under different cyclic stress ratios (CSRs) to obtain liquefaction assessment criteria, determine the liquefaction resistance, improve the excess pore water pressure (EPWP) growth model and clarify the relationship between the shear modulus and damping ratio. The results indicate that the initial liquefaction assessment criteria for the loose and dense silts are a double-amplitude axial strain of 5% and an EPWP ratio of 1. The increase in the anti-liquefaction ability for the dense silt is more significant under lower confining pressures. The CSR of loose silt falls well within the results of the sandy silt and Fraser River silt, and the dense silt exhibits a higher liquefaction resistance than the sand-silt mixture. The relationships between the CSR and loading cycles were obtained at a failure strain of 1%. The EPWP development in the dense and loose silts complies with the “fast-stable” and “fast-gentle-sharp” growth modes, respectively. The power function model can effectively describe the EPWP growth characteristics of the dense silt. Finally, based on the liquefaction behaviour of silt, a suggestion for reinforcing silt slopes or foundations is proposed.

FIRST RECORDS OF MICROLAIMUS TENUISPICULUM DE MAN, 1922 (NEMATODA: MICROLAIMIDAE) FROM THE BLACK SEA

First detection of free-living nematodes Microlaimus tenuispiculum de Man, 1922 from the Black Sea is marked. Species is found off the coast of Crimea and on the NW shelf of the Black Sea (in areas of Zernov’s Phyllophora Field and submarine Dnieper Canyon) at depths from 5 to 190 m on different types of sediment (sandy-silt, dense silt clay and silt with hydrogen sulphide). Description with illustrations of M. tenuispiculum is given. The Black Sea specimens differs by the shorter tail (c = 7.3–9.1 vs c = 6–7.5), shorter esophagus (b = 6.9–8.2 vs b = 6–6.9) and the presence of somatic setae.

Sedimentation in a small lake following conversion of bottomland forest to row cropping

Areas of native bottomland hardwood forest in the lower Red River basin in Louisiana were cleared for row cropping around 1970. Erosion and sediment deposition in channels and lakes presumably increased, affecting hydrologic connectivity and lake ecosystems. Sediment deposited in a representative small lake after land conversion was determined in 2000 from the distribution of cesium (137Cs) with depth. Sediment consisted of low-density clay deposited above dense silt loam. Organic carbon (C) and 137Cs profiles had lower and upper concentration maxima. The lower maxima established the circa 1970 lakebed at ≤0.9 m (3 ft) above the morphological discontinuity and from 2.1 to 1.3 m (6.9 to 4.3 ft) below the 2000 lakebed at positions midlake and halfway to the bank, respectively. The upper maxima were likely due to progressive land conversion around the lake, coupled with increasing clay content of sediment upwards to the 2000 lakebed. A quiescent settling model was used to estimate the composition of runoff water necessary to produce the depth, texture, and density of sediment above the lower 137Cs maxima. The Annualized Agricultural Nonpoint Source water quality model was calibrated to match this composition, and sediment accumulation under alternative management scenarios was calculated. Compared to conventional-till (CT) soybeans (Glycine max L.) for 30 years, CT with cover crop (CC), no-till (NT), NT with CC management, and forest might have reduced sedimentation in the lake by about 20%, 40%, 60%, and 98%, slowing changes in light penetration, temperature, turbidity, and chemistry that affect the lake ecosystem.

Large-Diameter Pipe Piles Driven for Ebey Slough Bridge Replacement Project, Marysville, Washington

This paper presents a case study of large-diameter open-end steel pipe piles for the Ebey Slough Bridge Replacement Project. The new Ebey Slough Bridge was an approximately 700-ft-long, four-lane bridge over Ebey Slough in Marysville, Washington. The project site was underlain by more than 300 ft of very loose to medium dense silt, silty sand, and silty clay. New bridge foundations consisted of 4- and 6-ft-diameter open-end steel pipe piles driven to depths ranging from approximately 150 to 240 ft. Geotechnical design of the open-end pipe piles was performed by Shannon & Wilson, Inc. Total pile compressive resistances were confirmed through a dynamic test pile program during pile installation. The static design methods provided in AASHTO are compared here to results of the dynamic test pile program. Results of the dynamic test program suggest that static design methods overestimate nominal side resistance of 4- and 6-ft-diameter open-end pipe piles. Comparison of factored side resistances using the static design methods and AASHTO resistance factors suggest potential limitations of AASHTO resistance factors for large-diameter piles.

Predicting wave-induced scour around a circular pile

This study presents gene-expression programming (GEP) as an alternative tool for the prediction of scour depth around a circular pile due to waves in a medium dense silt and sand bed. The proposed models are developed in terms of dimensional and non-dimensional parameters affecting scour process the most. The training and testing data sets of the proposed GEP and other models are experimental results sourced from the literature. The performance of GEP is then compared with the performance of neural networks technique, and also regression-based equations developed by the authors and others. The training and testing results are given in terms of the most widely used statistical measures and also scatter plots. The predictive performance of GEP models was found to be superior to the neural networks technique and regression-based equations.

Linear genetic programming for prediction of circular pile scour

Genetic programming (GP) has nowadays attracted the attention of researchers in the prediction of hydraulic data. This study presents linear genetic programming (LGP), which is an extension to GP, as an alternative tool in the prediction of scour depth around a circular pile due to waves in medium dense silt and sand bed. Field measurements were used to develop LGP models. The proposed LGP models were compared with adaptive neuro-fuzzy inference system (ANFIS) model results. The predictions of LGP models were observed to be in good agreement with measured data, and quite better than ANFIS and regression-based equation of scour depth at circular piles. The results were tabulated in terms of statistical error measures and illustrated via scatter plots.

Wave Scour around a Pile in Sand, Medium Dense, and Dense Silt

This paper summarizes the results of an experimental investigation on wave scour around a circular pile in three kinds of soil, namely in dense silt (with a relative density of Dr=0.74), in medium dense silt (with Dr=0.38), and in sand (with Dr=0.23). The dense silt was achieved by wave liquefaction. Upon the completion of the liquefaction/compaction process, the pile was subjected to wave induced scour. The range of the Keulegan-Carpenter number (KC), tested in the experiments is from practically 0 to approximately 20. The Shields parameter in the experiments was such that the bed was live. The scour depth was increased by a factor of 1.6–2 when the bed soil was changed from medium dense silt or sand to dense silt. This is partly due to an increase in the angle of friction. The time scale of scour also was influenced by the density of the soil. The time scale was largest for the dense silt case, and smallest for the sand case in the experiments.

The effect on anisotropy of rotating the principal stress axes during consolidation

It is well known that Ko-consolidated natural sediments have anisotropic strength, yielding and stiffness characteristics, particularly at low overconsolidation ratios. For example, the undrained triaxial compression shear strengths developed after Ko-consolidation far exceed those available in extension. This paper describes recent hollow cylinder apparatus research into other types of stress-induced anisotropy, reporting experiments on dense silt samples that involved rotation of the principal stress axes during consolidation. The results show strikingly different anisotropies from those developed by Ko-consolidated samples. The effective stress paths chosen for the laboratory studies were guided by the conditions expected under multi-stage embankments built on soft ground, but the results have considerable significance in other practical geotechnical problems.

Observations of minipile performance under cyclic loading conditions

Pressure-grouted minipiles were installed and tested to evaluate load-carrying capacity under reversed-direction, cyclic loading conditions. The minipiles, expected to support catenary structures along Amtrak's Northeast Shoreline East Corridor, were installed through loose to medium dense sand and silt. Tests were conducted such that loads were applied in varying increments and decrements of the calculated design capacity of 50 kip. Load tests, performed in accordance with the ASTM D1143 Quick Loading Method, showed considerable reduction in capacity after only two cycles of loading at as low as 60% of the ultimate capacity. This observation indicated that, similarly to previous tests on drilled shafts, minipiles installed in cohesionless soils have a critical level of repeat loading that is well below the ultimate pile capacity under static conditions. Des minipiles cimentées sous pression ont é té installées et testées afin d'évaluer leur capacité porteuse dans des conditions de charge cyclique, à direction inversée. Ces minipiles, qui doivent soutenir des structures de caténaires le long de la ligne Northeast Shoreline East Corridor de Amtrak ont é té installées dans des sables et limons de densité moyenne à meuble. Les essais ont été conduits de facçon a` ce que les charges soient appliquées en divers incréments et décréments de la capacité nominale calculée de 50 kip. Les essais de charge, effectués en conformité avec la méthode de chargement rapide ASTM D1143, ont montré une nette réduction de la capacité après seulement deux cycles de chargement à un bas niveau—60% de la capacité ultime. Cette observation indique que, de meê;me qu'avec les essais précédents sur des puits forés, les minipiles installeés dans des sols non cohésifs ont un niveau critique de chargement répétitif qui se situe bien en dessous de la capacité ultime de la pile en conditions statiques.

Testing of drivability of concrete piles and disturbance to sensitive clay

The results reported are of an investigation of a group of thirteen 12 in. (30 cm) diameter precast concrete piles driven through 60 ft (18 m) of sensitive marine clay followed by 10 ft (3 m) of silt and sand and 13 ft (4 m) of very dense silt to end bearing in glacial till. The purpose of the test is to study the drivability of the piles through very dense soil and to measure the disturbance caused to the sensitive clay by the driving of displacement piles. Following a literature review, the paper presents the soil conditions at the site and the testing program. The test results are discussed and experience gained from the follow-up of the driving of 520 piles at the site is presented.Visual observations during pile driving, and analysis of driving records, show that a high pile quality is necessary at the site. The large driving resistance encountered in the very dense silt (150 to 300 blows/ft) would prevent low quality piles from reaching the competent glacial till and developing the needed bearing capacity.Pile loading tests showed the piles to have an ultimate bearing capacity exceeding 450 tons (4.0 MN). It was established that the shaft resistance in the clay during test loading was between 100 and 125% of the undrained shear strength of the clay as measured by field vane testing. In comparison, an uplift test to failure showed that the uplift shaft resistance along the pile in the clay was only 60% of the undrained shear strength of the clay.The pile driving developed large pore pressures in the clay which exceeded the effective overburden stresses. The excess pore pressures dissipated over a period of slightly more than 3 months. Vane testing within the pile group immediately after driving showed that a shear strength reduction of about 15% was caused by the piles. At a distance of 2 ft (0.6 m) outside the pile group, no strength reduction was found. The reduction within the group was gradually regained during the dissipation of the induced pore pressures. Laboratory testing on clay samples obtained within the pile group 75 days after pile driving showed a smaller value of the preconsolidation pressure of the clay, but no change in the compression indices.

Temporary and Permanent Earth Anchors: Three Monitored Installations

This paper presents the results of measurements of earth anchor performance for three separate installations in Metropolitan Toronto. The first case records the results of instrumentation on the high grout pressure Bauer anchor used to support an approximately 30 ft (9.1 m) deep excavation in dense fine sand. The second presents the load measurements made on low grout pressure earth anchors installed in very stiff clay of a 29 ft (8.8 m) excavation. The third installation involved measurements on permanent vertical anchors set in extremely dense silt till.In the first instance the average measured load was somewhat lower than the installed load and the design assumption. In the second case, in the stiff clay, the load was somewhat higher than the design value but this was attributed to the probability of load transfer because of inadequate support at lower levels. In this case, considerable variation and possible overstressing of anchor wires was noted.A very high uplift resistance was recorded for the permanent anchors in dense till. Control of groundwater during installation of these anchors was the principal lesson learned from this work.

Instrumented Foundations for two 43-storey Buildings on Till, Metropolitan Toronto

Settlement records have been obtained for a two-year period during and following construction of two 43-storey buildings in mid-town Metro Toronto, Ontario. One structure is supported on caissons varying in length from 45 to 70 ft (13.7 to 21.3 m) long, belled to a maximum of 12 ft (3.7 m) diameter and supported on dense silt till. The other is supported upon a raft foundation above the till. Protected rods have been inserted in four heavily loaded caissons to determine total settlement as well as differential settlement along the concrete shaft. Settlement devices have been installed at two levels in the till below the raft foundation and a pattern of differential settlement under the building has been established. It appears that all load has reached the base of the caissons and therefore that no load of consequence is being taken by the massive caisson caps or by the shafts. The settlement under the raft follows the flexible foundation pattern only approximately. In both buildings there appears to be load redistribution due to rigidity.

Relaxation of Piles in Sand and Inorganic Silt

Many attempts have been made to modify the pile driving formulas to make them realistic in terms of modern driving practices and equipment. None seems to have had a long-lasting impact on the engineering profession. The driving impulse of a pile is always associated with a temporary remolding of surrounding soil, a zone of excessive pore water pressure and the dilatancy of dense fine sand. For piles subjected to loading tests or under the load of a structure, there is no displacement in the soil; therefore, no remolding, no dilatancy and no excessive pore water pressure arise around the pile. A review has been made of the basic mechanics relating to relaxation of pile resistance in dense fine sand or inorganic silt as well as the freeze of piles in soft clay or organic silt. The pile resistance at the beginning of redriving can be used more effectively in representing the static capacity of a pile than that encountered in initial driving.