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Journal Volume 41 No. 2 - June 2010
Abstract
The Performance Based Design in geotechnical engineering requires an extensive research work prior to the details establishment for the design. The seismic performance of the piles is certainly of this interest, thus worthwhile discussions for the engineers. This paper would allow one to find the example of the studies based on PBEE and EQWEAP analyse. A numerical study was conducted for the piles located in Taipei Basin where the seismic conditions are significantly important to the design engineers. Therefore the local seismic design concerns of the Building Code were also incorporated into the measurements. Follow the simplified form of PEER Framing equation, probabilities of the possible pile performance parameters were able to examine whereas the prospectives of such analyses are suggested accordingly.
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The authors were invited by the Malaysian Highway Authority to participate in the prediction of geotechnical performance in a large and comprehensive full scale trial embankment test on very soft Malaysian marine clay. Both basic in-situ and laboratory geotechnical data were provided to the predictors together with the embankment and site details. This paper describes the use of the conventional limit equilibrium slip circle method, and elasto-plastic finite element methods (using both a total stress soil model and an effective stress soil model) to predict the embankment behaviour during the field trial. The predictions were mainly concerned with the stability of the embankment and the development of vertical and horizontal deformations and excess pore pressures. Some of the computer predictions are compared with hand solutions which were carried out using simple conventional geotechnical methods. Comparisons are presented between measured and predicted behaviour, and predictions by three other predictors are also summarized.
Discrete wave equations can be used to monitor pile responses under superstructure loads and earthquake excitations. The procedure EQWEAP has been suggested to compute seismic pile responses based on wave equation analysis of the pile. Alternative solutions were adopted to model the effects of soil liquefaction and liquefaction induced lateral spreading. This paper aims to discuss the discrete equations and modelling concerns of these solutions. Comparisons of these solutions on a case study of pile foundation in 1995 Kobe earthquake were made. It can be seen that all the solutions are rational enough to provide essential and effective predictions providing that the model parameters are carefully calibrated prior to the analysis.
General solutions are developed for the rotational stability analysis of an embankment with and without reinforcement constructed on soft ground that has an undrained shear strength varying with depth. The general cases of an embankment having a berm, dry or wet tensile cracks, and multiple layers of reinforcement are considered. The additional friction caused by the reinforcement force normal to the slip plane is incorporated into the solution. The solutions are presented in the form of simple equations. The relationship between the critical slip circles through the embankment with and without reinforcement is expressed explicitly. The analysis procedures and supporting graphs allow the user to obtain the solutions using hand computations. A simple computer program in the form of a worksheet was developed to quickly obtain the final results. Applications and illustrative examples of embankments with one- and two-step berms, and distributed loads are given. The results obtained using the approach presented in this paper compare very well to the solutions obtained from the method of slices using the computer programs SB-SLOPE and PC-STABL6.
For piezocone penetration in clays, cavity expansion theory describes both the point resistance and induced excess pore water pressure in terms of the undrained shear strength (Cu) and rigidity index (Ir = G/Cu). Modified Cam Clay provides a simple effective stress representation of undrained behaviour in terms of stress history. Therefore, the two theories may be combined to provide an approximate determination of the in-situ overconsolidation ratio (OCR = σ′p/σ′vo) in terms of the effective stress friction angle (φ′) and normalized piezocone parameter (qT-Um)/σ′vo, in which qT = corrected cone resistance and Um = measured pore water pressure. The approach distinguishes between piezocones which measure pore water pressures on the cone tip/face (Ut) and those which measure just behind the tip (Ubt). Specific examples are presented to show the general applicability of this simple effective stress model for estimating the in-situ stress history of clay deposits with 1 < OCRs < 60 and 20° < φ′ < 40°.
The liquefaction induced pile responses have attracted research attentions for many years. Modern geotechnical performance-based design codes therefore require proper structural analyses to predict deformations and stresses of the piles during earthquake. With these regards, this paper suggests a simplified but effective procedure called EQWEAP for the modeling. In such procedure, seismic ground motions of a free-field site, where the possible liquefaction effects might occur, were first calculated from one-dimensional lumped mass model. The ground displacements were then used to solve the discrete wave equations to obtain the corresponding pile displacements. To procure better solutions, excess pore pressure from the empirical model was carefully calibrated with considering the liquefaction potential of the soils. A couple of case studies based on pile foundation failures reported on the Niigata earthquake in 1964 were conducted to see the applicability of this procedure. Overall, this solution, which is quite simple though, can predict the pile responses due to the soil liquefaction.
Pile foundations have been used to support embankments over soft soil. Conventional piled embankments require inclined piles to resist lateral thrust from the embankment soil and a large coverage of pile caps to prevent the formation of depression on the surface of the embankment. An alternative to conventional piled embankments is geosynthetic reinforced platform/piled embankments (GRP piled embankments), which eliminate inclined piles and minimize the need for the necessary coverage of pile caps. A survey of completed GRP piled embankments indicated that the average percent coverage of pile caps over total foundation areas was only 10% to 20% versus the 30% to 70% of conventional piled embankments. This paper focuses on studying the load transfer mechanisms among pile (caps), soil, and geosynthetic, reviewing and discussing field test data from piled embankments and loading tests, and conducting a simplified parameter study to demonstrate the influence of foundation soil resistance and geosynthetic on settlement of GRP piled embankments. The load transfer mechanisms between pile caps, geosynthetic, and soil are: 1) embankment soil arching, 2) tensioned membrane or apparent cohesion effect associated with the geosynthetic, and 3) stress concentration due to the stiffness difference between pile and foundation soil. Field studies show that the inclusion of geosynthetic reinforcement can significantly increase the stress concentration ratio, defined as the ratio of the stress on pile (caps) to that on the foundation soil. It is also shown that pile stiffness plays an important role in the stress concentration ratio. Parametric studies demonstrate that the increase of foundation soil resistance and/or apparent cohesion can reduce the equal settlement plane height above the geosynthetic reinforced platform.
Settlement and stability are the primary geotechnical considerations in the design of embankments founded on soft clay. Settlements are inevitably associated with lateral deformations. Lateral flow in turn is an indirect measure of the stability of embankments. Therefore, a detailed study of different settlement components and lateral deformations and their correlations will provide guidelines for an embankment design. This paper presents a new methodology, termed ''Field Deformation Analysis (FDA),'' which is based on a simple concept dealing with lateral and vertical deformation characteristics of soft foundations under embankment stage loading. This method is used to delineate and quantify different settlement components, namely, immediate settlement, consolidation settlement, and creep settlement, from the total settlement measured during field observations, for the loading and consolidation stages. Finite element method (FEM) of analysis was performed for comparison with FDA results. The FEM analysis was performed using the CRISP computer program, developed at Cambridge University, which uses many soil constitutive models including the modified Cam-clay model. In 1988, the Malaysian Highway Authority was authorized to build 13 full-scale test embankments at Muar Flats, of which two were constructed without any foundation ground improvements. A comparison study of the results from FDA and FEM, performed for both the untreated full-scale test embankments, revealed very good agreement during loading and consolidation stages. In addition, a consistent relationship between the different settlement components was also observed during the different stages of embankment loading.
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, k(h)', 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.
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; andCv(field)/Cv(lab) = 26; whereSuvis the uncorrected vane shear strength. It was also found that C„ 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 beginning of construction. Prediction of long-term settlements yields a good estimate for firmer sections using the method of Skempton and Bjerrum, while the method of Asaoka generally underpredicts. The elastic method of Davis and Poulos gives the best estimates of both construction and postconstruction settlements when backfigured parameters are used.
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 found to be less significant for spacing to diameter ratios above 75. The laboratory tests, in general, gave conservative values of the pullout resistances as compared with the field tests. The proposed prediction equations agreed well with the experimental data.
A case study for the reclamation of a slurry pond as part of an offshore reclamation project in Singapore is presented in this paper. The slurry pond covered an area of 180 ha. The slurry in the pond was recently deposited ultra-soft high-plasticity clay. The water content of the slurry was more than 120% and the undrained shear strength was less than 8 kPa. The reclamation was first carried out by spreading sand fill in thin layers 20 cm thick using a specially designed sand spreader. The filling speed was carefully controlled to allow the slurry to be consolidated before more fill could be placed. Despite the precautions a failure occurred, in the form of mud bursting. As a remedial measure, geotextile sheets were used to cover a total area of 630 000 m(2) before more sand fill was placed. After the completion of fill placement, fill surcharge and prefabricated vertical drains (PVDs) were used to improve and accelerate the consolidation of the slurry. As the performance of PVDs would deteriorate after they had undergone large deformation, they were installed in two passes. In the first pass PVDs were inserted with a square grid spacing of 2.0 m. After nearly 1.5 m of settlement had taken place, the second pass of PVDs with the same spacing was installed at the centre of the square grid of the PVDs installed in the first pass. After nearly 4 years of consolidation, the top of the slurry had settled more than 3 m. The undrained shear strength had also increased substantially. Therefore the use of PVDs for the improvement of the ultra-soft slurry was successful in this project.
The Changi East reclamation project was carried out in five phases along the foreshore of the east coast of Singapore. The water depths in the reclaimed area ranged from 5 to 15 m. The project involved hydraulic placement of 272 million m(3) of sand onto soft seabed marine clay up to 50 m thick. A linear total of 170,000 km of prefabricated vertical drains (PVDs) were installed for accelerating the consolidation process of the underlying soft marine clay. The soil improvement works covered a total area of approximately 1200 ha. In this paper, the site conditions and the soil improvement works adopted are described. Pilot tests with full-scale field instrumentations as well as laboratory and in situ tests were carried out to verify the design, check the effectiveness of the soil improvement works using PVDs, and establish the most suitable drain spacing. Field monitoring data obtained from both the pilot tests and the reclamation works are presented and interpreted. Degree of consolidation was calculated based on both settlement and pore pressure data.
The influence of stress history and stress state during consolidation and shearing were studied experimentally under undrained triaxial compression and extension modes, by using the Recompression and SHANSEP techniques. In the SHANSEP tests, the samples were consolidated to a vertical consolidation stress of about 1.5 to 2 times of the preconsolidation pressure under K. consolidation condition, followed by swelling to required overconsolidation ratio before subjecting to undrained shear. Whereas in the Recompression technique, the samples were directly consolidation to in situ effective stress before undrained shearing, the volumetric strains of the reconsolidation were less than 2%, indicating relatively reasonable sampling quality. From the undrained shear results, the Recompression tests give higher undrained shear strength than estimated from SHANSEP tests by about 28%, indicating that some destructuring of soil structure may have occurred in the SHANSEP tests due to large vertical deformation during consolidation. Consequently, the undrained shear strength and the undrained modulus obtained from the SHANSEP tests were much lower.
This paper presents the results of the coefficient of consolidation in the horizontal direction determined from the laboratory and the field through testing, along with back analysis from settlement measurement of embankment constructed with prefabricated vertical drains at the Suvarnabhumi Airport site in Bangkok. Constant rate of strain consolidation tests with radial drainage and standard oedometer tests were conducted to provide the consolidation characteristics of soft Bangkok clay. A 20-mm piezoprobe was used to measure the pore water pressure dissipation characteristics of the soft clay in the field, and the corresponding horizontal coefficients of consolidation were estimated based on established theory. The test results, such as the horizontal coefficients of consolidation and permeability, were compared with back analysis of the constructed runway embankment based on Asaoka method. The results show very good agreement in both horizontal coefficients of consolidation and permeability obtained from different testing methods and back analysis, implying the reliability of the testing methods adopted.
To reduce consolidation time it is necessary to shorten the length of flow paths within the soil. One way of doing this is to install vertical drains of high permeability. Thereby porewater can also escape in the horizontal direction towards the drains and flow freely along the drains vertically to a drainage blanket placed on the soil surface or to other highly permeable layers deeper down in the soil. Prefabricated drains were introduced into the field of geotechnical engineering in 1937, almost simultaneously with sand drains. Subsequently several types of band-shaped drains were developed all over the world and today the number of new prefab drains appearing on the market is rapidly increasing. The article discusses types of prefabricated drains that are available and design of them, including spacing, well resistance, effect of disturbance, filter requirements and other design factors. Refs.
This paper discusses the various issues involved in the design of piled embankments, and then describes the application of computer analyses of piled strip and raft behaviour to the piled embankment problem. These analyses are implemented via a program called GASP (Geotechnical Analysis of Strip with Piles). Using this program, the effects of other key parameters are also studied, and the design of transition areas is discussed. It is shown that optimum pile design will generally require the use of piles of different length and/or stiffness in order to even out the settlements. The ground movement arising from the piling platform construction may also have a major effect on this design.
In order to minimize differential settlement of a 4 km long runway for the proposed Changi International Airport in Singapore 100% primary consolidation of the marine clay prior to pavement construction was required. For the purpose of determining the field behavior of marine clay, a fully instrumented pilot test was conducted using vertical sand drains and flexible drains, for consolidating marine clay under static surcharge load. A separate test was made to study the influence of high impact energy on the consolidation process of marine clay. This paper describes the details of the pilot test which was planned with the information from site investigation and laboratory test data and the selection of an economical spacing for flexible drains based on the pilot test results. The field data are utilized to back calculate the geotechnical parameters operational in the field.
Three factors; the inclination angle, the depth of the potential failure layer and the catchment area, are deemed the most important of the many factors that are involved in surface mountain slope failures. A groundwater movement model is proposed with which to obtain the height of the groundwater table in the potential failure layer. Instead of the catchment area, the height of the groundwater table, which is influenced by the topographical characteristics of a mountain slope, is used in our new prediction method. This new prediction method, based on infinite slope stability analysis, takes into account the three most important factors. Results show that our new method can be used to predict accurately past failed sites.
It is an important topic to analyze the response of lateral pile subjected to liquefaction-induced flow pressure in designing pile foundation in liquefying ground. There are two methods currently available to perform the analysis. One is the force method that uses the liquefaction-induced flow pressure as the external force acting on the pile. The other is the displacement method that imposes a lateral ground displacement profile on the pile and softens lateral subgrade reaction to analyze pile response. Both two methods can capture the pile response very well. However they are so complicated that the analyses usually have to be solved by numerical methods. Based on some reasonable assumptions, this paper presents a simplified closed form solution for the analysis. It is a combination of the solutions of an Euler's beam and an elastic lateral pile. The solution is used to analyze the case of damaged pile due to lateral spreading caused by ground liquefaction during Kobe earthquake. The calculated result by the solution agrees the field performance well.
Embankments constructed on soft soil often lead up to structures such as bridges, that are founded on piles. Movement of the structure will be limited by the piled foundation, whereas the embankment may settle significantly and cause lateral spreading of the subsoil. One method of avoiding problems is to use a grid of piles to support the embankment in the vicinity of the structure. The paper presents an analysis of the arching action of granular embankment fill overlying a rectangular grid of pile caps. The analysis is based on experience gained from laboratory model tests. Expressions are developed giving the degree of support offered by the pile caps in terms of the geometry of the piles and the properties of the embankment. Comparisons with measurements from field and model tests show good agreement with the results of the analysis.
A simple, practical procedure for representing the nonlinear, stress-dependent, inelastic stress-strain behavior of soils was developed. The relationship described was developed in such a way that the value of the required parameters may be derived from the results of standard laboratory triaxial tests. Comparisons of calculated and measured strains in specimens of dense and loose silica sand showed that the relationship was capable of accurately representing the behavior of sand under triaxial loading conditions.
It is now possible to make reliable predictions of settlement of embankments on soft clays. In most situations, where the embankment is designed to resist undrained instability during construction, one-dimensional settlement analysis is applicable and is the most appropriate approach. Equipment and procedures for high-quality soil sampling for laboratory tests, as well as reliable in situ tests are available for detailed profiling of compressible ground. With the help of the computer, it is no longer necessary to idealize the compressible profile into one or two homogeneous layers. The most important information required for settlement analysis is for each layer, end-of-primary e-log σv′ curve, including reliable estimate of σp′, and e-log kv, as well as e-log kh relations when vertical drains are used. The proposed approach and procedures are illustrated by predictions and field observations of surface and subsurface settlement for ten large-scale embankment construction projects. Analysis of field observations suggest that prefabricated vertical drains in typical field situations mobilize discharge capacities significantly less than those measured in laboratory longitudinal flow tests. However, in most soft clay applications the mobilized discharge capacity of high-quality prefabricated drains is comparable to the minimum discharge capacity required for negligible well resistance.
The paper presents a simple solution for the calculation of consolidation of fine-grained soils by drain wells with regard to well resistance and smear. The result obtained by this solution is compared with existing but more complicated solutions. A parametric study is made with regard to the effect of discharge capacity of various drain types and to the effect of smear. Prefabricated band-shaped drains are discussed and their efficiency is compared with that of sand drains. Discharge capacity values of different prefab drains obtained in laboratory tests are presented. Filter requirements are analyzed.
The important factors affecting the dynamic response of saturated sand layers to earthquake motions are: (1)The initial shear modulus in situ; (2)the variation of shear modulus with shear strain; (3)contemporaneous generation and dissipation of pore-water pressures; (4)changes in effective mean normal stress; (5)damping; and (6)hardening. Constitutive relations are formulated that take all these factors into account and these are incorporated into a nonlinear method for the dynamic effective stress analysis of saturated sands. The method predicts the phenomenological features of the dynamic response of saturated sand layers that commonly occur as the pore-water pressure rises in the sand during earthquake shaking. It allows the distribution of pore-water pressure and the effects that drainage and internal flow have on the location and time of liquefaction to be determined quantitatively.
A critical review of field performance of sandy soil deposits during past earthquakes is conducted with special emphasis being placed on Standard Penetration Test N-values and fines content. The field relationship between adjusted dynamic shear stress ratio and normalized SPT N-values together with laboratory tests on undisturbed sands indicate that (1) sands containing more than 10 percent fines has much greater resistance to liquefaction than clean sands having the same SPT N-values, (2) extensive damage would not occur for clean sands with SPT N1-values (N-values normalized for effective overburden stress of 1 kgf/cm²) greater than 25, silty sands containing more than 10 percent fines with SPT N1-values greater than 20, or sandy silts with more than 20 percent clay, and (3) sands containing gravel particles seem to have less resistance to liquefaction than clean sands without gravel having the same SPT N-values.
On the basis of the above findings, an improved empirical chart separating liquefiable and non-liquefiable conditions is presented in terms of dynamic shear stress ratio, SPT N-values, fines content, and shear strain amplitude.
The Cα/Cc concept, which completely defines secondary compression behavior of any one soil in terms of a constant Cα/Cc and the EOP e-log is a powerful practical tool for settlement analysis and interpretation of data from load-controlled and deformation-controlled consolidation tests. The correct procedure for evaluating Cα/Cc for any soil is described. The Cα/Cc concept was used to obtain an expression for the behavior of the coefficient of earth pressure at rest, K0, during secondary compression. This approach predicts an increase in K0 during secondary compression. This approach also predicts that the K0 = 1 condition will not be reached during the typical geologic age of soft clay deposits. Laboratory measurements on the behavior of K0, including during secondary compression, are presented for four soft clays. The proposed approach also provides an estimate of in situ K0 in soft clay deposits. Two alternative laboratory procedures were used to determine in situ K0 for four soft clays. These values compare well with the predictions.
Thick marine clay deposits underlying reclamations have often been treated with vertical drains and surcharge to reduce excessive differential settlements before construction of roads, runways and other structures. Biot's theory of consolidation is implemented, using a 2 D plane strain finite difference scheme, in the solution of the field consolidation problems. To simulate the effect of vertical drains, the soil with drains installed was approximated to a soil with an equivalent increased vertical permeability in a rational manner. The numerical scheme was used to demonstrate the back pressure effect caused by the inflow and backup of excess pore pressure from the untreated clay into the treated zone causing a retardation of consolidation settlement in the latter. A study of the effect of drained-treatment width and surcharge width showed that these parameters significantly affect the rate of consolidation settlement in the treated zone, and therefore it is important to consider these parameters in the design of drains and surcharge in reclamation works.
The use of analytical solution of consolidation equation for settlement prediction is not always effective since such conditions as an initial distribution of excess pore water pressure, drain length, final vertical strain of soils and the coefficient of consolidation are sometimes quite uncertain in practical engineering problems. For this reason, an observational settlement prediction is freshly presented. First, the linear ordinary differential equation derived is demonstrated to give a settlement-time relationship. After that, by using the difference form of the equation (an autoregressive equation), observational procedure of settlement prediction is proposed. Two kinds of practical methods are presented. One is a graphical method, the advantage of which is its simplicity. The other is the method based on the Bayesian inference of the non stationary stochastic process, which can give a predictive probability distribution of future settlement and then also provide a preliminary theory for reliability-based design of settlement problems.The proposed methodology is demonstrated to be also applicable for some other special problems including settlement due to drainage from sand piles.
The field vane shear test is one of the most common in situ tests to obtain the undrained shear strength of soft clay. Uncoupling of the torque generated by the soil resistance along the vertical and horizontal planes of the vane has been done by conducting conventional direct shear test and newly developed vertical direct shear test on the soil. From the shear stress-displacement relationship of the direct shear tests, simple analysis is performed to simulate the field vane behavior at various depths. The results of the simulation agree well with those obtained from the field vane tests on soft Bangkok clay. The conventional method of computing the undrained shear strength of the field vane shear based on the maximum torque is close to the equivalent average value from the shear box tests. A special laboratory triaxial vane apparatus was also used to study the shearing behavior of the soft clay with the capability of K o -consolidating the sample before conducting the vane shear test. The results of the triaxial vane tests were also compared with the predictions. The predicted torque values are lower than the experimental data for the same angle of rotation.
This paper describes a method of determining the consolidation characteristics of soft Bangkok clay under the radial drainage condition by using a newly developed constant rate of strain (CRS) consolidometer. A new formulation for this type of test was proposed. A series of constant rate-of-strain consolidation tests were compared to the results of oedometer tests. The pore water pressure distribution across the specimen in the CRS tests was estimated from measurements made at two locations. The results agreed well with the theoretical solution. A simple method of estimating the preconsolidation pressure by means of the pore water pressure ratio is also proposed. Because the tests conducted at different strain rates indicate that apparent preconsolidation pressure increases with strain rate, it is believed that secondary compression occurred during primary consolidation for this clay. The consolidation characteristics, including coefficient of consolidation and coefficient of permeability, in the vertical and horizontal directions were also compared.
A new method called SRICOS is proposed to predict the scour depth z versus time t around a cylindrical bridge pier of diameter D founded in clay. The steps involved are: (1) taking samples at the bridge pier site; (2) testing them in an erosion function apparatus to obtain the scour rate z versus the hydraulic shear stress applied tau; (3) predicting the maximum shear stress tau(max), which will be induced around the pier by the water flowing at nu(o),before the scour hole starts to develop; (4) using the measured z versus tau curve to obtain the initial scour rate z(i) corresponding to tau(max); (5) predicting the maximum depth of scour z(max) for the pier; (6) using z(i) and z(max) to develop the hyperbolic function describing the scour depth z versus time t curve; and (7) reading the z versus t curve at a time corresponding to the duration of the flood to find the scour depth that will develop around that pier. A new apparatus is developed to measure the z versus t curve of step 2, a series of advanced numerical simulations are performed to develop an equation for the tau(max) value of step 3, and a series of flume tests are performed to develop an equation for the z(max) value of step 5. The method is evaluated by comparing predictions and measurements in 42 flume experiments.
This article deals with the prediction of the response to monotonic axial loading of single piles in various soil conditions. A 98-pile load test data base was obtained from the Mississippi State Highway Department and was used to evaluate 13 methods designed to predict the ultimate load of a pile and five methods designed to predict the settlement of a pile. The methods include SPT/5., methods, cone penetrometer methods, a pressuremeter method, and a dynamic formula method. The accuracy and precision of each method is quantified statistically, and a risk analysis is performed in order to properly assess the factor of safety. A cost analysis is also performed in order to find the factor of safety that will minimize the cost of construction plus the cost of a potential failure.
The two fundamental discrepancies between actual consolidation behavior of soils and that predicted by the Terzaghi consolidation theory were explained. Many implications of secondary compression phenomenon, including secondary settlement were explained and predicted by the law of compressibility. The proper role of compressibility with time was empirically established.
This paper presents the current U.S. state-of-practice for the design of the load transfer platform used in column supported embankments. Two design methods are in use in the U.S. today, the catenary and beam method. Both methods are presented, including the fundamental design assumptions that differentiate the two approaches. The paper also provides guidance on the determination of the geosynthetic properties for the load transfer platform based on the method used to design the platform.
Three case histories of failure of piles caused by ground lateral spreading are back studied using the beam on Winkler foundation method including nonlinear soil springs and a nonlinear moment-curvature relation for the pile. Soil loads on the pile are modeled based on the modified Bouc-Wen model. The lateral spreading effect is modeled by laterally displacing the soil spring support by an amount equal to the free field permanent deformation. Design procedures suggested by Tokimatsu et al. (1998) and by JRA (1996) were also used for case histories evaluation and compared to available observation results. Buckling analysis was performed to determine critical buckling load. Whether the cause of failure for the evaluated cases was due to either bending or buckling is also discussed in the paper.
The object of this paper is to furnish the engineer with a simple means of estimating the friction factors to be used in computing the loss of head in clean new pipes and in closed conduits running full with steady flow. The modern developments in the application of theoretical hydrodynamics to the fluid-friction problem are impressive and scattered through an extensive literature. This paper is not intended as a critical survey of this wide field. For a concise review, Professor Bakhmeteff’s (1) small book on the mechanics of fluid flow is an excellent reference. Prandtl and Tietjens (2) and Rouse (3) have also made notable contributions to the subject. The author does not claim to offer anything particularly new or original, his aim merely being to embody the now accepted conclusions in convenient form for engineering use.
A large volume of reliable measurements of one-dimensional settlement, observed in the laboratory and in the field for a wide variety of natural soil deposits, demonstrate that during secondary compression ΔS/ Δ log t may remain constant, decrease, or increase over a significant period of time. This important body of observed data and associated explanations in terms of the Cα/Cc law of compressibility have been apparently overlooked in attempts to describe secondary compression by means of mathematical formulas. Data are presented to illustrate the limitations of "first-order rate equations" to describe secondary settlement.