Sand Drain Research Articles

Progressive Consolidation Settlement of Naturally Deposited Clayey Soil Under Embankment Loading

ABSTRACT In a naturally deposited soil foundation subject to embankment loading, a delayed settlement can often be observed after the embankment's completion, sometimes also showing acceleration over time. Frequently in such cases the soil exhibits an increase rather than a dissipation of excess pore pressure in some of its parts, a phenomenon which cannot be explained by conventional elasto-plastic consolidation theory. In this paper the possible mechanism for this kind of delayed settlement is investigated numerically using a soil-water coupled elasto-plastic computation under plane strain conditions. It is assumed that the soil section contains a medium dense sand layer and highly structured clay layers. A Super/subloading Yield Surface Cam-clay model is used to describe the elasto-plastic behavior of both the sand and the clay with respect to soil structure, overconsolidation and anisotropy. It is found that the delayed settlement behavior occurs under a certain constant embankment load, and persists over a period of 40 years, with increases in the settlement rate accompanied by both dissipation and a rise in excess pore pressure. The cause of this is the softening that co-occurs with the plastic compression of the soil skeleton. In other words, consolidation settlement can be considered as an example of “progressive consolidation with decay of structure”. Some typical characteristics of this delayed settlement behavior are also numerically examined with reference to the height and weight of the embankment, and to soil improvements using sand drains. When the embankment is much lower, the foundation does not undergo delayed consolidation, and when it is higher, the foundation becomes subject to circular slip failure. Soil improvement with sand drains can effectively shorten the length of time up to final settlement.

Improvement of estuarine marine clays for coastal reclamation using vacuum-applied consolidation method

Consolidation occurs in estuarine marine clays for coastal reclamation by dissipation of the excess pore pressure, which is induced by increasing the total overburden stress during conventional mechanical surcharging. The excess pore pressure can be decreased usually by the use of several construction methods such as sand drain and paper drain. Besides the drain methods, vacuum can also be used in the soil mass to consolidate the estuarine marine clays by decreasing the pore pressure as well as increasing the effective stress. The study on vacuum consolidation is devoted so far mainly for laboratory model tests or numerical analysis in Korea. Recently, an instrumentation system was applied to manage the vacuum-applied consolidation on a field, in which a sewage disposal plant was constructed. While vacuum was applied, the behaviors of estuarine marine clays such as the settlement, lateral deformation and pore water pressure have been investigated precisely. The behavior of estuarine marine clays during vacuum-applied consolidation shows some difference from the behavior of estuarine marine clays in the case of conventional preloading. A principal difference is that the lateral deformation corresponding to settlement is smaller than before vacuum application even though the surcharge height has been increased.

Applicability of CPT for Construction Control of Seawall on Soft Clay Improved by Sand Drain Method

A case study is presented of an application of the cone penetration test for construction control of a seawall construction on soft ground improved by sand drain. Effective construction control of such a soil structure requires a systematic way to collect accurate information about the progress of consolidation and gain in soil strength. An empirical correlation is proposed concerning cone resistance measured by a cone penetration test and the undrained shear strength of the ground. The relationship between cone resistance and the undrained shear strength is not affected by the state of consolidation of the ground. Based on the empirical correlation found in this study, gain in undrained shear strength during construction can be accurately evaluated by the cone penetration test. This paper also demonstrates the usefulness of cone penetration test to monitor the degree of consolidation of the improved ground. Also estimated by the cone penetration test are aging effect, classification of clay layer and strength increment ratio in normally consolidated state. Aspects geotechnical behavior of the ground are discussed such as the process of strength increment, aging effect, sequence of various shear tests to examine change in strength and considerations on shear strength of improved ground after deformation. The results of this study clearly show that the cone penetration test is a very useful investigation method and has high applicability for construction control.

Sand Drain Design Based On Cyclic Strain-Path Controlled Triaxial Data

Sand Drain Design Based On Cyclic Strain-Path Controlled Triaxial Data

地盤改良 汚泥固化・破砕材の土質工学的性質とドレーン材としての利用に関する研究

As an effective reuse method of surplus soil and sludge, the authors proposed the crushed cement-stabilized sludge which is made of cement, polymer, surplus soil and dewatered sludge. Its geotechnical properties and applicability to the drainage material in sand drain and sand compaction pile methods were investigated. The geotechnical properties were almost similar to those of general granular materials except high alkaline. The crushed cement-stabilized sludge was applicable to the dranage material judging from its acceleration effect of soil consolidation.

地盤改良 都市ごみ直接溶融スラグの地盤改良材としての適用性に関する基礎試験

In the metro area, cheap and high quality ground improving material for backfilling is in shortage and development of its alternative is required. On the other hand, volume reduction, harmlessness and recycling of municipal solid waste (MSW) becomes necessary due to present MSW dumping sites are almost beyond their capacity. In these situations, we studied, through chemical, physical and mechanical testing, the applicability of MSW direct melting slag as ground improving material which is produced from “direct melting, recycling system” developed by us. As a result, we confirmed that the MSW direct melting slag cleared the standard of ground improving material with excellent applicability. The ground improving method stands for Sand Compaction Pile Method and Sand Drain Method in this report.

NUMERICAL ANALYSIS FOR DEFORMATION BEHAVIOR OF SHEET-PILE QUAYWALL UNDER CONSTRUCTION

Two-dimensional finite element analysis on ground-structure interaction system is conducted. The FEM program consisits of a generalized elastoplastic constitutive moden (tij-model). Now using this program, movement of sheet-pile quaywall and reclaimed land of a fishing port on soft ground treated by the sand drain piles is estimated. Effect of the treatment by the sand drain method and width of preloading on the behavior of sheet piles and deformation of reclaimed land is shown.

Shear Strength Characteristics of Madinah Clay with Sand Compaction Piles

Abstract Shear strength characteristics of soft Madinah clay have been investigated from a series of consolidated undrained (CU) direct shear tests on specimens without and with circular sand drains of variable diameters. The investigation is conducted to study the shear strength behavior of soft Madinah clay in the presence of sand drains provided for the purpose of accelerating drainage and enhancing its response towards stabilization by preloading. The experimental shear strength test results have been compared with the theoretical values based on shear strength of clay-sand composite material derived from the shear properties of the individual materials. The shear strength parameters obtained from this study are expected to be of benefit and practical use for carrying out stability analysis of structures like embankments and foundations supported by clay and stabilized with vertical sand drains. Useful data were obtained showing a positive influence of the sand drain system on the enhancement of shear strength characteristics of soft Madinah clay.

Experience with the fabrication of flat sand drains

Experience gained under field conditions with the development of rational method of installing vertical sand drains with a cross section in the form of a circle or rectangle has been brought to light.

Laboratory and field studies of response of structures to heave of expansive clay

Laboratory and field studies are presented concerning the interaction that takes place between expansive soils and structures. A model floating slab and fixed slab were constructed on a highly expansive soil contained in a stainless steel box, which was also used to obtain large, undisturbed soil samples and used as a part of the laboratory experiment. A controlled heave test was conducted to investigate the effect of heave rate on swelling pressure. In the field, an instrumented, reinforced concrete structure and an in situ test were carried out to investigate heave movement, structure—expansive soil interaction and structural damage, while the ground was artificially wetted through vertical sand drains. The field and laboratory tests were compared with the results of the conventional oedometer test. The swelling pressure obtained from the constant volume test, in which the volume of the specimen was kept constant throughout the test, almost coincides with the average pressure predicted from the braced fixed slab test. A major reduction in swelling pressure takes place if the expansion is not completely restrained, as revealed from both the unbraced fixed slab and the instrumented field tests. The presence of non-uniform fissures in clay could lead to a differential heave and a reduction in swelling pressures. Les auteurs présentent des études de laboratoire et sur le terrain portant sur ľinteraction entre les sole expansifs et les ouvrages. Its ont construct un modèle de dalle flottante et de dalle fixe dans un sol très expansif contenu dans une caisse en acier inoxydable, qˇils ont également utilisée pour obtenir de grands échantilIons de sol intact et pour les expériences en laboratoire. Ils ont effectué un essai contrô1é de soulèvement pour examiner ľeffet du taux de soulèvement sur la pression de gonflement. Sur le terrain, un ouvrage instrumenté en béton armé a servi à étudler les mouvements de soulèvement, ľinteraction entre ľouvrage et le sol expansif et les dégâts subis par ľouvrage après ľhumidification artificielle du sol à ľaide de pieux drainants. Les résultats des essais sur le terrain et en laboratoire ont été comparés à ceux ďun essai oedométrique classique. La pression de gonflement donnée par ľessai à volume constant, où le volume du spécimen reste constant pendant tout ľessai, coincide presque exactement avec la pression moyenne prédite par ľessai de la dalle fixe renforcée. Une forte réduction de la pression de gonflement se product si ľexpansion ňest pas entièrement refrénée, comme ľont montré les essais avec la dalle fixe non renforcée et les essais instrumentés sur le terrain. La présence de fissures non uniformes dans ľargile pourrait expliquer la variation du soulèvement et la réduction des pressions de gonflement.

Consolidation of Clay by Sand Drain under Time-Dependent Loading

The mathematical theory and physical laws of one-dimensional consolidation of clayey soils are well-known. Sand drains accelerate the consolidation process. Several analytical and experimental studies have already reported on sand drain consolidation of clayey soils. However, the literature does not contain a nonlinear theory of sand drain consolidation under time-dependent loading that can take into account any effective stress! void ratio/permeability variations. A generalized governing equation, capable of yielding a large class of ana­ lytical solutions for these variations is derived in this paper. Closed-form solutions are presented for the variation of pore water pressure with a time factor and load increment ratio under time-dependent loading. The analytical formulation is validated by comparing the solution with the standard results available in the literature for in­ stantaneous loading, constant permeability, and constant compressibility. Following the equal strain approach, this paper presents a particular form of generalized governing equation, capable of yielding a large class of analytical solutions for time-depen­ dent loading, which can handle any effective stress!void ratio/ permeability variations. The use of this governing equation is illustrated by presenting the closed-form solution for the case where the effective stress/void ratio/permeability response takes the form U) a~~r) =1 :leo (~;) In the equal strain approach, e is a function of t only. Therefore

地盤改良 兵庫県南部地震による埋立地の液状化と地盤条件

In this paper, two aspects of the investigation into the liquefaction behaviour that occurred in the reclaimed lands by the Hyogo-Nanbu earthquake are discussed. Firstly, the conventional simplified method of predicting liquefaction based upon a grain size distribution curve has been proven to lead to a discrepancy between theory and practise. Therefore, by considering the representative diameter of grain size from the distribution curve as the basis, a predicting method in proposed to get the result harmonizing with other engineering properties. Regarding the second aspect, in some zones where liquefaction occurred, it was found that such measures as sand compaction, sand drain, packed drain, and rod compaction were also to be considered for improvement. Therefore, using the effective stress dynamic analysis, it is proposed that a critical strength level exists for protecting or reducing the degree of damage cauesd by liquefaction due to strong earthquakes.

Sand drain works for a large‐scale man‐made Island

Many ground improvement techniques have been developed for the safe support of structures constructed on weak ground. The sand drain method is an easy‐to‐design, highly economical method of ground improvement using the principle of accelerated consolidation, which has been used successfully many times for structures of various sizes and types. Kansai International Airport was constructed on a man‐made island that was formed by land reclamation in deep water, 33 m thick, on a soft seabed. The sand drain method was carried out in a 20‐m layer of alluvial clay, and using the results of soil investigation and the monitoring of behavior of the ground, analyses were performed on ground settlement and strength improvement These methods were effective in reducing residual and uneven settlement and preventing the sliding of the seawall

Mass Permeability Concept in the Analysis of Treated Ground with Sand Drains

When a soft clay foundation under embankment loading is considered, settlement behavior is affected by the mass permeability and by the magnitude of applied load intensity, which is normalized by the initial undrained bearing capacity. Using these two parameters, the characteristic consolidation settlement behavior of a clay foundation can be represented by a family of S shaped curves. The range of mass permeability affecting residual settlements is confined to a narrow limit. For an embankment foundation, when these two parameters are known, settlement behavior can be determined uniquely. The effects of improvement of mass permeability by sand drains on a clay foundation are investigated using the macro element method (Sekiguchi et al., 1986). The sand drains improve the mass permeability to 30-300 times that of the non-treated ground. The above findings are applied to two case studies. In the first, where the ground is treated with sand drains under a high applied load it is found that only settlement observations can be used to assess the usefulness of sand drains in this ground. The other case is on coral soils which exhibit high permeability and a high initial undrained bearing capacity compared with common clay deposits. The effectiveness of sand drains in this ground is evidenced by a significant decrease in residual settlement.

Construction of an Island

In January of 1987 work began on one of the most challenging construction projects in recent time. The Kansai International Airport Co. is responsible for reclaiming 1,263 acres (511 ha) of land in Osaka Bay. The resulting man‐made island will be the foundation for Japan's first 24‐hr airport. This paper focuses on the various stages involved in the reclamation process. To accommodate the settlement that accompanies most reclamation work, the consolidation of the seafloor was accelerated using three methods: sand drains, sand compaction piles, and deep cement‐mixing. The seafloor improvement also enhances the stability of the island's seawall, which surrounds it entirely. The construction of this seawall is presented. Furthermore, an enormous amount of fill was used to reclaim the land that now forms the island, and the procedure for placing this fill is described. Also, some of the problems encountered during the construction phase of the project are explored.

Hyperbolic method for settlements in clays with vertical drains

Estimation of the total primary settlement is critical in determining when the required compression has been achieved and a surcharge loading can be removed. Conventionally, the total primary settlement is predicted using laboratory-determined compressibility data. However, the rectangular hyperbolic-fitting method allows estimation of the total primary settlement during the process of consolidation. In this paper, the hyperbolic-fitting method is extended to the case of consolidation with combined vertical and radial flow, which occurs when vertical drains are used to speed consolidation. Solutions are presented for the slope of the first linear segments between the 50 and 90% settlement points of the theoretical hyperbolic plots (time/settlement versus time). The proposed hyperbolic-fitting method was tested using data from the case history of the Changi Airport field test in Singapore, where Geodrains and sand drains were used for soil improvement following land reclamation and prior to airfield pavement construction. The predictions of the proposed method agree well with the measured and estimated soil settlements from compressibility calculations. The method can complement existing methods to provide a practical means of monitoring the progress of consolidation in field applications using drains and surcharge, and to determine the appropriate time for surcharge removal, if required. Key words : consolidation, vertical drains, settlements, hyperbolic method.

An experimental study of the performance of geosynthetic band drains

The performance of two basic types of geosynthetic band-shaped/strip drains — a composite drain (core surrounded by a geotextile filter) and a monolithic drain (without a geotextile filter) — has been compared by means of radial consolidation tests. Tests were repeated employing the monolithic drain wrapped in the same filter fabric as the composite drain, a cylindrical porous stone and a sand drain. Two fine-grained soils of varying plasticity and gradation were used, initially at a water content equal to their respective liquid limits. The results were evaluated to compare the rate and amount of consolidation in each case and to assess the possible effect of clogging on the performance of geosynthetic drains. It was observed that the composite drain performed better than the monolithic drain, especially in the case of finer soil. Wrapping the monolithic drain with the geotextile filter significantly increased its performance.

CENTRIFUGE MODEL TESTS ON SOFT CLAY IMPROVED BY FABRI-PACKED SAND DRAIN

羽田沖合展開事業第III期地区は高含水比の超軟弱地盤であるため, 砂杭を繊維素材の袋で包み込んだ袋詰めサンドドレーン工法の適用が計画されている. 本研究では, 遠心模型実験装置を用いた模型実験を行い, 改良地盤の圧密挙動に及ぼす袋の引張り剛性の影響を検討した. その結果, 袋詰めサンドドレーンが超軟弱地盤中で安定性に優れ, 砂杭への応力集中も比較的小さいことなどが分った.

Large-scale sand drain works for the Kansai International Airport island : Arai, Y; Oikawa, K; Yamagata, N Proc International Conference on Geotechnical Engineering for Coastal Development, GEO-COAST'91, Yokahama, 3–6 September 1991P281–286. Publ Japan: Coastal Development Institute of Technology, 1991

Large-scale sand drain works for the Kansai International Airport island : Arai, Y; Oikawa, K; Yamagata, N Proc International Conference on Geotechnical Engineering for Coastal Development, GEO-COAST'91, Yokahama, 3–6 September 1991P281–286. Publ Japan: Coastal Development Institute of Technology, 1991

Settlement observations of breakwater on improved ground by sand drain method : Yamaguchi, S; Ikeya, T; Kawabata, M Proc International Conference on Geotechnical Engineering for Coastal Development, GEO-COAST'91, Yokahama, 3–6 September 1991P273–276. Publ Japan: Coastal Development Institute of Technology, 1991

Settlement observations of breakwater on improved ground by sand drain method : Yamaguchi, S; Ikeya, T; Kawabata, M Proc International Conference on Geotechnical Engineering for Coastal Development, GEO-COAST'91, Yokahama, 3–6 September 1991P273–276. Publ Japan: Coastal Development Institute of Technology, 1991