Long-term Consolidation Tests Research Articles

Analysis of long-term settlement of road embankment on peat ground during its service period

Roads on peat grounds are subject to stringent requirements in terms of controlling the residual settlement during their service period in order to minimize the post-construction maintenance work. This paper addresses the applicability of the Finite Element Method (FEM) by incorporating a time-dependent model for peats to an evaluation of the residual settlement. The applicability of isotach viscoplasticity, used to describe the peats’ behavior under variable-rate compression, was confirmed in laboratory tests. Long-term consolidation test results and a model simulation revealed the particular importance of two mechanisms in the residual settlement in peat grounds, namely, the stress-dependency of the coefficient of consolidation, cv, and the viscosity-induced secondary consolidation. A model peat ground, capturing these mechanisms, was implemented for the FEM and applied to a case history of a high-standard road construction in Hokkaido, Japan. The viscoplastic parameters determined from standard oedometer tests successfully reproduced the observed long-term settlement in a peat-dominated section of the expressway. The analysis was extended to address the settlement in the peat ground with the installation of prefabricated vertical drains (PVDs). The results indicate that the delayed primary consolidation due to the stress-induced cv reduction can be significantly alleviated, while the settlement arising from the secondary consolidation over a longer term is little affected by the PVDs. These insights point to the importance of untangling the two mechanisms of long-term settlement for the sake of making accurate predictions of the residual settlement in different time scales.

Secondary consolidation characteristic of bentonite by long-term consolidation tests of 2.7, 3.7 and 4 years

Secondary consolidation characteristic of bentonite by long-term consolidation tests of 2.7, 3.7 and 4 years

An insight into the creep mechanisms of a clayey soil through long-term consolidation tests

An insight into the creep mechanisms of a clayey soil through long-term consolidation tests

Closure to “Settlement of the Kansai International Airport Islands” by G. Mesri and J. R. Funk

Closure to “Settlement of the Kansai International Airport Islands” by G. Mesri and J. R. Funk

하중재하기간이 재성형 점토의 압밀특성에 미치는 영향 - 광양항 해성점토를 중심으로 -

이 연구에서는, 균질한 재성형 점토를 이용한 실내시험을 통해 정규압밀 영역에서의 하중재하기간이 점성토의 압축 및 장기압밀 특성에 미치는 영향을 명확히 하고자 하였다. 또한 각 하중재하기간에 따른 현장에서의 유효상재하중에 해당하는 초기압밀하중을 변화시킨 장기압밀 시험을 수행하여 표준압밀시험시의 하중단계별 재하방법과 하중재하기간의 증가에 따른 압축곡선의 특성을 비교/분석하여 하중재하기간에 따라 최종침하량을 예측하는 방법을 제안하고자 하였다. 연구 결과 하중재하기간에 따른 점성토의 압축특성은 초기압밀하중을 가한 후 하중재하기간이 증가할수록 주어진 단계에서의 압밀후반부의 2차압밀의 증가로 선행압밀하중이 약간씩 감소하는 경향을 나타내었다. 그와 동시에 2차압밀이 유사과압밀 현상 및 점토골격의 안정화를 유발하여 정규압밀영역에서의 압축지수에 미치는 영향은 미미했으며 과압밀영역에서는 유사과압밀 현상으로 재압축지수의 증가를 유발하는 것으로 나타났다. This study sets it's face to define effects of the various loading periods in normal consolidation area on clay's compression and long-term consolidation characteristics through a laboratory test using homogeneous remolded clay. Moreover, by carrying out a long-term consolidation test which diversifies initial consolidation applicable to effective overburden loading in the various loading period. This study intended to suggest the method predicting the final settlement on the basis of loading periods by comparing and analyzing compression curve's characteristics according to loading weight of each stage and increase in loading period when carrying out the standard consolidation test. From the test results, the study shows that as of the soft clay's compression characteristics on the basis of various loading periods, preconsolidation load has a tendency to be decreased slightly as the loading period is getting more and more longer at each step after initial consolidation load puts on the remolded clay which is caused by secondary consolidation's increase in the latter part of each phase. And those effects have an weaker influence on compression index in normal consolidation area at the same time as secondary consolidation brought out quasi-overconsolidation and stabilization of clay's structure, have an influence re-compression index is increased in overconsolidation area on the other hand.

장기압밀시험에 의한 광양항 점성토의 응력이력 특성 연구

본 연구에서는 재성형한 광양항 점성토를 이용하여 응력이력과 OCR이 연약 점성토의 장기압밀특성에 미치는 영향을 규명하기 위해 표준압밀시험기를 개조하여 장기압밀 시험을 수행하였다. 과압밀상태의 점토 시료에 대해, OCR이 1.5를 초과한 경우, 이차압밀 및 최종침하량은 OCR이 2.0에서 3.0으로 증가함에도 큰 차이를 보이지 않았으며, 이로부터 이차압밀과 최종침하량을 저감하기 위해 현장적용 OCR은 1.5로 나타났다. 더욱이 선행하중 재하기간과 장기압밀 거동 특성사이의 관계를 알아보기 위해 광양항 재성형 점토를 이용한 실험결과로부터 압밀도 70~80%를 초과하여 재하하중을 제거하여도 장기압밀에 미치는 영향은 크지 않은 것으로 나타났다. In this present study, the long-term consolidation tests were performed using the remolded Kwang-Yang port clayey soil to clarify the effect of stress history and over-consolidation ratio (OCR) on the long-term consolidation characteristics of the soft clayey soil. For the over-consolidated state clayey soils, in case OCR exceeds 1.5, there are no great differences of secondary consolidation settlement and final settlement even if OCR increases from 2.0 to 3.0. Therefore, it has been understood that the value of OCR applied on the field site to reduce the secondary consolidation settlement and the final settlement is about 1.5. In addition, in order to investigate the relationship between the pre-loading period and the characteristics of long-term consolidation behavior obtained from the test results using the remolded Kwang-Yang port clayey soils, the influence on long-term consolidation behavior was not large though the pre-load was unloaded with the consolidation degree 70~80% exceeded.

Long-term consolidation behavior interpreted with isotache concept for worldwide clays

The consolidation characteristics interpreted with the isotache concept have been studied by many researchers, including the authors. The aim of most of these studies has been to calculate secondary consolidation with high accuracy in order to evaluate the long-term settlement of large-scale structures. In a previous study, the long-term consolidation characteristics of Osaka Bay clay, collected from the construction site of the Kansai International Airport, were examined, and a simplified method based on the isotache concept, using a compression curve and the relationship between the consolidation yield stress (preconsolidation pressure) and the strain rate, was proposed. The former and the latter were obtained from constant rate of strain consolidation (CRS) tests and long-term consolidation (LT) tests, respectively. The latter is expressed by an equation with three isotache parameters. In addition, it is noteworthy that the isotache parameters can be commonly determined for the Osaka Bay clays retrieved from various depths up to 300m below the seabed. In the present study, the proposed method was applied to worldwide clays with various characteristics using the common values for the isotache parameters determined for the Osaka Bay clays. It was found that the long-term consolidation behavior of those worldwide clays can be well characterized by the proposed method, along with the common values for the isotache parameters.

Long-Term Consolidation Settlement Prediction of D-Runway in Tokyo International Airport

In the construction of the D-runway in Tokyo International Airport (Haneda Airport), “the settlement prediction and management system (HSAP)” which can efficiently evaluate the consolidation settlement of artificial reclamation was developed. The reclamation history data base which reflected the actual construction until July, 2009 and the reclamation plan after that was made. The actual measurement and the calculation value were compared and the various consolidation parameters were identified. Moreover, the long-term consolidation test and constant strain rate consolidation test were executed, and the secondary consolidation parameter was set based on the isotache model's concept. Based on the prediction result of the residual consolidation settlement, the filling height of the D-runway at the start of in-service period was decided to be 0.70m, which is required from the aviation operation.

과압밀 및 정규압밀영역의 응력상태에 따른 부산점토 장기압밀특성

Numerouslong-term consolidation and secondary compression settlements may occur in Busan clay, which is astructured soft clay and consists of a thick clay deposit. As a surcharge load is applied to soils, soils experience different stress paths with depth. Therefore, it is necessary to study the long-term consolidation behavior of Busan clay considering stress conditions such as OC or NC states. In this study, a series of long-term consolidation tests were performed to investigate the consolidation characteristics of Busan clay for 20 days. The undisturbed clay samples were taken from 3 sites located in the Nakdong River estuary. The results showed that the creep rate of the Busan clay gradually decreased with time, which indicated that the secondary compression settlement decreased with time. In addition, the experimental results for 3 samples showed that the ratios were about 0.0363 and 0.051, respectively.

Long-Term Consolidation and Strength Behavior of Marine Clay Improved with Fly Ash

This paper presents an investigation of the long-term consolidation and strength behavior with fly ash as an additive in improving soft marine clay in Wando, Korea. 0%, 5%, 10%, 20% and 25% of the soil was replaced with fly ash. Consolidation tests were performed as incremental loaded tests. In addition, unconfined compressive strength were determined after 1, 14, 28 and 90 days. A series of forty-two long-term consolidation tests that lasted for 60 days under the constant loading were also conducted. Creep settlements of the blends decreased significantly with an increase in fly ash content. The shear strength properties increased with an increase in fly ash content. Statistical evaluation reveals an excellent correlation between the measured and predicted undrained shear strengths.

Coupled model of consolidation and creep for consolidation test

For most soft soil, the consolidation process and the creep process were coupled and the character of settlement time curve was obtained by the consolidation test at the same time. A simple and continuous function was presented to express the whole process of consolidation including immediate settlement stage, the primary consolidation stage and the secondary consolidation stage. And the features of the continuous function were analyzed. The results of the long-term (duration to 18 months) consolidation test on clays from the Chek Lap Kok formation proved the rightness of the method. In the end, the parameter meanings of the continuous function were discussed.

Consolidation Behavior of Natural Soils Around pc Value —Long Term Consolidation Test—

ABSTRACT It has been reported in many research papers that considerable settlements are observed in the Osaka Pleistocene clay layers, even though their stress levels are less than their yield consolidation pressure (pc). To study the consolidation behavior around the pc value, Long Term Consolidation (LTC) and Inter-Connected Oedometer (ICO) tests were carried out. This paper presents the consolidation behavior measured by the LTC, while the companion paper describes the results from ICO test. The LTC test is conducted using the conventional oedometer, whose diameter and initial height are 60 mm and 20 mm, respectively. The maximum duration for the consolidation was half a year. The tested clays are mainly Osaka Pleistocene clays. Test results from these clays are compared with those from Holocene clays retrieved from various sites across the world. Relationship between the strain and elapsed time measured by this study has been analyzed in terms of the strain rate theory. Based on test results from the Osaka Pleistocene clays, the family of equi-strain rate lines is proposed, consisting of three regions. However, in case of other clays, whose OCR is probably created by stress changes, i.e., mechanically overconsolidated clays, the consolidation behavior is different from that of the Osaka Pleistocene clays: i.e., a certain pressure exists where no more strain is yielded even after the strain rate becomes small.

Long-term consolidation mechanisms based on micro–macro behavior and in situ XRD measurement of basal spacing of clay minerals

An important issue in the area of geological disposal of high-level radioactive waste (HLW) is to demonstrate the long-term mechanical stability of the buffer. In particular, it has to be clarified whether a waste package would continue to sink in the buffer over a long time period, resulting in a significant decrease in the buffer thickness. The candidate buffer material in Japan is a mixture of silica sand and bentonite. Consolidation tests have revealed that the bentonite shows secondary consolidation phenomena similar to clay in general. Therefore, it is important to investigate the mechanism of secondary consolidation behavior. Bentonite is a microinhomogeneous material consisting of clay minerals, macrograins (mainly quartz) and others. The unique combination of molecular dynamics (MD) and homogenization analysis (HA) procedures, termed the unified MD/HA method, has been proposed for estimating the micro to macro behavior of such an inhomogeneous material (Ichikawa, Y., Kawamura, K., Nakano, M., Kitayama, K., Kawamura, H., 1998. Unified molecular dynamics/homogenization analysis for water flow in bentonite. Proc. 1998 Int. High-Level Radioactive Waste Management Conf., Las Vegas. American Nuclear Society, La Grange Park, IL, pp. 422–428). In this study, the unified MD/HA method is applied to bentonite in order to understand its long-term consolidation mechanism. Thus, it was found that the permeability decreases significantly with a decrease in the void ratio due to the evolution of consolidation. It was therefore assumed that secondary consolidation is governed by drainage from the interlayer pores (micropores) with very low permeability, and that this is the reason why secondary consolidation is very slow. This paper also documents the result of an X-ray diffraction (XRD) experiment on bentonite under consolidation (in situ XRD), which was performed in order to validate the assumption mentioned above. It was observed that interlayer space starts to decrease after the latter half of primary consolidation. This finding strongly supports the long-term consolidation mechanism presumed above from a microscopic point of view. One-dimensional consolidation analyses of the bentonite, into which the relationship between the void ratio and the permeability determined using the unified MD/HA method was introduced, were performed for comparison with a long-term consolidation test. The good agreement between the analytical result and the test result including secondary consolidation behavior also supports the long-term consolidation mechanism presumed above.

Applicability of the rectangular hyperbolic method to settlement predictions of sabkha soils

In this paper, the applicability of the hyperbolic method to predict settlements of sabkha formations was investigated. Conventional and long-term consolidation tests were conducted, and the fit of the experimental data to a rectangular hyperbolic relationship was examined. The validity of the hyperbolic form as a representation of the settlement-time response of sabkha soils was further ascertained by analysing settlement records measured under an instrumented test embankment. The laboratory results indicated that the settlement-time behaviour could reasonably be represented by the hyperbolic relationship. Settlement estimates determined as the inverse of the slope of the initial linear segment multiplied by the slope of the theoretical curve, or obtained based on the radial slopes corresponding to 50% and 90% consolidation points, all underestimated the observed total settlements. However, the inverse of the slope of the final linear segment of the hyperbolic curve gave excellent estimates of the observed total settlements. The agreements between the predicted and observed in situ ultimate primary consolidation settlements are considered reasonable. Finally, except when the hyperbolic plot follows a straight line, the use of the hyperbolic method for prediction of total settlements of sabkha soils with prominent secondary compression behaviour has been shown to be both uncertain and impractical.

Long-Term Settlement of the Reclaimed Quasi-Overconsolidated Pleistocene Clay Deposits in Osaka Bay

In Osaka Bay of Japan, a number of large-scale reclamations have been executed. The settlement due to those reclamations has been serious enough to provoke investigation. The compression of the stiff Pleistocene clay deposits has caused the half of this settlement, and it makes the quality control of the reclaimed lands very difficult. According to the geological history, the Pleistocene clays in Osaka Bay are thought to be normally consolidated aged clays that exhibit seemingly overconsolidated behavior due to the nature of quasi-overconsolidation. This makes the problem of settlement more complex. In this paper, characteristics of the long-term settlement of the reclaimed islands in Osaka Port are discussed based on the in-situ measured data. Long-term compression is found to occur even in the deeper Pleistocene clay layers, stress conditions of which remain close to or less than pc. Discussion is extended to the applicability of conventional procedure in terms of elasto-viscoplastic finite element method to the long-term settlement measured in the Maishima Reclaimed Island in Osaka Port. The conventional procedure to assess the settlement is found to function well for normally consolidated clays, however, serious limitation exists for describing the time- dependent behavior of the Pleistocene clays, in which stress states remain close to or less than pc. A series of long-term consolidation tests is done to assess the property of the quasi-overconsolidated Pleistocene clays. Laboratory experimental results also provide remarkable time-dependent behavior even in the region less than pc. It is found that the rational modeling for compression in the region of close to and less than pc is indispensable to describe the actual time-dependent behavior of the quasi-overconsolidated Pleistocene clays in Osaka Bay.

Long-Term Consolidation Tests on Solis from the Chek Lap Kok Formation

This paper presents the results of a series of long-term consolidation tests conducted on stiff clays taken from the Chek Lap Kok Formation below the new airport platform. The soil specimens were subjected to effective vertical stresses similar to those encountered in the field for duration of up to eighteen months. These tests constituted one of the longest load duration tests in Hong Kong and elsewhere. The tests in this study were specially designed to provide information on the variation of rate of secondary compression with time. This paper also presents a review on the study of secondary compression conducted by other investigators, including factors affecting secondary compression index and its determination.

Preloading for reduction of compressibility characteristics of sabkha soil profiles

Sabkha soils are coastal and inland salt flat deposits of arid climates, which invariably contain an appreciable amount of organic materials. They are, therefore, characterized by being highly compressible with a significant part of the settlement taking place as secondary compressions. In this study, the applicability of a preloading technique in improving the compressibility characteristics of sabkha sediments was investigated through construction of an instrumented test embankment on a typical sabkha formation from the southwest coast of Saudi Arabia. Settlement and pore pressure measurements were taken for an observation period lasting 1 year. Compressibility parameters were determined in the laboratory from extensive standard and long-term consolidation tests on undisturbed samples taken from the site before and after the preloading process. The laboratory test results substantiated by the relatively large settlements measured under the test embankment indicate that the precompression method is an effective technique that can eliminate the primary consolidation settlements and reduce the secondary compressions of sabkha sediments. The field behavior was predicted utilizing the conventional theory of consolidation and the finite element method. Using laboratory-determined compressibility parameters, the one-dimensional theory of consolidation highly overestimated the measured settlements and significantly underestimated the observed settlement-time behavior. However, close agreement between observed and predicted behavior was obtained when field parameters were used in the analyses. Although substantially overestimating the time required for completion of primary settlements, the finite element predictions of the magnitude and the rate of settlements are considered satisfactory.

Long-Term Consolidation Characteristic of Diluvial Clay in Osaka Bay

ABSTRACT On large-scale reclamation works, the consolidation settlement of diluvial clays which lie deep underground should be discussed. The diluvial clay in Osaka Bay is in a quasi-overconsolidated state by cementation bonding. The values of the compression index and the void ratio are very large in spite of the large overburden pressure. Therefore, its consolidation characteristic is considered to be different from that of the alluvial clay. In this paper, a series of long-term consolidation tests is carried out, and it is revealed that the value of coefficient of secondary compression (Cα) under a load in the quasi-overconsolidated region becomes to be that in the normally consolidated region as time elapses. Considering the effect of strain rate, this result shows that the yield stress is dependent on the strain rate. This also means that even if a clay behaves as an overconsolidated clay in the test, it might behave as a normally consolidated clay in the site. Therefore, it should be considered that the in-situ secondary compression settlement was underestimated if it was calculated by using Cα of the laboratory test. In addition, the settlements on two reclamation works in Osaka Bay are calculated by a proposed long-term settlement analyzing method using strain rate and time relationship, and the results are in good agreement with the observed settlement data at sites.

Secondary compression of sabkha ‘saline’ soils : Engng Geol V30, N2, April 1991, P155–169

Abstract Sabkha soils are coastal and inland saline deposits of arid climates consisting mainly of loosely cemented sandy silt to silty clay particles. Invariably the soils contain an appreciable amount of organic material and therefore are characterized by being highly compressible. A significant part of the soil settlement takes place as secondary compression. Prediction of field settlement is very important since one of the most feasible methods of soil improvement is the preloading technique. In this study settlements were predicted using the conventional theory of consolidation and the Lo rheological model utilizing long-term consolidation test parameters. The prediction was compared with the field settlement of the compressible sabkha layer loaded by an instrumented test embankment. It was found that the model provides a better approximation with regard to the rate of settlement, which was underestimated by Terzaghi's theory. The magnitudes of primary and secondary consolidation settlement were adequately estimated by the model. Furthermore, almost identical values of the measured and predicted combined settlements were obtained at the end of the nine week period of observation.

Secondary compression of sabkha “saline” soils

Sabkha soils are coastal and inland saline deposits of arid climates consisting mainly of loosely cemented sandy silt to silty clay particles. Invariably the soils contain an appreciable amount of organic material and therefore are characterized by being highly compressible. A significant part of the soil settlement takes place as secondary compression. Prediction of field settlement is very important since one of the most feasible methods of soil improvement is the preloading technique. In this study settlements were predicted using the conventional theory of consolidation and the Lo rheological model utilizing long-term consolidation test parameters. The prediction was compared with the field settlement of the compressible sabkha layer loaded by an instrumented test embankment. It was found that the model provides a better approximation with regard to the rate of settlement, which was underestimated by Terzaghi's theory. The magnitudes of primary and secondary consolidation settlement were adequately estimated by the model. Furthermore, almost identical values of the measured and predicted combined settlements were obtained at the end of the nine week period of observation.