Songyu Liu

Research of soil-water characteristics and shear strength features of Nanyang expansive soil

Abstract Nanyang expansive soil is investigated in its unsaturated state in this paper. The wetting–drying cycle tests of soil–water characteristics of Nanyang expansive soil have been performed in the laboratory. The test results show that the soil–water characteristic curve of the pre-load specimen can well reflect the soil property function of expansive soil. The strength features of the different suction states of the unsaturated expansive soil are also investigated. The hyperbolic model of the suction strength is presented and the parameters of this model are easily determined by tri-axial tests of unsaturated soils. The hyperbolic model is conveniently applied to predict suction strength of an unsaturated soil.

Field Investigations on Performance of T-Shaped Deep Mixed Soil Cement Column–Supported Embankments over Soft Ground

The soil cement deep mixing method has been used to improve soft clayey soils under embankment loading conditions. A compacted granular fill layer or geosynthetic reinforcement layer is placed over the top of soil cement deep mixed (DM) columns to reduce differential settlement between DM soil and the surrounding untreated soil, which, in turn, increases embankment stability. Typically, in conventional deep mixing methodology, the soil cement columns are closely spaced, indicating large area replacement ratios in the con- struction projects. Such practice could increase construction costs substantially. In this research, a new type of DM column, called a T-shaped DM (TDM) column, was designed and used as an alternative to the large-area-replacement-ratio DM columns employed in the field. Unlike in the conventional column, the cross section of the new column varies along the installation depth. Large amounts of cement slurry are injected and thoroughly mixed with the native shallow soil using specially designed mixing blades. At greater depths, deep mixing methodology is applied only to smaller-diameter columns, resulting in large-diameter columns near the surface and smaller-diameter columns deeper. Field trials were conducted to investigate the performance of TDM column-supported soft ground under embankment loading. For comparison, performance of conventional DM column-supported soft ground under similar embankment loading is presented. Differences in quality control studies and in situ plate loading tests on TDM and conventional DM columns are discussed. Under field embankment loading con- ditions, stress concentration ratio, excess pore water pressures generated in the soft clays, total monitored settlement, and lateral soil dis- placement near embankment toes are analyzed and discussed for both treatments. It is concluded that TDM columns have considerable advantages over conventional DM because they both mitigate settlement and enhance the performance of the embankments while reducing construction costs. DOI: 10.1061/(ASCE)GT.1943-5606.0000625.

Assessment of Unconfined Compressive Strength of Cement Stabilized Marine Clay

Two aspects of deep mixing method, the difference relating strength gain in dry jet mixing (DJM, reagent powder introduced into the ground) and cement deep mixing (CDM, reagent slurry introduced into the ground), and prediction of unconfined compressive strength of cement stabilized marine clay, are discussed in this paper. The first part of this paper concentrates on the difference between DJM and CDM on strength gain, and suggests a guideline for DJM and CDM selection. An indicator in terms of water content ratio, which is defined as the ratio of water content to the liquid limit of the soil, is presented by statistical analysis from the laboratory and field test data as a guideline for the selection of DJM or CDM. Based on the laboratory test data, a mathematical model relating strength gain of cement stabilized marine clay to related variables is developed. A new simple index designated as total water-cement ratio, which is defined as the ratio of water weight in the soil-cement to the weight of cement in dry state, is proposed for interpretation of test data of soil-cement. The proposed method is then verified with available test data published by other different researchers.

Approach on the Engineering Properties of Lianyungang Marine Clay from Piezocone Penetration Tests

The use of the piezocone test (CPTU) in geotechnical site investigation offers direct field measurement on stratigraphy and soil behavior. Compared with some traditional investigation methods such as drilling, sampling, field inspecting method, or laboratory test procedures, CPTU can greatly accelerate the field work and thereby reduce corresponding operation cost. This article reviews previous interpretation methods of obtaining undrained shear strength, overconsolidation ratio, and coefficient of consolidation of soft soils from CPTU data, and introduces a new method, which the measured pore pressure into account. Piezocone tests with Vertek-Hogentogler CPTU truck have been complemented in a widely explored area in the soft marine deposit of Lianyungang City. Geotechnical design parameters (q t , f s , and u) obtained from CPTU and dissipation tests are evaluated for the marine clay in this area through methods based on cavity expansion (CE) and critical state (CS) theory proposed by Mayne, and compared with the result of vane shear tests and laboratory tests of undisturbed soil samples. Comparison of the results reveals the validity of CPTU tests to interpret the engineering properties of Lianyungang marine clay.

Predictions of coefficient of consolidation from CPTU dissipation tests in Quaternary clays

The coefficient of consolidation (cv or ch) is an important parameter in both geotechnical and geo-environmental engineering, measuring the flow characteristics of soils. In China, conventionally it is obtained from the oedometer test, which is time consuming and of limited accuracy due to inevitable sample disturbance. These difficulties can be overcome by in situ pizeocone dissipation tests which provide continuous measurements of pore water pressure with time. In this paper, existing methods for interpreting coefficient of consolidation in clays from piezocone dissipation tests are briefly reviewed. Piezocone tests were undertaken at different sites in the Jiangsu province of China and piezocone dissipation tests conducted at different penetration depths. Based on the reference cv values determined from the laboratory oedometer tests, comparisons with existing interpretation methods were undertaken. It is shown that the Teh and Houlsby’s interpretation method has a much higher accuracy for determining the coefficient of consolidation of Quaternary clay deposits while the values of ch obtained by the CPTU method are in the range of back-analyzed field values.RésuméLe coefficient de consolidation (Cv ou Ch) est un paramètre important en géotechnique et génie géologique. Il est obtenu conventionnellement en Chine par l’essai oedométrique qui demande beaucoup de temps et dont la précision est limitée du fait du remaniement inévitable des échantillons. Ces difficultés peuvent être surmontées par l’essai in situ au piézocône qui donne des mesures continues de la dissipation des pressions interstitielles en fonction du temps. Dans cet article, les méthodes permettant la détermination du coefficient de consolidation dans des argiles à partir d’essais au piézocône sont brièvement passées en revue. Les essais au piézocône ont été réalisés sur différents sites de la province de Jiangsu en Chine et pour différentes profondeurs dans le terrain. Considérant des valeurs de référence de Cv déterminées au laboratoire à partir d’essais oedométriques, des comparaisons avec différentes méthodes d’interprétation ont été réalisées. On montre que la méthode de Teh et Houlsby permet d’obtenir le coefficient de consolidation avec une très grande précision pour des dépôts argileux du Quaternaire tandis que les valeurs de Ch obtenues avec la méthode CPTU se présentent dans la plage de valeurs de terrain obtenues par rétro-analyse.

Assessment of the Coefficient of Lateral Earth Pressure at Rest (Ko) from In Situ Seismic Tests

The coefficient of the earth pressure at rest (Ko) is an important soil parameter that influences shear strength, stress-strain behavior, and compressibility characteristics of both cohesive and cohesionless soils. This paper presents a research study in which the Ko values of natural soil deposits are interpreted on the basis of seismic shear wave velocity measurements made at two research sites in Jiangsu province of China. Seismic piezocone penetration tests and cross-hole seismic logging tests were performed at both sites and these results have been used in two existing Ko-shear wave velocity models for prediction of Ko. The predicted Ko at both sites are compared with values determined utilizing Jaky’s formula via laboratory measured strength parameters. Certain variations between predictions and measurements are noted for soils at shallow depths, which are attributed to stress history and desiccation in these layers. Further analysis developed correction factors that accounted for both soil types and overconsolidation ratio effects. These factors can be used with original models for better interpretation of Ko for overconsolidated clays. This approach showed a reasonable match between interpreted Ko properties from both models and those that utilize laboratory test results.

Empirical Function Representing the Shear Strength of Unsaturated Soils

The paper presents a review of the general research of the shear strength of unsaturated soils. The hyperbola model is presented for predicting the suction strength based on the triaxial test of unsaturated soils. The predicted results compare well with the measured data and show that the hyperbola model can be used to represent the shear strength of unsaturated soils.

Investigation of Strength and California Bearing Ratio Properties of Natural Soils Treated by Calcium Carbide Residue

In this study, calcium carbide residue is used as a binder to treat over-wetted clays being used as embankment filling material in China highway engineering practice. To prepare the treated soil specimen, calcium carbide residue is added in the sampled soil with contents of 4%, 6%, and 8% (dry soil weight basis). For comparison, lime is also used as the binder to treat soils with contents of 4% and 6% (dry soil weight basis). To investigate the performance of treated over-wetted soils, unconfined compression strength (UCS) test, water soaking durability test, and California Bearing Ratio (CBR) test are carried out. The factors controlling the aforementioned mechanical properties of treated soils are discussed. From the tests, it is found that calcium carbide residue treated soils have better performance than that of lime treated soils. It is concluded that calcium carbide residue can be adopted as an alternative binder to treat over-wetted soils being used as highway embankment filling materials.

Evaluation and Quality Control of Dry-Jet-Mixed Clay Soil-Cement Columns by Standard Penetration Test

Dry jet mixing has been widely used since the 1980s for stabilization of soft soil. The quality and strength of the dry-jet-mixed columns must be evaluated to confirm the success of the stabilization. The standard penetration test (SPT) is shown to be a simple and effective method for this task. The strength characteristics along the length of the column were determined, and correlations between the SPT blow count and the unconfined compressive strength were developed.

Retesting of Liquefaction and Nonliquefaction Case Histories from the 1976 Tangshan Earthquake

A field investigation was performed to retest liquefaction and nonliquefaction sites from the 1976 Tangshan earthquake in China. These sites were carefully investigated in 1978 and 1979 by using standard penetration test (SPT) and cone penetration test (CPT) equipment; however, the CPT measurements are obsolete because of the now nonstandard cone that was used at the time. In 2007, a modern cone was mobilized to retest 18 selected sites that are particularly important because of the intense ground shaking they sustained despite their high fines content and/or because the site did not liquefy. Of the sites reinvestigated and carefully reprocessed, 13 were considered accurate representative case histories. Two of the sites that were originally investigated for liquefaction have been reinvestigated for cyclic failure of fine-grained soil and removed from consideration for liquefaction triggering. The most important outcome of these field investigations was the collection of more accurate data for three nonliquefaction sites that experienced intense ground shaking. Data for these three case histories is now included in an area of the liquefaction triggering database that was poorly populated and will help constrain the upper bound of future liquefaction triggering curves.