Soil and Rock Properties in a Young Volcanic Deposit on the Island of Hawaii

Deeply weathered lava flows of oceanic basalt reflect the mode and sequence of volcanic deposition, parent mineralogy, and postdepositional erosional and weathering processes. In turn, these are controlled by geology, geography, and climate. One particular site on the Island of Hawaii has been the focus of study to gain a better understanding of complex residual soil deposits, particularly in connection with a need to characterize seismic strong-motion propagation through decomposed surface soil and rock sequences. Materials at the site range from fully weathered volcanic soils, sometimes with unusual mineralogy and plasticity properties, to saprolite, weathered rock, vesicular basalt, and hard rock. Seismic surveys were conducted to investigate the distribution of these materials at the study site. Laboratory tests focused on saprolite and vesicular rock as two materials that are seldom reported on and that remain poorly characterized, at least with regard to conditions found in Hawaii.     

Singularities of Geotechnical Properties of Complex Soils in Seismic Regions

Volcanic activity results in a wide range of soil types with very unusual characteristics, the most remarkable of which are volcanic ash clays containing the clay minerals allophane and imogolite. In addition to these soils, volcanic activity often produces the special environmental conditions that result in the formation of diatomaceous soils, namely, water rich in dissolved silica. These soils consist of individual particles containing intraparticle voids filled with water, resulting in a very unique porous particle morphology that is quite different than stereotypical sedimentary soils. This paper presents a series of careful laboratory tests on samples of both materials found in Chile. These tests demonstrate that soils weathered from volcanic ash develop yield pressures that are similar to the preconsolidation pressure of sedimentary soils. This type of soil also shows a dramatic change in properties due to drying. In addition, diatomaceous soils and those containing allophane have very low densities, in spite of which they develop remarkably high shear strength. The need for their properties to be properly understood and taken into account in geotechnical design, especially seismic design, is emphasized, since the location of these soils generally coincides with earthquake activity, which, like volcanic activity, arises from tectonic plate interaction.     

Best-Fit Models to Estimate Modified Proctor Properties of Compacted Soil

Regression models were developed to estimate the optimum moisture content and maximum dry density of clayey and fine-grained soils using physical and index properties from 30 soil samples collected in Central Italy and 41 soils described in the literature. The liquid limit of the soils analyzed ranged between 18 and 82%, the plasticity index between 1 and 51%, and specific gravity between 2.47 and 3.09. The most significant regression variables were the specific gravity and the Atterberg limits. The developed models are accurate and can be used as a simple tool to approximate the maximum dry density and optimum water content of clayey and fine-grained soils.     

Assessment of the Liquefaction Susceptibility of Fine-Grained Soils

Observations from recent earthquakes and the results of cyclic tests indicate that the Chinese criteria are not reliable for determining the liquefaction susceptibility of fine-grained soils. Fine-grained soils that liquefied during the 1994 Northridge, 1999 Kocaeli, and 1999 Chi-Chi earthquakes often did not meet the clay-size criterion of the Chinese criteria. Cyclic testing of a wide range of soils found to liquefy in Adapazari during the Kocaeli earthquake confirmed that these fine-grained soils were susceptible to liquefaction. It is not the amount of “clay-size” particles in the soil; rather, it is the amount and type of clay minerals in the soil that best indicate liquefaction susceptibility. Thus plasticity index (PI) is a better indicator of liquefaction susceptibility. Loose soils with PI<12 and wc/LL>0.85 were susceptible to liquefaction, and loose soils with 120.8 were systematically more resistant to liquefaction. Soils with PI>18 tested at low effective confining stresses were not susceptible to liquefaction. Additionally, the results of the cyclic testing program provide insights regarding the effects of confining pressure, initial static shear stress, and stress-path on the liquefaction of fine-grained soils.     

Durability of Cement Stabilized Low Plasticity Soils

Three testing methods for predicting the durability of cement-stabilized soils—the tube suction (TS), 7-day unconfined compression strength (UCS), and wetting–drying durability tests—were tested and compared for their correlations and influence factors using a problematic low plastic silt clay from subgrade commonly encountered in Louisiana. A series of samples was molded at six different cement dosages (2.5, 4.5, 6.5, 8.5, 10.5, and 12.5% by dry weight of the soil) and four different molding moisture contents (15.5, 18.5, 21.5, and 24.5%). The test results indicate that the water–cement ratio of cement-stabilized soil had the dominant influence on the maximum dielectric value (DV), 7-day UCS, and durability of stabilized samples tested, although the dry unit weight of cement-stabilized soil could cause the variation of the results. This study confirms that TS, 7-day UCS, and wetting-drying durability tests are equivalent in predicting durability, and tentative charts to ensuring the durability of cement-stabilized low plasticity soils are developed using their 7-day UCS or the maximum DV values.     

Evaluation of Water Retention Functions and Computer Program “Rosetta” in Predicting Soil Water Characteristics of Seasonally Impounded Shrink–Swell Soils

Soil water retention is a critical factor influencing irrigation decisions and hence agricultural crop yields. However, information on soil water retention characteristics (SWRC) is seldom available for irrigation planning, crop yield modeling, or hydrological simulations, especially for problematic soils, such as seasonally impounded shrink-swell soils. As large scale direct measurement of SWRC is not viable due to a number of reasons, researchers have developed pedotransfer functions (PTFs) to estimate SWRC from easily measured soil properties, such as texture, organic matter content, bulk density, etc. However, PTF applicability in locations other than those of data collection has been rarely reported. One of the most recent PTFs that has shown overall reasonable predictions in evaluation studies is Rosetta, a numerical code for estimating soil hydraulic parameters with hierarchical pedotransfer functions. Relatively, the development of large databases makes it one of the widely used PTFs. If validated for spatial application, it has immense use potential in countries like India, where data on soil hydraulic properties are seldom available, a deficiency that hampers better simulations in processes, like partitioning runoff and infiltration, assessing evapotranspiration, irrigation scheduling, etc. Rosetta is also relatively flexible allowing estimation of hydraulic properties from easily available minimum input of textural fractions. This study was conducted to evaluate (1) an applicability of four widely used soil water retention functions to describe SWRC; and (2) the computer program Rosetta for its validity. Statistical indices, i.e., root mean square error (RMSE), mean absolute error, maximum absolute error, and degree of agreement (d) were computed to evaluate “goodness-of-fit” of the four functions to the measured SWRC data. These indices were also used to compare measured SWRC with estimates of SWRC by Rosetta. For soil samples collected from 41 profiles, 175 SWRC were measured in the laboratory. The van Genuchten function fitted relatively better (RMSE = 0.052?m3?m?3) to SWRC of clay soils, whereas the Brooks–Corey (BC) function was better in expressing SWRC of clay loam and sandy clay loam soils with RMSE = 0.06 and 0.07?m3?m?3, respectively. Campbell and Cass–Hutson (CH) functions were of intermediate value. Worst performing functions were BC (clay soils), Campbell (clay loam), and CH (sandy clay loam) with corresponding RMSE = 0.059, 0.065, and 0.077?m3?m?3. Estimates of two important points on the SWRC curve, i.e., field capacity and permanent wilting point were predicted with relatively better accuracy for clay and sandy clay loam soils by all the four functions. RMSE and d ranged from 0.027?to?0.043?m3?m?3 and from 0.73 to 0.88 for clay soils. Corresponding values for sandy clay loam soils were 0.008?–0.019?m3?m?3, and 0.92–0.98. However, in clay loam soils, only two functions were found suitable. Estimates of SWRC obtained by applying hierarchical rules in Rosetta were reliable (RMSE<0.05?m3?m?3). Magnitude of average RMSE increased progressively in clay loam, clay and sandy clay loam soils (0.028<0.035<0.042?m3?m?3). The study established that SWRC of the “Haveli” soils could be estimated using generic PTF and thus information that is prerequisite in simulating hydrological processes occurring in seasonally impounded soils could be acquired.     

Index Properties-Based Criteria for Liquefaction Susceptibility of Clayey Soils: A Critical Assessment

The Cooper marl in Charleston, S.C., a deep layer of clayey soils approximately 5–21?m below the ground surface, is generally recognized as nonliquefiable material. Data from field cone penetration tests and laboratory tests of samples taken from the Cooper marl are used to investigate the adequacy of index properties-based criteria for assessing liquefaction susceptibility of clayey soils. In particular, the criterion based on soil behavior type index (Ic) and that based on Atterberg limits are examined. The results show that the Atterberg limits-based criterion adequately reflected the characteristics of the marl, whereas the Ic-based criterion erroneously identified the marl as being liquefiable. A possible reason for the deficiency of Ic and a modification to overcome this deficiency are presented.     

Effect of Desiccation on Compacted Natural Clays

Specimens prepared from eight natural clayey soils used for clay liners and covers were subjected to cycles of wetting and drying. Volumetric shrinkage strains were recorded during drying. Specimens in which cracks formed during drying were subjected to hydraulic conductivity testing. Results of the study indicate that volumetric shrinkage strains are influenced by soil properties and compaction conditions. Volumetric shrinkage strain increased with increasing plasticity index and clay content, and as the compaction water content increased or decreased relative to optimum water content. Volumetric shrinkage strain decreased with increasing compactive effort. Specimens with the largest volumetric shrinkage strains typically contained the largest number of cracks. Hydraulic conductivity testing indicated that cracking of the specimens resulted in an increase in hydraulic conductivity, sometimes as large as three orders of magnitude.     

Sand Replacement Method for Determination of Shrinkage Limit of Fine-Grained Soils

Mercury is one of the many hazardous substances that has been recognized and banned by many natural codes of practice and governments. Because many laboratory works in research and practice require the use of mercury, safe alternative materials and procedures are being researched. One of the Atterberg limits dealing with volume stability of soils in the field is the shrinkage limit. The conventional method followed by many national codes of practice involves the use of mercury to measure the volume of dry soil pat. This paper proposes sand replacement method to determine the shrinkage limit of soils in the laboratory. This method uses sand of uniform gradation to determine the volume of dry soil pat. The proposed method is simple, safe, free from the limitations of the conventional mercury and wax methods, and eco-friendly. The shrinkage limit values obtained from the proposed sand replacement method compare very well with those from the mercury displacement method.     

Subsurface Characterization at Ground Failure Sites in Adapazari, Turkey

Ground failure in Adapazari, Turkey during the 1999 Kocaeli earthquake was severe. Hundreds of structures settled, slid, tilted, and collapsed due in part to liquefaction and ground softening. Ground failure was more severe adjacent to and under buildings. The soils that led to severe building damage were generally low plasticity silts. In this paper, the results of a comprehensive investigation of the soils of Adapazari, which included cone penetration test (CPT) profiles followed by borings with standard penetration tests (SPTs) and soil index tests, are presented. The effects of subsurface conditions on the occurrence of ground failure and its resulting effect on building performance are explored through representative case histories. CPT- and SPT-based liquefaction triggering procedures adequately identified soils that liquefied if the clay-size criterion of the Chinese criteria was disregarded. The CPT was able to identify thin seams of loose liquefiable silt, and the SPT (with retrieved samples) allowed for reliable evaluation of the liquefaction susceptibility of fine-grained soils. A well-documented database of in situ and index testing is now available for incorporating in future CPT- and SPT-based liquefaction triggering correlations.     

Interpretation of Secant Shear Modulus Degradation Characteristics from Pressuremeter Tests

Nonlinear shear modulus degradation characteristics are of interest in many geotechnical engineering applications, such as ground deformation caused by seismic shaking and deep excavations in clay, weathered rock, and stabilized soil. This paper presents an approach to derive the secant shear modulus degradation characteristics from in situ pressuremeter tests, which is based on a digital filter algorithm. The algorithm is described, and data preparation procedures are presented. Use of the algorithm is illustrated by means of pressuremeter data for soils stabilized with deep mixing methods on the Boston central artery/tunnel (CA/T). The nonlinear secant shear modulus degradation characteristics from the digital filter approach are shown to be in good agreement with those from the curve fitting and transformed-strain approaches. They also compare favorably with the results of other in situ and laboratory tests performed in conjunction with the CA/T stabilized soils. The algorithm is implemented by a 26-line MATLAB code in an appendix of the paper.     

Design of Compacted Lateritic Soil Liners and Covers

Laboratory tests were conducted on three lateritic soil samples to illustrate some pertinent considerations in the design of compacted lateritic soil liners and covers. The three design parameters investigated are hydraulic conductivity, desiccation-induced volumetric shrinkage, and unconfined compressive strength. Test specimens were compacted at various molding water contents using four compactive efforts. The compaction conditions were shown to have some relationship with soil compaction using either the plasticity modulus or the plasticity product (i.e., clay index). For construction quality assurance purposes, the traditional approach was compared with the modern criterion. Deficiencies associated with the traditional approach for soil liners found in literature also apply to lateritic soils. Overall acceptable zones were constructed on the compaction plane to meet design objectives for hydraulic conductivity, volumetric shrinkage strains, and unconfined compressive strength. The line of optimums was identified as a suitable lower bound for overall acceptable zones of lateritic soils. The volumetric shrinkage strain was also identified as the second most important design parameter for lateritic soils. The shapes of the acceptable zones were affected by the fines contents of the soils.     

Impact of Soil Type and Compaction Conditions on Soil Water Characteristic

Tests were conducted to determine the variation of water content and pore water suction for compacted clayey soils. The soils had varying amounts of clay fraction with plasticities ranging from low to high plasticity. The unsaturated soil behavior was investigated for six conditions, covering a range of compactive efforts and water contents. The experimental data were fit to four commonly used models for the water content-pore water suction relationship. Each model provided a satisfactory fit to the experimental data. However, the individual parameters obtained from the curve fits varied significantly between models. The soil water characteristic curves (SWCCs) were more sensitive to changes in compaction effort than changes in compaction water content. At similar water contents, the pore water suction increased with increasing compaction effort for each compaction condition and soil type. For all compaction conditions, the lowest plasticity soils retained the smallest water content and the highest plasticity soils retained the highest water content at a specified suction. In addition, SWCCs for soils compacted in the laboratory and in the field were similar.     

Determination of Atterberg Limits: Uncertainty and Implications

Arthur Casagrande made one of the most important contributions to Geotechnical Engineering; ordering and presenting clearly the existing differences between objectives for civil engineering soil classification and soil classification schemes intended for other purposes. However, more than 50 years after the Unified System of Soil Classification (USSC) was proposed, one of the main ideas expressed by Casagrande: “the plasticity chart representation of the plasticity parameters in different soil moistures, belonging to a common geological origin, is a straight line, parallel to the A line,” has received little scrutiny. The main purpose of this technical note is to begin a revision of Casagrande’s proposal under a probabilistic approach, suggesting some modifications to the application of the plasticity chart. Regression analysis is proposed as a valid technique to express the linear behavior of the Atterberg limits for a given soil. The problem considering plasticity index as a probabilistic variable is exposed demonstrating that the correct representation of the plasticity chart is in terms of liquid and plastic limits. Data from the Libertad–Dolores clays formations from Uruguay are presented, demonstrating the application of the proposed changes.     

Effects of Kiln Ash on the Compressibility of Residual Lateritic Soils

The potential for the use of kiln ash as an additive to Lateritic soils to improve their engineering characteristics as road construction material was experimentally investigated. The results of laboratory tests indicate that no significant improvement of the soil properties occurred until after several weeks of curing time. In general, as the content of kiln ash in the soil was increased, the soil pH increased from 5.5 to 11.8; the maximum unconfined shear strength increased from 340 to 423 kPa (corresponding to 0–8% kiln ash content), the soil liquid limit reduced from 59 to 49% (corresponding to 0–20% kiln ash as content). No significant change in the plasticity limits of the lateritic soil was observed, in the range of 0 to 8% kiln ash content. Relative to the compressibility of the natural soil (measured in terms of the total strain), a decrease of about 3% occurred for kiln ash contents of 5, 10, and 20% within 1 to 7 days; and that this decrease reached about 19% for 20% kiln ash content as time progressed (to more than 177 days). These results imply that significant and desirable changes in soil compressibility can be achieved after a few months if the soils are admixed with kiln ash. Soil solution pH changes cause a time-dependent increase in soil strength, where calcium cations combine with silica and aluminum of the soil to form insoluble cementitious materials.     

Organoclay with Soil-Bentonite Admixture as Waste Containment Barriers

Organoclays, clays modified by cationic surfactants, for engineering applications have recently drawn great attention because of their high organic removal capacity. In this study, the potential use of organoclays with soil-bentonite admixtures as waste containment barriers is investigated by experimental tests such as batch equilibrium sorption studies, compaction tests, and hydraulic conductivity tests. Sorption isotherms of total organic carbon (TOC), a gross organic term, by five different types of soil admixtures are nonlinear. The soil specimen with more organoclays exhibits higher organic sorption capacity and a larger retardation factor. The specimens with 20% by dry weight of bentonite have higher optimum water content and plasticity. With the addition of bentonite in the soil material consisting of completely decomposed volcanic rock (CDV) (natural soils) and organoclays, the hydraulic conductivity to leachate decreases from about 10?7 to 10?8 cm∕s. This indicates that the presence of bentonite in the admixtures is important in reducing hydraulic conductivity.     

滇东南建水稀土矿稀土数值特征及研究意义

为查明建水稀土矿的稀土数值特征,在长岭岗岩体风化壳的黏土层、全风化层、半风化层、弱风化层中采集了82件样品,进行全相稀土氧化物、离子相稀土氧化物质量分数分析,包括全相稀土氧化物的质量分数、离子相稀土氧化物的质量分数、全相与离子相稀土氧化物质量分数的相关系数、全相稀土氧化物在各个风化层位中的变化系数、离子相稀土氧化物在各个风化层位中的变化系数、结晶相稀土氧化物的质量分数。经资料整理,黏土层、全风化层、半风化层、弱风化层中的稀土数值有明显差异。造成稀土数值差异的主要原因为:成矿母岩的风化程度,稀土矿物离解程度,离子相稀土氧化物的迁移富集程度。加强稀土数值的研究,有助于深化风化壳离子吸附型稀土矿的成矿机理认识。     

Cyclic Behavior of Fine-Grained Soils at Different pH Values

The effects of pH on the liquefaction susceptibility of fine-grained soils were examined by performing undrained cyclic ring-shear tests on artificial mixtures and a natural soil under different pH conditions. Solutions of diluted sulphuric acid (H2SO4) and dissolved sodium hydroxide (NaOH) were used to create acidic and alkaline environments, respectively, while distilled water was used as a reference liquid. Low plasticity kaolin and illite-sand mixtures and a medium plasticity bentonite-sand mixture were selected to investigate the influence of plasticity and clay mineralogy on the pH-dependent response of soil to cyclic loading. The results showed that the effects of pH were more pronounced for the medium plasticity mixture, and depended greatly on the mineralogy of clay fraction. For example, in an acidic medium, the kaolin-sand mixture became slightly more resistant to liquefaction while the illite-sand mixture became more susceptible to liquefaction. The bentonite-sand mixture was observed to be the most sensitive to changes in pH environment. While resistant to liquefaction in distilled water, it rapidly liquefied in acidic and alkaline mediums. Cyclic behavior of a medium plasticity soil, which was collected from an earthquake-induced landslide, was also affected by changes in pH. Although being overall resistant to liquefaction regardless of pH, it decreased its cyclic strength in both acidic and alkaline environments. Based on the available literature and the obtained results, an attempt was made to explain the influence of pH on the undrained cyclic behavior of fine-grained soils.     

Laboratory Studies of Two Common Saprolitic Soils in Hong Kong

Two commonly encountered saprolitic soils in Hong Kong, weathered volcanic tuff (WT) and weathered granite (WG), were studied using high-quality intact samples. The intact samples exhibited quasi-preconsolidation pressure or yield stress under isotropic compression due to their bonded structures, but the yield was progressive and not abrupt. As the stress increased, significant volumetric changes were measured. These changes resembled clay-type behavior. The soils also exhibited anisotropic deformation under isotropic loading and unloading, which was associated with the features of their parent rocks. During the drained tests, shearing at the in situ stress-state produced peak strength and volumetric dilation. Undrained shearing showed complicated stress paths and dilatancy behavior in these soils. Phase transformation states and dilative shear failure were readily seen, which resembles typical sand-type behavior. Distinct shear band(s) appeared in the WT specimens during shearing, whereas a bulging type of failure appeared in the WG specimens. The soils ultimately approached the corresponding state guided by a unique critical state line, regardless of their complex initial states in relation to the bonded structure and drainage conditions.     

Threshold Shear Strain for Cyclic Pore-Water Pressure in Cohesive Soils

Threshold shear strain for cyclic pore-water pressure, γt, is a fundamental property of fully saturated soils subjected to undrained cyclic loading. At cyclic shear strain amplitude, γc, larger than γt residual cyclic pore-water pressure changes rapidly with the number of cycles, N, while at γc<γt such changes are negligible even at large N. To augment limited experimental data base of γt in cohesive soils, five values of γt for two elastic silts and a clay were determined in five special cyclic Norwegian Geotechnical Institute (NGI)-type direct simple shear (NGI-DSS), constant volume equivalent undrained tests. Threshold γt was also tested on one sand, with the results comparing favorably to published data. The test results confirm that γt in cohesive soils is larger than in cohesionless soils and that it generally increases with the soil’s plasticity index (PI). For the silts and clay having PI=14–30, γt = 0.024–0.06% was obtained. Limited data suggest that γt in plastic silts and clays practically does not depend on the confining stress. The concept of evaluating pore water pressures from the NGI-DSS constant volume test and related state of stresses are discussed.