Degree of Saturation and Liquefaction Resistances of Sand Improved with Sand Compaction Pile

Sand compaction pile (SCP) is a ground improvement technique extensively used to ameliorate liquefaction resistance of loose sand deposits. This paper discusses results of laboratory tests on high-quality undisturbed samples obtained by the in situ freezing method at six sites where foundation soils had been improved with SCP. Inspection of samples revealed that the improved ground was desaturated during the ground improvement. Degree of saturation (Sr) was lower than 77% for the sand piles and 91% for the improved sand layers, while Sr was approximately 100% for improved clayey and silty soils. A good correlation was found between Sr and 5% diameter of the soil; the larger 5% diameter of soils (D5), the lower the degree of saturation. It appeared that the variation of Sr with D5 for soils within a month after the ground improvement work was quite similar in trend to that after more than several years. Degree of saturation of soils after several years was noticeably, but not significantly, higher as compared with that shortly after ground improvement, indicating longevity of air bubbles injected in the improved soil. Undrained cyclic shear tests were also carried out on saturated and unsaturated specimens and effects of desaturation on undrained cyclic shear strength were studied. The test results were summarized in a form of liquefaction resistance with reference to normalized standard penetration test N-value.     

In-Situ Desaturation Test by Air Injection and Its Evaluation through Field Monitoring and Multiphase Flow Simulation

Desaturation of ground by air injection attracts considerable attention in recent years as an innovative technique for a liquefaction countermeasure. Several research programs were conducted in laboratories regarding the related topics. This paper describes an in situ air-injection test that aims to examine the effectiveness of the air injection to desaturate ground and the validity of observation techniques to monitor the evolution of the unsaturated zone. In the test, air was injected from an air injector deployed in a targeted saturated-sand layer at a depth of 6?m. Observations revealed that the air-flow rate increased linearly with increasing air-injection pressure and the desaturated zone was generated within 4?m from the injection point. A 3-dimensional electric resistivity tomography technique was effective for evaluation of the desaturated zone. The degree of saturation of the in situ soil was observed by using high quality undisturbed samples obtained by the ground freezing method. The degree of saturation ranged from 68–98%, which was low enough to almost double the liquefaction resistance of the soil at the site. Numerical analyses were also conducted with a gas-liquid two-phase flow simulator to describe the evolution of the soil desaturation. Qualitatively, predictions show a relatively good agreement with the in situ measurements of the 3D electric resistivity tomography and are quantitatively compatible with the in-field degree of saturation measured indirectly by using the frozen soil samples. Actual liquefaction resistance was evaluated utilizing the undisturbed samples by conducting a triaxial test under cyclic shear conditions, which revealed that desaturated samples were indeed less susceptible to liquefaction compared with the fully saturated samples.     

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.     

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.     

Embankment Dam on Liquefiable Foundation—Dynamic Behavior and Densification Remediation

Earthquake-induced liquefaction is a major concern for embankment dam safety. Many liquefaction-induced earth embankment failures or near failures have been reported around the world during various earthquakes. Such embankment damages were particularly destructive when the underlying saturated granular soils liquefied, resulting in cracking, settlement, lateral spreading, and slumping of the embankment. Through a series of four highly instrumented geotechnical centrifuge model tests, seismic behavior of a zoned embankment dam with saturated sandy soil foundation was studied under moderate earthquake conditions. The beneficial effects of foundation densification were investigated. Valuable insights into the dynamic behavior of the employed embankment–foundation systems are provided. Test results suggest that there may be an optimum depth of densification treatment beneath an earth dam beyond which the reduction of the earthquake-induced deformations are relatively minor and that relatively small and isolated zones (e.g., at depth) of loose material within a densified volume of soil may not impair the overall effectiveness of treatment and do not necessarily result in damaging displacements.     

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.     

Yield Strength Ratio and Liquefaction Analysis of Slopes and Embankments

A procedure is proposed to evaluate the triggering of liquefaction in ground subjected to a static shear stress, i.e., sloping ground, using the yield strength ratio, su(yield)/σv0′. Thirty liquefaction flow failures were back analyzed to evaluate shear strengths and strength ratios mobilized at the triggering of liquefaction. Strength ratios mobilized during the static liquefaction flow failures ranged from approximately 0.24 to 0.30 and are correlated to corrected cone and standard penetration resistances. These yield strength ratios and previously published liquefied strength ratios are used to develop a comprehensive liquefaction analysis for ground subjected to a static shear stress. This analysis addresses: (1) liquefaction susceptibility; (2) liquefaction triggering; and (3) post-triggering/flow failure stability. In particular, step (2) uses the yield strength ratio back-calculated from flow failure case histories and the cyclic stress method to incorporate seismic loading.     

Axial Compression of Footings in Cohesionless Soils. II: Bearing Capacity

An extensive database of full-scale field load tests was used to examine the bearing capacity for footings in cohesionless soils. Each load test curve was evaluated consistently to determine the interpreted failure load (i.e., bearing capacity) using the L1-L2 method. This test value then was compared with the theoretical bearing capacity, computed primarily using the basic Vesi? model. The comparisons show that, for footing widths B>1?m, the field results agree very well with the Vesi? predictions. However, for B<1?m, the results indicated a relationship between B and the predicted-to-measured bearing capacity ratio. Accordingly, a simple modification was made to the bearing capacity equation, and the resulting predictions are very good.     

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.     

Evaluation of Cyclic Softening in Silts and Clays

Procedures are presented for evaluating the potential for cyclic softening (i.e., onset of significant strains or strength loss) in saturated silts and clays during earthquakes. The recommended procedures are applicable for fine-grained soils with sufficient plasticity that they would be characterized as behaving more fundamentally like clays in undrained monotonic or cyclic loading. The procedures are presented in a form that is similar to that used in semiempirical liquefaction procedures. Expressions are developed for a static shear stress correction factor and a magnitude scaling factor. Guidelines and empirical relations are presented for determining cyclic resistance ratios based on different approaches to characterizing fine-grained soil deposits. The potential consequences of cyclic softening, and the major variables affecting such consequences, are discussed. Application of these procedures is demonstrated through the analysis of the Carrefour Shopping Center case history from the 1999 Kocaeli earthquake. The proposed procedures, in conjunction with associated liquefaction susceptibility criteria, provide an improved means for distinguishing between the conditions that do and those that do not lead to ground deformations in fine-grained soil deposits during earthquakes.     

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.     

Accounting for Soil Aging When Assessing Liquefaction Potential

It has been recognized that liquefaction resistance of sand increases with age due to processes such as cementation at particle contacts and increasing frictional resistance resulting from particle rearrangement and interlocking. As such, the currently available empirical correlations derived from liquefaction of young Holocene sand deposits, and used to determine liquefaction resistance of sand deposits from in situ soil indices [standard penetration test (SPT), cone penetration test (CPT), shear wave velocity test (Vs)], are not applicable for old sand deposits. To overcome this limitation, a methodology was developed to account for the effect of aging on the liquefaction resistance of old sand deposits. The methodology is based upon the currently existing empirical boundary curves for Holocene age soils and utilizes correction factors presented in the literature that comprise the effect of aging on the in situ soil indices as well as on the field cyclic strength (CRR). This paper describes how to combine currently recorded SPT, CPT, and Vs values with corresponding CRR values derived for aged soil deposits to generate new empirical boundary curves for aged soils. The method is illustrated using existing geotechnical data from four sites in the South Carolina Coastal Plain (SCCP) where sand boils associated with prehistoric earthquakes have been found. These sites involve sand deposits that are 200,000?to?450,000?years in age. This work shows that accounting for aging of soils in the SCCP yields less conservative results regarding the current liquefaction potential than when age is not considered. The modified boundary curves indicate that old sand deposits are more resistant to liquefaction than indicated by the existing empirical curves and can be used to evaluate the liquefaction potential at a specific site directly from the current in situ properties of the soil.     

Mechanically Stabilized Earth Wall Failure at Two Soft and Sensitive Soil Sites

Two highway bridge approaches, about 10 and 12?m in height, near Kolkata (Calcutta), India constructed with mechanically stabilized earth (MSE) failed recently. These structures were founded on sensitive, soft and compressible, fine-grained soils of the intertidal flats and backswamps of the Ganges delta. One of these MSE walls, which failed in the final stages of its construction, was constructed after foundation soils were strengthened with prefabricated vertical drain installation and preloading. The second MSE wall that failed within a month of its opening for traffic was constructed on unimproved ground. Fortunately, immediate collateral damage from these incidents was small. Using pre and postconsolidation shear strengths the MSE walls were redesigned. Reconstruction involved prefabricated vertical drain installation at the second site and construction of stabilizing berms at both locations. The facilities are now operational and appear to be performing satisfactorily. Details of the failures, postfailure investigations, and monitoring, redesign, and reconstruction are presented in this paper.     

Verification of the Soil-Type Specific Correlation between Liquefaction Resistance and Shear-Wave Velocity of Sand by Dynamic Centrifuge Test

Liquefaction of granular soil deposits is one of the major causes of loss resulting from earthquakes. The accuracy of the liquefaction potential assessment at a site affects the safety and economy of an engineering project. Although shear-wave velocity (Vs)-based methods have become prevailing, very few works have addressed the problem of the reliability of various relationships between liquefaction resistance (CRR) and Vs used in practices. In this paper, both cyclic triaxial and dynamic centrifuge model tests were performed on saturated Silica sand No. 8 with Vs measurements using bender elements to investigate the reliability of the CRR-Vs1 correlation previously proposed by the authors. The test results show that the semiempirical CRR-Vs1 curve derived from laboratory liquefaction test of Silica sand No. 8 can accurately classify the (CRR,Vs1) database produced by dynamic centrifuge test of the same sand, while other existing correlations based on various sandy soils will significantly under or overestimate the cyclic resistance of this sand. This study verifies that CRR-Vs1 curve for liquefaction assessment is strongly soil-type dependent, and it is necessary to develop site-specific liquefaction resistance curves from laboratory cyclic tests for engineering practices.     

Forensic Investigation of a Sulfate-Heaved Project in Texas

This paper focuses on the cause, possible solutions, and future prevention of pavement heave at a new construction project. We speculated that heaving on the east side of the project was caused by a reaction between the lime stabilizer and minerals in the soil. Because of a difference in soil chemistry, the west side of the project (which was still under construction) did not show evidence of heaving. A forensic investigation was initiated to test our hypothesis. The findings of the investigation concluded that the cause of the heaving on the east side of the road was related to the formation of the expansive mineral, ettringite. Ettringite formed due to the reaction of the lime stabilizer with seams of high sulfate soil on the east side. Laboratory testing did not find any effective stabilizer for the high-sulfate soils on the east side. Therefore, reconstruction would involve removing and replacing the treated layer with a select material that has less than 2,000?ppm sulfates. Test results indicate that there was no threat of sulfate heave on the west side. District personnel had performed the field conductivity tests to evaluate and monitor the concentration of the sulfate content on the remaining project. The treatment of 3%/72-h mellowing period/3% lime treatment was employed on the west side. The whole project has been completed for 1?year and no heave has been observed.     

Liquefaction Testing of Stratified Silty Sands

The cyclic behavior of stratified silty sandy soils is at present poorly understood, yet these materials are commonly found in alluvial deposits and hydraulic fill, which have a history of liquefaction during earthquakes. The main objective of this research project was to compare the behavior of stratified and homogeneous silty sands during seismic liquefaction conditions for various silt contents and confining pressures. A comprehensive experimental program was undertaken in which a total of 150 stress-controlled undrained cyclic triaxial tests were performed. Two methods of sample preparation were used for each soil type. These methods included moist tamping (representing uniform soil conditions) and sedimentation (representing layered soil conditions). The silt contents ranged from 10 to 50%, and confining pressures in the range of 50 to 250 KPa were considered. The results indicated that the liquefaction resistances of layered and uniform soils are not significantly different, despite the fact that the soil fabric produced by the two methods of sample preparation is totally different. The findings of this study justify applying the laboratory test results to the field conditions for the range of variables studied.     

Mechanism for Postliquefaction Water Film Generation in Layered Sand

Soil investigations at two sites demonstrate that layered structure or stratification in sand deposits is prevalent not only in reclaimed ground but also in natural alluvial ground. One-dimensional liquefaction tests in a lucite tube are then carried out for models of several types of layered sand, indicating that water films will develop under most circumstances beneath or within less-permeable sublayers. A basic mechanism for the water film generation is discussed based on the measurements of soil settlement and excess pore pressure. The development of the water film and the associated soil settlement are numerically simulated by a simple sedimentation analysis and a rational explanation of the test results is found. Thus a significant involvement of water films in liquefied sand deposits and their basic mechanism are clarified. It is highly probable that water films are involved as a part of a sliding surface and play a significant role in a seismically induced flow failure in loose and layered sand deposits during liquefaction.     

Liquefaction Resistance of Soils from Shear-Wave Velocity

A simplified procedure using shear-wave velocity measurements for evaluating the liquefaction resistance of soils is presented. The procedure was developed in cooperation with industry, researchers, and practitioners and evolved from workshops in 1996 and 1998. It follows the general format of the Seed-Idriss simplified procedure based on standard penetration test blow count and was developed using case history data from 26 earthquakes and >70 measurement sites in soils ranging from fine sand to sandy gravel with cobbles to profiles including silty clay layers. Liquefaction resistance curves were established by applying a modified relationship between the shear-wave velocity and cyclic stress ratio for the constant average cyclic shear strain suggested by R. Dobry. These curves correctly predicted moderate to high liquefaction potential for >95% of the liquefaction case histories and are shown to be consistent with the standard penetration test based curves in sandy soils. A case study is provided to illustrate application of the procedure. Additional data are needed, particularly from denser soil deposits shaken by stronger ground motions, to further validate the simplified procedure.     

Liquefaction Susceptibility Criteria for Silts and Clays

New liquefaction susceptibility criteria for saturated silts and clays are presented that are based on the mechanics of their stress-strain behavior and which provide improved guidance for selecting engineering procedures for estimating potential strains and strength loss during seismic loading. Monotonic and cyclic undrained loading test data for silts and clays show that they transition, over a fairly narrow range of plasticity indices (PI), from soils that behave more fundamentally like sands (sand-like behavior) to soils that behave more fundamentally like clays (clay-like behavior), with the distinction having a direct correspondence to the type of engineering procedures that are best suited to evaluating their seismic behavior. It is recommended that the term liquefaction be reserved for describing the development of significant strains or strength loss in fine-grained soils exhibiting sand-like behavior, whereas the term cyclic softening failure be used to describe similar phenomena in fine-grained soils exhibiting clay-like behavior. For practical purposes, clay-like behavior can be expected for fine-grained soils that have PI ≥ 7, although a slightly lower transition point for soils with a CL-ML classification (perhaps PI ≥ 5 or 6) would be equally consistent with the available data. Issues related to the practical application of these criteria are discussed.     

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.