Stress History And Normalized Soil Engineering Properties Research Articles

Evaluation of Stress History and Undrained Shear Strength of OC Clayey Soil in Northern Jakarta

It is difficult to determine the accurate undrained shear strength (su) of clay with complicated stress history. In addition to the laboratory tests such as Triaxial UU and Unconfined tests, the in-situ tests such as Vane Shear, SPT, and CPTu tests were conducted for undrained shear strength evaluation. Moreover, the overconsolidation ratio (OCR) by CPTu correlation presented the soil stress history profile along the depth and the Oedometer tests were used to evaluate the results. It was found that the clayey soil is overconsolidated up to -31.0 m below the surface in Northern Jakarta due to groundwater extraction. The Stress History and Normalized Soil Engineering Properties (SHANSEP) formula is widely used to model the relationship between undrained shear strength, OCR, and vertical shear stress. The su results from laboratory and in-situ tests showed good agreement with SHANSEP formula. Moreover, several empirical formulas for OC clayey soil were developed for future deep excavation projects in Jakarta area.

Laboratory Evaluation of Mechanical Properties of Draupne Shale Relevant for CO2 Seal Integrity

The mechanical integrity of caprocks overlying injection formations is one of the key factors for safe storage of carbon dioxide in geological formations. Undrained effects caused by CO2 injection on strength and elastic parameters should be properly considered in the operational design to avoid fracture creation, fault reactivation and unwanted surface uplift. This study presents results from eleven undrained triaxial compression tests and one oedometer test on the Draupne shale, which is the main caprock of the Smeaheia site in the North Sea, to extract parameters relevant for seal integrity. Tests have been performed on samples oriented perpendicular to and parallel with the horizontal layering of the rock to study the effects of sample orientation relative to the loading direction. Results from undrained triaxial tests showed only minor effects of sample orientation on friction and cohesion. However, when loading during undrained shearing was parallel with layering (horizontal samples), measured Young’s modulus was roughly 1.4 times higher than for the vertical samples. Undrained shearing of vertical samples generated 30–50% more excess pore pressure than for horizontal samples with similar consolidation stress owing to more volume compaction of vertical samples. With apparent pre-consolidation stress determined from a high-stress oedometer test, the normalized undrained shear strength was found to correlate well with the overconsolidation ratio following the SHANSEP (Stress History and Normalized Soil Engineering Properties) procedure.

Tunnels in squeezing clay-rich rocks

Squeezing ground conditions, which can lead to severe loads in tunnels, have historically been associated with the presence of clay minerals in the ground. Over the years, many methodologies have been proposed to predict squeezing in tunnels based on tunnel depth, in situ stress, ground mineralogy, and ground strength and deformation behavior. This paper presents a comprehensive review of methodologies to predict tunnel squeezing in clay-rich rocks. A new methodology is proposed where ground conditions and squeezing potential are assessed based on the Stress History and Normalized Soil Engineering Properties (SHANSEP) approach adapted to clay-rich rocks, Peck’s stability number and Hoek & Brown’s (1997) Geological Strength Index (GSI). A squeezing number S is suggested to classify ground conditions based on the level of squeezing that the ground may experience in response to tunneling. Finally, it is demonstrated that by combining the proposed classification system and an existing classification system for ground squeezing condition, an accurate estimate of tunnel strain can also be obtained. The proposed method is applied to four case studies of tunnels in squeezing ground in shale and mudstone.

SHANSEP-Based Side Resistance of Driven Pipe Piles in Plastic Soils: Revision and LRFD Calibration

AbstractThe empirical approach adapting the Stress History and Normalized Soil Engineering Properties (SHANSEP) concept relates the average overconsolidation ratio (OCR) of plastic soils to the ave...

The elastic undrained modulus Eu50 for stiff consolidated clays related to the concept of stress history and normalized soil properties

Abstract The paper presents the results of a triaxial test conducted on stiff, consolidated clays. The standard TXCIU procedure (isotropic consolidation and undrained shearing) was applied in the laboratory soil tests. The undrained elastic modulus Eu50 was determined from each test. The Eu50 values were determined for soil samples cut out from different depths and tested under different confining pressures. There was a significant scatter of values with depth, and no relationships between Eu50 modules or other geotechnical parameters (e.g., cu) were observed. This work presents the concept of normalization of Eu50 modulus values using modified normalization SHANSEP (Stress History And Normalized Soil Engineering Properties). This method was first proposed for estimating the value of the undrained shear strength cu normalizing the parameter relative to the in situ effective vertical stress σ′vo and loading history (overconsolidation stress σ′p and overconsolidation ratio OCR) of the soil. The study demonstrated that the concept of normalization of soil properties can also be used for testing elastic modulus Eu50 of consolidated natural clays and normalized values of geotechnical parameters taking into account the state of stress and load history can be correlated with the value of the overburden pressure.

Influence of Sample Disturbance on Estimated Side Resistance of Driven Piles in Cohesive Soils

AbstractThis paper describes the influence of sample disturbance on laboratory undrained shear strength tests used for pile capacity calculations of driven close-end pipe piles, referencing an approach based on the stress history and normalized soil engineering properties (SHANSEP) for estimating the side resistance of pipe piles in cohesive soils. The SHANSEP technique provides a rational basis for relating the soil overconsolidation ratio (OCR) to the normalized side resistance overcoming the problems related to sample disturbance. Sample disturbance of soils with OCR<2 is identified as a significant factor affecting the selection of values of side resistance for pile design. The empirical record of load test sites was modified to remove test data that were likely affected by sample disturbance effects from the current database referencing the SHANSEP-based approach to provide a reliable set of reference undrained strengths and measured side resistance values, which produces an equivalent new undrained ...

A Case History on Underpinning for a Distressed Building on Hard Residual Soil Underneath Non-Uniform Loose Sand

ABSTRACT This paper presents a case history on the failure of Suranivet 9, a student dormitory in the campus of Suranaree University of Technology (SUT), Thailand. The dormitory encountered excessive differential settlement due to the variation in soil profile. Part of the building was underlain by very stiff to hard SUT silty clay and part by loose clayey sand. Underpinning to extend the foundations down to stable stratum was employed to strengthen bearing capacity and minimize settlement. The underpinning design and procedure were summarized. In practice, the static formula was used for the preliminary micro-pile design (selection of pile section and length for different loads and soil profiles). The undrained shear strength (Su) of SUT silty clay was approximated using the Stress History and Normalized Soil Engineering Properties (SHANSEP) technique and standard penetration number (N). The finite element method was employed to predict the load-settlement curve of the micro-pile. Modified cam clay model was proved as a suitable model for this prediction. The measured settlements of the underpinned foundations after one year service were less than 0.5 mm. This small settlement guarantees the stability of the underpinned structure. It is also found that the settlement ratio (ratio of the measured settlement of underpinned foundations to the predicted settlement of single micro-pile) varied from 0.7 to 3.0.

Normalized undrained shear strength of clay shales

This paper examines the possibility of normalizing the undrained shear strength behavior of clay shales. Shales are formed in sedimentary basins by diagenetic processes, which turn young clay sediments into compacted and lithified shales. Cementation at grain contacts affects many properties of shales including the apparent preconsolidation and shear strength. Based on a study of 25 different types of materials, the normalized undrained shear strength of clay shales was found to correlate satisfactorily with overconsolidation ratio following the SHANSEP (Stress History and Normalized Soil Engineering Properties) normalization procedure for clays. The normalized undrained shear strength correlation appears valid regardless of the cause of the apparent preconsolidation. Correlations of the apparent preconsolidation stress with unconfined compressive strength and compressional wave velocity are proposed to predict the normalized undrained shear strength of clay shales.

Effects of sample disturbance and consolidation procedures on measured shear strength of soft marine Norwegian clays

After many decades of research, the issue of sample disturbance is still important as regards to determining reliable and representative soil parameters for foundation design in soft clays. Parallel laboratory tests have been carried out on high-quality block samples and ordinary piston tube samples from 12 deposits of soft Norwegian marine clays. Undrained triaxial and direct simple shear (DSS) tests on samples reconsolidated to the in situ effective stresses show that sample disturbance has a significant effect on the measured stress–strain–strength behaviour: the more disturbed the sample, the lower the shear stress at small strains and the higher the shear stress at large strains. Breakdown of the clay structure, including cementation bonds, is the assumed cause of lower shear resistance at small strains, whereas at large strains the shear resistance is governed mainly by the water content, which for soft clay samples, reconsolidated to the in situ effective stresses, will be lower, and the strength thereby higher, the more disturbed the sample. The work described herein also includes the effects of the consolidation procedure; in addition to the reconsolidation technique, both stress history and normalized soil engineering properties (SHANSEP) and delayed consolidation tests have been carried out.Key words: soft clays, sample disturbance, consolidation procedures, stress–strain–strength behaviour, stress–strain–time behaviour.

Behavior of Marine Sand-Clay Mixtures under Static and Cyclic Triaxial Shear

In situ Indian Marine soils occur as mixtures of sand and clay in widely varying proportions. Their engineering behavior has not been comprehensively and systematically studied. An experimental program on reconstituted Indian marine soils having different proportions of sand and clay was undertaken. The study comprised one dimensional consolidation tests and static and cyclic triaxial tests. This paper presents the results of this study and offers an interpretation of the behavior based on effective void ratio (EVR), a new parameter defined as the ratio of volume of voids to the volume of effective soil fraction. Experimental results indicate a roughly unique EVR-logσvc′ relationship and normalizability of undrained static behavior. Some predictions from the stress history and normalized soil engineering properties (SHANSEP) approach with EVR as basis, in close agreement with experimental data, have been presented. Hence EVR is proposed as an appropriate parameter for describing and predicting the behavior of sand-clay mixtures. The development of pore pressures and strains during cyclic loading is dictated by a combination of EVR and cyclic stress ratio for sandy clays and by a combination of void ratio and cyclic stress ratio for clayey sands.

Design Strengths for an Offshore Clay

Stability analyses for stage construction of a breakwater located offshore New Jersey required a detailed evaluation of the undrained stress‐strain‐strength properties of a plastic marine clay. One set of analyses, representing “conventional” practice, used UU triaxial compression tests to obtain the initial undrained strength (cu) and CIU triaxial compression tests to predict strength increases with consolidation. The second approach employed the Stress History And Normalized Soil Engineering Properties (SHANSEP) design procedure. This involved extensive consolidation testing to measure the in‐situ preconsolidation pressure and a comprehensive program of CKoU tests sheared in compression, extension and direct simple shear modes of failure at varying overconsolidation ratios. A strain compatibility technique was applied to the SHANSEP data to account for the effects of anisotropy and progressive failure in circular arc‐ and wedge‐type stability analyses. The SHANSEP approach yielded design strengths signi...