The field vane shear test is one of the most common in situ tests to obtain the undrained shear strength of soft clay. Uncoupling of the torque generated by the soil resistance along the vertical and horizontal planes of the vane has been done by conducting conventional direct shear test and newly developed vertical direct shear test on the soil. From the shear stress-displacement relationship of the direct shear tests, simple analysis is performed to simulate the field vane behavior at various depths. The results of the simulation agree well with those obtained from the field vane tests on soft Bangkok clay. The conventional method of computing the undrained shear strength of the field vane shear based on the maximum torque is close to the equivalent average value from the shear box tests. A special laboratory triaxial vane apparatus was also used to study the shearing behavior of the soft clay with the capability of Ko-consolidating the sample before conducting the vane shear test. The results of the triaxial vane tests were also compared with the predictions. The predicted torque values are lower than the experimental data for the same angle of rotation.

The geotechnical characterization of residual soils is a complex matter and is not always successful because current interpretation methodologies dedicated to sedimentary soils do not adequately respond to the behavior of this type of soils. The problem has been under scope by several Portuguese and international institutions. The work carried out in the experimental Site of the Polytechnic Institute of Guarda (IPG) since 2003, constituted by residual soils and decomposed rocks of the local granite massif, is highlighted herein. The work was strongly supported by MOTA-ENGIL (Portuguese construction company) and the Laboratory of Math Engineering (LEMA, Polytechnic Institute of Porto). The characterization of the test site and the respective research work is presented. The research work involved interpretation of in situ tests (SDMT, SCPTu, PMT, SPT, DPSH, and geophysical tests), tests in controlled chambers (DMT, geophysical, and suction tests), and laboratory tests (oedometric tests, direct shear tests, and triaxial tests with several stress paths). The tests were performed on natural structured soils, artificially cemented mixtures, and unstructured soils. Advanced math and statistical analysis were applied in the development of new correlations to obtain geotechnical parameters representative of these soils. Furthermore, the work also allowed to recognize the physical characteristics of the materials and better understand their mechanical behavior.

This paper focuses on evaluating the increase in axial pile resistance subjected to both consolidation and aging setups. Consolidation and aging setup models were first developed to estimate the setup parameters based on databases collected from literature, which include 10 instrumented piles for consolidation setup and 26 test piles for long-term aging. The eight top-performing pile cone penetration test (CPT) methods that were evaluated in a previous study were used to estimate the side resistance of soil layers at 14 days after pile driving. The developed consolidation and aging setup models were then used to extrapolate the results to evaluate the side resistance of each soil layer at the end of consolidation and for long-term aging. The estimated side and total resistances were compared with the measurements from pile load tests considering both consolidation and aging setups. The resistances estimated before and after completion of excess pore water pressure dissipation indicates that significant aging takes place after consolidation setup. The value of consolidation setup parameter (Ac) was 0.53, and, for aging, the setup parameter (Ag) was 0.23 in clay and 0.16 in sand. The results show that all pile CPT methods with/without using a consolidation setup model tend to underestimate the unit side resistance of clay soil layers. The use of pile CPT methods in combination with an aging model improved the accuracy of pile CPT methods, and this was verified using load test results for five piles subjected to aging. The Philipponnat and University of Florida (UF) methods showed the best performance on estimating the total resistance of piles subjected to aging.

In northern China, abundant summer rainfall and a higher water table can weaken the soil due to salt heave, collapsibility, and increased moisture absorption, thus the chlorine saline soil (silty clay) needs to be stabilized prior to use in road embankments. To optimize chlorine saline soil stabilizing programs, unconfined compressive strength tests were conducted on soil treated with five different stabilizers before and after soaking, followed by field compaction test and unconfined compressive strength test on a trial road embankment. In situ testing were performed with the stabilized soils in an expressway embankment, and the results demonstrated that the stabilized soil with lime and SH agent (an organic stabilizer composed of modified polyvinyl alcohol and water) is suitable for road embankments. The appropriate addition ratio of stabilized soil is 10% lime and 0.9% SH agent. SH agent wrapped soil particles, filled soil pores, and generated a silk-like web to improve the moisture stability, strength, and stress-strain performance of stabilized soil.

PurposeThe paper aims to clarify the distribution of excess pore pressure during cone penetration in two-layered clay and its influence on penetrometer resistance.Design/methodology/approachAn arbitrary Lagrangian-Eulerian scheme is adopted to preserve the quality of mesh throughout the numerical simulation. Simplified methods of layered penetration and coupled pore pressure analysis of cone penetration have been proposed and verified by previous studies. The investigation is then extended by the present work to study the cone penetration test in a two-layered clay profile assumed to be homogeneous with the modified Cam clay model.FindingsThe reduction of the range of pore pressure with decreasing PF will cause a decrease of the sensing distance. The PF of the underlying soil is one of the factors that determine the development distance. The interface can be obtained by taking the position of the maximum curvature of the penetrometer resistance curve in the case of stiff clay overlying soft clay. In the case of soft clay overlying stiff clay, the interface locates at the maximum curvature of the penetrometer resistance curve above about 1.6D.Research limitations/implicationsThe cone penetration analyses in this paper are conducted assuming smooth soil-cone contact.Originality/valueA simplified method based on ALE in Abaqus/Explicit is proposed for layered penetration, which solves the problem of mesh distortion at the interface between two materials. The stiffness equivalent method is also proposed to couple pore pressure during cone penetration, which achieves efficient coupling of pore water pressure in large deformations.

This paper seeks to promote use of shear wave velocity (Vs) measurements in UK clays as a complement to more standard ground investigation techniques. Vs measurements seem to be repeatable and independent of the method of measurement used in isotropic soil conditions - for example, soft clays. However, in glacial tills, and especially in the overconsolidated clays of south-east UK, Vs measurements will differ depending on the direction of propagation and polarisation of the shear waves due to natural stress anisotropy and the fissured nature of the materials. Correlations between Vs and other in situ data and with a variety of soil properties can be very powerful and some have been proposed here for UK clays. However, these correlations should ideally be local and only applied to other soils and areas with great caution. Other uses of the techniques, beyond those of classical dynamic analyses, have been described together with some future challenges. Uncertainties in the methods have been well researched and several methods have been proposed to deal with these uncertainties. Nonetheless, advice from a geophysical colleague will enhance the geotechnical engineers' use of Vs data.