Self-boring Pressuremeter Tests Research Articles

Field testing of shear strength of granite residual soils

The characteristics of residual soils are very different from those of sedimentary soils. Although the strength characteristics of sedimentary soils have been studied extensively, the shear strength characteristics of granitic residual soils (GRS) subjected to the weathering of parent rocks have rarely been investigated. In this study, the shear strength characteristics of GRS in the Taishan area of southeast China (TSGRS) were studied by field and laboratory tests. The field tests consisted of a cone penetration test (CPT), borehole shear test (BST), self-boring pressuremeter test (SBPT), and seismic dilatometer Marchetti test (SDMT). The shortcomings of laboratory testing are obvious, with potential disturbances arising through the sampling, transportation, and preparation of soil samples. Due to the special structure of GRS samples and the ease of disturbance, the results obtained from laboratory tests were generally lower than those obtained from situ tests. The CPT and scanning electron microscopy (SEM) results indicated significant weathering and crustal hardening in the shallow TSGRS. This resulted in significant differences in the strength and strength parameters of shallow soil obtained by the BST. Based on the SDMT and SBPT results, a comprehensive evaluation method of shear strength for TSGRS was proposed. The SBPT was suitable for evaluating the strength of shallow GRS. The material index (ID) and horizontal stress index (KD) values obtained by the SDMT satisfied the empirical relationship proposed by Marchetti based on the ID index, and were therefore considered suitable for the evaluation of the shear strength of deep GRS.

Discussion of “Measuring strength and consolidation properties in lacustrine clay using piezocone and self-boring pressuremeter tests”

Discussion of “Measuring strength and consolidation properties in lacustrine clay using piezocone and self-boring pressuremeter tests”

Displacement of piles from pressuremeter test results - a summary of French research and practice

This paper presents the ‘load-transfer functions’ t-z and p-y methods for determining the axial and lateral displacements of single piles. They are based on the results of pressuremeter tests. The methods from the results of the Ménard pre-borehole pressuremeter tests (MPM) and the self-boring pressuremeter tests (PAF, for Pressiomètre AutoForeur in French) are described. Especially, the t-z and p-y methods derived from the MPM test results are commonly used in the French practice. For both t-z and p-y curves, some theoretical background (usually FEM calculations in linear elasticity) is given. The results of the t-z and p-y analyses are compared to the measurements from loading tests on full scale piles. A proposal concerning barrettes is also presented.

Stiffness decay characteristics and disturbance effect evaluation of structured clay based on in-situ tests

The structure of the sedimentary clay influences its mechanical behavior in non-negligible ways. This paper proposes an effective approach for investigating the in-situ stiffness characteristics from shear modulus and strain decay curves (G–γ curves) based on self-boring pressuremeter and seismic dilatometer tests. To evaluate the excavation disturbance effects on the structured clay, the stiffness parameters from pre-bored pressuremeter tests are compared with the results of self-boring pressuremeter tests. The result indicates that the complete in-situ G–γ curves can be acquired by integrating the strain-dependent tangent shear modulus Gt from self-boring pressuremeter tests and the small-strain modulus G0 from seismic dilatometer tests. Simultaneous observations of the G–γ curves with hyperbolic shapes in semi-logarithmic coordinates at the same strain scale show the similarity of the stiffness decay mode of the soil at different depths. The increase in the measured values of Gt and G0 with depth can be attributed to the improved consolidation pressures and cemented strength in the structured clay. Additionally, the G/G0–γ curves measured by the in-situ tests generally agree well with the results predicted by the Stokoe model. The excavation disturbance weakens the stiffness of the structured clay, as evidenced by Gt from the pre-bored pressuremeter data being significantly smaller than that from self-boring pressuremeter tests at the same depth. Based on quantitative analysis, the disturbance degree computed from the measured results has a low sensitivity to the soil depth and a strong negative correlation with the strain level of the soil. This study provides an effective method for predicting the stiffness parameters of structured soil based on in-situ tests.

Measuring strength and consolidation properties in lacustrine clay using piezocone and self-boring pressuremeter tests

As a result of the growing population in Switzerland, new infrastructure is increasingly founded in areas of extremely soft clays, which are challenging to build on. Reliable characterization of such sediments is, therefore, essential to facilitate efficient and economical designs. For various reasons, it is often beneficial to measure soil properties in situ, using probes like the piezocone or self-boring pressuremeter. The main objective of this study was to explore the key differences of these two site investigation techniques in terms of measuring undrained strength and consolidation characteristics in varved lacustrine clay. Experimental data from a field-testing campaign carried out in Switzerland demonstrate that both probes yield comparable results. The quality of the predictions was further assessed by comparing the field measurements to results from laboratory tests and existing empirical relationships. Additionally, a new method based on Monte Carlo simulations was presented, to provide context to the disparity between the consolidation coefficients estimated in the field ( ch) and laboratory ( cv), and to aid prediction of field values of ch from laboratory measurements.

Excess Pore Water Pressure Generation, Distribution and Dissipation in Self-boring Pressuremeter Test: Numerical Analysis

Excess Pore Water Pressure Generation, Distribution and Dissipation in Self-boring Pressuremeter Test: Numerical Analysis

Undrained Elastoplastic Solution for Cylindrical Cavity Expansion in Structured Cam Clay Soil Considering the Destructuration Effects

Soil structure has significant influences on the mechanical behaviors of natural soils, although it is rarely considered in previous cavity expansion analyses. This paper presents an undrained elastoplastic solution for cylindrical cavity expansion in structured soils, considering the destructuration effects. Firstly, a structural ratio was defined to denote the degree of the initial structure, and the Structured Cam Clay (SCC) model was employed to describe the subsequent stress-induced destructuration, including the structure degradation and crushing. Secondly, combined with the large strain theory, the considered problem was formulated as a system of first-order differential equations, which can be solved in a simplified procedure with the introduced auxiliary variable. Finally, the significance and efficiency of the present solution was demonstrated by comparing with the previous solutions, and parametric studies were also conducted to investigate the effects of soil structure and destructuration on the cavity expansion process. The results show that the soil structure has pronounced effects on the mechanical behavior of structured soils around the cavity. For structured soils, a cavity pressure that is larger than the corresponding reconstituted soils when the cavity expands to the same radius is required, and the effective stresses first increase to a peak value before decreasing rapidly with soil structure degradation and crushing. The same final critical state is reached for soils with different degrees of the initial structure, which indicates that the soil structure is completely destroyed during the cavity expansion. With the increase of the destructuring index, the soil structure was destroyed more rapidly, and the stress release during the plastic deformation became more significant. Moreover, the present solution was applied in the jacking of a casing during the sand compact pile installation and in situ self-boring pressuremeter (SBPM) tests, which indicates that the present solution provides an effective theoretical tool for predicting the behavior of natural structured soils around the cavity.

Site Investigations of the Lacustrine Clay in Taihu Lake, China, Using Self-Boring Pressuremeter Test

Site investigations of the soils are considered very important for evaluation of the site conditions, as well as the design and construction for the project built in it. Taihu tunnel is thus far the longest tunnel constructed in the lake in China, with an entire length of over 10 km. However, due to the very insufficient site data obtained for the lacustrine clay in the Taihu lake area, a series of self-boring pressuremeter (SBPM) field tests was therefore carried out. Undrained shear strengths were deduced from the SBPM test, with the results showing generally higher than those obtained from the laboratory tests, which may be attributed to the disturbance to the soil mass during the sampling process. Degradation characteristics of the soil shear modulus (Gs) were mainly investigated, via a thorough comparison between different soil layers, and generally, the shear modulus would cease its decreasing trends and become stable when the shear strain reaches over 1%. Meanwhile, it was found that a linear relationship between the plasticity index and the shear modulus, and between the decay rate of the shear modulus and the plasticity index as well, could be developed. Further statistical analysis over the undrained shear strength and shear modulus distribution of the soils shows that the undrained shear strength of the soils follows a normal distribution, while the shear modulus follows a log-normal distribution. More importantly, the spatial correlation length of the shear modulus is found much smaller than that of the undrained strength.

A pressuremeter-based evaluation of structure in London Clay using a kinematic hardening constitutive model

The self-boring pressuremeter (SBP) test was designed to measure in situ engineering properties of the ground with a relatively small amount of disturbance. The properties that may be inferred from the test depend on the mechanical model used for its interpretation and on the significance given to other previously available information. In this paper, numerical modelling using the advanced kinematic hardening structure model (KHSM) for natural soils has been performed to investigate the influence of the initial structure and the degradation of structure on the SBP cavity pore pressures and expansion curves within London Clay. The validation of the KHSM against well-known analytical solutions and the calibration procedure used to identify the material parameters are presented. The numerical analyses reveal that the simulations of the SBP tests using the KHSM model provide a very close match of the expansion curves to the experimental data, but underestimate the pore pressures at the initial stage of the SBP expansion test. A parametric study has been carried out to determine the effects induced by the parameters of the destructuration model along with the disturbance experienced during the SBP installation, which is difficult to estimate in situ. Two disturbance scenarios were considered where the initial structure was assumed to vary linearly across an area close to the wall of the cavity. These simulations indicate that accounting for installation disturbance leads to a substantial improvement in pore pressure predictions for the SBP.

An optimization strategy for evaluating modified Cam clay parameters using self-boring pressuremeter test data

This paper presents an efficient, practical, and automated strategy for deriving modified Cam clay parameters from undrained self-boring pressuremeter (SBPM) data. A mixed approach involving a parametric sweep and numerical optimization is used, with a focus on parameter groups that dominate the modified Cam clay response in undrained cavity expansion. The proposed technique is illustrated using data from SBPM tests carried out in soft estuarine clay. The resulting parameters are used to back-analyse large-scale foundation load tests and are shown to provide an excellent match to the measured foundation response.

Stiffness parameters from cone pressuremeter tests at Changi East, Singapore

A large-scale land reclamation project was carried out in the eastern part of Singapore involving 2000 hectares of land at a foreshore location from 1991 to 2005. The land was reclaimed, by placing sand hydraulically on the seabed comprising soft marine clay. Prefabricated vertical drains with surcharge preloading and deep compaction techniques, were used to improve the soft marine clay and reclaimed sand fill. Several specialist in situ tests were conducted during the project, such as with the cone penetration test (CPT), cone pressuremeter test (CPMT), dilatometer test and self-boring pressuremeter tests. The CPMT is an in situ testing method used to measure both the soil strength and stiffness parameters. The CPMT combines the advantages of a conventional pressuremeter test and a CPT. The CPT provides a continuous profile of the soil by measuring the stress on the cone tip, the sleeve friction and the pore-water pressure. The CPMT enables the assessment of the soil strength and stiffness at selected depths. CPMT tests were conducted on both the reclaimed sand and underlying soft marine clay layers during the Changi East reclamation project.

Comparison of diaphragm wall movement prediction and field performance for different construction techniques

The demand for deep excavation for basement construction is growing rapidly in Bangkok due to the limited availability of land. Recently, the maximum depth of excavation has increased up to approximately −25 m. Deep excavation in Bangkok subsoils requires consideration of the soil conditions and the real piezometric level of ground water. In general, Bangkok subsoil consists of 13~16 m of thick, dark grey soft-to-medium clay, followed by stiff, silty clay, before the first sand layer at 21~30 m. The piezometric level of ground water has risen to −13 m from its previous level of −23 m due to the control of deep well pumping for twenty years by the Thai Government. A diaphragm wall is normally used as a soil retaining structure. The behavior and performance of a diaphragm wall is usually predicted by the finite element method (FEM) using Mohr–Coulomb soil modeling as failure criteria, with the soil modulus parameters for soft and stiff Bangkok clay from the self-boring pressuremeter test. This paper presents a comparison between the diaphragm wall movements from FEM analysis predictions and field measurements for two projects, the new Bank of Thailand head office and the Rosewood Hotel, which were constructed with different techniques. The predicted movement agreed well with the field measurements.

A proposed method to determine in-situ shear modulus and shear strain decay curves in different structured soil

This paper illustrates the application of the self-boring pressuremeter test and the seismic dilatometer test to acquire the in-situ decay curves of stiffness with shear strain level (G-γ decay curves) of three types of structural soil, which are granite residual soil, structural soft soil and expansive soft rock. The proposed approach in combines the functions of SBPT and SDMT to provide the high standard of accuracy for the small-strain stiffness (from SDMT) and the major attenuation stage of stiffness (from SBPT). Using the proposed mathematical model can properly describe the tendency in typical in-situ G-γ decay curves based on the data of tests. To analyse the suitability of the proposed approach, the G-γ curve obtain from the resonant column test of granite residual soil is also employed to compare with the in-situ curves. The shear modulus G obtained from laboratory tests is found to be smaller and the stiffness attenuation rate is found to be faster than the curve of the in-situ test, which reflects the process of sampling, transporting and preparation of soil samples could cause unrecoverable damages in soil.

Undrained cavity expansion analysis with a unified state parameter model for clay and sand

This paper presents a new analytical solution for undrained expansion of spherical and cylindrical cavities in soils with a unified state parameter model for clay and sand (CASM). Large strain and effective stress solutions are derived for soils in the elastic, plastic and critical-state regions. The key advantage of using the state parameter model CASM is that it can model both clay and sand and is generally able to capture overall soil behaviour as observed in the laboratory. The newly developed solution provides the stress and strain fields during the expansion of a cavity from an initial to a final radius. Following the validation with the original Cam Clay solution, a simple parametric study is conducted to investigate the effects of key model parameters on stress distributions and cavity expansion curves. Applications to the analysis of pile installation and self-boring pressuremeter tests highlight some important implications in geotechnical practice.

Interpretation of in situ horizontal stress from self-boring pressuremeter tests in sands via cavity pressure less than limit pressure: a numerical study

The paper presents a numerical finite difference model of self-boring pressuremeter test (SBPM) using FLAC software. Different cavity expansion theories in sand have been compared to the results of numerical analyses carried out in this study. Limit pressure is believed to be used as a key parameter for the estimation of soil parameters from pressuremeter tests. In practice, SBPM tests are conducted up to 10–15% cavity strains, and the strain level associated with the limit pressure state is not reached. Therefore, determination of limit pressure usually needs extrapolation. In this paper, the authors suggest to use cavity pressure at 10% strain (P10) for the interpretation of in situ horizontal stress from SBPM test rather than limit pressure. For this purpose, more than 5000 numerical analyses of SBPM are carried out, and cavity pressures associated with 10% strain are deduced. Based on these extensive numbers of numerical analyses, a new relationship is established with the aid of genetic algorithm which correlates P10 to soil parameters. The estimated values of P10 from the proposed relationship are compared to a large database of measured ones obtained from laboratory and field results available in the literature. It was shown that the proposed relationship gives satisfactory predictions of P10. A chart was established for deduction of the in situ horizontal stress using the proposed relationship. This method can be used as a complement to liftoff method which is not reliable for estimation of the in situ horizontal stress when soil disturbance occurs at cavity wall.

At-Rest Lateral Stress Coefficient in Sands from Common Field Methods

AbstractA new relationship for estimating the in situ at-rest lateral stress coefficient (K0) in sands consisting predominantly of silica particles is derived in this technical note using the calibration chamber test results reported in the literature. Variables in the relationship, in order of significance, are overconsolidation ratio, dilatometer horizontal stress index, and normalized cone tip resistance. Values of in situ K0 estimated with the new relationship generally compare well with K0 determined from self-boring pressuremeter tests. Estimates of K0 in Pleistocene sands are, on average, about 10% higher than in Holocene sands.

Gmax of Reclaimed Ground on the Western Coast of Korea Using Various Field and Laboratory Measurements

The maximum shear modulus of soil is a principal parameter for the design of earth structures under static and dynamic loads. In this study, the statistical data of the maximum shear moduli of reclaimed ground in the Songdo area on the western coast of Korea were evaluated using various field and laboratory tests, including the standard penetration test (SPT), piezocone penetration test (CPTu), self-boring pressure meter test (SBPT), down-hole seismic test (DHT), seismic piezocone penetration test (SCPTu) and resonant column test (RCT). Soils were classified variously by using a conventional unified soil classification system and classification charts for CPTu data. For the soils containing mostly sand and silt, the soil classifications using the classification charts for CPTu data show good agreement with the unified soil classification. Based on the statistical analysis on various maximum shear moduli, new site-specific empirical correlations between the shear moduli and SPT and CPTu values were proposed. Predictions of the maximum shear moduli using the proposed correlations were compared with the data obtained from the DHT, which is comparatively exact in evaluating the maximum stiffness of soils. The good agreement confirmed that the proposed correlations reasonably predicted the maximum shear moduli of soils in western coastal area of Korea.

In Situ Lateral Stress Measurement in Glaciolacustrine Seattle Clay Using the Pressuremeter

Pressuremeter testing was conducted for the State Route (SR) 99 Bored Tunnel project in Seattle, Washington, to estimate in situ soil stress-deformation parameters along the tunnel alignment. Many of the tests were conducted in a very stiff to hard glaciolacustrine clay known as Seattle clay. This unit is historically known for deep-seated slope failures and many of these failures have been attributed to the release of high, locked-in lateral stresses. Estimation in situ lateral stresses along the tunnel alignment was a primary focus of the exploration program. Due to the hard consistency of this unit and the potential for cobbles, neither self-boring pressuremeter nor dilatometer testing was feasible; therefore, prebored pressuremeter testing was used. Using several lateral stress estimation techniques, including a novel in situ creep testing approach, the in situ lateral stresses in the Seattle clay were estimated to be significantly higher than what would be expected by assuming a simple, laterally constrained, vertical loading and unloading stress path due to glaciation. Deformational features commonly encountered in Seattle clay indicate its stress history also has included significant lateral shearing. The memory of this shearing within the fabric of the clay may influence the in situ stress state and response to lateral unloading.

Evaluating the in-situ hydraulic conductivity of soft soil under land reclamation fills with the BAT permeameter

In-situ tests were undertaken with a BAT permeameter as part of a hydrogeological study to determine the horizontal hydraulic conductivity of Singapore marine clay at Changi. BAT permeameter tests were undertaken in marine conditions prior to land reclamation at a Test Site. An additional series of tests were undertaken after land reclamation and subsequent ground improvement works with prefabricated vertical drains after 23months of surcharge loading. The BAT permeameter results were compared to laboratory test results carried out using a Rowe consolidation cell as well as hydraulic conductivity tests interpreted from other in-situ dissipation tests including Piezocone Penetration Test (CPTU), Dilatometer Test (DMT) and Self-Boring Pressuremeter Test (SBPMT). The BAT permeameter was found to be suitable for horizontal hydraulic conductivity measurements. The BAT permeameter has the advantage that it measures horizontal hydraulic conductivity directly whereas other in-situ test methods require the introduction of additional parameters to evaluate the hydraulic conductivity indirectly. The horizontal hydraulic conductivity measured using the BAT permeameter was however lower than that expected which is attributed to smear effect. The horizontal hydraulic conductivity was found to decrease in the vertical drain treated area as compared to the prior to reclamation results which is attributed to the significant void ratio reduction at the vertical drain treated area.

Discrete element modelling of cavity expansion and pressuremeter test

Cavity expansion in soil or rock is an important area in theoretical geomechanics because it provides a useful and simple tool for modelling many complex geotechnical problems. This paper describes the simulation of cylindrical cavity expansion and pressuremeter testing of granular materials using the discrete element method (DEM). The Pressuremeter test is one of the most important applications of cavity expansion theory. The theory of cylindrical cavity expansion has been adapted by geotechnical researchers and engineers as the most important interpretation method for self-boring pressuremeter tests in soil and rock. It is also used to describe the soil properties of cone pressuremeter tests. To compare the DEM simulation results with continuum analysis, analytical solutions of large strain expansion of Mohr-Coulomb material are also given. For simplicity, the soil stress-strain behaviour is considered as elastic-perfectly plastic. Some biaxial test simulations using DEM are performed to obtain the basic granular material properties for obtaining cavity expansion analytical solutions based on continuum mechanics. Macro properties of the samples for various input micro parameters are presented and used to obtain the theoretical cavity expansion solutions. The comparison between the numerical simulations and analytical solutions shows good agreement. A range of pressuremeter test simulations of various initial porosities using different particle shapes were conducted. The simulations demonstrated the validity of DEM simulations of the pressuremeter test, providing micromechanical insight into the behaviour.