Pore Water Pressure Transducers Research Articles

Centrifuge Seismic Test on Seismic Behavior of Pile Group in Liquefiable Soil

A series of grouped-model piles (2×2) centrifuge shaking table tests at an acceleration of 80 g was conducted to simulate seismic responses of a grouped-piles embedded in liquefiable sandy soil subjected to different magnitudes of earthquake loading. The tested grouped-piles connected with a pile cap are used to support 4 sets of model dry storage tank.Different test conditions including elevations of pile cap, elevations of ground water table, and dry and saturated sand beds all are reported in the study. Sensors (i.e., strain gauges along the depths of pile for measuring the bending moments, accelerometers for measuring the accelerations at different depths, LVDTs and pore water pressure transducers) densely instrumented in the piles and the surrounding soils provide valuable information for examining their evolution at various degrees of liquefaction. The magnitudes of bending moment along pile depths would increase with the increases of base shaking. The lowest bending moments were measured for the grouped–piles with the pile cap embedded in the dry sand bed while the largest lowest bending moments for the grouped–piles with the pile cap embedded in the saturated sand bed with the water table at the surface. The test results can be used to validate the results derived from the numerical simulation.

Experimental study of water infiltration on an unsaturated soil-geosynthetic system

This investigation presents experimental results from soil-geosynthetic column tests constructed to study the drainage capability of geosynthetics installed within an unsaturated soil and subjected to a water infiltration process. Two different types of permeable geosynthetics were tested; namely, non-woven geotextile and woven non-woven geocomposite. The infiltration process was monitored using negative/positive pore water pressure and volumetric water content transducers placed above and below the geosynthetic. The results showed that the geosynthetics behaved as an impermeable layer until the surrounding soil was nearly saturated. The geosynthetics started draining water laterally only when the pore water pressure within the soil above it was positive or negative but close to zero. This study intends to provide some insights into the physics of soil-geosynthetics performance, and to complement the available technical data used to conduct numerical simulations of complex soil-structures subjected to water infiltration processes.

An Instrumented Flume to Characterize the Initiation Features of Flow Landslides

Abstract Rainfall-induced landslides are on the rise due to global warming but the associated initiation mechanisms remain unclear. To observe the local initiation features of flow landslides under different rates of water supply, a well-instrumented flume capable of tightly controlling the inflow from the groundwater supply pipes and upstream discharge was built. Basal porewater pressure transducers (PPT) were installed to monitor the water pressure evolution, and a simple method to retrofit pressure transducers into PPTs was introduced. Internal movement behaviors of the slope body prior to the onset of and during a full failure were monitored with low-cost and small-size MEMS (Micro-Electro-Mechanical-Systems) accelerometers. A MEMS sensing package, termed the Smart Soil Particle (SSP, first generation), was also developed in conjunction with the laboratory testing program for field implementation in the future. In a set of experiments designed to investigate the initiation mechanism of a loose soil sample under a small and slow constant groundwater inflow, the MEMS accelerometers and basal PPTs successfully captured the intricate internal movement features and porewater pressure patterns. This warrants more systematic studies of the flow landslide initiation mechanism using the newly developed flume instrumentation.

편마풍화토의 다짐밀도에 따른 불포화 흡수응력 특성

본 연구에서는 다짐된 편마풍화토의 불포화토 전단강도특성을 규명하기 위하여, Constant Water Content Compression (CWCC) 시험을 실시하였다. 두 가지 상대밀도로 구분하여 정적 다짐으로 공시체가 제작되었고, 초기 포화도를 변화시킴으로써 초기 흡수력 및 최대전단강도가 구현될 때의 흡수력에 따른 전단거동을 살펴보았다. 흡수력은 세라믹디스크와 간극수압계의 설치에 의해 직접 측정되었고, 이 흡수력을 적용하여 흡수응력(ps)이 추정되었다. CWCC 시험에서 얻어진 최대압축강도에 대한 결과는 삼축압축시험에서의 포화상태 파괴선(Mp Line)과의 관계, 즉 흡수력에 의해 발현된 전단강도의 변화를 흡수응력을 이용하여 살펴보았다. 또한, Kim 등(2010)이 제안한 Suction stress-SWCC Method (SSM)을 활용하여 흡수응력의 적용성에 대해 논하였다. In order to examine the unsaturated shear strength characteristics of compacted weathered gneiss soils, the constant water content compression (CWCC) test was carried out. Specimens were made by static compaction under two densities conditions. The shear behavior in accordance with an initial suction obtained by varying initial degrees of saturation was evaluated. The suction could be directly measured by the use of the ceramic disk and the pore-water pressure transducer. The results of the peak shear strength from the CWCC test were examined using the relationship with Mp line from triaxial test under the saturated state, that is, by means of the suction stress which was calculated using the measured suction. In addition, the applicability of the suctions stress to the unsaturated shear behaviour of compacted weathered gneiss soils was discussed by applying Suction stress-SWCC Method (SSM).

Seepage behavior of drainage zoning in a concrete faced gravel-fill dam via centrifuge and numerical modeling

Sandy gravel materials have recently been utilized in place of crushed rock materials as the main rockfill materials in Concrete Faced Rockfill Dams (CRFD) to address geological and environmental problems. In this paper, an experimental scheme for centrifuge modeling was developed to simulate a Concrete Faced Gravel-fill Dam (CFGD). The dam considered in this study was designed to implement a drainage zone of high permeability in the main gravel-fill zone to enhance safety against accidental water infiltration into the dam. Two centrifuge tests were performed and compared to investigate the performance of the drainage zone. The first test was done with the drainage zone and the second without the drainage zone. In the centrifuge tests, water infiltration was simulated by raising the water table over pre-implemented cracks on the model face slab. The infiltration behaviors were monitored by pore water pressure transducers. The centrifuge tests showed that the drainage zone of the CFGD effectively drains infiltrating water out of the dam body in a short time. Numerical modeling was also performed to help understand the process of seepage through cracks.

Design and Application of Simple Shear Liquefaction Box

Abstract A cyclic simple shear liquefaction box (CSSLB) was designed and manufactured to allow laboratory testing of saturated sands under cyclic or transient strain-controlled conditions. The box accommodates pore water pressure transducers, linear variable displacement transducers, and bender elements and bending disks. To induce shear strains, the box has two rotating walls connected to two translating rigid walls with a flexible sealant. When the tops of the rotating walls are fixed against translation and the base of the CSSLB, which rests on a shaking table, is excited with a displacement time history, shear strains are induced in a soil specimen. Two-dimensional numerical analyses of plan and elevation sections of the CSSLB were performed, demonstrating that the design of the box and the mechanism for shearing can induce controlled shear strains in sand specimens with minimal boundary effects. Example test results from sand specimens subjected to cyclic and earthquake shear strain time histories are presented and illustrate how well the CSSLB with its instrumentation is suited for conducting tests on relatively large soil specimens.

Permeability measurement of fresh cement paste

Fresh cement paste permeability is a key parameter to understand the hydro-mechanical behavior of cement-based materials, i.e., rhelogical properties and static stability. However, its permeability measurement is not easy to assess. The porous medium is not rigid and tends to change due to hydration kinetics. Two measurement methods, with 70 mm and 20 mm initial height specimens respectively, are presented and compared in this paper. The first uses a basic cell of soil permeability measurement and consists of simultaneous consolidation and percolation tests. The second uses a displacement-controlled oedometer cell equipped with pore water pressure transducers, and consists in inducing consolidation to a given void ratio first and, consecutively, in accurately measuring the permeability. A good correlation of results is observed. A comparison with theoretical models confirms that, from one fitted parameter relative to particle characteristics, a relationship between permeability and void ratio can be established.

Thermo-hydraulic characterisation of soft rock by means of heating pulse tests

Low-permeability clayey rocks, currently considered as suitable host rocks for high-level nuclear waste disposal, pose a challenge for the determination of thermal, hydraulic and mechanical properties. A thermo-hydraulic stainless steel cell, capable of testing undisturbed soil or rock cores 70 mm in diameter and 100 mm long, has been developed and used to identify thermal properties (conduction coefficient, heat capacity, thermal expansion), permeability (derived from gas and water tests) and swelling behaviour. The cell is operated in a constant-temperature bath. Miniature pore water pressure transducers and thermocouples are installed in different positions of the specimen. Strain gauges attached to a reduced-thickness ring section of the cell provide information for swelling pressure determinations. Temperature changes are applied by a thin heater centred in the axis of the specimen. A computer code was specifically written to perform and control experiments. Air permeability is determined by means of a pulse decay technique, whereas liquid permeability is directly interpreted at steady-state conditions. However, back-analysis of the complete measured response of the specimen (pore pressures, temperatures and swelling pressures) provides the best procedure for identifying properties. A testing protocol involving a sequence of undrained and drained heating tests has been developed to determine, in an ordered way, the thermal properties and the permeability. The procedure requires the concourse of a coupled thermo-hydro-mechanical code in order to simulate test results. The program CODE_BRIGHT, developed at UPC, was used for these purposes. The procedure was applied to the identification of the thermal properties of Opalinus clay shale.

An In Situ Test Method for Evaluating the Coupled Pore Pressure Generation and Nonlinear Shear Modulus Behavior of Liquefiable Soils

Abstract An in situ test method for evaluating the coupled response between excess pore water pressure generation and nonlinear shear modulus behavior has been developed. This technique is an active, strain-based method that may be used to directly evaluate the liquefaction resistance of soils in place. The test is based on the premise of dynamically loading a native soil deposit in a manner similar to an earthquake while simultaneously measuring its response with push-in sensors. Dynamic loading is performed via a large, buggy-mounted hydraulic shaker (vibroseis) that is used to generate vertically propagating (downward), horizontally polarized shear waves (Svh-waves) of varying amplitude within an instrumented portion of a liquefiable soil deposit. The newly-developed, push-in sensors consist of a three-component (3D) MEMS accelerometer and a miniature pore water pressure transducer. The new test method has been used to conduct field experiments in liquefiable soil deposits approximately 3 to 4 m below the ground surface. These tests were successful at measuring: (1) excess pore water pressure generation, and (2) nonlinear shear modulus behavior in native silty-sand deposits as a function of induced cyclic shear strain and number of loading cycles. These accomplishments represent a large step forward in the ability to accurately evaluate the susceptibility of a soil deposit to earthquake-induced liquefaction. While typical test results are presented herein, this paper primarily focuses on the equipment, field testing practices, and data analysis procedures for the new test method.

In situ measurements of till deformation and water pressure

AbstractA newly developed hammer was used to insert two autonomous probes 0.8 m and 2.1 m into clast-rich subglacial till under Black Rapids Glacier, Alaska, USA. Both probes were instrumented with a dual-axis tilt sensor and a pore-water pressure transducer. The data are compared to a 75 day record of surface velocities. Till deformation at depth was found to be highly seasonal: it is significant during an early-season speed-up event, but during long periods thereafter measured till deformation rates are negligible. Both tilt records show rotation around the probe axis, which indicates a change in tilt direction of about 30°. The tilt records are very similar, suggesting spatial homogeneity on the scale of the probe separation (4 m horizontal and 3.3 m vertical). There is evidence that during much of the year sliding of ice over till or deformation of a thin till layer (<20 cm) accounts for at least two-thirds of total basal motion. Basal motion accounts for 50–70% of the total surface motion. The inferred amount of ice–till sliding is larger than that found at the same location in a previous study, when surface velocities were about 10% lower. We suggest that variations in ice–till coupling account for the observed variations in mean annual speed.

Development of Wireless Pore Water Pressure Transducer and Measurement at Embankment Dams

Development of Wireless Pore Water Pressure Transducer and Measurement at Embankment Dams

Modified Triaxial Apparatus for Shearing-Infiltration Test

Abstract A triaxial apparatus was modified and developed for performing shearing-infiltration tests under saturated and unsaturated conditions. Miniature pore-water pressure transducers were installed at different heights of the soil specimen for pore-water pressure measurement. Two different types of miniature pressure transducers were used, and problems associated with the transducers are discussed. Ancillary works and equipment to install the miniature transducers onto the soil specimen are also discussed. The measurement of air entry value of the small disk in the transducer was found to be very difficult. The results show that the soil specimen failed during infiltration due to increase in pore-water pressure or decrease in matric suction.

One-Dimension Compression of Slurry With Radial Drainage

The behavior of the self-weight consolidation of suspension has been studied by the Oxford group (Been and Sills, 1981). However the deformation behavior of slurry-like soil upon additional load is not well understood. Due to the high demand for land in coastal areas and surrounding city areas, reclamation or remediation of land on ultra soft soil like waste ponds and mine tailing ponds has become necessary. Materials in such waste ponds and mine tailing ponds are extremely soft, and high water content which is usually above the liquid limit. In addition to this, these materials are in an underconsolidated condition and are still undergoing self-weight consolidation. A laboratory study with a large diameter consolidation cell equipped with pore water pressure transducers was carried out to find out the deformation behavior of slurry-like soil under a one dimensional vertical load. It was noted that before commencing Terzaghi's consolidation process, the slurry was deformed solely due to the expelling of water from the slurry. This deformation was as high as 19% strain and no pore water pressure dissipation was detected during this period. The behavior in the laboratory results was confirmed by a case study carried out with a trail embankment on slurry-like soil contained in the containment bund.

Rapid Density Profiling of Consolidating Clay Using Synchrotron Radiation

Abstract The high-energy, highly collimated X-ray beam at the Cornell High Energy Synchrotron Source (CHESS) was used to provide rapid and high-resolution temporal and spatial density distributions in a consolidating saturated clay specimen. Porewater pressure at the undrained base of the clay was obtained by a porewater pressure transducer. Test results show good agreement between theoretical and experimental density distributions and indicate that synchrotron radiation is a promising and unique method to study consolidation.

Numerical and Experimental Investigation of Thermally Induced Effects in Saturated Clay

The finite element program HOT CRISP developed at Cambridge University allows the two dimensional coupled heat conduction and consolidation analysis of soil barriers subjected to temperature gradients. The analysis uses an elasto-plastic soil model based on the critical state principles. This paper presents prediction of temperature and pore water pressure changes in kaolin clay and comparison with experimental data. The experiments undertaken involved triaxial samples subjected to temperature changes at the outer boundary by a temperature controlled water circulation system. Temperature sensors and miniature pore water pressure transducers were used for the monitoring of temperature and pore water pressures at two locations in the soil samples. Tests were performed both under undrained and drained conditions. The comparison of data between experiments and analyses showed very satisfactory results.

A new instrument for the measurement of soil moisture suction

Current methods of determining soil moisture suction are outlined and their shortcomings identified. A new instrument is then described which will overcome a number of these problems by the use of a miniature pressure transducer, and minimum volume of water between the active face of the transducer and the porous stone. The instrument uses an Entran EPX-500 stainless steel miniature pore water pressure transducer, with a working range up to 3500 kPa, shrouded by a stainless steel sheath fitted with a porous stone. The mechanics of the instrument and its evaluation against known values of suction are outlined. Reliable measurements of suction were achieved up to 1500 kPa.