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Bezprzewodowy pomiar ciśnienia wody w porach gruntu w aparacie trójosiowego ściskania

Witowski Marcin

Przegląd Budowlany

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2023

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R. 94, nr 7-8

188--192

PL

Aparat trójosiowego ściskania jest jednym z najbardziej rozpowszechnionych w laboratoriach geotechnicznych urządzeń badawczych służących do określania parametrów charakteryzujących zachowanie się gruntów pod względem wytrzymałości i sztywności. Urządzenie to ma możliwość pomiaru szeregu kluczowych parametrów, wśród których zasadniczą rolę odgrywa pomiar siły osiowej, odkształcenia osiowego oraz ciśnienia wody porowej w gruncie. Wskazane w normie europejskiej (Eurokod 7) podejście w zakresie projektowania geotechnicznego i sprawdzania stanów granicznych wymaga korzystania z parametrów efektywnych. Tym samym ich oznaczanie w warunkach laboratoryjnych wymaga prawidłowej (w zakresie procedury nasycania) i poprawnej (w zakresie lokalizacji pomiaru) rejestracji ciśnienia wody w przestrzeni porowej gruntu w trakcie badania. Standardowo pomiar tego ostatniego parametru wykonywany jest w dolnej części próbki lub w bardziej zaawansowanej formie, w połowie wysokości próbki. To drugie podejście jest bardziej miarodajne, ale wprowadza jednak wymóg przerwania ciągłości membrany otaczającej próbkę gruntu, co może prowadzić do niekontrolowanej penetracji wody z komory do wnętrza próbki. Rozwiązaniem tej niedogodności było opracowanie autorskiego projektu czujnika objętego postępowaniem patentowym. Zapewnienie pomiaru bezpośredniego na próbce przy jednoczesnym uniknięciu potencjalnej nieszczelności było możliwe poprzez zastosowanie nowatorskiego czujnika, który mierzy ciśnienie wody w porach gruntu i w sposób bezprzewodowy przesyła wyniki na zewnątrz komory. W artykule przedstawiono opis tego rozwiązania oraz sposób integracji nowego czujnika z rejestratorem i pozostałymi komponentami zestawu aparatu „trójosiowego” ściskania. Skuteczność zaproponowanego rozwiązania wykazano poprzez przeprowadzenie pełnej kalibracji wyników uzyskiwanych z czujnika. Uzyskane wyniki wykazały skuteczności zastosowanego bezprzewodowego czujnika do bezpośredniego pomiaru ciśnienia wody w gruncie.

EN

The triaxial compression apparatus is one of the most popular research devices in geotechnical laboratories used to determine the parameters characterizing the behavior of soils in terms of strength and stiffness. This device has the ability to measure a number of key parameters, among which the measurement of axial force, axial deformation and pore water pressure in the ground plays an essential role. The approach to geotechnical design and limit state verification indicated in the European standard (Eurocode 7) requires the use of effective parameters. Thus, their determination in laboratory conditions requires correct (in terms of the saturation procedure) and correct (in terms of measurement location) recording of water pressure in the soil pore space during the test. As a standard, the measurement of the latter parameter is performed in the lower part of the sample, or in a more advanced form, in the middle of the sample’s height. The latter approach is more reliable, but it introduces a requirement to break the continuity of the membrane surrounding the soil sample, which may lead to uncontrolled penetration of water from the chamber into the sample. The solution to this inconvenience was the development of a proprietary sensor design covered by patent proceedings. Providing direct measurement on the sample while avoiding potential leakage was possible by using an innovative sensor that measures the water pressure in the soil pores and wirelessly sends the results outside the chamber. The article presents a description of this solution and the method of integrating the new sensor with the recorder and other components of the triaxial compression apparatus set. The effectiveness of the proposed solution was demonstrated by carrying out a full calibration of the results obtained from the sensor. Validation of the results was performed on several series of tests carried out on several types of soils with different filtration properties. The obtained results showed the effectiveness of the wireless sensor used for direct measurement of water pressure in the ground.

2

Mechanical behavior and constitutive model of lining concrete in triaxial compression infiltration process under pore water pressure

Xue Weipei, Jing Wei, Wang Zhongjian, Zhang Hanwen, Lin Jian

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 1

art. no. e20, 2023

EN

Underground concrete structures are affected by groundwater, the effects of which are different from those of stress environments experienced by ground engineering concrete structures. This study experimentally and theoretically investigates the mechanical behavior, permeability evolution, and deformation failure mechanism of lining concrete under pore water pressure. Results show that an increase in pore water pressure promoted the coupling of seepage and stress fields in concrete. This caused the microcracks to propagate further, which led to a decrease in concrete strength and elastic modulus. Through triaxial compression infiltration, the concrete successively underwent initial compaction, linear elastic deformation, and nonlinear deformation after yielding. Accordingly, its permeability exhibited three trends: gradual decrease, stable development, and a sharp increase. The change in permeability was closely related to the number of pores and the development of microcracks in concrete. The concept of primary pore strain was proposed according to the characteristics of deformation and failure. Moreover, a triaxial compression infiltration constitutive model was derived for concrete based on the principle of effective stress. This model considers the influence of pore water pressure and the initial compaction characteristics. This study can be used to guide the design of lining concrete structures in underground engineering.

3

The influence of material characteristics on dam stability under rapid drawdown conditions

Utepov Yelbek, Lechowicz Zbigniew, Zhussupbekov Askar, Skutnik Zdzisław, Aldungarova Aliya, Mkilima Timoth

Archives of Civil Engineering

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2022

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Vol. 68, nr 1

539--553

EN

A fast reduction of a reservoir level may result in instability of an earth dam caused by the high pore water pressures that remain relatively high in the embankment. Moreover, the dissipation of the accumulated pore water pressures is highly dependent on the permeability of the materials used for the embankment and the storage characteristics of the reservoir. Therefore, in the design of embankment dams, the stability analysis under rapid drawdown loading conditions is an important design case. In this study, the influence of different permeability rates on dam stability under different cases of rapid drawdown was investigated using the finite element method in SEEP/W and SLOPE/W of the GeoStudio with a case of the Lugoda dam in Ndembera catchment, Tanzania. The modeling process considers the time-dependent hydraulic conditions and the transient flow conditions using different water levels during rapid drawdown for evaluation of the factor of safety. From the 1 m per day drawdown rate; the lowest minimum factor of safety value (0.90) was obtained from the 10-7 m/s material permeability of the upstream zone of the dam. It means that, at a drawdown rate of 1m per day, there is a potential for failure of the embankment if the hydraulic conductivity value will be somewhere below 10-6 m/s.

PL

Szybkie obniżenie poziomu zwierciadła wody w zbiorniku może wywołać utratę stateczność zapory ziemnej wynikająca z dużych wartości ciśnienia wody w porach pozostających w strefie odwodnej zapory. Rozpraszanie się ciśnienia wody w porach w zaporze ziemnej zależy od przepuszczalności materiałów użytych w nasypie oraz właściwości retencyjnych zbiornika. W projektowaniu zapór nasypowych analiza stateczności podczas szybkiego opróźniania zbiornika jest ważnym przypadkiem obliczeniowym. W niniejszym artykule przeanalizowano wpływ przepuszczalności materiałów na stateczność zapory przy różnych prędkościach szybkiego opróżniania zbiornika z wykorzystaniem metody elementów skończonych przy pomocy programów SEEP/W i SLOPE/W oprogramowania GeoStudio na przykładzie zapory Lugoda w Ndemberze zlewni w Tanzanii. W procesie modelowania uwzględniono warunki hydrauliczne zależne od czasu oraz przejściowe warunki przepływu przy różnych poziomach wody podczas szybkiego opróżniania zbiornika przy ocenie współczynnika stateczności. Przy szybkim opróźnianiu zbiornika wynoszacym 1 m na dobę zaobserwowano, że najmniejsza wartość współczynnika stateczności (0,90) uzyskano przy wartości przewodności hydraulicznej wynoszacej 10-7 m/s. Oznacza to, że przy prędkości obniżania poziomu wody w zbiorniku o 1 m na dobę, istnieje możliwość utraty stateczności nasypu, jeśli wartość przewodności hydraulicznej będzie mniejsza niż 10-6 m/s.

4

Effects of full displacement pile installation on the stress and deformation state of surrounding soil: review

Kabeta Worku Firomsa

Archives of Civil Engineering

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2022

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Vol. 68, nr 4

445--466

EN

Several field and model tests have been conducted to investigate the impact of pile installation on bearing capacity. However, little is known about how piles behave during installation, how they interact with the surrounding soil, and how this affects sandy soil properties. This review paper investigates the effect of pile driving on surrounding sandy soil as it compacts sandy soil near to the pile. For this purpose, various related literature was studied based on the observation of the pile installation effect on earth pressure or lateral stress, relative density, and pore water pressure in the sandy soil. A change in the deformation and stress state of surrounding sandy soil due to pile driving was presented. The installation of fully displacement piles can lead to significant stresses and deformations in the surrounding sandy soil. This is one of the main causes of uncertainty in the design and analysis of pile foundations. According to this study, the sandy soil around the pile is compacted during pile driving, resulting in lateral and upward displacement. This leads to the densification effect of pile driving on loose sandy soil. Sandy soil improvement with driven piles depends on pile shape, installation method, and pile driving sequences. This study concludes that in addition to its advantages of transferring superstructure load to deep strata, the increased relative density of loose sand, the change in the horizontal stress, and the influence of compaction on the sandy soil parameters during pile driving should be considered during pile design and analysis.

5

Zmiany ciśnienia porowego w warunkach stałego wzrostu obciążenia i ich wpływ na konsolidację CL na przykładzie wybranych gruntów spoistych centralnej Polski

Stajszczak Piotr, Dobak Paweł

Przegląd Geologiczny

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2021

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Vol. 69, nr 12

873--883

EN

The article presents the results of CRL tests of cohesive soils of different origins and grain size compositions. The aim of the work is to investigate the relation between the physical properties of cohesive soil and the course of loading and the nature of pore pressure changes during CL consolidation. The implemented program of laboratory tests confirms the significant role of pore water pressure in the assessment of seepage and consolidation parameters. The CRL research was supplemented by observations in a scanning electron microscope.

6

Undrained shear and pore space characteristics of treated loose sands with lime-activated zeolite in saturated settings

Jamhiri Babak, Pakbaz Mohammad Siroos

Civil and Environmental Engineering Reports

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2020

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Vol. 30, no. 2

105--132

EN

This research investigates the mechanical behavior of artificially cemented sandy soils formed by lime alkali activation of natural zeolite under saturation settings. In order to verify the bar capability of cemented sands with this new method, an analysis of the undrained shear strength of the soil with pore water pressure ratio measurements was performed from the interpretation of the results of unconfined compression tests. The effect of zeolite-lime blend on treated sands was also visualized by scanning electron microscopy. For the studied soils, it was concluded from the unconfined compression stress values that the soil is fully capable of withstanding compressions due to overburden pressure. Additionally, this study seeks to evaluate the effect of the void ratio on the pore space and undrained shear strength. The results showed that pore water B-ratio increases with the decrease of the void ratio. Moreover, with the increase of zeolite content, confining pressure, and curing age, the peak failure strength increases. The results indicated a promising consistency of treated samples with lime and zeolite under various values of undrained shearing and B-ratios, making this method an ideal treatment for loose sand deposits.

7

Czujniki do pomiaru ciśnienia porowego dla potrzeb rozpoznania położenia powierzchni poślizgu osuwiska

Stanisz J.

Zeszyty Naukowe Instytutu Gospodarki Surowcami Mineralnymi i Energią PAN

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2015

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nr 89

77--92

PL

Profilowanie głębokościowe zmian ciśnienia porowego może być pomocne w określaniu położenia powierzchni poślizgu osuwiska. Jest to możliwe dzięki zastosowaniu specjalnych sond złożonych z czujników pomiarowych ciśnienia porowego. Wykorzystanie takich czujników pozwala na wskazanie położenia stref, gdzie następuje wzrost lub spadek ciśnienia porowego, spadek naprężeń efektywnych i często uplastycznienie ośrodka. Taki stan prowadzi do rozwoju powierzchni poślizgu. Jest to szczególnie widoczne po okresach intensywnych opadów. W artykule przedstawiono różne rodzaje czujników do pomiaru ciśnienia porowego. Opisano ogólne zasady pomiarów z ich użyciem. Przedstawiono zasadę działania czujników typu BAT, strunowych, piezorezystywnych, pojemnościowych, hydraulicznych, pneumatycznych oraz optoelektronicznych. Wskazano wady i zalety ich stosowania. Uznano czujniki z przetwornikiem strunowym za najbardziej odpowiednie do prowadzenia długookresowych pomiarów ciśnienia porowego w celu rozpoznania położenia powierzchni poślizgu osuwiska.

EN

Depth profiling of pore pressure changes can be helpful in determining the location of slip surfaces of landslides. This is possible due to using special probes made up of pore pressure sensors. The use of such sensors enables the indication of the location of the zones where there is an increase or decrease in pore pressure, or a decrease of effective stresses and frequent zone plasticization. Such a situation leads to the development of the slip surface. This is especially true after periods of heavy rainfall. The article presents various types of sensors used for the measurement of pore pressure. It describes the general rules for the measurements. It illustrates the principle for the operation of BAT sensors, vibrating-wire, piezoresistive, capacitive, hydraulic, pneumatic and optoelectronic sensors. The advantages and disadvantages of their use were pointed out. Vibrating-wire sensors were determined to be the most suitable to carry out long-term measurements of pore pressure in order to identify the location of landslide slip surfaces.

8

Evaluation of consolidation parameters in CL tests; theoretical and practical aspects

Dobak P.

Geological Quarterly

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2008

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Vol. 52, No 4

397-397

EN

The paper presents theoretical solutions of the consolidation problem with respect to the different conditions of continuous loading and its application. The author introduces modified consolidation parameters and dimensionless parameters characterizing the course of the consolidation process. Therefore it is possible to calculate the theoretical pore water pressure distribution for various loading procedures in continuous loading (CL) consolidation tests occurring in constant rate loading (CRL), constant rate of strain (CRS) or controlled gradient (CG) tests. The calculation results allow presentation of the attributes that differentate CL consolidation and classical incremental loading (IL) consolidation. A new method of calculation cv (coefficient of consolidation) is proposed using theoretical diagrams of porewater pressure distribution and results of laboratory measure ments during the CL test. A comparative analysis of the methods currently used for cv calculation and the new method is presented here. The cv values estimated by means of method referring only to the seepage factor of consolidation, are usually higher than those based on the strain course. Proper projection of the seep age factor of consolidation makes it possible to shorten the time of consolidation tests in accordance with results of many field observations. The methods described herein can be useful in studying physical conditions of sedimentation, glacial geology, early diagenetic process and applied geology.

9

Attenuation of wave-induced groundwater pressure in shallow water. Part 2. Theory

Massel S. R., Przyborska A., Przyborski M.

Oceanologia

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2005

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No. 47 (3)

291-323

EN

In this Part 2 of the paper (Part 1 was published by Massel et al. 2004) an exact close-form solution for the pore-water pressure component and velocity circulation pattern induced by surface waves is developed. This comprehensive theoretical model, based on Biot's theory, takes into account soil deformations, volume change and pore-water flow. The calculations indicate that for the stiffness ratio G/E'w ? 100, the vertical distribution of the pore pressure becomes very close to the Moshagen & T?rum (1975) approach, when the soil is rigid and the fluid is incompressible. The theoretical results of the paper have been compared with the experimental data collected during the laboratory experiment in the Large Wave Channel in Hannover (see Massel et al. 2004) and showed very good agreement. The apparent bulk modulus of pore water was not determined in the experiment but was estimated from the best fit of the experimental pore-water pressure with the theoretical one. In the paper only a horizontal bottom is considered and the case of an undulating bottom will be dealt with in another paper.

10

Attenuation of wave-induced groundwater pressure in shallow water. Part 1

Massel S. R., Przyborska A., Przyborski M.

Oceanologia

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2004

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No. 46 (3)

383-404

EN

A coastal aquifer has a dynamic seaward boundary at the beach face where physical and ecological processes are influenced by oceanic water level fluctuations. Many basic groundwater concepts and the role of the impact of groundwater seepage on beach ecosystems are still poorly understood. Studies are needed to improve our understanding of the relationships between surface and subsurface flow processes on beaches. This is particularly helpful in clarifying the interaction of the physical processes, biodiversity and productivity of sandy beaches, sediment transport and coastal structure stability and modern beach nourishment techniques. As the estimation of infiltration into beach sand is very difficult to carry out under real sea conditions, a control led large-scale laboratory experiment was carried out in the Large Wave Channel in Hannover (Germany) as part of a project supported by the European Community (contract HPRI-CT-2001-00157). First part of the paper describes the technology applied in the experiment and reports some preliminary results.