Pore Water Pressure Monitoring Research Articles

Hydraulic Transient Impact on Surrounding Rock Mass of Unlined Pressure Tunnels

The frequent pressure pulsations due to hydraulic transients in hydropower plants induce cyclic loading on the rock mass that may contribute to increased instances of block falls and increased risk of tunnel collapse over the power plant lifetime. This study focuses on understanding the effect of frequent start and stop sequences of hydropower in unlined pressure tunnels. For this purpose, data from a pore water pressure monitoring system is utilized, which was installed at the downstream end of the headrace tunnel at the 50 MW Roskrepp hydropower plant in southern Norway. The objective of this study is to analyze the recorded data and quantify the impact of the hydraulic transient on the surrounding rock mass in the unlined pressure tunnel. The monitoring of pressure data over several years clearly shows that frequent load changes could cause a considerable effect on the rock mass and constituent joint system. A delayed response of the pressure in boreholes in the rock mass compared with inside the tunnel is seen in all start and stop sequences and is considered to be the main reason for instability caused by transients. The response of pore pressure in boreholes is greatly influenced by the characteristics of joints. The results show that the start sequence and shorter shutdown duration exert a greater impact on rock mass as compared to the stop sequence and longer shutdown duration. Therefore, it is recommended to increase the shutdown duration so that the impact can be minimized to increase the tunnel lifetime. This study recommends implementing a more conservative design approach in tunnels with weak rock masses in projects that involve frequent load changes.

Experimental Study on Pore Pressure Variation and Erosion Stability of Sandy Slope Model under Microbially Induced Carbonate Precipitation

With the development of a free trade port on Hainan Island, the construction of tourist roads around the island is currently underway. However, the weather conditions on Hainan Island, which include strong typhoons and rainstorms, pose challenges for the construction of highway-cutting slopes on the coastal weak sandy terraces. These slopes are susceptible to sand loss and erosion from rainfall. To address this issue, MICP green spray irrigation solidification technology is used to strengthen the sandy cutting, and pore water pressure monitoring is carried out on the slope model during MICP solidification and rainfall scour. Combined with the model pore water pressure and flow slip failure pattern, a dynamic analysis was conducted. The results show that MICP sprinkler irrigation technology can solidify the surface of the slope model in a short time, and after three sets of rotation reinforcement, the model achieved a cementation depth of 4 cm, with a well-reinforced surface and closely connected sand samples. Under the erosion effect of simulated rainfall intensity, the sand loss of the slope was weakened, without damage to the sand binding, and the integrity was enhanced. The cementation between the sand grains facilitated the conversion of most of the rainfall into runoff. However, despite these efforts, the slope eventually slid after 150 s. During the sliding process, the leading edge of the slope model lost sand and became unloaded, and the failure mode was graded a creep slip failure. Finally, the slope was divided into several blocks due to the continuous expansion of cracks following the slope failure. The erosion stability of the sandy slope under heavy rains was optimized and the sand loss was prevented effectively. This study proposes a new method of MICP remediation techniques that serve as a new test basis for the practical application of MICP technology in engineering projects.

Numerical interpretation of regressive localized internal erosion in a real-scale levee physical model

This paper presents the numerical interpretation of a recent experiment on a real-scale levee physical model, in order to investigate the process of Backward Erosion Piping (BEP) and validate a recently proposed finite element formulation able to model both the simultaneous processes observed in backward erosion piping, i.e. the propagation of the pipe tip and the enlargement of the conduit cross-section, as well as the time-dependent effects. In previous papers, the numerical formulation already demonstrated its ability in reproducing available experimental data of full-scale physical models of levees, e.g. for the IJkdijk and for the Delta Flume tests. In the present work, as a further validation for the aforementioned formulation, we consider the numerical interpretation of the regressive localized internal erosion observed in the newly constructed real-scale levee at the Flood Proof Holland facility test site in Delft, The Netherlands. This test was mainly focused on the experimental evaluation of the time-dependent effects typically observed in these phenomena. To this purpose the levee foundation was equipped with an effective and accurate pore water pressure monitoring system. The aforementioned formulation was considered for the numerical interpretation of the test, in view of its ability in modeling the time-dependent effects in backward erosion piping. Indeed, a good agreement between calculated and measured piezometric heads and pipe tip propagations was obtained.

Pore water pressures and hydraulic conductivity in the slip zone of a clayey earthflow: Experimentation and modelling

Rainfall is among the most relevant triggering factors of landslides. With the aim of defining a model of the influence of rainfall on deep landslides, this paper presents data of a long-term monitoring of pore water pressures in a clayey earthflow, and the results of many field permeability tests carried out with several procedures. Pore water pressures are being monitored in the Costa della Gaveta slope since 2005. In the last years, new instruments have been installed and permeability tests have been carried out in the stable formation, in the landslide body and in the slip zone. The hydraulic conductivities of the three different zones of the subsoil have been evaluated by two types of field tests: falling head tests (by Casagrande piezometers and test wells), and localized constant head tests (by a permeameter ad hoc designed). The experimental data show that: a) pore water pressures along the slip zone respond to rain more than in the landslide body and in the stable formation, even at about 25 m depth; b) the hydraulic conductivity ksz of the slip zone is much higher than that of the landslide body, kl, in turn higher than the hydraulic conductivity of the stable formation, kf. The numerical 3D modelling of steady-state reference conditions and of transient processes caused by the historical rainfall series shows that the occurrence of ksz higher than kl and kf determines an overall drainage effect which makes the global limit equilibrium safety factor SF greater than that evaluable for other possible conditions. On the other side, even the lowest measured hydraulic conductivity ksz provides seasonal rain effects on water pressures along the slip surface such to determine significant SF variations in phase with the observed seasonal displacement rates.

Research on FBG Technology Applied in Highway Soft Foundation Pore Pressure Monitoring

The pore water pressure monitoring of soft ground pavement is one of the important technical links in highway construction monitoring. The use of traditional electrical measuring instruments to monitor pore water pressure has disadvantages such as low degree of automation, non-real-time data transmission, and high manual monitoring costs. However, fiber grating monitoring technology has developed rapidly due to its advantages of stable data transmission, convenient collection, and dynamic monitoring. . Therefore, relying on the soft foundation pore water pressure monitoring project of Jiujiang Ring Expressway, the monitoring principle of the fiber grating seepage pressure sensor and the buried installation technology in the soft foundation are introduced. Through the long-term monitoring practice on the construction site, it is confirmed that the optical fiber monitoring system is applied to the soft foundation. The stability of base pore water pressure monitoring provides a reference for similar monitoring projects and engineering construction.

Integrating local pore water pressure monitoring in territorial early warning systems for weather-induced landslides

A methodology designed to integrate widespread meteorological monitoring and pore water pressure measurements is proposed. The procedure is tested in 30 hydrological basins highly susceptible to weather-induced landslides in Norway. The following data are used: a catalog of 125 weather-induced landslides in soils registered between January 2013 and June 2017, widespread meteorological monitoring data employed in a territorial warning model, and pore water pressure measurements retrieved from boreholes installed for a variety of geotechnical projects. The territorial warning model is initially applied to identify the warning events and the correspondent warning level in the test areas over the analysis period. Afterwards, a method for assessing the territorial warning events by analyzing the trends of the monitored pore water pressures is proposed. Finally, an augmented territorial warning model is calibrated and validated using statistical indicators widely adopted in literature. The analysis of the results reveals a satisfactory correspondence between days with landslides and the warning levels provided by the augmented territorial warning model. A final comparison between the results of the model calibration and the model validation highlighted the consistency of the model performance, once the three model parameters are adequately set.

Examination of the Effects of Solids Content on Thickened Gold Mine Tailings Sedimentation and Self-Weight Consolidation

Abstract Thickening is being increasingly adopted by the mining industry because of its economic and environmental attributes, such as decreased amounts of water released following deposition and a smaller footprint of the tailings site. This study presents an assessment of the continuous process of sedimentation and the self-weight consolidation of slurry and thickened mine tailings. The results of a series of settling column tests performed with specimens with solids contents between 50 % and 72 % are presented and discussed. Lower solids contents that are more characteristic of slurry tailings were also included to cover a wide range of settling behavior. High-precision monitoring of pore water pressure was used to identify the transition from sedimentation to self-weight consolidation, which likely occurs between solids contents of 65 % and 68 % for this material, and it highlighted the fact that the combination of these two settlement processes accelerates ue dissipation. The displacement results for the tailings–water interface corroborate values in the technical literature related to the settlement of suspensions. Equilibrium was reached within a narrow time range (i.e., 400 to 500 min) despite the wide range of initial solids content in the slurries tested (i.e., 50 % S to 65 % S).

Comparison Among Several Subsea Ground Settlement And Pore Water Pressure Monitoring Instruments In Offshore Deep-Water Channel Project

The monitoring of subsea ground settlement and pore water pressure is key indexes for evaluating the safety of offshore channel engineering cases. The monitoring of settlement and pore water pressure for onshore cases is easy to proposed, and lots of instruments can meet the need. While for offshore engineering cases, the monitoring instruments should survive under extreme bad environment. This paper analyzed several monitoring instruments based on a 12.5 deep offshore channel engineering located at Nanjing city. A suit of instrument was final chosen after comparison.

An analytical model for the monitoring of pore water pressure inside embankment dams

The hydraulic behaviour of embankment dams is influenced by many factors, such as hydrostatic loads and settlement. Particularly, the delayed response due to the diffusion phenomena plays a crucial role in the interpretation of the monitoring data gathered in embankment dams. The paper describes a statistical analysis model named EFR (EFfet Retard - Delayed effect), based on the HST (Hydrostatic-Season-Time) model, for the monitoring of pore water pressure inside embankment dams. The model allows separating the influence of the most important factors and takes into account the delayed hydrostatic effect. The use of this model leads to a better estimation of the irreversible trend and enables an earlier detection of abnormal pore water pressures. An application of this model to a French embankment dam is provided in the second part of the paper. Based on this application, the influence of different diffusion models, calculation methods for the equivalent reservoir water levels and the irreversible term versions on the EFR analysis results are discussed.

Monitoring of Inland Tide Embankment of Binzhou Port

For the purpose of foundation and structure stability during the construction of tide embankment, three monitoring projects including embankment settlement monitoring, berm platform settlement monitoring and pore water pressure monitoring are installed. Integrated monitoring data shows that foundation appears oversize instantaneous settlement on account of high construction speed, short loading interval at initial stage. Following with the shaping of embankment, stable monitoring data range, slow change rate and high dissipation speed of pore water pressure come along. Based on actual embankment settlement data, consolidation degree of soil mass is high and foundation stability becomes strong by means of hyperbolic curve.

원심모형실험을 이용한 증고 저수지 제체의 거동특성 연구

본 연구는 현장응력상태 및 수위변동을 재현한 원심모형실험을 통하여 증고 및 비증고 제체의 거동을 평가하는 것을 그 목적으로 한다. 실험 결과, 제체의 증고시 수위상승에 따른 제정부 침하량이 크게 나타났으나, 비증고 제체의 월류 발생시 제정부 및 이에 근접한 제체 상류부 일부와 제체 하류측 사면에 세굴에 의한 파괴가 발생하는 반면, 동일한 수위에서 증고 제체는 안정성을 확보함을 알 수 있었다. 따라서, 기후변화 대처 및 저수량 증대를 도모하기 위해 증고를 통한 노후 저수지의 재개발이 필요한 것으로 판단되며, 이 경우 호우 등에 따른 급격한 수위 증가시 간극수압 및 변위 계측치를 실시간 모니터링하여 저수지의 안정성을 유지하도록 하여야 한다. This study aims to investigate the behavior of raised reservoir levee via centrifugal model test. The experimental results demonstrate that the overflow failure occurred at crown, at a part of front side and at rear side of the original reservoir levee, while, the stability of the raised reservoir levee was ensured at the same water level although the subsidence of crown of the raised levee due to the water level raising was larger than that of the original levee. Thus, it is significant to redevelop the superannuated reservoir levee through the levee raising for countermeasure to climate change and storage capacity improvement of reservoir. In addition, the real-time monitoring of pore water pressures and displacements is required to ensure the levee's stability.

지속적 수위변동 및 월류에 따른 저수지 제체의 거동 연구

본 연구에서는 현장응력상태 및 수위변동을 재현한 원심모형실험을 통하여 속도변화를 고려한 지속적 수위승강에 따른 제체의 거동을 검토하였으며, 기후변화에 따른 기습적 폭우 상황을 상정한 월류 시 제체의 파괴거동을 모사하였다. 실험 결과, 제체내의 간극수압 및 변위는 수위상승 및 하강속도에 비례하여 증감하며, 제정부 및 제체 하류측 사면부의 변위증분은 수위승강속도에 대하여 독립적임을 알 수 있었다. 또한 반복적이고 지속적인 수위변동은 변위의 누적을 통해 제체의 변형을 진행시키는 요인이 되며, 월류에 의해 저수지 제체의 안정성이 급격히 저하됨을 확인하였다. 따라서 호우 등으로 수위가 급상승하는 경우 간극수압, 변위 등을 실시간으로 감시하고, 이상 발생 시 수문개방 등을 통해 저수지의 수위를 조절하는 조치를 강구할 필요가 있다. In this study, the behavior of fill dam with continuous water level change considering velocity changes via centrifugal model test was investigated. In addition, the collapse of fill dam due to the overflow was also experimentally simulated. The experimental results demonstrate that the pore water pressures and displacements vary in proportion to the water-level-change velocity, and the displacement increment is independent to the water-level-change velocity. Also, it is confirmed that the continuous water level change induces to the progress of fill-dam deformation due to displacement accumulation and the fill-dam stability dramatically degrades owing to the overflow. Hence, the real-time monitoring of pore water pressures and displacements of fill dam, and the control of water level in heavy rain through the countermeasure such as opening sluice gates are needed to ensure the stability of fill dam.

<i>In Situ</i> Study on Soil Disturbance Induced by Shield Tunneling in Tianjin

In urban environment, the soil disturbance induced by shield tunneling can be sensitive because it can cause deformation of the ground and damage the near structure. To study this disturbance in the construction process of Tianjin metro line No.3, in-situ monitoring of pore water pressure, soil pressure and ground settlement were conducted. The pore water pressure was monitored for the soil around the tunnel. The soil pressure was monitored for the soil around the tunnel and on the tunnel face. It was revealed that the pore water pressure and soil pressure changed twice in the tunneling process and these changes were induced by cutting face and grouting at the shield tail. The soil pressure on the tunnel face reached its maximal value when the distance between the cutting face and the sensor elements was around the diameter of the tunnel. Ground settlement developed in the tunneling process. The shape of ultimate settlement trough is closed to the one obtained by Pecks method.

Experimental Research of Soft Soil Ground Treatment in Yangpu Port by Static-Dynamic Drainage Consolidation

Yangpu Port has inhomogeneous soft soil with the properties of high water content, high void ratio, high compressibility and low shear strength. Based on soft soil ground treatment engineering practice, the geological characteristics are summarized, the ground treatment methods are comparatively analyzed, static-dynamic drainage consolidation method is chosen to treat the soft soil ground, the reinforcing mechanism of vertical and horizontal drainage system are discussed, the design of drainage system, preloading and dynamic consolidation are researched and the surface settlement monitoring, pore water pressure monitoring, side piling displacement monitoring, laboratory soil test and plate loading tests are carried out. The results show that average surface settlement is 1170.8 mm, the physical and mechanical properties of soft soil are improved and the characteristic value of foundation bearing capacity is greater than 120kPa.

Investigating the impacts of climate change on slopes: field measurements

AbstractClimate change has the potential to have significant effects on the stability and serviceability of earthworks slopes, impacting on the performance of transport infrastructures. This paper describes how a unique facility for engineering and biological research was established in NE England through the BIONICS Project (Biological and Engineering Impacts of Climate Change on Slopes). It describes the building and monitoring of a full-scale embankment representative of road/rail embankments in the UK. The paper presents the results of monitoring of pore water pressure carried out between 2007 and 2009. The pore water pressures within the upper 3 m of the embankment have been largely positive, in some case approaching hydrostatic conditions after wetter periods. This is largely due to the wet nature of the summers in both 2007 and 2008 since monitoring began, as well as the application of artificial inundation using a climate control system. Negative pore water pressures (suctions) of the order of −30 kPa were recorded at greater depths below 3 m. The experimental facility provides essential field measurements that can be used to calibrate numerical models of soil responses to climatic changes and gain a better understanding of the response of engineered UK fills to climate events.

Soil suction monitoring for landslides and slopes

Rainfall is the most frequent triggering factor for landslides and the development of early warning systems has to take account of this. It is suggested that direct measurement of pore pressure gives the most reliable prediction of failure of a slope. The amount of rainfall can be only a crude indicator of failure as the processes that occur between rain falling on a slope and the resulting pore water pressure change are complex, highly non-linear and hysteretic. The paper describes highcapacity tensiometers developed within the EU-funded MUSE Research Training Network that have been used for measuring suctions in slopes. High-capacity tensiometers are capable of direct measurement of pore water pressure down to −2 MPa and are also able to record positive pore water pressures. Two methods of field installation are discussed; one developed by ENPC in France uses a single tensiometer per hole, and the second technique, developed by Durham University in the UK, allows multiple tensiometers to be used at different depths within a single borehole. Continuous monitoring of pore water pressure has been carried out over several months and shows the responses to climatic events.

Ground conditions around an old tunnel in London Clay

This paper reports the findings of a field study of the ground conditions around an old tunnel in London Clay at a greenfield site in Kennington, South London. Ground conditions were identified from a borehole investigation incorporating a programme of in situ pore water pressure monitoring, geotechnical testing and sampling. Additionally, laboratory classification of the samples and a suite of high-quality triaxial tests were carried out. The results of this investigation are presented and discussed in conjunction with published London Clay data. The presence of a tunnel beneath the site allowed the investigation of its influence on the local soil and groundwater conditions.

Ground conditions around an old tunnel in London Clay

This paper reports the findings of a field study of the ground conditions around an old tunnel in London Clay at a greenfield site in Kennington, South London. Ground conditions were identified from a borehole investigation incorporating a programme of in situ pore water pressure monitoring, geotechnical testing and sampling. Additionally, laboratory classification of the samples and a suite of high-quality triaxial tests were carried out. The results of this investigation are presented and discussed in conjunction with published London Clay data. The presence of a tunnel beneath the site allowed the investigation of its influence on the local soil and groundwater conditions.

Pore water pressure monitoring during the screw plate testing in a soft clay : Proc International Symposium on Computer and Physical Modelling in Geotechnical Engineering, Bangkok, 3–6 December 1986 P269–278. Publ Rotterdam: A A Balkema, 1989

Pore water pressure monitoring during the screw plate testing in a soft clay : Proc International Symposium on Computer and Physical Modelling in Geotechnical Engineering, Bangkok, 3–6 December 1986 P269–278. Publ Rotterdam: A A Balkema, 1989