Pore Water Pressure Measurements Research Articles

Measurement of Excess Pore-Water Pressure in Frozen Soil at Subfreezing Temperatures Close to 0°C

Response of pore-water pressure has crucial effect on the engineering geological performance of permafrost ground. However, there is a dearth of literature on the measurement of pore-water pressure in frozen soils due to challenges with regard to technical and operational method. To validate the generation of pore-water pressure and to reveal its variation property in frozen soils at subfreezing temperatures close to 0°C, a miniature pressure transducer was utilized to conduct a number of confined compression tests. Double-wall structure avoided damage to the transducer during frozen soil sampling. The transducer at sample bottom perceived a pressure fluctuation as varying air pressure imposed on sample surface, proving the connectivity among the pores in frozen soils with a hysteretic effect on pressure transmission. Pore-water pressure experienced a progressive increase followed by a slow dissipation under invariable load and temperature conditions when water drainage was permitted, while a monotonic increase in pressure was observed for an undrained sample. With decreasing temperature, a smaller peak and a more dilatory dissipation were displayed. When the sample was exposed to a stepwise warming process, a similar performance for the pressure was obtained with abrupt rise at the turning point of temperature.

Simple Shear Strength Analysis of Inherent Anisotropy for a Tropical Alluvial Soil

ABSTRACT Tropical alluvial soils have unusual engineering properties and their behavior is not typical of fine-grained soils. The literature regarding strength properties of alluvial soils is limited. This study presents an experimental evaluation of inherent anisotropy of undisturbed tropical alluvial soil samples by comparing the direct simple shear (DSS) test results of 52 specimens cut in horizontal and vertical orientations. The tests were carried out under consolidated undrained constant volume with excess pore water pressure measurements. The peak shear strength, effective stress paths, and secant shear modulus analyses showed that the difference in properties between horizontally and vertically cut specimens was negligible. Nonetheless, the results for vertically cut specimens presented a higher random error compared to the results for horizontal specimens in all aspects. A good relationship between the undrained shear strength and over-consolidation ratio was found but was not comparable to past DSS results for natural clays. Scanning electron microscopy images revealed flocculated edge-to-edge and edge-to-face particle associations. Directionality analysis of microfabric showed that the alluvial soils had low preferred orientation of particles. The general notion that all alluvial soils are highly anisotropic was not evident, based on the experiments reported in this study. The findings herein are useful for geotechnical engineers to better understand the strength behavior of tropical alluvial soils.

Measurement of Physical Parameters for Transient Seepage Assessment of Levees

Abstract An embankment was instrumented and monitored as part of a multiyear project to assess appropriate pore-water pressure distributions and soil water retention curves for use as initial conditions in transient seepage analyses. The increased use of unsaturated soil mechanics and transient seepage has led to the need for practical methods of assigning accurate properties and initial conditions in these types of analyses. Monitoring results were validated against published pore-water pressure measurements collected from multiple embankment studies. The collected distributions showed nonlinear behavior in near-surface embankment soils due to infiltration and evapotranspiration processes. Seasonal variations in pore-water pressure and the soil moisture deficit were shown to correlate at the monitoring site. The seasonal response of the embankments exhibited a large variation in pressures between summer and winter. Assessment of flood occurrence showed the distribution of pore pressures during flood loading was typically near −10 kPa at a depth of 2 m at the onset of the flood. Laboratory soil water retention testing of undisturbed samples collected from the embankment showed that when compared with field measurements, they overestimated the field response for the considered initial water content and dry density values. Also, comparisons between hydrostatic pore pressures above the phreatic surface showed that at soil moisture deficits greater than 20 mm, the difference between the measured and hydrostatic pore pressures greatly increased. The laboratory and monitoring results were used to provide practical methods of assigning representative pore-water pressure distributions and material properties necessary for performing transient seepage analyses. These results will aid in more accurate transient seepage analyses of flood control embankments.

Possible Effects of Multiphase Methane Evolution During a Glacial Cycle on Underpressure Development in Sedimentary Basins: An Analysis With Application to the Northeast Michigan Basin

In low-permeability systems, groundwater may be accompanied by separate-phase fluids, and measured pore water pressures may deviate from those expected in steady-state, single-phase systems. These same systems may be of interest for storage of nuclear waste in Deep Geologic Repositories. Therefore, it is important to understand the relationship between the presence of a separate phase and anomalous pressure development. At the Bruce site in Southern Ontario, a significant underpressure was observed, and there is evidence for the presence of gas-phase methane in situ. This study used a one-dimensional (vertical) numerical model of the subsurface down to a depth of 844 m beneath the Bruce site to evaluate possible effects of hydromechanical coupling with multiphase flow on pressure evolution during glacial loading and unloading. The simulated pressure conditions were affected strongly by the amount of methane initially present in the system, and the maximum simulated underpressure varied nonmonotonically with increasing initial methane content. When the initial methane content was below the solubility limit, exsolution led to underpressures that briefly exceeded those that formed in the single-phase case. At intermediate initial methane contents (sufficient to produce an immobile gas phase), the gas phase dampened the hydromechanical effects of the glacial cycle. At large initial methane contents (when a mobile gas phase was present), gas migration caused a large decrease in relative liquid permeability, which further contributed to underpressure development in the pore water. Multiple scenarios that spanned a range of initial methane contents yielded underpressures like those observed at the Bruce site.

Analysis of Load Transfer Law of Short Pile-Net Composite Foundation for High-Speed Railway

Although pile-net composite foundation has been widely used in the construction of high-speed railway, load transfer characteristics of its structural system during the filling of roadbed are seldom studied, so field studies are conducted in the Gan-Long (Ganzhou-Longyan) high-speed railway DK86 + 998.0–DK87 + 191.2 test section, aiming to explore the bearing characteristics of a short pile-net composite foundation over low to medium compressible soil. The study encompasses a field measurement of Earth pressure and pore water pressure which lasted almost two years, and a systematic analysis of variation law of soil pressure between piles and their tops and that of pore pressure in reinforcement zone and retaining layer in medium and low compressibility soil area. The results suggest that the soil in the test section bears the characteristic of a low water content, low porosity ratio, and high liquid limit, with compression factor being approximately 0.25, and test values of the natural soil pressure and the lateral distribution are close to the theoretical values. Soil pressure at the top of the piles is higher than that between the piles by approximately 2.4 times because of the differences in pile-net rigidity. Besides, the soil pressure of the pile-net composite foundation follows the pattern of “jagged” in the transverse direction of the roadbed. The filling load of the composite foundation soil arch is 80 kPa and the composite foundation reaction coefficient is 6.4 kN/m3 when the filling is stable. The pile-soil stress ratio at the shoulder and the center of the line is 3.2 and 2.8, respectively. The change of the hole pressure at the pile end point is larger than that at the reinforcement area, and the side verification short pile can effectively transmit the additional stress of the upper part to the pile end soil layer.

A hybrid exploration approach for the prediction of geological changes ahead of mechanized tunnel excavation

The application of effective exploration techniques in mechanized tunneling is crucial in order to obtain a knowledge of the subsoil prior to drilling. We present a three-staged method, which seeks to image the excavation environment in detail, also reducing the computational demand of common exploration techniques. The algorithm combines two approaches: supervised machine learning and full waveform inversion. Firstly, the machine learning algorithm is applied on data sets of measured pore water pressures and ground settlements during tunnel propagation, making a primary prediction of geological changes ahead of the boring machine. Secondly, seismic measurements are acquired for full waveform inversion based on parameter identification. This method incorporates the primary predictions from the supervised machine learning in the form of a parametrization of the position, shape and material properties of the disturbance. Thirdly, the subsurface model gained out of the second stage is utilized as a starting model for a second full waveform inversion using the adjoint method, providing an even more detailed image of the subsurface. The exploration algorithm is tested on a synthetic shallow tunnel environment with an unknown obstacle ahead of the tunnel boring machine. It is shown that the algorithm finds the unknown obstacle with improved accuracy.

Removal of atmospheric CO2 by engineered soils in infrastructure projects

The use of crushed basic igneous rock and crushed concrete for enhanced rock weathering and to facilitate pedogenic carbonate precipitation provides a promising method of carbon sequestration. However, many of the controls on precipitation and subsequent effects on soil properties remain poorly understood. In this study, engineered soil plots, with different ratios of concrete or dolerite combined with sand, have been used to investigate relationships between sequestered inorganic carbon and geotechnical properties, over a two-year period. Cone penetration tests with porewater pressure measurements (CPTu) were conducted to determine changes in tip resistance and pore pressure. C and O isotope analysis was carried out to confirm the pedogenic origin of carbonate minerals. TIC analysis shows greater precipitation of pedogenic carbonate in plots containing concrete than those with dolerite, with the highest sequestration values of plots containing each material being equivalent to 33.7 t C ha−1 yr−1 and 17.5 t C ha−1 yr−1, respectively, calculated from extrapolation of results derived from the TIC analysis. TIC content showed reduction or remained unchanged for the top 0.1 m of soil; at a depth of 0.2 m however, for dolerite plots, a pattern of seasonal accumulation and loss of TIC emerged. CPTu tip resistance measurements showed that the presence of carbonates had no observable effect on penetration resistance, and in the case of porewater pressure measurements, carbonate precipitation does not change the permeability of the substrate, and so does not affect drainage. The results of this study indicate that both the addition of dolerite and concrete serve to enhance CO2 removal in soils, that soil temperature appears to be a control on TIC precipitation, and that mineral carbonation in constructed soils does not lead to reduced drainage or an increased risk of flooding.

High-Precision Large-Range Optical Fiber Interferometric Piezometer and Its Wideband Interferometry for Water Pressure Measurement

A high-precision large-range fiber-optic interferometric piezometer is designed, packaged, and demonstrated for pore water pressure measurement. The piezometer is an optical fiber extrinsic Fabry–Perot interferometer (EFPI), which comprises a fiber ferrule connector/flat contact (FC/FC) connector and an aluminum foil pasted on a thin metal plate. The EFPI forms a sealed chamber with only the outer plane of the aluminum alloy plate being subjected to the water pressure through another hydraulic chamber with a standard filter stone. The deformation of the metal plate is analyzed and simulated for parameter optimization by using the small deflection theory. By adopting the conventional wavelength tracking method, the theoretical simulation and experimental results show a high measurement accuracy of the cm level but a limited measurement range. To resolve the problem, several wideband interferometry (WBI) methods, including free spectral range (FSR)-based, spatial frequency, interference order, and fitted FSR, are employed to analyze the spectrum of the EFPI for comparison. The fitted FSR method has demonstrated its superiority in applications that require simultaneous high resolution and large measurement range. A gas pressure test verifies that the proposed piezometer can work in a wide range of up to 0.5 MPa that is equivalent to a water depth of 50 m. In addition, the proposed piezometer offers several advantages, such as cost-effectiveness, robustness, repeatability, and stability, which further benefits its practical application.

Shaking-Induced Sublayer Vertical Strains of Saturated Sands Estimated from Partially Drained Dynamic Centrifuge Tests

Earthquake-induced free-field settlement of coarse-grained soils has historically been assessed using laboratory element tests under drained or undrained conditions. However, in saturated sands, dynamic centrifuge and 1g shaking table tests illustrate that excess porewater pressure generation/dissipation and settlement occur simultaneously during shaking under partially drained conditions. The average vertical strains computed from measured surface settlements in these tests neglect (1) the impact of effective stress on compressibility and (2) settlements that occur in denser and potentially nonliquefiable sands present in the centrifuge models. Here, the authors employ a simple procedure that uses measured porewater pressure and surface settlement time histories from partially drained centrifuge and 1g shaking table tests to properly distribute vertical strain throughout the coarse-grained soil profiles, thereby incorporating variations of effective stress and relative density on vertical strain. The vertical strains are resolved into a shaking-induced component and a post-shaking reconsolidation component, and the procedure yields computed surface settlement time histories that reasonably match the rate and magnitude of measured settlements both during and after shaking. Using this procedure, we interpreted 151 individual (sublayer) estimates of vertical strain from 34 shaking events applied in dynamic centrifuge and 1g shaking table tests. Combined with the sublayer shaking intensities, the 151 vertical strain values constitute a new database that can be used to develop shaking-induced settlement correlations for realistic partially drained conditions.

Unsaturated Flow Processes and the Onset of Seasonal Deformation in Slow‐Moving Landslides

AbstractPredicting rainfall‐induced landslide motion is challenging because shallow groundwater flow is extremely sensitive to the preexisting moisture content in the ground. Here, we use groundwater hydrology theory and numerical modeling combined with five years of field monitoring to illustrate how unsaturated groundwater flow processes modulate the seasonal pore water pressure rise and therefore the onset of motion for slow‐moving landslides. The onset of landslide motion at Oak Ridge earthflow in California’s Diablo Range occurs after an abrupt water table rise to near the landslide surface 52–129 days after seasonal rainfall commences. Model results and theory suggest that this abrupt rise occurs from the advection of a nearly saturated wetting front, which marks the leading edge of the integrated downward flux of seasonal rainfall, to the water table. Prior to this abrupt rise, we observe little measured pore water pressure response within the landslide due to rainfall. However, once the wetting front reaches the water table, we observe nearly instantaneous pore water pressure transmission within the landslide body that is accompanied by landslide acceleration. We cast the timescale to reach a critical pore water pressure threshold using a simple mass balance model that considers variable moisture storage with depth and explains the onset of seasonal landslide motion with a rainfall intensity‐duration threshold. Our model shows that the seasonal response time of slow‐moving landslides is controlled by the dry season vadose zone depth rather than the total landslide thickness.

Assessment of Water Retention Test by Continuous Pressurization Method

Abstract The water retention test involving the stepwise pressurization method (SPM) and a pressure plate extractor has been mainly used to obtain the soil–water characteristic curve (SWCC) of soils. The disadvantage of this test is that the measurement of the drying and wetting paths of the SWCC is time consuming. Thus, a water retention test involving a continuous pressurization method (CPM) in this paper was proposed, and the experiments for three kinds of soil samples were performed. Unlike the SPM, the pore air pressure in the CPM is continuously given to the specimen at a constant pressurization rate. In particular, for the measurement of the transient pore water pressure inside specimen according to the applied pore air pressure, a microtensiometer (height: 25 mm, diameter: 3 mm) was placed vertically at the center of the specimen. The suction for the specimen was defined as the difference between the applied pore air pressure and the measured pore water pressure. It was confirmed that the testing time for the drying and wetting paths of the SWCC in the test involving the CPM was remarkably shortened. The results of the CPM for its verification were compared with those of the SPM under the same initial condition of the specimen. The two test results showed good agreement regardless of the soil samples. Furthermore, the effect of the pressurization rate of the pore air pressure for the CPM was examined. Finally, the proposed water retention test involving the CPM was found to be highly efficient and accurately measure the drying and wetting paths of the SWCC in a short time.

Interpretation of undrained shear strength observed in confined triaxial compression tests on compacted clay

This paper presents an interpretation technique to quantify the effects of compaction state and matric suction on the undrained shear strength of compacted clay under confined undrained triaxial compression. This novel technique is based on the mathematical frameworks of the “stress history and normalized soil engineering property” (SHANSEP) method for saturated soil and the “Barcelona basic model” (BBM) for unsaturated soil. Test data of compacted Calgary till were analyzed and interpreted using the proposed technique. The interpretation technique is very useful in delineating the relative impacts of the factors on the behavioural trends in measured undrained shear strength. It was found that in addition to the initial compacted void ratio and suction, soil structure and failure mode exert significant influence on the undrained shear strength of compacted clay. This technique is attractive to engineering practitioners because the confined undrained compression tests (with no pore-air and pore-water pressure measurement) are much simpler and less time-consuming compared to rigorous laboratory tests on unsaturated soil.

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.

Experimental study of the evolution of pore water pressure and total stresses during and after the deposition of slurried backfill

Mining backfill is increasingly used in underground mines to fill stopes. Its successful application depends on the stability of barricades built to retain the backfill in stopes. The design of barricades requires a good estimation of pore water pressure (PWP) and total stresses during and after the deposition. On this regard, a large number of works have been published on analytical and numerical solutions. There are however very few experimental results with simultaneous measurements of PWP as well as horizontal and vertical total stresses that can be used to validate or calibrate the analytical and numerical solutions. For a specific project, field measurements are interesting in terms of representativeness to field conditions, but the results are very difficult to be correctly interpreted because the treated problem can involve a large number of uncertainties and the obtained results are due to combined effects of several influencing factors. Laboratory tests with simplified and well-controlled conditions are thus preferred. Until now, however, the most previous laboratory tests were conducted with dry backfill or with a tailings slurry instantaneously poured in a confining structure without simultaneous measurements of PWP as well as horizontal and vertical total stresses. Studies on the effects of filling rate and solid content of backfill on the variation of PWP and total stresses during the filling operation are absent. To fill these gaps, a series of column backfilling tests were conducted with simultaneous measurements of PWP as well as vertical and horizontal total stresses during and after the deposition of slurried backfill. When the filling rate is high, the test results showed that the PWP, horizontal and vertical total stresses increase at the same rate and equal to the iso-geostatic overburden pressure during the deposition of backfill slurry. Their peak values appear at the end of deposition. The backfill thus behaves like a liquid with little generation of effective stresses during the deposition. High filling rate and/or high solid content lead to high PWP and horizontal total stresses at the end of deposition. When the filling rate is small, the PWP and total stresses exhibit also peak values at the end of filling operation, but the vertical total stress at the center can continue increasing with time after the end of deposition due to the suspended sensor and occurrence of a phenomenon known as stress shielding effect. The results also showed that the settlement of settled backfill after the end of slurry deposition can generally exhibits a fast evolution rate stage, followed by a slow evolution rate stage. The duration of the fast evolution rate stage and the final settlement of the settled backfill increase as the solid content decreases. The final settlement after the end of slurry deposition is related to the solid content, not to the filling rate.

СПОСОБ ГЕОТЕХНИЧЕСКОГО МОНИТОРИНГА ПОРОД ТАШТУНСКОГО РАЗЛОМА ЮГО-ЗАПАДНОГО БОРТА КАДЖАРАНСКОГО КАРЬЕРА

A method has been suggested for geotechnical monitoring of tectonic fault rock mass of the south-west wall in Qajaran open-pit mine by applying the pseudo-static method of CPTu (Cone Penetration Test with in-situ pore water pressure measurements) which gives an opportunity to define the root parameters of soils such as: pore water pressure, unit weight, drained and undrained shear strength. The versatile in-situ CPTu methods allow to profile simultaneously the geotechnical properties of each soil strata with permanent penetrating speed, and also while using the SCPTu (Seismic Cone Penetration Test with in-situ pore water pressure measurements) method, as well as determine horizontal and shear seismic wave velocities from the given geomechanical environment. At that, it also becomes possible to pull out independently intact samples from tectonic-fault-soils for future laboratory testing. Two different approaches for geomechanical proposition of the south-west wall stability of Qajaran open-pit mine based on the limit equilibrium theory and outputs from the proposed in-situ geotechnical seismic monitoring (SCPTu) have been analysed. The difference of the results from the two analyzed approaches (USA vs ESA) was about 8 to 10% in estimating the slope stability. Based on the analyzed results of the stability of the south-west wall of Qajaran open-pit mine, it is recommended to apply undrained strength analysis for undrained tectonic-fault soils (USA – Undrained Strength Analysis) instead of the effective drained strength analysis (ESA – Effective Strength Analysis) for drained rocks by taking into account the developed excess pore water pressure when saturated clayey soils sheared in undrained conditions.

Proof-of-concept for a probe to measure pore water pressure in oil-water saturated porous rock

The identification of the Oil/Water Contact (OWC) in a hydrocarbon reservoir is crucial for the determination of its volume and it is also important for detailed petrophysical calculations. Estimation of the OWC requires the determination of the Free Water Level (FWL). Routine practice in the oil and gas industry involves drilling multiple discovery wells since the undulation of the rock layers confining the hydrocarbon reservoir does not generally enable a single discovery well to intercept the water phase. Well drilling is expensive and industry looks forward to approaches to reduce the number of wells required for estimation of the OWC. In this context, this paper presents the proof-of-concept for a probe to measure pore water pressure in oil-water saturated porous rock. This would allow predicting the depth of the FWL in hydrocarbon reservoirs even if the single discovery well does not go through the OWC. This probe could significantly improve the appraisal process and guide the drilling campaigns, saving time, money and reducing the environmental impact of hydrocarbon search. The probe prototype was validated at laboratory scale via measurements of water pressure in core plugs saturated with water and oil. Mock-up tests on sandstone core plugs have shown that the probe can successfully measure water pressure in samples saturated with water and oil as long as the water phase is continuous in the pore space. The paper has therefore provided a proof-of-concept for a technology that can now be moved to the next readiness level.

Forecasting the long-term deterioration of a cut slope in high-plasticity clay using a numerical model

This paper details development of a numerical modelling approach that has been employed to forecast the long-term performance of a cut slope formed in high plasticity clay. It links hydrological and mechanical behaviour in a coupled saturated and unsaturated model. This is used to investigate the influence of combined dissipation of excavation-generated excess pore water pressures and seasonal weather-driven near-surface cyclic pore water pressures. Deterioration of slope performance is defined in terms of both slope deformations (i.e. service) and factor of safety against shear failure (i.e. safety). Uniquely, the modelling approach has been validated using 16 years of measured pore water pressure data from multiple locations in a London Clay cut slope. Slope deterioration was shown to be a function of both construction-induced pore water pressure dissipation and seasonal weather-driven pore water pressure cycles. These lead to both transient and permanent changes in factor of safety due to effective stress variation and mobilisation of post-peak strength reduction over time, respectively, ultimately causing shallow first-time progressive failure. It is demonstrated that this long-term (90 year) deterioration in slope performance is governed by the hydrological processes in the weathered near surface soil zone that forms following slope excavation.

Shear strength characteristics of a sand clay liner

This study investigated shear strength behaviour of compacted sand–clay mixtures used as liners, with 10%, 20%, and 30% clay contents. A natural high-plasticity and highly expansive clay found in the eastern province of Saudi Arabia was used. A series of consolidated undrained triaxial tests and pore water pressure measurements of saturated samples with various clay contents and confining pressures was conducted using a computer-controlled Bishop and Wesley triaxial cell. The unit was equipped with pressure volume controllers and a pressure transducer for measuring sample volume changes and excess pore water pressure. The experimental test results indicate that clay content and confining pressure significantly affect stress strain response curves, pore water pressure generation curves, and steady-state shear strength. Sand–clay mixtures with clay content less than 10% showed a tendency toward contractive behaviour. The failure line slope increased in accordance with clay content increase. The deviator stress versus axial strain of saturated sand–clay mixtures indicated a hyperbolic trend. The stress ratio versus axial strain representation was more informative for the shear strength behaviour assessment. Clay content did not significantly affect critical-state friction angle. Scanning electron microscope images of the sand-clay mixtures with different clay contents are presented.

Monitoring and Early Warning Technology of Hydrate-induced Submarine Disasters

With the depletion of fossil energy sources, such as coal and petroleum, natural gas hydrate has been proposed as an alternative energy source. However, the synthesis of natural gas hydrate may cause marine engineering disasters, such as submarine cable breaks and the collapse of sub-sea oil rigs, and even submarine earthquakes, triggering tsunamis and seriously endangering human safety. Hydrate test production monitoring in various countries focuses on the temperature, pressure, and methane concentration near test production wells. Effective observation equipment and methods for the monitoring and early warning of submarine geological hazards are lacking. This paper reviewed the possible geological hazards caused by deep seawater hydrate mining and the monitoring and early warning technologies for deep seawater hydrate mining in various countries and introduced the in-situ Surveying Equipment of Engineering Geology in Complex Deep Sea (SEEGeo). The equipment uses 3D resistivity measurement and data inversion technology, seabed sediment acoustic measurement and data inversion technology, seabed sediment pore water pressure measurement and data inversion technology, and renewable energy seawater-dissolved oxygen battery power supply technology. SEEGeo can realize the in situ, real-time, long-term, effective monitoring and early warning of geological disasters induced by hydrate development. At present, the equipment has conducted two sea trial experiments on the continental slope of the South China Sea, equipped with the “Marine Geology No. 6” scientific research vessel of the Guangzhou Marine Geological Survey and the “Dongfanghong No.3” scientific research vessel of the Ocean University of China, and obtained in situ engineering geological data of the South China Sea.

Behaviour of discrete piles used to stabilise a tree-covered railway embankment

Many clay railway embankments in the UK are well over 100 years old, and now suffer from a range of stability and serviceability problems. A common means of remediating earthworks that have either suffered, or are assessed as being at risk of, deep-seated slope failure is to install a row of discrete piles along the mid-slope. This paper presents field data from a 9 m high, pile-stabilised embankment at Mill Hill, north London. Initial pore water pressure measurements had shown that the trees present on the earthwork maintained low pore water pressures during winter; thus the trees were left in place after piling to aid stability. The piles initially bent upslope, as a result of inward shrinkage of the embankment over a period of dry weather, before then being loaded by shallower downslope movements of the clay. Later cycles of seasonal movement caused a small but gradual ratcheting upward of pile bending moments. The largest bending moments measured over 6 years of monitoring were those resulting from the initial inward shrinkage of embankment, which reached about 25% of the design capacity of the piles. At the end of the monitoring period, the measured bending moments resulting from shallower downslope ground movements were about 20% of the pile design capacity.