High Pore Water Pressure Research Articles

Polyphase structural evolution of a fine-grained, fold-dominated end moraine, Brúarjökull surge-type glacier, Iceland

The glaciotectonic architecture and structural evolution of a fine-grained end moraine formed by the 1890 glacier surge of Brúarjökull is described from four excavated cross-sections. The end moraine ridge is a morphological expression of a marginal sedimentary wedge formed during the last days of the surge. The actual end-moraine ridge was formed on the last day of the 1890 surge when the glacier became coupled to the bed and ploughed into the reverse slope of the marginal sediment wedge. Ductile deformation, favoured by high porewater pressure, dominated the construction of the end moraine while brittle deformation was induced when porewater pressure decreased, particularly at the end of the surge. Thus, the deformation was polyphase, developing from open folding to multiple overfolding when porewater pressure was high and finally to overthrusting, faulting and shearing at the very end of the surge when porewater pressure dropped severely upon porewater blow-out in front of the moraine. This structural continuum is exhibited by the four cross-sections. The glaciotectonic stress was absorbed within a relatively narrow zone due to high friction along a basal décollement. A new model illustrates the structural evolution of a fine-grained, fold-dominated end moraine and may serve as an analogue to similar end moraines in modern and Pleistocene environments.

Primary Study on Mechanism of Earthquake-Induced Differential Settlement of Buildings on Liquefiable Subsoil

The shaking table test on liquefied soil - structure interaction was desighed. In the test, the building model and the soil were evenly arranged, after being put horizontal sine wave acceleration time history, building symmetrical basal dynamic stress, pore water pressure and earthquake-induced settlement time history were obtained. The results are: (1) symmetrical basal vertical dynamic stress, pore water pressure, earthquake-induced settlement reaction time history appeared antisymmetric distribution; (2) basal dynamic stress is controlled by the input waveform, the basal vertical dynamic stress plays a decisive role in the increase of the pore water pressure, while difference of pore water pressure decides difference of earthquake-induced settlement, which causes the building tilts toward the direction of higher pore water pressure; (3) a correlation exists among input wave, basal vertical dynamic stress, pore water pressure and structural earthquake-induced settlement. The mechanism of earthquake-induced settlement is: acceleration waveform  form of both sides basal dynamic stress cumulative form of both sides basal pore pressure form of earthquake-induced settlement.

Microstructural analyses of a Middle Pliocene till from the James Bay Lowlands, Canada—evidence of “potential” fast ice streaming

Abstract Sediment from the Attawapiskat area near James Bay, Northern Ontario was sampled for micromorphological analyses. The sediment is a glacial diamicton (till) of subglacial origin. The till contains entrained and scavenged sediments of proglacial and/or subglacial glaciofluvial/glaciolacustrine origin from a subglacial deforming layer that was emplaced due to both stress reduction and/or porewater dissipation. Evidence of porewater escape, clay translocation and other microstructures all point to emplacement under active subglacial bed deformation. The limited number of edge to edge (ee) grain crushing events, however, point to lower stress levels than might anticipated under a thin fast ice lobe of the James Bay during the Middle Pliocene. Microstructures of Pleistocene tills were quantitatively compared with the Attawapiskat till and the limited number of ee events at Attawapiskat further highlighted that grain to grain contact was curtailed possibly due to high till porosity, high porewater pressures and low strain rates or alternatively due to a high clay matrix component reducing grain crushing contact events. It is suggested that this Middle Pliocene till may be indicative of sediments emplaced under ice lobe surging conditions or fast ice stream subglacial environments. This proposal has significant implications for the glaciodynamics of this part of the Middle Pliocene James Bay lobe. This research highlights a crucial link between subglacial conditions, till microstructural analyses and glaciodynamics.

Sedimentological Signature of A Deformable Bed Preserved Beneath An Ice Stream In A Late Pleistocene Glacial Sequence, Ross Sea, Antarctica

Abstract Subglacial processes are described using a nested set of samples from AND-1B drill core collected from beneath the Ross Ice Shelf as part of the ANtarctic geologic DRILLing program (ANDRILL). An interval from the late Pleistocene was chosen for study because it is preserved in the sedimentary record, yet the depositional processes are applicable to the widely studied glacial conditions at the Last Glacial Maximum. A complete glacial–interglacial sequence, between two glacial surfaces of erosion (GSEs) at 41.9 and 47.7 meters below sea floor, was studied by centimeter-scale core logging based on X-radiographs of the archive core halves in addition to core description, bulk samples and 45 mm × 65 mm thin sections of diamictites for micromorphology analysis. Above the lower GSE, 4.6 m of subglacial till occurs including a sequence of thin muddy conglomerate with diverse pebble lithologies, massive clast-rich muddy diamictite, and stratified diamictite with clast-rich and clast-free beds. The sand-size fraction of these deposits is dominated by aggregate grains, termed till pellets following terminology used for Ross Sea deposits. We present the first detailed description and two different conceptual models of tillpellet formation beneath an ice stream: one is related to mechanical processes, and the other is related to thermodynamics. Till pellets are rounded, spherical to prolate in form, and are associated with turbate structures and aligned grains in thin sections. The core of the pellet is either a lithic grain or stiff till with additional clay plastered on the outside, forming rounded grains from originally angular ones. Galaxy structures, skelsepic fabric, and pressure shadows around grains are indicative of rotational deformation within the till. Till pellets form in situ within a highly porous deformable bed under an ice stream either by mechanical shearing or by alternating thermal conditions in the till. In the first model, a slow glacial advance under dry subglacial conditions fractures the till, increasing the porosity as shear induces dilation. Basal melting and high pore-water pressure develop as the ice stream thickens, decreasing the intergranular effective stress and inducing rotation of the angular till aggregates. An alternative model calls for basal freezing with preferential ice growth in larger pore spaces causing rotation of fine-grained till aggregates due to concentration of shear stresses in a thin zone beneath the glacier sole. Survival of till pellets is enhanced in subglacial diamictite as the thin zone of deformation moves upward toward the base of the ice stream. A thin granular bed enriched in till pellets is melted out in the grounding zone, and this deposit marks the transition from subglacial till to stratified silty claystone representing sub–ice shelf deposits.

PILE RESPONSE DUE TO EARTHQUAKE INDUCED LATERAL SPREADING

Liquefaction assessment is a key aspect when the pile foundations are designed under seismic loading. The liquefaction associated with lateral spreading and flow failures that can affect the overall stability of the pile foundations. This study is emphasized to investigate the extent of the liquefaction zone and the effect of the liquefaction on the pile is also monitored by the means of estimating the maximum bending moment developed due to lateral ground displacement. The investigation site is located at I.I.T. Kharagpur Extension Centre, Block No. HC, Plot. 7, Sector-III, Salt Lake City, Kolkata, India. The diameter and pile shaft length are 0.45 m and 22 m, respectively. The soil samples are collected from three boreholes located at the site of investigation and it is explored to a depth up to 30.45 m below the ground level. The boreholes reveal that the subsoil generally consists of six types of soil layers and the water table is at a depth of 1.25 m below the ground surface. A finite element model is simulated as per the field conditions using QUAKE/W (GeoStudio, 2007) to determine the depth of the liquefaction zone. The soil layers are idealized as 14 nodded rectangular elements. Initial static and dynamic analyses is performed by considering the linear elastic and equivalent linear models of soil using the earthquake history of peak acceleration of 0.16g. It is observed that the layer 1 susceptible to liquefaction due to high excess pore water pressure in that layer. Analytical study is carried out for the estimation of the maximum bending moment induced in the pile subjected to lateral ground displacement. The maximum deflection of the pile is also estimated due to the lateral ground displacement caused by the liquefaction.

Geotechnical Aspects of the Sumatra Earthquake of September 30, 2009, Indonesia

This paper reports and discusses the results of a field survey conducted by a joint scientific group from Japan and Indonesia to assess the geotechnical aspects of the Sumatra earthquake (Mw=7.6) of September 30, 2009. The studied area included the Padang and Pariaman cities, where a number of buildings collapsed as a result of strong shaking, and a mountainous part of the Pariaman district, a place where massive landslides buried several villages, claiming more than 400 human lives. The main objective of the survey was to investigate the causes and mechanisms of catastrophic landslides; however, other geotechnical problems such as lateral spread and liquefaction were also addressed. Field observations indicated that the catastrophic landslides occurred on relatively gentle slopes, then mobilized into debris flows, and traveled several hundred meters from their points of origin. The failure surfaces developed along the boundary of highly weathered pumice tuff with more intact and less weathered bedrock. Data from a portable cone penetration test showed that the sliding material was rather weak, having SPT N-values in the range of 5-10. The results of the field survey suggested that the main cause of slope instability was high pore-water pressures that generated in the soil mass during the earthquake.

Slope Stability Problems in Central and Northern Jordan

Over the last four decades excessive hill-slope disturbances have been identified during highway construction and urban development in central and northern Jordan. Most of the major engineering projects were implemented on natural, steep slopes, related to old landslide complexes, weak geological structures, and soft lithological units of low-shearing resistance. Thus a wide range of landslides was reactivated, causing serious damage to highways and urban areas. Engineering activities often took place without previous appreciation of the geological, geomorphological, and hydrological setting. The human impact of the increased probability of landslides was also ignored. The final triggering factor responsible for these slope failures was the build-up in the materials of high pore-water pressures, caused by recurrent, high-intensity rainstorms. Geomorphological stability evaluation was carried out along the Amman-Jerusalem and Amman-Irbid highways and in the greater Amman area. It is concluded that hill-slo...

Strain Soft Numerical Simulation for Destroy Process of Subsea Rock with High Ground Stress and Hydraulic Pressure

Aiming at the characters of high ground stress and high pore water stress, which resulting in water invasion risk in excavation of subsea rock, FLAC is adopted to simulate the strain localization phenomena of surrounding rock with different pore water pressure and confining pressure. In calculation, the strain soft constitutive relation and “first loading then unloading” pattern are used. Simulation result states that, the bigger the confining pressure is the more destruct the surrounding rock is, and the water invasion risk is more serious. In high confining pressure condition, shortly after excavation, the destroy zone is thin ring, subsequently, the arc shoulder and arc bottom occurs shallow hole, the destroy zone increasing, which presents zonal disintegration. Pore pressure has obvious influence at plastic strain of rock, the high pore water pressure results in surrounding rock destroy zone enlarging, which changing the seepage field of rock, and probably lead to seepage instability.

Pingos of the Tuktoyaktuk Peninsula Area, Northwest Territories

Most pingos have grown in residual ponds left behind by rapid lake drainage through erosion of ice-wedge polygon systems. The field studies (1969-78) have involved precise levelling of numerous bench marks, extensive drilling, detailed temperature measurements, installation of water pressure transducers below permafrost and water (ice) quality, soil, and many other analyses. Precise surveys have been carried out on 17 pingos for periods ranging from 3 to 9 years. The field results show that permafrost aggradation in saturated lake bottom sediments creates the high pore water pressures necessary for pingo growth. The subpermafrost water pressures frequently approach that of the total litho-static pressure of permafrost surrounding a pingo. The water pressure is often great enough to lift a pingo and intrude a sub-pingo water lens beneath it. The basal diameter of a pingo is established in early youth after which time the pingo tends to grow higher, rather than both higher and wider. The shutoff direction of freezing is from periphery to center. When growing pingos have both through going taliks and also permeable sediments at depth, water may be expelled downwards by pore water expulsion from freezing and consolidation from self loading on saturated sediments. Pingos can rupture from bursting of the sub-pingo water lens. Otherwise, pingo failure is at the top and periphery. Hydraulic fracturing is probably important in some pingo failures. Water loss from sub-pingo water lenses causes subsidence with the subsidence pattern being the mirror image of the growth pattern; i.e. greatest subsidence at the top. Small peripheral bulges may result from subsidence. Old pingos collapse from exposure of the ice core to melting by overburden rupture, by mass wasting, and by permafrost creep of the sides.

Active surface faulting or landsliding in the Lower Tagus Valley (Portugal)? A solved controversy concerning the Vila Chã de Ourique site

The Lower Tagus Valley has experienced significant (M 6–7) historical seismicity, evidencing the presence of seismogenic faults. These are still deficiently known due to the low strain rates and the recent alluvial sedimentation of the Tagus River that buries most of the structures, though Paleoseismic evidence was allegedly found by a research team in the Tagus valley, at a site 60 km N of Lisbon, near Vila Chã de Ourique (VCO). According to this team, trenching at the VCO site exposed an active thrust fault, evidencing the surface rupture of a large earthquake that occurred in 1531. Our studies performed at this site, comprising field observations with a reappraisal of the trench outcrops previously excavated, borehole drilling, soil mechanics laboratory testing, and seismic reflection acquisition, pointed to the alternative interpretation that the outcropping structures are gravitational and not of tectonic origin. The interpretation of new outcrops crosscutting the structures exposed at the trenches, as well as newly acquired high-resolution seismic reflection data, definitely exclude the active thrust fault explanation and support a gravitational slip model for all the observed structures. Gravitational slip in the river bank slope was promoted by low shear strength clays and high pore water pressure coupled with slope toe river erosion. Gravitational slides must have occurred prior to development of the present sedimentation level of the Tagus alluvial plain, which was attained in the last few thousand years as indicated by borehole data and estimations of sedimentation rates.

Analysis on Excess Pore Water Pressure Caused by Prestressed Concrete Pipes Construction in Saturated Clay Ground

Prestressed concrete pipes construction by hammer cause high excess pore water pressure in deep soft soils because Soil disturbance by violent and poor permeability of soft soil. Taking the typical soft ground in passenger special line from Hang Zhou to Ning Bo as the engineering example, the in-situ measuring of the excess pore water pressure in saturated clay ground during the construction of the piles was carried out, and the comparison analysis with the solutions from Vesic theory was also done. The changing rules of excess pore water pressure and its influence range during the sinking of the piles were studied, which would provide an important basis for the design and construction of the similar projects.

Features and sealing mechanism of shallow biogenic gas in incised valley fills (the Qiantang River, eastern China): A case study

Late Quaternary shallow biogenic gas reservoirs have been discovered and exploited in the Qiantang River (QR) estuary area, eastern China. The fall of global sea level during the Last Glacial Maximum resulted in the formation of the QR incised valley. From bottom to top, the incised valley successions can be grouped into four sedimentary facies: river channel facies, floodplain–estuarine facies, estuarine-shallow marine facies, and estuarine sand bar facies. All commercial biogenic gas pools occur in floodplain–estuarine sand bodies of the QR incised valley and its branches. The deeply incised valleys provided favorable conditions for the generation and accumulation of shallow biogenic gas. The clay beds that serve as the direct cap beds of the gas pools are mostly restricted within the QR incised valley, with burial depths ranging from 30 to 80 m, remnant thicknesses of 10–30 m, and porosities of 42.2–62.6%. In contrast, the mud beds cover the whole incised valley and occur as indirect cap beds, with burial depths varying from 5 to 35 m, thicknesses of 10–20 m, and porosities of 50.6–53.9%. The pore-water pressures of clay and mud beds are higher than that of sand bodies, and the difference can be as much as 0.48 MPa. The pore-water pressures of clay or mud beds can exceed the total pore-water pressure and gas pressure of underlying sand reservoirs. Shallow biogenic gas can be completely sealed by the clay and mud beds, which have higher pore-water pressure. The direct cap beds have better sealing ability than the indirect cap beds. Generally, the pore-water pressure dissipation time of clay and mud beds is conspicuously longer than that of sand beds. This indicates that the clay and mud beds have worse permeability and better sealing ability than the sand beds. However, once the gas enters the sand lenses, the pore-water pressure cannot release efficiently.

Formation of submarginal and proglacial end moraines: implications of ice‐flow mechanism during the 1963–64 surge of Brúarjökull, Iceland

The morphology, sedimentology and architecture of an end moraine formed by a ∼9 km surge of Brúarjökull in 1963–64 are described and related to ice‐marginal conditions at surge termination. Field observations and accurate mapping using digital elevation models and high‐resolution aerial photographs recorded at surge termination and after the surge show that commonly the surge end moraine was positioned underneath the glacier snout by the termination of the surge. Ground‐penetrating radar profiles and sedimentological data reveal 4–5 m thick deformed sediments consisting of a top layer of till overlying gravel and fine‐grained sediments, and structural geological investigations show that the end moraine is dominated by thrust sheets. A sequential model explaining the formation of submarginal end moraines is proposed. The hydraulic conductivity of the bed had a major influence on the subglacial drainage efficiency and associated porewater pressure at the end of the surge, thereby affecting the rates of subglacial deformation. High porewater pressure in the till decreased its shear strength and raised its strain rate, while low porewater pressure in the underlying gravel had the opposite effect, such that the gravel deformed more slowly than the till. The principal velocity component was therefore located within the till, allowing the glacier to override the gravel thrust sheets that constitute the end moraine. The model suggests that the processes responsible for the formation of submarginal end moraines are different from those operating during the formation of proglacial end moraines.

Pore Water Pressure Contribution to Debris Flow Mobility

Problem statement: Debris flows are very to extremely rapid flows of saturated granular soils. Two main types of debris flow are generally recognized: Open slope debris flows and channelized debris flows. The former is the results of some form of slope failures, the latter can develop along preexisting stream courses by the mobilization of previously deposited debris blanket. The problem to be addressed is the influence of the mode of initiation on the subsequent mechanism of propagation. In particular the role of pore water pressure on debris flow mobility in both types was debated. Approach: Laboratory flume experiments were set up in order to analyze the behavior of debris flows generated by model sand slope failures. Failures were induced in sand slopes by raising the water level by seepage from a drain located at the top end of the flume, and by rainfall supplied by a set of pierced plastic pipes placed above the flume. Video recordings of the tests were performed to analyze debris flow characteristics. Results: In all the tests the sand water mixture flows were unsteady and non uniform and sand deposition along the channel bed was a relevant phenomenon. The flows were characterized by a behavioral stratification of the sand water mixture along the flow depth. Back analyzed pore water pressure were just in excess to the hydrostatic condition. The reliability of the experimental results was checked by comparison with other flume experiment data. Conclusion: Debris flow behavior was influenced by the mode of initiation, the inclination of the channel and grain size of the soils. These factors affected the attained velocities and the pore water pressure values. The mobility of debris flows was not always enhanced by high excess pore water pressure values.

Internal soil moisture and piezometric responses to rainfall-induced shallow slope failures

Better knowledge regarding internal soil moisture and piezometric responses in the process of rainfall-induced shallow slope failures is the key to an effective prediction of the landslide and/or debris flow initiation. To this end, internal soil moisture and piezometric response of 0.7-m-deep, 1.5-m-wide, 1.7-m-high, and 3.94-m-long semi-infinite sandy slopes rested on a bi-linear impermeable bedrock were explored using a chute test facility with artificial rainfall applications. The internal response time defined by the inflection point of the soil moisture and piezometric response curves obtained along the soil–bedrock interface were closely related to some critical failure states, such as the slope toe failure and extensive slope failures. It was also found that the response times obtained at the point of abrupt bedrock slope decrease can be used as indicators for the initiation of rainfall-induced shallow slope failures. An investigation of spatial distributions of soil water content, ω (or degrees of saturation, S r ), in the slope at critical failure states shows that the 0.2 m – below – surface zone remains unsaturated with S r ≒ 40–60%, regardless of their distances from the toe and the rainfall intensity. Non-uniform distributions of ω (or S r ) along the soil–bedrock interface at critical failure states were always associated with near-saturation states ( S r ≒ 80–100%) around the point of bedrock slope change or around the transient ‘toe’ upstream of the slumped mass induced by the retrogressive failure of the slope. These observations suggest the important role of the interflow along the soil–bedrock interface and the high soil water content (or high porewater pressure) around the point of bedrock slope deflection in the rainfall-induced failure of sandy slopes consisting of shallow impermeable bedrocks. The present study proposes an ‘internal response time’ criterion to substantiate the prediction of rainfall-induced shallow slope failures. It is believed that the ‘internal response time’ reflects the overall characteristics of a slope under rainfall infiltration and can be as useful as the conventional meteorology-based threshold times. The ‘internal response time’ theory can be generalized via numerical modeling of slope hydrology, slope geology and slope stability in the future.

新潟地域の大規模地すべりと異常高圧熱水系

High salinity Na-Cl-type geothermal waters have often been found in the anticlinal hilly terrains and landslide-prone areas of Niigata Prefecture by boring to depths of more than 1,000 meters. These fluid pressure gradients are much higher than the hydrostatic pressure gradient and approach the lithostatic pressure gradient with increasing depth. The geothermal waters in the Matsunoyama area, Tokamachi City, have the highest orifice temperature in Niigata Prefecture. Eight geothermal water wells in this area were drilled along the anticlinal axis of a nearby hilltop or higher breast of the Matsunoyama dome and ranged in depth from 170 to 1,170 meters and in temperature from 35 to 95°C. For example, the Takanoyu-1 geothermal water well is only 170 meters in depth but has an orifice temperature of 90°C. These waters show geyser action associated with methane gas, and typically have very high salinity with considerable amounts of chloride. Hydrogen and oxygen isotope values and chloride concentration of approximately 9,000mg/L suggest that the origin of the waters is altered fossil seawater trapped in organic-matter-bearing sedimentary rocks. The temperature and depth of the primary reservoir are estimated to be 139°C and 3,000 to 4,000 meters, respectively, using a Li-Mg geothermometer and the mean geothermal gradient of 30-40°C/km in the Niigata sedimentary basin. Na-Cl-type groundwaters emerged from several landslides located in the Higashi-kubiki and Naka-kubiki areas including the Matsunoyama area. Well loggings were carried out to profile the electric conductivity and hydrochemistry of groundwater in the Utsunomata landslide in the neighborhood of the Matsunoyama area. Profiles in the active landslide mass showed sharp increases of the electric conductivity and the NaCl components at around the depth of the sliding surface. In contrast, no significant variations of the profiles were recognized in the inactive landslide mass. Na-Cl-type groundwaters are formed by mixing deep Na-Cl-type geothermal waters with meteoric groundwaters. These phenomena suggest that the geothermal water injection into shallow aquifers in landslide mass generates a partially high pore water pressure around the sliding surface and causes landslides.

Large scale failure of the external waste dump at the “South Field” lignite mine, Northern Greece

This paper presents the failure process of the external waste dump of the South Field Mine, the major open pit mine in Greece. The waste materials of the mine were deposited in three phases, forming an average inclination slope 10% and a total height of 110 m from the ground surface. The failure occurred when the third phase of the deposit was initiated. The high moisture content of the waste materials and their deposition over a spring, choking its flow, had as a result the development of high pore water pressure in clayey and marly materials in the base of the deposit. As a consequence, a large scale slope failure incident occurred. The landslide involved the mobilization of waste material in the order of 40 Mm 3, while the material that moved outside the boundaries of the waste dump was in the order of 2.5 Mm 3. The stability of the waste dump was investigated using the limit equilibrium analysis and different types of models. Limit equilibrium analyses were performed using different methods and considering the clay layer of small shear resistance that exists in the base of the deposit. They do not indicate activation of failure mechanism, only that there is a combination of high pore water pressure that developed in the deposit because the covering of the spring with the clayey materials of the dump.

Stability of highway embankments constructed on sloping ground against translational failure

A translational failure of a highway embankment constructed on sloping ground may occur either in the mode of overall instability or in the mode of local instability. The stability analysis of the first mode is based on the assumption that the whole cross-section of the embankment will slide along the inclined base surface, whilst the second mode is based on the assumption of Rankine's active state of stress. In this paper the determination of the prevalent mode of failure – overall or local – is provided via a chart derived from force polygon analysis, with the dimensionless parameter, c′/γH, and the effective friction angle, φ′, as its axes. Furthermore, the determination of the most probable failure plane in the cross-section of the embankment is attempted and additionally the role of the cohesion in the stability is discussed. Finally, an estimation of the amplitude of failure at the road surface in the case of local instability is given. A confirmation of the aforementioned was achieved through case studies of highway embankments that have failed as a consequence of water infiltration and the development of high pore water pressures. A comparison between the local and the respective overall instability safety factor is given.

Pore Water Pressure as a Trigger of Shallow Landslides in the Western Ghats of Kerala, India: Some Preliminary Observations from an Experimental Catchment

The Western Ghats mountain chain of Kerala, India, is prone to landslides mainly caused by anthropogenic disturbances and very high rainfall amounts. Here, some initial observations on the apparent relationship among pore water pressure fluctuations, rainfall characteristics, and landslide initiation are presented based on monitoring in an experimental catchment in the upper Tikovil River basin. On June 21 and 22, 2007, continuous rain fell for over 10 hours with a total precipitation of 147 mm, causing three shallow landslides in the catchment. Measurements using piezometers in three hollows of the catchment indicate that the rain spell resulted in the development of high pore water pressure from the beginning of the storm that persisted through the time of occurrence of shallow landslides. The pore water pressure patterns in these monitored hollows are possible representatives of the pore water pressure pattern in the hollows where the landslides initiated. This similarity of response pattern enables such data to be used for the calibration and validation of physically based slope hydrology models coupled with slope stability models.

Slope failures and their response to rainfall intensity: an example from Co. Antrim, Northern Ireland, July 2007

ABSTRACTIn 2007 Northern Ireland had the wettest June (154.5mm) on instrumental record, surpassing the previous record of 147mm for June 1931. On 16 July, 23mm hr-1 was recorded over southern and eastern areas of the Antrim Plateau. This produced local flooding in several places in Northern Ireland. However, only minor, near-surface slope failures occurred, even on the steep slopes of the Antrim coast. Those that did occur were only a minor impediment to traffic flow on the Antrim coast road. At the Minnis North mud flow-slide area, no slope failure resulted from this storm, despite the site having a long-term record of substantial failures. Flowside failure requires the development of high pore water pressures, but such pressures are only achieved with wet antecedent conditions, and are rarely produced by single, intense storm events. This observation illustrates the difficulty of using weather patterns to predict mechanically complex slope failures.