Cone Penetration Test (CPT or CPTu) is commonly used for estimating soil types and also for the g... more Cone Penetration Test (CPT or CPTu) is commonly used for estimating soil types and also for the geotechnical design of pile foundation. However, the level of agreement between the CPT-based soil types and the traditional identification of soil types based on samples may vary significantly; and it is not clearly understood if this variation has any sort of relationship with the CPT-based pile design. To investigate into this area, a ground investigation trial was carried out at six different locations as part of a highway scheme in East of England. At each location the trial comprised one CPTu adjacent to one borehole (BH) with conventional sampling and laboratory testing. The soil types were estimated from the CPTs and compared with the boreholes findings, and the levels of correlation between them were established. Similarly, the ultimate bearing capacity of a typical bored pile based on the CPTs and on the BHs were calculated and compared. Despite the variable level of disagreemen...
The efficiency of bio self-healing of pre-cracked mortar specimens incubated in sand was investig... more The efficiency of bio self-healing of pre-cracked mortar specimens incubated in sand was investigated. The investigation examined the effect of soil pH representing industrially recognised classes of exposure, ranging from no risk of chemical attack (neutral pH ≈ 7) to very high risk (pH ≈ 4.5). Simultaneously, the soil was subjected to fully and partially saturated cycles for 120 days to resemble groundwater-level fluctuation. Bacillus subtilis with nutrients were impregnated into perlite and utilised as a bacterial healing agent. The healing agent was added to half of the mortar specimens for comparison purposes. Mineral precipitations were observed in both control and bio-mortar specimens, and the healing products were examined by SEM–EDX scanning. The healing ratio was evaluated by comparing (1) the repair rate of the crack area and (2) by capillary water absorption and sorptivity index—before and after incubation. The results indicated that bacteria-doped specimens (bio-mortar)...
In the Federal District of Brazil, groundwater extraction is challenged by fractured aquifers wit... more In the Federal District of Brazil, groundwater extraction is challenged by fractured aquifers with difficulty in identification of hydraulic traps and significant uncertainty in the estimation of recharge potential. This study aims to optimize the demarcation of new locations of tubular wells by the aid of geophysical investigation. In the first stage of this study, the total exploitable amount of groundwater were calculated from the information of the physical environment and the existing wells. Second, electrical resistivity tomography (ERT) method was carried out on the selected sites – based on their surficial characteristics. The possible hydraulic traps (where groundwater might exist) were identified from the inversion of the resistivity measured by the dipole–dipole array and from the delineation of the resultant conducting zones (including the weathered rocks and fractures). Using this approach, we predicted the position and number of tubular wells required and ranked them a...
Reliable characterization of the karst system is essential for risk assessment where many associa... more Reliable characterization of the karst system is essential for risk assessment where many associated hazards (e.g., cover-collapse dolines and groundwater pollution) can affect natural and built environments, threatening public safety. The use of multiple geophysical approaches may offer an improved way to investigate such cover-collapse sinkholes and aid in geohazard risk assessments. In this paper, covered karst, which has two types of shallow caves (vadose and fluvial) located in Tarimba (Goias, Brazil), was investigated using various geophysical methods to evaluate their efficiency in the delineation of the geometry of sediments filled sinkhole. The methods used for the investigation were Electrical Resistivity Tomography (ERT), Seismic Refraction Survey (SRS), Seismic Refraction Tomography (SRT) and the Very Low Frequency Electromagnetic (VLF-EM) method. The study developed several (2D) sections of the measured physical properties, including P-wave velocity and electrical resis...
Landslides can substantially impact the fluvial systems, which is why the continuous mapping of t... more Landslides can substantially impact the fluvial systems, which is why the continuous mapping of their extent, evolution and stability assessment is crucial. However, in such environments, material identification (e.g. colluvium) and subsurface characterization by the methods used for geologic mapping and geotechnical investigation is often a challenging task. Thus, these classical invasive methods may benefit from geophysical techniques to enable and enhance our understanding of the subsurface in these areas. To examine such integrated approach, Multi-Channel Analysis of Surface Waves (MASW) combined with Electrical Resistivity Tomography (ERT) were applied on a geomorphologically active fluvial valley in Sobradinho (the Federal District of Brazil). The subsurface materials showed a specific range of resistivity values as dry soil, saprolite, and landslide slip surface. The 1D shear wave velocity (Vs) model showed an increasing trend of Vs with depth at a location away from the landslide mass, while the longitudinal profile (over the landslide) showed an anomalous change in Vs (~ 250 to 400 m/sec). Based on the existing information about the landslide, the ERT appeared to be an effective method over MASW. This study shows how the integration of geophysical data with the geological and geotechnical investigation helps to obtain a more realistic or unambiguous model of the subsurface.
Mudflow is often associated with seismic activities. The present study applied a seismic based de... more Mudflow is often associated with seismic activities. The present study applied a seismic based detection of the surface waves generated by the mudflow of Brumadinho dam collapse using records of Brazilian Seismographic Network. The signal envelope and time-frequency spectrograms of the mudflow signals were used in the analysis. As a result, the mudflow signals were successfully detected from the data recorded at a nearby seismic station. The findings of this study provide a good basis for future research to develop a flood early warning system based on cost-effective, remote and contentious seismic monitoring approaches.
The use of geophysical characterization of karst systems can provide an economical and non-invasi... more The use of geophysical characterization of karst systems can provide an economical and non-invasive alternative for extracting information about cavities, sinkholes, pathways for water infiltration as well as the degree of karstification of underlying carbonate rocks. In the present study, three geophysical techniques, namely, Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT) and Very Low Frequency Electromagnetic (VLFEM) methods were applied at three different locations in relation to fluvial karst, which is listed as an environmentally sensitive area in Rio Vermelho, MambaÃ, Goiás, Brazil. In the data acquisition phase, the GPR, direct-current (DC) resistivity and VLFEM profiles were obtained at the three locations in the area. Data were analyzed using commonly adopted processing workflows. The GPR results showed a well-defined lithology of the site based on the amplitude of the signal and radar typologies. On the other hand, the inverted resistivity cross-se...
Geohazard Assessment of Landslides in South Brazil: Case Study
Geotechnical and Geological Engineering
Slope instability phenomena such as mudslides represent a major geohazard in Brazil, which has ca... more Slope instability phenomena such as mudslides represent a major geohazard in Brazil, which has caused devastation in many states and affected the lives of people, particularly in self-built settlements on steep slopes. This paper presents and discusses slope stability issues encountered in Caxias do Sul in the State of Rio Grande do Sul, which exemplifies the existing situation of landslide risk assessment in southern Brazil. Local geology and ground conditions of the area in relation to slope instability were reviewed and gaps in information required for mitigating risk were identified, such as inadequate geotechnical information and lack of full inspection and continuous monitoring of active landslides. Although risk assessment has been developed for the city and regarded as a fundamental management tool in the mitigation of landslide hazards, the study showed that the risk assessment works are outdated and not effectively considered for the development of the city. With significant unplanned urban expansion (where houses have been self-built on very steep terrains without geotechnical assessment of the ground and slope conditions), new geohazard mapping is essentially required. Several key recommendations were provided for mitigating the destructive effect of landslides and improving their management in mountainous urban settings.
The provision of suitable incubation environments is vital for successful implementation of bio s... more The provision of suitable incubation environments is vital for successful implementation of bio self-healing concrete (bio-concrete). We investigated the effect of soil incubation to examine if the self-healing process can be activated in comparison with the conventional incubation environment (water). The data was collected from laboratory-scale experiments conducted on mortar specimens. The mortar was impregnated with Bacillus subtilis and this bacteria was encapsulated in calcium alginate for protection from the production process. The mortar specimens were mechanically cracked and then incubated within fine-grained fully saturated natural soil for about 4 weeks. The cracks were inspected before and after incubation by light microscopy to evaluate the healing ratio. The mineral precipitations on crack surfaces were examined by Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray Spectrometry (EDX). The data reflects the efficiency of bio-concrete for certain structures such as tunnels and deep foundation, where concrete elements are exposed to ground conditions.
Reactivation of a landslide is usually accompanied by microseismic signals emitted from the defor... more Reactivation of a landslide is usually accompanied by microseismic signals emitted from the deforming soil mass. The reproduction of similar signals in a physical model test conducted under control conditions can allow researchers to explore and test such complicated signals to improve the prediction of full-scale failure. The present study investigates the similarity between the slidequakes (microseismicity) naturally emitted from an existing colluvial landslide (Sobradinho, Brazil) in response to rainfalls and the emissions generated by a pullout test of an expander body (EB) pile in tropical soil under controlled conditions. The microseismic signals emitted from both experimental sites (i.e. the landslide and the EB pile test) were recorded and compared. Data were acquired by mini-arrays of four short-period seismometers. For the signal nomenclature, a typological scheme was adopted, in which sonograms/spectral contents of the signals were used. As a result, short duration microseismic signals were observed during the pullout test. In contrast, at the Sobradinho landslide, the testing detected signals of different characteristics whose source mechanisms have remained ambiguous, mainly because of the short duration of the data campaigns. However, at the landslide, propagating events were observed that might be attributed to the energies generated by the river bedload during the heavy rains. The present study offers some insight into the pre-collapse dynamic behavior of unstable slopes in clayey formations.
The application of geophysical monitoring technologies may offer an opportunity to understand the... more The application of geophysical monitoring technologies may offer an opportunity to understand the dynamic of slopes in response to factors triggering their instability. In this study, Ambient Noise Interferometry was used as a monitoring approach on a man-made reduced-scale vertical slope and on a natural-scale landslide in Sobradinho (Brazil), under the influence of mechanical stress and rainfall, respectively. For both experiments, we adopted similar data acquisition system and processing workflow. After preprocessing of ambient seismic noise, the time-lapse changes were determined in terms of relative velocity changes using the moving window cross spectral technique. For the vertical slope, terrestrial laser scanning was also performed to detect crack or fissure generation. The prototype experiment results showed a decreasing trend of relative velocity changes and reached a minimum value of-0.6% at the end of the experiment. No change was detected on the digital elevation model that was computed from terrestrial laser scanning images, due to the absence of centimeter scale superficial fissures. At natural scale (Sobradinho landslide), no significant variation in relative velocity changes was detected for the rainy and non-rainy days, mainly because of the inadequate change in the degree of saturation, which was found within a relatively short period of data acquisition.
Structures built on shallow foundations in expansive clay, where vegetation and weather condition... more Structures built on shallow foundations in expansive clay, where vegetation and weather conditions can significantly reduce the moisture content, must overcome the risk associated with excessive desiccation conditions, such as shrinkage and settlement. For many existing structures, removal of trees may not necessarily be an effective solution, as it can cause swelling and heave in the long term. This study explores a system that could be operated during prolonged drought periods to rehydrate and neutralise the negative pore pressures of expansive clay, avoiding the development of excessive desiccation. Electrokinetics is a proven method that has increasingly been adopted for dewatering and consolidation of fine-grained soils. The hypothesis presented is to reverse the electrokinetics process by extracting water from a saturated stratum below the groundwater level and force it into the 'early-stage' desiccated area, accelerating rehydration and reducing suction. The theory was examined by a laboratory model using moderately expansive clay. After draining the soil for 23 days to reach a moderate desiccation state, water was allowed into the lower part of the soil while applying the EK treatment using nine electrodes, placed in a radial pattern and inserted 110 mm into the soil with approximately 30% of their lengths below the water level. As a result of the electro-osmotic process, the average moisture content increased in the model by more than twofold within 8 h. The suction measurement (taken in the middle of the desiccated area) showed an initial slow response followed by fast and consistent reduction rate, where suction dropped by 93% within 5 h and ultimately down to 1 kPa at the end of the treatment. This paper offers some insight into the factors controlling the proposed system and provides a good basis for future research to manage the risks associated with desiccation of expansive soils.
International Journal of Rock Mechanics and Mining Sciences
Time-dependent characterisation of rocks for the entire strain range (i.e. up to and beyond the y... more Time-dependent characterisation of rocks for the entire strain range (i.e. up to and beyond the yield point, where rocks are expected to be fractured) have received considerable attention for improving the long-term stability of deep underground openings. Although extensive experimental studies have been carried out on creep of different types of rocks, very limited studies exist, which investigate intact as well as fractured rock samples taken from the same type of rock. In this paper, the time-dependent behaviour of muddy siltstone was investigated to determine and compare creep properties of intact and fractured rock samples. A series of multistage uniaxial and triaxial creep tests were conducted on the rock samples at room temperature. In addition, multistage triaxial testing was conducted on the rock (intact and fractured) to determine the instantaneous (short-term) stiffness and explore its correlation with creep properties. All stain curves showed an initial instantaneous strain followed by two phases of timedependent strain including transient creep phase (particularly for the first loading stage) and a steady state creep phase. The results indicate that both the instantaneous and creep strain are proportional to the deviatoric stress and confining pressure. This is clearly evident in the fractured rock samples, where larger deviatoric stress resulted in an increased creep strain and strain rate. The relationship between axial strain and time was successfully fitted to Burgers creep model. In comparison with the intact rock, creep parameters (of the Burgers model) for the fractured rock were found to be significantly smaller, corresponding to the larger creep deformation and steady-state creep rate experienced by the fractured rock samples. Despite this difference between the intact and fractured rock samples, the study showed a considerable correlation between the creep parameters of both types of rock samples and their instantaneous elastic modulus (obtained at typical confining pressures). Regression analysis revealed that creep parameters could be reasonably estimated from instantaneous elastic modulus using an exponential function. Furthermore, based on the experimental findings, an improved characterisation of timedependent properties was proposed. We believe this approach provides a good basis for future research to enhance geotechnical modelling of long-term stability of abandoned mines as well as for the application of underground disposal of radioactive waste and oil and gas storage.
Managing Geotechnical Risks in Civil Engineering Projects
All civil engineering projects (buildings, roads, bridges, dams, tunnels and water tanks ..) are ... more All civil engineering projects (buildings, roads, bridges, dams, tunnels and water tanks ..) are constructed on , with, or in the ground. Engineers are required to identify and avoid the major risks posed by ground conditions. This presentation provide an overall view of risks posed by ground giving examples from real case histories.
Assessment of a Bridge Pier Pile Foundation Subjected to Bearing Replacement
This paper reports on the geotechnical aspects of Highway maintenance work, which has been planne... more This paper reports on the geotechnical aspects of Highway maintenance work, which has been planned recently for A14 Orwell Bridge, Pier 5. The pier is (one of nineteen) supported by a group of 50 bored piles founded in Chalk. Because the bearings will be replaced for one side of the pier resulting in additional forces from a temporary supporting system erected on one side of the pile cap, a geotechnical assessment of the pier foundation has been required. The investigations has included the back analysis of a pile load test using PLAXIS to evaluate the engineering parameters of the Chalk and the pile bearing capacity calculations, and hence helped to reduce the uncertainty usually encountered in the estimation of skin friction in Chalk. To check for any potential for overstressing or excessive rotation, the load deformation response of the pile group under the new working load conditions was analysed using two different softwares: PIGLET and REPUTE. In general, the paper provides si...
Cone Penetration Test (CPT or CPTu) is commonly used for estimating soil types and also for the g... more Cone Penetration Test (CPT or CPTu) is commonly used for estimating soil types and also for the geotechnical design of pile foundation. However, the level of agreement between the CPT-based soil types and the traditional identification of soil types based on samples may vary significantly; and it is not clearly understood if this variation has any sort of relationship with the CPT-based pile design. To investigate into this area, a ground investigation trial was carried out at six different locations as part of a highway scheme in East of England. At each location the trial comprised one CPTu adjacent to one borehole (BH) with conventional sampling and laboratory testing. The soil types were estimated from the CPTs and compared with the boreholes findings, and the levels of correlation between them were established. Similarly, the ultimate bearing capacity of a typical bored pile based on the CPTs and on the BHs were calculated and compared. Despite the variable level of disagreemen...
The efficiency of bio self-healing of pre-cracked mortar specimens incubated in sand was investig... more The efficiency of bio self-healing of pre-cracked mortar specimens incubated in sand was investigated. The investigation examined the effect of soil pH representing industrially recognised classes of exposure, ranging from no risk of chemical attack (neutral pH ≈ 7) to very high risk (pH ≈ 4.5). Simultaneously, the soil was subjected to fully and partially saturated cycles for 120 days to resemble groundwater-level fluctuation. Bacillus subtilis with nutrients were impregnated into perlite and utilised as a bacterial healing agent. The healing agent was added to half of the mortar specimens for comparison purposes. Mineral precipitations were observed in both control and bio-mortar specimens, and the healing products were examined by SEM–EDX scanning. The healing ratio was evaluated by comparing (1) the repair rate of the crack area and (2) by capillary water absorption and sorptivity index—before and after incubation. The results indicated that bacteria-doped specimens (bio-mortar)...
In the Federal District of Brazil, groundwater extraction is challenged by fractured aquifers wit... more In the Federal District of Brazil, groundwater extraction is challenged by fractured aquifers with difficulty in identification of hydraulic traps and significant uncertainty in the estimation of recharge potential. This study aims to optimize the demarcation of new locations of tubular wells by the aid of geophysical investigation. In the first stage of this study, the total exploitable amount of groundwater were calculated from the information of the physical environment and the existing wells. Second, electrical resistivity tomography (ERT) method was carried out on the selected sites – based on their surficial characteristics. The possible hydraulic traps (where groundwater might exist) were identified from the inversion of the resistivity measured by the dipole–dipole array and from the delineation of the resultant conducting zones (including the weathered rocks and fractures). Using this approach, we predicted the position and number of tubular wells required and ranked them a...
Reliable characterization of the karst system is essential for risk assessment where many associa... more Reliable characterization of the karst system is essential for risk assessment where many associated hazards (e.g., cover-collapse dolines and groundwater pollution) can affect natural and built environments, threatening public safety. The use of multiple geophysical approaches may offer an improved way to investigate such cover-collapse sinkholes and aid in geohazard risk assessments. In this paper, covered karst, which has two types of shallow caves (vadose and fluvial) located in Tarimba (Goias, Brazil), was investigated using various geophysical methods to evaluate their efficiency in the delineation of the geometry of sediments filled sinkhole. The methods used for the investigation were Electrical Resistivity Tomography (ERT), Seismic Refraction Survey (SRS), Seismic Refraction Tomography (SRT) and the Very Low Frequency Electromagnetic (VLF-EM) method. The study developed several (2D) sections of the measured physical properties, including P-wave velocity and electrical resis...
Landslides can substantially impact the fluvial systems, which is why the continuous mapping of t... more Landslides can substantially impact the fluvial systems, which is why the continuous mapping of their extent, evolution and stability assessment is crucial. However, in such environments, material identification (e.g. colluvium) and subsurface characterization by the methods used for geologic mapping and geotechnical investigation is often a challenging task. Thus, these classical invasive methods may benefit from geophysical techniques to enable and enhance our understanding of the subsurface in these areas. To examine such integrated approach, Multi-Channel Analysis of Surface Waves (MASW) combined with Electrical Resistivity Tomography (ERT) were applied on a geomorphologically active fluvial valley in Sobradinho (the Federal District of Brazil). The subsurface materials showed a specific range of resistivity values as dry soil, saprolite, and landslide slip surface. The 1D shear wave velocity (Vs) model showed an increasing trend of Vs with depth at a location away from the landslide mass, while the longitudinal profile (over the landslide) showed an anomalous change in Vs (~ 250 to 400 m/sec). Based on the existing information about the landslide, the ERT appeared to be an effective method over MASW. This study shows how the integration of geophysical data with the geological and geotechnical investigation helps to obtain a more realistic or unambiguous model of the subsurface.
Mudflow is often associated with seismic activities. The present study applied a seismic based de... more Mudflow is often associated with seismic activities. The present study applied a seismic based detection of the surface waves generated by the mudflow of Brumadinho dam collapse using records of Brazilian Seismographic Network. The signal envelope and time-frequency spectrograms of the mudflow signals were used in the analysis. As a result, the mudflow signals were successfully detected from the data recorded at a nearby seismic station. The findings of this study provide a good basis for future research to develop a flood early warning system based on cost-effective, remote and contentious seismic monitoring approaches.
The use of geophysical characterization of karst systems can provide an economical and non-invasi... more The use of geophysical characterization of karst systems can provide an economical and non-invasive alternative for extracting information about cavities, sinkholes, pathways for water infiltration as well as the degree of karstification of underlying carbonate rocks. In the present study, three geophysical techniques, namely, Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT) and Very Low Frequency Electromagnetic (VLFEM) methods were applied at three different locations in relation to fluvial karst, which is listed as an environmentally sensitive area in Rio Vermelho, MambaÃ, Goiás, Brazil. In the data acquisition phase, the GPR, direct-current (DC) resistivity and VLFEM profiles were obtained at the three locations in the area. Data were analyzed using commonly adopted processing workflows. The GPR results showed a well-defined lithology of the site based on the amplitude of the signal and radar typologies. On the other hand, the inverted resistivity cross-se...
Geohazard Assessment of Landslides in South Brazil: Case Study
Geotechnical and Geological Engineering
Slope instability phenomena such as mudslides represent a major geohazard in Brazil, which has ca... more Slope instability phenomena such as mudslides represent a major geohazard in Brazil, which has caused devastation in many states and affected the lives of people, particularly in self-built settlements on steep slopes. This paper presents and discusses slope stability issues encountered in Caxias do Sul in the State of Rio Grande do Sul, which exemplifies the existing situation of landslide risk assessment in southern Brazil. Local geology and ground conditions of the area in relation to slope instability were reviewed and gaps in information required for mitigating risk were identified, such as inadequate geotechnical information and lack of full inspection and continuous monitoring of active landslides. Although risk assessment has been developed for the city and regarded as a fundamental management tool in the mitigation of landslide hazards, the study showed that the risk assessment works are outdated and not effectively considered for the development of the city. With significant unplanned urban expansion (where houses have been self-built on very steep terrains without geotechnical assessment of the ground and slope conditions), new geohazard mapping is essentially required. Several key recommendations were provided for mitigating the destructive effect of landslides and improving their management in mountainous urban settings.
The provision of suitable incubation environments is vital for successful implementation of bio s... more The provision of suitable incubation environments is vital for successful implementation of bio self-healing concrete (bio-concrete). We investigated the effect of soil incubation to examine if the self-healing process can be activated in comparison with the conventional incubation environment (water). The data was collected from laboratory-scale experiments conducted on mortar specimens. The mortar was impregnated with Bacillus subtilis and this bacteria was encapsulated in calcium alginate for protection from the production process. The mortar specimens were mechanically cracked and then incubated within fine-grained fully saturated natural soil for about 4 weeks. The cracks were inspected before and after incubation by light microscopy to evaluate the healing ratio. The mineral precipitations on crack surfaces were examined by Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray Spectrometry (EDX). The data reflects the efficiency of bio-concrete for certain structures such as tunnels and deep foundation, where concrete elements are exposed to ground conditions.
Reactivation of a landslide is usually accompanied by microseismic signals emitted from the defor... more Reactivation of a landslide is usually accompanied by microseismic signals emitted from the deforming soil mass. The reproduction of similar signals in a physical model test conducted under control conditions can allow researchers to explore and test such complicated signals to improve the prediction of full-scale failure. The present study investigates the similarity between the slidequakes (microseismicity) naturally emitted from an existing colluvial landslide (Sobradinho, Brazil) in response to rainfalls and the emissions generated by a pullout test of an expander body (EB) pile in tropical soil under controlled conditions. The microseismic signals emitted from both experimental sites (i.e. the landslide and the EB pile test) were recorded and compared. Data were acquired by mini-arrays of four short-period seismometers. For the signal nomenclature, a typological scheme was adopted, in which sonograms/spectral contents of the signals were used. As a result, short duration microseismic signals were observed during the pullout test. In contrast, at the Sobradinho landslide, the testing detected signals of different characteristics whose source mechanisms have remained ambiguous, mainly because of the short duration of the data campaigns. However, at the landslide, propagating events were observed that might be attributed to the energies generated by the river bedload during the heavy rains. The present study offers some insight into the pre-collapse dynamic behavior of unstable slopes in clayey formations.
The application of geophysical monitoring technologies may offer an opportunity to understand the... more The application of geophysical monitoring technologies may offer an opportunity to understand the dynamic of slopes in response to factors triggering their instability. In this study, Ambient Noise Interferometry was used as a monitoring approach on a man-made reduced-scale vertical slope and on a natural-scale landslide in Sobradinho (Brazil), under the influence of mechanical stress and rainfall, respectively. For both experiments, we adopted similar data acquisition system and processing workflow. After preprocessing of ambient seismic noise, the time-lapse changes were determined in terms of relative velocity changes using the moving window cross spectral technique. For the vertical slope, terrestrial laser scanning was also performed to detect crack or fissure generation. The prototype experiment results showed a decreasing trend of relative velocity changes and reached a minimum value of-0.6% at the end of the experiment. No change was detected on the digital elevation model that was computed from terrestrial laser scanning images, due to the absence of centimeter scale superficial fissures. At natural scale (Sobradinho landslide), no significant variation in relative velocity changes was detected for the rainy and non-rainy days, mainly because of the inadequate change in the degree of saturation, which was found within a relatively short period of data acquisition.
Structures built on shallow foundations in expansive clay, where vegetation and weather condition... more Structures built on shallow foundations in expansive clay, where vegetation and weather conditions can significantly reduce the moisture content, must overcome the risk associated with excessive desiccation conditions, such as shrinkage and settlement. For many existing structures, removal of trees may not necessarily be an effective solution, as it can cause swelling and heave in the long term. This study explores a system that could be operated during prolonged drought periods to rehydrate and neutralise the negative pore pressures of expansive clay, avoiding the development of excessive desiccation. Electrokinetics is a proven method that has increasingly been adopted for dewatering and consolidation of fine-grained soils. The hypothesis presented is to reverse the electrokinetics process by extracting water from a saturated stratum below the groundwater level and force it into the 'early-stage' desiccated area, accelerating rehydration and reducing suction. The theory was examined by a laboratory model using moderately expansive clay. After draining the soil for 23 days to reach a moderate desiccation state, water was allowed into the lower part of the soil while applying the EK treatment using nine electrodes, placed in a radial pattern and inserted 110 mm into the soil with approximately 30% of their lengths below the water level. As a result of the electro-osmotic process, the average moisture content increased in the model by more than twofold within 8 h. The suction measurement (taken in the middle of the desiccated area) showed an initial slow response followed by fast and consistent reduction rate, where suction dropped by 93% within 5 h and ultimately down to 1 kPa at the end of the treatment. This paper offers some insight into the factors controlling the proposed system and provides a good basis for future research to manage the risks associated with desiccation of expansive soils.
International Journal of Rock Mechanics and Mining Sciences
Time-dependent characterisation of rocks for the entire strain range (i.e. up to and beyond the y... more Time-dependent characterisation of rocks for the entire strain range (i.e. up to and beyond the yield point, where rocks are expected to be fractured) have received considerable attention for improving the long-term stability of deep underground openings. Although extensive experimental studies have been carried out on creep of different types of rocks, very limited studies exist, which investigate intact as well as fractured rock samples taken from the same type of rock. In this paper, the time-dependent behaviour of muddy siltstone was investigated to determine and compare creep properties of intact and fractured rock samples. A series of multistage uniaxial and triaxial creep tests were conducted on the rock samples at room temperature. In addition, multistage triaxial testing was conducted on the rock (intact and fractured) to determine the instantaneous (short-term) stiffness and explore its correlation with creep properties. All stain curves showed an initial instantaneous strain followed by two phases of timedependent strain including transient creep phase (particularly for the first loading stage) and a steady state creep phase. The results indicate that both the instantaneous and creep strain are proportional to the deviatoric stress and confining pressure. This is clearly evident in the fractured rock samples, where larger deviatoric stress resulted in an increased creep strain and strain rate. The relationship between axial strain and time was successfully fitted to Burgers creep model. In comparison with the intact rock, creep parameters (of the Burgers model) for the fractured rock were found to be significantly smaller, corresponding to the larger creep deformation and steady-state creep rate experienced by the fractured rock samples. Despite this difference between the intact and fractured rock samples, the study showed a considerable correlation between the creep parameters of both types of rock samples and their instantaneous elastic modulus (obtained at typical confining pressures). Regression analysis revealed that creep parameters could be reasonably estimated from instantaneous elastic modulus using an exponential function. Furthermore, based on the experimental findings, an improved characterisation of timedependent properties was proposed. We believe this approach provides a good basis for future research to enhance geotechnical modelling of long-term stability of abandoned mines as well as for the application of underground disposal of radioactive waste and oil and gas storage.
Managing Geotechnical Risks in Civil Engineering Projects
All civil engineering projects (buildings, roads, bridges, dams, tunnels and water tanks ..) are ... more All civil engineering projects (buildings, roads, bridges, dams, tunnels and water tanks ..) are constructed on , with, or in the ground. Engineers are required to identify and avoid the major risks posed by ground conditions. This presentation provide an overall view of risks posed by ground giving examples from real case histories.
Assessment of a Bridge Pier Pile Foundation Subjected to Bearing Replacement
This paper reports on the geotechnical aspects of Highway maintenance work, which has been planne... more This paper reports on the geotechnical aspects of Highway maintenance work, which has been planned recently for A14 Orwell Bridge, Pier 5. The pier is (one of nineteen) supported by a group of 50 bored piles founded in Chalk. Because the bearings will be replaced for one side of the pier resulting in additional forces from a temporary supporting system erected on one side of the pile cap, a geotechnical assessment of the pier foundation has been required. The investigations has included the back analysis of a pile load test using PLAXIS to evaluate the engineering parameters of the Chalk and the pile bearing capacity calculations, and hence helped to reduce the uncertainty usually encountered in the estimation of skin friction in Chalk. To check for any potential for overstressing or excessive rotation, the load deformation response of the pile group under the new working load conditions was analysed using two different softwares: PIGLET and REPUTE. In general, the paper provides si...
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Papers by Omar Hamza