Solution to the Breach of the Dike of Keur Bara KAIRE, Located in the Commune of Notto Diobasse in the Department of Thiès, Senegal

This article studies the rupture of the Keur Bara KAIRE dike, located in the commune of Notto Diobasse in the department of Thiès in Senegal. The village is crossed by a stream which collects rainwater from the west to the east, following a natural slope. The overflow of this stream causes serious flooding, leading to the total cutting of the road and the isolation of the population. These floods had tragic consequences, resulting in two losses of human life. To regulate the water level, prevent flooding, and protect agricultural and urban areas from overflows, the Senegalese authorities initiated the project to build the Keur Bara KAIRE dike in 2004, but unfortunately, the latter gave way in 2017. The geotechnical analysis was carried out on samples taken from various points on the site, revealing that the terrain is mainly composed of fine sand and the embankment is made with clayey sand. Morphometric and hydrological investigations highlight that the watershed of the Keur Bara KAIRE dike covers an area of 3.72 km2, with a projected flow of 54.99 m3/s. The resizing of the dike revealed the following data: a length of 132 meters and a height of 3 meters. The spillway is 52.99 meters long with a reservoir height of 1.22 meters. The bay walls have a thickness of 50 cm and the embankments have a slope of 1/2 upstream and downstream. The stability calculation on the broken dike reveals a sliding safety factor (FSG) of 1.84 which complies with the standard and an overturning safety factor (FSR) of 0.13 which is not verified. The surface of the watershed which is equal to 3.72 km2, also the smallest height of precipitation is equal to 234.9 mm and the largest is 664.4 mm, according to the ORSTOM and CIEH methods for hydraulic calculations.

Seismic responses of high concrete face rockfill dams:A case study

Seismic responses of the Zipingpu concrete face rockfill dam were analyzed using the finite element method. The dynamic behavior of rockfill materials was modeled with a viscoelastic model and an empirical permanent strain model. The relevant parameters were obtained either by back analysis using the field observations or by reference to parameters of similar rockfill materials. The acceleration responses of the dam,the distribution of earthquake-induced settlement, and the gap propagation under the concrete slabs caused by the settlement of the dam were analyzed and compared with site investigations or relevant studies. The mechanism of failure of horizontal construction joints was also analyzed based on numerical results and site observations. Numerical results show that the input accelerations were considerably amplified near the top of the dam, and the strong shaking resulted in considerable settlement of the rockfill materials, with a maximum value exceeding 90 cm at the crest.As a result of the settlement of rockfill materials, the third-stage concrete slabs were separated from the cushion layer. The rotation of the cantilever slabs about the contacting regions, under the combined action of gravity and seismic inertial forces, led to the failure of the construction joints and tensile cracks appeared above the construction joints. The effectiveness and limitations of the so-called equivalent linear method are also discussed.

Numerical Analysis of Interaction Between Pile-Supported Pier and Bank Slope

Two and three-dimensional finite element analysis programs for pile-soil interaction are compiled. Duncan-Chang's Model is used. The construction sequence of the pier is modeled. The pile-soil interface element is used. The influence of the combination type of piles on the deformation of bank slope and pile behaviour is analyzed. Different designs of a pile-supported pier are compared thoroughly. Calculation results show that the stresses and displacements of the pile are directly related to the distance from the bank slope and the direction of inclination. An inclined prop pile set in the rear platform would remarkably reduce the stresses of piles and the displacement of the pier.

Centrifugal and field studies on water infiltration characteristics below canals under wetting-drying-freezing-thawing cycles

Seepage is one of the main causes for the deformation and instability of canal slopes in Xinjiang,China.In this study,centrifugal model tests under wetting-drying(WD)and wetting-drying-freezing-thawing(WDFT)cycles were performed to investigate the water infiltration characteristics below a canal.The results show that the shallow soil of the canal models was fully saturated in the wetting process.Compared with the canal model under the WD cycles,the canal model under the WDFT cycles had larger saturated areas and a higher degree of saturation below the canal top after each cycle,indicating that the freezing-thawing(FT)process in the WDFT cycles promoted the water infiltration behavior below the canal slope.The cracks on the surface of the canal model under the cyclic action of WDFT developed further and had a higher connectivity,which provided the conditions for slope instability from a transverse tensile crack running through the canal top.On this basis,a field test was conducted to understand the water infiltration distribution below a typical canal in Xinjiang,China,which also verified the accuracy of the centrifugal results.This study provides a preliminary basis for the maintenance and seepage treatment of canals in Xinjiang,China.

Fly Ash/Paraffin Composite Phase Change Material Used to Treat Thermal and Mechanical Properties of Expansive Soil in Cold Regions

Phase change materials(PCMs)can store large amounts of energy in latent heat and release it during phase changes,which could be used to improve the freeze-thaw performance of soil.The composite phase change material was prepared with paraffin as the PCM and 8%Class C fly ash(CFA)as the supporting material.Laboratory tests were conducted to reveal the influence of phase change paraffin composite Class C fly ash(CFA-PCM)on the thermal properties,volume changes and mechanical properties of expansive soil.The results show that PCM failed to establish a good improvement effect due to leakage.CFA can effectively adsorb phase change materials,and the two have good compatibility.CFA-PCM reduces the volume change and strength attenuation of the soil,and 8 wt.%PCM is the optimal content.CFA-PCM turns the phase change latent heat down of the soil and improves its thermal stability.CFA-PCM makes the impact small of freeze-thaw on soil pore structure damage and improves soil volume change and mechanical properties on a macroscopic scale.In addition,CFA-8 wt.%PCM treated expansive soil has apparent advantages in resisting repeated freeze-thaw cycles,providing a reference for actual engineering design.

Research on shape optimization of CSG dams

The multi-objective optimization method was used for shape optimization of cement sand and gravel （CSG） dams in this study. The economic efficiency, the sensitivities of maximum horizontal displacement and maximum settlement of the dam to water level changes, the overall stability, and the overall strength security were taken into account during the optimization process. Three weight coefficient selection schemes were adopted to conduct shape optimization of a dam, and the case studies lead to the conclusion that both the upstream-and downstream dam slope ratios for the optimal cross-section equal 1：0.7, which is consistent with the empirically observed range of 1：0.6 to 1;0.8 for the upstream and downstream dam slope ratios of CSG dams. Therefore, the present study is of certain reference value for designing CSG dams.

Prediction of plastic zone size around circular tunnels in non-hydrostatic stress field

This paper discusses the calculation of plastic zone properties around circular tunnels to rock-masses that satisfy the Hoek–Brown failure criterion in non-hydrostatic condition,and reviews the calculation of plastic zone and displacement,and the basis of the convergence–confinement method in hydrostatic condition.A two-dimensional numerical simulation model was developed to gain understanding of the plastic zone shape.Plastic zone radius in any angles around the tunnel is analyzed and measured,using different values of overburden(four states)and stress ratio(nine states).Plastic zone radius equations were obtained from fitting curve to data which are dependent on the values of stress ratio,angle and plastic zone radius in hydrostatic condition.Finally validation of this equation indicate that results predict the real plastic zone radius appropriately.

Gradation equation of coarse-grained soil and its applicability

Gradation equation is one way to describe the gradation of coarse-grained soil conveniently,exactly and quantitatively.With the gradation equation,the influence of gradation on the mechanical behaviors of coarse-grained soil can be expressed quantitatively.A new gradation equation with a parameter is proposed.The basic properties and applicability of the new equation are studied.The results show that the proposed equation has the applicability to express coarse-grained soil gradation(CSG),and the range of the parameter β is found to be 0<β<1.The value ofbdetermines the gradation curve shape.If β>0.5,the gradation curve is sigmoidal,otherwise the gradation curve is hyperbolic.For well graded gradations,the parameter has the value of 0.13<β<1.Several CSGs used in domestic and foreign earth-rockfill dams are probed,and the value of the parameterbfalls in the range of 0.18 to 0.97.The investigation of the range of β is of value to guide the design for CSG of earth-rockfill dam.

Influence of zeolite and cement additions on mechanical behavior of sandy soil

It is well known that the cemented sand is one of economic and environmental topics in soil stabilization. In this instance, a blend of sand, cement and other materials such as fiber, glass, nanoparticle and zeolite can be commercially available and effectively used in soil stabilization in road construction. However, the influence and effectiveness of zeolite on the properties of cemented sand systems have not been completely explored. In this study, based on an experimental program, the effects of zeolite on the characteristics of cemented sands are investigated. Stabilizing agent includes Portland cement of type II and zeolite. Results show the improvements of unconfined compressive strength （UCS） and failure properties of cemented sand when the cement is replaced by zeolite at an optimum proportion of 30% after 28 days. The rate of strength improvement is approximately between 20% and 78%. The efficiency of using zeolite increases with the increases in cement amount and porosity. Finally, a power function of void-cement ratio and zeolite content is demonstrated to be an appropriate method to assess UCS of zeolite-cemented mixtures.

Rock borehole shear tests in dam foundation of Xiangjiaba hydropower station

Xiangjiaba hydropowcr station is one of the complicated geological conditions of its dam foundation, parameters of rock masses are very important issues. To cascade power stations on the Jinsha River, China. Due to the evaluating the rock mass quality and determining the mechanical address these issues, several groups of rock borehole shear tests （RBSTs） were conducted on the black mudstone in the dam foundation of Xiangjiaba hydropower station in the second construction phase. Forty three groups of shear strengths of black mudstone samples were obtained from RBSTs, and the shear strength parameters （c and f） were calculated using the least squares method. In addition, the limitations and merits of RBST employed in the Xiangjiaba hydropower station were discussed. Test results indicate that the shear strength parameters obtained from RBST have a good correlation with the results from sotmd wave test in borehole. It is believed that RBST has a good adaptability and applicability in geotechnical engineering.

Caving performance through the integration of microseismic activity and numerical modeling at DOZ-PT Freeport,Indonesia

This article describes an undergoing research at PT Freeport, Indonesia, in which the main goal is to use the microseismic information recorded as a result of mining to analyze cave propagation and stress performance on the actual production and fixed infrastructure. At the moment, several numerical experiments have been conducted to correlate the mining activity with the microseismic events using the data collected during year 2005 and 2006. As a result of the preliminary analysis a micro- and a macrocracking envelop were proposed on the basis of computation of stress behavior at the location of the events. Stresses have been computed using standard elastic continuous boundary element models. The correlation between the average source radius and the stress performance has provided a method to propose a macrocracking criterion. Several techniques have been tested to nucleate the microseismic activity around different geological features. This last attempt was aimed to look at potential overstresses induced over the undercut and extraction level drifts. A method was devised to integrate the microseismicity into a 3-dimensional ride distribution model. This model has shown to be very effective to quantify the overstress induced as a result of computing volumetric microseismicity density. The volumetric microseismic model showed to induce overstress up to 10 MPa over a period of two months. The future work will concentrate on the calibration of the integrated model with actual damage observations made at the current mining infrastructure.

Laboratory-scale investigation of the material distribution characteristics of landslide dams in U-shaped valleys

Material distribution characteristics during sliding and depositing is particularly significative to investigate the internal structure and spatial variation of landslide dams,which are fundamentally determining the mechanical and hydraulic behavior and the susceptibility to cause dam failure.However,limited by longevity shortages and special geographic environments,the material distribution characteristics and their formation mechanisms are difficult to observe in the field.Therefore,an experimental apparatus modeling a landslide dam was developed in this paper,designing three sampling methods with two valley states.The internal deposit characteristics,void ratio variation and relative content of the particle size range(PSR)were analyzed,and the mechanics of deposit structure were also delicately ascertained.The results indicate that granular material deposited in valley shows a structure of inverse grain size accumulation in both vertical and horizontal directions,exhibiting spatial variability of particle gradation and void ratio.The characteristic PSR decreases from 22-30 mm in the two-dimensional state to 10-14 mm in the threedimensional state.Vibration excitation and vibration sieve are the intrinsic mechanisms of granular flow segregation,intrinsically inducing the formation of inverse grading deposit structures.Consequently,spatial variability in size is mainly trig gered by segregation,whereas coarse particle content and deposition boundaries merely exacerbate the difference degree.

Regional Mapping of Vertical Hydraulic Gradient Using Uncertain Well Data: A Case Study of the Toyohira River Alluvial Fan, Japan

Vertical hydraulic gradient (VHG) provides detailed information on 3D groundwater flows in alluvial fans, but its regional mapping is complicated by a lack of piezometer nests and uncertainty in conventional well data. Especially, determining representative depth of well screen in each well is problematic. Here, a VHG map of the Toyohira River alluvial fan, Sapporo, Japan, is constructed based on groundwater table elevation (GTE), using available well-data of various screen lengths and depths. The water-level data after 1988, when subway constructions are mostly completed in the city, are divided into those of shallow wells (≤20 m deep), and those of deep wells (>20 m deep). First, the GTE map is generated by kriging interpolation of shallow well data with topographic drift. Next, the individual VHG value of each deep well is calculated using its top, middle, and bottom elevations of the screen depths, respectively. The VHG maps of three cases are then obtained using neighborhood kriging. The VHG map of the bottom screen depths has proven most valid by cross-validation. The VHG map better visualizes that downward flows of groundwater are predominant over the fan. Positive area of VHG is mostly vanished around the fan-toe, indicating urbanization effect such as artificial withdrawals. A negative peak of VHG corresponds to recharge area, and is seen along the distinct losing section in the river. The negative peak also expands upstream to the fan-apex where a basement is suddenly depressed.

Evaluation of Subsoil Corrosivity Condition around Baracaia Area Using the Electrical Resistivity Method--A Case Study from the Muglad Basin, Southwestern Sudan

This paper evaluate subsoil corrosivity using the electrical resistivity method which was carried out to determine the subsoil resistivity and estimate the degree of corrosion, the resistivity measurements were conducted by using SAS300c resistivity meter. This involves applying a voltage into the soil through metal electrode and measuring the resistance to the flow of electric current. An AC-power supplies current flow （I） between two outer electrodes and the resultant voltage different （V） between two inner electrodes is measured using the Wenner Arrangement. The soil resistance given by R = V/I. This needs to be standardized over a unit length, the resistivity p which measured in ohm-m the equation is, ρ= 2ДdR. There are many factors control the ground resistivity such as soil composition, moisture content, pore water chemistry and pH. The results of the survey show inverse proportion between corrosivity and electrical resistivity, therefore resistivity method is very useful to incipient the corrosion as well as effective, quick, reliable and economic method. Structures such as natural gas, crude oil pipelines and steel constructions were reported to have been affected by soil corrosion all around the world, it can be concluded that sub soil corrosivity around the study area increases southwestern ward with depth.

Numerical Simulation of Vacuum Preloading for Chemically Conditioned Municipal Sludge

Municipal sludge is a sedimentation waste produced during the wastewater process in sewage treatment plants.Among recent studies,pilot and field tests showed that chemical conditioning combined with vacuum preloading can effectively treat municipal sludge.To further understand the drainage and consolidation characteristics of the conditioning sludge during vacuum preloading,a large deformation nonlinear numerical simulation model based on the equal strain condition was developed to simulate and analyze the pilot and field tests,whereas the simulation results were not satisfactory.The results of the numerical analysis of the pilot test showed that the predicted consolidation degree was greater than that measured by the field tests,which is attributed to the relatively low permeability layer formed during the preloading process of the prefabricated vertical drain.To better reflect the consolidation process of the conditioned sludge,a simplified analysis method considering the low permeability layer around the prefabricated vertical drain was proposed.The initial permeability coefficient of the low permeability layer is determined via numerical simulations using finite difference method.The predicted settlement curve was in good agreement with the measured results,which indicated that the numerical simulation based on the equal strain condition considering the relatively low permeability layer can better analyze the consolidation process of ferric chloride-conditioning sludge with vacuum preloading.

A reappraisal of active faults in central-east Iran(Kerman province)

Fault lineaments are the main input data in earthquake engineering and seismology studies.This study presents a digitally-based active fault map of the Kerman region in central-east Iran which experienced several devastating earthquakes on poorly exposed and/or not identified active faults.Using Landsat 8 data,we have carried out the image-based procedures of fault mapping,which include applying the contrast stretching technique,the principal component analysis,the color composite technique,the spectral rationing,and creating the false-color composite images.Besides,we have cross-checked the resulting map with the geological maps provided by the Geological Survey of Iran to decrease the associated uncertainties.The resulting map includes 123 fault segments,still,a part of which has been expressed in the previously compiled active-fault maps of Iran.Indeed,the new one is mapping the poorly exposed active faults,so-called secondary faults,which are able to produce strong events.These faults are primarily associated with poorly defined areas that accommodate low levels of seismicity;however,sporadic strong events are likely to occur.It has also been investigated that these kinds of faults are seismogenic and are able to produce destructive events.In total,the outcome of this study can also be jointed with seismic studies for investigating parts of the earthquake activity in central-east Iran,in particular for the fault-based approaches in impending earthquake-resistant buildings.

Accurate detection method of high-density polyethylene fi lm leakage location based on secondary electric potential difference

High-density polyethylene(HDPE)film leakage location detection is frequently accomplished using the double-electrode technique.The electric potential and potential difference are the main physical parameters in the double-electrode approach.Due to the impact of the complex geoelectric environment,the electric potential and the electric potential difference are not sensitive enough to respond to minimal leakage.The tiny leaking area cannot be precisely located using the electric potential and electric potential difference.Using the COMSOL Multiphysics software,this study created a standard geoelectric model of the double-electrode method.We calculated a new parameter—the G parameter through secondary electric potential difference—based on the response characteristics of the electric potential and the electric potential difference while the HDPEfilm is leaking.The experiment demonstrates that the G parameter is more sensitive than the electric potential and electric potential difference for detecting the leaking area of HDPE film.The G parameter is more effective at detecting leakage than the electric potential and electric potential difference.The results of this study can be used to locate HDPEfilm leakage areas in a landfill.

The establishment of 3D visualization modeling for the jointed slope

The 3D visualization model of slop with structural plane can displayed the characters of structural plane in slop directly, and illustrated the spatial combination. It is a modem and critical question in the field of geotechnical engineering. Based on the peculiarity of the reconnaissance and the research of the visualization by formers, systemized the method fit for building 3D visualization model of slop with structural plane. Write the special program with Visual C^-＋ computer language and illustrated it by OpenGL, the program can displayed and captured the random section plane. The program has a satisfied result by proving with the real projects.

Mapping of the Water Table Levels of Unconfined Aquifers Using Two Interpolation Methods

The spatial prediction of the water table can be used for many applications related to civil works (foundations, excavations) and other urban and environmental management activities. Deterministic and geostatistical interpolation methods were used to predict the spatial distribution of water table levels (unconfined aquifers) of important geological formations of the Joao Pessoa City (capital of Paraiba State, Brazil) with dense urban occupation and high demand for new civil works. The deterministic (topo to raster) and geostatistical (ordinary kriging) interpolation methods were evaluated using a Geographic Information System (GIS)-based investigation. The water table levels were obtained from 276 boring logs of Standard Penetration Test (SPT) in situ investigation distributed over the geological formations studied (an area of 59.8 km2, covering 40 districts of the Joao Pessoa City). The Nspt values and textural characterization data are stored for levels of 1 m depth. Some boreholes located in the area investigated were not included in the interpolation processes in order to be compared with estimated values (validation of the results). Maps of the water table depths were also produced to further analyze the quality of the water table surfaces interpolated by both methods. The phreatic surface interpolations provided satisfactory results for both methods (RMSE = 1.8 m). The topo to raster method showed a slight general tendency to be less affected by local values in relation to the kriging method and also has the advantage of integrating the drainage flow system, which is a relevant aspect for spatial models of the water table levels of unconfined aquifers. The ordinary kriging (geostatistical method) provides a prediction surface and some measure of the certainty or accuracy of the predictions.

Physical and Mechanical Features of the Quaternary Basanites of the Cap-Vert Peninsula of Dakar (Senegal, West Africa)

This work presents the results of geotechnical tests carried out in the laboratory on specimens of Quaternary olivine basanites from the Cap-Vert peninsula of Dakar. The samples were taken following geotechnical investigations in the Fann-PE, Mermoz-Ouakam, Yoff and Ngor areas respectively. The results obtained show a dry density between 20.45 and 29.30 kN/m3 which corresponds to medium to high density basanites. The porosity varies between 0.33% and 4.20%. For microlitic basanites, the porosity remains low, on the other hand, for micrograined basanites;a slight increase in porosity is noticed. As for the methylene blue adsorption test value measured, it is between 0.25 and 1.10. The uniaxial compression strength (Rc) and Young’s modulus (E) vary respectively from 12.19 MPa to 41.748 MPa and from 1477.6 MPa to 7699.1 MPa. The low strength values are recorded in altered and vesicular basanites. Also, a correlation was made between uniaxial compression strength and porosity and showed a gradual decrease in strength with increasing porosity.