Experimental investigation on the permeability of gap-graded soil due to horizontal suffusion considering boundary effect

The boundary condition is a crucial factor affecting the permeability variation due to suffusion.An experimental investigation on the permeability of gap-graded soil due to horizontal suffusion considering the boundary effect is conducted,where the hydraulic head difference(DH)varies,and the boundary includes non-loss and soil-loss conditions.Soil samples are filled into seven soil storerooms connected in turn.After evaluation,the variation in content of fine sand(ΔR_(f))and the hydraulic conductivity of soils in each storeroom(C_(i))are analyzed.In the non-loss test,the soil sample filling area is divided into runoff,transited,and accumulated areas according to the negative or positive ΔR_(f) values.ΔR_(f) increases from negative to positive along the seepage path,and Ci decreases from runoff area to transited area and then rebounds in accumulated area.In the soil-loss test,all soil sample filling areas belong to the runoff area,where the gentle-loss,strengthened-loss,and alleviated-loss parts are further divided.ΔR_(f) decreases from the gentle-loss part to the strengthened-loss part and then rebounds in the alleviated-loss part,and C_(i) increases and then decreases along the seepage path.The relationship between ΔR_(f) and Ci is different with the boundary condition.Ci exponentially decreases with ΔR_(f) in the non-loss test and increases with ΔR_(f) generally in the soil-loss test.

Impact of clay particle reattachment on suffusion of sand-clay mixtures

The detached clay particles directly filtrated through the sand-clay mixture lead to suffusion;however,if the detached clay particles are subjected to reattachment,the degree of suffusion may be less significant.This study investigates the impact of clay particle reattachment on suffusion of sand-clay mixtures through laboratory soil-column experiments.The observed breakthrough curves(BTCs)of kaolinite,illite,and montmorillonite for 5 different column lengths(3 in,6 in,9 in,12 in,and 18 in;1 in=2.54 cm)indicated that a higher breakthrough concentration was observed as the column length(L)decreased for kaolinite and illite,whereas a reverse trend was observed for montmorillonite.In addition,the increase in the fraction of filtrated clay particles(Me)with an increase in L(Me=10.42%for L=3 in and Me=3.59%for L=18 in)for the sand-illite mixture indicated that the reattachment effect became more significant as the travel length of detached clay particles increased.The observed BTCs,retention profiles after injection,and fraction of filtrated clay presented herein suggest the need to incorporate the reattachment effect when assessing the suffusion of clay-containing soils.

CFD-DEM modelling of suffusion in multi-layer soils with different fines contents and impermeable zones

Suffusion in broadly graded granular soils is caused by fluid flow and is a typical cause of geo-hazards.Previous studies of it have mainly focused on suffusion in homogeneous soil specimens.In this study,the coupled discrete element method(DEM)and computational fluid dynamics(CFD)approach is adopted to model suffusion in multi-layered soils with different fines contents,and soils with one or more impermeable zones.The parameters of the CFD-DEM model are first calibrated with the classic Ergun test and a good match with experiment is obtained.Then suffusion in multi-layered soils with different fines contents and impermeable zones is simulated and discussed.The simulation results show that,for soils with multiple layers,the cumulative eroded mass is mainly determined by the fines content of the bottom layer.In general,the higher the fines content of the bottom soil layer,the higher the cumulative eroded mass.In addition,suffusion is more severe if the fines content of the layer above is decreased.Impermeable zones inside soil specimens can increase the flow velocity around those zones,facilitating the migration of fine particles and intensifying suffusion.

Experimental and numerical study of seepage-induced suffusion under K_(0) stress state

Suffusion in gap-graded soil involves selective erosion of fine particles through the pores formed by coarse particles under seepage forces.As the fines content(FC)decreases,the hydraulic and mechanical behavior of the soil will change,posing a huge threat to engineering safety.In this study,we first conduct a series of experimental tests of suffusion by using gap-graded soils and then analyze the evolution process of suffusion and the effect of the hydraulic gradient.Subsequently,according to the physical model,a discrete element method(DEM)numerical model with dynamic fluid mesh(DFM)is developed to extend the experimental study to the pore scale.Our results reveal the migration process of fines and the formation of erosion zones.A parametric study is then conducted to investigate the effect of the hydraulic gradient,FC,and K_(0) pressure(which limits the lateral displacement of the sample and applies vertical pressure)on eroded weight.The results show that the eroded weight increases with the increase of the hydraulic gradient and FC but decreases with the increase of K_(0) pressure.

Experimental and Numerical Investigation of Stress Condition in Unstable Soil

In unstable soils, a special erosion process termed suffusion can occur under the effect of relatively low hydraulic gradient. The critical hydraulic gradient of an unstable soil is smaller than in stable soils, which is described by a reduction factor α. According to a theory of Skempton and Brogan (1994) [1], this reduction factor is related to the stress conditions in the soil. In an unstable soil, the average stresses acting in the fine portion are believed to be smaller than the average stresses in the coarse portion. It is assumed that the stress ratio and the reduction factor for the hydraulic gradient are almost equal. In order to prove this theory, laboratory tests and discrete element modelings are carried out. Models of stable and unstable soils are established, and the stresses inside the sample are analysed. It is found that indeed in unstable soils the coarse grains are subject to larger stresses. The stress ratios in stable soils are almost unity, whereas in unstable soils smaller stress ratios, which are dependent on the soil composition and on the relative density of the soil, are obtained. A comparison between the results of erosion tests and numerical modeling shows that the stress ratios and the reduction factors are strongly related, as assumed by Skempton and Brogan (1994) [1].

State Cadastral Account of the Developments of Hazardous Geological Processes in Uzbekistan

Mountain territories of Uzbekistan present themselves as the subjects of hazardous geological processses, such as landslides,suffosions,and collapses. Mountain area is 21.3%.For monitoring above-mentioned processes there exist State monitorring service in Uzbekistan,that was founded 50 years ago.During this period,8362 events of landslides were observed.

Karst and Pseudokarst of the West Kazakhstan (Republic of Kazakhstan)

An analysis of the formation of karst and karst-suffosion forms on the territory of the West Kazakhstan region is presented in this paper. Numerous literary sources were used as the information database for the analysis of the relief features of the West Kazakhstan region. Evaluation of the morphometric features of the collapsed new formations on the basis of materials of our own field research is presented here for the first time. According to the research objectives there were defined localization places of the karst-collapsed phenomena where the reconnaissance field surveys were carried out. Survey points’ localization has been carried out by means of GPS system with the help of 12-channel GPS-receiver of Garmin eTrex model. Geoinformational technology, based on MapInfo 9.5 and ArcGIS 9.2 packages was used for the building of the information and cartographic database. Original thematic maps compiled on the basis of the research results’ analysis have been obtained in this research. The features of the Caspian Basin’s karst landscapes, formed as a result of salt-dome tectonic manifestations (Inder Mountains, Malaya Bogdo Mountain, Bish-Chokho hill) are described in this paper. The important elements of the Caspian Basin salt-dome landscapes are landforms of the karst origin from large karst depressions of the karst-tectonic origin to modern forms of the sulfate karst: sinkholes, wells, polje, knobs (“Kurgantau”), arches, caves and grottoes. Some karst formations have a non-salt-dome origin. Three areas with the collapsed forms that have the karst-suffosion origin have been identified (near Konyr village, Berezovka village and Zhanatalap village). The mechanism of the sinkholes formation is due to the changes of the groundwater regime and the displacement of limestone eluvium as a result of active anthropogenic impacts. The sinkholes occurence near Zhanatalap village, which is located near the Karachaganak oil and gas field, is probably due to the anthropogenic initiation of karst-suffosion processes.