Model test study on the formation and development of underground erosion ground fissures in the Kenya Rift Valley

The Kenya Rift Valley is relatively prone to underground erosion ground fissures and associated disasters,which gravely hinder local engineering construction and economic development.In this research,we performed field and experimental studies on ground fissures in the Kenya Rift Valley area,and determined the structural characteristics of underground erosion fissures.Based on a geological survey of the area,we generalized a geological model for typical ground fissures and reproduced the intermediate process of ground fissure propagation using a large-scale physical model test.Further,the development process of underground erosion fissures were categorized into four stages:uniform infiltration,preferential infiltration,cavity expansion,and collapse formation stages.During the development of underground erosion fissures,water content was distributed symmetrically along the fissures,and these fissures acted as the primary infiltration paths of water.When the ground collapsed,the increase in negative pore water pressure was greater,whereas the increase in positive pore water pressure was less in the shallow soil;moreover,in the deep soil,the increase in positive pore water pressure was greater than that of negative pore water pressure.Additionally,the earth pressure increment initially increased and then decreased with the development of erosion.During underground erosion collapse,the water content and pore water pressure appeared to increase and decrease rapidly.These results can be employed to predict the occurrence of underground erosion ground fissures and the resulting soil collapse.

Treatment of compost leachate by the combination of coagulation and membrane process

This study describes the treatment of composting leachate by the combination of coagulation and nanofiltration process. Poly ferric sulfate （PSF） was used as coagulant, and the effect of pH value and PSF dosage on the coagulation performance was investigated. The results indicated that the chemical oxidation demand （COD） and turbidity removal efficiency could reach to 62.8% and 75.3%, respectively at an optimum dosage of 1200 mg·L-1 at pH 6,0. During the nanofiltration process, the operation conditions such as temperature and pressure were optimized, 89.7% of COD, 78.2% of TOC, 72,5% of TN, 83,2% of TP, and 78,6% of NH3-N were retained when tested at 0.6 MPa at 25 ℃. The final leachate effluent concentration of COD, BODs, NH3-N, TOC, SS was 92 mg.L 1, 31 mg,L 1 21 mg.L 1, 73 mg·L-1 and 23 mg·L -1, respectively, which reached the local discharge standard. The combination of coagulation-filtration is useful for composting leachate treatment.

Pore evolution and shear characteristics of a soil-rock mixture upon freeze-thaw cycling

The changes in pore structure within soil-rock mixtures under freeze-thaw cycles in cold regions result in strength deterioration,leading to instability and slope failure.However,the existing studies mainly provided qualitative analysis of the changes in pore or strength of soil-rock mixture under freeze-thaw cycles.In contrast,few studies focused on the quantitative evaluation of pore change and the relationship between the freeze-thaw strength deterioration and pore change of soil-rock mixture.This study aims to explore the correlation between the micro-pore evolution characteristics and macro-mechanics of a soil-rock mixture after frequent freeze-thaw cycles during the construction and subsequent operation in a permafrost region.The pore characteristics of remolded soil samples with different rock contents(i.e.,25%,35%,45%,and 55%)subjected to various freeze-thaw cycles(i.e.,0,1,3,6,and 10)were quantitatively analyzed using nuclear magnetic resonance(NMR).Shear tests of soil-rock samples under different normal pressures were carried out simultaneously to explore the correlation between the soil strength changes and pore characteristics.The results indicate that with an increase in the number of freeze-thaw cycles,the cohesion of the soil-rock mixture generally decreases first,then increases,and finally decreases;however,the internal friction angle shows no apparent change.With the increase in rock content,the peak shear strength of the soil-rock mixture rises first and then decreases and peaks when the rock content is at 45%.When the rock content remains constant,as the number of freeze-thaw cycles rises,the shear strength of the sample reaches its peak after three freeze-thaw cycles.Studies have shown that with an increase in freeze-thaw cycles,the medium and large pores develop rapidly,especially for pores with a size of 0.2–20μm.Freeze-thaw cycling affects the internal pores of the soil-rock mixture by altering its skeleton and,therefore,impacts its macro-mechanical characteristics.

A simplified three-dimensional extension of Hoek-Brown strength criterion

The Hoek-Brown(HB)strength criterion has been applied widely in a large number of projects around the world.However,this criterion ignores the intermediate principal stress s2.Many evidences have demonstrated that the rock strength is dependent on s2.Thus it is necessary to extend the HB criterion into a three-dimensional(3D)form.In this study,the effect of s2 on the strength of rocks is identified by reviewing the true triaxial tests of various rock types reported in the literature.A simple 3D strength criterion is developed.The modified criterion is verified by the true triaxial tests of 13 rock types.The results indicate that the modified criterion can achieve a good fit to most of rock types.It can represent a series of criteria as b varies.For comparisons,several existing 3D versions of the HB criterion are selected to predict the strengths of these rock types.It is indicated that the proposed criterion works better than other criteria.A substantial relationship between parameter b and the unconfined compressive strength is established,which guarantees that the proposed criterion can still work well even in the absence of true triaxial test data.

Effect of salts on earthen materials deterioration after humidity cycling

Salt weathering leads to destruction of many valuable cultural heritage monuments and porous building material. The present study aims at providing more laboratory evidence for evaluating the effects of salt precipitation on the deterioration process. In view of this, the remoulded soil specimens were mixed with three kinds of salts(i.e., NaCl, Na_2SO_4 and their mixture) with different salt concentrations, and the specimens were kept in environment cabinet for undergoing different wet-dry cycles. After each cycle, the ultrasound velocity measurements were employed to monitor the deterioration process. For the specimens that have suffered three wet-dry cycles, the mechanical properties(i.e. shear strength and compression strength) were determined to evaluate the degree of deterioration. Furthermore, considering the realistic conservation environment of earthen sites, mechanical stability of these specimens against sediment-carrying wind erosion was conducted in a wind tunnel. These experiments results indicate that the overall average velocities of the specimens after the third cycle are significantly lower than those subjected to only one cycle. Ultrasound velocity, mechanical strength and wind erosion rate decrease when salt content increases. However, the internal friction angle increases firstly, and then decreases with the increase in salt content added to the specimens. Na_2SO_4 contributes most of the surface deterioration, while NaCl plays little role in the deterioration. The damage potential of the salt mixture is less obvious and largely dependent on the crystallisation location.

Multiscale characteristics of the wetting deformation of Malan loess in the Yan’an area,China

Loess is prone to collapse upon wetting due to its open metastable structure,which poses a considerable threat to the environment,construction processes and human life.In this study,double oedometer tests and scanning electron microscopy and mercury intrusion porosimetry analyses were conducted on loess from Yan’an to study the macroscopic and microscopic characteristics of loess wetting deformation and the underlying mechanism.The wetting collapse of loess under loading depends on the changes in different microstructure levels and elements.This collapse chain reaction is manifested by the dissipation,scattering and recombination of the cementation,deformation and reorganization of the particles,blocking of the pore channels,decrease in the dominant size and volume of unstable macropores(>14μm)and abundant mesopores(2.5-14μm),increase in the volume of small pores(0.05–2.5μm),and volume contraction at the macroscale.This process is dependent on the initial water content,stress level and wetting degree.These findings can facilitate collapsible loess hazard prevention and geological engineering construction.

Discrete Element Modeling of Tangjiagou Two-Branch Rock Avalanche Triggered by the 2013 Lushan MW6.6 Earthquake,China

Two branches of Tangjiagou rock avalanche were triggered by Lushan earthquake in Sichuan Province,China on April 20th,2013.The rock avalanche has transported about 1500000 m3 of sandstone from the source area.Based on discrete element modeling,this study simulates the deformation,failure and movement process of the rock avalanche.Under seismic loading,the mechanism and process of deformation,failure,and runout of the two branches are similar.In detail,the stress concentration occur firstly on the top of the mountain ridge,and accordingly,the tensile deformation appears.With the increase of seismic loading,the strain concentration zone extends in the forward and backward directions along the slipping surface,forming a locking segment.As a result,the slipping surface penetrates and the slide mass begin to slide down with high speed.Finally,the avalanche accumulates in the downstream and forms a small barrier lake.Modeling shows that a number of rocks on the surface exhibit patterns of horizontal throwing and vertical jumping under strong ground shaking.We suggest that the movement of the rock avalanche is a complicated process with multiple stages,including formation of the two branches,high-speed sliding,transformation into debris flows,further movement and collision,accumulation,and the final steady state.Topographic amplification effects are also revealed based on acceleration and velocity of special monitoring points.The horizontal and vertical runout distances of the surface materials are much greater than those of the internal materials.Besides,the sliding duration is also longer than that of the internal rock mass.

Groundwater resources survey of tongchuan city using the audio magnetotelluric method

The development of Tongchuan City,Shaanxi Province,located in the northwestern region of China,is restricted by water resources.The direct current resistivity and induced polarization sounding methods are typically applied in finding urban groundwater.These methods,however,are not effective due to their complicated topography and geological conditions.The application practice shows that the audio magnetotelluric(AMT)method has a large depth of exploration,high work effi ciency,and high lateral resolution.To investigate the distribution of groundwater resources,we deployed three audio-frequency magnetotelluric profiles in the city area.The impedance tensor information of AMT data is obtained using SSMT2000.AMT data dimension analysis reveals that the two-dimensional structural features of the observation area are obvious.The main structure of the observation area is about 45°northeast,as indicated by structural trend analysis.A shallow two-dimensional electrical profile of 1 km in Tongchuan City is obtained by two-dimensional nonlinear conjugate gradient inversion.Finally,combined with regional geological information,the geological structure characteristics reflected by the electrical profile were obtained along with the detailed characteristics of water-rich structures in the area.The infl uence of the structure on the groundwater distribution was analyzed,and the water-rich areas were identifi ed.This work contributes to the prospective development of Tongchuan City.

Discussion on Cultural Inheritance of Water Parks in the Yellow River Basin

At the Symposium on Ecological Protection and High-quality Development of the Yellow River Basin, General Secretary Xi Jinping pointed out that "it should deeply explore the time value contained in the Yellow River culture, tell the story of the Yellow River well, and protect, inherit and carry forward the Yellow River culture". Water park is an important carrier of the Yellow River culture transmission. In this paper, the basic characteristics and regional distribution of water parks in the Yellow River basin are analyzed. For the problems faced by cultural heritage of water parks in the Yellow River basin, from three aspects of exploring and integrating the connotation, innovating communication methods, and shaping brand IP, cultural heritage of water parks in the Yellow River basin is discussed. It is beneficial to carry forward the Yellow River culture, and better meet the spiritual and cultural needs of the people.

Freeze–thaw effects on erosion process in loess slope under simulated rainfall

Seasonal freeze–thaw processes have led to severe soil erosion in the middle and high latitudes.The area affected by freeze–thaw erosion in China exceeds 13%of the national territory.So understanding the effect of freeze–thaw on erosion process is of great significance for soil and water conservation as well as for ecological engineering.In this study,we designed simulated rainfall experiments to investigate soil erosion processes under two soil conditions,unfrozen slope(UFS)and frozen slope(FS),and three rainfall intensities of 0.6,0.9 and 1.2 mm/min.The results showed that the initial runoff time of FS occurred much earlier than that of the UFS.Under the same rainfall intensity,the runoff of FS is 1.17–1.26 times that of UFS;and the sediment yield of FS is 6.48–10.49 times that of UFS.With increasing rainfall time,rills were produced on the slope.After the appearance of the rills,the sediment yield on the FS accounts for 74%–86%of the total sediment yield.Rill erosion was the main reason for the increase in soil erosion rate on FS,and the reduction in water percolation resulting from frozen layers was one of the important factors leading to the advancement of rills on slope.A linear relationship existed between the cumulative runoff and the sediment yield of UFS and FS(R2>0.97,P<0.01).The average mean weight diameter(MWD)on the slope erosion particles was as follows:UFS0.9(73.84μm)>FS0.6(72.30μm)>UFS1.2(72.23μm)>substrate(71.23μm)>FS1.2(71.06μm)>FS0.9(70.72μm).During the early stage of the rainfall,the MWD of the FS was relatively large.However,during the middle to late rainfall,the particle composition gradually approached that of the soil substrate.Under different rainfall intensities,the mean soil erodibility(MK)of the FS was 7.22 times that of the UFS.The ratio of the mean regression coefficient C2(MC2)between FS and UFS was roughly correspondent with MK.Therefore,the parameter C2 can be used to evaluate soil erodibility after the appearance of the rills.This article explored the influence mechanism of freeze–thaw effects on loess soil erosion and provided a theoretical basis for further studies on soil erosion in the loess hilly regions.

Development characteristics and formation analysis of the Liangjia Village earth fissure in the Weihe Basin,China

Liangjia Village earth fissure,one of the 79 earth fissures along the Kouzhen-Guanshan fault located in the northern Weihe Basin,causes severe damage to buildings and farmlands.Since the late 1950s,40 earth fissures have occurred in a similar east-west(EW)direction parallel to the Kouzhen-Guanshan fault,and a further 39 earth fissures have occurred with north-west,east-north,or north-east orientations intersecting the fault.In this study,a case study of Liangjia Village earth fissure was conducted to investigate the mechanisms of fissure generation in detail.Geotechnical and geophysical methods including measurements,trenching,drilling,and seismic exploration were used to reveal the basic characteristics,geological background,and origin model of the Liangjia Village earth fissure.This earth fissure,with a total length of 800 m in 2014,runs EW parallel to the Kouzhen-Guanshan fault,and it has damaged buildings and farmlands by forming sinkholes,gullies,subsidence,and a scarp.The trenching results indicated that this fissure underwent multi-phase activity.Analysis of geological drilling and shallow seismic profiling results showed that the fissure also possessed characteristics of a synsedimentary fault.Regarding its genesis,the fissure was formed through the combined actions of three factors:an earthquake created the fissure,the Kouzhen-Guanshan fault controlled its development,and loess erosion and groundwater runoff subsequently enlarged the fissure.Regional extension first generated many buried faults along the hanging wall of the Kouzhen-Guanshan fault before seismic activity caused the buried faults to propagate to the surface,where loess erosion and ground-water runoff promoted the formation of the current earth fissure.

多次干湿循环后原状和重塑黄土的持水性试验研究

干湿循环的风化作用是引发中国黄土地区基础设施破坏的重要影响因素。黄土的持水性能是此类黄土工程问题物理成因的关键物性。为了探究在干湿循环的环境驱动作用下不同地区原状和重塑黄土的持水性能及其变化规律,利用压力板仪和电镜扫描仪(SEM)开展了持水曲线(SWRC)和微观结构的系列室内试验。研究结果表明,干湿循环的风化作用对原状和重塑黄土的持水性能有显著影响,且第一次循环的影响程度最为明显;原状黄土的SWRC呈双峰型,重塑黄土的SWRC呈单峰型;利用概念模型很好地解释了持水性的特征、变化规律及其与微观结构之间的联系。提出了一个考虑干湿循环次数、土的结构、区域差异影响的新持水模型,可以统一描述具有双峰特性的原状黄土和具有单峰特性的重塑黄土的持水特性,模型参数能够很好表达SWRC的变化特征,所提出模型在预测黄土和其他土的持水性能方面,具有较高的实用性和有效性。

Long-Term Settlement Characterization of High-Filling Foundation in the Mountain Excavation and City Construction Area of the Yan’an New District,China

Mountain Excavation and City Construction(MECC)represents a prominent anthropogenic endeavor aimed at facilitating urban expansion in the Loess Plateau of China.It is important to comprehend the long-term settlement behavior at MECC engineering sites to effectively assess the project’s success in reshaping landscapes and expanding urban areas.In this study,a typical MECC project,specifically the upstream area of the Liujiagou Valley within the new district of Yan’an City,is selected as a case study to investigate long-term settlement characteristics.The research involved conducting creep tests on soil samples with varying dry densities and moisture content and continuous in-situ monitoring of ground surface settlement at 17 specific points.Furthermore,a numerical model was developed and calibrated using the in-situ monitoring data to predict the long-term settlement.The findings reveal that an increase in soil dry density and a decrease in soil water content contribute to reduced deformation.Notably,settlement primarily manifests within the filled areas,with greater soil thickness exacerbating settlement effects.Over time,cumulative settlement exhibits a progressively diminishing rate of deformation until it attains a stable state.These results provide insights for assessing the long-term stability of MECC projects,facilitating decision-making in future endeavors within this region.

Formation Mechanism of Ground Fissures Originated from the Hanging Wall of Normal Fault:A Case in Fen-Wei Basin,China

This paper takes Fen-Wei Basin(FWB)as a case to study the ground fissures controlled by normal fault.Based on the field investigation,geophysical exploration,drilling,GNSS data and numerical calculation,the characteristics and mechanism of ground fissures originated from the hanging wall of normal faults are revealed.The results show that the distribution of ground fissures in the hanging wall and heading wall of the active faults is not uniform.Ground fissures are mostly distributed in the hanging wall of active faults and show a linear distribution on the surface,their strike is consistent with the fault,mainly characterized by vertical offset and horizontal tension.Ground fissures destroy the farmland and building foundation through which they pass and cause the rupture or displacement.In profile section,the ground fissure shows the characteristics of normal faults and dislocates the strata,and is connected with the underlying faults.Numerical analysis shows that the vertical displacement of normal fault activity in hanging wall is much larger than that in heading wall,which is the reason that tectonic ground fissures mainly originate from hanging wall.The range of dangerous area of ground fissures is controlled by the depth of fault,the strength of the ground fissures disaster is mainly controlled by the activity of fault.The formation of the ground fissures originated from the hanging wall of the fault experienced three stages:the main fault activity stage,the secondary fault activity stage and the fissure formation stage.

A Comprehensive Method for the Risk Assessment of Ground Fissures:Case Study of the Eastern Weihe Basin

Ground fissures are influenced by the coupling of geological factors and human activi-ties.They threaten the safety of infrastructure and restrict town planning in many areas in China.One of the area most severely affected by ground fissures is the Weihe Basin in North China,which has the most extensive distribution of ground fissures and all the elements that control their occurrence,pro-viding an ideal study area for the study of ground fissures.In this study,we took the eastern Weihe Ba-sin as the study area and determined the distribution and hazard characteristics of ground fissures via field investigation.Based on the analytic hierarchy process,we propose a multi-level,comprehensive method for evaluating the hazards of ground fissures.This method considers the geological back-ground,development status,and triggering factors of ground fissures,including all nine currently known assessment indices of ground fissures.We used judgment matrices to rank the constructed ground fissure assessment index system at the single and total levels and quantified the nine assessment indices of ground fissures according to the field survey data.Finally,we plotted the ground fissure risk zoning map and evaluated the ground fissure risk at the study area.Our findings indicated that the proposed method could facilitate ground fissure hazard assessment and prediction and provide support for hazard prevention and urban/rural planning.

A new method of studying collapsibility of loess

A new triaxial testing system that could control suction in wetting-induced collapsible tests was success-fully developed to study the suction effects on wetting-induced collapsible deformation.The pedestal of the triaxial cell was made up of two parts,and the equipment not only could control suction but also could make water accessible to soil.A pressure/volume-controlled equip-ment was combined with the triaxial system to measure the water volume absorbed by samples accurately and to add pressure on water to filtrate into the sample.The apparatus could measure volume change precisely and keep the deviator stress unvaried,as well as measure the volume of water filtrating into the samples exactly.A triaxial collapsible testing procedure was described using the new apparatus for undisturbed collapsible loess with controlled suction.Furthermore,a series of double triaxial collapsible tests were conducted under different suctions and the same net cell pressure,and tests under different net cell pressures and the same suction were also done.It was indicated that the collapsible deformation increased with the increasing suction,and the effect of the net cell pressure on collapsible deformation was remarkable.The new triaxial apparatus was a useful facility to study the collapsible behavior of loess.