Coefficients of earth pressure at rest in thick and deep soils

The effect of test methods and stress paths on the experimental value of the coefficient of earth pressure at rest, K0, was investigated under high pressures. The results indicate that the rigid pressure chamber and flexible lateral confining pressure medium method gives a stress ratio at the initial stage that is not the real K0. Moreover, K0 increases during the loading process becoming greater at high pressures. In the unloading process, however, K0 increases only at the initial stage but decreases thereafter. In addition, the incremental magnitude definition, K0=dσ3/dσ1, gives higher values than the total magnitude definition, K0=σ3/σ1, under loading. This is also true during initial stages of unloading. The experiment results also indicate that earth pressure at rest in deep and thick soils can be estimated by a power function of axial and confining pressures. It is necessary to choose the appropriate Kn to avoid some accidents.

Nitrogen availability regulates deep soil priming effect by changing microbial metabolic efficiency in a subtropical forest

In terrestrial ecosystems,deep soils(below 30 cm)are major organic carbon(C)pools.The labile carbon input could alter soil organic carbon(SOC)mineralization,resulting in priming effect(PE),which could be modified by nitrogen(N)availability,however,the underlying mechanism is unclear for deep soils,which complicates the prediction of deep soil C cycling in response to N deposition.A series of N applications with ^(13)C labeled glucose was set to investigate the effect of labile C and N on deep SOC mineralization.Microbial biomass,functional community,metabolic efficiency and enzyme activities were examined for their effects on SOC mineralization and PE.During incubation,glucose addition promoted SOC mineralization,resulting in positive PE.The magnitude of PE decreased significantly with increasing N.The N-regulated PE was not dependent on extracellular enzyme activities but was positively correlated with carbon use efficiency and negatively with metabolic quotient.Higher N levels resulted in higher microbial biomass and SOC-derived microbial biomass than lower N levels.These results suggest that the decline in the PE under high N availability was mainly controlled by higher microbial metabolic efficiency which allocated more C for growth.Structural equation modelling also revealed that microbial metabolic efficiency rather than enzyme activities was the main factor regulating the PE.The negative effect of additional N suggests that future N deposition could promote soil C sequestration.

Bearing Capacity Assessment of Collapsible Soils Improved by Deep Soil Mixing Using Finite Element Method

Problematic soils usually cause considerable problems to engineering projects. As an example, soil structure collapse caused by moisture increment or rising underground water level results in huge settlements. This type of problematic soil, named collapsible soil, can cause dramatic problems and should be amended where exists. Today, the use of different techniques for soil reinforcement and soil improvement is widely used to treat soil properties. One of these methods is Deep Soil Mixing (DSM) method. This method becomes more important in the cases of studying and examining collapsible soils. In this research, the settlement of amended collapsible soils, applying deep soil mixing method, is examined. The experiments show that soil amendment using this method, well prevents the settlement of collapsible soils giving rise to bearing capacity.

Distribution of soil aggregates and organic carbon in deep soil under long-term conservation tillage with residual retention in dryland

To ascertain the effects of long-term conservation tillage and residue retention on soil organic carbon(SOC) content and aggregate distribution in a deep soil(>20-cm depth) in a dryland environment,this paper analyzed the SOC and aggregate distribution in soil, and the aggregate-associated organic carbon(OC) and SOC physical fractions. Conservation tillage(reduced tillage with residue incorporated(RT) and no-tillage with residue mulch(NT)) significantly increased SOC sequestration and soil aggregation in deep soil compared with conventional tillage with residue removal(CT). Compared with CT, RT significantly increased the proportion of small macroaggregates by 23%–81% in the 10–80 cm layer, and the OC content in small macroaggregates by 1%–58% in the 0–80 cm layer. RT significantly increased(by 24%–90%) the OC content in mineral-SOC within small macroaggregates in the 0–60 cm layer, while there was a 23%–80% increase in the 0–40 cm layer with NT. These results indicated that:(1) conservation tillage treatments are beneficial for soil aggregation and SOC sequestration in a deep soil in a dryland environment; and(2)the SOC in mineral-associated OC plays important roles in soil aggregation and SOC sequestration. In conclusion, RT with NT is recommended as an agricultural management tool in dryland soils because of its role in improving soil aggregation and SOC sequestration.

Deep soil water infiltration and its dynamic variation in the shifting sandy land of typical deserts in China

Soil moisture is the key resource constraint in arid ecosystems, and has been a focus of research on restoration. However, quantitative studies on the contribution of rainfall to deep soil rainfall infiltration are lacking. In this study, we used the YWB-01 Deep Soil Infiltration Water Recorder which had been invented by ourselves to measure the quantity of rain infiltration into deep soil, 150 cm below ground, in four locations in China: Mu Us Sandy Land and Ulan Buh, Tengger, and Badan Jilin deserts over a 2-year period. We found:(1) Deep soil rainfall infiltration decreased progressively from east to west and from semiarid to arid areas, with two locations completely lacking rainfall infiltration. Heavy rain was important to deep soil infiltration in shifting sandy land of arid and semiarid areas.(2) Seasonal variation of infiltration was correlated with rainfall, with a time lag that was less apparent in areas with more rainfall.(3) For single intense rainfall events, infiltration maximums occurred 40–55 h after the rainfall, during which the infiltration rates increased rapidly before reaching a peak, and then decreased slowly. Continuous infiltration could last about 150 h. Rainfall infiltration was determined by the combined action of intensity, quantity and duration. Rainfall with low intensity, long duration, and large quantity was most favorable for deep soil infiltration. Our results can be used in water resource assessments and protection during eco-restoration in the arid and semiarid areas in China.

Effects of land use and cultivation time on soil organic and inorganic carbon storage in deep soils

The vertical distribution and exchange mechanisms of soil organic and inorganic carbon(SOC,SIC)play an important role in assessing carbon(C)cycling and budgets.However,the impact of land use through time for deep soil C(below 100 cm)is not well known.To investigate deep C storage under different land uses and evaluate how it changes with time,we collected soil samples to a depth of 500 cm in a soil profile in the Gutun watershed on the Chinese Loess Plateau(CLP);and determined SOC,SIC,and bulk density.The magnitude of SOC stocks in the 0-500 cm depth range fell into the following ranking:shrubland(17.2 kg m-2)>grassland(16.3 kg m-2)>forestland(15.2 kg m-2)>cropland(14.1 kg m 2)>gully land(6.4 kg m 2).The ranking for SIC stocks were:grassland(104.1 kg m^2)>forestland(96.2 kg m^2)>shrubland(90.6 kg m-2)>cropland(82.4 kg m 2)>gully land(50.3 kg m-2).Respective SOC and SIC stocks were at least 1.6-and 2.1-fold higher within the 100-500 cm depth range,as compared to the 0-100 cm depth range.Overall SOC and SIC stocks decreased significantly from the 5th to the 15th year of cultivation in croplands,and generally increased up to the 70th year.Both SOC and SIC stocks showed a turning point at 15 years cultivation,which should be considered when evaluating soil C sequestration.Estimates of C stocks greatly depends on soil sampling depth,and understanding the influences of land use and time will improve soil productivity and conservation in regions with deep soils.

Simulation of Excess Pore Water Pressure During Deep Soil Mixing Columns Installing

Most of current studies of deep soil mixing (DSM) methods are focused on the soil strength improvement and soil treatment effectiveness. But the DSM installation leads to excess pore water pressure and soil disturbance, which will bring great harm to adjacent structures, such as shell tunnels and historic buildings. The procedure of excess pore water pressure buildup while large number DSM columns are installed is complicated. In order to find methods to predict and simulate the excess pore water pressure during DSM column installation, the complicated dissipation and buildup of excess pore water pressure through in-situ test are studied in this paper. In-situ test was conducted in soft clay near the Huangpu River in Shanghai. The pore water pressure was investigated by an automatic monitoring system. Test results indicate that the excess pore water pressure induced by one DSM column installation is composed of the compaction pressure and the reversing pressure. The empirical equations of excess pore water pressure dissipation and buildup were built by mathematical fitting methods. A compound method is proposed to simulate the excess pore water pressure due to DSM installation. Using this method to predict the excess pore water pressure in the situ test, results show a well agreement between the prediction and the measurements.

Deep profile soil moisture distribution characteristics for different microtopographies on the semi-arid Loess Plateau, China

Soil moisture is a limiting factor for vegetation restoration on the Loess Plateau, China. Micro-topography may cause heterogeneities in the distribution of soil moisture, but little is known about its effect on deep soil moisture. Our study aims to explore the distribution and impact of soil moisture within the upper 10 m of soil for different microtopographies. Taking undisturbed slope as the control, five micro-topographies were selected. Soil moisture over a depth of 0-10 m from 2017 to 2019 was investigated, and soil particle size and soil organic matter were measured. Variance analysis and multiple comparisons were used to analyze the difference in soil moisture for different microtopographies and multiple-linear regression was used to analyze the influence of micro-topography on soil moisture. There are significant differences in soil moisture within the different layers underlying the examined micro-topographies, while the inter-annual variation in soil water storage for the selected microtopographies increase with increased rainfall. The depth of influence of micro-topographic vegetation on soil moisture exceeded 1000 cm for a gully(GU), 740 cm for a sink hole(SH), 480 cm for a scarp(SC), 360 cm for an ephemeral gully(EG) and 220 cm for a platform(PL). Micro-topography will cause the heterogeneous distribution of soil moisture in the shallower layers, which changes the vegetation distribution differences between micro-topographies. This may be the survival strategy of herbaceous vegetation in response to climate change in the Loess Plateau. For future vegetation restoration efforts, we need to pay attention to the influence of microtopography on soil moisture.

Effects of deep soil mixing on existing shield tunnels in soft soil ground

To mitigate the impact of adjacent construction on existing shield tunnels,deep soil mixing(DSM)has been widely used to reinforce the soft soil ground around shield tunnels.However,the construction of DSM may cause the movement of existing shield tunnels under soft soil and sensitive ground conditions,and reasonable installation parameters will reduce the impact of DSM construction on the existing shield tunnels.Based on the field tests of DSM installation parameters and a program of field measurements of existing shield tunnels during the DSM construction in Suzhou,the reasonable installation parameters of DSM were selected,and the movement of soil behind the soil mixing walls(SMWs)during multirow DSM installation was investigated.The movement of the shield tunnels caused by DSM construction were discussed in detail.The field test results showed that the DSM columns installed at a higher speed and a lower water-cement ratio enlarged the movement of the surrounding soil.The DSM should be installed at a lower speed and a higher watercement ratio to reduce the movement of the shield tunnels.The field measurement results showed that the displacement of the tunnel lining was primarily caused by the construction of DSM zones beside the shield tunnels,which led to vertical compression and horizontal expansion of the tunnel lining.The construction of DSM immediately above the shield tunnels caused uplift to the tunnels.In addition,the deformed shapes of the two shield tunnels were asymmetric,and the displacement of the spring lining was larger than that of the crown.By taking the reasonable installation parameters of DSM and under the protection of the SMWs,the deformation of the shield tunnels caused by the construction of DSM was effectively controlled,and the maximum displacement was within the control value of the shield tunnels in this study.

Parasitic contamination of surface and deep soil in different areas of Sari in north of Iran

Objective:To study the parasitic contamination of soil in selected areas of Sari,north of Iran.Methods:A cross-sectional study was conducted to identify all available parasites in surface and deep soil.In this study 580 soil samples(278 deep soil and 302 topsoil samples)from 21 different locations were collected from pathways,parks,greenhouses,estates around the city,cemetery,main squares,farmlands,fenced gardens and seashores.Depending on the soil type,two samples were prepared,from surface and deep soil at the depth of 3 to 5 cm.After performing various stages of preparation,including cleaning and washing,smoothing and flotation,parasitic elements were examined microscopically and quantitative parasite counting was done using a McMaster slide.Results:The results showed that the highest rate of parasitic contamination was related to nematodes larvae(26.11%).Other contaminants such as Entamoeba and Acanthamoeba cysts,vacuolization Blastocystis hominis form,oocyte containing sporocysts,Toxascaris eggs,nematoda larvae,Hymenolepis eggs,Ascaris eggs,Fasciola eggs,hookworm eggs,Toxocara eggs,insects'larvae and other ciliated and flagellated organisms were also observed.The results of this study showed that the highest contamination was found in public garden(25.80%)both in surface(29.30%)and in deep soil(21.12%),while the lowest level of contamination was observed in seashore surface soil(4.90%).Conclusions:The results showed that soil can provide a potential medium for the spread of soil transmitted parasitic diseases in the environment;therefore,preventive programs are needed.

Analysis of temperature field characteristics based on subgrade site measurements of Harbin-Qiqihar High-speed Railway in a deep seasonal frozen soil region

Recent years have seen a large number of high-speed railways built and will be built in seasonal frozen soil regions ot China. Although high-speed railways are characterized by being fast, comfortable and safe, higher standards for defor- mation of the railways＇ frozen subgrade are required. Meanwhile, changes in subgrade soil temperatures are the main factors affecting the deformation of frozen subgrade. Therefore, this paper selected typical test subgrade sections of the Harbin-Qiqihar Line, a special line for passenger transport built in the deep seasonal frozen soil regions of China, to monitor field temperatures. Also, the temperature changing laws of railways＇ subgrade in this region was analyzed by using testing data, the aim of which is to provide a technical support for future design and construction of buildings and structures in a deep seasonal frozen soil region.

Study on the shear strength of deep reconstituted soils

Based on analytical methods of strength studies for deep soils, direct shear tests were carried out to investigate the shear strength of deep reconstituted soils at different initial dry densities and amounts of water.The results indicate that the shear strength of deep reconstituted soils for identical amounts of water below the plastic limit is enhanced with increasing dry density and but reduced sharply at the critical density, the point at which coarse particles break down.Moreover, the shear strength for identical dry density decreases with additional amounts of water and the rate of degradation is the greatest at the critical density.This is because the friction resistance between coarse particles reduces with increasing amounts of water higher than the plastic limit.In order to obtain reliable strength of deep reconstituted soils, suitable dry densities and amounts of water are necessary.

Research of deformation prediction method of soft soil deep foundation pit

In view of the characteristics of soft soil deep foundation pit for the construction and geotechnical characteristics of the special medium,it is difficult to calculate theoreti- cally accurately structural deformation of the foundation pit,so in the course of excavation on the construction of the information is particularly important.The analysis and compari- son of several popular non-linear forecasting methods,combined with the actual projects, set up a grey theoretical prediction model,time series forecasting model,improved neural network model to predict deformation of the foundation pit.The results show that the use of neural network to predict with high accuracy solution,it is the foundation deformation prediction effective way in underground works with good prospects.

Soil Nitrogen Distribution and Plant Nitrogen Utilization in Direct-Seeded Rice in Response to Deep Placement of Basal Fertilizer-Nitrogen

Deep placement of controlled-release fertilizer increases nitrogen (N) use efficiency in rice planting but is expensive. Few studies on direct-seeded rice have examined the effects of deep placement of conventional fertilizer. With prilled urea serving as N fertilizer, a two-year field experiment with two N rates (120 and 195 kg/hm2) and four basal N application treatments (B50, all fertilizer was broadcast with 50% as basal N;D50, D70 and D100 corresponded to 50%, 70% and 100% of N deeply placed as basal N, respectively) were conducted in direct-seeded rice in 2013 and 2014. Soil N distribution and plant N uptake were analyzed. The results showed that deep placement of basal N significantly increased total N concentrations in soil. Significantly greater soil N concentrations were observed in D100 compared with B50 at 0, 6 and 12 cm (lateral distance) from the fertilizer application point both at mid-tillering and heading stages. D100 presented the highest values of dry matter and N accumulation from seeding to mid-tillering stages, but it presented the lowest values from heading to maturity stages and the lowest grain yield for no sufficient N supply at the reproductive stage. The grain yield of D50 was the highest, however, no significant difference was observed in grain yield, N agronomic efficiency or N recovery efficiency between D70 and D50, or between D70 and B50, while D70 was more labor saving than D50 for only one topdressing was applied in D70 compared with twice in other treatments. The above results indicated that 70% of fertilizer-N deeply placed as a basal fertilizer and 30% of fertilizer-N topdressed as a panicle fertilizer constituted an ideal approach for direct-seeded rice. This recommendation was further verified through on-farm demonstration experiments in 2015, in which D70 produced in similar grain yields as B50 did.

Characteristics of deep drainage and soil water in the mobile sandy lands of Inner Mongolia, northern China

Quantification of deep drainage and the response of soil water content to rainfall patterns are critical for an effective management strategy of soil water conservation and groundwater utilization. However, there has been little information on how rainfall characteristics influence soil water dynamics and deep drainage in mobile sandy lands. We used an underground chamber to examine the responses of deep drainage and soil water content in mobile sandy lands to rainfall characteristics in Inner Mongolia during the growing seasons of 2010, 2011 and 2012. Results showed that rainfall in this area was dominated by small events （〈5 mm）, which increased soil water con- tent in the surface soil layers （0-40 cm）, but did not increase soil water content in the deeper soil layers （greater than 40 cm）. Soil water content at the 0-100 cm depth increased significantly when the total amount of rain was 〉20 mm. Rainfall amount, intensity and the duration of dry intervals were significantly related to the soil water content in different soil layers. Deep drainage was significantly correlated with rainfall amount and intensity, but not with the duration of dry intervals. The coefficients of deep drainage in the mobile sandy lands ranged from 61.30% to 67.94% during the growing seasons. Our results suggested that rainfall infiltration in the mobile sandy lands had considerable potential to increase soil water storage while recharging the groundwater in this region.

Characterization of aliphatic hydrocarbons in deep subsurface soils near the outskirts of Beijing, China

Thirty-nine deep subsurface soils(150—180 cm depth) near the outskirts of Beijing were investagated. The concentrations including n-alkanes from C_ 13 to C_ 36, pristane and phytane were in the range of 0.60 to 170.10 μg/g, with a median value of 4.26. Carbon preference index values for n-alkanes ranged from 1.08 to 2.98, with a median value of 1.48. The percentage contribution of “wax' n-alkanes was in the range of 6.03%—46.22%. A predominance of odd/even carbon n-alkanes and unresolved complex mixtures with different shapes and ranges were frequently observed. Factor analysis reduced the data set into three principal components and confirming contributions from low(19.58%), medium(20.49%) molecular weight species and long-chain n-alkanes(43.41%), respectively. Molecular biomarkers such as pristane, phytane, hopanes and steranes were detected. Based on the principal component analysis, the concentration profiles and molecular markers, it was found that the aliphatic hydrocarbons were from both biogenic and anthropogenic sources.

Collapse of a Deep Excavated Foundation Pit in the Soft Soils by 3-D FEM

In view of the collapse of a deep excavated foundation pit of the Xianghu subway underground station in Hangzhou of China,the main features of the accident are analyzed,and the induced factors of the accident are summarized. Then,a 3-D FEM analysis model is created to demonstrate the soil-support structures interaction system,and the effect of the main factors,such as the volume replacement ratio of the bottom soil reinforcing,the asymmetric ground overload,the embedded depth of the diaphragm wall,the shear strength of the bottom soils disturbed by the construction,and the excessive excavation of the bottom soil,are analyzed and compared. The results show that the ineffective original reinforcement plan for the bottom soft soil is the most prominent factor for the accident,and the disturbance effect of the deep excavation on the shear strength of the bottom soft soil is another significant factor for the accident. Meanwhile,if the reinforcement of the bottom soft soil is canceled,an appropriate extension of the diaphragm retaining walls to the under lying harder soil layer can also effectively prevent the collapse of the deep excavated foundation pit. In addition,the partly excessive excavation in the process has a great influence on the axial force of the most nearby horizontal support but few effect on the stability of the diaphragm wall. Thus,the excessive excavation of the bottom soils should not be the direct inducing factor for the accident. To the asymmetric ground overload,it should be the main factor inducing the different damage conditions of the diaphragm walls on different sides. According to the numerical modeling and actual engineering accident condition,the development process of the accident is also identified.

开挖顺序及内支撑早期刚度对软土基坑稳定性影响规律

深基坑开挖变形控制是软土基坑工程的难题,工程中常采用密集的混凝土内支撑来提高支撑刚度,然而实际工程中未能合理考虑软土深基坑的开挖顺序和混凝土内支撑早期刚度影响,往往导致基坑实际变形远大于设计值。结合珠三角水资源配置工程的软土深基坑,利用验证后的数值模拟方法研究了不同开挖顺序及混凝土内支撑早期刚度对基坑受力和变形特性的影响规律,得出了分层分区非对称开挖和对称开挖对地连墙水平位移和地表沉降的影响规律。结果表明:尽管非对称开挖会造成基坑两侧的地连墙位移和地表沉降差异,但是密集内支撑条件下非对称开挖比对称开挖对于基坑周围地表沉降和地连墙水平位移影响更小并能够大量节约工期;受混凝土内支撑早期刚度影响,施作内支撑后越早进入下一步开挖,地连墙水平位移和周围地表沉降越大;考虑内支撑早期刚度影响时基坑上部的内支撑轴力会增大,而下部的内支撑轴力会减小,早期刚度越小,这种趋势越明显;现场施工时难以实时动态监测混凝土的弹性模量,极易造成内支撑轴力的早期监测数据失真,甚至给工程带来错误决策。

深覆土梯形拱明洞静力特性及卸荷效果

为研究深覆土条件下梯形拱结构–填土相互作用对周围土压力的影响机制和卸荷机理,明确梯形拱明洞相较于传统矩形明洞的优势,采用室内模型试验和数值模拟相结合的方法,对深覆土梯形拱明洞静力特性及卸荷效果进行分析。结果表明:无减载时,梯形拱明洞两侧回填土沉降大于上方回填土沉降,两侧回填土土压力向明洞上方转移,土压力随着填土高度的增大而增大,基本呈线性变化趋势;减载时,明洞上方回填土沉降大于两侧回填土沉降,回填土内部产生土拱效应,明洞上方回填土土压力向两侧转移,铺设减载层不会改变深覆土明洞结构受力分布,但会极大地减小其内力及变形,并提高结构安全系数;减载后,梯形拱明洞的最大轴力、最大正弯矩和最大负弯矩分别减少17.5%、34.1%、29.9%,最大变形减小32.9%。矩形和梯形两种截面形式下明洞的最大轴力均出现在中隔墙底部,最大正弯矩、最小安全系数和最大变形均出现在顶板中央位置;铺设减载层后两种截面形式拱明洞最小安全系数分别增大42.6%和100.0%,梯形拱明洞安全系数提高的比例更大,效果更显著。该研究可为深覆土梯形拱明洞结构的设计和施工提供理论指导和技术支持。

深松铲对砖红壤扰动行为影响的仿真与试验

针对香蕉地深松作业相关研究较少,深松铲-土壤耦合机理尚未明确等问题,结合海南热区香蕉地砖红壤土的物理特性,利用离散元虚拟仿真试验,堆积生成了耕作层、犁底层和心土层3层土壤模型,建立了滑切深松铲-土壤耕作模型,并通过对比虚拟仿真试验,研究了滑式深松铲和国标深松铲对海南香蕉地土壤的扰动情况。结果表明:在相同的作业条件下,滑式深松铲作用下的土壤颗粒在x、y和z方向的最大运动速度均明显大于国标深松铲对土壤颗粒的作用,且滑式深松铲的扰动轮廓要明显大于国标深松铲作业的扰动轮廓,同时滑式深松铲作用下土壤蓬松度和土壤扰动系数均大于国标深松铲作用产生的深松效果,进一步验证了所设计的滑式深松铲更适用于海南香蕉地的深松作业。