Soil Box Research Articles

Effects of Carbon-Based Modified Materials on Soil Water and Fertilizer Retention and Pollution Control in Rice Root Zone

To seek an appropriate stabilization and remediation scheme for cadmium (Cd) and arsenic (As) pollution in farmland, a typical polluted soil sample was selected from a mining area in Southwest China for a soil box simulation experiment. Biochar (BC), a modified type of biochar made from rice husk with different mass ratios of ferric chloride and rice husk, was set up (the mass ratio of ferric chloride to rice husk was 1:9 (defined as LFB), 3:7 (defined as MFB), and 5:5 (defined as HFB) and the control group (BL)) to explore the effects of soil water and fertilizer loss, the bioavailability of Cd and As, and the bioenrichment effects of plant organs during the growth period of rice. The results showed that the porous structure and large specific surface area of biochar effectively regulated soil aggregate composition and improved soil water holding capacity. Compared to the BL treatment, soil water storage under the four carbon-based material control modes increased from 8.98% to 14.52%. Biochar has a strong ion exchangeability and can absorb soil ammonium, nitrogen, and phosphoric acid groups, effectively inhibiting the loss of soil fertilizer. Biochar improves soil pH and reduces the specific gravity of exchangeable Cd. In addition, the oxygen-containing functional groups in biochar can react with metals in a complex manner. The diethylenetriaminepentaacetic acid (DTPA) concentrations of Cd in soils treated with BC, LFB, MFB, and HFB were 79.69%, 72.92%, 64.58%, and 69.27% lower, respectively, than those treated with BL. In contrast, the Fe3+ in ferric chloride combines with As after hydrolysis and oxidation to form amorphous ferric arsenate precipitates or insoluble secondary minerals. Therefore, the curing effect of the modified biochar on As was more potent than that of applied biochar alone. In conclusion, ferric chloride-modified biochar can effectively inhibit the effects of water and fertilizer loss in farmland soil and realize cross-medium long-term inhibition and control of combined Cd and As pollution.

Accelerated surface carbonation of non-plastic silt mixed with hydrated lime

Chemical stabilization via hydration reactions with cement or lime is a universally applied method to improve the mechanical properties of shallow soils. Accelerated soil carbonation is a nascent approach intended to bypass this reaction. Carbon dioxide gas is deliberately introduced at high concentrations to react with the alkali additives and precipitate a carbonate binder that permanently sequesters carbon dioxide in the process. A large soil box experiment was performed to examine the efficacy of an accelerated surface carbonation approach, which has the potential to be applied over large areas. High concentrations of carbon dioxide gas were introduced at grade beneath a seal to facilitate vertical penetration into lime-mixed silt. The real-time progression of accelerated soil carbonation was captured with a gas flowmeter and a distributed array of embedded thermocouples and bender elements for the first time. Post-carbonation measurements of binder content and California Bearing Ratio (CBR) verified the degree of carbonation and associated mechanical improvement. Synthesis of real-time monitoring data and post-carbonation measurements indicate carbonation progressed top-down 150 to 200 mm below grade within 5 h, resulting in a substantial increase in strength and stiffness. Potential challenges and benefits associated with adoption of accelerated surface carbonation are discussed.

Assessing a semi-empirical model performance to predict the wetting patterns in subsurface drip irrigation

ContextBecause of the complexity of soil water distribution, accurate prediction of wetting pattern is not easily accessible and this has led to a inefficiency in some proposed models in the literature. These models do not consider the hydraulic characteristics of the irrigation system and are developed solely on the basis of the water volume or infiltration rate, soil hydrodynamic properties, and other conditions of the percolation environment. ObjectiveDue to the importance of the estimation of wetting front beneath Subsurface Drip Irrigation (SDI) laterals, a semi-empirical model using easily accessible data of the SDI system is proposed to predict the wetting patterns in both distribution and redistribution phases. The aforementioned model has been developed based on a novel approach that couples the governing equations of the lateral hydraulics with empirical equations derived by dimensional analysis. MethodsTo develop the model and evaluate its performance, three 16-mm drip line pipes with 0.2, 0.4, and 0.5 m emitter spacing, and 2–5 l/h discharge were placed at 0.20 m depth in a soil box filled with clay loam soil. Water was applied for 3 hours at 50, 100, and 150 kPa operating pressures, and the wetting patterns’ geometries were measured in each lateral after 1, 2, 3, and 24 h. The performance of the model was then assessed and compared with that of three other models. Results and conclusionThe result demonstrated that the proposed model provides the most accurate estimations of the wetting depths and widths. RMSE and MAE statistical indexes of the wetting depth were 0.001–0.002 m and 0.004–0.009 m, respectively, whereas those associated with the wetting width were 0.001–0.003 m and 0.005–0.016 m, respectively. These values resulted in the lowest error when compared with the corresponding obtained from other well-known models. Consequently, the model allows acceptable predictions of the wetting patterns using accessible hydraulic parameters of the SDI system. SignificanceUniquely, the results of the lateral hydraulic analysis were applied to determine the wetting front dimensions in this study. Also, the results demonstrated that the model was successful in wetting pattern prediction beneath the lateral as a line source. While other models usually are used to estimate the wetting front around a point source.

Shaking Tables Test on Seismic Responses of a Long-Span Rigid-Framed Bridge Considering Traveling Wave Effect and Soil–Structure Interaction

The traveling wave effect and soil–structure interaction have significant influence on the seismic response of large-span bridges with complex site conditions. In this paper, a 1/10 scaled-down large-span rigid-framed bridge model was designed and fabricated, and a shaking tables test considering the traveling wave effect and soil–structure interaction was carried out on a large-scale continuous rigid bridge model by a real-time substructure hybrid test technique. Influences of the traveling wave effect and soil–structure interaction on the seismic responses of the rigid-framed bridge specimen were systematically analyzed with experimental data. The test results showed that when the apparent wave speed was small, the traveling wave effect increased the seismic responses of the rigid-framed bridge. With the increase in apparent wave speed, the structural response under traveling wave excitation and uniform excitation was basically the same. The SSI effect lead to a great change in the seismic input peaks and spectral characters at the bottom of the pier, and increased the seismic responses of the rigid-framed bridge. When both traveling wave and the SSI effect were considered, there was a phase difference in the seismic excitation. The dynamic responses of a continuous rigid-framed bridge could not be simply obtained by superposition of the separate traveling wave effect or SSI effect. Meanwhile, the real-time substructure test method in this paper solved the problems that the traditional soil box experiment cannot be applied to the test of a large-scale model, the soil and bridge structure find it difficult to meet the unified similarity ratio, and the boundary conditions are difficult to simulate accurately.

Biochar reduces antibiotic transport by altering soil hydrology and enhancing antibiotic sorption

The performance of biochar (BC) in reducing the transport of antibiotics under field conditions has not been sufficiently explored. In repacked sloping boxes of a calcareous soil, the effects of different BC treatments on the discharge of three relatively weakly sorbing antibiotics (sulfadiazine, sulfamethazine, and florfenicol) via runoff and drainage were monitored for three natural rain events. Surface application of 1 % BC (1 %BC-SA) led to the most effective reduction in runoff discharge of the two sulfonamide antibiotics, which can be partly ascribed to the enhanced water infiltration. The construction of 5 % BC amended permeable reactive wall (5 %BC-PRW) at the lower end of soil box was more effective than the 1 %BC-SA treatment in reducing the leaching of the most weakly sorbing antibiotic (florfenicol), which can be mainly ascribed to the much higher plant available and drainable water contents in the 5 %BC-PRW soil than in the unamended soil. The results of this study highlight the importance of BC’s ability to regulate flow pattern by modifying soil hydraulic properties, which can make a significant contribution to the achieved reduction in the transport of antibiotics offsite or to groundwater.

Comprehensive wood dwelling tests for Post‐and‐Beam and Shear‐Wall structures reflecting foundation boundaries

AbstractThis paper focuses on the ultimate state of three‐story wood dwellings with high aspect ratios, which are increasing in Japan's urban areas. Using shaking table test results from the 2019 full‐scale shaking table test, a comprehensive study is conducted on the accuracy of evaluating ultimate state through the story shear failure mode at the first story, the tension fracture mode at the wall base of the first story, and foundation sliding mode on the soil. Methods evaluating the dynamic response behaviors of the building systems are also investigated. In the test, the current Japanese seismic design guidelines were applied, and two Grade‐3 buildings were prepared. One adopted the Post‐and‐Beam structure (A‐building), and the other the Shear‐Wall structure (B‐building). A series of tests planned very different physical boundary conditions surrounding their reinforced concrete (RC) mat foundations. The sills, column bases and wall bases of the upper wood structures were anchored to the RC foundations by steel anchor bolts, according to the current Allowable Stress Design (ASD) requirements. In the first stage, A‐building equipped a Base‐Isolation system, while B‐building represented a generic foundation constructed on a 1.5 m‐height real soil ground by preparing a rigid soil box (Foundation‐Soil system). In the second stage of A‐building and B‐building, the foundation was firmly fixed (Fixed‐Foundation system), and shaking table motions were fully applied to the foundations. The entire test system was setup on the large shaking table facility at E‐Defense, and a series of tests were conducted using JMA‐Kobe motion and JR‐Takatori motion recorded in the 1995 Kobe earthquake as Maximum‐Considered‐Earthquake motions. Confirmed was the change in the structural mechanism due to the upper structural systems and the foundation boundaries. Regarding the upper wood structure performance in the Fixed‐Foundation system, a story shear failure mode was observed at the first story in A‐building, while a tension fracture mode at the base of the first story in B‐building. This difference of failure mode is difficult to determine with ASD. The maximum strength were more than four times higher than the ASD base shear force. Tension fracture capacity at the wall base was mainly enhanced by the presence of the steel anchor bolts. Regarding the foundation performance in Foundation‐Soil system of B‐building, a horizontal displacement up to 240 mm was observed between the foundation and soil when JMA‐Kobe 100% was applied. A response reduction effect was observed in the upper wood structure, similar to the Base‐Isolation system of A‐building. The initial friction and cyclic friction strength capacities between the foundation and soil were quantitatively evaluated considering the horizontal two‐directional sliding. The representative test results were converted to the corresponding SDOF systems based on the first mode response assessment. In the Fixed‐Foundation system, the dynamic response characteristics of the upper wood structures were properly represented using Ibarra‐Medina‐Krawinkler pinching model in the equivalent SDOF system.

Qualitative investigations into floodways under extreme flood loading

AbstractThe Australian use of the term floodway refers to a trafficable transverse structure designed to facilitate the safe crossing of watercourses. Floodways are also commonly referred to as fords and causeways. This research explores areas of focus through experimental, numerical and survey methods to improve floodway resilience with regard to flood risk management. The industry‐based survey provides a dataset relating to user experiences, deduces the likeliness of floodways to sustain damage, defines several key focus areas, and reveals that the current risk levels are primarily managed without significant investigation into design. A floodway experimental and numerical simulation program was developed to investigate the lateral forces induced through debris impact using scaled models in a soil box and finite element analysis. Qualitatively, crack propagation and displacement correlated closely with the strain concentrations and displacements in the numerical simulation, with failure attributed to tensile strength being exceeded, followed by plastic strain development within the soil elements. It was concluded through this research that floodway failure during flood is complex and can be attributed to several different failure modes including concrete failure, yielding of adjoining soil material, and hydraulically via scour.

Coupled aero-hydro-geotech real-time hybrid simulation of offshore wind turbine monopile structures

Real-time hybrid simulation (RTHS) divides a structural system into an analytical and experimental substructure. The former is based on a well-established analytical model while the latter consists of a physical model in the laboratory, for which there is not a well-established analytical model. This paper extends real-time hybrid simulation to monopile-type Offshore Wind Turbines (OWTs) to enable the investigation of their behavior considering the response of pile foundations under operational and more severe conditions. The embedded foundation and surrounding soil of the OWT are modeled physically in a soil box in the laboratory while the remaining parts of the system and loading are modeled analytically. The program OpenFAST, developed by the National Renewable Energy Laboratory (NREL), is linked to the RTHS coordinator to determine the hydrodynamic and aerodynamic loads acting on the OWT, along with modeling the dynamics of the electric power generation equipment and associated controller for the OWT. The RTHS framework along with its initial implementation and validation are described in this paper. RTHSs of a 5 MW OWT subjected to operational and more severe conditions are performed to experimentally validate the framework. The framework offers a realistic approach to investigate the behavior of OWT structures supported on monopiles. This approach accounts for the coupled response of the OWT structure with its foundation, while experimentally capturing the nonlinearities of the soil-foundation interaction in real-time.

Research on Underground Drip Irrigation and Soil Redistribution - Take Heshan District of Yiyang City as an Example

Abstract: The drip flow and the buried depth of drip irrigation zone are not only important parameters of subsurface irrigation design and operation management, but also important factors affecting the migration and redistribution of soil water and fertilizer. Crop growth is closely related to soil water and nitrogen leaching, water and fertilizer transport patterns and redistribution characteristics. It is of great significance to study the migration and redistribution of soil water and fertilizer under subsurface drip irrigation for improving the utilization efficiency of water and fertilizer and improving the system of subsurface drip irrigation. In this paper, the migration mode and redistribution characteristics of water and nitrogen in subsurface drip irrigation were studied and analyzed by means of laboratory soil box experiment, considering the two factors of drip flow and the buried depth of drip irrigation belt. The main research conclusions are as follows: Ⅰ. Different drip flows had effects on soil moisture front, soil moisture content and soil water redistribution. If other conditions remain unchanged, increasing the drip flow can increase the moist body area of soil and increase the moisture content of soil. The distance between vertical and horizontal directions increased with the large drip flow, and the soil water content decreased with the increase of distance. Large drip flow can promote the redistribution of soil water after drip irrigation. Ⅱ. Different drip depth had effects on soil moisture content and soil water redistribution. When the drip depth was 0cm, the surface shape of the wet body was a "horizontal" semi-ellipse after drip irrigation. When the drip depth was 10cm and 20cm, the surface of the wet body was an "upright" semi-ellipse after drip irrigation. The larger the buried depth of the drip can make the distribution of soil moisture more uniform, and the larger the buried depth of the drip can promote the migration of water in the soil. Ⅲ. Different drip discharge had an effect on soil nitrogen redistribution, and large drip discharge promoted soil nitrogen redistribution after drip irrigation. The Nitrate Nitrogen (NO3--N) content in the moist body is lower than that near the edge of the wetting front. The content of Ammonium Nitrogen (NH4+-N) near the edge of the wetting peak is higher than that inside the wetting body. Ⅳ. The redistribution of soil nitrogen was affected by different buried depth of drip head, and the greater buried depth of drip head could promote the redistribution of soil nitrogen. In terms of vertical and horizontal migration of ammonium nitrogen and nitrate nitrogen, on the day after drip irrigation, the cumulative effect of Nitrate Nitrogen (NO3--N) buried at a depth of 20cm was more significant near the wetting front edge at a larger vertical downward distance, and the cumulative effect of Nitrate Nitrogen (NO3--N) buried at a depth of 20cm was more significant inside the wetting body at a larger vertical downward distance. At the same time, the drip buried depth of 20cm can spread the cumulative effect inside the wet body and near the edge of the wet front to a longer horizontal distance.

Influence of composite flocculants on electrokinetic properties and electroosmotic vacuum preloading behavior of sludge

In recent years, dredging projects in rivers and lakes have generated large volumes of sludge that exhibit high water content and low permeability. This dredged sludge needs to be treated quickly to reduce its volume, thus reducing transportation costs and environmental impacts. Flocculation combined with electroosmotic vacuum preloading is a new technology for dewatering sludge. At present, the influence of flocculants on the electrokinetic properties of sludge has not been thoroughly studied, and composite forms of these have not been applied in electroosmotic vacuum precompression. Therefore, inorganic flocculant and organic flocculant were combined to form a composite flocculant, which was used in electroosmosis vacuum preloading to increase the water discharge effect of dredged sludge. Based on analyzing the mechanism of flocculants, two kinds of composite flocculants, PAC-APAM and FeCl3-APAM, were configured, and the optimal ratio of inorganic flocculant and organic flocculant in the composite flocculant was determined with a settling column test. The properties, including pore size distribution, electric conductivity, and electroosmotic permeability coefficient, of the sludge mixed with flocculants PAC, FeCl3, APAM, PAC-APAM, and FeCl3-APAM were analyzed by NMR tests and Miler Soil Box tests. In addition, a model test of electroosmotic vacuum preloading treatment of dredged sludge was conducted, and the influences of different types of flocculants on the surface settlement, water discharge, current, pore water pressure, and shear strength of the sludge were compared and analyzed. The results showed that the composite flocculants suggested in this study were able to increase the electroosmotic permeability coefficient of sludge more significantly than single-type flocculants. In situations where electroosmotic vacuum preloading combined with composite flocculants was used to treat sludge, water discharge, and consolidation settlement were larger, and the shear strength of the treated sludge was higher. Compared with FeCl3-APAM, PAC-APAM showed better performance in electroosmotic vacuum preloading.

A novel pipe-segment shear test apparatus: polypropylene pipe behaviour over sand beds versus element interface tests

This study describes a novel laboratory test apparatus for investigating the axial interaction between pipeline and soil. Contrary to the majority of existing pipe–soil shear rigs, the proposed apparatus applies a relative pipe–soil shear displacement through driving a soil box below an axially restrained pipe segment, which is instrumented to measure the pipe settlement and the axial resistance at the pipe–soil contact surface. Through axial shear tests of polypropylene pipe segment on sand, this study explores the effect of vertical loads, soil types, and densities on the resulting axial resistance and estimates the interface stress evolution. The coefficients of axial resistance obtained from large-scale pipe–soil shear tests are compared to those obtained via planar element interface shear tests with consideration of the wedging effect. Their consistency suggests that under the low stress levels investigated in this study, the effect of both pipeline curvature and settlement on the resultant data are minor. The agreement provides validation for the novel apparatus to generate high-quality data under controlled conditions for future studies. The findings of this study will also potentially help reduce the uncertainties around subsea pipeline design when linking the interface shear behaviour at element scale to large-scale pipe–soil interaction.

Nondestructive testing of seepage in check dams using high-density electrical resistivity tomography based on laboratory test

One of the most significant factors that endanger the safety of check dams is seepage. How to quickly identify the seepage location and pinpoint the seepage path in check dams is directly related to the effectiveness of soil and water conservation measures in the Chinese Loess Plateau. In this study, the improved Miller Soil Box was used to carry out laboratory test of remolded soil, and the effects of moisture content and compactness on soil resistivity were thoroughly examined. On this foundation, the nondestructive testing of seepage was conducted on the Dongmengou check dam based on the different configuration modes of high-density electrical resistivity tomography technology. The laboratory test demonstrates that the soil resistivity and the moisture content exhibit a decreasing power function, while the soil compactness has a negative correlation with the soil resistivity. The interpretation quality of the high-density electrical resistivity tomography technology is significantly improved by the laboratory test, allowing the field test to more precisely detect seepage inside the check dam. As a result, the high-density electrical resistivity tomography technology has good applicability and feasibility in the nondestructive testing of seepage in check dams, and offers a number of benefits, including non-destructiveness, high detection efficiencies and rich data information. It provides an efficient tool for the quick, widespread, and nondestructive detection of dam seepage.

Performance of a Corrugated Metal Pipe with Shallow Burial Depth in Loosely Compacted Sand: Soil Box Test and 3D Finite Element Modeling

There have been many studies that have investigated the behavior of buried corrugated metal pipes (CMPs) in culvert applications. However, full-scale testing of buried culverts is a major undertaking since performing numerous large-scale tests is not always possible. A large-scale physical test was done on a corrugated metal pipe with a 1.52 m diameter under a monotonic loading test. The finite element modeling (FEM) tool (ABAQUS) was employed to verify and simulate different behaviors of a pipe-soil system. The finite element model showed a suitable match with the laboratory test results and properly identified local buckling as the failure mode for testing conditions, a CMP buried under shallow cover. The FE model indicated satisfactory performance in predicting the strains, bending moments, thrusts, and pressure distribution in the CMP. Subsequently, the behavior of CMP pipes was examined by increasing 25% and 100% in the burial depth and loading pad area, respectively. Results indicated that with an increase in the burial depth by 25%, the maximum deformation of the pipe at the crown decreased by approximately 31%. An increase in loading pad size by 100% led to a decrease in minimum factor safety at the crown by approximately 93%.

Centrifuge test of large-diameter segmented ductile iron pipes crossing strike-slip faults

Seismic ground faults are severe hazards for buried pipes. To explore and model the failure mechanisms of segmented pipes crossing faults, a centrifuge test of a socket-type ductile iron pipe crossing a strike-slip fault is conducted. In the test, a segmented ductile iron pipe with five segments is buried in a soil box. Then, at a centrifugal gravity level of 30.7 g, 60 mm ground displacements are applied through translation of half of the test soil box. Thus, a 2646.2 mm-diameter pipe with a length of 27.4 m subjected to a 1.84 m-long strike-slip fault is simulated. The responses of the joint deformation and the pipe strain are obtained. Results show that the joint deformation is the main response of the pipes subjected to strike-slip faults, the joint near the fault trace is vulnerable, the pipe strain is relatively small, and the peak pipe strain occurs at a certain distance from the fault. Lastly, a theoretical method is presented to obtain the joint deformation of the pipes crossing a strike-slip fault, and a good agreement between the test and theoretical results is observed. The test can be a benchmark for theoretical and numerical models. Meanwhile, the proposed theoretical method has clear physical mechanisms and can obtain the pipe joint deformation effectively.

Transverse response of utility tunnel under near fault ground motions: Multi-shake table array tests

This paper presents shaking tests conducted on a 1/30-scale utility tunnel model employing a multi-shaking table array system. The model utility tunnel-soil system was subjected to input motions simulating near-fault ground motions with and without velocity pulse. The test data were collected and analyzed including acceleration, strain and displacement of the soil bed and model tunnel responses. The soil data analysis indicated that the boundary effect of the model soil box used in the test was negligible. The observed small soil settlements confirmed that the physical and mechanical properties of the model soil did not change significantly in tests. The results also demonstrated that, in general, the transverse dynamic responses of the utility tunnel and surrounding soil under near-fault ground motion with velocity pulse were much greater than the case without velocity pulse. Therefore, the effect of velocity pulse should be considered in the design of utility tunnels.

Numerical Analysis and Experimental Study on Seismic Coupling Response of Pipe-Soil System Under Bidirectional Seismic Excitation

The seismic response of buried pipeline is significantly affected by the soil around the pipeline. In this study, a numerical analysis model of the pipeline and the soil around the pipeline is built, and the finite element numerical analysis of its seismic response law is conducted to address the problem of pipeline soil seismic coupling response. A shaking table test of the seismic response of buried pipeline under two-way seismic excitation is performed based on the developed two-way layered shear continuum model soil box. The peak strain response at the middle section of the pipeline grows fastest, the peak strain of the pipeline under non-uniform seismic excitation constantly exceeds that under uniform excitation, and the axial strain of the pipeline exhibits more sensitivity to earthquake than the bending strain, as indicated by the results of numerical analysis and shaking table test. The peak value of soil acceleration response under non-uniform excitation exceeds under uniform excitation. The displacement of soil increases with the height. The pipeline soil interaction becomes more intense under non-uniform excitation, and the relative movement between pipeline and soil becomes more significant. The seismic excitation more significantly affects the axial displacement of soil. The peak value of soil acceleration response varies from larger along the pipeline to larger along the axis with the increase of the loading grade. A slight difference exists between the peak value of axial and transverse acceleration response of the pipeline. The peak value of pipeline acceleration response declines in the axial direction than the peak value of soil acceleration response, whereas it rises in the transverse direction than the peak value of soil acceleration response, especially under non-uniform excitation. As revealed by the above results, the effect of bidirectional non-uniform seismic excitation on the lateral pipeline soil interaction is enhanced, and soil is more seriously damaged.

Experimental study on soil-structure interaction of steel frame under seismic excitations

Three types of shaking table tests were carried out to investigate the soil-structure interaction (SSI) effects on the seismic performance of the steel frames resting on soft soil ground. Three different models were involved in the shaking table tests including a ten-story steel frame resting on a soft soil ground, a ten-story steel frame resting on a rigid ground, and a free field with soft soil, respectively. First, the characteristics of soils were studied to choose suitable soft soil for the tests. Then, a laminar shear soil box was developed to contain soft soil and simulate the soil in the free field. Finally, the three models were subjected to various intensity seismic excitations of the El-Centro earthquake, the Kobe earthquake, and the Taft earthquake. The results showed that SSI effects noticeably affect the propagation of seismic waves, the dynamic characteristics, and the dynamic responses of the steel frame. For the steel frame resting on the rigid ground, the fundamental frequency of the SSI system decreased, but the damping ratio increased. The peak acceleration of the steel frame decreased when rested on the soft soil ground, but the inter-story drift increased. Consequently, the seismic SSI has a complicated influence on the dynamic responses of steel frames and should be considered reasonably to provide a rational seismic design for steel frames resting on soft soils.

Multi-temporal spatial modelling to assess runoff and sediment dynamics under different microtopographic patterns

Soil erosion is a multi-scale geographical interface process with high spatiotemporal variability. This study aimed to assess runoff and sediment dynamics under different microtopographic patterns based on wavelet analysis and SIMulated Water Erosion model (SIMWE). Three rainfall intensities of 1.0 mm min−1, 1.5 mm min−1, and 2.0 mm min−1, combined with three slope gradients of 10°, 15°, and 20°, were utilized to conduct rainfall simulations on three soil boxes measuring 4 m in length and 0.8 m in width. The soil boxes exhibited distinct microtopographic patterns, including smooth slope (CK), artificial digging (AD), and ridge tillage (RT). The results showed that the runoff and sediment reduction benefits of different tilled slopes decreased with an increase in both slope and rainfall intensity. The AD and RT slopes reduced runoff yields by 8.4% − 50.2% and 17.3% − 75.0% respectively compared to CK slope. Although sediment yields from AD and RT slopes were reduced by 4.2% − 51.6% and 1.8% − 53.0%, respectively, the sediment control benefits of AD and RT slopes were basically lost when the slope gradient increased to 20°. The rill erosion was the main source of soil erosion on different tilled slopes, accounting for 72% − 87% of the total soil loss. And the rates of both soil erosion and rill erosion exhibited a power function relationship with an increase in rainfall intensity and slope. The impact of slope gradient on soil erosion on the RT slope was greater than those on the CK and AD slopes. During the development of rill erosion, non-stationary and multi-scale periodic phenomena exist in the time series of runoff and sediment on different microreliefs. As surface microrelief increased, the fluctuations in runoff and sediment on tilled slopes intensified, resulting in a gradual shortening of the variation period. And this study verified the feasibility of the SIMWE model to simulate the runoff and sediment dynamics on microtopographic scale under a single rainfall event. The results can provide a theoretical basis for the scientific layout of soil and water conservation practices in sloping farmland and the construction of soil erosion model in purple soil area.

Specific power or droplet shear stress: Which is the primary cause of soil erosion under low-pressure sprinklers?

Specific power and droplet shear stress are generally considered to be the most critical indicators of soil erosion in sprinkler irrigation, but there is controversy about which indicator has a greater impact. This creates uncertainty in the optimization design of low-pressure sprinkler irrigation systems. In this study, a commonly used low-pressure sprinkler, i.e., Nelson D3000, was used to carry out in soil box experiments, to study the effects of specific power and average droplet shear stress at the end of a spray jet on soil erosion during sprinkler irrigation under three nozzle diameters (3.97, 5.95, and 7.94 mm), two operating pressures (103 and 138 kPa), and two soil textures (loamy sand and silty loam). Overall, the larger specific power or average droplet shear stress resulted in higher initial and steady runoff rates and a shorter time until runoff occurs and stabilizes. Enlarging the specific power or average droplet shear stress could significantly increase the initial infiltration rate, sediment yield, and surface soil bulk density, but the infiltration depth prior to runoff and surface soil porosity decreased. Furthermore, the specific power was observed to have greater correlations than average droplet shear stress with the surface runoff rate, initial infiltration rate, and increase in the soil bulk density and decrease in the soil porosity after irrigation. However, it was weakly related to the infiltration depth prior to runoff and sediment yield, indicating that the specific power could more accurately reflect the soil erosion with respect to the shear stress. To minimize the risk of soil erosion, a small operating pressure (103 kPa) is recommended in the design of center pivot irrigation systems, especially for the overhang of the system with large nozzle diameters. This research can provide the technical support for soil erosion prevention under low-pressure sprinkler irrigation.

Investigation of Backfill Compaction Effect on Buried Concrete Pipes

The present study deals with the experimental investigation of buried concrete pipes. Concrete pipes are buried in loose and dense conditions of gravelly sand soil and subjected to different surface loadings to study the effects of the backfill compaction on the pipe. The experimental investigation was accomplished using full-scale precast unreinforced concrete pipes with 300 mm internal diameter tested in a laboratory soil box test facility set up for this study. Two loading platforms are used namely, uniform loading platform and patch loading platform. The wheel load was simulated through patch loading platform which have dimensions of 254 mm *508 mm, which is used by AASHTO to model the wheel load of a HS20 truck. The pipe-soil systems were loaded up to pipes collapse. Pipes were instrumented with strain gauges to measure circumferential strains, in addition to dial gauges, for measurements of the pipe vertical deflections and settlement of the loading platforms. The test results indicated that flexure governed the buried pipe behavior. Flexural cracks formed slightly before the ultimate load. A comparison of soil backfill, between a loose and dense compaction, showed that the dense backfill improve largely the pipe installation and the strength ofpipe-soil system