In this study, parallel-plate loading tests for nonperforated and perforated single-wall corrugated plastic pipes were conducted, finite element method (FEM) models were established for parallel-plate loading tests using ANSYS Workbench software, and the models were verified according to the test results. Based on the FEM, we analyzed the influence of perforation characteristics, including the perforation location and size, number of rows of perforations, and perforation arrangement type, on the capacity of pipes to resist circumferential deflection. The results indicated that perforations should be avoided at the crown, invert, and springlines of the pipe. It is recommended that the perforation width not exceed 1/2 of the corrugation valley width. The number of rows of perforations should be evenly distributed around the whole circumference in fewer than four rows, and the perforation arrangement type should be arranged in a dislocation pattern.

This study develops a coupled model for the combined clogging and permeability coefficient of a geotextile envelope. Based on the characteristics of pore size distribution and its impact on permeability coefficient after clogging, a permeability coefficient model assuming the geotextile is composed of multiple layers of planar mesh is developed. Then, based on the range of pore size after clogging, hypotheses for large-pore clogging area and small-pore permeable area are proposed to simulate the process of decreasing the theoretical maximum pore size of the geotextile and the increasing area of large-pore clogging area. The physical and chemical clogging models are coupled and field sampling was used to confirm the availability of the model. Results indicate that the model effectively simulates the impact of clogging on the permeability coefficient. Additionally, sensitivity analysis and trend simulations show that permeability reduction coefficient (beta 1), area density (mu g0), and saturation index (SI) are the main factors affecting combined clogging and permeability, with beta 1 and mu g0 having significant early impacts, while SI has a greater impact in the later stages. When beta 1 is equal to 0.3 and SI is greater than 1.0, the geotextile envelope for subsurface drainage faces a high risk of combined clogging.

This study investigates the morphological characteristics, development process, and impact on permeability of physical-chemical combined clogging on geotextile envelopes, through laboratory experiments involving particle flow coupled with chemical precipitation. The results show that there is a synergistic effect between physical clogging caused by soil particle accumulation and chemical clogging due to salt precipitation. Chemical precipitation exacerbates physical clogging, while physical clogging promotes the formation of chemical precipitation. The chemical precipitates on the upstream of the geotextile envelope binds the particles to each other and to the fibers of the geotextile envelope, while on the downstream, precipitates tends to encapsulate the fibers, with less physical clogging. After combined clogging, the permeability coefficient of the geotextile envelope decreases rapidly with the increasing of the clogging material, and then decreases slowly. When the area density of the clogging material is less than 91.02 g/m2, it shows a linear decrease, and then followed by a logarithmic decrease. Physical-chemical combined clogging is more severe than single physical or chemical clogging. After the permeability stabilizes, for the same clogging mass, the decrease in permeability caused by combined clogging is 1.2 times and 2 times greater than that caused by physical and chemical clogging, respectively.

The effects of the concentration and flow velocity of the solution on calcite precipitation process in porous media and its permeability were investigated with a combined experimental and modeling approach. In the column precipitation experiments, calcite precipitation was mainly distributed at the inlet of experimental column and quickly decreases along the flow direction, and precipitates completely wrapped the quartz sands at the inlet, and the gaps between the quartz sands were filled. The permeability coefficient of experimental column decreases quickly in the early stage and then decreases slowly. The calcite precipitates in the experimental column increased with the saturation index and gradually stretched along the flow direction with the flow velocity in-crease. The precipitates were distributed within 1.0 cm of the experimental column inlet. In the model, based on the classical Kozeny-Carman equation and the principle of series superposition, a coupled model of mineral precipitation and permeability coefficient in porous media was developed, the model was verified, and the parameter sensitivity was analyzed. It revealed that the mineral precipitation at the inlet interface of experimental column was the dominant factor determining the permeability coefficient of porous media. When considering solution conditions, the saturation indices SI and flow velocity V were the main factors affecting calcite precipitation and permeability coefficient in porous media. When the solution conditions were not considered, the quartz sand diameter ds, the length of quartz sand column L and porosity phi aiming at mineral precipitation had higher sensitivity, and the porosity phi aiming at permeability coefficient had higher sensitivity.

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Objectives This study aims to evaluate the morphological features of gubernacular tract (GT) for erupting permanent mandibular canines at different ages from 5 to 9 years old with a three-dimensional (3D) measurement method. Methods The cone-beam CT images of 50 patients were divided into five age groups. The 3D models of the GT for mandibular canines were reconstructed and analysed. The characteristics of the GT, including length, diameter, ellipticity, tortuosity, superficial area, volume, and the angle between the canine and GT, were evaluated using a centreline fitting algorithm. Results Among the 100 GTs that were examined, the length of the GT for mandibular canines decreased between the ages of 5 and 9 years, while the diameter increased until the age of 7 years. Additionally, the ellipticity and tortuosity of the GT decreased as age advanced. The superficial area and volume exhibited a trend of initially increasing and then decreasing. The morphological variations of the GT displayed heterogeneous changes during different periods. Conclusions The 3D measurement method effectively portrayed the morphological attributes of the GT for mandibular canines. The morphological characteristics of the GT during the eruption process exhibited significant variations. The variations in morphological changes may indicate different stages of mandibular canine eruption.

Subsurface drainage is widely used in farmland. Entrance resistance occurs when water flows into a perforated drain pipe, reducing the drainage efficiency and resulting in a high water table. Using the real radius will overestimate the drainage discharge. Accurately calculating effective radius is essential for subsurface drainage calculation and simulation. New effective radius formulas for corrugated drains wrapped with a thin geotextile were proposed by dividing the entrance resistance into corrugation and perforation resistance. The accuracy of the formulas was verified by sand tank experiments. Sensitivity analysis was conducted to determine the factors that affected effective radius, indicating that corrugation was the main factor. When the radius and structure of the drain wall were determined, the opening area exhibited high sensitivity with interactivity between it and drainage discharge. The effect of the opening area and position of the perforations on the effective radius was evaluated for different drainage discharges. Putting the perforations on the bottom was better for drainage efficiency. For small drainage discharge of less than 0.1 cm3 s-1 cm-1, the opening area was not significant, and an opening area of 15 cm2 m-1 was sufficient. However, for greater drainage discharge, an opening area of 60 cm2 m-1 with three or more row perforations would be required.

Open ditches and subsurface drainage are effective measures for improving saline soils. Installations of subsurface drainage are now complementing surface drainage in Northwest China, but their optimisation has not been attempted. Therefore, the drainage and desalination performance of a combined subsurface drainage-open ditch system was analysed using two years of field experiments. The data were then utilised to calibrate and validate a water and salt transport model. The drainage volume in surface drains were 9-fold those in subsurface pipes. Additionally, 25 sets of orthogonal numerical experiments were designed with the subsurface pipe length, depth, and open ditch depth as variables. The results revealed that these three factors significantly affected the desalination efficiency of saline-alkaline farmland (P < 0.05). The ditch depth, pipe length, and pipe depth F values were 9.954, 50.286, and 6.557, respectively, and no interactions were observed among these factors. When a single open ditch was used for drainage, the desalination rate initially increased and then decreased as the distance from the open ditch increased. The inflection point varied with the open ditch depth and occurred within a range of 32-43 m when the ditch depth was 180-300 cm. The combination of an open ditch and a subsurface pipe produced a larger desalination area, and its efficiency was 170% that of a single open ditch. Within the inflection point range, the desalination rate increased with increasing ditch depth. Beyond the inflection point, subsurface drainage played a primary role, and the desalination rate increased as the subsurface drainage depth increased but remained relatively stable along the drainage direction. The optimal installation depth for subsurface pipes was estimated to be 90-110 cm, and the depth of ditches was 180-210 cm in a combined system. The maximum length for full flow in long-distance subsurface drainage was 750-850 m. This study provides references for the optimal application of combined subsurface drainage-open ditch systems in arid Northwest China.

A reasonable layout of subsurface drainage systems is considered essential for maximizing its drainage and salt control effectiveness. In the saline-alkali farmland of arid regions in Northwest China, low-permeability interlayers (clay, clay-loam or silty-loam) within the soils are common. However, the influence of the low-permeability interlayers on the layout of the subsurface drainage has not been extensively considered in the literature. This study investigated the process of subsurface drainage and salt discharge in salt-affected fields with silty-loam interlayers using field experiments and numerical simulations. Four field experiments were conducted, considering three different relative positions between the drainage pipes and silty-loam interlayers. The results showed that the silty-loam interlayers hindered water infiltration, and the distribution of soil salinity in the soil profile varied with the buried depth of drainage pipes at different positions relative to the silty-loam interlayer. When the buried depth of drainage pipes increased, the amount of water and salt discharged from drainage pipes increased, and the increase rate in salt discharge was greater than water drainage. A numerical model was calibrated and validated using the field experiment data, and 25 orthogonal numerical experiments were conducted to investigate the soil desalination effects of buried depth of drainage pipes, spacing between the pipes, saturated hydraulic conductivity of the interlayer, and position of the low-permeability interlayer. The results showed that the drainage pipe buried depth, spacing, and saturated hydraulic conductivity of the low-permeability interlayer had significant effects on the desalination rate (P < 0.01), while the position of the low-permeability interlayer had no significant effect (P > 0.05). Subsurface drainage pipes should be placed below the low-permeability interlayer. The desalination rate linearly increased with the buried depth of drainage pipe and saturated hydraulic conductivity of the interlayer, and it increased exponentially with decreased spacing. An empirical formula for soil desalination rate considering interlayer and subsurface drainage pipe layout parameters was fabricated and used to determine the appropriate layout parameters.

In this study, the microstructural characteristics of geotextile envelopes were investigated via two-dimensional (2D) and three-dimensional (3D) image analysis. A pore network model was constructed to predict the hydraulic properties of the geotextile envelopes. Based on image analysis, the representative domain size of the geotextile envelopes was estimated and was further confirmed by pore network modeling. The results showed that while nonuniformity existed in geotextile envelopes, no noticeable difference was observed in porosity among samples of different sizes. The porosity derived from 3D image analysis was much closer to the theoretical value, with relative error less than 12%. The fibers of the geotextile envelopes were mainly distributed in the inplane direction and were nearly uniform. The prediction of the permeability coefficient was optimal when hybrid cones and cylinders were considered as the geometric shapes and when the equivalent diameter, inscribed diameter, and total length were used as the geometric properties of the extracted pore network. The capillary pressure curves matched experimental values more closely when using the equivalent diameter for throat diameter. The representative domain size of geotextile envelopes was at least 3500 mu m, but no meaningful length could be found along the through-plane direction.

Subsurface drainage is an important agriculture drainage measure. It is primary to select suitable drain pipes and envelopes for efficient subsurface drainage. And now, corrugated drains and geotextile envelopes are widely used. However, the effects of geotextile envelopes and perforations on the drainage of corrugated drains are not well understood. This study conducted a series of sand tank experiments of steady-state flow with or without geotextile envelopes and with different perforation patterns. The drainage flow and the profile head distributions were analyzed and compared. Furthermore, the applicability of theoretical formulas, which are used to calculate effective radius considering the resistance of different perforation patterns, was evaluated. Results showed that the geotextile envelope weakened the effect of perforations on streamlines, thereby causing the value of effective radiuses to be close to that of the actual radius. The drainage flow of the drain with a geotextile envelope was six times that of the bare drain. The relationship between drainage flow and opening area could be described by inverse proportional function. Meanwhile, the drainage flow was affected by the perforation arrangement. Drain with small longitudinal perforation spacing had a drainage flow of approximately 15% larger than that with wider longitudinal perforation spacing. The bottom perforations drained out first and most, and the drainage flow of the drain opened at the bottom could be 11% higher than that at the top. Low-efficiency perforations cause higher head loss near the pipe wall. Existing formulas of entrance resistance were not suitable for geotextile-wrapped corrugated drains, the effect of geotextile envelope and orifice entrance loss at perforations should be considered.

This study develops a coupled model of chemical clogging and permeability coefficient of geotextile envelope. Based on the distribution characteristics of crystal precipitates on geotextile envelope and their influence on the permeability coefficient, a permeability coefficient model of an actual geotextile envelope that considers the overlapping effect is developed. Then, the densification effects of geosynthetic fiber hypothesis and the filter cake effect hypothesis are proposed to simulate the processes of increasing fiber diameter after crystal precipitation and the accumulation of crystal precipitates on the surface of geotextile envelope. The crystal precipitation module and permeability coefficient module are coupled, and their experimental values are used to confirm the availability of the model. Results indicate the satisfactory performance of the model. In addition, the parameter sensitivity analysis and trend prediction show that the saturation index SI and solution flow rate V are the main factors that affect the chemical clogging and permeability of geotextile envelope. When the solution conditions are not considered, the sensitivity of geotextile envelope parameter df increased with the amount of precipitation in crystal precipitation. When the pores of the geotextile envelope are completely clogged, the permeability coefficient of the geotextile envelope will drop sharply, then decline slowly.

The geometric structure of corrugated plastic pipes affects performance in agricultural subsurface drainage systems. To explore the influence of pipe geometry on flow field characteristics and the characterization of water movements, we developed a three-dimensional (3D) steady-state subsurface drainage model based on computational fluid dynamics (CFD). An analysis of the CFD and sand tank results indicated that the proposed model can accurately simulate the subsurface drainage process (R2 = 0.99). The corrugation structure parameters of the drainpipe, including the outside diameter, corrugation valley width and corrugation height, were taken as the objects for this study, and the influence of corrugation parameters on drainage discharge was orthogonally analysed. During drainage, the soil water initially collects in the corrugation valley and then approximately ninety percent of the water flows into the pipe through the bottom perforations; increasing the contact face area between the corrugation valley and soil can increase the flow rate of the drainpipe and the water table height above the pipe, which decreases the intersection position of the pipe and water table. The results of the analysis of the range and variance of the orthogonal experiment showed that the order of the primary and secondary factors influencing the drainage discharge was the outside diameter, corrugation valley width and corrugation height, with the outside diameter being most critical influencing factor.

This paper focuses on the effects of chemical precipitation on the permeability of geotextile envelopes for a subsurface drainage system in arid areas by conducting precipitation experiments of the geotextile in static or flowing solution. The results show that the precipitation process is not significantly promoted or inhibited by the network structure of geotextile. The precipitates in the form of rhombus wrap around the fiber surface. The number of geotextile pores with the smaller diameters decreases significantly after precipitation experiments. As the increase of the area density of precipitates (ΔR), the variation of the pore area (ΔS) and the variation of permeability coefficient (ΔK) of the geotextile decrease rapidly at first and then slowly. The ΔK and ΔS VS ΔR data were best fitted with logarithmic trend line. This study provides a preliminary reference for quantifying the chemical clogging process of geotextile envelopes in arid areas.

为了探究暗管排水"有效半径"理论对合成外包材料的适用性,开展了不同类型与厚度外包材料条件下的暗管排水野外实验,考虑了砂砾石、热黏长丝无纺布、纺黏长丝无纺布等3种材料,对两种合成材料又考虑了厚度的影响,共设置五组试验,观测了其排水过程,并与排水理论公式、融合"有效半径"理论的地下水运动数值模拟所得到的排水过程进行了对比分析,结果表明:"有效半径"理论将外包材料对暗管排水的影响通过材料渗透系数Ke和铺设厚度de改变暗管有效半径来实现,这导致厚度越大排水量越大,与野外试验结果和排水理论公式计算结果相反.传统的外包材料排水"有效半径"理论不适用于合成外包材料,有必要对该理论进行修正.

氯离子渗透性是评价高性能混凝土耐久性的重要指标,混凝土在长期服役过程中会受到很多外在的约束,约束状态会影响混凝土的内部结构.应用板式混凝土早期收缩开裂试验架制成约束状态下C50高性能混凝土,采用ASTM C1202直流电通量法,研究C50高性能混凝土在约束和自由状态下抗氯离子渗透性能.结果表明:与自由状态相比,约束状态降低了混凝土抗氯离子渗透性;在约束状态下,同一配合比混凝土,不同位置的抗氯离子渗透性有所差异;粉煤灰及聚丙烯纤维的加入降低了混凝土抗氯离子渗透性,而掺入硅灰会增强混凝土的抗氯离子渗透性.