Prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum

This study focuses on the analytical prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum considering the volumetric deformation modes of the soil above the tunnel crown.A series of numerical analyses is performed to examine the effects of cover depth ratio(C/D),tunnel volume loss rate(h t)and volumetric block proportion(VBP)on the characteristics of subsurface settle-ment trough and soil volume loss.Considering the ground loss variation with depth,three modes are deduced from the volumetric deformation responses of the soil above the tunnel crown.Then,analytical solutions to predict subsurface settlement for each mode are presented using stochastic medium theory.The influences of C/D,h t and VBP on the key parameters(i.e.B and N)in the analytical expressions are discussed to determine the fitting formulae of B and N.Finally,the proposed analytical solutions are validated by the comparisons with the results of model test and numerical simulation.Results show that the fitting formulae provide a convenient and reliable way to evaluate the key parameters.Besides,the analytical solutions are reasonable and available in predicting the subsurface settlement induced by shield tunnelling in sandy cobble stratum.

Deep learning to estimate ocean subsurface salinity structure in the Indian Ocean using satellite observations

Accurately estimating the ocean subsurface salinity structure(OSSS)is crucial for understanding ocean dynamics and predicting climate variations.We present a convolutional neural network(CNN)model to estimate the OSSS in the Indian Ocean using satellite data and Argo observations.We evaluated the performance of the CNN model in terms of its vertical and spatial distribution,as well as seasonal variation of OSSS estimation.Results demonstrate that the CNN model accurately estimates the most significant salinity features in the Indian Ocean using sea surface data with no significant differences from Argo-derived OSSS.However,the estimation accuracy of the CNN model varies with depth,with the most challenging depth being approximately 70 m,corresponding to the halocline layer.Validations of the CNN model’s accuracy in estimating OSSS in the Indian Ocean are also conducted by comparing Argo observations and CNN model estimations along two selected sections and four selected boxes.The results show that the CNN model effectively captures the seasonal variability of salinity,demonstrating its high performance in salinity estimation using sea surface data.Our analysis reveals that sea surface salinity has the strongest correlation with OSSS in shallow layers,while sea surface height anomaly plays a more significant role in deeper layers.These preliminary results provide valuable insights into the feasibility of estimating OSSS using satellite observations and have implications for studying upper ocean dynamics using machine learning techniques.

Rock physics model for fluid identification and saturation estimation in subsurface reservoirs

A method for fluid identification(water,oil,gas or CO_(2))and saturation estimation in subsurface rock formations using the prestack inverted Seismic by calculating the target fluid saturation(Sfl)(114)in a reservoir given the magnitude obtained from the Pto S-wave velocity ratio(Vp/Vs)(103),and acoustic impedance(AI)(102)extracted from the seismic data inversion,comprising the following steps:(a)obtaining wireline log data within a zone of interest in a nearby well(101)and determining the suitable cementation and mineralogy factors by calibrating the background water-bearing sand trend with the reference 0%(or 0 fraction)Sfl curve onto the acoustic impedance-Vp/Vs ratio plane(110),(b)calibrating Sfl computed from the acoustic impedance-Vp/Vs ratio curves with Sfl obtained from a conventional method by iterating P-wave velocity(Vpf)and density(ρfl)of the target fluid(111).

Combined effect of subsurface dam and layered heterogeneity on groundwater flow and salinity distribution in stratified coastal aquifers

In this paper,for the first time,we investigated the combined effect of subsurface dams and a typical stratified aquifer(two high-permeability layers with a low-permeability layer between them)on groundwater flow and salinity distribution in a tidally influenced coastal unconfined aquifer.Subsurface dams can inhibit the invasion of saltwater,and the low-permeability layer(LPL)and tide action can increase the effect of subsurface dams and the removal rate of residual saltwater.Through sensitivity analysis,it was discovered that shifting the dam location towards the inland resulted in a reduction in the effective heights of the dam.The upper saline plume contracted with increasing dam height,and the upper boundary of LPL was moved to shallower regions.And the natural removal time increased significantly with increasing dam height and the bottom boundary of LPL was moved to deeper regions.In addition,if the dam location was close to the sea boundary and the bottom boundary of LPL was moved to deeper regions,we could increase the subsurface dam height to reduce the risks of control of saltwater intrusion.This study provides us a comprehensive understanding of the complex hydrodynamics of saltwater intrusion and provides guides for the design of subsurface dams aimed at saltwater intrusion control in stratified coastal aquifers.

Subsurface banding of blended controlled-release urea can optimize rice yields while minimizing yield-scaled greenhouse gas emissions

Controlled-release urea(CRU)is widely reported to supply crop nitrogen(N)demand with one basal application,thus effectively replacing split applications of urea without diminishing grain yield and N use efficiency(NUE).However,its use for replacement for high-yield split applications of urea(CK)for rice is untested.In addition,the degree to which greenhouse gas(GHG)emissions in rice systems are affected when CRU is substituted for CK remains unclear.During 2017 and 2018,we sampled plant growth and gas emissions in a rice paddy field treated with three CRU types(sulfur-coated urea[SCU],polymer-coated urea[PCU],and bulk blended CRU[BBU])applied via two methods(surface broadcasting on the soil and subsurface banding at 5 cm depth),with CK as a control.The three CRUs led to different soil NH_(4)^(+)-N dynamics,and the N supply pattern under BBU was more beneficial for rice seedling establishment than under SCU and PCU,resulting in grain yield and NUE comparable to those under CK.CRU type showed no significant effect on either CH_(4) emissions or N_(2)O emissions,and broadcast CRUs exhibited significantly higher total GHG emissions than CK.However,banded CRUs significantly reduced the total GHG emissions in comparison with broadcast CRUs,by 9.2%averaged across the two years.Reduced CH_(4) emissions,particularly during the period prior to the middle drainage,contributed largely to the GHG difference.With comparably high grain yield and low total GHG emissions,banded BBU showed a low yield-scaled GHG(GHG emissions divided by grain yield)comparable to that under CK in both years.Overall,our study suggested that N management synchronized with rice demand and contributing to a high NUE tended to minimize yield-scaled GHG.Broadcast CRU can hardly substitute for CK in terms of either grain yield or GHG emissions,but banded BBU is a promising N management strategy for sustaining rice production while minimizing environmental impacts.

The Subsurface and Surface Indian Ocean Dipoles and Their Association with ENSO in CMIP6 models

This study assesses the reproducibility of 31 historical simulations from 1850 to 2014 in the Coupled Model Intercomparison Project phase 6(CMIP6) for the subsurface(Sub-IOD) and surface Indian Ocean Dipole(IOD) and their association with El Ni?o-Southern Oscillation(ENSO). Most CMIP6 models can reproduce the leading east-west dipole oscillation mode of heat content anomalies in the tropical Indian Ocean(TIO) but largely overestimate the amplitude and the dominant period of the Sub-IOD. Associated with the much steeper west-to-east thermocline tilt of the TIO, the vertical coupling between the Sub-IOD and IOD is overly strong in most CMIP6 models compared to that in the Ocean Reanalysis System 4(ORAS4). Related to this, most models also show a much tighter association of Sub-IOD and IOD events with the canonical ENSO than observations. This explains the more(less) regular Sub-IOD and IOD events in autumn in those models with stronger(weaker) surface-subsurface coupling in TIO. Though all model simulations feature a consistently low bias regarding the percentage of the winter–spring Sub-IOD events co-occurring with a Central Pacific(CP) ENSO, the linkage between a westward-centered CP-ENSO and the Sub-IOD that occurs in winter–spring, independent of the IOD, is well reproduced.

An Improved Angle Polishing Method for Measuring Subsurface Damage in Silicon Wafers

We present an improved angle polishing method in which the end of the cover slice near the glue layer is beveled into a thin,defect-free wedge,the straight edge of which is used as the datum for measuring the depth of subsurface damage. The bevel angle can be calculated from the interference fringes formed in the wedge. The minimum depth of the subsurface damage that can be measured by this method is a few hundred nanometers. Our results show that the method is straightforward, accurate, and convenient.

Experimental investigation of subsurface damage depth of lapped optics by fluorescent method

Subsurface defects were fluorescently tagged with nanoscale quantum dots and scanned layer by layer using confocal fluorescence microscopy to obtain images at various depths. Subsurface damage depths of fused silica optics were characterized quantitatively by changes in the fluorescence intensity of feature points. The fluorescence intensity vs scan depth revealed that the maximum fluorescence intensity decreases sharply when the scan depth exceeds a critical value. The subsurface damage depth could be determined by the actual embedded depth of the quantum dots. Taper polishing and magnetorheological finishing were performed under the same conditions to verify the effectiveness of the nondestructive fluorescence method. The results indicated that the quantum dots effectively tagged subsurface defects of fused-silica optics, and that the nondestructive detection method could effectively evaluate subsurface damage depths.

Subsurface Damage in the Monocrystal Silicon Grinding on Atomic Scale

A molecular dynamics （MD） simulation is carried out to analyze the effect of cutting edge radius,cutdepth, and grinding speed on the depth of subsurface damage layers in monocrystal silicon grinding processes on an atomic scale. The results show that when the cutting edge radius decreases in the nanometric grinding process with the same cut-depth and grinding speed, the depth of the damage layers and the potential energy between the silicon atoms decrease too. Also, when the cut depth increases, both the depth of the damage layers and the potential energy between silicon atoms increase. When the grinding speed is between 20 and 200m/s,the depth of the damage layers does not change much with the increase of the grinding speed under the same cutting edge radius and cut depth conditions. This means that the MD simulation is not sensitive to changes in the grinding speed, and thus increasing the grinding speed properly can shorten the sion,the subsurface damage of monocrystal silicon is silicon atoms, which is verified by the ultra-precision simulation time and enlarge the simulation scale. In conclumainly based on the change of the potential energy between grinding and CMP experiments.

Soil Enzyme Activities with Greenhouse Subsurface Irrigation

Various environmental conditions determine soil enzyme activities, which are important indicators for changes of soil microbial activity, soil fertility, and land quality. The effect of subsurface irrigation scheduling on activities of three soil enzymes (phosphatase, urease, and catalase) was studied at five depths (0-10, 10-20, 20-30, 30-40, and 40-60 cm) of a tomato greenhouse soil. Irrigation was scheduled when soil water condition reached the maximum allowable depletion (MAD) designed for different treatments (-10, -16,-25,-40, and-63 kPa). Results showed that soil enzyme activities had significant responses to the irrigation scheduling during the period of subsurface irrigation. The neutral phosphatase activity and the catalase activity were found to generally increase with more frequent irrigation (MAD of -10 and -16 kPa). This suggested that a higher level of water content favored an increase in activity of these two enzymes. In contrast, the urease activity decreased under irrigation, with less effect for MAD of -40 and -63 kPa. This implied that relatively wet soil conditions were conducive to retention of urea N, but relatively dry soil conditions could result in increasing loss of urea N. Further, this study revealed that soil enzyme activities could be alternative natural bio-sensors for the effect of irrigation on soil biochemical reactions and could help optimize irrigation management of greenhouse crop production.

Yield and Quality Response of Cucumber to Irrigation and Nitrogen Fertilization Under Subsurface Drip Irrigation in Solar Greenhouse

The aims of this research were to compare subsurface drip irrigation scheduling and nitrogen fertilization rates in cucumber, and evaluate yield and quality of cucumber fruit, water （WUE）, irrigation water （IWUE）, and nitrogen use （NUE） efficiencies in the solar greenhouse in Southwest China. The irrigation water amounts were determined based on the 20 cm diameter pan （Ep） placed over the crop canopy, and cucumber plant was subjected to three irrigation water levels （I1, 0.6 Ep; I2, 0.8 Ep; and I3, 1.0 Ep） in interaction with three nitrogen fertilization levels （N1, 300 kg ha-1; N2, 450 kg ha-1; and N3, 600 kg ha-1）. The results showed that the cucumber fruit yield increased with the improvement of irrigation water. Irrigation water increased yields by increasing the mean weight of the fruits, and also by increasing fruit number. But the highest values of IWUE and WUE were obtained from I2 treatment. NUE significantly decreased with the improvement of N application, but increased by irrigating more water. The quality of cucumber fruit decreased with the improvement irrigation water and nitrogen fertilization. In conclusion, the optimum irrigation level and nitrogen fertilizer application level for cucunber under subsurface drip irrigation in the solar greenhouse in Southwest China were 0.8 Ep and 450 and 600 kg ha-1, respectively.

Performance of a subsurface-flow constructed wetland in Southern China

The operational performance of a full scale subsurface flow constructed wetland, which treated the mixed industrial and domestic wastewater with BOD 5/COD mean ratio of 0 33 at Shatian, Shenzhen City was studied. The constructed wetland system consists of screens, sump, pumping station, and primary settling basin, facultative pond, first stage wetland and secondary stage wetland. The designed treatment capacity is 5000 m 3/d, and the actual influent flow is in the range of <2000 to >10000 m 3/d. Under normal operational conditions, the final effluent quality well met the National Integrated Wastewater Discharge Standard(GB 8978\_1996), with the following parameters(mean values): COD 33 90 mg/L, BOD 5 7.65 mg/L, TSS 7.92 mg/L, TN 9.11 mg/L and TP 0 56 mg/L. Seven species of plants were selected to grow in the wetland: Reed, Sweetcane flower Silvergrass, Great Bulrush, Powdery Thalia and Canna of three colours. The growing season is a whole year round. The seasonal discrepancy could be observed and the plants growing in the wetland are vulnerable to lower temperature in winter. The recycling of the effluent in the first stage of the wetland system is an effective measure to improve the performance of the wetland system. The insufficient DO value in the wetland system not only had significant effect on pollutants removal in the wetland, but also was unfavourable to plant growth. The recycling of effluent to the inlet of wetland system and artificial pond to increase DO value of influent to the wetland is key to operate the subsurface constructed wetland steadily and effectively.

Tomato Root Response to Subsurface Drip Irrigation

Four depth treatments of subsurface drip irrigation pipes were designated as 1) at 20,2) 30 and 3) 40 cm depths all with a drip-proof flumes underneath,and 4) at 30 cm without a drip-proof flume to investigate the responses of a tomato root system to different technical parameters of subsurface drip irrigation in a glass greenhouse,to evaluate tomato growth as affected by subsurface drip irrigation,and to develop an integrated subsurface drip irrigation method for optimal tomato yield and water use in a glass greenhouse. Tomato seedlings were planted above the subsurface drip irrigation pipe. Most of the tomato roots in treatment 1 were found in the top 0-20 cm soil depth with weak root activity but with yield and water use efficiency (WUE) significantly less (P ---- 0.05) than treatment 2; root activity and tomato yield were significantly higher (P = 0.05) with treatment 3 compared to treatment 1; and with treatment 2 the tomato roots and shoots grew harmoniously with root activity,nutrient uptake,tomato yield and WUE significantly higher (P= 0.05) or as high as the other treatments. These findings suggested that subsurface drip irrigation with pipes at 30 cm depth with a drip-proof flume placed underneath was best for tomato production in greenhouses. In addition,the irrigation interval should be about 7-8 days and the irrigation rate should be set to 225 m3 ha-1 per event.

Application of computational fluid dynamic to model the hydraulic performance of subsurface flow wetlands

A subsurface flow wetland(SSFW)was simulated using a commercial computational fluid dynamic(CFD)code.The constructed media was simulated using porous media and the liquid resident time distribution(RTD)in the SSFW was obtained using the particle trajectory model.The effect of wetland configuration and operating conditions on the hydraulic performance of the SSFW were investigated.The results indicated that the hydraulic performance of the SSFW was predominantly affected by the wetland configuration.The hydr...

Methods for Detection of Subsurface Damage:A Review

Subsurface damage is easily induced in machining of hard and brittle materials because of their particular mechani?cal and physical properties. It is detrimental to the strength,performance and lifetime of a machined part. To manu?facture a high quality part,it is necessary to detect and remove the machining induced subsurface damage by the subsequent processes. However,subsurface damage is often covered with a smearing layer generated in a machining process,it is rather di cult to directly observe and detect by optical microscopy. An e cient detection of subsur?face damage directly leads to quality improvement and time saving for machining of hard and brittle materials. This paper presents a review of the methods for detection of subsurface damage,both destructive and non?destructive. Although more reliable,destructive methods are typically time?consuming and confined to local damage infor?mation. Non?destructive methods usually su er from uncertainty factors,but may provide global information on subsurface damage distribution. These methods are promising because they can provide a capacity of rapid scan and detection of subsurface damage in spatial distribution.

Phytoplankton composition and its ecological effect in subsurface cold pool of the northern Bering Sea in summer as revealed by HPLC derived pigment signatures

CHEMTAX analysis of high-performance liquid chromatography （HPLC） pigment was conducted to study phytoplankton community structure in the northern Bering Sea shelf, where a seasonal subsurface cold pool emerges. The results showed that fucoxanthin （Fuco） and chlorophyll a （Chl a） were the most abundant diagnostic pigments, with the integrated water column values ranging from 141 to 2160 μg/m2 and 477 to 5 535 μg/m2, respectively. Moreover, a diatom bloom was identified at Sta. BB06 with the standing stock of Fuco up to 9214 μg/m3. The results of CHEMTAX suggested that the phytoplankton community in the northern Bering Sea shelf was dominated by diatoms and chrysophytes with an average relative contribu- tion to Chl a of 80% and 12%, respectively, followed by chlorophytes, dinoflagellates, and cryptophytes. Dia- toms were the absolutely dominant algae in the subsurface cold pool with a relative contribution exceeding 90%, while the contribution of chrysophytes was generally higher in oligotrophic upper water. Additionally, the presence of a cold pool would tend to favor accumulation of diatom biomass and a bloom that occurred beneath the halocline would be beneficial to organic matter sinks, which suggests that a large part of the phytoplankton biomass would settle to the seabed and support a rich benthic biomass.

Application of subsurface wastewater infiltration system to on-site treatment of domestic sewage under high hydraulic loading rate

In order to enhance the hydraulic loading rate （HLR） of a subsurface wastewater infiltration system （SWIS） used in treating domestic sewage, the intermittent operation mode was employed in the SWIS. The results show that the intermittent operation mode contributes to the improvement of the HLR and the pollutant removal rate. When the wetting-drying ratio （RwD） was 1.0, the pollutant removal rate increased by （13.6 ± 0.3）% for NH3-N, （20.7 ± 1.1）% for TN, （18.6± 0.4）% for TP, （12.2 ± 0.5）% for BOD, （10.1 ± 0.3）% for COD, and （36.2 ± 1.2）% for SS, compared with pollutant removal rates under the continuous operation mode. The pollutant removal rate declined with the increase of the HLR. The effluent quality met The Reuse of Urban Recycling Water - Water Quality Standard for Scenic Environment Use （GB/T 18921-2002） even when the HLR was as high as 10 cm/d. Hydraulic conductivity, oxidation reduction potential （ORP）, the quantity of nitrifying bacteria, and the pollutant removal rate of NH3-N increased with the decrease of the RWD. For the pollutant removal rates of TP, BOD, and COD, there were no significant difference （p 〈 0.05） under different RwDS. The suggested RWD was 1.0. Relative contribution of the pretreatment and SWlS to the pollutant removal was examined, and more than 80% removal of NH3-N, TN, TP, COD, and BOD occurred in the SWIS.

The Mars rover subsurface penetrating radar onboard China's Mars 2020 mission

China's Mars probe,named Tianwen-1,including an orbiter and a landing rover,will be launched during the July-August 2020 Mars launch windows.Selected to be among the rover payloads is a Subsurface Penetrating Radar module(RoSPR).The main scientific objective of the RoSPR is to characterize the thickness and sub-layer distribution of the Martian soil.The RoSPR consists of two channels.The low frequency channel of the RoSPR will penetrate the Martian soil to depths of 10 to 100 m with a resolution of a few meters.The higher frequency channel will penetrate to a depth of 3 to 10 m with a resolution of a few centimeters.This paper describes the design of the instrument and some results of field experiments.

The Potential Contribution of Subsurface Drip Irrigation to Water-Saving Agriculture in the Western USA

Water shortages within the western USA are resulting in the adoption of water-saving agricultural practices within this region. Among the many possible methods for saving water in agriculture, the adoption of subsurface drip irrigation （SDI） provides a potential solution to the problem of low water use efficiency. Other advantages of SDI include reduced NO3 leaching compared to surface irrigation, higher yields, a dry soil surface for improved weed control, better crop health, and harvest flexibility for many specialty crops. The use of SDI also allows the virtual elimination of crop water stress, the ability to apply water and nutrients to the most active part of the root zone, protection of drip lines from damage due to cultivation and tillage, and the ability to irrigate with wastewater while preventing human contact. Yet, SDI is used only on a minority of cropland in the arid western USA. Reasons for the limited adoption of SDI include the high initial capital investment required, the need for intensive management, and the urbanization that is rapidly consuming farmland in parts of the western USA. The contributions of SDI to increasing yield, quality, and water use efficiency have been demonstrated. The two major barriers to SDI sustainability in arid regions are economics （i.e., paying for the SDI system）, including the high cost of installation; and salt accumulation, which requires periodic leaching, specialized tillage methods, or transplanting of seedlings rather than direct-seeding. We will review advances in irrigation management with SDI.

Formation of subsurface cracks in silicon wafers by grinding

Single-crystal silicon is an important material in the semiconductor and optical industries.However,being hard and brittle,a silicon wafer is vulnerable to subsurface cracks(SSCs)during grinding,which is detrimental to the performance and lifetime of a wafer product.Therefore,studying the formation of SSCs is important for optimizing SSC-removal processes and thus improving surface integrity.In this study,a statistical method is used to study the formation of SSCs induced during grinding of silicon wafers.The statistical results show that grinding-induced SSCs are not stochastic but anisotropic in their distributions.Generally,when grinding with coarse abrasive grains,SSCs form along the cleavage planes,primarily the{111}planes.However,when grinding with finer abrasive grains,SSCs tend to form along planes with a fracture-surface energy higher than that of the cleavage planes.These findings provide a guidance for the accurate detection of SSCs in ground silicon wafers.