Field testing of shear strength of granite residual soils

The characteristics of residual soils are very different from those of sedimentary soils.Although the strength characteristics of sedimentary soils have been studied extensively,the shear strength characteristics of granitic residual soils(GRS)subjected to the weathering of parent rocks have rarely been investigated.In this study,the shear strength characteristics of GRS in the Taishan area of southeast China(TSGRS)were studied by field and laboratory tests.The field tests consisted of a cone penetration test(CPT),borehole shear test(BST),self-boring pressuremeter test(SBPT),and seismic dilatometer Marchetti test(SDMT).The shortcomings of laboratory testing are obvious,with potential disturbances arising through the sampling,transportation,and preparation of soil samples.Due to the special structure of GRS samples and the ease of disturbance,the results obtained from laboratory tests were generally lower than those obtained from situ tests.The CPT and scanning electron microscopy(SEM)results indicated significant weathering and crustal hardening in the shallow TSGRS.This resulted in significant differences in the strength and strength parameters of shallow soil obtained by the BST.Based on the SDMT and SBPT results,a comprehensive evaluation method of shear strength for TSGRS was proposed.The SBPT was suitable for evaluating the strength of shallow GRS.The material index(ID)and horizontal stress index(KD)values obtained by the SDMT satisfied the empirical relationship proposed by Marchetti based on the ID index,and were therefore considered suitable for the evaluation of the shear strength of deep GRS.

Effects of soil crust on the collapsing erosion of colluvial deposits with granite residual soil

Collapsing erosion is a unique phenomenon commonly observed on the granite residue hillslopes in the tropical and subtropical regions of southern China,characterized by its abrupt occurrence and significant erosion volumes.However,the impacts of soil crust conditions on the erosion of colluvial deposits with granite residual soils have only been studied to a limited extent.To address this issue,this study investigates the impacts of three soil crust conditions(i.e.,without crust,10-minute crust,and 20-minute crust)on gully morphology,rainfall infiltration,and runoff and sediment yield during slope erosion of colluvial deposits with granite residues(classified as Acrisols)in Yudu County,Ganzhou City,Jiangxi Province,China,using simulated rainfall tests and photographic methods.The results showed that as the strength of the soil crust increased,the capacity of moisture infiltration and the width and depth of the gully as well as the sediment concentration and yield ratio decreased;at the same time,the runoff ratio increased.The sediment yield in the without-crust test was found to be 1.24 and 1.43 times higher than that observed in the 10-minute crust and 20-minute crust tests,respectively.These results indicate that soil crusts can effectively prevent slope erosion and moisture infiltration,while providing valuable insights for the management of soil erosion in natural environments.

Mesoscopic measurement of damage and shear bands of granite residual soil using Micro-CT and digital volume correlation

The mesomechanics of geotechnical materials are closely related to the macromechanical properties,especially the mesoscale evolution of shear bands,which is helpful for understanding the failure mechanism of geotechnical materials.However,there is lack of effective quantitative analysis method for the complex evolution mechanism of threedimensional shear bands.In this work,we used X-ray computed tomography(CT)to reconstruct volume images and used the digital volume correlation(DVC)method to calculate the three-dimensional strain fields of granite residual soil samples at different loading stages.The trend of the failure surface of the shear bands was obtained by the planar fitting method,and the connectivity index was constructed according to the projection characteristics of the shear bands on the failure trend surface.The results support the following findings:the connectivity index of the shear band increases rapidly and then slowly with increasing axial strain,which is characterized by a near'S'curve.As the stress reaches the peak value,the connectivity index of the shear bands almost exceeds 0.7.The contribution of the new shear band volume to the connectivity of the shear bands becomes increasingly small with increasing axial loading.Affected by quartz grains and stress at the initial stage,the dip angle gradually and finally approaches the included angle of the maximum shear stress from the discrete state with increasing axial loading.The tendency and dip angle of the resulting shear bands are dynamic,and the tendency slightly deflects with increasing loading.

Use of X-ray computed tomography to study structures and particle contacts of granite residual soil

A small problem about soil particle regularization and contacts but essential to geotechnical engineering was studied.The soils sourced from Guangzhou and Xiamen were sieved into five different particle scale ranges(d<0.075 mm,0.075 mm≤d<0.1 mm,0.1 mm≤d<0.2 mm,0.2 mm≤d<0.5 mm and 0.5 mm≤d<1.0 mm)to study the structures and particle contacts of granite residual soil.The X-ray micro computed tomography method was used to reconstruct the microstructure of granite residual soil.The particle was identified and regularized using principal component analysis(PCA).The particle contacts and geometrical characteristics in 3D space were analyzed and summarized using statistical analyses.The results demonstrate that the main types of contact among the particles are face-face,face-angle,face-edge,edge-edge,edge-angle and angle-angle contacts for particle sizes less than 0.2 mm.When the particle sizes are greater than 0.2 mm,the contacts are effectively summarized as face-face,face-angle,face-edge,edge-edge,edge-angle,angle-angle,sphere-sphere,sphere-face,sphere-edge and sphere-angle contacts.The differences in porosity among the original sample,reconstructed sample and regularized sample are closely related to the water-swelling and water-disintegrable characteristics of granite residual soil.

Effects of dry-wet cycles on three-dimensional pore structure and permeability characteristics of granite residual soil using X-ray micro computed tomography

Due to seasonal climate alterations,the microstructure and permeability of granite residual soil are easily affected by multiple dry-wet cycles.The X-ray micro computed tomography(micro-CT)acted as a nondestructive tool for characterizing the microstructure of soil samples exposed to a range of damage levels induced by dry-wet cycles.Subsequently,the variations of pore distribution and permeability due to drywet cycling effects were revealed based on three-dimensional(3D)pore distribution analysis and seepage simulations.According to the results,granite residual soils could be separated into four different components,namely,pores,clay,quartz,and hematite,from micro-CT images.The reconstructed 3D pore models dynamically demonstrated the expanding and connecting patterns of pore structures during drywet cycles.The values of porosity and connectivity are positively correlated with the number of dry-wet cycles,which were expressed by exponential and linear functions,respectively.The pore volume probability distribution curves of granite residual soil coincide with the χ^(2)distribution curve,which verifies the effectiveness of the assumption of χ^(2)distribution probability.The pore volume distribution curves suggest that the pores in soils were divided into four types based on their volumes,i.e.micropores,mesopores,macropores,and cracks.From a quantitative and visual perspective,considerable small pores are gradually transformed into cracks with a large volume and a high connectivity.Under the action of dry-wet cycles,the number of seepage flow streamlines which contribute to water permeation in seepage simulation increases distinctly,as well as the permeability and hydraulic conductivity.The calculated hydraulic conductivity is comparable with measured ones with an acceptable error margin in general,verifying the accuracy of seepage simulations based on micro-CT results.

Influence of groundwater drawdown on excavation responses e A case history in Bukit Timah granitic residual soils

Performances of a braced cut-and-cover excavation system for mass rapid transit （MRT） stations of the Downtown Line Stage 2 in Singapore are presented. The excavation was carried out in the Bukit Timah granitic （BTG） residual soils and characterized by significant groundwater drawdown, due to dewatering work in complex site conditions, insufficient effective waterproof measures and more permeable soils. A two-dimensional numerical model was developed for back analysis of retaining wall movement and ground surface settlement. Comparisons of these measured excavation responses with the calculated performances were carried out, upon which the numerical simulation procedures were calibrated. In addition, the influences of groundwater drawdown on the wall deflection and ground surface settlement were numerically investigated and summarized. The performances were also compared with some commonly used empirical charts, and the results indicated that these charts are less applicable for cases with significant groundwater drawdowns. It is expected that these general behaviors will provide useful references and insights for future projects involving excavation in BTG residual soils under significant groundwater drawdowns.

Influences of different modifiers on the disintegration of improved granite residual soil under wet and dry cycles

The disintegration of granite residual soil is especially affected by variations in physical and chemical properties. Serious geologic hazards or engineering problems are closely related to the disintegration of granite residual soil in certain areas. Research on the mechanical properties and controlling mechanisms of disintegration has become a hot issue in practical engineering. In this paper, the disintegration characteristics of improved granite residual soil are studied by using a wet and dry cycle disintegration instrument, and the improvement mechanism is analyzed. The results show that the disintegration amounts and disintegration ratios of soil samples treated with different curing agents are obviously different. The disintegration process of improved granite residual soil can be roughly divided into 5 stages:the forcible water intrusion stage, microcrack and fissure development stage, curing and strengthening stage, stable stage, and sudden disintegration stage. The disintegration of granite residual soil is caused by the weakening of the cementation between soil particles under the action of water. When the disintegration force is greater than the anti-disintegration force of soil, the soil will disintegrate. Cement and lime mainly rely on ion exchange agglomeration, the inclusion effect of curing agents on soil particles, the hard coagulation reaction and carbonation to strengthen granite residual soil. Kaolinite mainly depends on the reversibility of its own cementation to improve and strengthen granite residual soil. The reversibility of kaolinite cementation is verified by investigating pure kaolinite with a tensile, soaking, drying and tensile test cycle. Research on the disintegration characteristics and disintegration mechanism of improved granite residual soil is of certain reference value for soil modification.

Evolution of cracks in the shear bands of granite residual soil

The evolution of shear bands and cracks plays an important role in landslides.However,there is no systematic method for classification of the cracks,which can be used to analyze the evolution of cracks in shear bands.In this study,X-ray computed tomography(CT)is used to observe the behavior of granite residual soil during a triaxial shear process.Based on the digital volume correlation(DVC)method,a crack classification method is established according to the connectivity characteristics of cracks before and after loading.Cracks are then divided into six classes:obsolete,brand-new,isolated,split,combined,and compound.With evolution of the shear bands,a large number of brand-new cracks accelerate the damages of materials at the mesoscale,resulting in a sharp decrease in strength.The volume of brandnew cracks increases rapidly with increasing axial strain,and their volume is greater than 50%when the strain reaches 12%,while the volume of compound cracks decreases from 54%to 21%.As cracks are the weakest areas in a material,brand-new cracks accelerate the development of shear bands.Finally,the coupling effect of shear bands and cracks destroys the soil strength.

Flow-slide characteristics and failure mechanism of shallow landslides in granite residual soil under heavy rainfall

Affected by typhoons over years, Fujian Province in Southeast China has developed a large number of shallow landslides, causing a long-term concern for the local government. The study on shallow landslide is not only helpful to the local government in disaster prevention, but also the theoretical basis of regional early warning technology. To determine the whole-process characteristics and failure mechanisms of flow-slide failure of granite residual soil slopes, we conducted a detailed hazard investigation in Minqing County, Fujian Province, which was impacted by Typhoon Lupit-induced heavy rainfall in August 2021. Based on the investigation and preliminary analysis results, we conducted indoor artificial rainfall physical model tests and obtained the whole-process characteristics of flow-slide failure of granite residual soil landslides. Under the action of heavy rainfall, a granite residual soil slope experiences initial deformation at the slope toe and exhibits development characteristics of continuous traction deformation toward the middle and upper parts of the slope. The critical volumetric water content during slope failure is approximately 53%. Granite residual soil is in a state of high volumetric water content under heavy rainfall conditions, and the shear strength decreases, resulting in a decrease in stability and finally failure occurrence. The new free face generated after failure constitutes an adverse condition for continued traction deformation and failure. As the soil permeability(cm/h) is less than the rainfall intensity(mm/h), and it is difficult for rainwater to continuously infiltrate in short-term rainfall, the influence depth of heavy rainfall is limited. The load of loose deposits at the slope foot also limits the development of deep deformation and failure. With the continuous effect of heavy rainfall, the surface runoff increases gradually, and the influence mode changes from instability failure caused by rainfall infiltration to erosion and scouring of surface runoff on slope surface. Transportation of loose materials by surface runoff is an important reason for prominent siltation in disaster-prone areas.

Resilient modulus prediction of soft low-plasticity Piedmont residual soil using dynamic cone penetrometer

Dynamic cone penetrometer（DCP） has been used for decades to estimate the shear strength and stiffness properties of the subgrade soils. There are several empirical correlations in the literature to predict the resilient modulus values at only a specific stress state from DCP data, corresponding to the predefined thicknesses of pavement layers（a 50 mm asphalt wearing course, a 100 mm asphalt binder course and a200 mm aggregate base course）. In this study, field-measured DCP data were utilized to estimate the resilient modulus of low-plasticity subgrade Piedmont residual soil. Piedmont residual soils are in-place weathered soils from igneous and metamorphic rocks, as opposed to transported or compacted soils.Hence the existing empirical correlations might not be applicable for these soils. An experimental program was conducted incorporating field DCP and laboratory resilient modulus tests on "undisturbed" soil specimens. The DCP tests were carried out at various locations in four test sections to evaluate subgrade stiffness variation laterally and with depth. Laboratory resilient modulus test results were analyzed in the context of the mechanistic-empirical pavement design guide（MEPDG） recommended universal constitutive model. A new approach for predicting the resilient modulus from DCP by estimating MEPDG constitutive model coefficients（k;,k;and k;） was developed through statistical analyses. The new model is capable of not only taking into account the in situ soil condition on the basis of field measurements,but also representing the resilient modulus at any stress state which addresses a limitation with existing empirical DCP models and its applicability for a specific case. Validation of the model is demonstrated by using data that were not used for model development, as well as data reported in the literature.

Dynamic stress accumulation model of granite residual soil under cyclic loading based on small-size creep tests

The creep behaviors of granite residual soil with pre-stress of 100 kPa was investigated by a series of small size creep tests. Three different types of strain curves were obtained at different stress levels. Based on creep characteristics of the granite residual soil under different stress levels, a creep model of the granite residual soil was established by rheological theory, and related parameters of the model were determined according to the experimental data at the same time. Further on, based on the established creep model, a theoretical model of dynamic stress accumulation in the granite residual soil under cyclic loading was deduced. It is found that there is a threshold of dynamic stress accumulation in this theoretical model. The dynamic stress accumulation laws of the granite residual soil are different under different cyclic loading stress. Finally, with the dynamic stress accumulation laws in the small-size samples of granite residual soil under different cycle loading studied and the experimental results comparing with the theoretical results, it verifies the validity of the theoretical model.

Indexing the engineering properties of residual soils in the southern slopes of Mashhad,NE Iran

Residual soils are weathering products of rocks that are commonly found under unsaturated conditions.The properties of residual soils are a function of the degree of weathering.A series of index properties,engineering properties and geophysics survey examinations were performed on residual soils from two major geological formations in Iran.In the present research,the index properties of residual soils in the south of Mashhad city in Iran are investigated.Natural and artificial trenches were analyzed for evaluating the weathering profiles and collecting soil samples.Disturbed and undisturbed samples were obtained from each of the soil profile horizons resulting from weathering of different parent rocks.Subsequently,physical properties and mechanical properties of the soil samples were determined in accordance with ASTM standards.Also,the mineralogical composition,chemistry,and texture of the soil were evaluated in 51 profiles.The field observations showed the difference in the weathering profile of residual soils deposited on various rocks(igneous,sedimentary,and metamorphic).These profiles mainly consisted of two horizons includingresidual soil on top and saprolite at the bottom.The results of laboratory tests and geotechnical data showed that the properties of residual soil samples change by depth.Moreover,depending on the type of origin rock,the properties are different in various types of residual soils.In most of the samples,the moisture content of soil horizons was also increased by depth.Based on the unified soil classification(USCS),the soils of the upper horizons appeared to be classified as ML(Lean silt)and CL(Lean clay)while the soils of the lower horizons(saprolite zone)fall in SC(clayey sand),SM(silty sand),and SW(wellgraded sand)classes.Moreover,the results demonstrated that the particle size of the soil was increased by depth.Comparison of results of the geotechnical tests showed that properties of residual soils are changed by variations of depth,weathering level,and type of parent rock.Considering the concentration of the number of lines and the concentration of the points of intersection,the length and dimension fractal of lineaments in the southeastern part of the study area,it is evident that this zone possesses weathering severity and soil thickness.Fieldwork data from this zone have also verified the severity of weathering conditions.The analysis of lineaments trends in different parts of the study area indicated that the lineaments with the NW-SE trend have a strong effect on weathering development.The weathering depth depends on the orientation of bedding joints with respect to the slope in the study area.Slope inclination and soil thickness are controlled by weathering and erosion processes.

Evaluation of Coefficient of Permeability on Contaminated Granitic Residual Soil

This paper reports laboratory research carried out on natural and contaminated granitic residual soil from Covilha region （Portugal） to evaluate the coefficient of permeability in accordance with Darcy＇s law. The soils are contaminated with hydrocarbon （Benzene Toluene Etilbenzene and Xilenes elements） and leached of urban solid waste. The specimens remained saturated and the consolidation and swelling are substantially completed at different effective confining pressures （25 to 400 kPa） before the measurements are performed at different hydraulic gradient to determine the effect of the void ratio, fabric and contamination of soil.

Influence of changes in extreme daily rainfall distribution on the stability of residual soil slopes

Many landslides triggered by intense rainfall have occurred in moun-tainous areas in Thailand,causing major economic losses and infra-structure damage.Extreme daily rainfall is a significant trigger for hillslope instability.Increases in extreme daily rainfall intensity due to climate change may be one of the key factors responsible for the increased landslides.Thus,in this context,changes in the intensity of extreme daily rainfall in Chiang Mai Province in North Thailand and their effects on hillslope stability are analyzed.Extreme rainfall is modeled using a generalized extreme value distribution and esti-mated for various return periods.A numerical analysis of seepage and an infinite slope stability model are combined to understand the hillslope response under extreme rainfall conditions.The analysis period is divided into two periods of 34 years:1952 to 1985 and 1986 to 2019.According to the analysis results,the distribution of extreme daily rainfall changes in terms of location.The average annual daily maximum rainfall increased by approximately 11.13%.The maximum decrease in the safety factor is approximately 4.5%;therefore,these changes in extreme daily rainfall should be consid-ered in future landslide prevention policies.

Discussion of“Site observations of weathered granitic soils subjected to cementation and partial drainage using SCPTU”[J Rock Mech Geotech Eng 15(2023)984e996]

Comprehensive data from in situ and laboratory tests in residual soil have been presented by Zhang et al.(2023).A number of issues addressed in the paper have been the interest of the discussers,namely the characterisation and behaviour of residual soils,limitation of piezocone testing due to the capacity of the entire system,measurement of shear wave velocity,rate effect of piezocone(CPTU)testing and piezocone testing with dual pore pressure penetrometers.Clarification and complementation of these issues are required with regard to both the execution and interpretation of the tests.

Performance of braced excavation in residual soil with groundwater drawdown

In densely built-up Singapore,relatively stiffsecant-bored piles and diaphragm walls are commonly used in cut-and-cover works to minimize the impact of ground movement on the adjacent structures and utilities.For excavations in stiffresidual soil deposits,the asso-ciated wall deflections and ground settlements are generally smaller than for excavations in soft soil deposits.However,if the residual soil permeability is high and the underlying rock is highlyfissured or fractured,substantial groundwater drawdown and associated seepage-induced settlement may occur.In this study,the excavation performance of four sites in residual soil deposits with maximum excavation depths between 20 and 24 m is presented.The maximum wall deflections were found to be relatively small compared to the significantly larger maximum ground settlements,owing to the extensive lowering of the groundwater table.In this paper,details of the subsurface conditions,excavation support system,field instrumentation,and observed excavation responses are presented,with particular focus on the large groundwater drawdown and associated ground settlement.Specific issues encountered during the excavation,as well as the effectiveness of various groundwater control measures,are discussed.The case studies will provide useful references and insights for future projects involving braced excavations in residual soil.

Engineering properties of the Bukit Timah Granitic residual soil in Singapore

Extensive site investigations were conducted prior to the construction of a Mass Rapid Transit project in Singapore that was predominantly in the Bukit Timah Granite(BTG)formation residual soil.This paper evaluates the engineering properties of the BTG formation residual soil based on data from 208 site investigation boreholes from four different sites.Based on the results from 2481 conventional laboratory tests and 1192 in-situ tests,this paper summarizes the engineering properties of the highly variable BTG residual soil,including conventional composition analysis,index and hydraulic properties,and strength and deformation parameters required for geotechnical analysis and design.Based on these results,the BTG formation is found to be quite heterogeneous.As the degree of weathering decreases with depth from the top of the formation,the BTG residual soil becomes sandier,with reduced silt and clay fractions.The coefficient of permeability and the compression index of the BTG residual soil vary significantly.In addition,the empirical equations relating the shear strength(index)to the standard penetration test(SPT)-N,as well as the equations and charts for determining stiffness,are proposed.These findings,together with the proposed equations or charts,can be used for design guidance of similar projects related to granitic residual soils in Singapore.

Construction strategies for a NATM tunnel in Sao Paulo, Brazil, in residual soil

Due to the fast growth of urban areas worldwide,the demand for tunnels in developed areas is increasing.The design and construc-tion of those tunnels are complex because of their shallow depths and their interaction with existing aboveground and buried structures,which results in rather limited allowable ground deformations induced by the tunnel excavation and support.In tropical regions,residual porous soils near the surface are common.Those soils are highly deformable;thus,tunneling may induce large ground deformations that may damage nearby structures.The new Austrian tunneling method(NATM)and the sprayed concrete lining(SCL)technique are being widely employed in several big cities in tropical regions,but little research has been conducted to assess the induced ground deformations in residual soils,common in tropical areas.This paper provides insight into this issue.A well-documented metro tunnel in Sa˜o Paulo,Brazil,in a residual red porous clay,was analyzed using 3D finite element method(FEM).The behavior of the residual red porous clay was approximated by an advanced constitutive soil model calibrated with triaxial tests on intact samples extracted at the site.Predictions of the tunnel deformations during construction matched the field data.The calibrated model was then used to explore the tunnel per-formance under different construction strategies.The influence of partial face excavation,unsupported span length,support stiffness and pipe roof umbrella were assessed.The numerical results showed that partial face excavation was effective to reduce ground deformations ahead of the face of the tunnel and to improve face stability;however,the settlements behind the face increased because of the delay in closing the primary lining.The installation of a stiffer liner closer to the face reduced the ground deformations significantly.The pipe roof umbrella was the most effective technique to reduce the ground deformations around the tunnel;however,the numerical results did not consider deformations that could be induced by the drilling and grouting operations.The results shown in this paper provide both qual-itative and quantitative information about the ground deformations induced by NATM tunneling in residual porous soils,that could help designers and contractors choose the optimum support and construction methods to minimize ground deformations.

Strength Model of Soda Residue Soil Considering Consolidation Stress and Structural Influence

Soda residue(SR)is a type of industrial waste produced in the soda process with the ammonia-soda method.Applying SR to backfilling solves the land occupation and environmental pollution problems in coastal areas and saves material costs for foundation engineering.The strength characteristics of soda residue soil(SRS)under different consolidation conditions are the key points to be solved in the engineering application of SRS.Triaxial compression tests were performed on the undisturbed SRS of Tianjin Port.The shear properties of SRS under different consolidation conditions were then discussed.Meanwhile,a structural strength model(SSM)based on Mohr-Coulomb theory was proposed.SSM reflects the influence of soil structure on undrained strength(Cu)and divides the Cu into the following two parts:friction strength(C_(uf))and original structural strength(C_(u0)).C_(uf)characterizes the magnitude of friction between soil particles,which is related to the consolidation stress.Meanwhile,C_(u0)represents the structural effect on soil strength,which is related to the soil deposition and consolidation processes.SSM was validated by the test data of undisturbed soils.Results reveal that the undisturbed soil generally had a certain C_(u0).Therefore,the SRS strength model was established by combining the experimental law of SRS with SSM.Error analysis shows that the SRS strength model can effectively predict the Cu of undisturbed SRS in Tianjin Port under different consolidation conditions.

Evaluating the Effects of Aquaculture Wastewater Irrigation with Fertilizer Reduction on Greenhouse Tomato Production,Economic Benefits and Soil Nitrogen Characteristics

The utilization of aquaculture wastewater as irrigation is an effective way to recycle and reuse water and nitrogen fertilizer resources because it contains numerous nutrients.However,it is still unclear that the pattern of substituting aquaculture wastewater irrigation for fertilizer supplementing is conducive to improving the soil nitrogen status,fruit yield and water-fertilizer use efficiency for tomato production.In this context,the experiment was intended to establish the appropriate irrigation regime of aquaculture wastewater in tomato production for freshwater replacement and fertilizer reduction to ensure good yields.Pot experiments were conducted with treatments as farmers accustomed to irrigation and fertilization used as control(CK),1.75 L aquaculture wastewater with base fertilizer(W1),2 L aquaculture wastewater with base fertilizer;and 2.25 L aquaculture wastewater with base fertilizer(W3).We examined the effects of aquaculture wastewater irrigation on soil nitrogen distribution,Nrelated hydrolases,tomato yield,and economic benefits.The results showed that the control treatment had the highest N input,about 24.68%higher than the W3 treatment,while the yield was only about 7.81%higher than W3.This indicated that the overuse of chemical fertilizer was present in the current tomato production.Although the reduction of fertilizer in aquaculture wastewater irrigation caused a decrease in tomato production,this economic loss can be compensated by cost savings in the wastewater disposal.Among aquaculture wastewater treatments,the W3 treatment had the highest overall benefit,achieving 62.63%freshwater savings,37.50%fertilizer input reduction,and an economic return of approximately 19,466 Yuan per hectare higher than the control.Additionally,increasing the irrigation volume of aquaculture wastewater could provide more available nutrients to the soil,which were more prevalent in the form of organic nitrogen.The lower soil nitrate reductase activities(NR)under aquaculture wastewater treatments after harvesting also proved that this pattern was beneficial to reduce soil nitrate nitrogen residues.Overall,the results demonstrate that aquaculture wastewater irrigation alleviates the soil nitrate residues,improves nutrient availability,and results in more economic returns with water and fertilizer conservation for the greenhouse production of tomatoes.