Fuzzy Decision of Ground Improvement Method

With the rapid development of expressway in China, the ground improvement is becoming more and more important. The decision of the ground improvement method often depends on the experience of an engineer. This paper sets up a module of multi-level fuzzy decision of the ground improvement method in the expressway construction which is mainly to set up multi-level structure module, to get value of the affected factors at rule level and index level, to set up the character index matrix of project level and to have a total evaluation on the projects. Combined with the project of ground improvement on the Second Cincture Road in Wuhan, a case study is carried out with satisfactory results.

Plate Load Tests on Municipal Solid Waste Dump Site to Assess Ground Improvement Alternatives

Urbanization is the physical growth of urban areas as a result of global change. As the land cost is increasing tremendously and decreasing availability of good construction site is building up pressure on the engineers to utilize even the poorest site either by providing special type of foundation or by improving ground in urban centres. In this context literature is reviewed for use of landfill site for housing. The site exploration for old dump site was carried out to assess subsoil characteristics. The objective was to evolve strategy for economical feasible ground improvement technique to obtain permissible bearing capacity of 150 kPa and total settlement not more than 50 mm. The tests carried out are load tests with geotextile mat and stone filled wire mess matress. The analysis was attempted to evaluate the soil response and bearing capacity. The site can be used for construction of low rise housing for rehabilitation of displaced persons under TP scheme within city area utilizing old landfill sites.

Consolidation of high replacement ratio stone column-reinforced ground:Analytical solutions incorporating clogging effect

The utilization of stone columns has emerged as a popular ground improvement strategy,whereas the drainage performance can be adversely hampered by clogging effect.Despite the ample progress of calculation methods for the consolidation of stone column-improved ground,theoretical investigations into the clogging effect have not been thoroughly explored.Furthermore,it is imperative to involve the column consolidation deformation to mitigate computational error on the consolidation of composite ground with high replacement ratios.In this context,an analytical model accounting for the initial clogging and coupled time and depth-dependent clogging of stone columns is established.Then,the resulting governing equations and analytical solutions are obtained under a new flow continuity relationship to incorporate column consolidation deformation.The accuracy and reliability of the proposed model are illustrated by degradation analysis and case studies with good agreements.Subsequently,the computed results of the current study are juxtaposed against the existing models,and an in-depth assessment of the impacts of several crucial parameters on the consolidation behavior is conducted.The results reveal that ignoring column consolidation deformation leads to an overestimate of the consolidation rate,with maximum error reaching up to 16%as the replacement ratio increases.Furthermore,the initial clogging also has a significant influence on the consolidation performance.Additionally,the increment of depth and time-clogging factors a and b will induce a noticeable retardation of the consolidation process,particularly in the later stage.

Discussion on the mechanism of ground improvement method at the excavation of shallow overburden tunnel in difficult ground

Tunnel construction opportunities involving shallow overburdens under difficult(e.g.,soft,unconsolidated)grounds have been increasing in Japan.Various auxiliary methods for excavating mountain tunnels have been developed and can satisfy stringent construction requirements.The ground improvement method,which is one of the auxiliary methods for shallow overburden tunnels,has demonstrated its ability to effectively control the amount of settlement under soft ground.However,the mechanism of the ground improvement method has not been clarified,nor has a suitable design code been established for it.Therefore,because the strength of the improved ground and the suitable length and width of the improved area have not been fully understood,an empirical design has been applied in every case.In this paper,the mechanical behavior during the excavation,including that of the stabilized ground,is evaluated through trapdoor experiments and numerical analyses.In addition,the enhancement of tunnel stability resulting from the application of the ground improvement method is discussed.

Assessment of compressive strength of jet grouting by machine learning

Jet grouting is one of the most popular soil improvement techniques,but its design usually involves great uncertainties that can lead to economic cost overruns in construction projects.The high dispersion in the properties of the improved material leads to designers assuming a conservative,arbitrary and unjustified strength,which is even sometimes subjected to the results of the test fields.The present paper presents an approach for prediction of the uniaxial compressive strength(UCS)of jet grouting columns based on the analysis of several machine learning algorithms on a database of 854 results mainly collected from different research papers.The selected machine learning model(extremely randomized trees)relates the soil type and various parameters of the technique to the value of the compressive strength.Despite the complex mechanism that surrounds the jet grouting process,evidenced by the high dispersion and low correlation of the variables studied,the trained model allows to optimally predict the values of compressive strength with a significant improvement with respect to the existing works.Consequently,this work proposes for the first time a reliable and easily applicable approach for estimation of the compressive strength of jet grouting columns.

Mechanical behaviors of warm and ice-rich frozen soil stabilized with sulphoaluminate cement

The warm and ice-rich frozen soil is characterized by high unfrozen water content, low shear strength and large compressibility, which is unreliable to meet the stability requirements of engineering infrastructures and foundations in permafrost regions. In this study, a novel approach for stabilizing the warm and ice-rich frozen soil with sulphoaluminate cement was proposed based on chemical stabilization. The mechanical behaviors of the stabilized soil, such as strength and stress-strain relationship, were investigated through a series of triaxial compression tests conducted at -1.0℃, and the mechanism of strength variations of the stabilized soil was also explained based on scanning electron microscope test. The investigations indicated that the strength of stabilized soil to resist failure has been improved, and the linear Mohr-Coulomb criteria can accurately reflect the shear strength of stabilized soil under various applied confining pressure. The increase in both curing age and cement mixing ratio were favorable to the growth of cohesion and internal friction angle. More importantly, the strength improvement mechanism of the stabilized soil is attributed to the formation of structural skeleton and the generation of cementitious hydration products within itself. Therefore, the investigations conducted in this study provide valuable references for chemical stabilization of warm and ice-rich frozen ground, thereby providing a basis for in-situ ground improvement for reinforcing warm and ice-rich permafrost foundations by soil-cement column installation.

Experimental and numerical interpretation on composite foundation consisting of soil-cement column within warm and ice-rich frozen soil

Affected by climate warming and anthropogenic disturbances, the thermo-mechanical stability of warm and ice-rich frozen ground along the Qinghai-Tibet engineering corridor(QTEC) is continuously decreased, which may delay the construction of major projects in the future. In this study, based on chemical stabilization of warm and icerich frozen ground, the soil-cement column(SCC) for ground improvement was recommended to reinforce the foundations in warm and ice-rich permafrost regions. To explore the validity of countermeasures mentioned above, both the original foundation and the composite foundation consisting of SCC with soil temperature of -1.0℃ were prepared in the laboratory, and then the plate loading tests were carried out. The laboratory investigations indicated that the bearing capacity of composite foundation consisting of SCC was higher than that of original foundation, and the total deformation of original foundation was greater than that of composite foundation, meaning that overall stability of foundation with warm and ice-rich frozen soil can be improved by SCC installation. Meanwhile, a numerical model considering the interface interaction between frozen soil and SCC was established for interpretating the bearing mechanism of composite foundation. The numerical investigations revealed that the SCC within composite foundation was responsible for the more applied load, and the applied load can be delivered to deeper zone in depth due to the SCC installation, which was favorable for improving the bearing characteristic of composite foundation. The investigations provide the valuable guideline for the choice of engineering supporting techniques to major projects within the QTEC.

Influence of cement-fly ash-gravel pile-supported approach embankment on abutment piles in soft ground

Abutment piles in soft ground may be subjected to both vertical and horizontal soil movements resulting from approach embankment loads. To constrain the soil movements, the soft soil ground beneath the approach embankment is often improved using composite pile foundations, which aim at mitigating the bump induced by high-speed trains passing through the bridge. So far, there is limited literature on exploring the influence of the degree of ground improvement on abutment piles installed in soft soil grounds. In this paper, a series of three-dimensional （3D） centrifuge model tests was performed on an approach embankment over a silty clay deposit improved by cement-fly ash-gravel （CFG） piles combined with geogrid. Emphasis is placed on the effects of ground replacement ratio （m） on the responses of the abutment piles induced by embankment loads. Meanwhile, a numerical study was conducted with varying ground replacement ratio of the pile-reinforced grounds. Results show that the performance of the abutment piles is significantly improved when reinforcing the ground with CFG piles beneath the approach embankment. Interestingly, there is a threshold value of the replacement ratio of around 4.9% above which the effect of CFG pile foundations is limited. This implies that it is essential to optimize the ground improvement for having a cost-effective design while minimizing the risk of the bump at the end of bridge.

Consolidation of partially saturated ground improved by impervious column inclusion:Governing equations and semi-analytical solutions

This study focuses on the consolidation behavior and mathematical interpretation of partially-saturated ground improved by impervious column inclusion.The constitutive relations for soil skeleton,pore air and pore water for partially saturated soils are proposed in the context of partially-saturated ground improved by impervious column inclusion.Settlement equation and dissipation equations of excess pore air/water pressures for a partially saturated improved ground are then derived.The semi-analytical solutions for ground settlement and pore pressure dissipation are then obtained through the Laplace transform and validated by the existing solutions for two special cases in the literature and the numerical results obtained from the finite difference method.A series of parametric studies is finally conducted to investigate the influence of some key factors on consolidation of partially saturated ground improved by impervious column inclusion.Based on the parametric study,it can be found that a higher value of the area replacement ratio or modulus of the pile results in a longer dissipation time of excess pore air pressure(PAP),a shorter dissipation time of excess pore water pressure(PWP),and a lower normalized settlement.

Analysis of ground deformation development and settlement prediction by air-boosted vacuum preloading

Vacuum preloading has been widely used to improve soft soils in coastal areas of China.An increasing amount of evidence from field operations has shown that conventional vacuum preloading is prone to clogging in prefabricated vertical drains(PVDs)and demands a large volume of sand fills.In recent years,air-boosted vacuum preloading has been developed to overcome these limitations;however,this method still requires more data to verify its performance.In this study,a field test for air-boosted vacuum preloading was conducted,and a large-strain two-dimensional(2D)finite element(FE)model was developed and validated against the field test data.Then,a series of FE parametric analyses was performed to assess key factors,i.e.the air injection pressure,the injection spacing,and the characteristics of cyclic injection,which affect the performance of the air-boosted vacuum preloading.The results showed that the ground settlement and lateral displacement of the soils increased due to an increase in the injection pressure,a decrease in the injection spacing,or increases in the number and duration of the injection cycles.Based on the parametric analyses,an empirical formula for ground settlement prediction was proposed and compared with a case history reported in the literature,showing good agreement.

Road Foundation Improvement by Explosive Force

A highway was constructed in Jiangxi Province, China, through mountainous area. Some sections of the highway went through valleys where a soft clay layer of 6,8.5 m deep was encountered. A new explosive method was developed and adopted for this project. In this method, blasting is used to remove and replace soft clay with crushed stones. Explosive charges are placed in the soil to be improved according to a certain pattern. Crushed stones are piled up behind the area where charges are installed. The explosion removes most of the soil in the exploded area and causes the pile of crushed stones to slide into the area where the soil is removed by blasting. A formular was suggested to calculate the charge weight used for improving a certain type of soil. The effectiveness of the method is evaluated using borehole exploration, plate load tests,and ground-probing radar tests.

Application of artificial neural networks for predicting the impact of rolling dynamic compaction using dynamic cone penetrometer test results

Rolling dynamic compaction(RDC),which involves the towing of a noncircular module,is now widespread and accepted among many other soil compaction methods.However,to date,there is no accurate method for reliable prediction of the densification of soil and the extent of ground improvement by means of RDC.This study presents the application of artificial neural networks(ANNs) for a priori prediction of the effectiveness of RDC.The models are trained with in situ dynamic cone penetration(DCP) test data obtained from previous civil projects associated with the 4-sided impact roller.The predictions from the ANN models are in good agreement with the measured field data,as indicated by the model correlation coefficient of approximately 0.8.It is concluded that the ANN models developed in this study can be successfully employed to provide more accurate prediction of the performance of the RDC on a range of soil types.

Estimation of jet grouting parameters in Shahriar dam,Iran

Jet grouting is a method for improving of soil and its physical characteristics.However,in this method,grouting of cement slurry with high pressure and velocity may cause damaging to soil structure,and then excavated grains of soil are removed from the borehole and replaced with cement slurry.The grains,which are remained around the borehole,mixed with slurry（cement） in-situ,can create an improved mass of soil.This mass is named＂Soilcrete＂.Soilcrete mass has special characteristics such as high strength,low deformability and very low permeability.In this paper,principles of jet grouting and effective parameters have been analyzed.Then the test results obtained from Soilcrete column have been investigated.Finally,the paper concludes with presenting amount of principle jet grouting parameters at foundation of Shahriar dam according to the results of jet grouting test.Based on the measurements,the diameter,Soilcrete UCS（uniaxial compression strength）,amount of the water,grout and air pressure and lifting and rotating speed in original site of jet grouting are 1.2～1.5 m,2～3 MPa,370～390 bar,10～15 bar,6～8 bar,7～8 cm/min and 7～8 cm/min,respectively.Also it can be seen that while the column diameter falls within the upper half of the range,some values of the compressive strength are close to the lower limit of the range.

Study on Key Technology of Using Shell Sand as Backfill for Sea Reclamation

The results of a study on the key technology of using shell sand, a kind of sea sand, as backfill for sea reclamation are described briefly. Iaboratory tests show that the physical and mechanical properties of shell sand are as good as normal quartz sand. Based on the chemical test and durability test of shell sand it could be concluded that the influence of corrosion of shell sand by acid rain and sea water might be ignored in the evaluation of the safety and durability of the engineering project. The results of field improvement tests show that the bearing capacity of shell sand backfill foundation is more than 200 kPa after vibmflotation improvement or dynamic compaction improvement. The shell sand is a good backfill material for sea reclamation.

Estimation of thermal conductivity of cemented sands using thermal network models

Effective thermal conductivity of soils can be enhanced to achieve higher efficiencies in the operation of shallow geothermal systems.Soil cementation is a ground improvement technique that can increase the interparticle contact area,leading to a high effective thermal conductivity.However,cementation may occur at different locations in the soil matrix,i.e.interparticle contacts,evenly or unevenly around particles,in the pore space or a combination of these.The topology of cementation at the particle scale and its influence on soil response have not been studied in detail to date.Additionally,soils are made of particles with different shapes,but the impact of particle shape on the cementation and the resulting change of effective thermal conductivity require further research.In this work,three kinds of sands with different particle shapes were selected and cementation was formed either evenly around the particles,or along the direction parallel or perpendicular to that of heat transfer.The effective thermal conductivity of each sample was computed using a thermal conductance network model.Results show that dry sand with more irregular particle shape and cemented along the heat transfer direction will lead to a more efficient thermal enhancement of the soil,i.e.a comparatively higher soil effective thermal conductivity.

Effects of porosity,dry unit weight,cement content and void/cement ratio on unconfined compressive strength of roof tile waste-silty soil mixtures

One of the conventional ways to improve the mechanical behavior of soils is to mix them with cementing agents such as cement, lime and fly ash. Recently, introduction to alternative materials or sub-products that can be adopted to improve the soil strength is of paramount importance. Therefore, the present study aims to investigate the effects of porosity(h), dry unit weight(gd) of molding, cement content(C)and porosity/volumetric cement content ratio(h/Civ) or void/cement ratio on the unconfined compressive strength(quor UCS) of silty soileroof tile waste(RT) mixtures. Soil samples are molded into four different dry unit weights(i.e. 13 kN/m^3, 13.67 kN/m^3, 14.33 kN/m^3 and 15 kN/m^3) using 3%, 6% and 9%cement and 5%, 15% and 30% RT. The results show that with the addition of cement, the strength of the RT esoil mixtures increases in a linear manner. On the other hand, the addition of RT decreases quof the samples at a constant percentage of cement, and the decrease in porosity can increase qu. A dosage equation is derived from the experimental data using the porosity/volumetric cement content ratio(h/C_(iv)) where the control variables are the moisture content, crushed tile content, cement content and porosity.

A method for predicting consolidation settlements of floating column improved clayey subsoil

A method of predicting the consolidation settlement-time curve of floating soil-cement column on improved soft clayey subsoil has been proposed.The degree of the consolidation(U(t))of the system is calculated by the double soil-layer consolidation theory,and the methods for evaluating the equivalent hydraulic conductivity(k)and the coefficient of volume compressibility(mv)of the part of the column improved layer have been proposed.The effectiveness of the method was verified by comparing predictions with the results of finite element analysis(FEA)using a unit cell model.The consolidation settlement(s(t))can be calculated by the method of treating a part of the column improved layer as an unimproved layer and using the corresponding average U(t)value.By comparing the predicted results with the measurements of laboratory model tests and three case histories in Fukuoka,Japan,the effectiveness of the proposed methods has been verified.It is suggested that the method can be used for designing the soft clayey subsoil improvement using floating soil-cement columns.

Transportation infrastructure settlement and heave distress:challenges and solutions

Transportation agencies spend millions of dollars annually to repair civil transportation infrastructure including pavements,earth structures and approach slabs distressed by soft compressible soils and expansive soils.Several research studies performed at the University of Texas at Arlington(UTA) focused on stabilizing these problematic soils so that they will provide better and more stable support to the transportation infrastructure.This paper focuses on a summary of two major distresses and mechanisms,and remedial measures for addressing these distress problems.A combined lime-cement stabilization method is fully evaluated in providing better support of pavement infrastructure,and these results are described here.Another major transportation infrastructure problem involving bridge approach slabs requires different treatment methods,and these results are briefly described.As a part of the recently completed research study assessments,both shallow and deep soil treatment methods for stabilizing soils are fully evaluated for their effectiveness in arresting the distress posed to the pavements and bridge approach slabs.These results along with a few future research needs are presented in this paper.

Liquefaction-induced damage evaluation of earth embankment and corresponding countermeasure

Liquefaction of sandy soils is a big threat to the stability and the safety of an earth embankment laid on saturated soils.A large number of liquefaction-induced damages on embankment due to different types of earthquakes have been reported worldwide.In this research,the dynamic behaviors of earth embankment and the reinforcement effects of grouting as remediation method,subjected to moderate earthquake EQ1 and strong earthquake EQ2,were numerically investigated.The seismic behaviors of ground composed of cohesionless sandy soil and cohesive clayey soil were uniformly described by the cyclic mobility(CM)model,which is capable of describing accurately the mechanical property of the soil due to monotonic and cyclic loadings by accounting for stress-induced anisotropy,over-consolidation,and soil structure.It is known from the numerical investigation that the embankment would experience destructive deformation,and that the collapse mode was closely related to the properties of input seismic motion because high intensities and long durations of an earthquake motion could lead to significant plastic deformation and prolonged soil liquefaction.Under the strong seismic loading of EQ2,a circular collapse surface,combined with huge settlement and lateral spread,occurred inside the liquefication zone and extended towards the embankment crest.In contrast,in moderate earthquake EQ1,upheaval was observed at each toe of the embankment,and instability occurred only in the liquefied ground.An anti-liquefaction remediation via grouting was determined to significantly reduce liquefaction-induced deformation(settlement,lateral spreading,and local uplift)and restrain the deep-seated circular sliding failure,even though the top sandy soil liquefied in both earthquakes.When the structure was subjected to EQ2 motion,local failure occurred on the embankment slope reinforced with grouting,and thus,an additional appropriate countermeasure should be implemented to further strengthen the slope.For both input motions,the surface deformation of the considered embankment decreased gradually as the thickness of reinforcement was increased,although the reinforcement effect was no longer significant once the thickness exceeded 6 m.

Field study on performance of new technique of geosynthetic-reinforced and pile-supported embankment at bridge approach

Vehicle bumps at a bridge approach caused by the differential settlement between a bridge and an adjacent backfill embankment are one of the most difficult problems in geotechnical engineering. Large vehicle bumps make drivers uncomfortable and cause large impact loads on vehicles and the bridge abutment. A new ground-improvement technique called fixed-geosynthetic-reinforced and pile-supported embankment(FGT embankment) was developed and used to alleviate vehicle bumps at a trial bridge-approach site located in central China. To distribute the differential settlement between the bridge and adjacent backfill embankment over a long transition zone, the following three techniques were used at the trial bridge-approach site:(a) the FGT embankment,(b) conventional geosynthetic-reinforced and pile-supported embankment(CT embankment), and(c) geosynthetic-reinforced embankment without piles(GR embankment). The performance of all three techniques in the field trial was investigated by field measurements involving earth pressure cells, geosynthetic deformation sensors, and settlement gauges. The FGT and CT embankments exhibited better performance than the GR embankment. Compared with the CT embankment, the FGT embankment was more effective at ground improvement. At an elevation of 4.0 m from the base of the embankment, the pressures below the geosynthetic were smaller than those above the geosynthetic at the closest measurement point. The difference between the pressures between above and below the geosynthetic tended to increase with the embankment height.