Anti-clogging Model of Dredged Clays Dewatering with Ventilating Vacuum Method

Ventilating vacuum method can overcome the clogging problem which often occurs on the traditional vacuum method dewatering dredged clays with high initial water contents. However, how to analyze the anti-clogging behavior of ventilating vacuum method is an important issue in practical engineering. A radial drainage model was established based on the filtration theory developed by Ruth. The vanity of the model was verified using the test results of ventilating vacuum, and the change law in average radical dewatering resistance of dewatering layer which reflects the filtration performance was investigated during the dewatering process. It is indicated that the dewatered layer is compacted by traditional vacuum method during the dewatering process. Its corresponding pore structure is unstable, thus the drainage pipeline often clogs. While the technique of ventilating vacuum provides a powerful way to overcome the clogging problem, and the pore structure is stable during the dewatering process.     

Analyses on Stability of Saturated-Unsaturated Bank Slope with Revetment During Rise and Fall of River Level

The bank slope failure is closely related to the rise and fall of river level generally. In order to analysis the influence of the rise and fall of river level on Jin’an River bank slope stability in Fuzhou, the saturated-unsaturated seepage of bank slope with revetment was modelled based on the engineering geological condition of some bank of Jin’an River, and the effect of rise and fall of river induced by the DRWWOS(Drawing River Water to Wash Out Sewage) project on bank slope stability was studied. The results show the silt lying on the slope toe impedes pore water change, manifesting as in its sphere of influence river water is hard to flow into the bank when river rises, and the pore water pressure can not dissipate in time when drawdown. The faster the river rises, the more stable the bank slope becomes. On the contrary, the larger river level falling rate is more likely to leads to bank slope failure. Due to the poor bank drainage performance, the frequent rise and fall of river level results in pore water pressure increasing further, then impairing the bank slope stability. During DRWWOS project, the river level falling rate control and pore water pressure dissipation must be paid enough attention to. Also, replacing silt lying on the slope toe by good permeable material is a good choice to reinforce the bank slope.     

On Elasto-Plastic Consolidation Settlement of Saturated Soft Clay

The specific properties of soft clay are characterized by higher void ratio, lower permeability and higher compressibility, the consolidation settlement of soft clay is affected by the imposed stress history, the stress paths, the consolidation pressure and the soil properties. In this paper, the porous media theory based on the mixture theory was applied in the study on the consolidation settlement of soft clay, which was more rigorous than the conventional consolidation settlement theory and the coupling between soil and water can be taken into account in the analysis.     

Experimental Analysis of Water Transference in Unsaturated Expansive Soil

On the condition of constant temperature, grouping dry wet soil with different initial water content and different time intervals, the experiments were carried out to study vaporous transfer, vaporous liquid transfer and the relationship of unsaturated expansive soil.And it was found that the soil behavior, water content and water content gradient were pivots for the transfer.Vaporous transfer, vaporous liquid transfer were increased with the increase of moisture gradient in a complex non linear relationship with times and locations.And with the less water, the adsorption capacity of soil was strong, resulting in larger gradient of moisture.While for larger water content, free water was more with more even of the moisture.     

Single Compression Experimental Analysisand Failure Mode of Loess with Different Structural

Based on the single compression experiments in laboratory, the structural change characteristic of loess with different initial structural in single compression stress conditions was studied. The conclusions are: compared to the single axial compression strength between intact loess and remold loess in the same moisture conditions, strength of intact loess was way bigger than remold loess; when the water content was low, all of a sudden, the destruction model of loess samples was mainly brittle tensile failure; when the water content was low, there was relative little effect on metastable of structural and was relative little loss of initial structural strength, and relative more variability; and then, there was way higher initial structural strength. The structural index decreased sharply with the moisture increase of intact loess, and the effect of water content on initial structural is obvious; when the water content reached a certain value, moisture effect on initial structural of intact loess become more and more unobvious, and structural index of loess was relative small. In other words, the initial structural has been fully released by remolding and saturating; the reasonability of structural index which was quantitative described the initial structural of loess was verified.     

Effects of Fines Content on Evolutionary Characteristics of Dynamic Pore Water Pressure of Saturated Sands

With the GDS dynamic triaxial system, undrained dynamic triaxial tests on the saturated sand with different fines content are performed, and the effects of fines content on evolutionary characteristics of dynamic pore water pressure of saturated sands in the process of liquefaction are analyzed based on Seed pore water pressure stress model. It is found that fines content has great effect on the dynamic pore water pressure of saturated sands by the parameter θ for Seed model. The relationship between parameter θ and fines content isnt linear. Parameter θ decreases with the increase of fines content at first, and then reaches its smallest value when the critical value of fines content is 30%. After that, parameter θ increases gradually with the rise of fines content. According to the experimental study on effects of fines content on evolutionary characteristics of dynamic pore water pressure of saturated sands, the existence of critical fines content with 30% is further proved in the sandy soil used in the test.     

Seepage Characteristics of Rock during Damage Process

Four evolution patterns of rock permeability in damage process are summarized. And how rock pore, micro cracks and lithology form the four patterns of rock permeability evolution is analyzed. The impact of confining pressure on permeability is also presented. The permeability reduces along with the increase of confining pressure before rock failure, however, it is complex after rock failure, and it is necessary to do further research. Statistical analysis is carried out to analyze the variation range of permeability in the process of damage, which shows soft rocks vary less while hard rocks vary more. In the experiments in which the confining pressure is between 1 MPa to 40 MPa, permeability variation of 85.9% rock is within 100 times, 97% within 1000 times. Furthermore, the difference between instability of seepage and that of structure under the function of seepage is distinguished. It is proposed that the presence or absence of non-Darcy flow should be considered from the point of effective stress law.     

Experimental analysis of the deformation of sandstone under cyclic pore water pressure and wavelet transformation

To explore the characteristics of deformation of sandstone under cyclic pore water pressure, the experiments with different axial stresses (60%, 70% and 80% of peak intensity) of sandstone subjected to cyclic pore water loading are investigated by using MTS815 rock mechanics testing system, and irregular small deformation in deformation curve of sandstone are also processed by wavelet transformation of Matlab. The results show that with the increase of constant axial stress, fatigue deformation under cyclic pore water pressure will accelerate the failure of the sandstone. With the increase of the number of cyclic pore water pressure, the deformation evolution of the plastic-loop is illustrated as sparse-dense-sparse. The deformation curves of sandstone under cyclic pore water pressure affected by many factors are decomposed, reconfigurable processed and evaluated by using wavelet transformation, which indicates that the basic curve with optimal decomposition scale fits well with the experimental curves and reveals the deformation evolution of sandstone.     

Effect of Deflection Characters on Self oscillating Water Jet

The deflective mechanism of the oscillating water jet is analyzed and the effects of jet deflection on the self oscillating water jet are investigated. It is experimentally shown that the deflective angle may reach 9.53 degree, the pressure fluctuation is more intensive and more regular and the jet can efficiently eliminate the water cushion effect and increase the ability in cutting.     

Pressure-Dependent Analysis of Water Supply Network Damaged by Earthquake Based on Emitter Model

When the water supply network suffered earthquake damages, pipeline leaks and bursts may occur. In the period in post-earthquake emergency rescue and repair, the network is supplying water with additional outflow of damages (leaks and breaks), which result in pressure deficient. According to the frictional head loss along the break pipeline, a model with additional emitter at the endpoint of the disconnect pipeline was proposed to simulate the break, which simplifies the modeling of breaks. The pressure-dependent demand relationship was adopted in the process of pressure-deficient hydraulic simulation to avoid node negative pressure. Meanwhile a backtracking and line search procedure was utilized to control the iteration step of pipeline network nonlinear equations, which ensure the global convergence of the hydraulic simulation. The effectiveness of the proposed method was verified by a case study.     

Dynamic Behavior of Geogrid Reinforced Pile Supported Embankments under Moving Load

In order to investigate the dynamic behavior of geogrid reinforced pile supported embankments (GRPS) under moving load, a three dimensional coupled mechanical and hydraulic model was built by FLAC 3D. The results from two cases including unreinforced and no pile embankments, and geogrid reinforced pile supported embankments were presented. The behaviors of vertical displacement, pile soil stress ratio, excess pore water pressure, and vertical acceleration under two cases were compared and discussed. Additionally, studies on the effect of speed and weight of the moving load were performed. It is indicated that the value of vertical displacement, pile soil stress ratio, excess pore water pressure, and vertical acceleration of GRPS decrease evidently compared with those of unreinforced and no pile embankment, which is caused by the soil arching effect and the reinforcement effect. It is also shown that the greater the axle load value is, the less the beneficial effect of GRPS on the vertical displacement. With the increase of the moving speed of the load, the vertical displacement increases.     

Creep Characteristics Considering Stress Paths of Dredger Fill

To study the influence of stress path on the long-term deformation, creep tests of dredger fill in Tianjin Binhai New Area in three different stress paths, namely decrease p paths (DEP)、constant p paths (CNP) and increase p paths (INP) respenctively, were carried out by using the WF stress paths tester and grading loading method. The results showed that under the same deviate stress conditions, the creep strain decreased in three kinds of stress paths of DEP, INP and CNP in turn, deformation rate of stable stage in the procession of creep increased according to the three kinds of stress paths of DEP, CNP, INP. The pore water pressure were negative in the procession of creep with decrease p and constant p stress paths, and decreased along with the deviate stress increase. However, in the procession of creep with increase p stress paths , the pore water pressure increased with the increase of deviator stress. The long-term strength in decrease p and constant p stress paths was higher than that in increase p stress paths. Finally, the effect is better by using quadratic polynomial to fit stress-strain isochronous curve of the three stress paths.     

Elasto-plastic analysis on surrounding rock of roadways based on seepage, strain softening and dilatancy

According to seepage body force, strain softening and rupture expansion of rock mass, elastic-plastic mechanics theory, distribution laws of stress and displacement of surrounding rock in seepage field are derived, and relationships between different zonation range of the surrounding rocks, pore water pressure, strain softening and rupture expansion are established. The results show that the pore water pressure and rupture expansion rock mass have a more obvious impact on the surrounding rock rupture area than the plastic zone. Both the plastic zone and the rupture area are larger when the seepage field is considered. The impact of strain softening on both the plastic zone and the rupture zone of surrounding rock is very significant, and both seepage and strain softening rupture expansion affect deformation of surrounding rock of roadways obviously. It provides certain reference values for the roadway support engineering in seepage field.     

Evaluation on Effects of the Change of Hole-boring Distance During Splitting Grouting to Earth Dam

The technology of splitting grouting for earth dam is one of the important technical measures to improve the quality of dam. However, the consolidation mechanism of slurry in the dam is not clear, which can not evaluate the effects of seepage control of the dam after grouting. Therefore, assuming that the construction technology does not change and with the consideration of interaction between the layout of hole-boring distance and the effects of seepage control, the Mohr-Coulomb Hardening model and fluid-solid coupling method were used to analyze the rule of pore pressure, stress and strain in the dam during splitting grouting based on the finite element simulation. The consolidation mechanics was discussed and stability of the dam was evaluated.     

Experiments of coal’s gas seepage with outburst dangers

The experiments of outburst coal’s gas seepage are carried out by triaxial permeameter which is independently developed. Under the condition of fixed gas pressure, different confining pressures and axial pressures acting on raw coal test samples are tested. It shows that as the increasing of confining pressure, coal sample seepage velocity tends to decline, and this phenomenon is more obvious for the coal with serious original injury. The relationship between seepage velocity and confining pressure can be described as a quadratic function,and its general expression is established. Coal sample’s seepage velocity-strain path is similar to stress-strain path, therefore, the changes in coal seepage velocity indirectly reflects the process of the evolvement of coal damage. The influence of effective stress on coal sample seepage velocity can be concluded as hypersensitive stage and smooth stage, and in the hypersensitive stage, seepage velocity of the coal sample vary quickly, while in smooth stage, its variety is not obvious. In different stress conditions, the degree of development for hole and cranny of coal affect coal gas energy and elastic deformation energy in coal body as well as the form of coal destruction.     

Mechanism of crack-oriented of hydraulic fracture and its technique in mine

Drainage is inefficient of coal seam treated by hydraulic fracture due to disordered propagation of fracture. Therefore, we propose a novel approach of fracture-oriented via slotting a slitting in coal seam by high pressure water jet. Firstly,boreholes-oriented are drilled around the borehole of hydraulic fracture. Then we slot the coal seam via high pressure water jet. Finally,we carry out hydraulic fracture in the borehole. Shear destruction area which is formed under geostress is located on crack tip. And crack propagates along horizontal direction because the major principal stress direction is horizontal. Besides,we develop the technique of crack-oriented and apply it in typical low permeability coal seam. The results show that the technique is efficient. The diameter of hydraulic fracture is larger than 25 m,the concentration of gas drainage is 68% on average,and the gas flow is 0.037 m 3/min. The concentration and flow of gas increase 2.12 times and 11.26 times respectively comparing to those of traditional technique.     

Experimental Analysis on the Deformation of Sandstone underPore Pressure and Constant Time

In order to discuss the deformation characteristics of rock mass under different water levels changing between 145 and 175 meter in the Three Gorges reservoir area, an experiment was carried out for the studying sandstone deformation under the conditions of three different axial stresses(σ1=55.54,34.18,12.82 MPa), two cyclic pore pressures(Pmin=2 MPa,Pmax=6 MPa) and two kinds of constant time(the upper limit time and the lower limit time(ΔT=120,240 s).With ε1-T curves and p-T curves, as well as p-ε1  hysteresis curves, it was found that the curves were continuous sine wave-shaped curves.At first, the strain decreased with loading pore pressure.And then, it decreased to valley value with pore pressure at stable upper limit.Next, it increased with unloading pore pressure and increased to peak value with pore pressure at stable lower limit.The p-ε1  hysteresis curves of the sandstone had two typical stages.And one was caused by the closure of some primary pores and crack under increasing compaction, in which the strain did not form obviously hysteresis curves, and the other was pore pressure coupling stage which showed obvious hysteresis curve in form of the anti-clockwise from the dispersed to the dense.In addition, Δε-n curves in four sections (loading, unloading, steady upper limit, steady lower limit) of p-ε1 curves were compared and respectively ananlyzed in the condition of various axial stress and different constant time .     

Analysis on Mobility of Heavy Metals between Sediment water under Different Hydrodynamic Conditions

The mobility of heavy metals including Cd, Cr and As, among sediment, pore water and overlying water under different hydrodynamic conditions in 15 d was analyzed with hydrodynamic flumes. Three velocities were designed as 4.01 cm/s for slow flow in Flume A, 12.70 cm/s for middle flow in Flume B, and 20.23 cm/s for fast flow in Flume C. Results show that: 1) Increasing the velocities of flow can promote the release of heavy metals; 2) As of pore water presented higher concentration, which shows the mobile trends of As are from pore water to overlying water; 3) Sediments suspended are the main reason for the increase of concentration of heavy metals in the overlying water. Compared with the static condition, hydrodynamic conditions significantly affect the mobility of heavy metals. And the changing characters in each flume are different for each kind of metals in different kinds of medium (overlying water, pore water, and surface sediment). Moreover, the extent of hydrodynamic impacts on the mobility of heavy metals is overlying water>sediment>pore water.     

Effect and Mechanism of Styrene butadiene Rubber Latex on the Long Term Shrinking Performance of Mortar

The long term shrinking strain (1~90 d) of ordinary cement mortar and styrene butadiene rubber (SBR) latex modified cement mortar were tested by micrometer calipers, and the micro image and microstructure of mortar aged at 28 d was analyzed by pore size distribution method, density method and scanning electron microscope(SEM) image. The hydration heat of SBR latex modified neat cement mortar was measured. It was shown that the long term shrinking performance of mortars was improved when the content of SBR latex was above 3%, especially before the age of 28 d. The long term shrinking strains of mortars reduced as the increase of SBR latex content. The improving mechanisms of SBR latex on the shrinking of mortar were as follows: 1) The hydration heat reduced before 72 h, with which it reduced the thermal expansion crack of mortar. 2) The water around the SBR grain was lost during the processing of hydration, and polymer films were formed, with which it played the role of “micro fiber” and restrict the shrinking of mortar. 3).As the incorporation of SBR latex, the mean pore diameter, mode pore diameter, median pore diameter of mortar aged at 28 d decreased. And the quantity of harmful and multi harmful porosity reduced with the increase of quantity of harmless porosity. Therefore it was indicated that the microstructures of mortars were improved by the content of SBR latex. 4) The total porosity of mortars declined slightly as the incorporation of SBR latex, and the proportion of closed porosity to the total pore remarkable increased, which played the role of maintaining internal water of mortar.     

Experimental Investigation of Ultrafiltration Membrane With Different Pretreatment technology for Lake Water

In order to solve the problems that the exiting technologies do not adapt to the deterioration of the water quality in the water plant, the ultrafiltration was used to treat water respectively from ozone biological activated carbon pool (process 1), sand filtration pool (process 2) and sedimentation tank (process 3) in the region of river network of southern China.It is found that the average DOC removal rate were 33.08%, 23.60%, and 18.55%, and the average alga removal are 98.71%, 97.84%, and 98.13% in the process 1, process2 and process3, respectively.The turbidity of the effluent is lower than 0.1 NTU, and the particles with their size bigger than 2 μm were lower than 20 per milliliter in all the three process.The trans membrane pressure increased by 6.59% and the water production rate of the UF membrane was 98.02% during 45 days pilot experiment in the process 1.When 0.65mg/L chlorine was added before ultrafiltration membrane, the trans membrane pressure was recovered effectively after hydraulic flush.And the trans membrane pressure increased by 2.91% and the water production rate of the UF membrane was 97.63% during 10 days pilot experiment in the process 2.The trans membrane pressure increased by 13.52% and the water production rate of the UF membrane was 97.01% during 20 days pilot experiment in the process 3.