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泥漿黏度測量儀結(jié)構(gòu)設(shè)計 附錄2 外文文獻 The new clay mud and its improvement effects of tunnels a b s t r a c t During tunneling process by earth pressure balance (EPB) shield, the strata containing large amounts of sand and gravel are often encountered. The excavated soil in the shield chamber has poor plastic flow and larger permeability, so it leads to the difficult construction of the EPB tunnel. In order to ensure tunneling advance successfully, the excavated soil must be improved by adding modified materials to change its physical and mechanical properties, and make it to have a good plastic flow state, low friction angle and low permeability.Soil improvement techniques can guarantee the stability of excavation face, achieve the balance advance of shield tunnel, reduce machinery load and the ground settlement, and improve the excavation speed. The existing mud used in engineering practice is the dispersing mud and water system whose compositions are bentonite and water. Both the composition and function are simple. The existing mud has various problems, such as large amounts of waste mud emission, difficulties in controlling mud indicators, large areas for mud treatment and large uses of new mud materials and environmental pollution. In this paper, a kind of environmentally friendly clay mud was developed, and the laboratory and field tests were conducted to verify its adaptability and superiority. 1. Introduction With the development of shield construction technology and soil improvement techniques,shield construction technology is widely used in the underground construction, especially in the poor soil and complex geological conditions with high groundwater level. Currently, in the EPB shield construction exists many problems, for example,in the clay-silt layer, the cohesive soil will affect the flow plastic state of soil in the excavation chamber and the penetration of ground-water. In the sand soil layer, the cutter head of the shield machine wears quite seriously. In the gravel layer containing groundwater,the greater seepage pressure is applied to the excavation face, the soil pressure is difficult to control in the excavation chamber, and the boiling phenomenon may appear, the cutter head wears seriously as well. In the sand and pebble layer, the friction resistance among the sand–pebble particles is too large to obtain the good liquidity of the excavated soil. Therefore, when the excavation chamber and the spiral conveyor are full of excavated soils, the torque of the cutter head and the thrust force of the shield machine will increase, even if the spiral conveyor does not work (Yang and Li, 2012). In addition, in order to make the shield tunneling successful, the modified materials(e.g., mud, bubble and polymer) must be injected into the excavation face and excavation chamber (even in the spiral conveyor) to improve the excavated soil condition, and have a good plastic flow, have low friction angle and low permeability to guarantee the stability of excavation face, achieve the balance advance of shield tunneling, reduce the ground settlement, and improve the excavation speed.Currently, the research and application of soil improvement techniques lack normative standards, such as the selection of the conditioner types, mud composition, methods of determination, control of the performance parameter and objective, and selection and controlof the injection parameter, almost all of them are based on the engineering experience or the trial and error in the construction field.Usually, the simple slump cone test was used to measure the behavior of the conditioned soil scarried out the mixing tests to measure the power consumptionof a mortar mixer and assess the effectiveness of the soil conditioner.The vanesheardeviceis applied to measure the shear strength of soil mixtures under different pressures and vane velocities, and even evaluate the property of soil conditioned with foam and polymer additives. 2. Preparation of a new mud and its performance analysis 2.1. Preparation of a new clay mud During the EPB shield tunneling, the excavated soils in the excavation chamber should have a good plastic flow property to ensure that the thrust force applies evenly on the excavation face, and maintains the stability of the excavation face. At the same time, the excavated soils could be discharged smoothly through the screw conveyor. In this study, the improved material for the sand-gravel layer is the mineral mud. Based on the knowledge of drilling fluids, combined with the existing research results, the indoor experiments combining with the evaluation methods were conducted to select the mud mate-rials. Through the analysis of a series of indoor experiments, the mud materials were determined as water, bentonite, xanthan gum, sodium carbonate, and clay particles. Due to the particularity of the shield tunneling, the related performance of the new clay mud must be tested before it is used. In this study, the relative density, viscosity (including the marsh funnel viscosity, apparent viscosity, plastic viscosity, dynamic shear, gel strength, liquidity index and consistency coefficient), conventional static filter loss (API standard, which refers to the filter loss through the filtrate area with 4580 mm 2 within 30 min in the state of the normal temperature and 0.689 MPa.) and pH value of the new clay mud were measured to estimate whether they meet the requirements of the construction site. In order to obtain the better mud proportion,the orthogonal experiments were also conducted. It is noted that the content of raw material refers to the percentage of material mass and water mass. 2.2. Performance comparison of the existing mud and new clay mud Until now, the existing mud used in the EPB shield tunneling is the pure bentonite mud with 9% bentonite, namely, a ton of water has 90–120 kg bentonite. It is noted that, in order to facilitate the description, the new clay mud developed in this study be referred to as clay mud A, and the existing mud used in the EPB shield tunneling be re- ferred to as mud B. Therefore, the consistency of the mud B is high, and does not easily flow. Also, the mud B is difficult to flow out of the test tube after standing, and it is not conducive to the mud pumping systems. The apparent viscosity of the mud B is 13.5 mPa·s, the plastic viscosity is 3 mPa·s, and the marsh funnel viscosity is 40; compared with the clay mud A, mud B has a low viscosity. In addition, clay mud A has a high viscosity, so it can avoid mud spill, conducive to film, and ensure the stability of excavation face. Meanwhile, for the large size gravel layer, high viscous clay mud can prevent the deposition of gravel in the excavation chamber, and it is conducive to con- veying excavated soils. Therefore, the performance of the new clay mud A developed in this study is better than that of mud B used in the EPB shield tunneling. 3. Laboratory test of the new clay mud 3.1. Laboratory design for the improvement of the new clay mud To estimate the improvement effects of the new clay mud A, it is necessary to carry out some related experiments which contain soil mixing test, friction coefficient test, adhesive resistance test and slump test to fully analyze the improvement effects. 3.1.1. Soil mixing test Soil mixing test mainly imitates the real mixing process in the excavation chamber. By this test, the improvement effects of the new clay mud can be estimated, and take control of the content of clay mud by the change of power of mixing. Soil mixing test experiment contains mixer and power meter, as shown in Fig. 1. 3.1.2. Friction coefficient test The main purpose of taking friction coefficient test is to imitate the process of soil and the steel friction while the spiral unearthed device and getting the adhesion coefficient of drag. Achieve the instant adhesive resistance when the simulation shield machine starts working again. By the size of the force, the coefficient resistance of the soil act- ing on the steel can be determined. If the force is too large, the fluidity is too great and it needs more power to start the machine. The measuring machine is shown in Fig. 4 . 3.1.4. Slump test The slump test is needed to simulate the fluidity state of the conditioned soil. If the slump has no obvious change, there is no need to take the slump test because the following test is easily affected by the slump. The slump shouldn't be taken until the clay mud has certain effect on the soil. The requirement of the slump needs a certain series of tests to be determined. Based on the early experiments, the knowledge about slump test has been handled partly and the time of taking the test can be controlled easily. Each time takes 3–5 groups of tests and takes the average of the data. The experiment device for slump is the standard cave in barrel, as shown in Fig. 5. 3.2. Laboratory test and analysis of the new clay mud To evaluate the improvement effects of the new clay mud, both clay mud A and mud B were used to improve the round gravel soil and sandy soil to comparatively analyze the advantage of clay mud A.. Mixing test. Fig. 6 describes the comparative curve of the net power of clay mud A and mud B. From Fig. 6, it can be seen that the net mixing powers of the two improved soils obviously decrease after adding the clay mud A and mud B; the effects of the two muds on the mixing power are roughly equal. It can also be seen that, when the net power reaches zero, the excavated soil will be in the state of fluidity plastic. The net power of clay mud A is smaller than mud B, so the effects of decreasing the mixing power of clay mud A are better than mud B. 4. Field test to evaluate the effects of the new clay mud 4.1. Background In order to estimate the effects of the new clay mud on the property of plastic flow of the excavated soils, the region between Yuquan station and Fanjiacun station of the subway line 10 in Beijing was chosen to conduct field tests. 4.1.1. Geological condition Through investigation, in the region of shield tunneling, the maximum depth of the discovered layer is 42.7 m, where it contains miscellaneous filled soil, sandy silt, pebble bed, and round gravel soil. The major tunnel structure lies in the pebble bed. The particle size is usually within 2–10 cm, the maximum size reaches 15 cm, fine medium sand accounts for 30%, the parts of the layer contains floating stones which accounts for over 20% and the distribution is very random.The basic property of the layer is the loosing structure without cement, and with the distribution of different particle sizes. In addition,the void of the gravels was mainly filled with medium and rude sand without water. 4.1.2. Main form of the shield machine The cutterhead of the shield machine in this region is designed to six spokes with six panel, the cutters contain tearing knife, scraping knife, crushed stone knife, copying cutter, surrounding protecting knife, etc. The copying cutter is pushed by the hydraulic pressure,the size of the cutter head is 6240 mm long, and its aperture opening ratio is 41%. The dimension of the maximum particle getting through the cutter can reach 500 mm × 300 mm. 4.2. Field test The new clay mud A developed in this study was used in the field test. According to the field condition, the volume of the mixing tank was 3 m 3 , and it was filled with water. About 3% of the bentonite and sodium carbonate and medium grained clay were added into the mixing tank and mixed together, and then 1% of the bentonite and xanthan gum were mixed and added into the mixing tank using 2 mm granule sieve to prevent caking, as shown in Fig. 14. After mixing well (about 15 min), the new clay mud was transferred from the mixing tank to the storage pool, whose volume is 50 m 3 . The mud cannot be used until 12 h later. 4.3. Analysis of field test results The typical layer in the region from ring 661 to ring 665 (each ring is 1.2 m) was chosen to conduct the field tests. In order to analyze and compare the improvement effects of the clay mud A developed in this study, the ring 655 to 660 was also improved by the existing mud B for comparing purpose. 5. Conclusions In this study, a new type of clay mud was developed, and lots of laboratory tests and field tests were carried out to test and verify its improved performance. The following conclusions can be summarized as: The work presented in this paper was supported by the National Natural Science Foundation of China (41202220), the Research Fund for the Doctoral Program of Higher Education, the Fundamental Research Funds for the Central Universities and the Research Fund for Key Laboratory on Deep GeoDrilling Technology, Ministry of Land and Resources. - 8 -