Abstract:The ports in Guangdong-Hong Kong-Macao Greater Bay Area（hereinafter referred to as the Greater Bay Area）are one of the earliest and largest areas in the development of container transportation in China’s coastal ports. It has formed a container transportation pattern with trunk and branch connections and clear layers. It is an important support for the Greater Bay Area to build a world-class advanced manufacturing base and a modern industrial system，and a strategic platform to serve the national “double cycle” pattern. According to the development characteristics of container transportation in the port of the Greater Bay Area，this paper uses the structural prediction model of foreign trade containers in the mode of diversity and distribution to predict the throughput of container ports in the future. On this basis，regarding the problems and challenges faced by the ports in the Greater Bay Area，suggestions are put forward to promote the development of container ports in the Greater Bay Area from the aspects of promoting the sharing and sharing of channels and anchorages，optimizing the port collection and distribution system，promoting the high-level interconnection of port groups in the Greater Bay Area，and improving the port service level，so as to provide important support for the high-quality development of the Greater Bay Area.

Abstract:The port coastline is an essential strategic resource of the country. Strengthening the effective protection and reasonable utilization of the port coastline is of strategic importance to the sustainable and healthy development of transportation and even the national economy. This paper analyzes the main characteristics of the reserve，distribution，development and construction of the port coastline resources in China. It highlights the main problems in developing the port coastline，including unreasonable utilization，lack of measurement standard，and inadequate statistical system，etc. Then，it proposes relevant strategies to further promote the efficient utilization of the port coastline in China，such as improving shoreline measurement standards，establishing a normalized supervision mechanism，and optimizing the shoreline statistical system. The appropriate conclusions can provide a reference for the transport sector to formulate policy measures and comprehensive resource utilization management.

Abstract:Complex river engineering mapping is often affected by a variety of factors such as lush vegetation，weak signal link and mountain occlusion，which make it difficult to carry out traditional surveying and mapping means. Through the comparative study of UAV LiDAR and tilt photogrammetry in complex river engineering mapping，the complementary advantages and fusion methods between the two are found out. The experimental results show that the LiDAR data incorporating textured image information has accurate spatial geographic information and clear land boundary information.The detailed expression of the skew model corrected by LiDAR data is significantly improved，and the contour expression of the model is clear and manual interpretation is easier.The results effectively overcome the disadvantages of UAV single measurement technology and traditional measurement technology，and can quickly build a more accurate river digital twin model.

Abstract:The dredged sand in the lower reaches of the Yangtze River is mainly ultra-fine sand（with a fineness modulus of 0.1-0.5），with small particle size and uneven particle gradation，which can be hardly used in engineering. With dredged sand in the lower reaches of the Yangtze River as the main raw material，we replace ordinary cement with alkali-activated low-carbon geopolymers to prepare artificial blocks and test their mechanical properties and drying shrinkage characteristics. Moreover，we use chopped fibers to solve the problem of easy shrinkage and cracking caused by the alkali activation system. The test results show that：1）When the content of the activator Na2O is 5%，and the modulus is 1.0，the compressive strength and splitting tensile strength of the blocks after 28 days are 48.20 and 6.43 MPa，respectively，and the strength does not shrink in the later period. 2）Both basalt and polypropylene fibers can significantly inhibit the linear drying shrinkage of the blocks. Basalt fibers have stronger mechanical properties than polypropylene fibers，which can make the microstructure of blocks more compact and more integrated.

Abstract:This paper summarizes and compares the existing calculation methods for the average overtopping volume of mound breakwaters under oblique wave attack both at home and abroad. Taking a new mound breakwater of a port in North Africa as an example，we calculate the average overtopping volume and compare it with the result of a 3D physical model test. The results show that when the wave attack angle ranges from 0° to 20°，the reduction effect of oblique waves on the average overtopping volume is insignificant，and they can be considered perpendicular waves in design；when the wave attack angle is greater than 20°，the reduction effect is gradually significant，which should be taken into account. For AccropodeTM armored mound breakwaters with a wave attack angle of 30°，the calculation results of the neural network method and van Gent formula（Combination 2）are close to those of the physical model test，and the results of the Galland formula，van der Meer formula，and van Gent formula（Combination 1）are similar and relatively small. The calculation results by Chinese standards are conservative；the Lykke formula is risky，and thus it is not recommended.

Abstract:At present，the design theory of sheet-pile wharf with rigid load-relieving component is not mature，and the relevant specifications do not involve specific calculation methods. Prototype observation of wharf structure is an effective method to master the working characteristics of this new structure. In this paper，combined with the structural form and main construction technology of sheet-pile wharf with rigid load-relieving component，the prototype observation is carried out，and the variation laws of parameters such as stress，earth pressure and deep soil displacement of the steel pipe sheet pile in the front wall at different construction stages are obtained. The results show that due to the small pile spacing，the soil behind the sheet pile wall is obviously compacted by the pile foundation，the bending moment of the sheet pile in the front wall and the pile foundation of the bearing platform are less than the design value，and the maximum settlement and horizontal displacement of the wharf apron are greater than the calculated value in the serviceability limit state.

Abstract:The long-term safe service of wharf beam is related to the safety of the whole wharf structure，and the corrosion of steel bars caused by carbonization of concrete in inland river environment is the main reason for the strength degradation of wharf beam members. The inland river frame wharf located in the upper reaches of the Yangtze River is always in the service environment with relative humidity changes and is subjected to bending stress for a long time，which will aggravate the carbonization process of the wharf beam members and seriously threaten the durability of the overall structure of the wharf. Relying on the frame wharf structure of a typical port frame wharf structure in the upper reaches of the Yangtze River，based on the concrete carbonation model that comprehensively considers the combined effects of the changes in relative humidity and bending stress，combined with the time-varying model of the sectional area of corroded reinforcement of reinforced concrete material，the strength of corroded reinforcement，and the bearing capacity of flexural members，the time-varying probability distribution of the bending bearing capacity of the wharf beam members within the design service life of 50 years is calculated by Monte Carlo random simulation method. On this basis，the time-varying probability model of bending bearing capacity of beam members of inland river frame wharf is established through statistical analysis，which provides a theoretical basis for durability evaluation of inland river port wharf structures.

Abstract:Taking adventure cruise ships in areas to north of 60°N for example，we identify the ports of call of adventure cruise ships based on the schedule data released by third-party websites，and depict the spatial differentiation pattern of adventure cruise ships’ ports by Arc-GIS visual analysis tool，so as to further explore the port calling regularity of adventure cruise ships under the impact of COVID-19. The results show that there are two functional types of adventure cruise ship ports in areas to north of 60°N including port of departure and port of call，with a quantity ratio of 1：9. The distribution of adventure cruise ship ports is spatially unbalanced and varies significantly in scale. The ports of choice for adventure cruise ship operators during the COVID-19 pandemic are only Murmansk，Bergen and Alesund，which is closely related to port facilities location，port regional climate conditions and city economic level.

Abstract:Coastal ports are an important infrastructure of the national economy and social development，as well as an important strategic resource for China to participate in international economic cooperation and competition. It is necessary to track the construction，production，and operation conditions of ports and study the supply-side capacity adaptability of ports under the pattern of international and domestic circulations，which is an important basis for industry management by transport departments. This paper reviews the macroeconomic development trend of our country and the development of coastal port throughput during the 13th Five-Year Plan period and analyzes the capacity adaptability of coastal port terminals in detail by levels，regions，cargo categories，and structures. In the analysis，we consider factors such as equipment and technology improvement，adjustment of the conversion coefficient of container weight，and nuclear increase in general terminal capacity according to the actual development of coastal ports. Some suggestions are put forward to promote the professional transformation and pass capacity evaluation of existing general terminals，the intelligent production and operation of ports and the facilitation of public services，and the hub role of ports in the comprehensive three-dimensional transportation network.

Abstract:As a thin-walled member，the thickness of the outer wall and partition wall of a caisson is usually less than the thickness of its bottom slab. Hence，it is difficult to impose effective constraints on the bottom slab，which does not conform to the assumption of the four-edge consolidation slab in the current specification. Using the finite element model to simulate the actual constraint effect of the outer wall and partition wall of a caisson on the bottom slab，we analyze the internal force distribution of the bottom slab of the caisson and compare the calculation results with those of the four-edge consolidation slab. The results reveal that the mid-span bending moment calculated by the four-edge consolidation slab is about 10% smaller. When there is no cantilever toe plate，the bending moment of the support calculated by the four-edge consolidation slab is 25% larger. When there is a cantilever toe plate，that calculated by the four-edge consolidation slab is smaller，and the deviation degree is related to the scale of the cantilever toe plate. The relevant conclusions are of guiding significance for the design of caissons.

Abstract:Because a certain project in Pakistan is affected by the construction period and natural conditions，the whole unit unloading must be carried out in the specific window period when the wharf has not been completed，and the ship type used for transporting the ship unloader is far beyond the designed ship type of the wharf，so temporary mooring facilities need to be arranged. In this paper，a series of comparison and research work are carried out to analyze the mooring force of ships under the combined action of wind，wave and current by numerical simulation software，and a temporary gravity mooring scheme which can be quickly assembled and dismantled is proposed and put into practice. The engineering practice shows that the system has the advantages of high reliability，good economy and convenient construction.

Abstract:The port operation system is a complex with randomness，dynamics，lack of balance，and other complex characteristics. The emergence of multi-agent simulation modeling technology provides strong support for the simulation of the whole process of port operations，especially the research on the impact of LNG ships on navigation. Scientific and reasonable simulation results are mainly based on reliable basic data. On the basis of the Anylogic simulation modeling platform，this paper uses auxiliary means such as AIS for dynamic ship tracking and open ocean data to make the simulation more realistic. Using an engineering example，the paper carries out a multi-channelanalysis of navigation environment conditions，simulates the port operation environment，and studies the influence of LNG ships on the navigation and port service level. The results show that the simulation method is clear and easy to operate，which is helpful to the navigation impact analysis of similar projects.

Abstract:Regarding the problems of large depth and undulating terrain in the Majiang operation area of Guangxi，a plan study of the three-level platform and the second-level platform is carried out for the formation of the land area. The three-dimensional BIM excavation and filling method is adopted，and the three-level platform with the least abandonment is selected. Combined with the comprehensive comparative analysis of project construction method，construction investment，operation economy and construction feasibility，a secondary platform plan with slightly more abandonment，but with less investment and shorter construction period is finally selected. The results show that，for the land area with stepped layout，the land area elevation and road longitudinal slope should be comprehensively determined in combination with the access road，wharf platform，and land area depth. For the land formation of the river port project in the mountainous and hilly areas，it is difficult to achieve a complete balance of earth and stone excavation and filling. The plan for the formation of the land area should be as high as possible to reduce the amount of excavation and filling of earth and stone.

Abstract:Regarding the construction of the ecological channel of North Channel and South Passage planned in the Yangtze River Estuary，this paper analyzes the regional environmental characteristics and channel development needs，combs and summarizes the ecological construction of the deep-water channel in the Yangtze River Estuary，puts forward the core and construction mode of the ecological channel construction in the Yangtze River Estuary. The conclusions are as follows：1）The construction of the ecological channel of South Passage and North Channel should be based on ensuring the stability of the river regime. 2）It needs to form a linkage layout with tidal flat protection and ecological function area protection. 3）It is necessary to actively develop and apply the ecological structure，build the “artificial ecological reefs” and optimize the comprehensive environment. 4）Itis necessary to realize the resource and ecological utilization of channel dredged soil in combination with the demand of tidal flat sediment resources and the demand of channel construction for embankment sand. 5）It is necessary to strengthen the scientific management and ecological compensation system in the construction and operation，etc.

Abstract:To evaluate the navigable conditions of the Xiangjiaba ship lift，we coordinate with the shipping authorities at ministerial，provincial，and municipal levels to define the work process and organization mode for seaworthiness tests of actual ships and carry out prototype tests of “ship-ship lift-water” mutual adaptability in the dry and wet seasons. The results show that the ship lift and facilities providing navigation aids are in good condition，and the scheduling of ship security inspection and navigation routes are scientific and rational. Under flood discharge conditions，the navigable flow conditions in the downstream approach channel and the entrance area are poor，which has a great impact on navigation. Hence，we develop and apply a new method of the “unmanned aerial vehicle（UAV）+ automatic tracking float” and “three-dimensional（3D）vision” to observe flow conditions. We propose the dual-control navigable traffic standards of the outflow from the power station of 8 500 m3/s and the flood discharge of no more than 2 200 m3/s. The results provide data support for the follow-up trial operation and navigation acceptance of the ship lift.

Abstract:In recent years，affected by the Three Gorges reservoir and river regulation project，the river boundaries and water and sediment conditions in the lower reaches of the Yangtze River have changed significantly. In particular，the erosion and deposition of Laohaiba reach have changed dramatically in the year，which has an impact on river flood control，shipping and shoreline utilization. In this paper，the characteristics of riverbed evolution in Laohaiba danger section are discussed based on the topographic measured data of nearly 15 years，and the influencing factors are studied. The results show that：1）the plane variation of Laohaiba reach is small，the isobaths of -10 m and -30 m near the south bank are basically stable，and the depth range of -50 m is expanded.2）The transverse variation of river cross-section morphology is small，and the longitudinal variation is large，showing a trend of narrow and deep development.3）The implementation of the rubble-throwing revetment project of Laohaiba has changed the range of erosion and deposition of the riverbed in different isobaths，and intensified the range of erosion and deposition of the deep trough. The variation of erosion and deposition near the bank slope is relatively small，while the range of erosion and deposition of the deep trough is large. The evolution of erosion and deposition from the Jiulong Port to Shiyiwei Port is the most intense. 4）There is a negative correlation between the erosion and deposition of the deep channel below -30 m of Laohaiba section and the flow of the upstream Datong station. At the same time，affected by the geological boundary conditions of the river channel，the river bed will still be in a state of erosion for a long time under the action of the centrifugal force of the bend flow. The research results can provide reference for the study of river channel evolution and bank slope protection in the rapidly changing river regime area.

Abstract:Zhaoxian junction is located in the bend section of mountainous rivers. The upstream approach channel is in the main channel of the convex bank，and the entrance area of the downstream approach channel is on the concave bank. The entrance area and the connecting section have serious adverse hydraulic phenomena such as lateral flow velocity，backflow，and water surface boil and flow vortex，which are difficult to satisfy the requirements of navigation. This study employs the overall physical model test on a scale of 1：80 to study the main reasons for the formation of adverse flow conditions in the upstream and downstream channels. We effectively reduce the velocity of cross-flow，lateral flow，and backflow by taking comprehensive measures such as adjusting the operation mode of the junction and dredging local downstream channels and make all hydraulic indicators up to specifications. As a result，flow conditions in both the upstream and downstream approach channels and the entrance area are greatly improved，which can ensure the safety of ships passing through the lock. The research results can provide a reference for related junction projects.

Abstract:Considering the problem that different technical schemes adopted for important technical problems involved in different stages of Guangxi and domestic ship locks cause the different utilization effects of inland navigation resources，this paper uses the method of summary and analysis to study the relationship between the technical schemes selected by Guangxi’s ship locks at different stages of reform and opening up and the utilization effects of inland navigation resources from a technical point of view. Then the paper sorts out important technical problems affecting the full utilization of inland navigation resources in the early planning stage，construction stage and operation stage，and puts forward plans or views to solve important technical problems. The results show that to make full use of inland navigation resources，we must systematically solve the important technical problems of the lock in the early planning stage，construction stage and operation stage.

Abstract:In order to further expand the berthing and departure window time of 400 m container ships in Qingdao Qianwan Port area，and improve the utilization rate of berths at the wharf，this paper aims at the current demand for berthing of 400 m container ships in Qianwan Port area and high risk coefficient of the berthing and unberthing process in the restricted harbor basins. Combined with container ship mooring operation results in the harbor basins and ship maneuvering simulation test，the paper simulates the 400 m container ships in the harbor basins under different wind，current and draft conditions to carry out three typical mooring operation tests at the near-end，mid-end and far-end berths，and obtains the condom mooring conditions and ship traffic organization according to the test results. The results show that under the given condom mooring conditions and the established ship traffic organization，Qingdao Qianwan Port area can routinely carry out the mooring operation of two 400 m container ships.

Abstract:Automatic hydraulic grabbing beams are the key equipment for the opening and closing of multi-section deep-hole gates in port and waterway engineering. The conventional automatic hydraulic grabbing beams with two lifting points have no self-balancing function and require that the connection line between the two lifting points coincide with the center of gravity line of the gate. Therefore，they are not readily applicable to the opening and closing of gates with different center of gravity lines. Given the poor universality of automatic hydraulic grabbing beams with two lifting points，this paper focuses on the development of a self-balancing automatic hydraulic grabbing beam with four lifting points. The proposed automatic hydraulic grabbing beam adopts a frame structure，where four lifting points are arranged，and connects its beam body with the hoist by a connecting rod and a hydraulic cylinder. When opening and closing gates with different center of gravity lines，the grabbing beam levels incline gates through the extension and retraction of the hydraulic cylinder. The results show the proposed self-balancing automatic hydraulic grabbling beam with four lifting points can well solve the universality problem of the conventional grabbing beams，simplify the gate design and reduce the project amount and investment of the gate.

Abstract:It is important to reasonably determine the maximum burial depth for the design of the underwater tunnel project in the lower reaches of the Yangtze River. Taking the second tunnel project of Jiangyin as an example，this paper analyzes the characteristics of riverbed evolution and water and sediment movement of the project reach in recent years and determines the typical water and sediment control conditions for model tests from the point of view of engineering safety. The paper uses the physical model test to predict the maximum scouring depth of the riverbed near the second tunnel project of Jiangyin and compare the results with those calculated by the mathematical model. The results indicate that the research results of the physical model and mathematical model are consistent. Under different hydrological conditions，the riverbed is generally scoured. The maximum scour of the secondary channel of Jiangyin on the left side occurs on the right side of the deep channel，and the maximum scour of the main channel on the right side occurs on the left side of the deep channel.

Abstract:Although the long section from the Xingan junction to Longtoushan junction on the Ganjiang River is Longtoushan junction reservoir section，there are still many navigable safety problems，such as insufficient water depth in local area，obstruction of navigation by pre-regulated buildings and poor navigable bridge area. Considering the above problems，we put forward some regulation schemes，such as channel dredging，groin removal and route adjustment，and uses two-dimensional flow mathematical model of long river to conduct experimental research on the regulation scheme of Ⅱ level channel of the river reach. The results show that after the implementation of the regulation scheme，the navigable flow condition of the channel is improved and the channel scale can reach the construction standard. Specifically，the water depth within the designed channel line can meet the minimum navigable water depth of 3.8 m，the cross-current in the channel decreases，the bad flow state disappears，and the route is more straight.

Abstract:In view of the poor joint quality and low strength of the pressurized water seal for the working gate of the lower lock head of the Three Gorges ship lift，we need to reduce the impact of the pressurized water seal on the overall service performance of the working gate of the lower lock head. Hence，this paper optimizes the molding method of the pressurized water seal joint by comprehensively considering the transportation and on-spot installation conditions of the pressurized water seal. As a result，we propose a new joint molding method of rubber water seal with “mold feeding by sections and forming as a whole.” Specifically，we adopt two different molding methods to make samples of the pressurized water seal joint，measure the porosity of the samples，and test their tensile properties and abrasion resistance. The results reveal that the molding method of “mold feeding by sections and forming as a whole” could prolong the service life of the pressurized water seal by substantially improving its quality and strength，with little impact on its hardness and other mechanical and physical properties.

Abstract:During the expansion of a second-line ship lock，constraints such as the terrain，construction，navigation，land acquisition and demolition，and investment should be comprehensively considered. Taking the Xiangqi second-line ship lock project as an example，this paper focuses on the design principles，site selection，and layout ideas and methods of the second-line ship lock and comparatively selects a layout scheme：It should be on the left bank of the first-line ship lock，and the distance between the axes of the two locks is 80 m，with the ship going straight in and curving out. We use the physical model test to analyze and optimize the navigable flow conditions of the entrance area and put forward the measures to improve the navigable flow conditions，such as extending the upstream and downstream partition walls，dredging the downstream riverbed of the power station，and optimizing the dispatching mode. Moreover，we propose the innovation and optimal design concept with strong universality for the floating access gates，breasting dolphins，and partition walls.

Abstract:After the operation of the Three Gorges Reservoir，the unbalanced erosion and deposition occurred in the bifurcation reaches of the middle and lower reaches of the Yangtze River，and the bifurcation relationship was significantly adjusted，resulting in the difference of navigation-obstruction characteristics of the corresponding shoals. Based on the research of braided reach riverbed evolution and the navigation obstruction characteristics of the shoals in the middle and lower reaches of the Yangtze River，this paper discusses the channel management ideas of the braided reach. The main conclusions are as follows：1）The shallow reach of the braided river in middle and lower Yangtze River has occurred further scour depth after the impounding and operation of Three Gorges project，associating with the shrinks of bottomland and the adjustments in the characteristics of channels. 2）The flood diversion ratio of the main stream in the branching section decreases，the flood diversion ratio falling ranges is less than low water for the bending and straight braided river，but the flood diversion ratio falling range is less than low water for the goose head shape braided river.3）The controlled intensity of the navigation main braided channel on distributaries tends to decline after Three Gorges Reservoir impoundment，the inlets of the navigation main braided channel often staggered or scattered bad shoals form，such as channel conditions deterioration，shallow shoal hinders navigation. 4）To maintain or improve the channel scale，the branch reach can be controlled step by step，and the regulation measures such as beach control and guidance，edge and center beach shaping or branch control technology can be implemented.

Abstract:The C-shaped sealing plate in the butt sealing device of the Three Gorges ship lift is prone to fractures，and its sealing maintenance is inconvenient. Hence，this study builds the mechanical models of the C-shaped sealing plate and connecting bolts in different operating conditions. The analysis of the bolt strength check shows that the tensile stress on the connecting bolts of the C-shaped sealing plate is greater than the tensile stress limit of the material in the process of discharging interstitial water. According to the analysis results and the structural characteristics of the field equipment，we design the reinforcement tooling of the C-shaped sealing plate，and the installation and application verify that the stress on the bolt can meet the design requirements. Meanwhile，we design a C-shaped sealing maintenance platform to satisfy the requirements of rapid maintenance and replacement，which solves practical engineering problems.

Abstract:Regarding the problem of excessive deformation of double steel sheet-pile in soft soil stratum，we take a foundation pit of a shipyard as an example，study the deformation characteristics of double steel sheet-pile in soft soil stratum by means of field test data analysis，theoretical calculation and numerical simulation，and analyze the causes of excessive deformation. By means of the identification of limit state and the inversion of critical state parameters，we put forward the emergency treatment method of backfill back pressure according to the field data and reinforcement measures of double-row cast-in-place piles with large row spacing. The results show that the proposed emergency treatment method and reinforcement measures achieve good results.Double steel sheet-pile cofferdam is often deformed greatly in soft soil foundation pit，and it will be deformed rapidly when it enters critical state. Effective reinforcement measures should be taken to avoid overbreak.

Abstract:Regarding the influence of the arrangement of gravel pile composite foundation on the whole stability of bank slope，numerical modeling analysis and field test are carried out. Using the method of Geostudio finite element software combined with the slope engineering example of a gravel pile composite foundation for simulation calculation，the influence of different gravel pile spacing，driving range and periodic tidal level changes on the stability of the bank slope is analyzed. Meanwhile，the comparative monitoring of the test section of adding gravel pile at the sea front is carried out. The results show that the variation of gravel pile spacing has little influence on the stability of bank slope，the floating range of safety coefficient on the sea side is larger than that on the land side under periodic tidal level variation，and increasing the range of gravel pile in front of bank slope is conducive to the overall stability of bank protection. Under the condition of not changing the pile diameter and pile spacing，widening the scope of gravel pile on the front of the seaside bank slope can enhance the overall shear strength ratio of composite foundation in the sliding surface，and achieve the effect of improving the stability of the bank slope.

Abstract:The blocking process of the geotextile tube in the closure gaps is obviously affected by hydraulic force，and the geotextile tube is prone to slip and instability，which leads to the failure of the blocking of the junctions，resulting in increased construction costs and delays in the construction period. To reduce the risk of the failure，based on the theoretical analysis，this paper uses the FLOW 3D and FLAC 3D numerical simulation software to analyze the stability of the weir top geotextile tube，and compares it with the actual project. The results show that：1）The hydrostatic pressure and the horizontal thrust of the water flow generated by the overflow at the top of the weir are the main factors for the slip failure of the top geotextile tube. 2）The sliding critical head is positively related to the width of top bag，the equivalent friction coefficient between bags and the weight of bag filling. 3）The calculation results of the prediction formula are more consistent with the actual engineering，and have certain engineering reference value.

Abstract:The dredging project of Yancheng Binhai port area has complex working conditions and uneven soil stratification，the upper silt has the characteristics of small particle size，dense and hard，the power of cutter fluctuates obviously during ship construction. The density of subclay soil in the lower layer is high，and the long row distance of 14 km is easy to cause pipe blocking. There are many blocks and obstacles in the construction area，and the suction and pump blockage often occur. For the newly-built ship “HAO HAI LONG”，the applicability of different cutter stone prevention schemes is analyzed by replacing the cutter to find the balance point between mud concentration，flow rate and construction efficiency，and the ship machine performance is tested. The results show that when excavating dense silt，the use of general cutter can increase the soil breaking capacity and reduce the fluctuation amplitude and frequency of cutter power. The installation of steel grating at the suction port can effectively reduce the blockage of suction and pump. When excavating the lower layer，the balance between productivity and transportation efficiency can be achieved by properly reducing the mud concentration.

Abstract:Relying on the ship lock cofferdam with a large head difference in Wan’an，Jiangxi Province，this study adjusts the water-binder ratio，the bentonite content，and other parameters of the plastic concrete mix used in the cutoff wall according to water resources and hydropower engineering standards. The paper determines the optimal plastic concrete mix ratio（the water-binder ratio is 0.80，and the bentonite content is 25%）with high ultimate strain，low compressive strength，a low elastic modulus，and a low permeability coefficient for cofferdam with a large head difference，then tests the plastic concrete by the field water injection test and the high-density electrical method. The results show that the plastic concrete cutoff wall has excellent impermeability，good section continuity，and good overall integrity. During the service period of the cofferdam，the strain monitoring results in the plastic concrete cutoff wall indicate that the plastic concrete is in a safe compressive state，and the cutoff effect of the wall is good.

Abstract:This paper takes the large geotechnical sand bag as the research object，and builds the mathematical equation based on the force analysis. The paper discusses the influence of friction coefficient of sand bag and lateral pressure coefficient of the filling on the deformation of large geotechnical sand bag，then analyzes mechanism of the two factors，and verifies the results with the design and selection of sand bag in an actual project. The results show that the tension of the bag increases and bulges continuously with the increase of friction coefficient. The tension of the bag increases with lateral pressure coefficient changes but the shape is nearly stable. The friction coefficient of sand bag has more obvious effect than lateral pressure coefficient of filling. The built mathematical model is basically reliable，and has excellent practical value.