Study on strength properties and soil behaviour type classification of Huanghe River Delta silts based on variable rate piezocone penetration test

Fine-grained silt is widely distributed in the Huanghe River Delta(HRD)in China,and the sedimentary structure is complex,meaning that the clay content in the silt is variable.The piezocone penetration test(CPTu)is the most widely approved in situ test method.It can be used to invert soil properties and interpret soil behavior.To analyse the strength properties of surface sediments in the HRD,this paper evaluated the friction angle and its inversion formula through the CPTu penetration test and monotonic simple shear test and other soil unit experiments.The evaluation showed that the empirical formula proposed by Kulhawy and Mayne had better prediction and inversion effect.The HRD silts with clay contents of 9.2%,21.4%and 30.3%were selected as samples for the CPTu variable rate penetration test.The results show as follows.(1)The effects of the clay content on the tip resistance and the pore pressure of silt under different penetration rates were summarized.The tip resistance Q_t is strongly dependent on the clay content of the silt,the B_(q)value of the silt tends to 0 and is not significantly affected by the change of the CPTu penetration rate.(2)Five soil behavior type classification charts and three soil behavior type indexes based on CPTu data were evaluated.The results show that the soil behavior type classification chart based on soil behavior type index ISBT,the Robertson 2010 behavior type classification chart are more suitable for the silty soil in the HRD.

Spatial differentiation and dynamic mechanism of micro-geomorphology based on acoustic spectrum data of the Huanghe(Yellow)River Delta

Submarine micro-geomorphology is a geo-morphological type occurring in shallow and surface areas of seabed.The combined relationships and distribution of the micro-geomorphology indirectly reflect coupling relationships among the sediment deposition,dynamic environment,and geomorphologic evolution.Spatial differentiation and dynamic changes in micro-geomorphology were studied based on acoustic data interpretation from a wide range(3200 km^(2))of the Huanghe(Yellow)River delta(HRD).The combination of the sub-bottom profiler and the side-scan sonar methods allowed for the identification of submarine shallow micro-geomorphologic types,as well as their scale and spatial distributions.There were seven typical micro-geomorphologic features in the shallow and surface areas of the HRD,including buried ancient channels,stratigraphic disturbances,scour troughs,sand waves,pits,erosional remnants,and sand spots.The coupling and superposition of the sediment,sediment characteristics,seabed scouring and silting,and hydrodynamic conditions of the Huanghe River had combined effects on the patterns of micro-geomorphologic types,characteristics,and ranges.From the perspective of acoustic profile interpretations,the scale,range,and spatial locations of the microgeomorphology in the HRD revealed seasonal variation characteristics,and the spatial distributions displayed significant regional differentiation characteristics.In addition,strong stratigraphic disturbances and areas with densely distributed buried ancient channels reflected the activity and instability of the submarine shallow strata.Through the interpretation of the sub-bottom profile detection data,the diversion processes of the flow paths in the lower reaches of the Huanghe River were obtained for a certain historical period in the coastal waters of the HRD.This study further clarified the relationships between the micro-geomorphologic features and spatial combinations,which is important for research on micro-geomorphologic features and their dynamic mechanisms.

Modeling of suspended sediment transport with wave-induced longshore current in Huanghe (Yellow) River Delta

A three-dimensional suspended sediment model （SED） developed by the present authors is coupled with the combinatorial model of COHERENS （Luyten et al., 1999） （the three-dimensional coupled hydrodynamical-ecological model for Regional and Shelf Seas） and SWAN （Holthuijsen et al., 2004） （the third generation wave model）. SWAN is regarded as a subroutine of COHERENS and gets time- and space-varying current velocity and surface elevation from COHERENS. COHERENS gets time- and space- varying wave relevant parameters provided by SWAN. Effects of wave on current are applied in bottom shear stress, wave-induced depth-dependent radiation stress and surface drag coefficient calculation. At the same time, the damping function of suspended sediment on turbulence is introduced into COHERENS. So the sediment model SED has feedback on circulation model COHERENS. The SED obtains current associated parameters from COHERENS. Then a coupled hydrodynamic-sediment model COHERENS-SED being able to account for interaction between wave and current is obtained. COHERENS-SED is adopted to simulate three-dimensional suspended sediment transport in the Huanghe River delta. In terms of simulation results, there is obvious difference between top and bottom layer of wave-induced longshore current. The values of time series of sediment concentration gotten by COHERENS-SED have, generally, an accepted agreement extent with measurement. Significant wave heights and wave periods obtained by COHERENS-SED show that wave simulation case with currentts effect can give better agreement extent with measurement than case without current＇s effect. In the meantime, suspended sediment concentration distributing rule obtained by COHERENS-SED is similar to former researches and measurement.

Evolution history and trend of the modern Huanghe River Delta

The evolvement history of modern Huanghe River Delta tidal flat, coastline and underwater terrain were studied based on the analysis of remote sensing images and water depth data. Based on the analysis of seafloor terrain evolution on different historical stages, a formula simulating the erosion and deposition evolvement model of subaqueous Huanghe River Delta slope was proposed, and the evolvement trend of the subaqueous delta terrain was predicted. The result shows that the equilibrium transition zone is near the water depth of 12 m with seabed erosion in shallower water and accumulation in deeper water during the first 150 a after the river channel was deserted. In the meantime, the underwater slope became gentler and the coastal erosion rate became slow gradually. Then, the subaqueous delta slope changed to up concave from upper convex, and the shape of subaqueous delta disappeared. The coast type changed to silt-mud coast about 100-150 a after the river course was deserted. The erosion depth in the foot of the seawall is calculated based on the formula.

Paleo-environmental evolution based on high-resolution phytolith since 26 ka B. P. in Huanghe River Delta

The Huanghe River Delta is one of the world＇s large rivers, the Huanghe River Delta paleoenvironmental evolution in the Huanghe River has been a hot issue since the Last Glacial. Based on the core time series established by combining AMS 14C dating of Core DYZK1 sediments in submerged of Huanghe River Delta and acoustic sequence on sub-bottom profile, phytolith analyses are carried out on 96 sediment samples. The grain size parameters, magnetic susceptibility are combined with the vertical changes of biostratum to reconstruct the paleo-sedimentary and climatic conditions in the Huanghe River Delta. The study results show that there is a significant vertical change law in the index parameters, and that sedimentary environment of Huanghe River Delta experienced an evolutionary process of fluvial facies-sealand transition facies-tidal flat facies-neritic facies- delta facies since 26.0 ka B. P.. The phytolith analyses results are as following. Firstly, The phytoliths are divided into lanceolate, smooth-elongated, spiny-elongated, rondel, long rectangular, bulliform and other types. In different sedimental environment, the phytolith content changes regularly, indicating that the phytolith assembles in the same sedimentary environment has a certain degree of stability. Secondly, The lanceolate, smooth-elongated and spiny-elongated categories of phytoliths have greater contents in the tidal flat facies and delta deposition, while have a smaller contents in the neritic facies and fluvial facies environment. Thirdly, Through comparative analysis of variation coefficient, the content of major phytolith categories in the sediment has a greater change amplitude in the sealand transition facies and fluvial facies deposition, while being more stable in the tidalflat facies and delta facies deposition.

The sedimentary facies and dynamic environment of the Diaokou lobe in the modern Huanghe River Delta of China

The Huanghe River captures the Diaokou River in 1964 and forms a deltaic lobe in the subsequent 12 a. The progradational process of the Diaokou lobe is in associated with complicated evolution of riverine sheet flooding, merging, and swinging. On the basis of 11 borehole cores and 210 km high resolution seismic reflection data set, the sedimentary sequence and dynamic environment of the Diaokou lobe Cone subdelta lobe of the modern Huanghe River Delta） are studied. The stratigraphy of the lobe is characterized by an upward-coarsening ternary structure and forms a progradational deltaic clinoform. Totally six seismic surfaces are identifiable in seismic profiles, bounded six seismic units （SUs）. These SUs correspond to six depositional units （DUs） in the borehole cores, and among them, SUs 4-6 （DUs D to F） consist of the modern Diaokou lobe. Lithological and seismic evidences indicate that the delta plain part of the Diaokou lobe is comprised primarily by fluvial lag sediments together with sediments from sidebanks, overbanks, fluvial flood plains and levees, while the delta front part is a combination of river mouth bar sands （majority） and distal bar and deltaic margin sediments （minority）. As a result of the high sedimentation rate and weak hydrodynamic regime in the Huanghe River Delta, the sediments in the delta front are dominated by fine-grained materials. The grain size analysis indicates the Huanghe River hyperpycnal-concentrated flow shows the suspension, transportation and sedimentation characteristics of gravity flow, and the sediment transportation is primarily dominated by graded suspension, while uniform suspension and hydrostatic suspension are also observed in places. The strength of the hydrodynamic regime weakens gradually offshore from riverbed, river mouth bar, sidebank, distal bar subfacies to delta lateral margin and flooding plain subfacies.

Deposits and depositional sequence nearby Iluanghe Harbour in the Huanghe River Delta

The sedimentary sequence of the upper 4 m deposits in the Huanghe Harbour Pit is as follows, 1, Distributary mouth bar deposits formed before 1964; 2. lower delta plain (tidal flat) and subaqueous delta lateral deposits formed in the period of 1964-1972; 3. deposits of crevasse splay and distributary channel near mouth, formed in the period of 1972-1974; 4. tidal flat deposits formed in the period of 1975-1984. The sequence shows superimposition of sedimentary environments parallel to coastline.

CPT-Based estimation of undrained shear strength of fine-grained soils in the Huanghe River Delta

The Huanghe River(Yellow River)Delta has a wide distribution of fine-grained soils.Fluvial alluviation,erosion,and wave loads affect the shoal area,resulting complex physical and mechanical properties to sensitive finegrained soil located at the river-sea boundary.The cone penetration test(CPT)is a convenient and effective in situ testing method which can accurately identify various soil parameters.Studies on undrained shear strength only roughly determine the fine content(FC)without making the FC effect clear.We studied four stations formed in different the Huanghe River Delta periods.We conducted in situ CPT and corresponding laboratory tests,examined the fine content influence on undrained shear strength(S_(u)),and determined the cone coefficient(N_(k)).The conclusions are as follows.(1)The fine content in the area exceeded 90%,and the silt content was high,accounting for more than 70%of all fine particle compositions.(2)The undrained shear strength gradually increased with depth with a maximum of approximately 250 kPa.When the silt content was lower than 60%–70%,the undrained shear strength decreased.(3)The silt and clay content influenced undrained shear strength,and the fitted f_(s)h/q_(t) function model was established,which could be applied to strata with a high fine content.The cone coefficients were between 20 and 25,and the overconsolidated soil layer had a greater cone coefficient.

The magnetic properties of sediment and sedimentary environment in the Huanghe Delta area after the last glacial maximum

On the basis of measuring the magnetic parameters of sediment in Core YDZ1, combined with a grain size analysis and Carbon-14 dating, the magnetic properties of sediment and sedimentary environment in the Huanghe（Yellow River） Delta area after the last glacial maximum have been studied. The results show that the ferrimagnetic minerals of a pseudo single domain and multi domain particles dominate the magnetic properties of sediment in Core YDZ1. The imperfect anti ferrimagnetic minerals have more contribution on sediment in a depth of 24.0–22.1 m, and more stable-single domain and pseudo single domain particles exist. The susceptibility of anhysteretic remanent magnetization and the ratio of the susceptibility of anhysteretic remanent magnetization to saturation isothermal remanent magnetization show a decrease trend below depth of 24 m, a marked increase trend in a depth of 24.0–13.5 m, and a rapid decrease at depth of 13.5 m, then a fluctuation trend upward. The above two magnetic parameters and the ratio of the susceptibility of anhysteretic remanent magnetization to the mass susceptibility can be regarded as the proxy indicators for the content of clay（〈4 μm）and the fine-grained size（〈32 μm）. The sedimentary environment after the last glacial maximum in the Huanghe Delta area has experienced the fluvial facies, the tidal flat facies, the neritic facies, the pro delta facies, the delta front facies and the floodplain facies. Thickness of the Holocene transgression layer is 10.5 m and the depth of substrate is about 24 m according to the YDZ1 core. The sedimentary dynamic has a variation trend with strongweak-strong, which has been proved by the Flemming triangular schema.

Examining the evolution of tidal creeks in the Huanghe River delta using multi-temporal Landsat images

Coastal tidal creeks are important channels for exchanges of material and energy between sea and land,and play an important role in the ecological protection of tidal flats.Although tidal creeks have evolved differently in various regions,the evolutionary process of tidal creeks in the Huanghe(Yellow)River delta of China,one of the most active deltas worldwide,is not entirely clear.Therefore,the evolution of tidal creeks in the delta from 1981 to 2021 was investigated by quantitatively analysing the tidal creeks and developing a standard for dividing their evolution periods.Visual interpretation and supervised classification methods were applied to the Landsat images to extract the tidal creek network,and 17 groups of tidal creek systems were selected.Results indicate that Creek S 1 was the most developed creek for having 113 tidal creeks totaling 65.8 km in length,while Creek E 3 had the fastest growth rate for having average annual increase of 1.9 km.Meanwhile,the level of tidal creeks increased,the average and median lengths of tidal creeks increased,and the number of tidal creeks decreased since 1981.The evolution of the tidal creek system could be divided into four stages,namely,rising,developing,stabilizing,and degrading.Analyses of a representative tidal creek show that there was no degenerated tidal creek during the rising period,with an increase in the number of 50 and a length increase of 57.9 km between 1981 and 1989.The proportion of new tidal creeks in the developing period was more than 50%and the new tidal creeks in the stabilizing period were equal to the degraded tidal creeks.Extinct tidal creeks were greater than 50%during the degrading period.There was no fixed order of tidal creek evolution in each period,and there may be a skip in evolution.Our findings provided a reference for studying the evolution of tidal creeks.