Master of Science

Topics in geology, which inevitably excite professional discussion and even tempered debate, often present challenging targets for the exploratory jabs of Master's degree candidates. The Portland Hills Silt and the controversy concerning its genesis provides just such an object. Although the physical descriptions of the silt are generally in agreement, they remain somewhat generalized and, at present, no single definition is generally accepted. Moreover, incongruities concerning structural and textural details--notably, the presence of minor stratification and/or scattered pebbles in the silt--have resulted in considerable disagreement regarding its mode of origin.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN / Bibliography: leaves 130-131. / by Robert Anthony Grazer. / M.S.

Yes / When ocean waves propagate over porous seabed, they cause variations of the pore pressure within seabed, leading to the possible wave attenuation and soil liquefaction. In order to advance and improve our understanding of the process of wave-induced seabed liquefaction and its impact on wave propagation, systematical experiments are carried out in a wave flume with a soil basin filled with silt. Both the pore pressures and water surface elevations are measured simultaneously, while the seabed liquefaction is videotaped using a high-speed camera. Laboratory measurements show that the pore pressure in surface layer mainly oscillates over time, while the wave period averaged pore pressure has little change. In the deep layer, however, the wave period averaged value of the pore pressure builds up dramatically. The results show that the wave height decreases rapidly along the direction of wave propagation when seabed liquefaction occurs. Such a wave attenuation is greatly enhanced when the liquefaction depth further increases. The experiments also demonstrate that the conditions (wave height and wave period) of incident waves have significant impacts on the wave-induced pore pressures, liquefaction depth and wave attenuation in a silt bed. / National Natural Science Foundation of China (Grant No. 51479053), the 111 Project (Grant No. B12032), the marine renewable energy research project of State Oceanic Administration (GHME2015GC01), the Fundamental Research Funds for the Central University, China (Grant No. 2013B31614), the Colleges and Universities in Jiangsu Province Plans to Graduate Research and Innovation (Grant No. B1504708), and Open Foundation of State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University (Grant No: 2016491011).

Accumulations of fine sediments in deep-ocean contourites form a sedimentary record that has been hypothesized to be directly related to bottom-current behavior. This is known as the 'sortable silt' hypothesis and states that the non-cohesive, coarse silt in the 10 to 63 µm size range within a deposit can be used as a proxy for paleocurrent velocity. Slow deposition rates on contourites (2−10 cm/kyr) make it difficult to test this hypothesis in the field and few laboratory studies have been conducted. To test the 'sortable silt' hypothesis in the laboratory, a non-recirculating flume was constructed in which silt and clay could be deposited under a variety of velocities, sediment concentrations, and silt to clay ratios. Samples of the deposited material from each experiment were analyzed to determine the grain-size distribution using a Micromeritics Sedigraph 5120 particle size analyzer. The results of these experiments were used to evaluate the following two hypotheses: 1. The proportion of sortable silt (SS%) compared to the proportion of clay is a better indicator of current velocity than the mean size of the sortable silt (SS). 2. The presence of clay will impact the movement and sorting of silt in the bed. Results show that increased velocity correlates with increased (SS), and that (SS) generally decreases downstream of the sediment source. (SS) was found to be more representative of velocity than (SS%) and, counter to the original hypothesis, clay did not have a significant effect on silt deposition. / Master of Science / The ’sortable silt’ hypothesis states that there is a relationship between the velocity of an ocean current and the size of the sediment that deposits on the bottom of the ocean. These deep-ocean deposits consist of material smaller than sand such as clay and silt. Smaller particles require less force than larger particles to remain suspended, and higher current velocities produce larger forces. For this reason larger current velocities are thought to be associated with the deposition of coarser sediments. It is challenging to test this hypothesis in the field because of the cost and the slow rates at which change occurs. Laboratory studies can help to overcome these challenged by test scenarios otherwise impossible in the field. For this research, a flume was constructed and used to examine how different sediment types sort under flowing water. Most laboratory flumes recirculate water using pumps, but this flume does not. A mixture of dry material and water flows through the flume, depositing a bed over time. This deposited material can then be tested for its size parameters. These size parameters are compared to the material type and the velocity of the current in the flume to help answer two main questions: 1. Is the amount of silt in a sample a better indication of the current velocity than the average size of the material deposited? 2. Will the addition of clay will change the way silt deposits in the system?. Results show that silt does sort with increasing velocity and that the mean sortable silt size is good indicator of current velocity.

An investigation of the amount of exchangeable potassium found in the surface and subsoils of a 33-year rotation experiment at Blacksburg, Virginia, was made. The rotation is located on Dunmore silt loam, Which is rated as a relatively fertile soil in Virginia. There are indications that sheet erosion has removed considerable amounts of the surface soil from the steeper slopes of the first nine treatments, and it is evident that an accumulation of this material has occurred on the four lower plots. It is believed by the writer, and others familiar with these plots, that.this erosion occurred prior to the beginning of the rotation in 1909. Composite soil samples were taken from each of the 8 treatments in each of the 4 series of this rotation and resulted in a total of thirty-two fertilized subplot samples, and a corresponding thirty-two unfertilized subplot samples were collected and analyzed for exchangeable potassium. Similar analyses were ma.de on the thirty-two subsoils of both the fertilized and the unfertilized treatments. The resulting data from the surface and subsoils were then statistically analyzed and the following conclusion drawn: 1. The applications of both muriate of potash and manure significantly increased the amount of exchangeable potassium found in both the surface and subsoils. 2. The surface soils are significantly higher in exchangeable potassium than the subsoils. 3. Exchangeable potassium may be leached from the surface horizon to the subsoil when applied in a complete fertilizer in excess of plant needs. 4. Manure applications which contained considerably less potassium than the potassium added to the soils in the muriate applications, resulted in larger amounts of exchangeable potassium in the surface soils, a 30 per cent increase in crop yields, and significantly less exchangeable potassium leached to the subsoils. 5. The difference in exchangeable potassium between the fertilized subplots receiving muriate of potash. and the unfertilized subplots. resulted in an increase in the amount of potassium found in the surface soils which was equivalent to 996 pounds of 50 per cent potash fertilizer, and this figure would represent an amount equivalent to 15 per cent of the total muriate added to the surface soils. 6. The difference in exchangeable potassium found in the subsoil between the fertilized and unfertilized plots represents an equivalent of approximately 9 per cent of the total potash added. 7. Significantly larger amounts of exchangeable potassium were leached to the subsoil from plots, receiving muriate of potash than soils which received manurial treatments. Greater utilization of the applied potassium is indicated by the manurial applications. 8. A chemical analysis should be made of the manure which is applied to this experiment in order to obtain a more comprehensive understanding of the yields, and physical and chemical properties of these soils. / M.S.

An extensive literature review and experimental study were performed to investigate whether cavitation and dissolved gases exiting solution from soil pore water are the cause of the erratic undrained behavior often observed in triaxial tests on saturated, dilatant silts. The literature indicates that ground water contains various amounts of dissolved gases and that gases dissolved in soil pore water will have sufficient time to exit solution to some extent, due to the pore pressure reductions which occur during sampling and unconsolidated-undrained triaxial tests. The exit of dissolved gases from solution would increase the soil volume and affect its undrained behavior. Experiments were performed on saturated silts to measure the pore pressure reductions which occur during sampling and unconsolidated-undrained triaxial tests. The amount of dissolved air that could come out of solution and the desaturation that a saturated soil sample could experience were also estimated. Gas bubble formation and growth within the pores of a saturated silt could affect intergranular forces and influence the stress-strain behavior of the soil in undrained tests. Variations in the amount of dissolved gas exiting solution and forming bubbles from one specimen to another could be the cause of the erratic undrained behavior often observed for saturated silts. Bubble growth within the soil pores is believed to have lead to abrupt strain-softening in a number of the undrained tests performed in this research. Variations in specimen disturbance may also contribute to the erratic behavior observed in undrained tests on silts. Disturbance levels and their influence on soil behavior are difficult to quantify. Due to the unusual properties of water under negative pressure, the initial value of pore water pressure within the soil appears to have a direct influence on the undrained strength of the soil. As a result, laboratory pore water pressures should be similar to in-situ pore water pressures, in order to give reasonable undrained strength measurements. The findings of this research are believed to be worthy of further study. / Ph. D.

Slope processes are important to understand if we are to protect fragile environments. Every year slope development in weak soils put nearby infrastructure in risk zones of sliding and ravine erosion takes away field areal from farmers as they grow even larger. Many methods for doing a risk analysis of a slope and its soil are complicated and require a lot of equipment. A simple way to do a slope investigation is explained in this report, along with its advantages and disadvantages. The authors construct a shear ring, an apparatus to measure peak shear stress of soils before fracturing. LIDAR scanning of two small ravines are also made to illustrate how laser scanning can be used to accurately measure denudation in slopes. The results vary, the shear ring is mostly a success aside from errors caused by difficulty in taking representative samples and disturbance. Some of the laboratory work made to determine material properties fail at giving good results, often a result of bad samples or disturbance in the tests. The LIDAR is determined to be a good instrument when working with slope development. / Sluttningsprocesser är viktiga att förstå och studera om vi ska kunna skydda känsliga områden. Varje år så sätter svaga jordar i sluttningar närliggande infrastruktur i riskzonen för att ligga på ett glidplan som snabbt kan släppa om jorden blir för blöt eller om för mycket tyngd läggs ovanpå. Samtidigt så tar ravinerosion bort åkerareal från bönder varje år medan ravinerna blir större och större. Många metoder för att göra riskanalyser av sluttningar är komplicerade och kräver mycket utrustning. I denna rapport så testas ett enkelt sätt att göra en sluttningsanalys med tillhörande diskussion kring dess fördelar och nackdelar. Författarna konstruerar en shear ring, en apparat som används för att testa jordens möjlighet att motstå en applicerad kraft. Två sidoraviner scannas även med LIDAR som en bas för att studera denudation i sluttningar. Resultaten varierar, shear ring-apparaturen bestäms som väl fungerande med undantag från vissa utförda tester, där svårigheter uppstod då jordproverna var störda eller mindre representativa. Vissa av laborationerna på jorden misslyckas med att ge bra värden, vilket ofta är ett resultat av dåliga eller störda prover. Laserscanningar av raviner med LIDAR bestäms som ett bra sätt att studera utvecklingen i sluttningar samt att mäta erosion.

Thesis. 1977. Sc.D.--Massachusetts Institute of Technology. Dept. of Civil Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Vita. / Bibliography: leaves 381-386. / Sc.D.

The overall objective is to improve the one-dimensional numerical prediction of the fine and non-cohesive bed material load in alluvial rivers, especially during high intensity episodes during which sediment beds are strongly remobilized. For this reason, we attempt to reduce the major inaccuracy sources coming from the alluvial resistance and bed material load relations needed to close the mathematical system. Through a shared parameter called the control factor m, the interactions occurring in alluvial rivers are incorporated more deeply into the mathematical model and more particularly into the closure laws: bed material load (SVRD, Suction-Vortex Resuspension Dynamics) and the energy slope (Verbanck et al. 2007). The control factor m is assumedly related to the Rossiter resonance modes of the separated flow downstream the bed form crest. To further improve the representation of the flow-sediment-morphology interactions, a fully coupled model approach has been naturally chosen. In this work the terminology fully coupled means that the three equations forming the system are solved synchronously and that the terms often neglected by more traditional decoupled models are kept. The feasibility of the new closure methodology has been drawn up by reproducing numerically the silt-flushing experiment conducted by the Yellow River Conservancy Commission (Y.R.C.C.) in the Lower Yellow River (LYR) in Northern China. The objective of the silt flushing experiment is to reverse the aggradation trend of the Lower Yellow River which, in the last decades, has become a perched river. The numerical simulation specifically reproduces the silt-flush effects in a reach of LYR located in the meandering part of the river. This reach (around 100 km) is delimited by Aishan and Luokou hydrometric stations. Since the SVRD formulation has been developed from flume observations, the law has first been confronted to river datasets. The confrontation has revealed that the SVRD law becomes less suitable for fine sediment fluxes (ratio of water depth over median particle size > 5000). Therefore, a modified equation SVRD-2 has been built to enlarge the validity range. The suitability of the SVRD-2 equation to predict fine sediment fluxes has been tested on data available from several hydrometric stations located in the meandering reach of the LYR: historical observations and measures collected during the flushes. The SVRD-2 has also been compared with relations specifically calibrated for this configuration. The comparison has pointed out that the performance of the two formulas is similar, which is encouraging for the SVRD-2 approach as it has not been calibrated on those data. The closed equation system has been written on its quasi-linear form and is solved by a Finite Volume Method combined with a linearized Riemann algorithm. The numerical model has been checked up on two test cases: deposition upstream of a dam and the aggradation experiment conducted by Soni 1975. As it is not yet possible to predict dynamically the value of the control factor m, a possible solution would be to extract its value from the measured data at the inlet cross section. Unfortunately, the necessary data are not measured locally. Moreover, a uniform value of the control factor m may not suffice to reproduce the flow along the whole reach. Therefore, it has been proposed to work temporarily in the reverse way. From the comparison between the numerical results and the experimental data, a time evolution of the control factor m has effectively been extracted and it has been shown that it varies along the reach. At Aishan, the evolution of the control factor m corresponds to the evolution expected from the data analysis previously conducted on other data sets: the value of the control factor m decreases during the flush as it tries to reach the optimal value m=1. The time evolution at Luokou behaves differently to the one at Aishan, but remains in agreement with m evolution patterns observed historically for the river section flowing round Jinan City walls. For Luokou, the highlighted differences may come from three dimensional effects coming from the meander bend upstream the station. Generally, the results obtained for the hydraulics, the sediment transport and bed adaptation are encouraging but still need improvements and additional feeding from the experimental data. The results for the concentration and therefore the bed elevation are very sensitive to the value of the control factor m as it influences most of the terms of the bed material load equation (SVRD-2). The major remaining difficulties are, firstly, to deal with the rapid transients for which the model is less suitable and, secondly, to improve the prediction of the value of control factor m. Before paying more attention into the transients, enhancements concerning the flow along the reach (initial condition and discharge rates during the first days of the flush) must be conducted in priority. Indeed as the prediction of the bed or the cross section evolutions depend directly on the quality of the prediction of the sediment concentration and the hydraulics, one should first improve these aspects. To perform this study, more information about the water levels or sediment concentrations is necessary at some intermediate stations. One solution is to lengthen the studied reach, upstream to Sunkou and downstream to Lijin, totaling a river length of 456 Km. A more entire signal of the energy slopes and the associated bed configurations at different stations would enlighten how the control factor m evolves along the reach during the silt-flush events.