Bay Mud Research Articles

Self-Boring Pressuremeter Study of San Francisco Bay Mud

In the early 1970's a self-boring capability was added to the pressuremeter by workers in England and France in order to reduce disturbance effects during the insertion of the pressuremeter in the ground. However, during the intervening years since the introduction of the probe, the results obtained using it have been largely at odds with those determined in high quality laboratory tests. In this investigation, self-boring pressuremeter tests were performed at two sites in San Francisco Bay Mud. It was found that the details of the drilling and flushing procedures used during probe advance were very important to the quality of the results obtained. Working out the proper techniques by trial, soil parameters were obtained for San Francisco Bay Mud which were in good agreement with those from high quality consolidated undrained laboratory tests. Also pressuremeter tests performed at the site of a slurry wall supported excavation were successful in picking up the stress changes induced by the excavation.

The ontogeny, palaeoecology and palaeogeographical inference of the ostracod Roundstonia globulifera

The discovery of an abundant monospecific population of Roundstonia globulifera (Brady) 1868 from an early Flandrian (9000–8500 B.P.) Dublin Bay mud horizon at ‐ 18 m Ordnance Datum has resulted in an ontogenetic analysis of the ostracod. Data on size, shape and morphological development through eight growth‐stages are presented. It occurs with a monospecific population of the foraminifer Elphidium clavatum subclavatum Gudina, the ecology of which is known. From this, and sedimentological data, it is inferred that the assemblages lived in shallow, muddy estuarine channels. Information from other parts of the Irish Sea provides evidence of the course of the Flandrian transgression. It is proposed that early in Boreal times, water masses invading from the north and south, were separated by a barrier south of Dublin until 8500 B.P.

Nonlinear Behavior of Soft Clays during Cyclic Loading

A new stress- strain model that accounts for the nonlinear and degradation characteristics in soft clays due to cyclic loading is developed based on the results of cyclic tests on specimens of San Francisco Bay Mud. The model parameters were obtained from controlled-strain tests and the model was extended for an arbitrary cyclic loading history, such as that occurring during earthquakes, and was used to predict stress-strain response of controlled-stress tests. The main features of the proposed model include: (1)During every cycle, the stress-strain behavior of the soil is defined by a backbone curve and by the Masing criterion; (2)the backbone curve is represented by the Ramberg-Osgood formulation; (3)the ordinates of the backbone curve decrease (degrade) during cyclic loading by an amount measured by a degradation index that represents an irreversible degradation process in the structure of the soil; and (4)the rate of degradation is controlled essentially by the amplitude of the cyclic strain.

Effects of local geological conditions in the San Francisco Bay region on ground motions and the intensities of the 1906 earthquake

abstract Measurements of ground motion generated by nuclear explosions in Nevada have been completed for 99 locations in the San Francisco Bay region, California. The recordings show marked amplitude variations in the frequency band 0.25 to 3.0 Hz that are consistently related to the local geological conditions of the recording site. The average spectral amplifications observed for vertical and horizontal ground motions are, respectively: (1, 1) for granite, (1.5, 1.6) for the Franciscan Formation, (3.0, 2.7) for the Santa Clara Formation, (3.3, 4.4) for alluvium, and (3.7, 11.3) for bay mud. Spectral amplification curves define predominant ground frequencies in the band 0.25 to 3.0 E for bay mud sites and for some alluvial sites. Amplitude spectra computed from recordings of seismic background noise at 50 sites do not generally define predominant ground frequencies. The intensities ascribed to various sites in the San Francisco Bay region for the California earthquake of April 18, 1906, are strongly dependent on distance from the zone of surface faulting and the geological character of the ground. Considering only those sites (approximately one square city block in size) for which there is good evidence for the degree of ascribed intensity, the intensities for 917 sites on Franciscan rocks generally decrease with the logarithm of distance as Intensity = 2 . 6 9 - 1 . 9 0 log ( Distance in kilometers ) . ( 1 ) For sites on other geological units, intensity increments, derived from this empirical relation, correlate strongly with the Average Horizontal Spectral Amplifications (AHSA) according to the empirical relation Intensity Increment = 0 . 2 7 + 2 . 7 0 log ( AHSA ) . ( 2 ) Average intensity increments predicted for the various geological units are −0.3 for granite, 0.2 for the Franciscan Formation, 0.6 for the Great Valley sequence, 0.8 for the Santa Clara Formation, 1.3 for alluvium, and 2.4 for bay mud. The maximum intensity map predicted on the basis of these data delineates areas in the San Francisco Bay region of potentially high intensity for large earthquakes on either the San Andreas fault or the Hayward fault. The map provides a crude form of seismic zonation for the region and may be useful for certain general types of land-use zonation.

Rigid and Flexible Bracing Systems on Adjacent Sites

Design, construction, and performance case histories are presented for rigid and flexible bracing systems supporting 45 ft deep basement excavations in soft soil (San Francisco bay mud). The rigid bracing system was a soldier-pile tremie-concrete wall braced with tiebacks and inclined rakers. The flexible bracing system was a sheet-pile wall supported by diagonal struts and inclined rakers. The slurry wall system, designed in accordance with conservative pressure criteria, limited adjacent ground movements to small magnitudes; pavements and utilities were undamaged. The sheet pile bracing system, designed in accordance with less conservative criteria, experienced moderately large deformations that caused minor to moderate damage to pavements, sidewalks, and buried utilities.

Nitrogen fixation by marine photosynthetic bacteria.

Summary. Potential nitrogen‐fixing marine photosynthetic bacteria isolated from the coastal waters and sea‐bed sediments of Cardigan Bay and adjoining mud flats, were investigated, using the acetylene reduction technique, to ascertain the magnitude of their contribution of fixed nitrogen to the coastal ecosystem. Aberystwyth harbour and Iceland fjord mud readily yielded Athiorhodaceae, the majority of which consistently reduced acetylene when grown as pure cultures on marine media. Only one such strain was isolated from local seawater, but they were more common in Iceland fjord water. No marine Thiorhodaceae were isolated. It was essential to monitor crude and pure culture systems for ethylene production in the absence of acetylene.

Seismic investigation of a san francisco bay mud site

abstract Measurements were made of the shear- and compressional-wave velocities necessary to determine the seismic response of a site on the edge of the San Francisco Bay, California. The shear wave is the most difficult to isolate because of the complications of earlier arriving energy. Downhole and surface measurements yielded shear-wave velocities of 90 to 130 m/sec and compressional-wave velocities of 1,400 m/sec for soft mud. The underlying older sediments had interval shear-wave velocities of 270 to 380 m/sec, increasing with depth. The corresponding P velocities for the older sediments were 1,600 to 1,840 m/sec. The horizontal traction technique of shear-wave generation proved to be the most successful of the methods tested.

Performance Tests of Drilling-Vessel Anchors

Holding-power tests on several types of anchors in a variety of mud and sand bottom revealed varying degrees of reliability. Balling up and failure to dig in were the principle problems encountered. A new streamlined anchor, the BOSS, generally outperformed the others by digging in quickly, holding well, and avoiding ball-up. Introduction The anchors used for mooring drilling vessels are usually of a lightweight design similar to the U. S. Navy Lightweight or the Danforth. Commonly used sizes range from 20,000 to 30,000 lb. Holding power in favorable sea floors may exceed 10 times anchor weight, but in some types of mud the holding power may be only one to two times anchor weight.Minimum holding-power requirements for drilling vessels range from about 100 kips per mooring line on a small vessel to as much as 300 kips on some of the larger units. These requirements are usually verified by applying a test load on the anchors before spudding the well. If the anchors fail to hold the test load, tandem anchors or pile anchors may be required to achieve the necessary holding power.A dependable mooring system is important in the safety of floating drilling operations. It is therefore desirable that drilling vessel anchors perform well and be reliable. That is, they should achieve holding powers of at least 10 times anchor weight, and should powers of at least 10 times anchor weight, and should be able to do so in all types of penetrable bottoms ranging from sand to very soft mud. This paper discusses the results of tests carried out by Esso Production Research Co. (EPR) on the performance of Production Research Co. (EPR) on the performance of anchors in a variety of bottom soils. A significant result of these tests was the development of a new type of anchor that showed improved performance and reliability. Reported Tests of Lightweight Anchors Various branches of the U. S. Navy have conducted anchor holding-power tests with lightweight anchors in sand and mud bottoms. Some of the test data are briefly summarized below, with the holding power shown as "holding-power ratio" (holding power/ anchor weight). The Naval Civil Engineering Laboratory tested two types of lightweight anchors in a mud bottom of San Francisco Bay and in a sand sea Boor near Port Hueneme, Calif. Average holding-power ratios for one type of lightweight anchor ranged from 3.8 to 13.3 in mud and from 12.4 to 23.6 in sand. Tests with the other type of lightweight anchor showed average holding-power ratios ranging from 2.1 to 5.1 in mud. The Naval Amphibious Test and Evaluation Unit tested lightweight anchors in both mud and sand at Little Creek, Va.:, Average holding-power ratios ranged from 5.5 to 7.5 in mud, and from 16.8 to 26.0 in sand. These U. S. Navy tests indicated that the lightweight anchors generally perform better in sand than in mud.In 1958, the Naval Civil Engineering Laboratory developed a new type of lightweight anchor that included large tripping palms. The anchor design aimed at good performance in both mud and sand. Four sizes of this anchor, with weight ranging from 3,000 to 12,000 lb, were tested in San Francisco Bay mud and Port Hueneme sand . 4 After 50 ft of drag in mud, the average holding-power ratios ranged from 13.3 to 19.2; and after 50 ft of drag in sand, the holding-power ratios ranged from 19.6 to 23.2. JPT P. 337

Cofferdam for BARTD Embarcadero Subway Station

Inward deformation of cofferdam walls during deep excavation in soft soils are inevitable but steps can be taken to minimize these movements. An excavation 1,160 ft (354 m) long by 55 ft (17 m) wide by 70 ft (21 m) deep in a busy downtown San Francisco street, flanked by major buildings, was performed for the BARTD Embarcadero station successfully in soil strata that contained varying depths of soft clay locally known as recent Bay mud. To provide an impervious rigid cofferdam wall of adequate strength and reasonable thickness a soldier pile and tremie concrete (SPTC) system of sheeting was selected. Successive excavation cuts below prescribed bracing levels were held to a practical minimum. Struts were preloaded to reduce compression deformations. Inclinometers recorded deflections of the walls while strain gages enabled determination of strut loads. The thicker the layer of soft clay the greater the inward movement of the walls notwithstanding the corresponding increases in wall sizes.

Excess Pore Pressures During Undrained Clay Creep

The objective of this presentation is to examine experimentally how the excess pore-water pressure is related to the mechanism for undrained creep of San Francisco Bay mud. The results are discussed in the context of creep mechanisms previously suggested in the literature and based on laboratory testing.It is found that shear strains occurring during undrained creep are directly related to a gradual but significant increase in excess pore pressure and, hence, reduction in effective stresses. The increase in magnitude of the pore pressure is, except immediately after the creep shear stress is applied, solely a function of the initial consolidation stress and consolidation period. The magnitude of the long-term build-up may be related to the amount of secondary compression which would occur during drained conditions. It increases with the organic content of the soil and decreases with the degree of remolding. The mechanism for the increase in pore-water pressure may be explained by drainage of water from micropores in the microstructure into the macrostructure.Unless one accounts for the increase in pore pressures during undrained creep, it is unlikely that one will be successful in formulating a generally valid mathematical model for stress–strain–strength–time behavior based on laboratory testing.

Secondary Consolidation and Strength of a Clay

The undrained strength and stress path of a soft marine clay subjected to different periods of secondary consolidation under isotropic stress was examined. The phenomenon of buildup of pore-water pressure has been shown to be due to the arresting of secondary compression. The effect of this phenomenon on the undrained strength and stress path was also studied. The results have been explained using the Cam-clay model. It is concluded that secondary compression would cause increase in undrained strength and stiffening of the stress-strain characteristics of bay mud, while the effect of the pore-water pressure buildup was to produce steeper undrained stress paths at small strains only.

Effects of local geology on ground motion near San Francisco Bay

abstract Measurements of ground motion generated by nuclear explosions in Nevada were made for 37 locations near San Francisco Bay, California. The results were compared with the San Francisco 1906 earthquake intensities and the strong-motion recordings of the San Francisco earthquake of March 22, 1957. The recordings show marked amplitude variations which are related consistently to the geologic setting of the recording site. For sites underlain by a layer of younger bay mud or artificial fill, maximum horizontal ground velocities generally increased with thickness of the layer and were as much as ten times greater than those recorded on nearby bedrock. The maximum vertical velocities for these sites were between 1 and 3.5 times greater. Spectral amplification curves clearly define a “dominant ground period” of about 1 second for sites underlain by younger bay mud. For sites underlain by older, more consolidated sediments, no clearly defined “dominant ground period” was found. Maximum ground velocities for the older bay sediment sites were about twice those recorded on bedrock. Consistent correlations of the results from the nuclear recordings with the 1906 earthquake intensities and the spectral amplification curves for the 1957 earthquake suggest that areas of high amplification determined from small ground motions may also be areas of high intensity in future earthquakes.

Bonding, Effective Stresses, and Strength of Soils

The theory of rate processes has been used to deduce values of interparticle bond energies and the number of interparticle bonds in different soils from the results of creep tests. Measured values of activation energy for creep are of the order of 30 kcal to 45 kcal per mole. The effective consolidation pressure was found to be directly proportional to the number of interparticle bonds per unit area of cross section. A single linear relationship was found to hold between the number of interparticle bonds and compressive strength which applies equally to wet and dried remolded illite, undisturbed normally consolidated and overconsolidated San Francisco Bay mud, and dry sand. These results support the hypothesis that the interparticle contact is the only significant region between soil grains where effective normal and shear stresses can be transmitted, interparticle contacts are effectively solid to solid, a single interparticle contact may contain many interparticle bonds, and the number of bonds per contact depends on the compressive force transmitted at the contact.

Cyclic Stress-Strain Characteristics of Clay

The decreases in moduli and increases in yield strain occurring during cyclic loading of sensitive clay under simple shear conditions are examined. The loading conditions are representative of those associated with the upward propagation of a seismic shear wave through a large mass of soil; i.e., the strain is completely reversed during each cycle at the rate of 1 cps. The moduli and yield strain reported are those defining the bilinear hysteresis models which best fit the nonlinear stress-strain characteristics obtained from the tests. For San Francisco Bay Mud the moduli are constant for strain levels greater than 2% and for loading cycles after the fiftieth. Yield strain, however, is proportional to cyclic strain level for at least 200 cycles. The strength and moduli measured under static loading conditions are decreased by cyclic loading involving large strains, but only the modulus is decreased by loading restricted to strains below about 1%.

Characteristics of a new vibrio-bacteriophage system.

A vibrio-bacteriophage system isolated from San Francisco Bay mud is described. The vibrio lyses readily in distilled water and appears to be a new species. In contact with the phage it becomes lysogenic and forms large clumps. The phage presents no unique features.

ENGINEERING GEOLOGY OF SAN FRANCISCO BAY, CALIFORNIA

The principal engineering problems that confront the geologist in San Francisco Bay are the strength of foundations, settlement of ground due to imposed load, stability of side slopes, support of piles, and source of borrow sand for fills. Work on the design of foundations for proposed new crossings of San Francisco Bay has shown that each geologic formation has more or less consistent characteristics with respect to these engineering problems. The geologist thus can facilitate the work of the engineer by advising him as to the engineering properties of the rocks and sediments in areas between bore holes or excavations, even though the bore holes may be several hundred feet apart. Bedrock beneath San Francisco Bay consists of the Franciscan formation of Jurassic (?) age. Prior to the deposition of the present sediments in the bay, this formation was severely deformed, broken by faults, and eroded to a surface of considerable relief. The formation thus poses problems in landing caissons for bridges across the bay. In such places knowledge of the relief, firmness, and distribution of weak and strong rocks is essential. The bay sediments consist of five formations of late Quaternary age, which correspond to deposits previously described by Lawson in his folio on the San Francisco Bay region. The oldest sediments belong to the Alameda formation, which ranges from 0 to more than 200 feet in thickness. The formation consists of a series of layers of firm sand, sandy clay, and clay, which everywhere forms a good foundation for engineering structures. The caissons in the east part of the bay on the present San Francisco-Oakland Bay Bridge rest on this formation. In more than 15 years the piers have not settled appreciably. The overlying San Antonio formation, 15 to 120 feet thick, consists of clay and sandy clay, with a little sand. The sediments in most places are moderately firm and give good pile support. The formation settles appreciably under loads of more than 1.5 tons per square foot. The succeeding formation, the Posey, 0 to 50 feet thick, consists of sand and sandy clay. It is firm and, where the underlying San Antonio formation is stiff, forms a good foundation. It also is a source of borrow sand. Subsequent to the deposition of the Posey formation, valleys 150 feet or more in depth and up to 1000 feet in width were formed. These valleys and adjacent flat land were then partially covered with the Merritt sand, 0 to 60 feet thick. This sand in part is wind-blown and in many places is a source of borrow sand. The youngest formation is the Bay mud, which fills the old valleys and blankets the adjacent land. It is soft, affords a poor support for structures and piles, settles under imposed load, and fails readily when covered by significant quantities of fill. The formation causes critical problems in the deep, filled valleys. These valleys lie near the mouths of the present streams, which flow from the mountains. Presumably, the valleys mark the course of drainage when sea level was lower than it is now, perhaps during some glacial epoch.