Geologic structural interpretations of Ishikari coal-field, for instance, differences of structural behavior between Sorachi coal-field and Yubari coal-field were discussed on the basis of lithologic characters and thickness of the strata. However the role of thick coverture of Poronai mudstones should not be overlooked because these overlaying sheets would, if present, act as important roof, especially in Sorachi coal-field. Based upon scale models in laboratory experiments, ACTIOANALYSIS-tracing of the deformation (action of boby) to the early period-is one of the geologic structural analysis applied to the area. Some applicable laboratory examples are presented as sections of the movement which were cut at suitable referable stages of the deformation course and shown as frozen pictures. Of many fundamental features derived from the new technique (ACTIOANALYSIS), some phenomena are discussed, after submission of new correlation set up with tuffaceous sand stone of Toranokawa as keybed resulting in the following conclusional remark: 1) Kamui Cretaceous buried hills exsisted before upheaval of northern Sorachi anticline. Sorachi anticline might be divided into at 1 east two segments, 2) In the north eastern corner of the area, relationships between western coal-bearing Tertiary and eastern Cretaceous system were eliminated towards the south by westwards advances of compressed Cretaceous rocks, 3) Bannosawa fault group is divided into two parts, but its fault mechanics remain unsolved. Northern parts of the faults appear to be in tension and the south in compression, 4) Mikasa Dam composed of Cretaceous rocks, controlled the deposition of oldest coal-bearing formations and in later stage subsided (Mikasa buried hill) accompanied with accumulation of Poronai mud stones, 5) Subsidence of Mikasa Dam acted as driving force to produce underthrust faults between Minenobu block (former under water area) and Ikushunbetsu-Poronai synclinal basin (former land). Structural situation of the syncline bottom of Poronai formation in the retrogressive step of fold shows six differnt attitudes in the area and transformation of fold form leads to suggest the following possible structural elements and activities; a) Northeastern marginal land, b) Mikasa Dam, and its subsidence, c) Mikasa buried hill, and d) Upheavals in the northern part of Sorachi anticline, Ikushunbetsu anticline and Manji-Yubari dome in later stages of structural sequence. Geologic Structurs of the area are controlled by Cretaceous foundation rather than by coverture of thick Poronai mud stones. Structural domains of the area, as one of many other possible interpretations, are arranged as follows; I Ashibetsu faulted synclinal area II Kamui buried hills III Sunagawa-Bibai coupled (horizontally) area IV Mikasa Dam and its subsequent subsidence IV' Mikasa buried hill V Yubari coupled (vertically) area.
Displacement of mud by cement slurry was investigated with a plastic model of annulus which was 4m tall, 52mm ID of outer pipe and 34mm OD of inner pipe. By the direct observation of the outer surface of cement, the height of cement head was determined. The ratio of this height to a calculated height obtained by the injected amount of cement slurry was used as an index of experimental results. As factors to determine the mud displacement, were selected both the density differential between mud and cement slurry and the ratio of apparent viscosity of both fluids under flowing conditions. Results obtained were as follows: (1) Effect of pipe position in case of the two factors kept properly: whereas the ratio of height was more than 0.8 in experiments using a concentric annulus, it decreased to about 0.7 in experiments using a eccentric annulus (50% standoff). (2) Results in a concentric annulus: although always good results could be obtained for the density differential of above 0.4g/cm3, the viscosity ratio had to be kept 4-5 for the density differential of 0.1-0.2g/cm3. (3) Results in an eccentric annulus: it is more important to control relative flow properties between mud and cement slurry, and for density differential of 0.5g/cm3, the viscosity ratio of about six was necessary to obtain a good result.