Research on Test Method of Foundation Bed Coefficient in Nanjing Soft Soil Area

Relying on the geotechnical engineering survey project of Nanjing Lukou Airport, this research adopts the method of combining in situ and indoor testing to analyze the coefficient of soil foundation under different conditions (flow plastic, plastic, and soft plastic). Based on the differences in test results, in situ and indoor test methods appropriate for the benchmark bed coefficient of Nanjing soft soil area are proposed. Research findings depicted that the bed coefficients obtained by different methods are not similar; therefore, if the data obtained by different methods need to be compared and analyzed, they have to be unified as K 30 . Simultaneously, in the indoor test, this study compared the foundation bed coefficient obtained by the consolidation method, the improved K 0 instrument consolidation method, and the triaxial method. Results revealed that the improved K 0 instrument consolidation method can better realize the test of the soil foundation coefficient. This study can provide a reference for geotechnical investigation and design of soft soil in the study area.

Quality Assessment of Dry Soil Mixing Columns in Soft Soil Areas of Eastern China

To investigate the quality of dry soil mixing (DSM) columns in different soft soil areas of east China, a large number of laboratory test results and field test results of DSM columns were collected and analyzed statistically. Furthermore, a quality assessment method for DSM columns is proposed in this paper. The hardness description (HD), standard penetration test (SPT), unconfined compressive strength (UCS), and soil-cement column quality designation (SCQD) are used as assessment indexes. The statistical analysis showed that the test results of SPT, UCS, and SCQD were scattered, particularly in shallow ground. The mean values of the SPT blow count, UCS, and SCQD of the DSM columns decreased with depth: the greater the depth, the worse the quality of DSM columns. The quality assessment results showed that the proportion of the great quality columns was 64.84%, and the proportion of the unqualified columns was 1.4%. The proportion of DSM columns with great quality in the lagoon soft soil area was greater than in other areas. The proportion of unqualified columns in the lacustrine soft soil area was the largest. For all soft soil areas, the proportions of great quality, good quality, general quality, and unqualified soil decreased in that order. The quality assessment of 8627 DSM columns showed the proportions of great quality and unqualified were 64.84% and 1.4%, respectively. It was found that the greater the depth of the DSM column, the more unqualified DSM columns, and the more difficult it was to control the quality of DSM columns.

Systematic Analysis Method for the Unusual Large Displacement in the Excavations in Soft Soil Area

Based on a subway station excavation construction project in the soft soil area in Nanjing, an informationized monitoring scheme was conducted during the construction of excavation, and the theories of displacement prediction were introduced into the scheme for the evaluation of the horizontal displacement of the retaining structure and the settlement of the surroundings around the excavation. Based on these theories and the monitoring data, a numerical simulation based on the commercial FEM numerical analysis software, Midas GTS NX, was conducted to simulate the whole construction process. To handle the large displacement of the retaining structure observed during the construction, the actual soil layers’ status discovered by excavating, which can reflect the physical characteristics of the soil, the construction condition, and the variation trend of the monitoring data, was used in the back analysis of the factors that induced the large deformation of the retaining structure, and the analysis result was fed back to the countermeasurement organization and design such as erecting temporary steel strut. The effectiveness of these measurements in the aspect of the reduction of the deformation rate was verified, which can provide reference to the design and construction of a similar project in soft soil area.

Komparasi Biaya Konstruksi Bangunan Atas Jembatan Slab On Pile di Atas Tanah Lunak untuk Beberapa Variasi Bentang

Jembatan tipe slab on pile umumnya terdiri dari dua bentang atau lebih. Sampai saat ini belum ada ketentuan atau pedoman terkait dengan panjang bentang terkecil dan terbesar. Dengan demikian penentuan panjang bentang jembatan slab on pile lebih kepada engineering judgment desainer dan/atau pemilik jembatan. Penelitian ini mencoba menentukan panjang bentang optimal yang dapat menghasilkan biaya konstruksi bangunan atas yang minimal dalam satuan rupiah per satuan luas jembatan slab on pile di daerah tanah lunak. Adapun lokasi penelitian berada di Jembatan Ray 2 Kabupaten Barito Kuala. Dalam penelitian ini, jembatan dibagi kedalam tiga tipe, yaitu Tipe I dengan bentang segmental 4 m dengan banyak bentang lima bentang dan panjang bentang total 20 m, Tipe II dengan bentang segmental 5 m dengan banyak bentang empat bentang dan panjang bentang total 20 m, dan Tipe III dengan bentang segmental 7 m dengan banyak bentang tiga bentang dan panjang bentang total 21 m. Berdasarkan hasil desain, biaya konstruksi bangunan atas per satuan luas untuk untuk jembatan slab on pile tipe I sebesar Rp5,795,673.4, jembatan slab on pile tipe II sebesar Rp5,313,707.8, dan jembatan slab on pile tipe III sebesar Rp4,925,033.0. Perbedaan biaya konstruksi ini dipengaruhi oleh jumlah pier head yang dimiliki jembatan, dimana tipe III memiliki jumlah pier head terkecil Abstract Slab on pile bridges consist of two spans or more. Until now, there are not codes state cleary about shortest and largest span of slab on pile bridge. Therefore, decision about length of span tends to engineering judgement of designer and/or owner of the bridge. This research tries to propose about optimal span that obtain a minimal construction cost of superstructure of slab on pile bridge on soft soil area in rupiah per square area. This research is located at Ray 2 Bridge in Barito Kuala District. In this research, bridge classifies in three types: type I (4 m segmental length, 5 spans, and 20 m total span length), type II (5 m segmental length, 4 spans, and 20 m total span length), and type III (7 m segmental length, 3 spans, and 21 m total span length). According to design results in this research, construction cost of superstructure for type I, II, and III are Rp5,795,673.4, Rp5,313,707.8, and Rp4,925,033.0. construction cos differs among types because the numbers of pier head, wherein type III has smallest number of pier head