The construction techniques of tunnel boring machine(TBM), which is firstly applied in the Pinglin tunnel of Taipei-Ilan expressway, is founded and been improved domestically. Many difficulties were encountered during the construction of TBM in Pinglin tunnel because of the complicated and fractured geological structure especially at station 39k + 079 of Pinglin pilot tunnel. Large groundwater inflow, I.e. approximately 150 l/s, with high water pressure over 20 kg/cm2 in hard and highly fractured Szeleng sandstone formation was encountered at station 39k+079 and approximately two years has been consumed to solve the geological difficulties since February 1996. This paper is to present and discuss the difficulties encountered and related construction techniques in the Pinglin tunnel in detail in order to upgrade the related techniques in the future.
Taiwan, located at the contact edge of two colliding tectonic plates, is composed of geological formations highly variable in geologic age and geologic structures of high complexity. In recent infrastructure development, many tunnel projects are concentrated within the western foothill and Hsuehshan Range geologic areas both of which are complicated in their geological features. Tunnelling in these areas is inevitably expected to encounter difficulties at two localities: at the portal areas where shallow overburden of friable rock mass is present; and along the alignment, where adverse effects arising from occurrence of faults and numerous shear zones tend to aggravated the situation. To overcome these difficulties, additional measures besides strengthening of the tunnel support have to be adopted to enable smooth execution of the projects. Tunnel forepoling method, among these additional measures, is one of the promising methods which have been implemented in tunnel construction for years in foreign countries. In tunnel forepoling method, a series of steel pipes is installed at the crown of the tunnel ahead of the driving face and then followed with consolidation grouting to form a protection vault or umbrella in the rock mass before excavation. With the subsequent tunnel excavation and support, the forepoled vault combined with the transverse support has, thus, established a 3-dimensional tunnel support system. This article, besides the details of the construction procedures of the forepoling method, is to introduce some tunnel construction projects, one by TBM and the other using backhoe and hydraulic breaker, those through application of tunnel forepoling method. Finally, we submit a discussion and suggestion according to the construction experience to tunnelling engineer for reference.
Dynamic compaction technique has been used to improve the soil condition in FPG Sixth Cracking Project. Therefore, 5 patterns of dynamic compaction pilot test have been executed on Hi-Feng site to find the best combination of the drop height, grid spacing and applied energy. The verification results indicate that the effective improvement depth is between 9 and 11 meters. Moreover, the best improvement result is that of TypeⅢ which has the greatest applied energy. And TypeⅠcomes in second. These results correspond well with those obtained from foreign experience. The improvement results of TypeⅡ、TypeⅣ and TypeⅤ, which have similar applied energy, are different due to their grid spacing, drop height, and numbers of drops. The above results clearly show that the construction planning is very important to dynamic compaction.
The construction of large storage tanks on reclaimed land faced problems including soil liquefaction, insufficient bearing capacity and excessive total settlement or differential settlement. It is generally considered that ground treatment is an economical and effective solution. In this paper, the improvement results using dynamic compaction, stone column and preloading are presented and compared in two respects, soil compressibility and foundation settlement.
The field cone penetration test and settlement monitoring results indicated that all of the three kinds of improvement techniques worked effectively to reduce the soil compressibility of reclaimed land. For loose sandy soil, the installation of stone column could reduce soil compressibility for about 50 to 70 %. For the foundation settlement of large tank, the improvement effect of preloading was the most significant , a reduction of 80 % of operation settlement .
Basement uplift is a phenomenon not uncommonly encountered for one-story or two-story basement excavation projects. Ground water temporarily out of control is the main culprit for such incidents, and it usually happens following the completion of basement structure, upon which the retaining sheet/soldier piles are withdrawn and dewatering operation ceased. Heavy rainfall in a short period may also lead to basement uplift under certain circumstances. The amount of uplift ranges between 30 ~ 100 cm, and the situation has to be more or less remedied before the construction can be resumed. A number of remedial schemes, including reloading, installing relief holes, pumping and wash boring, are currently available. These schemes can be used independently or in combination, pending on in-situ soil, ground water and uplift conditions.
This paper presents the sequence, failure mechanism and remedial measures of a piping failure occurring during a deep excavation at a harbor in southern Taiwan. The piping failure occurred after a 13.75 m deep excavation had been completed and after 5 days heavy raining. The causes of the pipping failure could be associated with the presence of a thin clay blanket below the bottom of excavation, together with the rising of groundwater table due to waves and heavy rains brought by a typhoon. After the incident, the remedial measures taken included instrumentation, groundwater pumping as well as grouting to fill cavities and to stabilize disturbed soils.
Taipei MRT for Panchiao Route Project had experienced a piping failure while excavating at the entrance face for shield tunneling in the starting shaft on Ho-ping W. Rd. site. The sudden piping had resulted in ground subsidence and tilt of a nearby 10-story building. For leveling and lifting of tilt building and ground subsidence, a series of remedial program have been performed successfully and are presented in this paper.
The laterally loaded behavior of a group pile is affected greatly by the interaction between piles while pile spacing is close. The interaction is termed as pile-soil-pile interaction or group effect. Pile properties, soil behavior, pile spacing, and loading direction are main factors affecting the behavior of a laterally loaded group pile; among which, pile spacing and loading direction are important factors controlling pile-soil-pile interaction. According to previous studies, group effect is insignificant while pile spacing is six to eight times pile diameter along the lateral loading direction or is four to five times pile diameter normal to the loading direction; the lateral behavior of a group pile can be modeled as that of a single pile. This article focuses mainly on discussion of the effect of pile-to-pile interaction on behavior of laterally loaded pile groups. Existing methods for analyzing laterally loaded pile groups are described. In addition, a recently developed concept and methodology for analyzing a laterally loaded pile group is introduced to provide geotechnical engineers with a way to reasonably calculate the stress and deflection of laterally loaded group piles.