【Excerpts】Foundation treatment effective stop loss, these methods must not know!

      During the foundation construction, the corresponding foundation reinforcement scheme should be adopted to improve the bearing capacity of the foundation, so as to avoid the problems such as too large foundation settlement, uneven foundation settlement, damage of expanded land foundation, damage of collapsible loess foundation, damage of frozen soil foundation and so on. The following are the points of attention to the foundation construction, take a look.

Foundation treatment method

01 Change the filling method

        The replacement method is to dig the weak soil layer (such as silt, miscellaneous soil) into solid soil, that is, sandy loam, ash soil, coarse sand, cement soil, gravel, etc., mainly used for the position is not correct, the place is not dense; or the compaction coefficient and bearing capacity inspection in accordance with the provisions. The construction shall be filled in layers, and the compaction thickness of each layer shall be 25cm. At the same time, the filler should be leveled by the bulldozer, and during the mechanical rolling, the construction should be conducted according to the principle of "first static pressure, then vibration rolling", "first light, then heavy", "first slow, then fast", "first two sides, then in the middle", to ensure the uniform foundation compaction and the filling compaction meets the requirements.

02 Strong ramming method

        Dynamic compaction method is the use of lifting machinery hammer to a certain height, again through the impact of free fall can repeatedly consolidate foundation, make the surface form a layer of dense hard shell, thus improve the strength of the soil, reduce compressibility, achieve the purpose of strengthening foundation, and improve the soil resistance to vibration liquefaction ability, eliminate soil collapsibility. The dynamic compaction method is mainly used for the minimum compaction times and the total compaction amount determined during the dynamic compaction, or the actual compaction depth does not meet the required influence depth, and the strength of the reinforced foundation does not meet the design requirements; or the bearing capacity is not tested according to the regulations.

03 Pre-pressure method

        The prepress method is mainly divided into heap load-prepress and vacuum-prepress method. The overload preloading method refers to the advance of the filling load not less than the design load before the construction of the foundation, so as to improve the strength of the foundation and reduce the settlement of the foundation. This method usually uses embankment filling as a pile up with low cost. During construction, loads should be applied in layers to control the loading rate, so that the strength of the foundation can be slowly improved to avoid shear damage of the foundation. Vacuum prepressure method refers to the reinforcement in the soft soil foundation sand well or plastic drainage plate, and covered on the airtight sealing film isolated from the atmosphere, through the vacuum device in the membrane air discharge, inside and outside the membrane pressure difference, pressure difference into the load on the foundation, so that the foundation does not produce shear damage. This method does not need to load, can reduce the loading and unloading process, shorten the prepressing time, save a lot of stacking materials, the construction technology is simple, suitable for large area construction.

Method of improving the foundation performance

01 The shear characteristics improved

        The shear failure of the foundation is manifested in the insufficient bearing capacity of the foundation of the building; the structure instability or the slope instability during earthwork excavation; and the adjacent foundation uplift or the foundation pit excavation uplift. Therefore, in order to prevent shear damage, it is necessary to increase the shear strength of the foundation soil.

02 Compression features improved

        The high compressibility of foundation is reflected in the settlement and differential settlement of buildings, so measures need to be taken to improve the compression modulus of foundation soil.

03 Improved permeability

The water permeability of foundation is manifested in the leakage of foundation produced by dam, house and other foundations; the flowing sand and pipe gushing occur during foundation pit excavation. Therefore, it is necessary to study and take measures to make the foundation soil impermeable or reduce its water pressure.

04 Power characteristics improved

        The dynamic characteristics of the foundation are shown when the powder and sand are liquefied during the earthquake. Therefore, it is necessary to study and take measures to prevent the liquefaction and improve the vibration characteristics to improve the seismic performance of the foundation.

05 Improvement of the characteristics of the poor foundations of the special soil

Eliminate or reduce the collapsible bility of loess and soil expansion and expansion of foundation treatment measures.

Important points for foundation treatment

1、After the treatment of the soft soil base, the superpore water pressure gradually dissipthrough the load, the pore ratio decreases, the soft soil base is strong, the soil density increases and the shear strength increases.

2、When filling the subgrade, back-pressure protection measures can be used to ensure the coordination and synchronization in the construction process and the pipeline construction between the subgrade work, to ensure the force balance of the foundation.

3、To deal with some special sections of the bridge, the overloading prepressing method can be adopted. In addition, in the soft land base water level is high, we must do a good job in drainage construction, deepen drainage and perfect drainage system.

4、In the construction process of filling the subgrade, in order to ensure the stability of the filling subgrade, the backpressure protection measures can be added, that is, half of the height of the original designed slope embankment.

Detection of the foundation treatment effect

01 Change the filling method

        After changing the foundation method, the ring knife method, static touch test, light dynamic touch test and standard penetration test should be used to test the effect of foundation treatment. During testing, the sampling point should be located at 2 / 3 of the thickness of each layer, and the appropriate load plate should be selected to apply the load to the foundation first, and then the sampling point should be arranged. The foundation pit shall be not less than 1 detection point every 10~20m; while the base groove shall not be less than 1 detection point every 50~100 ㎡.

02 Strong ramming method

        After the dynamic compaction method of the foundation, should interval time to the foundation reinforcement quality testing, namely in situ test (field load test and indoor geotechnical test, and the number of detection points should be based on the site complexity and the importance of the building to determine, usually each building foundation of detection points should be not less than 3, if the foundation is complex, should be appropriate to increase the inspection points. At the same time, the field tests such as dynamic touch test, static touch test, cross plate test, load test, wave speed test, side pressure meter test and partial shovel side expansion test should be carried out, and the number of detection points should not be less than 3 points, and not less than 1% of the number of pier points.

03 Pre-pressure method

        After the foundation, the treatment effect should be tested. During the testing, representative places should be reserved in the prepressing area, cross plate shear strength test of different depths and soil extraction for indoor test, and the quality effect of foundation reinforcement should be judged according to the anti-slip stability of hydrochloric acid foundation. Among them, the heap load-preloading method should be tested at different stages and after the vacuum extraction.