Alignment of excess deformations of buildings using the Geocomposite method

. One of the problems arising in the buildings in operation is the manifestation of excessive deformations, which leads to an emergency condition of the structure. It often occurs because of the heterogeneity of the construction site, the presence of weak soils in the base of the building and the presence of a variable groundwater level. We have proposed the Geocomposite method to compensate excessive subsidence by the example of an emergency building. In the article the calculations are made and the technology of application of this method is described.


Description of the object in question
As the object in question, we take a technical four-story building with an underground floor with dimensions of 90.0 x 30.0.The level of responsibility of the building II -normal.The main load-bearing elements are represented in the form of reinforced concrete monolithic walls.Covering -reinforced concrete slab.The spatial stiffness and stability of the building is ensured by the joint work of the unchangeable rigid discs of the monolithic reinforced concrete slab with monolithic reinforced concrete walls and columns, rigidly embedded in a monolithic reinforced concrete foundation.The foundation of the building is a monolithic reinforced concrete slab 500 -600 mm thick.Under the foundation slabs is performed concrete preparation of concrete class B7.5 with a thickness of 100 mm and gravel backfill thickness of 250 mm.
The working layer of soil under the foundation slab is the bulk underfilled soil, and further on, in the active zone of soil compression under the building, the fluid plastic and flowable soils prevail, having low strength and, more importantly in this case, deformation characteristics.
A characteristic feature of the site is a significant heterogeneity of its formation in area and depth and the presence in the geological section of layers of fluid and plastic soils with high compressibility and low strength, and bulk soils at the depth of the foundation of the erected building are undercompacted.
This site is also classified as seismically dangerous and has a score of 8 by SP 14.13330.2018Annex A.
Another of the negative factors affecting the manifestation of uneven settlements of the building is the development of the trench passing next to the foundations.In the process of excavating the trench, due to heavy precipitation, the soil at the base of the foundation was partially dislocated and decompacted.
All the negative factors eventually led to the development of uneven and hard to predict settlements of the building.It may be noted that these settlements are unpredictable in terms of development over time.

Calculation of settlements
In order to simulate the development of uneven building settlement, calculations were carried out in the software package Plaxis 2D.During the calculations, the values of settlements were obtained: -in the case of a uniform base; -in the presence of an excavation at the border of the building foot and soil decompaction.
According to the calculation results, trenching along the building led to significant additional deformation of the building foundations.The calculated values of additional settlements at conditionally specified parameters of the excavation reach 10.1 cm.The slope angle is unknown, so it was taken tentatively.During the calculations, the following results were obtained: As the loads on the foundation of the designed building are further realized (arrangement of finishes, facades, etc.), it is necessary to constantly monitor the deformations of the foundation and coordinate the obtained values with the designer of the specified building to make further decisions.After stabilization of the increase in settlement, it is necessary to provide additional measures to level the roll of the building.

Selection of fixing method
When building in such difficult conditions and in the presence of weak soils, they are reinforced or piles are used.This is done to ensure that the settlement of the building slab and its relative difference does not exceed the limits described in SP 22.1330.2016.
Already at the initial stage of construction, the building had uneven settlements, and at the time of construction they became excessive.
This was due to the fact that during the laying of utilities there was heavy precipitation, resulting in an increase in the groundwater level.Due to the fact that during the same period the trench was excavated, soil particles were removed from under the foundation and the clay soil of the working layer became pourable.Based on this situation, a decision was made to stabilize the weak soils at the base of the foundation slab of the building in order to increase its strength and deformation characteristics.

Design solutions
The Geocomposite method is based on compaction and consolidation of soils by injecting cement mortar into them at 10-15 atm.The improvement of the mechanical properties of the soils is due to the fact that compaction takes place with the creation of rigid bonds by introducing a solution with a higher strain modulus into the soils than that of the consolidated soil.
It was decided to carry out anti-damage operations in 7 basic cycles: 1 cycle.Preparatory work.This preparatory work includes mounting of equipment for preparation and supply of sealing mortar to the injection area on a special site, manufacture of metal injectors for pumping sealing mortar into the ground, laying of process pipelines, mounting of temporary fencing of work areas, which is to provide continuous and quality performance of all projected works.In the course of works, it is supposed to get the deformation modulus of bulk soils not less than Е*=20 МPа, soft plastic clays not less than Е*=12 МPа, flowable clays not less than Е*=10 МPа, flowable clays not less than Е*=10 МPа, flowable clays not less than Е*=8 МPа, flowable loams not less than Е*=10 МPа, semihard clays not less than Е*=11 МPа, flowable loam not less than Е*=10 МPа.
Injectors for injecting compacting mortar into the ground are made of 32.0 × 3.2 mm diameter pipes in accordance with GOST3262-75 with perforated bottom part with length from 2.5 m to 7.0 m.Round holes in the perforated part of the injectors are arranged in four directions at an angle of 90º.
The composition of the sealing mortar for different stages of the work is given in Table 1.The mortar must be prepared immediately before it is injected into the ground.The works on injectors dipping and injecting the sealing mortar of the 3rd cycle of works are carried out in 4 stages: -on the first stage of works 50% of injectors are drilled and evenly submerged along the entire length of the shield; -in the second stage of the project 50% of injectors are evenly injected along the full length of the blanket, one injector being dipped first; in the second stage the sealant is evenly injected along the full length of the blanket; -in the third stage of works drilling and immersion of the remaining injectors is carried out; -in the fourth stage of work, injection in the remaining injectors is performed.The protective screen technology adopted in the project creates a reliable protection against leakage of cement mortar outside the consolidated soil volume and takes into account the need to squeeze out water during the subsequent creation of a rigidly reinforced mass under the slab foundation of the building.

Partial leveling of foundation slab settlements
Partial leveling of tilted buildings is designed to be performed after the work on consolidation of the foundation soils of the upper horizon of the soil mass under the footing of slab foundations is completed and the work on consolidation of foundation soils is completed.
The alignment is designed to be performed by injecting compacting cement mortar into the base of slab foundations of buildings using a part of injectors sunk into the ground, used earlier for the consolidation of soils of their slab foundations.
The first phase of the work aligns the annex building; the second phase aligns the building itself.
The leveling work is supposed to be performed in three cycles for each of the buildings: 1st cycle -injection of compacting mortar into the ground, then flushing the injectors with water; 2nd сycle -injection of sealing mortar into the ground, then flushing of injectors with water; 3rd сycle -injection of sealing fluid into the ground.
The number of injection cycles can be changed taking into account the results of monitoring the actual displacements of the building structures.

Conclusions
One of the negative factors affecting the construction is the manifestation of excessive deformations.At the facility in question their manifestation was caused by several factors: the presence in the geological section of unevenly distributed in depth layers of plastic and flowing clay soils, the seismicity of the area, a variable groundwater table and difficult weather conditions that can affect the occurrence of groundwater.The presence of a trench near the foundation was also important in terms of deformation and settlement.
The development of building settlement began during the construction phase and reached its above-standard values after the construction works were completed.
In this situation the decision to stabilize weak soils in order to create a homogeneous (deformation properties) soil mass at the base of the basement slab with better physical and mechanical properties than in the natural state is the right one.This makes it possible to level and stabilize building settlement, prevent the emergency situation development and create conditions for bringing the building to a normal operating condition.
After the hydraulic fracturing method was used, the building settlement was no longer excessive and stabilized.Relative difference of sediments is within the allowable values specified in the normative documents.
The main recommendation is to conduct monitoring in order to detect deviations from the normative values.

Fig. 1 . 2023 Fig. 2 .Fig. 3 .
Fig. 1.Deformations of the soil mass at the stage of construction of the designed building

Cycle 2 .
Grouting of macadam basement under the slab foundations of servicetechnical building and outbuilding.Cycle 3. Arrangement of vertical safety screen on the perimeter of the slab foundation of service-technical building and outbuilding.The first stage of works.Cycle 4. Arrangement of stiff-reinforced mass of the upper horizon of soil under the foundation slab of service and technical building and annexes.The first stage of works.Cycle 5. Construction of vertical safety screen along the service-technical building Cycle 6. Partial removal of tilting of outbuildings and then service-technical building.Cycle 7. Arrangement of a rigidly reinforced array of the lower horizon under the foundation slab of the service-technical building.The second stage of works.

Table 1 .
The composition of the sealing mortar for different stages of the work